Hydrogenation process

Abstract

 Active sulfur compounds, especially thiols and thiophenols are effective catalysts for. hydrogen transfer reactions, catalyzing the transfer of hydrogen from aliphatic and alkylaromatic compounds.A preferred hydrogen donor is shale oil which may be used as the donor solvent in a coal liquefaction process in which a thiol or thiophenol is used as a catalyst to promote transfer of hydrogen from the shale oil to the coal.

Description

[0001] This invention relates to hydrogenation processes, and especially to coal liquefaction using hydrogen donor solvents.

[0002] Various hydrogen donor solvents and processes employing them are known, for example, various heavy oil upgrading processes and coal liquefaction processes. In all these processes, the characteristic reaction which takes place is the transfer of hydrogen from the donor to the acceptor and on this basis the donor has been selected for the readiness with which it will participate in this reaction. Normally, polycyclic hydrocarbons such as tetralin-(tetrahydronaphthalene) and decalin - (decahydronaphthalene) have been the solvents of choice in most H donor processes since they not only transfer hydrogen readity to acceptors such as oils and coal hydrocarbons but, in addition, are readily regenerated by hydrogenation so that they can be recycled. Up to the present, aliphatic compounds and the side chains of alkyl aromatics such as the alkylbenzenes, have generally been considered unsatisfactory. It would, however, be desirable to find some way of using certain aliphatic and alkylaromatic feedstocks as hydrogen donors in donor solvent processes since they may be more readily available for processing. One particular aliphatic feedstock which would have significant potential for use in this way is shale oil since it is available in large quantities and is often produced in areas near large coalfields, for example, in the mountain states of the western U.S.A.

[0003] One characteristic of the H donor coal liquefaction processes is that the ratio of hydrogen to carbon in the coal liquids is increased by the addition of hydrogen from the donor In donor solvent liquefaction processes, the comminuted coal is mixed with a solvent which is capable of transferring hydrogen to the coal under the reaction conditions employed. The coal may be reacted with the solvent in the presence of hydrogen gas in order to increase the hydrogen content further and catalysts may be present in order to facilitate transfer of hydrogen from the solvent to the coal and from the gaseous hydrogen phase if this is present. At the same time, the inorganic content of the coal together with impurities such as sulfur may be removed in the solvent and subsequently extracted from the solvent by washing with an alkaline wash such as monoethanolamine - (MEA). The effluent from the hydrogenation step is separated to remove spent solvent and the raw coal liquids product subjected to further treatment such as fractionation and ash removal. The spent solvent is rehydrogenated and then recycled to the liquefaction step.

[0004] Generally, it is intended that the process should be largely self-sustaining in its use of solvent That is, the process should be capable of making good solvent losses from the products of coal liquefaction. In the Exxon donor solvent process, for example, as described in Chem. Eng. Progr. 72. 145 (1976) the solvent which is produced by selective catalytic hydrogenation of the middle fraction of the coal liquifaction product, contains substantial quantities of tetralin which gives up four hydrogen atoms to free radicals formed by the thermal cracking of the coal during the liquifaction step to form naphthalene. The naphthalene is converted back into tetralin in the solvent hydrogenation step and losses of solvent are made good from the liquefaction product- However, depending upon the nature of the coal and the processing conditions which are used, the process may not be self-sufficient in process-derived solvents and it would therefore be desirable to devise a process in which certain cheap, synthetic feedstocks could be used as solvents in the liquefaction step. One type of feedstock which might be considered for this purpose is shale oil since this material is potentially available in large quantities from domestic sources. However, as mentioned above, shale oil has generally been considered unsatisfactory as a donor solvent because the long chain alkyl groups which are present in it do not readily release hydrogen to the acceptor molecules. Use of shale oil in this way has, however, remained a desirable objective because of its potential for promoting the use of domestic coal and oil shale resources.

