Hydrodesulfurization Often Abbreviated to HDS

8/8/2019 Hydrodesulfurization Often Abbreviated to HDS

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Questes

Diesel? Quantos compostos? Ou a faixa? Dados cinticos e termodinmicos?

Devera ter tratamento de H2S? Se houver e as especificaes de segurana?

Tem que haver uma unidade de produo de hidrognio?

Qual a porcentagem de enxofre que tem na entrada e na sada?

hydrodesulfurization Often abbreviated to HDS. A general term for processes that

convert sulfur compounds in petroleum fractions to hydrogen sulfide, and simultaneously

convert highmolecularweight hydrocarbons to more volatile ones. The process operates in the

liquid phase under hydrogen pressure, in a trickle flow reactor containing a heterogeneous

catalyst. The catalyst is typically a mixture of cobalt and molybdenum oxides on alumina. They

are converted to their sulfides prior to use. More recently, transition metal phosphides have

been proposed as catalysts. Such processes with special names that are described in this

dictionary are Alkacid, Alkazid, Autofining, Cycloversion, Diesulforming, GO-fining, Gulfining,

Hycon, Hyperforming, Iso-therming, RDS Isomax, Residfining, Trickel, Ultrafining, VGO Isomax,

VRDS Isomax.

Reynolds, J.G., Chem. Ind. (London), 1991, 570.

Startsev, A.N., Catal. Rev. Sci. Eng., 1995, 37(3), 353.

Nagai, M., Fukiage, T., and Kurata, S., Catal. Today, 2005, 106(14), 201.

Hydrodesulfurization and hydrodemetallization activities cannot be predicted by such

conventional measurements as total sulfur, metals, or asphaltene content, or Conradsoncarbon value (Dolbear et al., 1987). To choose effective processing strategies, it is necessary to

determine properties from which critical reactivity indices can be developed. Indeed, properties

of heavy oil vacuum residua determined by conventional methods are not good predictors of

behavior of feedstocks in upgrading processes (Dawson et al., 1989). The properties of residua

vary widely and the existence of relatively large numbers of polyfunctional molecules results in

molecular association that can affect reactivity. Therefore, it is evident that more knowledge is

needed about the components of residua that cause specific problems in processing, and how

important properties change during processing (Gray, 1990).

In summary, upgrading heavy oils and residua must, at some stage of the refinery

operation utilize hydrodesulfurization. Indeed, hydrodesulfurization (HDS) processes are usedat several places in virtually every refinery to protect catalysts, to meet product specifications

related to environmental regulations Thus, several types of chemistry might be anticipated as

occurring during hydrodesulfurization Similarly, hydrodenitrogenation (HDN) is commonly used

only in conjunction with hydrocracking, to protect catalysts. Other hydrotreating processes are

used to saturate olefins and aromatics to meet product specifications or to remove metals from

residual oils.


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SULFUR IN PETROLEUM

The sulfur content of petroleum varies from less than 0.05 to more than 14% wt. but

generally falls in the range 1 to 4% wt. Petroleum having less than 1% wt. sulfur are referred to

as low-sulfurpetroleum and those above 1% wt. as high-sulfurpetroleum Most of the sulfur

present in petroleum is organically bound and any dissolved hydrogen sulfide and/or elementalsulfur usually represent only a minor part of the total sulfur. One exception that springs to mind

is the heavy crude oil that is (used to be?) recovered from the reservoir by steam injection from

the formation at Qayarah in Northeast Iraq. The total sulfur contact of this oil is approximately

8% wt. of which 6% wt. is organically-bound sulfur and the remaining 2% wt. is elemental sulfur.

Sulfur is spread throughout most fractions of petroleum but, generally, the largest amount (ca.

60% or more of the sulfur) of fraction is in the high-molecular-weight components.

