Production of Methanol From Natural Gas

Production Of Methanol From Natural Gas

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Methanol Methanol is an Alcohol whose chemical formula can be written as CH3OH. It is a clear, colourless liquid with a mild odour, and dissolves readily in most common organic solvents. Methanol is one of the largest volume chemicals produced, with a world wide annual production of about 13 million tons. Methanol was first obtained commercially some 150 years ago by the destructive distillation of wood. Today it is produced mainly from the steam reforming of natural gas via a synthesis gas intermediate. Methanol can and is , however also being produced from such alternative feed stocks as coal and residual fuel oil. Methanol has been traditionally used as a chemical intermediate for the production of formaldehyde, solvents, methyl derivatives(chemical groups containing CH3) and increasingly acetic acid. Recently methanol has gained importance as a clean burning fuel and fuel additive in such diverse uses as a boiler fuel for NOx control , as an octane booster for gasoline by direct blending or as a methyl tertiary butyl ether derivative and for fuel cell application .

1.1 Physical Properties.-

Methanol (CH3OH) is an alcohol fuel. Methanol is the simplest alcohol, containing one carbon atom. It is a colorless, tasteless liquid with a very faint odor and is commonly known as "wood alcohol."As engine fuels, ethanol and methanol have similar chemical and physical characteristics. Methanol is methane with one hydrogen molecule replaced by a hydroxyl radical (OH).

Physical Properties

Molecular weight 32.04

Boiling point 64.7C

Vapor pressure 97 Torr at 20C

Formula CH3OH

Freezing point -97.68C

Refractive index 1.3284 at 20C

Density 0.7913 g/mL (6.603 lb/gal) at 20C

0.7866 g/mL (6.564 lb/gal) at 25C

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Dielectric constant 32.70 at 25C

Dipole moment 2.87 D at 20C

Solvent group 2

Polarity index (P') 5.1

Eluotropic value on alumina 0.95

Eluotropic value on octadecylsilane 1.0

Viscosity 0.59 cP at 20C

Surface tension 22.55 dyn/cm at 20C

Solubility in water Miscible in all proportions

Melting Point -97.7 0C

Flash point 11 oC

Auto ignition temperature 455 oC

Explosive limits 7-36 %

Heat of Formation -201.3 MJ/kmol

Gibbs Free Energy -162.62 MJ/kmol

Critical temperature 512.6 K

Critical pressure 81 bar abs

Critical volume 0.118 m/kmol

Heat of Vaporization 35278 kJ/kmol

Regulatory and Safety Data

Acute effects Poisonous by ingestion or inhalation, may cause respiratory failure, kidney failure, blindness.

Chronic effects As acute. Skin contact can cause dermatitis.

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1.2 Reactions Of Methanol Methanol is the 1st in a series of aliphatic, monohydric alcohols and undergoes many of the reactions typical of this class of chemical compound , Methanol is also a typical member of this series since it contains only one carbon atom . Methanol, for example can not undergo elimination of the hydroxyl group and hydrogen to form the analogous olefins as do many of the higher alcohols. The reactions of the aliphatic alcohols including methanol generally involve hydroxyl group, either through breaking of the C-O bond or O-H bond and substitution or displacement of the H or _OH group, . the O-H and C-O bonds in alcohols are relatively strong, albeit polar and kinetically labile. Hemolytic bond dissociation energies are in the order of 90 100 Kcal/ mole. Because of this bond strength in alcohols, some activation of these bonds is often necessary to achieve acceptable reaction rates.

1.3 CHEMICAL PROPERTIES OF METHANOL: CH3OH

Combustion of Methanol:

Methanol burns with a pale-blue, non-luminous flame to form carbon dioxide and steam.

2CH3OH + 302 ===> 2CO2 + 4H2O

Oxidation of Methanol:

Methanol is oxidized with acidified Potassium Dichromate, K2Cr2O7, or with acidified Sodium Dichromate, Na2Cr2O7, or with acidified Potassium Permanganate, KMnO4, to form formaldehyde.

CH3OH ===> HCHO + H2

Methanol Formaldehyde

2H2 + O2 ===> 2H2O

If the oxidizing agent is in excess, the formaldehyde is further oxidized to formic acid and then to carbon dioxide and water.

HCHO ===> HCOOH ===> CO2 + H2O Formaldehyde Formic Acid

Catalytic Oxidation of Methanol:

The catalytic oxidation of methanol using platinum wire is of interest as it is used in model aircraft engines to replace the sparking plug arrangement of the conventional petrol engine. The heat of reaction is sufficient to spark the engine.







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Dehydrogenation of Methanol:

Methanol can also be oxidized to formaldehyde by passing its vapor over copper heated to 300 C. Two

atoms of hydrogen are eliminated from each molecule to form hydrogen gas and hence this process is

termed dehydrogenation.

Cu

300C CH3OH ===> HCHO + H2 Methanol Formaldehyde

Dehydration of Methanol:

Methanol does not undergo dehydration reactions. Instead, in reaction with sulphuric acid the ester, dimethyl sulphate is formed.

Conc H2SO4 2 CH3OH ===> (CH3)2SO4 + H2O Methanol Dimethyl Water Sulphate

Esterification of Methanol

Methanol reacts with organic acids to form esters.

H(+) CH3OH + HCOOH ===> HCOOCH3 + H2O Methanol Formic Methyl Water Acid Formate

Substitution of Methanol with Sodium

Methanol reacts with sodium at room temperature to liberate hydrogen. This reaction is similar to the reaction of sodium with ethanol.

2 CH3OH + 2 Na ===> 2CH3ONa + H2

Methanol Sodium Sodium Hydrogen Methoxide

Substitution of Methanol with Phosphorus Pentachloride

Methanol reacts with phosphorus pentachloride at room temperature to form hydrogen chloride, methyl chloride, (i.e. chloroethane) and phosphoryl chloride.

CH3OH + PCl5 ===> HCl + CH3Cl + POCl3 Methanol Phosphorus Hydrogen Methyl Phosphoryl




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Pentachloride Chloride Chloride Chloride

Substitution of Methanol with Hydrogen Chloride

Methanol reacts with hydrogen chloride to form methyl chloride (i.e. chloromethane) and water. A dehydrating agent (e.g. zinc chloride) is used.

ZnCl2 CH3OH + HCl ===> CH3Cl + H2O Methanol Methyl Chloride

1.4 USES OF METHANOL:- The major portion of the methanol produced is used for making formaldehyde and a number of chemical derivatives. Other applications include its use as solvents extractant and air automation antifreeze. .

Methanol As A Solvent:- Methanol is miscible with most organic liquids and is a solvent for variety of substance like dyes, nitro cellulose, polyvinyl, butyl ethyl cellulose, Shellac and modified resin. It is used in the manufacturing of wood and metal polishes. Water proofing formulation, coated fabrics, aniline, and other inks, and duplicator fluids. Its solution have lower viscosities than similar solution, made from other alcohols, methanol is uses in combination with 5 to 10 % of polyhydroxy alcohol as a solvent for water soluble aniline dyes in the manufacture of non-=grain-raising wood-stain, it is also used as a solvent for aniline dyes for leather and is especially useful where uniform colour development is essential. Other application of this products include its addition to asphalts paints to decrease their drying time and its use in both natural and synthetic rubber solutions to lower the viscosity during processing . Methanol does not dissolve cellulose acetate and acetate butyrate, polystyrene, polyethene, methylcrylate resin, polyvinyl chloride, and co-polymers.

Methanol As An Extractant:- Methanol is employed in a large scale in many industrial chemical processes as an extractant. In the refining of gasoline and heating oil. The unisol process use caustic methanol solutions to remove undesirable mercaptan impurities. Methanol may also be used to extract the aromatic potion of petroleum form other hydrocarbons and patent literature describe its use in extraction organic nitrites. From non polar hydrocarbon in the secondary recovery of crude oil by th miscible phase method using alcohol methanol is the least expensive and most easy recovered. A process has been developed to use a solvent of methanol and hexane in the extraction of tars from Texas Lignite deposits. Methanol is also uses for removing acid impurities from vegetable oils, dewaxing dimmer gum, flash washing water soluble crystals, extracting inorganic salt such as potassium iodide and barium and strontium halides, purifying hormones and crystallizing steroid.








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Methanol As A Ceansing Agent:- Methanol is used in many cleansing operations such as in washing steel surfaces before coatings are applied , rinsing the interiors of electronic tubes before they are evacuated , cleaning resin sheets before further processing , It is employed as a reducing agent in the vapor phase cleaning of copper, the bright annealing of brass and in soldering fluxes. Its is also used in special preparation for dry cleaning leather goods, in glass cleaners and in flushing fluids for hydraulic brake system.