[0005] Other H-donor processes in which aliphatic and at- kylaromatic donor solvents might be readily used include heavy oil upgrading, for example, as described in U.S. Patents 4,292,₁68 and 4,395,324, since various feedstocks containing aliphatic and alkylaromatic components are often readily available in the same petroleum refineries as the heavy oils which are to be upgraded.

[0006] It has now been found that certain active sulfur-containing compounds, especially thiols and thiophenols, are effective catalysts for hydrogen transfer processes in which hydrogen is transferred from a donor to a substrate. These catalysts are effective with aliphatic and alkylaromatic compounds which have previously been considered unsatisfactory H-donors and accordingly, the use of these compounds opens up the possibility for the use of such compounds as H-donors in hydrogen transfer processes, especially heavy oil upgrading and coal liquefaction- One type of material which is able to function effectively as a hydrogen donor in the presence of these catalysts is shale oil, that is, the oil derived from the thermal processing of oil shale. The use of - shale oil as a hydrogen donor in coal liquefaction is considered to be particularly attractive because, as mentioned above, shale oil is available in large quantities, often close to major coalfields in the U.S.A.

[0007] According to the present invention, there is therefore provided a process for the transfer of hydrogen from a hydrogen donor, usually a solvent liquid, to a hydrogen acceptor or substrate to increase the hydrogen content of the substrate, which is carried out in the presence of a catalytic amount of an active sulfur-containing compound, particularly a thiol or a thiophenol The hydrogen donor is an aliphatic compound or an alkylaromatic compound containing an alkyl side chain of at least four and advantageously at least ten carbon atoms. Shale oil is a preferred donor solvent. Useful examples of such hydrogenation processes include the hydroprocessing of heavy petroleum oils and hydrogenative coal liquefaction, either in the presence or absence of added hydrogen. In a preferred aspect of the invention, there is provided a process for the liquefaction of solid carbonaceous material in which the solid carbonaceous material is hydrogenated in the presence of shale oil as a hydrogen donor solvent at elevated temperatures and in the presence of a catalyst comprising an organic active sulfur containing compound.

[0008] The characteristic reaction in the process of the invention is hydrogen transfer, that is, the abstraction of hydrogen from a donor, usually in the liquid state, to a substrate or acceptor, to increase the hydrogen content of the acceptor.

[0009] The reaction is carried out, generally at an elevated temperature depending upon the particular process in question, but usually at least 200°C and often higher, for example 350° or 400°C or above. The system may be maintained under autogenous pressure or superatmospheric pressure in order to maintain the reactants in the liquid phase.

[0010] The hydrogen transfer reaction which takes place in the presence of the thiol or thiophenol catalyst may be utilized in a number of different types of reaction. For example, it may be used in the hydroprocessing of petroleum oils including residua, tars, pitches, heavy gas oils, fractionator tower bottoms, heavy cyclic oils and other heavy oils by hydrogen transfer processes such as hydrogen donor diluent cracking, hydrogen donor visbreaking, and other heavy oil upgrading processes. Processes such as these are described in U.S. Patents 4,347,120, 4,292,₁68, 4,179,229, 4,176,046, 4,090,947, and 2,953,513, to which reference should be made for details of such processes.

[0011] A catalytic amount of an active sulfur compound is present during the reaction, that is, a compound which contains an -SH group. This may be an aliphatic thiol or mercaptan or an aromatic thiophenolic compound. Suitable aliphatic thiols include the alkyl thiols such as methyl mercaptan, ethyl mercaptan, propyl mercaptan, butyl mercaptan and dodecyl mercaptan. The active sulfur compound may also be a thiophenolic compound, for example, thiophenol, 1-thionaphthol or 2-thionaphthol, a substituted thiophenol in which the substituent is, for example, halo such as chloro or bromo, or sulfonate, or a substituted thionaphthol.

