NAME: M FAISAL ISMAIL

CLASS: CHE-01-B

REG #: 42

[ ]FUEL AND COMBUSTION

AMINE GAS TREATING

Amine gas treating refers to a group of processes that use aqueous solutions of various amines to remove hydrogen sulfide (H2S) and carbon dioxide (CO2) from gases. It is a common unit process used in refineries, petrochemical plants, natural gas processing plants and other industries. The process is also known as Gas sweetening and Acid gas removal.

There are many different amines used in gas treating:

Monoethanolamine (MEA)

Ethanolamine, also called 2-aminoethanol or monoethanolamine (often abbreviated as MEA), is an organic chemical compound which is both a primary amine (due to an amino group in its molecule) and a primary alcohol (due to a hydroxyl group). Like other amines, monoethanolamine acts as a weak base. Ethanolamine is a toxic flammable corrosive colorless viscous liquid with an odor similar to ammonia.

Ethanolamine is commonly called monoethanolamine or MEA to distinguish it from diethanolamine (DEA) and triethanolamine (TEA). Monoethanolamine is produced by reacting ethylene oxide with ammonia. Further treatment with ethylene oxide can yield DEA and/or TEA. Ethanolamine is the second most abundant head group for phospholipids.

Ethanolamine also refers to a class of antihistamines containing an ethyl-amine group attached to a diphenyl structure. Examples of drugs within this class include diphenhydramine (Benadryl), phenyltoloxamine (Percogesic), and doxylamine (Unisom Sleep Tablets). They are one of the oldest classes of antihistamine drugs, yet remain the most effective for treating allergy symptoms, even exceeding the effectiveness of new OTC and prescription antihistamines such as loratadine (Claritin) and Fexofenadine (Allegra). However, all ethanolamines are extremely sedating, even more so than many barbiturates. For this reason, they are not always desirable drugs for treatment, and less-effective drugs are indicated to avoid the substantial drowsiness inherent in ethanolamines. On the other hand, they are such effective sedatives that they are marketed as over-the-counter sleep-aids in addition to anti-allergy medications.

Uses of monoethanolamine (MEA)

MEA is used in aqueous solutions for scrubbing certain acidic gases and is also used in surface active agents, emulsifiers, polishes, pharmaceuticals, corrosion inhibitors, chemical intermediates. In pharmaceutical formulations, MEA is primarily used for buffering or preparation of emulsions.

Aqueous solutions of MEA (solutions of MEA in water) are used as a gas stream scrubbing liquid in amine treaters. For example, aqueous MEA is used to remove carbon dioxide (CO2) from flue gas. Aqueous solutions can weakly dissolve certain kinds of gases from a mixed gas stream. The MEA in such solutions, acting as a weak base, then neutralizes acidic compounds dissolved in the solution to turn the molecules into an ionic form, making them polar and considerably more soluble in a cold MEA solution and thus keeping such acidic gases dissolved in this gas-scrubbing solution. Therefore, large surface area contact with such a cold scrubbing solution in a

scrubber unit can selectively remove such acidic components as hydrogen sulfide (H2S) and CO2 from some mixed gas streams. For example, basic solutions such as aqueous MEA or aqueous potassium carbonate can neutralize H2S into hydrosulfide ion (HS-) or CO2 into bicarbonate ion (HCO3

-).

H2S and CO2 are only weakly acidic gases. An aqueous solution of a strong base such as sodium hydroxide (NaOH) will not readily release these gases once they have dissolved. However, MEA is rather weak base and will re-release H2S or CO2 when the scrubbing solution is heated. Therefore, the MEA scrubbing solution is recycled through a regeneration unit which heats the MEA solution from the scrubber unit to release these only slightly acidic gases into a purer form and returns the regenerated MEA solution to the scrubber unit again for reuse.

Diethanolamine (DEA)

Diethanolamine, often abbreviated as DEA, is an organic chemical compound which is both a secondary amine and a dialcohol. A dialcohol has two hydroxyl groups in its molecule. Like other amines, diethanolamine acts as a weak base.

Other names or synonyms are bis(hydroxyethyl)amine, diethylolamine, hydroxydiethylamine, diolamine, and 2,2'-iminodiethanol.

DEA and its chemical variants are common ingredients in cosmetics and shampoos, where they are used as to create a creamy texture and foaming action. Variants of DEA include lauramide diethanolamine, coco diethanolamide, cocoamide diethanolamine or coconut oil amide of diethanolamine, lauramide DEA, lauric diethanolamide, lauroyl diethanolamide, and lauryl diethanolamide.

