GB2170508A

GB2170508A - Production of H2/CO synthesis gas

Info

Publication number: GB2170508A
Application number: GB08601157A
Authority: GB
Inventors: Siegfried Michel; Bernd Kandziora
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 1985-01-17
Filing date: 1986-01-17
Publication date: 1986-08-06
Also published as: DE3501460A1; GB8601157D0

Abstract

A method for the production of a stoichiometric H2/CO synthesis gas which comprises catalytically converting a substantially sulphur-free or desulphurized hydrocarbon stream in the presence of CO2, by endothermic catalytic oxidation, (reforming) to produce a gas mixture comprising predominantly H2 and CO in stoichiometric proportions and wholly or partially separating CO2 from the gas mixture to produce a stoichiometric synthesis gas.

Description

SPECIFICATION Production of H2/CO synthesis gas The present invention relates to the production of H2/CO synthesis gas, particularly a substantially stoichiometric synthesis gas, which is useful in the production of methanol.

Traditionally, a hydrocarbon-containing feed material, e.g., natural gas, refinery gas, other gaseous hydrocarbons, or vapourizable liquid hydrocarbons, has been reacted in a steam reformer in the presence of steam and, if desired, CO2, to produce and H2/CO synthesis gas. This steam reformer gas contains a maximum of 16% by volume CO and, besides H2 and CO2, a very high concentration of CH4, i.e., up to 4% by volume.

However, a high CO content is required in order to produce stoichiometric H2/CO synthesis gases.

Depending on the particular synthesis product to be manufactured, the desired H2/CO ratios range from about 2.3 (corresponding to about 29% by volume CO for synthesis gas to produce methanol) up to 0.5 (corresponding to 66% by volume CO for synthesis gas to produce vinyl acetate), and even more.

It has now been found possible to provide a method for the production of a stoichiometric H2/CO synthesis gas, particularly such gas having CO contents ranging from about 29 to 75% by volume.

According to the present invention there is provided a method for the production of a stoichiometric H2/CO synthesis gas which comprises catalytically converting a substantially sulphur-free or desulphurized hydrocarbon stream in the presence of C02, by endothermic catalytic oxidation, to form a reforming gas comprising predominantly H2 and CO in stoichiometric proportions and wholly or partially separating CO2 from the reforming gas to produce a stoichiometric synthesis gas.

By means of the method according to the invention, a methanol synthesis gas having a stoichiometric (as related to H2) CO content and a very low CH4 content (less than 0.01% by volume) can be produced. The CO2 can be removed from this gas in conventional fashion, for example by adsorption, down to the desired content, for example, about 3% by volume, as required in the synthesis gas for the production of methanol.

Due to the very low CH4 content for example, of about 0.004% of the synthesis gas, the carbon yield, for example in the methanol synthesis gas is increased from about 92 to 98%. This loss has previously been encountered because the CH4 contained in the steam reformer gas did not partake in the synthesis reaction, but instead was merely accumulated in the synthesis reactor and thus had to be continuously removed.

During the elimination of CH4 as the purge gas, however, synthesis gas was also always lost. Thus, this deficiency of the known method of any synthesis plant has been eliminated.

A major advantage of the synthesis gas produced according to the invention is that for a given methanol product quantity in comparison to the steam reformer process, smaller synthesis gas quantities are required by the process, thus leading to reduced investment costs. Thus, the same yields can be obtained using smaller reactors.

The hydrocarbon stream may be derived from natural gas, refinery gas, other gaseous hydrocarbons, or vapourizable liquid hydrocarbons.

Suitable materials for the method of the present invention include light, reformable hydrocarbons, expecially C2to Cg hydrocarbons, having a high C02 content. In practice the C02 quantity in the reformer feed is limited to the amount of C02 recovered from the reformed gas which results in a H2/CO ratio of the reformed gas of approximately 3.0. By increasing the CO2 quantities and adapting the steam quantities correspondingly in the feedstock, H2/CO ratios in the range of 2.3 to 0.5 as required for synthesis purposes can be produced directly (without excess H2).These can be obtained from, for example, natural gases, residual gases from pressure swing adsorption plants for H2 purification, sewer gas from sewerage treatment installations or dumps, rich gas from the catalytic conversion of heavy hydrocarbons, or other gaseous mixtures.

To this reforming feedstock the desired stoichiometric amount, for example about 0 to 100% of 002 taken from the CO2 fraction removed in the downstream CO2 separator, in order to obtain a CO2 concentration in the feedstock of 30 to 90% by volume (dry basis) and, correspondingly steam, are mixed so that a reactant mixture possessing the required H2/CO product quantity ratio in the reforming gas without the presence of an excess of H2. No steam is added in cases where low H2/CO ratios (approximately 0.3 to 1.5) are required.

For this purpose, the separated CO2 fraction may be recycled and introduced either entirely or partially upstream of the reformer, usually into the C02-contai ni ng gaseous mixture. Alternatively, in addition to the separated C02 fraction, further C02, in the form of another CO2 supply or a CO2-containing gaseous mixture may be fed into the gaseous mixture upstream of the reformer. Steam may also be introduced into the catalytic reformer with the hydrocarbon stream.