Organic sulfur compounds vary in polarity and chromatographic behavior such that

some elute during liquid chromatography with the aromatic hydrocarbon fraction while others

elute with the more polar nitrogen, oxygen, and sulfur fractions that include the resins and

asphaltenes. Until recently, precise organic molecular structures have been established only for

relatively low molecular weight sulfur compounds. These compounds contain lower molecular

weight constituents, generally with fewer than 15 carbon atoms and have boiling points below

250300C (480570F). This unsatisfactory state of knowledge is aggravated by the fact that

generally 6080% of the sulfur is in the asphaltene and resin fraction that contain innumerable

individual constituents of speculative chemical structure.

Although many of the lower-boiling sulfur compounds in petroleum have been

identified (Speight, 1999 and references cited therein), it can only be surmised (with some

degree of confidence) that the same types of organic sulfur extend into uncharacterized

fractions. However, it is also believed that the distributions of sulfur functional types differ in

the high-boiling fractions. In fact, there is the distinct likelihood that many of the more polar

and higher molecularweight compounds containing more than one heteroatom (Coleman et al.,1971; Galpern, 1971; Rall et al., 1972; Thompson, 1981; Aksenova and Kamyanov, 1981;

Galpern, 1985; Orr and White, 1990).

To summarize all of this work in very general terms, the distribution of the sulfur-

containing constituents of petroleum has been determined to include the following compound

types:

1. nonthiophenic sulfur, i.e. sulfides (R-S-R1),

2. thiophenes,

3. benzothiophenes,

4. dibenzothiophenes,5. benzonaphthothiophenes, and

6. dinaphthothiophenes.

Kinetics

1. The reactions can be described in terms of simple first-order expressions.


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2. The reactions can be described by use of two simultaneous first-order expressions;

one expression for easy-to-remove sulfur and a separate expression for difficult-to-

remove sulfur.

3. The reactions can be described using a pseudo-second-order treatment.

Each of the three approaches has been used to describe hydrodesulfurization of residuaunder a variety of conditions with varying degrees of success, but it does appear that pseudo-

second-order kinetics are favored. In this particular treatment, the rate of hydrodesulfurization

is expressed by a simple second-order equation:

C/(1-C) = k (1/LHSV)

Where C is the wt% sulfur in product/wt% sulfur in the charge, k is the reaction rate

constant, and LHSV is the liquid hourly space velocity (volume of liquid feed per hour per

volume of catalyst). Application of this model to a residuum desulfurization gave a linear

relationship (Figure 4-7)(Beuther and Schmid, 1963). However, it is difficult to accept that the

esulfurization reaction requires the interaction of two sulfurcontaining molecules (as dictated

by the second-order kinetics). To accommodate this anomaly, it has been suggested that, as

there are many different types of sulfur compounds in residua and each may react at a different

rate, the differences in reaction rates offered a reasonable explanation for the apparent

second-order behavior. For example, an investigation of the hydrodesulfurization of an Arabian

light-atmospheric residuum showed that the overall reaction could not be adequately

represented by a first-order relationship (Figure 4-8) (Scott and Bridge, 1971). However, the

reaction could be represented as the sum of two competing first-order reactions and the rates

of desulfurization of the two fractions (the oil fraction and the asphaltene fraction) could be

well represented as an overall second-order reaction.

If each type of sulfur compound is removed by a reaction that was first order withrespect to sulfur concentration, the first-order reaction rate would gradually, and continually,

decrease as the more reactive sulfur compounds in the mix became depleted. The more stable

sulfur species would remain and the residuum would contain the more difficult-to-remove

sulfur compounds. This sequence of events will, presumably lead to an apparent second-order

rate equation which is, in fact, a compilation of many consecutive first-order reactions of

continually decreasing rate constant. Indeed, the desulfurization of model sulfurcontaining

compounds exhibits first-order kinetics, and the concept that the residuum consists of a series

of first-order reactions of decreasing rate constant leading to an overall second-order effect has

been found to be acceptable. Application of the second-order rate equation to the

hydrodesulfurization process has been advocated because of its simplicity and use forextrapolating and interpolating hydrodesulfurization data over a wide variety of conditions.