[0012] The sulfur compound may be added to the reactants and the hydrogen acceptor as such or in the form of a - precursor which will be converted into a suitable catalyst under the reaction conditions employed. For example, it has been found that benzothiophene, although itself not an active sulfur containing compound, is effective to transfer hydrogen from alicyclic compounds to various hydrogen acceptors. It is believed that under appropriate conditions,hydrogen transfer to benzothiophene or an alkylben- zothiophene (including benzothiophenes substituted on the sulfur-containing ring or on the carbocyclic portion with alkyl groups), occurs to produce a saturated sulfur-containing ring attached to the benzenoid nucleus and that this ring then opens to form a species containing an available active sulfur, probably as a free radical. By contrast, dibenzothiophene is inactive as an H-transfer catalyst; it is believed that this may be because ring opening in dibenzothiophene would be less favored as it would require the cleavage of a bond leading to the production of a phenyl radical.

[0013] The hydrogen acceptor is normally an organic liquid in which it is desired to increase the content of hydrogen. In most cases, the acceptor will be a hydrocarbon or a mixture of hydrocarbons, possibly with a certain content of hetero atoms, especially oxygen, nitrogen and sulfur, as in various petroleum residua and coal liquids. Metals may also be present, usually in the form of soluble compounds such as porphyrins and the like. In heavy petroleum oil upgrading processes such as donor visbreaking and donor cracking, as described for example, in U.S. Patent 4,395,324, the acceptor will be a heavy hydrocarbon residual oil with an initial boiling point of at least 350°C or even higher, for example 400°C or 425°C. Feedstocks of this kind include the residual fractions obtained by the catalytic cracking of gas oils, solvent extracts from lube oil processing, asphalt precipitates from deasphalting operations, high boiling vacuum tower resids and heavy cycle oils. When the H-transfer reaction is applied to coal liquefaction, as described below, the acceptor comprises the coal liquids produced in the liquefaction process, these frequently containing oxygen, nitrogen and sulfur as hetero atoms.

[0014] The H-donor is the source of the hydrogen transferred to the acceptor. Although known types of H-donors such as tetralin may be used in the presence of the present thiol and thiophenol catalysts, the activity of these catalysts for the hydrogen transfer reaction permits other hydrogen-containing compounds, especially aliphatic and alkylaromatic hydrocarbons to be used as the donor liquids. The aliphatic hydrocarbons used as hydrogen donors will contain alkyl chains of at least 4 and generally at least 10, preferably at least 12 carbon atoms. Because transfer of hydrogen to the acceptor may be accompanied by cyclization of the donor material, donors which readily form cyclic derivatives by loss of hydrogens are preferred. Branched chain aliphatics and alkyl aromatics may be employed and substituents, for example hydroxyl, halo, amino may be present Alkyl aromatic compounds such as the alkyl benzenes and alkyl substituted polycyclic (fused ring) aromatics are also effective donors in the presence of the sulfur-containing catalysts; in fact, alkyl benzenes and higher alkyl (C 6 +) substituted benzenes, for example nonylbenzene, are particularly effective donors. In alkylaromatics, the alkyl group is one containing at least 4, and preferably at least 6 carbon atoms, with the potential for undergoing cyclization upon abstraction of the transferrable hydrogens.

[0015] A preferred aliphatic donor liquid is shale oil, the oil produced by the thermal processing of oil shale, for example by the surface or in- §fly retorting of oil shale. The shale oil may either be raw shale oil or it may first be refined to remove impurities such as metals, oxygenates and basic nitrogen compounds. Generally, because a sulfur-containing catalyst is used, the sulfur content of the shale oil will be no problem. The properties of a typical raw shale oil are given in Table ₁ below and of a typical refined shale oil in Table 2 below.