Methanol As An Anti Freezing Agent Methanol offers the advantages of low molecular weights, low costs and high efficiency when used as an automotive or industrial antifreeze. The pressure up cap on the radiator of the modern engine cooling system prevent losses by evaporations. Methanol-antifreeze solutions are considered less result of internal leakage then the high boiling type. Fuel system antifreeze and windshield washer fluid based on methanol add to the dependability and convenience of motor transport in methyl ester of 2-4 D is a selective weed killer, methyl salicylate is used in medicines flavorings and perfumes., dimethylpthalate is as insect repellent and a plasticizer for cellulose acetate methyl P=hydroxyl benzoate is a mold inhibitor for aqueous preparations, containing starch guans and oil. Methylcrylate polymerizes readily to form clear plastics.

Formaldehyde:- Worldwide, the largest amount of formaldehyde is consumed in the production of urea-formaldehyde resins, the primary end use of which is found in building products such as plywood and particle board .The demand for these resins, and consequently methanol, is greatly influenced by housing demand. In the United States, the greatest market share for formaldehyde is again in the construction industry. However, a fast-growing market for formaldehyde can be found in the production on acetylenic chemicals, which is driven by the demand for 1, 4 butanediol and its subsequent downstream product, spandex fibers.

Methyl T-Butyl Ether:- MTBE is used as an oxygen additive for gasoline. Production of MTBE in the United States ha increased due to the requirements of the 1990 Clean Air Act amendments, and has surpassed formaldehyde as the largest domestic consumer of methanol. Projection for this use of methanol are difficult to estimate due to the varying political and environmental considerations that promote the use of cleaner burning motor fuels.

ACIDS:- Methanol carbonylation has become the process of choice for production of this staple of the organic chemical industry, which is used in the manufacture of acetate fibers, acetic anhydride, and terephthalic acid, and for fermentation,




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Methanol As An Alternative Fuel Utilization of methanol as alternative fuel can be done through two different ways that is by using directly in an internal combustion engine or by implementing methanol fuel cell powered vehicles. Pure methanol (M100) has been used in heavy-duty trucks and transit buses equipped with compression-ignition diesel engines. Since 1965, M100 has been the official fuel for Indianapolis 500 race cars. (The last time gasoline was used in the Indianapolis 500 was in 1964, when the race suffered a pile-up of cars that resulted in a gasoline fire and deaths.) Typically, a blend of 85 percent methanol and 15 percent gasoline (M85) is used in cars and light trucks. Pure methanol can also be reformed in fuel cells into hydrogen, which is then used to power electric vehicles. Methanol-powered vehicles have been found largely in the West, primarily in California. They can also be seen in the fleets of the federal government and the New York

STORAGE AND SAFETY

Because methanol is corrosive to some metals and damaging to rubber and some plastics, fuel storage tanks and dispensing equipment must be corrosion and damage resistant. California requires that underground storage tanks for methanol be double walled. Because methanol is water soluble, it could be quickly diluted in large bodies of water to levels that are safe for organisms. Environmental recovery rates for methanol spills are often faster than for petroleum spills. As with gasoline, methanol can be fatal when ingested. Inhalation of fumes and direct contact with skin can also be harmful. Because pure methanol flames are nearly invisible in daylight, gasoline is added as a safety precaution to provide color to a flame. Added gasoline also serves to add a smell to this otherwise odorless liquid. Because of its high flash point, methanol is less volatile than gasoline. It burns more slowly and at a lower temperature. Methanol is transported by barge, truck, or rail. In the event of an

EMISSIONS

The methanol molecule has a simple chemical structure, which leads to clean combustion; reports from emissions studies, however, vary more widely for methanol than for other fuels probably because of differences among fuel blends used across the country and because vehicles may not be optimized for using methanol. Comparisons of M100 with gasoline and diesel have shown these results:

Carbon monoxide: Emissions vary sometimes lower, but are usually equal or slightly higher. Ground-level-ozone-forming potential: 30 to 60 percent less. (In order to take advantage of this characteristic, vehicles must be properly adjusted.) Nonmethane evaporative hydrocarbons: Usually less. Toxics: M100 contains none of the carcinogenic ingredients such as benzene, 1,3-butadiene, and acetaldehyde. M85 (with 15 percent gasoline) has 50 percent fewer toxic air pollutants than gasoline.


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Formaldehyde levels: Much higher, although still low. The toxicity of formaldehyde is lower than that of other toxics, and formaldehyde emissions can be reduced dramatically with new technology, such as improved catalytic converters. Nitrogen oxides: Usually comparable or less. Greenhouse gases: Comparable to gasoline. Particulate matter: Buses using M100 emit significantly less than diesel-fueled buses.

Internal Combustion Engines Using Methanol Several factors effect the use and selection of any fuel. Among the important ones are engine design, net energy per pound, net energy per gallon and the sulfur content of alternative fuel properties. a-Pure methane b-Octane rating above 100 are correlated with given conc. Of tetra ethyl lead in 150 octane. c-Natural sulfur content very low but measurable. Measuring a fuels selective potential energy can easily be done by defining that fuels BTU content. A Btu defined as the amount of heat necessary to raise one pound of water, one-degree Fahrenheit. At ambient temperature and atmospheric pressure, liquid methanol is basically similar to gasoline or diesel fuel. Therefore methanol is easy to be stored and transported compared to CNG & LNG. These characteristics make the price of methanol vehicles and refueling station lower than the price of CNG or LNG vehicles and refueling station. For a certain type, methanol vehicle is offered at lower price than gasoline vehicles, for the purchase of certain No. OF vehicles. Present design internal combustion engines run on liquid fuels. Methanol required few of any engine modification to extract the maximum power from this fuel. As compared to gasoline, methanol lowers some tailpipe emissions, namely the sulfur based HC, CO, as well as NOx. Methanol contains only half the energy per gallon of gasoline but has a very high octane rating. Increased compression ratios could yield 5-20 %. More power. When methanol is used as a gasoline additive antiknock compound and fuel extender, it becomes economical with very positive results especially from the emissions stand point. It contains zero sulfur thereby reducing tailpipe acid significantly. Of the six most popular attractive fuels presently available methanol has the second lowest Btu/lb, net energy yield. As a result, fuel tanks will need to be enlarged for vehicles that run on pure methanol.

1.5 A Historical Overview

In their embalming process, the ancient Egyptians used a mixture of substances, including methanol, which they obtained from the pyrolysis of wood. Pure methanol, however, was first isolated in 1661 by Robert Boyle, who called it spirit of box, because he produced it via the distillation of boxwood. It later became known as pyroxylic spirit. In 1834, the French chemists Jean-


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Baptiste Dumas and Eugene Peligot determined its elemental composition. They also introduced the word methylene to organic chemistry, forming it from the Greek words methu, meaning "wine," and hyle, meaning "wood". The term methyl was derived in about 1840 by back-formation from methylene, and was then applied to describe methyl alcohol. This was shortened to methanol in 1892 by the International Conference on Chemical Nomenclature.

In 1923, the German chemist Matthias Pier, working for BASF developed a means to convert synthesis gas (a mixture of carbon monoxide and hydrogen derived from coke and used as the source of hydrogen in synthetic ammonia production) into methanol. This process used a zinc chromate catalyst, and required extremely vigorous conditionspressures ranging from 30100 MPa (3001000 atm), and temperatures of about 400 C. Modern methanol production has been made more efficient through the use of catalysts capable of operating at lower pressures.

. The first large scale commercial synthetic methanol process was introduced by BASF in 1923. The process was based on the reaction of synthesis gas (a mixture of hydrogen and carbon oxides) over a zinc chromite catalyst at relative high temp (300 to 400 Co) and high pressure (250-350 atm). The synthesis gas was derived from coal via the water gas reaction. The first synthetic methanol unit in the USA was located at Belle, West Virginia, at the ammonia plant of Lazote, Inc, a subsidiary of Dupont and began operation in 1927. The unit was actually installed to remove the 1 to 2 % carbon monoxide impurity in the ammonia synthesis gas by utilizing the methanol synthesis reaction as purification step. Up till the end of World War II, methanol was mainly produced as a co product using synthesis gas from coke via the water gas or blue gas reactions as well as using off-gases form fermentation, coke ovens and steel furnaces. These methanol units were relatively small (less than 200 thousand tons per year, most in the 30 to 90 thousand tons per year range). One of the major technological changes often overlooked in the methanol industry was conversion from water-gas to natural gas as a source of synthesis gas for feed to the methanol converters. Natural gas derived synthesis gas was much higher quality , contained much less impurities and catalyst poisons , and was readily available in nearly unlimited quantity. 71% of the carbon monoxide uses for the synthesis of methanol was obtained form coke or coal , where as by 1948 about 77% was derived from natural gas. In 1966 , Imperial Chemical Industries (ICI) in England announced the second major break through in methanol technology , the ICI low pressure process for synthesis of methanol using a propri9etary copper based catalyst. The high activity copper based catalyst allowed the methanol synthesis reaction to proceed at commercially acceptable levels tat relatively low temp. (22-280 oC) thus allowing operation at significantly reduced pressure (50 atm) from that needed for the high pressure process (350 atm ). A number of improvements have been made in these early methanol process, principally in the area of improved energy efficiency. Subsequent low pressure process have revolutionized the industry and have allowed for the construction of more energy efficient and cost effective plant. Now a days, modern low pressure methanol units have a capacity of about 400-1000 thousand tons per year, operates at 50 to 100 atm.