However, while the hydrodesulfurization process may appear to exhibit secondorder kinetics at

temperatures near 395C (745F), at other temperatures the data (assuming second-order

kinetics) does not give a linear relationship (Ozaki et al., 1963).

On this basis, the use of two simultaneous first-order equations may be more

appropriate. The complexity of the sulfur compounds tends to increase with an increase in

boiling point and the reactivity tends to decrease with complexity of the sulfur compounds, and


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residua (and, for that matter, the majority of heavy oils) may be expected to show substantial

proportions of difficult-to-desulfurize sulfur compounds. It is anticipated that such an approach

would be more consistent with the relative reactivity of various sulfur compound types

observed for model compounds and for the various petroleum fractions that have been

investigated.

FEEDSTOCK

TYPES

Low-Boiling Distillates

The hydrodesulfurization of light (low-boiling) distillate (naphtha) is one of the more

common catalytic hydrodesulfurization processes since it is usually used cobalt and

molybdenum (catalyst) sulfides. In such a case, presulfiding can be conveniently achieved by

the addition of sulfur compounds to the feedstock or by the addition of hydrogen sulfide to the

hydrogen.

Generally, hydrodesulfurization of naphtha feedstocks to produce catalytic reforming

feedstocks is carried to the point where the desulfurized feedstock contains less than 20 ppm

sulfur. The net hydrogen produced by the reforming operation may actually be sufficient toprovide the hydrogen consumed in the desulfurization process.

The hydrodesulfurization of middle distillates is also an efficient process and

applications include predominantly the desulfurization of kerosene, diesel fuel, jet fuel, and

heating oils which boil over the general range of 250 to 400C (480 to 750F). However, with

this type of feedstock, hydrogenation of the higher-boiling catalytic cracking feedstocks has


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become increasingly important where hydrodesulfurization is accomplished alongside the

saturation of condensed-ring aromatic compounds as an aid to subsequent processing.

PROCESS VARIABLES

The efficiency of the hydrodesulfurization process is measured by the degree of sulfur

removal or, in other words, by the yields of sulfur-free products. However, there are several

process variables (Table 5-8) that need special attention as any one of these variables can have

a marked influence on the course and efficiency of the hydrodesulfurization process.

The major process variables are (1) reactor temperature; (2) hydrogen pressure; (3)

liquid hourly space velocity; and (4) hydrogen recycle rate. Other variables such as reactor type

and catalyst type have been discussed in an earlier part of this chapter, while the influence of

the feedstock type will be discussed

Reactor Temperature

The temperature in the hydrodesulfurization reactor is often considered to be the

primary means by which the process is controlled. For example, at stabilized reactor conditions,

a rise of 10C (l8F) in the reaction temperature will substantially increase, and may even

double, the reaction rate. Generally, an increase in the temperature (from 360 to 380C, i.e.,

from 680 to 715F) will increase the conversion slightly (Figure 5-11) (Pachano et al., 1977) or

for a fixed conversion of about 90% enables the quantity of catalyst necessary for the process

to be halved.

In the same manner as in hydrocracking (Dolbear, 1997), hydrogen is added at

intermediate points in hydrodesulfurization reactors. This is important for control of reactor

temperatures. The mechanical devices in the reactor, called reactor internals, which accomplish

this step are very important to successful processes.

If redistribution is not efficient, some areas of the catalyst bed will have more contact

with the feedstock. This can lead to three levels of problems:


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1. Poor selectivity: Ratios of hydrogen, oil, and catalyst outside design ranges will change

the yield structures. Some parts of the bed will be hotter than other parts. Some fractions of

the feedstock will be cracked to undesirable low molecular weight (light hydrocarbon) products

and

conversion will be lower.

2. Rapid catalyst aging: Higher than desirable hydrogenation can increase local reactor

temperatures markedly. Catalysts can sinter, losing surface area and activity and shortening run

length.

3. Hot spots: When local reactor temperatures are well above 400C (750F), thermal

cracking can become important. Thermal cracking produces olefins, which add hydrogen,

releasing heat. This increases the temperatures further, and thermal cracking rates go up.

