[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.

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.