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RAW MATERIALS

Long-term availability energy consumption and environmental aspects are all considered in choosing a raw material, however financial consideration are of primary importance. Keeping above described factors in view, a fuel containing sufficient amount of hydrogen and carbon monoxide is a possible raw material commonly known as synthesis gas for methanol production. Major resources from which synthesis gas be produced are 1. Natural Gas 2. Coal 3. Naphtha 4. Heavy hydrogen feed stock. Extraction of synthesis gas from these sources is further described here:

2.1 SYNTHESIS GAS FROM COAL:-

The production of gaseous fuel from coal has been practiced for 100 of years but most of the process for gasification was gradually replaced in the 1950s and 1960s by processes based on low cost petroleum hydrocarbons. The oil shortage of the 1970 renewed a worldwide interest in coal as chemical feedstock. However, recent falling prices of oil in the world have moderated that short lived interest. During gasification, falling ground coal reacts with oxygen and steam at elevated temp. to form a synthesis gas comprised mainly of carbon monoxide and hydrogen, with lesser amount of carbon-dioxide, methane, nitrogen, argon, hydrogen sulphide, tar and phenols. The quantities of the lesser components depend on the amount of impurities found in the coal and in the amount of oxygen fed to the gasifier. The heart of the coal based partially oxidation process in the gasification step. To achieve maximum efficiency, a gasifier should operate at an elevated pressure, have low oxygen and steam demand, have high carbon conversions and have low heat losses. It is also desirable to achieve high reliability, to minimize or eliminate by-product formation and to accept a wide variety of coals. Low temperature gasifiers produce considerably more methane, oils, phenols and tar than high temperature ones. A slagging gasifier operated at temperature above the fusion point so that ash is removed in the molten form; that temperature is typically b/w 2400-2700 oC. Selecting the best gasifier for a particular operation is usually a matter of compromise, since the designer must weigh many variables including the type of coal available, capacity, by-product rates, and capital investment efficiency and so on. Most gasifiers fall into one of three general categories atmospheric or low pressure, high pressure and second generation.

2.2 The Koppers-Totzok (K-T):-

Gasifier is an atmospheric process with extensive commercial experience in Europe, Asia and South Africa. It will handle all coals; make virtually no by-products operate with high thermal efficiency and high conversion. However, there is an extra cost associated with this






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process (Low Pressure Process), because it operates at atmospheric pressure; the product synthesis gas must be compressed before introduction to methanol synthesis loop. THE WINKLER GASIFIER is another low pressure process widely used in Europe, Japan and India. However, as a low-pressure process, it has the same advantages and disadvantages as the K-T process A high pressure process, the LURGIDRY ASH GASIFIER is the most widely used commercial process. It has even more disadvantages than K-T process, forms numerous by-products, has a limited ability to handle caking coals, and produces as large amount of methane (which must be purged from the converter loop, if the gas is used for the methanol synthesis).

2.3 The British Gas Council Lurgi (BGC-Lurgi):- Gasifier is another high pressure process, more efficient than LURGI DRY ASH PROCESS. Due to reduced steam usage and higher capacity, however, it produces great amount of by-

products and has only a limited ability to handle caking coals. The Texaco and Shell-Koppers:-

Gasifiers are two of the most promising second-generation process. Both offer many of the similar advantages as the atmospheric gasifiers, but both are high pressure operations, that accept all coals and make virtually no by- products. A large number of purification steps are necessarily required to produce methanol synthesis gas from the crude product gas leaving the gasifier since the raw gases contain no large number of undesirable by-products. Some or all of the following process steps may be required. Cooling with steam generation, water washing, compression, sulfur removal, shift conversion of carbon monoxide and after that hydrogen and carbon dioxide removal.

Kopper

Totzek Winkler Lurgi BGC Lurgi Taxaco Shell

Kopper

Pressure(atm) 1.4 1.4 2.1 20 -27 20 - 27 21 - 83 31 Temp.(oC) 1500 930 540-590 480-540 1290 1480

OxygenReqd. High Medium Low Low High High

Steam Reqd. Low Medium High Low None Low

Capacity (tons/day)

850 1000 500 1250 2000 1000

Raw Product gas analysis Vol%

---- ---- ---- ---- ---- ----

Carbon monoxide

58.1 35.0 24.6 60.6 46.3 67.7

Hydrogen 29.3 40.8 39.8 27.8 35 29.9

Carbon dioxide

11.0 22.0 24.6 2.6 17 1.1

Methane 0.1 1.2 8.7 7.6 0.2 0.2

Hydrocarbon ---- Trace 1.1 0.4 ---- ----

Inerts (N2, Ar) 1.5 1.0 1.2 1.0 1.5 1.1



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2.4 SYNTHESIS GAS FROM NAPHTHA During the 1950s an oversupply situation in Europe made naphtha an economical feed stock for steam reforming. A series of alkali promoted catalyst was developed specifically for naphtha, and by the early 1960s many European procedures where preparing synthesis gas from light distillate naphtha. At the present time the price of the naphtha feedstock and mixing it with a hydrogen stream so that the combined stream contain approximately 5% hydrogen stream so that the combined stream contain nickel molybdate catalyst to convert organic sulfur compounds to hydrogen sulfide and also to saturate alkenes. Desulphurization is then conducted as described above for hydrogenation. The sulfur free gas is fed to a reformer which contains catalyst specially designed for naphtha reforming. A stream to carbon ratio as lo as 2 is used, where pressure range from 1500-4000 Kpa (200 to 575 Lb/in2g). Small amount of carbon dioxide can be added optionally to yield synthesis gas composition similar to those obtained via hydrocarbon reforming.

2.5 SYNTHESIS GAS FROM NATURAL GAS:- The majority of methanol synthesis plants now use catalytic reforming of natural gas for the production of synthesis gas. The process consists of two steps Desulphurization and the steam reforming section.

a) Desulphurization:-

Natural gas contains both organic and inorganic sulfur compounds that must be improved to protect the both reforming and down stream methanol synthesis catalysts. They can position the catalyst even as low as 0.5 PPM. Hydrodesulphurization across a cobalt or nickel molybdenum zinc oxide fixed bed sequence is the basis for an effective purification system. The temperature in the range of 340-370 0C may be necessary.

R-SH + H2 R.H + H2S ZnO + H2S ZnS + H2O Zinc oxide is capable to reduce the H2S concentration down to 0.3 PPM.The disadvantages are that it is non-regenaratable must eventually be replaced. To have the advance warning before the ZnO bed is completely converted to ZnS at this point is provided at 755 of bed depth. When the ZnO changes to ZnS at this point, it is the time to renew the bed.Chlorides and mercury may also be found in natural gas, particularly from off shore reservoirs.Activated alumina or carbon beds can remove these poisons.


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b. STEAM REFORMING:- Once the sulphur has been removed from the hydrocarbon feed stream, the gas is mixed with steam and reform to produce methanol synthesis gas. The following reactions occur in the reformer.

CnH2n+2 + nH2O nCO + (2n+1) H2 -1 CnH2n+2 + 2nH2O nCO2 + (2n+1) H2 -2 CnH2n+2 (n-1/2) H2O (3n-1)/4 CH4 + (n-1)4 CO2 -3

All three of these reactions are endothermic, and in full scale commercial reformer, all three proceed essentially to completion. The primary reforming equilibrium reaction involves methane and steam:

CH4 + H2O CO + 3H2 H298 = 206.08 KJ/g -4 The equilibrium reaction of carbon monoxide with steam, often referred to as the water gas shift reaction, is also a significant contributor in this process.

CO + H2O CO2 + H2 H298 = - 41.17 KJ/g -5 Note that the reforming reaction (4) is endothermic and the water gas shift reaction (5) is exothermic. Undesirable reactions may occur in the reformer, resulting in deposition o carbon on the reactor walls, on the catalyst surface, or in the pores of the catalyst. This reduces the catalyst activity.