These hot spots can easily reach temperatures higher than the safe upper limits for the reactor

walls, and results can be catastrophic.

Effect of temperature on the desulfurization process.


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There are, however, limits to which the temperature can be increased without adversely

affecting process efficiency; at temperatures above 410C (770F), thermal cracking of the

hydrocarbon constituents becomes the predominant process that can lead to formation of

considerable amounts of low-molecular-weight hydrocarbon liquids and gases. In addition,

increasing the partial pressure of the hydrogen cannot diminish these high-temperature

cracking reactions. In addition, excessively high temperatures (above 400C or 750F) lead todeactivation of the catalyst much more quickly than lower temperatures.

The hydrodesulfurization of low boiling (naphtha) feedstocks is usually a gas-phase

reaction and may employ the catalyst in fixed beds and (with all of the reactants in the gaseous

phase) only minimal diffusion problems are encountered within the catalyst pore system. It is,

however, important that the feedstock be completely volatile before entering the reactor as

there may be the possibility of pressure variations (leading to less satisfactory results) if some

of the feedstock enters the reactor in the liquid phase and is vaporized within the reactor.

In applications of this type, the sulfur content of the feedstock may vary from 100 ppm

to 1% and the necessary degree of desulfurization to be effected by the treatment may vary

from as little as 50% to more than 99%. If the sulfur content of the feedstock is particularly low,

it will be necessary to presulfide the catalyst. For example, if the feedstock only has 100 to 200

ppm sulfur, several days may be required to sulfide the catalyst as an integral part of the

desulfurization process even with complete reaction of all of the feedstock sulfur to, say, One

particular aspect of the hydrodesulfurization process that needs careful monitoring, with

respect to feedstock type, is the exothermic nature of the reaction.

The heat of the reaction is proportional to the hydrogen consumption and with the

more saturated lower-boiling feedstocks where hydrocracking may be virtually eliminated, the

overall heat production during the reaction may be small, leading to a more controllable

temperature profile. However, with the heavier feedstocks where hydrogen consumption is

appreciable (either by virtue of the hydrocracking that is necessary to produce a usable product

or by virtue of the extensive hydrodesulfurization that must occur), it may be desirable toprovide internal cooling of the reactor. This can be accomplished by introducing cold recycle gas

to the catalyst bed to compensate for excessive heat.

One other generalization may apply to the lower-boiling feedstocks in the

hydrodesulfurization process. The process may actually have very little effect on the properties

of the feedstock (assuming that hydrocracking reactions are negligible)removal of sulfur will

cause some drop in specific gravity which could give rise to volume recoveries approaching (or

even above) 100%. Furthermore, with the assumption that cracking reactions are minimal,

there may be a slight lowering of the boiling range due to sulfur removal from the feedstock

constituents. However, the production of lighter fractions is usually small and may only amount

to some 1 to 5% by weight of the products boiling below the initial boiling point of thefeedstock.

One consideration for the heavier feedstocks is that it may be more economical to

hydrotreat and desulfurize high-sulfur feedstocks before catalytic cracking than to hydrotreat

the products from catalytic cracking. This approach (Speight and Moschopedis, 1979; Decroocq,

1984) and has the potential for several advantages, such as:

1. the products require less finishing;


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2. sulfur is removed from the catalytic cracking feedstock, and corrosion

is reduced in the cracking unit;

3. coke formation is reduced;

4. higher feedstock conversions; and

5. the potential for better-quality products.

The downside is that many of the heavier feedstocks act as hydrogen sinks in terms oftheir ability to interact with the expensive hydrogen. A balance of the economic

advantages/disadvantages must be struck on an individual feedstock basis.

As the trend toward utilizing heavier petroleum feedstocks continues, the hydrotreating

processes used to upgrade such stocks become increasingly important.