The reforming reaction typically proceeds at temperatures of about 850 to 1 1000C, preferably 900 to 1100,0 and pressures of 120 to 2000 kPa (1.2 to 20 bar) preferably 200 to 2000 kPa (2 to 20 bar) and in the presence of catalysts such as nickel based catalysts at various metal concentrations. A wide variety of synthesis gases having H2/CO ratios ranging between about 0.3 to 2.3 can thus be obtained by using feedstocks having 002/0 ratios of between about 0.3 to 5 and H2O/C ratios of about 0 to 5 in the reforming feedstock. (In the above ratios, C denotes all the hydrocarbons). The conventional reforming reactions are typically undertaken according to the teachings, for example, of CO2/C ratios less than 0.3 and H2O/C ratios of between 1.5 and 5.

Suitable synthesis gas feedstocks produced by this method can be utilized, for example, in the production of methanol, oxoalcohols, acetic acid/anhydride, ethylene glycol, methyl formate, vinyl acetate monomer, acetonitrile, ethyl acetate, ethanol, higher alcohols, carboxylic acids, high octane gasoline (petrol), and oxygenated C2-compounds.

The method according to the invention may be further described with reference to the accompanying drawing and the following Example, illustrating a schematically represented embodiment for the production of a stoichiometric methanol synthesis gas. All parts and percentages are by weight, unless otherwise specified.

Example Referring to the single figure of the accompanying drawings, by way of a line 1, 21.4 kmol/hr of a feedstock comprising H2 1.1 kmol/hr CO2 0.2 kmol/hr CH4 17.1 kmol/hr C2H5 1.4kmol/hr C3+ 1.6kmol/hr is introduced and, after admixture of 9.2 kmol/hr of CO2 from line 3 and 40.3 kmol/hr of steam from line 4, is conducted to a reformer 2. The CO2 is line 3 stems in part from 2.2 kmol/hr of a recycled downstream CO2 separator stage, and in part from 6.8 kmol/h of CO2 introduced by way of line 5.

In reformer 2, the hydrocarbons are catalytically reacted in the presence of a nickel based catalyst in the presence of the CO2, which acts as an oxygen donor, at a pressure of 200 to 2000 kPa (2 bar to 20 bar) and at a temperature of 900"C to 11 000C, so that there is withdrawn, by way of line 6, 101.2 kmol/hr of a reforming gas having the following composition: H2 67.7 kmol/hr CO 29.3 kmol/hr CO2 5.2 kmol/hr CH4 0.01 kmol/hr The CO2 (2.2 kmol/h) is separated from the reforming gas in 7, for example by adsorption, so that 100 kmol/h by a methanol synthesis gas is obtained by way of line 8. This separated CO2 is introduced to the feedstock upstream of the reformer by way of line 9 and line 3. The process can thereby be operated in a continuous manner.

Claims

1. A method for the production of a stoichiometric H2/CO synthesis gas which comprises catalytically converting a substantially sulphur-free or desulphurized hydrocarbon stream in the presence of CO2, by endothermic catalytic oxidation, to form a reforming gas comprising predominantly H2 and CO in stoichiometric proportions and wholly or partially separating CO2 from the reforming gas to produce a stoichiometric synthesis gas.

2. A method as claimed in claim 1, in which the separated CO2 is at least partially recycled to upstream of the reformer.

3. A method as claimed in claim 1 or 2, in which in addition to the separated CO2 fraction, further CO2 or a gas mixture containing CO2 is also fed to upstream of the reformer.

4. A method as claimed in any of claims 1 to 3, in which the hydrocarbon stream is derived from natural gas, refinery gas, other gaseous hydrocarbons, orvapourizable liquid hydrocarbons.

5. A process as claimed in any of claims 1 to 4, in which an effective amount of steam is introduced into the catalytic reformer along with the light hydrocarbon gas.

6. A process as claimed in any of claims 1 to 5, in which the stoichiometric H2/CO synthesis gas formed has a CO content ranging from about 29 to 75% by volume.

7. A process as claimed in any of claims I to 6, in which the formed stoichiometric synthesis gas is suitable for methanol production.

8. A process as claimed in claim 7, in which the synthesis gas has a methane content less than 0.01 vol-%.

9. A process as claimed in any of claims 1 to 8, in which the unreacted CO2 separated from the product reforming gas is removed by adsorption.

10 A process as claimed in any of claims 1 to 9, in which the hydrocarbon stream comprises a C1 to C5 hydrocarbon stream having a CO2 content from 30 to 90% by volume (on a dry basis).

11. A process as claimed in any of claims 1 to 10, in which the H2/CO ratios range from about 0.3 to 2.3.

12. A process as claimed in any of claims 1 to 11, in which the hydrocarbon stream has a CO2/C ratio of between about 0.3 to 5.0.

13. A process as claimed in any of claims 1 to 12, in which the H2O/C ratio ranges from about 0 to 5.

14. A process as claimed in any of claims 1 to 13, in which the endothermic catalytic oxidation in the reformer occurs at temperatures ranging from about 850 to 11 00 C.

15. A process as claimed in claim 14, in which the endothermic catalytic oxidation in the reformer occurs attemperatures ranging from about 900 to 1100 C.

16. A process as claimed in any of claims 1 to 14, in which the endothermic catalytic oxidation in the reformer occurs at pressures ranging from about 120 to 2000 kPa (1.2 to 20 bar).

17. A process as claimed in claim 16 in which the endothermic catalytic oxidation in the reformer occurs at pressures ranging from about 200 to 2000 kPa (2.0 to 20 bar).

18. A process according to claim 1, substantially as hereinbefore described with particular reference to the foregoing Example and as illustrated in the accompanying drawings.