CnH2n+2 nC + (n 1) H2 -6 CH4 C + 2H2 -7 2CO C + CO2 -8 CO + H2 C + CO2 -9 CO + 2H2 C + 2H2O -10 A critical examination of the equations presented above allows one to make some preliminary conclusions concerning reformer operation. Since reforming reaction (4) is endothermic and the water gas shift reaction (5) is exothermic , it is obvious that less methane and more carbon monoxide and hydrogen would be obtained at higher temperature. It is also suggested that decreasing pressure would decrease the amount of methane in the reformer product stream.


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In a similar manner , increasing the partial pressure of the steam would result in a decrease in the amount of methane in the product. A set of equations , which is used to calculate the composition of exit stream, is eq.(4),(5) and eq.(8). Carbon composition via eq-8 can theoretically be prevented by ensuring that steam is present in excess of some minimum amount calculated using the equilibrium equations. Any increase in steam also has the effect of increasing methane conversion. Most Commertial reformers operate safely with steam carbon ratio in the range of 3 to 4.5. Reforming catalysts contain from 12 to 25 % nickel as nickel oxide supported on calcium aluminate , alumina or calcium titanate .Alkali metal compounds added to prevent carbon formation and increase catalyst durability. The feed stream to the reformer is distributed over hundreds of parallel catalyst filled tubes, the tubes are subjected to a temperature range of 860 to 950 oC, wit process gas exit temperature in the range of 750 to 850 oC & pressure range from 4 to 35 atm (450 to 3550 Kpa). Gas hourly space velocities are usually on the order of 5000 to 8000 based on wet feed. The flue gases temperatures are in the range of 980 to 1040 oC. These hot flue gases are transferred to a convection section where they are cooled and used to super heat steam for provide motive power for compressors and large pumps, process steam for reforminf and reboil duty for distillation.

2.6 SELECTION OF RAW MATERIAL Natural gas is the only most convenient and economical raw material available in Pakistan. This God gifted treasure is found in large reserves at Sui, Mari and some other areas. Natural gas is easily available , cheap raw material , containing low impurities and there are no transportation and storage costs involved. Hence natural gas is the most economically suitable raw material for synthesis gas. Coal is another source for the Sun. gas production in Pakistan. Coal available in Pakistan at MAkerwal, Dhodak and Kalabagh but its quality is very poor. However , the largest reservoirs of coal in world now found in Pakistan at Thar. No doubt, these reservoirs contain small amounts of sulfur about 0.1-0.7% but there are some other factors involved in degrading the coal selectivity for Syn. Gas production , such as high transportation cost , handling and storage cost , further more additional equipment (gasifier etc) and process costs. Coal contains much impurities and mineral materials (as compared to the natural gas) lead to the formation of the various pollutants during combustion having adverse environmental impacts when emitted into the atmosphere. The environmental aspects that are associated with the use of coal are, the formation of pollutants such as fly ash , sulfur oxides, nitrogen oxides and other mineral materials. Also coke formation occur and this is higher compared to the natural gas and this reduces the activity of catalyst and may stick to the walls of steam reformer which reduce the heat transfer rate. Naphtha is not economically viable for Syn gas production in Pakistan, its reservoirs are limited in Pakistan and do not meet sufficiently the other demands (motor fuels). Its costs are too much as compared to the natural gas, hence it is not usable , same is the matter involved in selection of heavy hydrocarbons.


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Capacity Selection

As mentioned earlier that currently thee is no methanol producing plant in Pakistan and all is being imported from other countries (see in table).Major exporters are Saudi Arabia and Iran. Methanol consumption in Pakistan is about 26800 tons / year (90 tons /day), report issued by Federal Bureau of Statistics 2004-2005. Lets take a look to the international market ; methanol production is going to increase and foreign methanol producers are extending their capacities in order to meet the growing demand (as shown in the tables, where world methanol plants capacities supply /demand by the year 1998- 2007 are given , which contains the previous , present and anticipated capacities and shows comprehensive increasing trend in demand).


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Also rising image so methanol as an Alternative Fuel for motor vehicles is a matter of great consideration for scientists. As far as Pakistan is concerned , gasoline and diesel prices are high and unstable. CNG and LPG are used as alternative fuels but methanol is easy to be stored and transported compared to CNG and LPG (it is a liquid fuel. These characteristics make the prices of methanol vehicles and refueling stations cheaper than the price of CNG and LPG vehicles and refueling stations. These methanol based vehicles will be available by the year 2005 in foreign markets and some major motor manufacturing companies may also invest in Pakistan, Raw material foe methanol synthesis (N.G) is cheaper here in Pakistan, which is a primary factor involved in reducing its price ,also methanol is environmental friendly. In Pakistan , methanol is being employed in making urea formaldehyde , acetic acid and methalated spirit for pharmaceutical and dyes etc. industries. Now a new formaldehyde plant is being installed by Dyno chemicals at Hub Industrial And Trading Estate. Super Chemicals (Karachi) , Wah Nobel Chemicals (Wah Cantt.) and Pakistan Resins (Azad Kashmir) are also manufacturing urea formaldehyde. As A result of this brief discussion , we may say that our capacity of 150 tons/ day is reasonable , where 90 tons / day is present consumption in Pakistan and remaining 60 tons/ day could be exported and If demand of Pakistani market increases , we may reduce or stop its export to fulfill out demand.

3.1 Methanol Imports In Pakistan

Countries 2002-2003 2003-2004 2004-2005

LTR Rs * 103 LTR Rs * 103 LTR Rs * 103

Asian Countries NS

18000 336 26800 610 - -

Bangladesh - - 200000 2700 - -

China - - 132040 5217 - -

Dubai - - 450000 5434 2309723 23752

Germany 210000 2140 9751 534 58612 2478

Indonesia - - 26080 647 - -

Iran - - 101570 1662 4099556 41170

Kuwait - - 100000 2892 - -

Laos 13040 200 - - - -

Malaysia 373651 3094 13040 328 114338 1934

Natherland 690180 10042 281600 11671 101100 4481

New Zealand - - 13040 249 - -

Saudi Arabia 254266 213426 31965758 394528 27093185 298683

Singapore - - 440000 11410 13040 273


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South Africa Rep

14768 148 - - 104 40

Spain - - - - 79200 1024

Turkey 25600 386 - - - -

Thailand - - - - 200000 2033

U.S.A 424633 2863 - - - -

U.K - - 3000 145 - -

Total (LTR) 27196520 232635 33762679 438026 34068859 375831

Tons 26800 36559 43800


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4.1 Methanol Manufacturing Process

The Methanol Industry in Trinidad began with the construction of a 1,200 MT state-owned methanol plant in 1983 (Trinidad and Tobago Methanol Companys first plant). Since that time, the industry has expanded to include four larger plants with an annual production capability close to 3 million MT of methanol.

At the MHTL Point Lisas Methanol Complex, methanol is made using the ICI Low Pressure Methanol Synthesis Process. The two main raw materials used are natural gas (96% methane) received from the National Gas Company (NGC) to provide the carbon and hydrogen components and water from the Water and Sewerage Authority (WASA) to provide the oxygen component. These raw materials undergo a series of chemical reactions to produce crude methanol which is then purified to yield refined methanol, having a purity exceeding 99.9%.

The plants operate continuously 24 hours a day in a production process that can be divided into four main stages: Feed Purification, Reforming, Methanol Synthesis and Methanol Purification as shown in the flow sheet below:

STEP1 FEED PURIFICATION

The two main feed stocks, natural gas and water, both require purification before use. Natural Gas contains low levels of sulphur compounds and undergo a desulphurization process to reduce, the sulphur to levels of less than one part per million. Impurities in the water are reduced to undetectable or parts per billion levels before being converted to steam and added to the process. If not removed, these impurities can result in reduced heat efficiency and significant damage to major pieces of equipment.






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STEP 2: REFORMING

Reforming is the process which transforms the methane (CH4) and the steam (H2O) to intermediate reactants of hydrogen (H2), carbon dioxide (CO2), carbon monoxide (CO). Carbon dioxide is also added to the feed gas stream at this stage to produce a mixture of components in the ideal ratio to efficiently produce methanol. This process is carried out in a Reformer furnace which is heated by burning natural gas as fuel.

STEP 3 : METHANOL SYNTHESIS

After removing excess heat from the reformed gas it is compressed before being sent to the methanol production stage in the synthesis reactor. Here the reactants are converted to methanol and separated out as as crude product with a composition of methanol (68%) and water (31%). Traces of byproducts are also formed. Methanol conversion is at a rate of 5% per pass hence there is a continual recycling of the unreacted gases in the synthesis loop.

This continual recycling of the synthesis gas however results in a build-up of inert gases in the system and this is continuously purged and sent to the the reformer where it is burnt as fuel. The crude methanol formed is condensed and sent to the methanol purification step which is the final step in the process.