Difficulties are encountered in the development of catalysts with high resistance to

deactivation. Another important challenge is that of designing three-phase reactors capable of

processing large quantities at high temperatures and pressures.Desirable features of such reactors are low-pressure drop, in the presence of deposits

and low mass transfer resistance between gas-liquid and liquid-solid. The monolithic reactor

offers a viable alternative in which the monolith is typically 1 mm or a few millimeters in

diameter. Each channel is bounded by either a porous wall or a solid wall onto which a porous

washcoat may be applied. In these narrow channels, gas and liquid flow concurrently.

Reactor designs for hydrodesulfurization of various feedstocks vary in the way in which

the feedstock is introduced into the reactor and in the arrangement, as well as the physical

nature, of the catalyst bed. The conditions under which the hydrodesulfurization process

operates (i.e., high temperatures and high pressures) dictate required wall thickness

(determined by the pressure/temperature/strength ratio). In addition, resistance of the reactor

walls to the corrosive attack by hydrogen sulfide and hydrogen (to name only two of the

potential corrosive agents of all of the constituents in, or arising from, the feedstock) can be a

problem.

Precautions should be taken to ensure that wall thickness and composition yield

maximum use and safety.


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With these criteria in mind, various reactors have been designed to satisfy the needs of

the hydroprocesses, including hydrodesulfurization (McEvoy, 1996).

Thus, reactors may vary from as little as 4 ft. in diameter to as much as 20 ft. in diameter

and have a wall thickness anywhere from 4.5 to 10 in. or so. These vessels may weigh from 150

tons to as much as 1000 tons. Obviously, before selecting a suitable reactor, shipping and

handling requirements (in addition to the more conventional process economics) must be givenserious consideration.

The hydrodesulfurization process operates using high hydrogen pressure, typically 1500

to 2500 psi and temperatures are on the order of 290 to 370C (550 to 700F). Several process

configurations are used, depending on the feed and the design criteria. All include provisions

for the addition of cold hydrogen at several points in the hydrocracking reactor to control

reactor temperatures, since a great amount of heat is released by hydrogenation. Reactor

internals provided for this function are complex mechanical devices.

Finally, and before a discussion of the various reactor-bed types used in

hydrodesulfurization, a note that the once-popular once-through reactors, where the

incompletely converted or unconverted fraction of the feedstock is separated from the lower-

boiling products are being replaced by recycle reactors. In these reactors, any unconverted

feedstock is sent back (recycled) to the reactor for further processing. In such a case, the

volume flow of the combined (fresh and unconverted) feedstock is the sum of the inputs of the

fresh feedstock and recycled feedstock:


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Distillate Unionfining for ULSD (Ultralow-Sulfur Diesel)

Recent environmental regulations will require a quantum leap in the reduction of sulfur

in diesel fuels. While present regulations mandate a sulfur content of 500 wt ppm (U.S.) and

350 wt ppm (Europe), recently enacted legislation requires that the sulfur level be reduced to

15 wt ppm (by 2006 in the United States) and 10 wt ppm (by 2007 in Europe) before the end of

the decade. To meet these more stringent regulations, new, more active catalysts are requiredas well as more severe operating conditions.

To achieve these very low levels of sulfur, the catalyst must be able to desulfurize the

most difficult sulfur speciessterically hindered dibenzothiophenes. These compounds contain

alkyl groups in the 4- and 6-positions, thus greatly restricting access to the sulfur atom. An

illustration of the difficulty of desulfurizing these types of compounds is given in Fig. 8.3.10.

Since the difficult sulfur species are thiophenic, lets consider the relative reaction rates shown

in Fig. 8.3.10, starting with thiophene which is assigned a desulfurization rate of100. As the

thiophene molecule becomes more complex and bulky with the addition of an aromatic ring, as

in benzothiophene, the desulfurization rate drops to 60. With the addition of another aromatic

ring, dibenzothiophene, the rate of desulfurization decreases by an order of magnitude to 5.

Addition of substituents to the rings at positions far removed from the sulfur atom, as in 2,8-

dimenthyldibenzothiophene, do not affect the rate of desulfurization.