Shale oil is a waxy material which is also high in basic nitrogen content For the most part, the components of shale oil have boiling points in the upper levels of the boiling ranges of hydrocarbons, at least half the oil generally boiling above 400°C. In addition, shale oils usually contain long alkyl chains, usually straight chain or with few branch- ings, which are generally not considered good hydrogen donors. However, the addition of active sulfur compounds accelerates transfer of hydrogen to acceptors such as coal liquids and permits the shale oil to be used as a convenient source of hydrogen. The abstraction of the hydrogen atoms from the shale oil components during the transfer converts the long chain alkyl groups to aromatic groups by dehydrogenation and cyclization. In this way, a highly aromatic product is obtained and this may be further processed by hydrocracking to produce lower molecular weight aromatics which are desirable components of motor gasolines and other refinery and chemical feedstocks.

[0016] The shale oil is particularly useful as a donor solvent in the H-donor coal liquefaction process. In this process, a solid carbonaceous material, usually coal, is hydrogenated in the presence of the hydrogen donor at elevated temperatures and in the presence of the sulfur-containing catalyst.

[0017] The solid carbonaceous material which is subjected to the liquefaction process will generally contain less than 96% by weight carbon and may be, for example, an anthracite coal, a bituminous coal, a sub-bituminous coal, lignite or peat. Solid carbonaceous materials of this kind may contain substantial amounts of organic oxygen and pyritic and organic sulfur together with considerable amounts of nitrogenous compounds and inorganic compounds. Carbonaceous materials are referred to in this specification for convenience as "coal" but any of the materials mentioned above should be considered as suitable for use in the process.

[0018] The coal is comminuted in a conventional manner either in the dry state or in the presence of a liquid, for example the solvent used in the liquefaction step and although the average particle size of the comminuted material will not generally be critical, it will normally be 100 mesh - (U.S. Standard) or smaller. After comminution, the coal is slurried with the solvent and then passed to the liquefaction step where it is reacted at elevated temperatures, typically from 300° to 600°C, and more usually in the range of 320° to 500°C. At these temperatures, the coal will depolymerize but will not undergo any substantial degree of carbonization and depending upon the readiness with which the coal takes up the hydrogen, conditions may be adjusted to optimize processing. Temperatures in the range of 350° to 450°C will often be adequate. The pressure during the liquefaction step is maintained high enough so that the solvent remains in the liquid phase and generally pressures will range from 20 to 200 bar, typically 40 to 100 bar. Average residence times will depend upon the reaction components and the temperature but will generally be from 1 to 240 minutes, with average residence times of 3 to 60 minutes being typical and preferred.

[0019] The liquefaction step may be carried out in the presence or absence of added hydrogen gas and generally it is preferred that molecular hydrogen should be present in order to promote hydrogenation of the coal to produce the desired hydrocarbon product The effluent from the liquefaction step is then treated to remove solid residues and high boiling hydrocarbons, for example material boiling above 540°C. This may be conveniently accomplished in a vacuum tower and the overhead product separated into heavy and light fractions.

[0020] The shale oil may be used as a hydrogen donor solvent, either on its own or in combination with other solvents. The other solvents may be essentially inert solvents or they may be donor solvents themselves. Solvents which may be used in combination with the shale oil include, for example, tetralin and other aromatic compounds which may be readily hydrogenated and dehydrogenated under the conditions employed, for example, 9, 10-dihydroanthracene, 9, 10-dihydrophenanthrene and other donors. Various aromatic petroleum refinery streams may contain these compounds in sufficient quantities to operate in the present process and the presence of other, essentially inert, refractory hydrocarbons in these streams may generally be tolerated, particularly since these other components may themselves act as solvents for the coal.

[0021] As mentioned above, the shale oil is aromatized during the hydrogen transfer sequence and the nature of the products is such that regeneration by hydrogenation is not practicable. However, if other donor solvents, for example hydroaromatics are used in addition to the shale oil, they may be regenerated after separation by rehydrogenation, as by hydrotreating in the presence of a catalyst such as cobalt molybdate in a fixed bed hydrotreating system. Gas product from the hydrotreating step as well as from the product fractionation may be scrubbed to remove acidic components such as H_zS using an alkaline scrub such as monoethanolamine (MEA) and returned to the liquefaction step. Makeup hydrogen may be added from the hydrogen manufacturing plant

[0022] The present liquefaction process results in improved coal upgrading since hydrogen from the shale oil will be capable of quenching radicals produced during the coal liquefaction, resulting in lower boiling products. It also enables the shale oil to be converted into valuable, aromatic- containing streams and to permit the more effective use of shale oil resources.