STEP 4 : METHANOL PURIFICATION

The 68% methanol solution is purified in two distinct steps in tall distillation columns called the topping column and refining column to yield a refined product with a purity of 99% methanol classified as Grade AA refined methanol.The methanol process is tested at various stages and the finished product is stored in a large secured tankage area off the plant until such time that it is ready to be delivered to customers. Since

4.2 Methanol Process Description

The Leading Concept Methanol process in use at the Coogee Methanol Plant has various advantages compared to the conventional methanol processes. Some of those advantages are that it is efficient and compact and substantially reduces waste through the internal recycling of process effluents.




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Natural gas feedstock is delivered to the plant via a pipeline from the main Sui to plant location carrying Bass Strait gas. The gas is first compressed and then purified by removing sulphur compounds. The purified natural gas is saturated with heated and recycled process waste water. The mixed natural gas and water vapour then goes to the gas heated reformer to be partially converted to synthesis gas, a mixture of carbon dioxide, carbon monoxide and hydrogen. This partially converted gas is then completely converted to synthesis gas by reaction with oxygen in the secondary reformer.

The synthesis gas is then converted to crude methanol in the catalytic synthesis converter. The crude methanol is purified to standard quality specifications by removing water and organic impurities through distillation. The water and organic impurities are recycled.

Process Description

The Coogee Energy plant is designed to produce 164 tones per day of methanol from about 5 TJ/day of Bass Strait natural gas.

The plant consists of four main process steps : feed gas preparation, synthesis gas generation, methanol synthesis and distillation supported by utilities and offsite units.

Feedgas Preparation

Natural gas is compressed to about 45 bar and sulphur removed by hyrodesulphurisation in the purifier. The desulphurising gas is cooled and flows to the saturator where it contacts with hot water over a bed of packing. The saturated gas leaving the vessel contains about 92% of the steam required for reforming. Saturator make up is 90% process condensate and the balance refining column bottoms water. Prior to leaving the saturator the gas stream is contacted with recycled fusel oil where waste products from methanol synthesis are stripped off. A blow down stream is required to control dissolved solids. Additional steam generated in the boiler is made up to the gas stream to achieve 3.0:1 steam to carbon ratio for reforming.

The total feed stream is then heated in the gas heated reformer preheated. Both the preheated and boiler are fired with a mixture of synthesis loop purge gas and natural gas.

4.3 Synthesis Gas Generation

Reactions

There are three main chemical reactions which occur in this process step :

Steam reforming-

CH4 + H2O = CO + 3H2

Shift reaction - CO + H2O = CO2 + H2


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The net effect of these reactions is the production of a synthesis gas stream which is composed of carbon monoxide (CO), carbon dioxide (CO2) and hydrogen (H2).

Description

Preheated gas flows from the preheater to the tube side of the advanced gas heated reformer (AGHR). The feedstock is heated from the feed temperature of 425 C as it passed down through the catalyst and the reforming reactions start. The AGHR contains 19 reforming tubes which contain the reforming catalyst.

Hot reformed gas exits the bottom of the reforming tubes and flows to the tube side exit of the AGHR at about 700C. The heat required for the endothermic reforming reaction is derived from cooling the secondary reformer effluent in the shell side of the AGHR. About one quarter of the methane is reformed in the AGHR.

The partly formed gas flows from the AGHR to the combustor/secondary reformer where the bulk of the reforming takes place. The heat required for the endothermic reforming in both the AGHR and secondary reformer is provided by partially burning the AGHR effluent with pure oxygen in the combustor located integrally at the top of the secondary reformer. Oxygen is injected into the gas via a specially designed gun. About 0.50 tonne of oxygen per tonne of methanol is required.

The oxygen is completely consumed and the resulting hot gas stream passes over the secondary reforming catalyst. Reforming reactions continue and the gas leaves the secondary reformer at up to 1000C with less than 0.5% methane slip. The secondary effluent passes to the AGHR shell and thence through the heat recovery train to provide heat for the saturator circuit and distillation reboilers. The process condensate which condenses out of the reformed gas is recycled back to the saturator. After heat recovery the reformed gas is finally cooled and then compressed to about 70 barg in the synthesis gas compressor to be fed as synthesis gas to the synthesis loop.

Bass Strait natural gas contains about 93.6 mol% of methane, 3.5 mol% of ethane with the balance being predominantly propane, nitrogen and carbon dioxide. On an offshore facility with less sophisticated gas separation facilities there may be higher levels of higher hydrocarbons such as components but the oxygen consumption would increase.

The synthesis gas joins the synthesis loop recycle gas from the circulator to pass through the loop interchanger and be fed to the methanol converter at about 130 C. The converter is a tubular cooled converter design where the gas is preheated to reaction temperatures inside the tubes as it flows up through the hot catalyst bed. This type of converter maximizes catalyst efficiency as it enables a temperature profile to be maintained inside the converter that is close to the maximum reaction rate curve. The hot reacted gas leaves the converter and provides heat to the saturator water circuit and the loop interchanger before finally being cooled. Crude methanol is separated from the uncondensed gases in the loop catch pot and the gases recirculated back to the converter via the circulator.


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Distillation

Crude methanol from the loop catch pot is filtered to remove traces of wax, let down in pressure and fed to the product purification section. This section consists of a topping column and a refining column. Unlike most methanol distillation columns these columns are packed with structured packing. Reboiler duty is provided by reformed gas. The product methanol specification is for a water content of less that 0.10 wt %. The water bottoms from the refining column has a specification of less than 100 ppm of methanol and is recycled back to the saturator. Other synthesis byproducts such as higher alcohols are collected as fusel oil and recycled back the saturator.

4.4 LCM -The Low Cost Methanol Technology

Introduction The emphasis on reducing the cost of production of methanol is nothing new. Aside from a short period after the invention and commercial introduction of the Low Pressure Methanol Process by ICI in the mid-1960s, that pressure has always been present. ICI itself was no stranger to this as many of its older businesses were in commodity products whose profitability relied critically on minimizing the cost of production in order to maintain acceptable margins. However, cost of production is not just a case of reducing capital cost, although undoubtedly this is an important part of the total picture. Often the installed cost of the plant appears to be given greater weighting than is justified from a simple economic assessment. It is understandable, though, that at the time of selection of the technology vendor, everyone's mind tends to be focused on the need to raise the money, and fixed and variable costs of operation can recede into the distance. Methanex and Synetix have been working together for some time to identify the optimum route for syngas generation for the manufacture of methanol and other GTL products. Many options were investigated, but it was determined that the Synetix Syngas Generation (SGG) process offered the most economic route and the methanol process based on SGG, the LCM Process, was the most attractive option at high capacities.

Historical Perspective It was against a background of intense competitive pressure on its Fertilizer Business that ICI mandated its Catalyst and Technology Licensing Department (now a part of Synetix) to develop a compact reforming process to revolutionize the manufacture of ammonia. In many


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ways, the process that was developed, LCA, was revolutionary and ahead of its time, but the fundamental principles behind the project were similar to those operators need to adopt to prosper in today's highly competitive methanol industry.The legacy of ICI's commitment in building the LCA plants at its Severnside Works in the late 1980s is that the Synetix Gas Heated Reformer (GHR) can no longer be thought of as new technology. It is well-proven now, with over 30 operating years experience spread over the 4 plants that have been built around the technology. These plants are: Absolutely key to the successful operation of these units has been the adoption of the correct metallurgy to withstand the conditions within the reformer. There can be no doubt whatsoever, that metal dusting has been overcome as an issue within the range of operating conditions of these plants. However, without detracting from the importance of the metallurgy, it is the mechanical design of the reformer that turns concept into reality. With the introduction of the Advanced Gas Heated Reformer (AGHR) into the Coogee Energy MRP in April 1998, Synetix incorporated a number of novel features that significantly simplified the compact reformer in terms of design,construction, maintenance and operation.

Key Success Factors Clearly, many factors are important to an operator/investor in making a project successful. A number of these factors is listed below.

Selling price

Financing costs

Gas price

Import tariffs

Delivery costs

Maintenance costs

Manpower costs

Plant installed cost

Plant efficiency

Plant reliability Items 1-3 are commercial issues over which the operating company has varying degrees of influence. Items 4 and 5 will be very location specific, with the latter being a key factor as methanol is transported from more remote locations to the consuming markets. Items 6-10 are influenced by location, but it is in these aspects that choice of technology and the standard of engineering design can have a major impact. The focus of the rest of the paper will be mainly on these areas.