On the other hand, addition of substituents at positions adjacent to the sulfur atom, as

in 4,6-dimenthyldibenzothiophene, greatly reduces the rate of desulfurization to a relative rate

of 0.5. the difficulty in desulfurizing 4,6-dimethyldibenzothiophene (and compounds of a

similar structure with alkyl substituents adjacent to the sulfur atom) is due to the steric

hindrance these substituents present to access of the sulfur atom to the active site of the

catalyst. For the production of the ULSD, it is these most difficult sulfur species that must

undergo desulfurization.

In addition to the difficulty of desulfurizing the sterically hindered dibenzothiophenes,

the impact of a number of poisons for the desulfurization reaction must be considered. Theseinclude nitrogen and oxygen compounds. While the toxic effect of these poisons may have

been neglected in the past, it must be taken into account for a successful design of a unit for

ULSD production.

Based on fundamental mechanistic and kinetic studies, present theory suggests that in

order to desulfurize these molecules, one of the aromatic rings must first undergo saturation.

Since Ni/Mo catalysts have better saturation activity than Co/Mo catalysts, the former are

preferred for deep desulfurization of distillates to ULSD specifications. The requirement to

effect such a deep level of desulfurization will necessitate the application of much more severe

process conditions for distillate Unionfining than were necessary in the past (Table 8.3.2).


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CED [Conversion Extraction Desulfurization] A process for reducing the sulfur content of diesel

fuel. Peroxyacetic acid oxidizes the organic sulfur compounds to sulfones, which are removed

by solvent extraction. Developed in 2000 by Petro Star.

Chem. Eng. (N.Y.), 2000, 107(4), 17.

DHDS [Diesel deep HydroDeSulfurization] A petroleum refining process developed by the

Instituto Mexicano del Petroleo (IMP), with plans for it to be in operation at the Pemex refinery

at Cadereyta, Mexico, in 1999.

Diesulforming A *hydrodesulfurization process which used a molybdenum-containing catalyst.

Developed by the Husky Oil Company and first operated in Wyoming in 1953.

Oil Gas J., 1956, 54(46), 165.

Unzelman, G.H. and Wolf, C.J., in Petroleum Processing Handbook, Bland, W.F. and Davidson,R.L.,

Eds., McGraw-Hill, New York, 1967, 342.

Gulf HDS A process for *hydrorefining and *hydrocracking petroleum residues in order to make

fuels and feeds for *catalytic cracking. Developed by the Gulf Research & Development

Company.

Unzelman, G.H. and Wolf, C.J., in Petroleum Processing Handbook, Bland, W.F. and Davidson,

R.L.,

Eds., McGraw-Hill, New York, 1967, 323.

M-coke A homogeneous *desulfurization process that uses an oil-soluble molybdenum

compound as the catalyst.

Rueda, N., Bacaud, R., Lanteri, P., and Vrinat, M., Appl. Catal. A: Gen., 2001, 215(12), 81.

Beardon, C.L.A., Chem. Eng. Prog., 1981, 44.

OATS [Olefinic Alkylation ofThiophenic Sulfur] A gasoline desulfurization process. Thiophenes

and mercaptans are catalytically reacted with olefins to produce higher-boiling compounds that

can more easily be removed by distillation prior to hydrodesulfurization. This minimizes

hydrogen usage. The process uses a solid acid catalyst in a liquid-phase, fixed bed reactor.

Developed by BPAmoco in 2000 and tested in Bavaria and Texas. First used commercially at the

Bayernoil refinery, Neustadt, in 2001. The process won a European Environment Award in 2002.

Chem. Eng. (N.Y.), 2000, 107(13), 19.

Chem. Eng. (Rugby, Engl.), 2001, 21 June, Awards supplement, 5.


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Eur. Chem. News, 19 Nov 2001, 31.

Oil Gas J., 3 Dec 2001, 99(49), 8.

Proc. Eng., 2002, 83(10), 2.