DEA and its variants are suspected of increasing the risk of cancer. DEA can combine with amines present in cosmetic formulations to form nitrosamines (N-nitrosodiethanolamine), which are known to be highly carcinogenic.[1] Studies also show that DEA directly inhibits fetal brain development in mice by blocking the absorption of choline, a nutrient required for brain development and maintenance.[2] DEA is also associated with miscarriages in laboratory studies.

Methyldiethanolamine (MDEA)

MDEA (also MDE), which stands for 3,4-methylenedioxy-N-ethylamphetamine, is a psychedelic hallucinogenic drug and empathogen-entactogen of the phenethylamine family. It is chemically very similar to MDMA, the active chemical in the drug "ecstasy". MDEA differs from MDMA in that it has one more carbon atom, and two more hydrogen atoms in the substituent on the nitrogen atom. The difference is evidenced in its name by the "ethyl" prefix, rather than the "methyl" prefix designating a single-carbon chain (see Alkanes). MDEA is sometimes sold as a substitute for

ecstasy on the black market. It can be prepared by reductive amination of MDP2P.

MDEA works by releasing serotonin, a neurotransmitter that affects mood and perception. It requires a slightly larger dose (100 - 200 mg.) than MDMA with major effects lasting typically between 3 and 5 hours [1]. The subjective effects of MDEA are similar to MDMA. The euphoric 'loved up' feelings associated with MDMA use are not as pronounced. The effects are also not as stimulating as MDMA, MDE has somewhat of a stoning effect and may be responsible for rumors of heroin-laced ecstasy pills. However, MDEA does have a mildly hallucinogenic effect. This, coupled with an increase in the user's energy levels (similar to amphetamine use) had led some users to conclude that MDEA is more suitable as a nightclub drug.

Diisopropylamine (DIPA)

Diisopropylamine is a secondary amine with the chemical formula (CH3)2HC-NH-CH(CH3)2. It is best known as its lithium salt, lithium diisopropylamide, known as "LDA". LDA is a strong, non-nucleophilic base.

Diglycolamine (DGA)

The most commonly used amines in industrial plants are the alkanolamines MEA and DEA.

Amines are also used in many oil refineries to remove acid gases from liquid hydrocarbons such as liquified petroleum gas (LPG).

Description of a typical amine treater

Flow diagram of a typical amine treating process used in industrial plants

Gases containing both H2S and CO2 are commonly referred to as sour gases in the hydrocarbon processing industries. A typical amine gas treating process includes an absorber unit and a regenerator unit as well as accessory equipment. In the absorber, the downflowing amine solution absorbs H2S and CO2 (referred to as acid gases) from the uplflowing sour gas to produce a sweetened gas stream (i.e., an H2S-free gas) as a product and an amine solution rich in the absorbed acid gases. The resultant "rich" amine is then routed into the regenerator (a stripper with a reboiler) to produce regenerated or "lean" amine that is recycled for reuse in the absorber. The stripped overhead gas from the regenerator is concentrated H2S and CO2. In oil refineries, that stripped gas is mostly H2S, much of which often comes from a sulfur-removing process called hydrodesulfurization. This H2S-rich stripped gas stream is then usually routed into a Claus process to convert it into elemental sulfur. In fact, the vast majority of the 64,000,000 metric tons of sulfur produced worldwide in 2005 was byproduct sulfur from refineries and other hydrocarbon processing plants. [1][2] In some plants, more than one amine absorber unit may share a common regenerator unit.

In the steam reforming process of hydrocarbons to produce gaseous hydrogen for subsequent use in the industrial synthesis of ammonia, amine treating is one of the commonly used processes for removing excess carbon dioxide in the final purification of the gaseous hydrogen.

DEHYDRATION:

Dehydration is the removal of water from a compound, set of compounds, or other material. Dehydration refers not only to the removal of pre-existing water molecules from a solution, but also to the chemical formation of water by its removal from a compound to form a new compound. The simplest form of dehydration is evaporation, in which water spontaneously leaves the liquid phase. The evaporation rate can be increased with heat. As water leaves a solution, the remaining solution becomes increasingly concentrated. At sufficiently high concentrations, solute molecules or ions may exceed their solubility, and begin to crystallize. This process is one of the most common means of obtaining crystals, both in the laboratory and in nature.

Dehydration for the purpose of crystallization may be aided by vacuum, which lowers the vapor pressure above the solution to increase the rate of evaporation. Freeze-drying uses evacuation and cold to prevent deterioration of solutes during dehydration. Freeze-drying is an especially effective means of food preservation, since the water content can be brought down so low that most microorganisms cannot grow on the food.

For substances with lower boiling points than water, heating can be used to drive off the more volatile substance, which can then be collected by condensing it. This process is known as distillation, and is used to purify many low-boiling organic compounds, such as ethanol. Ethanol produced by fermentation is at most a 20% solution in water. Distillation can raise its percentage up to 95%.