Compact Reforming The term "Compact Reforming" implies that the main aim of the new technology is to reduce the size. This was indeed a consideration, and it may be the only benefit offered by certain types of compact reforming device. However, when Synetix was developing the syngas process for the new ammonia plants for ICI, there was a much broader goal, which included the complete elimination of steam generation and the steam system. This required a complete


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rethink and a major simplification of the whole heat recovery scheme. The intention was to use the hot reformed gas from the Secondary Reformer to provide the heat directly for the methane steam reaction in a heat exchanger reformer. It was not the first time such an idea had been proposed, but the major stumbling block was always the fact that metal dusting conditions were present on the hot side of the heat exchanger. Many options had been considered by others, including approaches that would avoid metal dusting by, for example, using ceramic tubes, but none had been successful. The breakthrough by Synetix came in first identifying materials that were resistant to metal dusting under the conditions envisaged and then in proving that they were resistant in a full-scale, single-tube reformer operating under real process conditions. This trial unit was built and operated on ICI's Bellingham, UK site and provided essential process design data, but more importantly verified the selection of metallurgy. The first successful implementation of compact, heat exchange reforming on the industrial scale was in the GHRs installed on the LCA plants at Severnside, UK in 1988. The first successful deployment of the AGHR was at Laverton, Australia in 1998.

Operability of the LCM Process The absence of steam raising and a steam system offers many benefits, but it does mean that there is no obvious source for the process steam required for the methane steam reforming reaction. Fortunately, this is an easy issue to address since Synetix have used a saturator circuit for many years as a way of recovering low grade heat and turning it into process steam without raising steam directly. Water is pumped through a set of heat exchangers and warmed up before being contacted in a packed tower with the natural gas feed from the Purification section. The saturator typically provides J to of the process steam required in a conventional plant, but this concept can easily be extended to provide all of the steam needed for the methane steam reforming reaction in the AGHR. Of course, as this is the only source of steam, the saturator circuit assumes a greater importance than before. In the LCM Process, between 30 and 40% of the heat being supplied into the saturator circuit comes from the methanol synthesis loop. So, if the synthesis loop were not running, there would be a significant shortfall of heat that would need to be acquired from elsewhere or the whole plant would have to shut down. Normally, whenever there is a trip on a plant, everything is done to try to maintain flow through the reformer and firing on it in order to avoid a temperature cycle. This is where another valuable feature of the LCM Process becomes important, and that is the ease of start-up and shut-down, which means that a temperature cycle on the reformer is of rather less concern. The AGHR can be thought of as simply a feed effluent exchanger around the Secondary Reformer. Start-up then requires nothing more than a mechanism to get the Secondary above the auto-ignition temperature of the feed gas and the whole unit will come on stream very quickly. Following a plant trip, heat is trapped within the Secondary by the feed effluent exchangers preventing it cooling too much. From a cold restart, heating is achieved using a simple catalytic combustor as a start-up heater generating hot syngas. On the LCM Process it may take up to 12 hours from introduction of feed gas before the plant is making methanol, whereas on a warm restart (which could occur even after several days off line) the time taken can be 6 hours or less.


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METHANOL SYNTHESIS The heart of any Methanol synthesis process is Methanol converter. The converter contains the catalyst over which synthesis gas is converted to methanol. The main difference between competing methanol process today lies in the converter and its method of temperature control and heat recovery.

5.1 TYPES OF CONVERTER:- The four basic types of converters are Quench Converter Multiple Adiabatic Converter Tube-cooled Converter Steam Raising Converter

1. QUENCH CONVERTER:- The quench converter was the basis for the initial ICI low pressure methanol process. Quench type converters used multiple catalyst beds, typically contain three to six catalyst beds. Bed volumes are sized to help control the exothermic methanol synthesis reaction. Additionally, cool feed gas is injected between beds to control or quench catalyst bed inlet temperature. Reaction heat is recovered through added heat recovery exchangers located downstream of the converter.

2. MULTIPLE ADIABATIC CONVERTER:- The adiabatic converter system employs heat exchanger rather than quench gas for introduce cooling. Because the beds are adiabatic, temperature profile exhibits still the same saw tooth approach to maximum reaction rate, but catalyst productivity is somewhat improved because all of the gas passes through the entire catalyst volume. Costs for vessels and exchangers are generally higher than for quench converter system.

3. TUBE-COOLED CONVERTER:- The tube cooled converter functions as interchanger, consisting of a tube filled vessel containing catalyst on the shell side. The combined synthesis and recycle gas enters the bottom of the reactor tubes, where it is heated by reaction taking place in the surrounding catalyst bed. The gas turns at the top of the tubes and passes down through the catalyst bed. The principle advantage of this reactor is in the reduced catalyst volume, since the reduction path move closely follows the maximum rate line. Converter performance can further be enhanced by extending the catalyst below the tube cooled area to act as a further adiabatic reaction zone.






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4. STEAM RAISING CONVERTER:- There are varieties of tubular steam raising converters available, which feature radial or axial flow, with the catalyst on either shell or tube side. The near isotherm reaction of this rector type is the most thermodynamically efficient of the types used, requiring the least catalyst volume, lower catalyst peak temperatures also results in reduced by-product formation and longer catalyst life.


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Low pressure drop, both in converter and heat exchanger equipment, to minimize recycle compression energy.

High conversion per pass that reduces required cycle, minimizes synthesis loop capital cost & maximizes reaction heat recovery.

Efficient recovery of exothermic reaction heat of methanol synthesis. Corrosion resistance to formation of iron carbonyls that can poison the catalyst and

promote formation of undesirable hydrocarbon by-products. A high yielding, commercially proven, long life synthesis catalyst to minimize costly

catalyst replacement. Low capital cost. Good economy of scale, high capacity single train converter.

5.2 METHANOL SYNTHESIS TECHNOLOGY TODAY Different companies have been involved in practicing their technologies for methanol synthesis. But the question is which company offers the most dependable and economically viable process. This is visualized by the percentages obtained by evaluating their practical applications as shown below: Company Name Production Rate

Imperial Chemical Industry (ICI) 61%

LURGI CORP. 27%

Mitsubishi Gas Chemicals (MGS) 8%

KELLOGG 3%

5.3 ICI LOW PRESSURE METHANOL PROCESS Most of the difficulties involved in developing the new Low Pressure methanol process were successfully overcome by the ICI 50atm process. Methanol was first synthesized commercially at low pressure when ICI commissioned its 300-tons/dayplant at Birmingham in December, 1966. a copper based catalyst, more active and selective was used. The greater activity of this catalyst permits the synthesis of methanol from gaseous mixture of hydrogen and carbon dioxide at much lower pressure and temperature of the order of 50 atm and 250 oC respectively. Several innovatory features were incorporated in the design. They include a new simple type of quench bed converters, larger in diameter then conventional converters and easy catalyst charging and discharging procedure. The use of rotary machine of synthesis gas compression which was significant, because it demonstrated the concept of single stream unit, well known in large scale ammonia plant, was now a practical proposition for small methanol production units.


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In 1972 ICI commissioned a 1100 tons/day plant based on their latest technology. It operates at 100 atm and uses a modified version of original low-pressure methanol synthesis catalyst. For capacity greater than 500 tons/day, the 100 atm process plants are adopted, whereas for smaller plants of outputs from 150-500 tons/day, the 50 atm process is used.

5.4 LURGI LOW PRESSURE METHANOL PROCESS At the end of fifties, Lurgi began development of a low pressure methanol process, using highly active copper catalyst at 50 atm pressure. At that time, the space time yield and catalyst life was not satisfactory (Sulfur Poisoning) which resulted in the suspension of further development work.


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In 1964 research work was resumed. At that time the purification of synthesis gas (Using Lurgi Rectisol (50 atm process) was no longer a problem. Several years of development work required in selecting from numerous catalysts available a suitable catalyst. Because of Lurgis experience in Fisher Tropsch synthesis reactor, the methanol reactor was based on a design worked out of Fisher Tropsch Synthesis. This reactor is similar to a vertical and tube heat exchanger and was a promising solution, to both reactor design and heat recovery problem. The tubes closed at their lower end by the hinged grid with boiling water, maintaining a substantially uniform catalyst temperature over the reactor cross section and over the full length of the tubes. Early 1970 Lurgi decided to build its own methanol plant with a small capacity to serve mainly for demonstration purposes and also to study the problems which might come up in the large scale plants. The first commercial plant with a capacity of 4000 tones/yr was built at wesseting (West Germany) in April, 1971. This plant was built in two days, was designed on the basis of a computer programme.

5.5 ADVANTAGES OF THE LOW PRESSURE METHANOL PROCESS Reduced by-product formation resulting in lower feed stock consumption per ton of

methanol. Reduced compression cost due to lower operating pressure. The ability to use steam directory compressors on small plants. Lower steam pressure through out the plant. The avoidance of CO2 addition in natural gas based plant without incurring large

financial penalties. Simplicity in design and low-pressure equipment, suitable for large and small plant. Commissioning period. Proved in wide practical services.