Prime-G, Prime-G+A deep *hydrodesulfurizing process for removing sulfur compounds prior to

*fluid catalytic cracking. It uses a fixed catalyst bed and conventional distillation. Developed by

IFP (now Axens) from 1999. The + version is an improvement on the original process. In 2001,

over 60 units had been licensed and 11 were operating commercially. First commercialized at

Gelsenkirchen, Germany, in 2001. Now operated in Finland, Belgium, and Canada.

Eur. Chem. News, 29 Nov 1999, 71(1887), 30.

Ptrole et Gaz Informations, JanFeb 2000 (1744), 17, Mar 2000 (1745), 43.

Chem. Eng. (N.Y.), 2001, 108(12), 23.

Hydrocarbon Process. Int. Ed., Aug 2002, 82(8), 38; Aug 2005, 84(8), 31.

Chem. Eng. (N.Y.), 2003, 110(9), 27.

RCD Unionfining [Reduced Crude Desulfurization] The latest version of UOPs process for

removing organic sulfur-, nitrogen-, and metal-compounds from heavy petroleum fractions.

Formerly called RCD Unibon, which succeeded the Black Oil Conversion process (BOC). Different

catalysts are used for different oils. Developed and licensed by UOP. The first commercial unit

started operating in Japan in 1967; since then, 27 more units have been licensed.

Marcos, F. and Rosa-Brussin, D., Catal. Rev. Sci. Eng., 1995, 37(1), 3.

Gillis, D.B., in Handbook ofPetroleum Refining Processes, 3rd ed., Meyers, R.A., Ed., McGraw-

Hill,New York, 2003, 8.43.

Sandwich desulfurization A *hydrotreating process for removing sulfur compounds from

petroleum streams. The sulfur compounds are first hydrogenated and then absorbed in a train

of three catalyst beds: the sandwich. In the first bed, zinc oxide absorbs hydrogen sulfide and

reactive sulfur compounds; in the second, cobalt molybdate on alumina hydrogenates

nonreactive thiophenes, forming hydrogen sulfide; in the third, zinc oxide absorbs the hydrogen

sulfide from the second bed. Developed and offered by ICI, particularly for use in the *ICI Steam

Naphtha Reforming process.

Sulfur-X A process for removing sulfur compounds (principally thiophene) from naphtha by

solvent extraction with sulfolane. Developed by UOP and announced in 2002. This process does

not require hydrogen, which gives it an advantage over competing desulfurization processes.

Chem. Eng. (N.Y.), 2003, 110(9), 29.

Nafis, D.A. and Houde, E.J., in Handbook ofPetroleum Refining Processes, 3rd ed., Meyers, R.A.,

Ed., McGraw-Hill, New York, 2003, 11.75.


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Trickle Hydrodesulfurization A process for removing sulfur-, nitrogen-, and heavy-

metalcompounds from petroleum distillates before *catalytic cracking. The preheated feed is

hydrogenated, without a catalyst, in an adiabatic reactor at 315 to 430C. Developed by Shell

Development Company. As of1978, 91 units had been installed.

Hoog, H., Klinkert, H.G., and Schaafsma, A., Pet. Refin., 1953, 32(5), 137.

Hydrocarbon Process., 1964, 43(9), 194.

Unionfining A group of petroleum *hydrodesulfurization and *hydrodenitrogenation processes

developed by the Union Oil Company of California, primarily for making premium-quality diesel

fuel. In 1991, 90 such units were operating. One variant is for purifying naphthalene by

selective hydrogenation. The naphthalene vapor is hydrogenated at 400C over a cobalt

molybdenum catalyst, thereby converting the sulfur in thionaphthalene to hydrogen sulfide.

The technology was acquired by UOP in 1995.

Hydrocarbon Process. Int. Ed., 1988, 67(9), 79.

Eur. Chem. News, 1995, 63(1653), 24.

Kokayeff, P., in Handbook ofPetroleum Refining Processes, 3rd ed., Meyers, R.A., Ed., McGraw-

Hill, New York, 2003, 8.31

Documents

Hydrodesulfurization Often Abbreviated to HDS