[0023] The following Examples illustrate the invention.

Example 1

[0024] Dodecane was used as a sample hydrocarbon representing the long chain alkyl group on shale oil. It was reacted with benzo-phenone as a hydrogen acceptor at 440°C for one hour. No conversion of benzophenone to diphenylmethane occurred, indicating that no hydrogen transfer from the dodecane had taken place. In a separate experiment, this reaction was performed in the presence of a small amount (10 wt. %) of thiophenol This resulted in significant conversion (67%) of the benzophenone to diphenyimethane, indicating that hydrogen transfer from the dodecane had taken place.

Examples 2 & 3

[0025] Samples of Paraho Shale Oil (0.2 g) were added to benzophenone (0.2 g) together with 0.0654 g of n-dodecyl- thiol (Ex. 2) and thiophenol (0.0165 g) (Ex. 3) as catalyst The mixtures were placed in heavy wall glass tubes which were then sealed and suspended in a fluidized sand bath at 454°C for 2.5 minutes (approx. 800°C Equivalent Reaction Temperature).

[0026] The tubes were removed and quenched by directing a strew of air at the tubes.

[0027] Reaction products were analyzed by gas chromatograph (Varian 3700) with flame ionization detection.

[0028] Response factors for each component were determined by gc analysis of known mixtures. Calculation of the moles of hydrogen transferred to benzophenone (from the initial amount of benzophenone and the observed ratio of diphenylmethane to diphenylmethane plus benzophenone) was made.

[0029] From the weight of sample used, a value of millimoles of hydrogen transferred per gram of sample is determined. This is called the "hydrogen donor effectiveness"-(HDonEff).

[0030] The results are given in Table 3 below:

Claims

1. A hydrogenation process in which hydrogen is transferred from a hydrogen donor selected from aliphatic compounds containing alkyl groups having at least 4 carbon atoms and alkylaromatic compounds containing alkyl groups having at least 4 carbon atoms, to a hydrogen acceptor in the presence of a catalyst characterized in that the catalyst is an organic active sulfur-containing compound.

2. A process according to claim 1, in which the active sulfur-containing compound is a thiophenol.

3. A process according to claim 1 or claim 2, in which the hydrogen donor comprises shale oil.

₄. A process according to any one of claims ₁ to 3, in which the hydrogen acceptor comprises coal liquids.

5. A process for the liquefaction of a solid carbonaceous material, which comprises hydrogenating a solid carbonaceous material in the presence of a hydrogen donor selected from aliphatic compounds containing alkyl groups having at least 4 carbon atoms and alkylaromatic compounds containing alkyl groups having at least 4 carbon atoms, at an elevated temperature in the presence of a catalyst, characterized in that the catalyst is an organic, active sulfur-containing compound.

6. A process according to claim 5, in which the solid carbonaceous material comprises anthracite, a bituminous coal, a sub-bituminous coal, lignite or peat

7. A process according to claim 5 or claim 6, in which the hydrogen donor comprises raw shale oil.

8. A process according to any one of claims 5 to 7, in which the solid carbonaceous material is hydrogenated at a temperature of 320° to 500°C.

9. A process according to any one of claims 1 to 8, in which the active sulfur-containing compound is an alkyl mercaptan.

10. A process according to claim 9, in which the alkyl mercaptan is a mercaptan of a C₂ to C₁₂ alkane.

11. A process according to any one of claims 1 to 8, in which the active sulfur-containing. compound is an aromatic active sulfur-containing compound.

12. A process according to claim 11, in which the aromatic active sulfur-containing compound is a thiophenol.