Thermal hydrogenation of hydrocarbon liquids

Abstract

 Methane-containing gases suitable for use as SNG are produced by the non-catalytic thermal hydrogenation of hydrocarbon oils using a hydrogenation gas produced by the partial oxidation of a hydrocarbon followed by shift conversion of the crude partial oxidation gasification product in admixture with steam and the crude product from the thermal hydrogenator. The crude shift conversion product is subjected to compression purification and separation into at least two streams. A first stream containing hydrogen is employed as the hydrogenating gas and the second stream is the methane-containing product gas.

Description

[0001] This invention relates to the production of methane-containing gases, particularly methane-containing gases suitable for use as substitute natural gas (SNG) by the non-catalytic hydrogenation of hydrocarbon liquids.

[0002] A number of processes are known for thermally hydrogenating hydrocarbon oils. For example, our UK Published Patent Specicication No. 1031717 describes a process in which a hydrocarbon oil is atomised and, in admixture with a hydrogen-containing gas, is caused to circulate along an endless path within a reaction vessel. The gas mixture is heated and the oil undergoes hydrogeantion. In our UK Patent Specification Nos. 1188113; 1154321 and 830960 are described processes wherein an oil is atomised and occluded onto solid carbonaceous particles. The particles are contacted with a hydrogenating gas and are maintained as a recirculating fluidized bed.

[0003] More recent developments in thermal hydrogenation are described in UK Patent Publiction No. 2062000 which also describes one of the commonly employed methods for producing hydrogenating gas by the partial oxidation of hydrocarbon materials in the presence of steam and oxygen.

[0004] In the manufacture of a hydrogenating gas by the partial oxidation of hydrocarbons it has been conventional to treat the product gas to upgrade it prior to use as hydrogenating gas. These treatments include a water gas shift reaction and an acid gas removal step.

[0005] We have now found that several unexpected advantages do accrue if the crude product gas from a partial oxidation stage is combined with crude product from a thermal hydrogenation stage and the mixed gas streams are subjected to treatments in common prior to separation of a hydrogen containing stream which is used as the hydrogenating gas in the thermal hydrogenation of a hydrocarbon.

[0006] In accordance with the present invention there is provided a process for the production of methane-containing gases by the non-catalytic thermal hydrogenation of hydrocarbon oils wherein said oil is caused to react with a hydrogen-containing gas at least a portion of which is produced by the partial oxidation of a hydrocarbon feedstock, characterised in that the crude products from the hydrogenation stage and the partial oxidation stage are admixed and the mixture is subjected to catalytic carbon monoxide conversion to produce a product gas containing hydrogen and methane, which is further treated to form separate methane-containing, and hydrogen-containing gas streams and recycling the hydrogen-containing gas for reaction with said hydrocarbon oil.

[0007] Although the hydrogenation stage, which is preferably a recirculating fluidized bed hydrogenator, and the partial oxidation stages are conventionally known, the manner of dealing with the crdue product gases is not. The two crude gas streams are mixed together and with added superheated steam are passed through a catalytic shift conversion stage wherein the carbon monoxide present reacts with steam to form hydrogen and carbon dioxide according to the reaction:

[0008] Shift conversion processes per se are known. However in the process of the present invention the reaction is carried out in the presence of methane which is produced during the hdyrogenation.

[0009] In addition to the water gas shift reaction (I) above other beneficial catalytic hydrogenation type reactions occure viz hydrogenation of hydrogen cyanide to ammonia and the hydrolysis of carbonyl sulphide to hydrogen sulphide. The ammonia can be removed by washing whereas the hydrogen sulphide can be readily removed, along with the formed carbon dioxide by known acid gas removal techniques, and disposed by, for example, the Claus reaction.

[0010] The invention will be described in further detail with reference to the accompanying drawings in which:

Figure 1 is a block flow diagram of a conventional process route employing fluidized bed hydrogenation, and

Figure 2 is a block flow diagram of an embodiment of the present invention in which fluidized bed hdyrogenation is employed in the manufacture of SNG.

[0011] Referring to Figure 1, an oil feedstock is divided into two parts. This may be by simple physical division or by a distillation process. One portion, which may be a residuum and is used as feedstock for a partial oxidation reaction is fed to a gasification unit 1 and a second portion, which may be a distillate, is used as feedstock for a thermal hydrogenation reaction and is fed to a gasifier 2 comprising a fluidized bed hdyrogenator associated with a gas cooling unit. The hydrogenator may be constructed in a manner as described, for example, in UK Patent Specification No. 1188113.

[0012] Hydrogenating gas is also fed into reactor 2 through line 3 which comprises freshly produced hydrogen from line 4 and excess hydrogen recovered from the reaction product, though line 5. After reaction, the gaseous product is subjected to several cooling stages to remove both heavy and light aromatic condensates. Fresh coke particles are also added (not shown) to the hydrogenator and agglomerated particles are withdrawn and together with the heavy condensate are employed as feedstock for the partial oxidation gasification unit and are supplied to the unit through lines 21 and 22,respectively. The light aromatic condensate is withdrawn via line 23.