Simple distillation cannot completely dehydrate ethanol, because it forms an azeotrope with water. An azeotrope is a mixture with a constant boiling point that cannot be separated by distillation. By adding a small amount of other organic liquids, the ethanol can be distilled to 100%.

Gases and non-aqueous liquids can be dehydrated by passing them over or through a hygroscopic substance, one that readily absorbs water. Solid calcium chloride is used for this purpose both in the laboratory and in the home, where cans of anhydrous ("without water") calcium chloride may be placed in damp closets, for instance, to prevent mildew. Anhydrous sodium hydroxide is another common laboratory desiccant, or substance that removes water. "Molecular sieves" made from zeolite clays are even more effective in many applications. The high internal surface area of these clays allow them to bind tightly with very large amounts of water.

Dehydration, in the sense of formation of a water molecule through chemical reaction, is an important part of organic chemistry and biochemistry. Alcohols such as ethanol (H3CCH2OH) can be dehydrated in this sense by reaction with heat in the presence of sulfuric acid, which acts not only as a catalyst, but as a hygroscopic medium to remove water as it is formed. The product, ethene (H2C=CH2) forms by removal of the OH from one carbon and an H from the other, leaving a double bond uniting the two carbons. This is one of the most common ways of synthesizing alkenes, double-bonded hydrocarbons.

Dehydration is perhaps the most common and vital reaction in the synthesis of biological macromolecules, such as proteins, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), carbohydrates, and fats. These four types of molecules are polymers, each formed from smaller building blocks, or monomers, which become linked by dehydration.

Claus Process

The Claus process is a catalytic chemical process for converting gaseous hydrogen sulfide (H2S) into elemental sulfur (S). The process is commonly referred to as a sulfur recovery unit (SRU) and is very widely used to produce sulfur from the hydrogen sulfide found in raw natural gas and from the by-product sour gases containing hydrogen sulfide derived from refining petroleum crude oil and other industrial facilities.

Hydrogen sulfide (H2S) is a smelly, corrosive, highly toxic gas. Besides its other bad habits, it also deactivates industrial catalysts. H2S is commonly found in natural gas and is also made at oil refineries, especially if the crude oil contains a lot of sulfur compounds.

Because H2S is such an obnoxious substance, it is converted to non-toxic and useful elemental sulfur at most locations that produce it. The process of choice is the Claus Sulfur Recovery process.

Description of the Claus Process

First the H2S is separated from the host gas stream using amine extraction. Then it is fed to the Claus unit, where it is converted in two steps:

1. Thermal Step. The H2S is partially oxidized with air. This is done in a reaction furnace at high temperatures (1000-1400 deg C). Sulfur is formed, but some H2S remains unreacted, and some SO2 is made.

2. Catalytic Step. The remaining H2S is reacted with the SO2 at lower temperatures (about 200-350 deg C) over a catalyst to make more sulfur.

A catalyst is needed in the second step to help the components react with reasonable speed. Unfortunately the reaction does not go to completion even with the best catalyst. For this reason two or three stages are used, with sulfur being removed between the stages. Engineers know how different factors like concentration, contact time and reaction temperature influence the reaction, and these are set to give the best conversions.

The reaction is as follows:

2H2S + SO2 ==> 3S + 2H2O

Inevitably a small amount of H2S remains in the tail gas. This residual quantity, together with other trace sulfur compounds, is usually dealt with in a tail gas unit. The latter can give overall sulfur recoveries of about 99.8%, which is very impressive indeed

CYROGENIC DISTILLATION:

Cryogenic distillation is very similar to any other distillation process except it is used to separate components of a gaseous mixture. The process is usually carried out at very low temperatures (liquid nitrogen temp) and is very energy intensive. It is most commonly used to separate nitrogen from natural gas.

Cryogenic separation is widely used commercially for purification of CO2 from streams that already have high CO2 concentration. Need for relatively high concentration of CO2 for cryogenic unit is important because in order to minimize CO2 loss from the top of the column it would be necessary to operate as close to the triple-point temperature as possible, but the minimum partial pressure of CO2 achievable in the vent gas would be 5.18 bar abs. this meant that as the concentration of other component  in the CO2/gas mixture increases the pressure of the stripping column would have to be increased in order to achieve a certain CO2 recovery from process. At 75% feed purity and 90% recovery, the column pressure would be about 26 bar pressure, for 95% recovery it would be 46 bar.

Cryogenic systems are a low temperature physical approach to separation, in which the CO2 is separated directly by phase change. This method is advantageous with respect to direct production of liquid CO2 or pure CO2 gas stream in high pressure which would be liquefied more easily. There are some difficulties for applying this method as well. For dilute CO2 stream, the refrigeration energy is high. Water has to be removed before the cryogenic cooling step to avoid blockage from freezing.