PROCESS SELECTION In 1966, an Imperial Chemical Industry (ICI) is the first, which announced the low pressure process for synthesis of methanol using proprietary copper based catalyst.


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A number of other companies in the late 1960s and early 1970s announced their own low pressure processes and proprietary copper-based catalyst; these companies included Lurgi, Mitsubishi etc. Today two processes are mostly used. 1) ICI low pressure (61%) 2) Lurgi low pressure process (27%) ICI process used Cu-Zn-Al catalyst while Lurgi process used CU-Zn-V or Cu-Mn-V catalyst. Besides the catalyst, these processes differ in their method of temperature control and heat recovery. ICI use quench type adiabatic converter with multiple catalytic beds. Bed volumes are sized to help control the exothermic methanol synthesis reaction. Additionally, cool feed gas is injected between beds to control or quench catalyst bed inlet temperature. Reaction heat is typically recovered through added heat recovery exchangers located downstream of the converter. Whereas Lurgi used shell and tube (Isothermal type) converter with boiling water for temperature controls. Overall results of quench type converter is best than other type of converter. The main drawback of water cooled tubular (Isothermal) converter is that internal tube sheets have failed in some tubular isothermal methanol converter design. The long down times associated with a catastrophic converter failure could financially devastate most procedures. In addition converter internal baffles, expansion joints, gas distributors and internal exchangers can fail and cause internal leaks. These components should be extremely rugged to withstand the operating abuse imposed by actual commercial operation. Cost is another major factor for the selection of process. ICI process has low cost as compare to the other processes. Therefore the ICI process is also called ICI LCM (Low Cost Methanol) process. Thats reason ICI LCM process is mainly used in the world. Considering these entire factor we select the ICI LCM process.


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6.1 DESULPHERIZER CATALYST Hydrocarbon feeds for steam reforming must have a very low sulfur contents, since nickel reforming catalysts are quite susceptible to poisonings even by levels as low as 0.5PPM. In many cases, sulfur can be removed b y adsorption over a bed of activated carbon at 15-500C. Frequent regeneration may be necessary; which can be accomplished by heating the bed and for stripping it with steam or hot gases. The activated carbon bed adsorbs high boiling sulfur compounds such as mercaptans, much more rapidly than low boiling compounds such as H2S .As a result, adsorption over a sacrificial guard bed of zinc oxide at temperature in the range of 340-370 0C. Hydrodesulphurization may be necessary for organic sulfur compounds that are not removed by either zinc oxide or carbon bed. This is accomplished by mixing the sulfur containing steam with hydrogen, so that the hydrogen contents are approximately 5%, the resulting mixture is passed over a bed of cobalt or nickel molybdate catalyst at temperature of 290-370oC. Under these conditions, sulfur compounds are conditions, sulfur compounds are converted to hydrogen sulfide, which can be removed in a zinc oxide bed. Now a days, codes are used to represent the catalysts shown here: The KATALCO range of absorbents and hydrogenation catalysts ensures an optimized system for meeting individual plant requirements. Sulfur Removal Catalysts Hydrodesulphurization Catalyst. KATALCO32-4 KATALCO 41-6 KATALCO 61-1 PURASPEC 2570 These catalysts are used by ICI.

6.2 STEAM REFORMING CATALYST Reforming catalyst usually contain from 12-25% nickel oxide supported on calcium aluminate titanate. Calcium aluminate has generally replaced calcium aluminum silicate, has support material to avoid the problem of silica migration encountered in earlier catalyst formulation. Alkali metal compounds added to prevent carbon formation and to increase catalyst durability include potassium aluminum silicate, potassium carbonate and potassium poly aluminate, sulfur chlorine and arsenic compounds. Poison the catalyst, sulfur poisoning is reversible, but chlorine and arsenic poisonings are severe and generally irreversible. Synetix has been associated with pre-reforming catalysts since the 1960s and together with kvaerner process technology recently launched the new CRGLH series of catalysts. These have been demonstrated to be the most active and robust commercially available product for this application. KATALCO 25-4 KATALCO 57-4 KATALCO 23-4

KATALCO 46-Serie KATALCO 23-4Q KATALCO 25-4Q


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6.3 METHANOL SYNTHESIS CATALYST High Pressure Catalyst Zinc Chromite catalyst, reduced zinc oxide promoted with Chromia was the catalyst used in the 1st large scale commercial methanol process developed by BASF in Germany in 1920s. The zinc Chromite catalyst with improvements over the years was only the catalyst of consequence used for the high process methanol process, up until the high pressure process was phased out in 1970s. Although BASF is credited with a 1st commercial methanol process generally attributed to G. TART in FRANCE in 1921. He defined his methanol catalyst has being all metal, oxides and salt active in hydrogenation. Small unit was built near Paris to test catalyst for PARTARTS process and began operation in 1923. The unit was designed to operate at 150-200 atm pressure. 300-6000C, with hydrogen to carbon monoxide feed gas ratio of 2:1. The BASF high pressure methanol process was operated at 250-3500 C, similar to the conditions purposed by PARTART. Now low pressure, process commonly called ICI low pressure process is used because of its practical feasibility.

6.4 LOW PRESSURE CATALYST Early in the developing methanol industry, it was recognized that to significantly improve the high pressure methanol process, a much more active catalyst than zinc chromite was needed. A more active catalyst would permit operation at lower temperatures and pressures, yet still allow acceptable production rates to be mentioned. Copper based catalysts known from the 1920s have been more active than zinc chromite. Copper based catalysts, however, were also known to be much more susceptible to poisoning by sulfur, chlorine, etc. than zinc Chromite, Zinc Chromite, for example, could tolerate sulfur levels of more than PPM in the feed gas, whereas for copper based catalysts, sulfur must be kept below 1 PPM. Generally poor quality of synthesis gas and the limited purification techniques available at that time resulted in an unacceptably short operating life for the copper based, catalysts and precluded their commercial use. A second breakthrough in the methanol technology occurred in 1966 with the introduction of ICIs low-pressure process for the production of methanol. This was made possible by a major improvement in synthesis gas quality from the introduction of hydrocarbon steam reforming and improved purification techniques for the hydrocarbon feed stock. The synthesis gas from steam reforming contained only trace quantities of impurities and proved ideal for methanol synthesis with a copper catalyst. The ICI process, using a much more active copper based catalyst could operate efficiently at 50 atm pressure and at temp. of 220-280oC. The copper based catalyst developed by ICI was also more selective than the high pressure zinc chromite catalyst and operated at a much lower temp. Consequently, it produced a significantly lower of impurities than zinc Chromite as shown in following table.


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LEVEL OF IMPURITES PRODUCED BY MS CATALYSTS

Impurity ZnO/Cr2O3 catalyst Cu/ZnO catalyst

Dimethyl ether 5000-10000ppm 20-150ppm

Carbonyl compds 80-220ppm 10-35ppm

Higher alcohols 3000-5000ppm 100-2000ppm

Methane Variable None

6.5 SOME OTHER SALIENT FEATURES Copper based catalyst produced no methane. The possibility of a highly exothermic runaway methanation reaction leading to catalyst sintering and possible converter damage was a continual threat in the high pressure process. This improvement is selectivity for the copper based catalyst over zinc Chromite was estimated to reduce feed stock requirements from 5-10% for the equivalent amount of methanol produced. Hence ICI methanol catalysts were both active and long lived and generally considered a benchmark in industry and represented a significant achievement in heterogeneous catalysis. Catalysts used by ICI in methanol synthesis in accordance with SYNETIX are:-

KATALCO 51-8 PPT for ARC-Reactors. KATALCO 51-8 PPT for Tubular and quench type reactors.

6.6 RECENT CATALYST DEVELOPMENTS Following ICIs breakthrough in methanol technology in 1966, other companies quickly followed with their own alternative low-press. Methanol processes and catalysts. Companies that currently have both a methanol process and catalysts, include ICI, Lurgi, Haldor Topsoe, BASF, Ammonia Casale and Mitsubishi Gas Chemical. A patent survey of representative copper based methanol catalysts is shows in following table.