[0013] The crude product gas from the hdyrogenator is then subjected to a series of washing steps, viz: in unit 6 with benzole to remove light mononuclear aromatics such as benzene, toluenl and xylene (BTX); in unit 7 with water to remove ammonia, carbon dioxide, hydrogen sulphide, and hydrogen cyanide and in unit 8 to hydrolyse carbonyl sulphide and to a wash with diethanolamine to remove the product and residual hydrogen sulphide.

[0014] The hydrogen consumed in the hydrogenator is provided by the partial oxidation of hydrocarbons. In gasification unit 1 residual oil feedstock, FBH condensate 22 and coke 21 are gasified in the presence of oxygen and steam. The resultant gas, containing mainly hydrogen and carbon monoxide, after cooling and admixed with super heated steam is passed over a catalytic carbon monoxide conversion stage 14 where carbon monoxide is converted to hydogen and carbon dioxide. Any carbonyl sulphide present is hydrolysed to hydrogen sulphide which is removed by an acid gas removal stage 15. The product gas stream 4 is combined with the recycle gas stream 5 to form the hydrogenation stream 3.

[0015] Referring to Figure 2, the fluidized bed hydrogenation and partial oxidation stages are essentially similar to those shown and described in connection with Figure 1. Thus the residual oil feedstock is reacted with hydrogen in unit 1 to produce a stream 16 rich in methane and unreacted hydrogen. This stream, after cooling is mixed with the partial oxidation product gas 17 and passed through a catalytic carbon monoxide conversion reactor 18 where, in addition to the conversion of steam and carbon monoxide to hydrogen and carbon dioxide, hydrogen cyanide is hydrogenated to ammonia and carbonyl sulphide is hydrolysed to hydrogen sulphide.

[0016] The gas from the catalytic converter is cooled in unit 17 to remove condensate containing ammonia, some carbon dioxide, hydrogen sulphide and other dissolved gases. The gas may be subjected to water washing (not shown) to remove final traces of ammonia before being compressed by compressor unit 10.

[0017] After compression the product gas subjected to acid gas purification 20 utilizing known processes such as Benfield, Silexol and Rectisol to separate out an hydrogen sulphide rich and carbon dioxide rich stream. Light mononuclear aromatic species which may still be present in the gas may also be removed and thereafter separated from the purification solvent to give a BTX stream (a mixture of benzene-toluene and xylene).

[0018] The purified gas stream is then subjected to hydrogen separation in unit 11, for example by cryogenic separation.

[0019] In a cryogenic separation stage species other than hydrogen are liquified and thus separated from the gaseous hydrogen. The liquor may then be fractionated and revaporised to yield a product gas suitable for use as SNG 12.

[0020] The cryogenic liquor comprises alkanes such as methane and ethane, carbon monoxide and inerts. By fractionating the mixture into several components, constituents streams may be produced. For example ethane can be separated out from the methane and added back to provide any necessary enrichment for SNG specification. Similarly, the carbon monoxide may be recycled back to the shift stage 18.

[0021] The operation of the present invention will be illustrated by the following example.

[0022] Using apparatus as described in connection with Figure 2 a hydrocarbon oil feedstock was fed to a hydrogenation unit and a partial oxidation gasification unit. In the hydrogenation unit the oil was reacted with a hydrogenating gas 5 having the composition (expressed as a feed rate) shown in the first column of the Table.

[0023] The product gas 16, having the composition shown in the second column is combined with the product 17 of the partial oxidation unit (having the composition shown in the third column) and to the combined gases are added 6591.14 Kg moles Hr-1 of superheated steam and the whole mixutre passed over a CO conversion catalyst at 207^0C at a pressure of 50.34 bar.

[0024] After shift conversion, the shift product is cooled, whereupon a condensate separates out containing dissolved gases including a ammonia. The shift product gas 24, after compression , has the composition shown in the fourth column of the Table.

[0025] The compressed gas is then subjected to acid gas purification and cryogenic separation 20 and 11. In the cryogenic separation stage the hydrogenating gas 5 (column 1) is separated from the final product gas stream 12 (fifth column), to which some carbon dioxide is blended to bring the gas up to SNG specification.

Claims

1. A process for the production of methane-containing gases by the non-catalytic thermal hydrogenation of hydrocarbon oils wherein said oil is caused to react with a hydrogen-containing gas at least a portion of which is produced by the partial oxidation of a hydrocarbon feedstock, characterised in that the crude products from the hydrogenation stage and the partial oxidation stage are admixed and the mixture is subjected to catalytic carbon monoxide conversion to produce a product gas containing hydrogen and methane, which is further treated to form separate methane-containing, and hydrogen-containing gas streams and recycling the hydrogen-containing gas for reaction with said hydrocarbon oil.

2. A process as claimed in Claim 1 wherein said thermal hydrogenation is carried out in a recirculating fluidized bed of carbonaceous particles.

3. A process as claimed in Claim 1 or Claim 2 in which said methane-containing gas stream is treated to remove carbon monoxide which is recycled back to said carbon monoxide conversion stage.

Drawing