Company Catalyst system

Typaical atomic ratio

Ammonia casale Cu-Zn-Al-Cr 29:47:6:18

BASF Cu-Zn-Al Cu-Zn-Al-Cr-Mn

32:42:36 38:38:0.4:12:12

DUPONT Cu-Zn-Al 50:19:31

HALDOR TOPSOPE Cu-Zn- Cr 37:15:48

ICI Cu-Zn-Al Cu-Zn-Al

61:30:9 64:23:13


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LURGI Cu-Zn-V Cu-Mn-V

61:30:9 48:30:22

MITSUBISHI GAS CHEMICAL

Cu-Zn-MP Cu-Zn- Cr Cu-Zn-B

55:43:2 55:43:2 61:38:1

SHELL Cu-Zn-Ag Cu-Zn-Re

61:24:15 71:24:5

UNITED CATALYSTS Cu-Zn-Al 62:21:17

6.7 CURRENT CATALYST COMPOSITION All commercial low-pressure methanol catalyst contains copper and zinc oxides together with one or more additional promoters, usually aluminum or chromium oxide. ICI, for example, reports a standard industrial catalyst to contain copper oxide, zinc oxide and Alumina in a ratio of 60:30:10, respectively.


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Balance Around Distillation Column Light ends (L) A = 150 Tons/day CH3OH 99.85% 149.775 tons H2O 0.14% 0.216 tons HCHO 0.003% 0.0045 tons A4 CH3COOH 0.003% 0.0045 tons

CH3OH 80% wt % H2O 18% CO2 0.20% W HCHO 0.40% Waste Water CH3OCH3 0.40% C2H5OH 0.30% C3H7OH 0.20% C5H11OH 0.20% CH3COOH 0.30%

Basis:- One day Operation

Methanol Balance:- 0.8 A4 = 0.9985 A A4 = 187.21 tons CH3OH in A4 = 149.775 tons H2O in A4 = 33.69 tons CO2 in A4 = 0.3748 tons HCHO in A4 = 0.748 tons CH3OCH3 in A4 = 0.748 tons Total light ends in A4 = 1.87 tons C2H5OH in A4 = 0.561 tons C3H7OH in A4 = 0.374 tons C5H11OH in A4 = 0.374 tons CH3COOH in A4 = 0.561 tons Total Heavy ends in A4 = 1.872 tons

Distillation Column (1)

Distillation Column (2)


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Calculation of W:-

Water in W = Water in A4 - Water in A = 33.48 tons CH3COOH in W = CH3COOH in A4 = CH3COOH in M = 0.557 tons C2H5OH in W = C2H5OH in A4 = 0.561 tons C3H7OH in W = C3H7OH in A4 = 0.374 tons C5H11OH in W = C5H11OH in A4 = 0.374 tons So, W = 35.35 tons

Now, % of H2O = 94.71 % % of CH3COOH = 1.57 % % of C2H5OH = 1.58 % % of C3H7OH = 1.05 % % of C5H11OH = 1.05 %

Calculation of L:- HCHO in L = HCHO in A4 - HCHO in A = 0.744 tons CO2 in L = CO2 in A4 = 0.374 tons CH3OCH3 in L = CH3OCH3 in A4 = 0.748 tons Total L = 1.86 tons % of HCHO = 39.85 % % of CO2 = 20.04 % % of CH3OCH3 = 40.09 %


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Now as A4 = 187.21 tons/day &1 day = 24 hrs 1 ton = 1000 kg So, A4 = 7800.78 Kg/hr Now arranging the whole data in a tabular form,

Component Wt % Wt Mol.Wt k.Mole Mole % CH3OH 80% 6240.6 32 195.0 70.54 H2O 18% 1404.1 18 78.0 28.21 CO2 0.2% 15.60 44 0.35 0.128 HCHO 0.4% 31.20 30 1.04 0.376 CH3OCH3 0.4% 31.20 46 0.67 0.245 C2H5OH 0.2% 23.40 46 0.50 0.184 C3H7OH 0.3% 15.60 60 0.26 0.094 C5H11OH 0.3% 15.60 88 0.17 0.064 CH3COOH 0.2% 23.40 60 0.39 0.141 276.4 So, A4 = 276.43 K.Mole/hr

Balance Around Converter:- Basis:- 1 hr Operation

Recycle stream B A7 A6 H2 75% Mol % CO 13% Mol % A5 CO2 9% Mol %

N2 3% Mol % A2 A3 A1 M H2 76.68% Mol % CO 13.78% Mol % CO2 9.41% Mol %

N2 0.13% Mol % A4 276.43 K.Mol /hr CH3OH 70.54 mol % H2O 28.21 mol % CO2 0.128 mol % HCHO 0.376 mol % CH3OCH3 0.245 mol % C2H5OH 0.184 mol % C3H7OH 0.0940 mol % C5H11OH 0.0641 mol %

C Balance:- CH3COOH 0.1410 mol %

23.19% A1 = 22% A7 + 72.79611 * A4/100 23.19% A1 = 22% A7 + 201.235 (1)

Reactor

Separator


49

N2 Balance:- 0.13% A1 = 3% A7

A1 = 2307.69% A7 (2)

Putting Eq (2) in (1), 535.15% A7 = 22% A7 + 201.235 513.15% A7 = 201.23 A7 = 39.21 K.Mol /hr So, H2 in A7 = 29.41 K.Mol /hr CO in A7 = 5.09 K.Mol /hr CO2 in A7 = 3.52 K.Mol /hr N2 in A7 = 1.17 K.Mol /hr So Eq(2) becomes, A1 = 904.96 K.Mol /hr Now, H2 in A1 = 693.93 K.Mol /hr CO in A1 = 124.70 K.Mol /hr CO2 in A1 = 85.15 K.Mol /hr

N2 in A1 = 1.176 K.Mol /hr

Reactor:- Now suppose, 50% conversion of CO & CO2 per pass 50% * {( 124.70 + 13% * A6 ) + ( 85.15 + 9% * A6)} = 195.0 50% * {( 209.86 + 22% * A6 )} = 195.0 209.86 + 22% * A6 = 390.03 22% * A6 = 180.17

A6 = 818.98 K.Mol /hr So, H2 in A6 = 614.23 K.Mol /hr CO in A6 = 106.46 K.Mol /hr CO2 in A6 = 73.70 K.Mol /hr N2 in A6 = 24.56 K.Mol /hr

Balance at point M:-

A= = A1 + A6


50

A2 = 1723.95 K.Mol /hr

Balance at point B:- A5 = A6 + A7 A5 = 858.20 K.Mol /hr

Balance Around the Separator:-

A3 = A4 + A5 A3 = 1134.63 K.Mol /hr Balance Around the Separator1:-

D2 A1 = 904.96 K.Mol /hr H2 76.68% Mol % H2 57.42% By vol CO 13.78% Mol % CO 10.32% By vol CO2 9.41% Mol % CO2 7.04% By vol N2 0.13% Mol % N2 0.10% By vol W1 H2O 25.11% By vol H2O 100%

Overall Balance:- D2 = W1 + A1 D2 = W1 + 904.96 (3) H2O Balance:-

25.11% * D2 = W1 (4) Putting (4) in (3), D2 = 25.11% * D2 + 904.96 74.89% * D2 = 904.96 D2 = 1208.39 K.Mol /hr So, H2 in D2 = 693.86 K.Mol /hr CO in D2 = 124.70 K.Mol /hr CO2 in D2 = 85.07 K.Mol /hr N2 in D2 = 1.18 K.Mol /hr H2O in D2 = 303.4 K.Mol /hr Now putting value of D2 in Eq(4) , we get, W1 = 303.4 K.Mol /hr

Separator


51

Balance Around Heat Exchanger:- D1 D2 = 1208.39 K.Mol /hr

As No mass transfer take place in Heat Exchanger, So D1 = D2 = 1208.39 K.Mol /hr and D1 has the same composition as the D2.

Balance Around the Steam Reformer:-

Natural gas D D1 = 1208.39 K.Mol /hr

CH4 93.40% By vol H2 57.42% By vol C2H6 3.50% By vol CO 10.32% By vol C3H8 1.50% By vol CO2 7.04% By vol CO2 1% By vol S N2 0.10% By vol N2 0.60% By vol H2O 100 % H2O 25.11% By vol Steam

C - Balance:-

105.9% * D = 209.77 D = 198.09 K.Mol /hr

H2 - Balance:- 402.7 + S = 997.29 S = 594.57 K.Mol /hr Natural gas to steam ratio:-

S/D = 3.00

This ratio matches with the value given in literature , which proves it to be right.

So, K.Mol /hr Mol. Wt Kg / hr CH4 in D = 185.0 16 2960.25 C2H6 in D = 6.93 30 207.99 C3H8 in D = 2.97 44 130.73 CO2 in D = 1.98 44 87.15 N2 in D = 1.18 28 33.27

Heat Exchanger

Steam Reformer


52

Total = 3419.439 Kg / hr So finally, 3419.4 Kg / hr = 82.06 tons/day & S = 594.57 K.Mol /hr 1 k.mol H2O = 18 Kg = 256.85 tons/day


53


54

Energy Balance

Balance Around Steam Reformer:-

S H2O = 1

450 oC

F = 198.08 K.mol/hr

Documents

Production of Methanol From Natural Gas