# Patent

## Title
Process for recovering carbon dioxide

## Abstract

In a process for obtaining CO2, desulfurized natural gas or gas which accompanies mineral oil is reformed autothermally with addition of oxygenous gas at a temperature of from 900 to 1200° C. and a pressure of from 40 to 100 bar (a) by partial catalytic oxidation to give a crude synthesis gas, and then converted catalytically to H2 and CO2 at a temperature of from 75 to 110 DEG C. and a pressure of from 50 to 75 bar (a) of CO, CO2 is scrubbed out of the synthesis gas obtained with methanol at a pressure of from 15 to 100 bar (a) and a temperature of from +10 to −80° C., and the absorbed CO2 is recovered by decompression. A further possible use of the process consists in converting the recovered CO2 to the supercritical state.

## Background
This application is a 371 application of PCT/EP2007/009442 filed Oct. 31, 2007, which claims priority to the German application DE 10 2006 054 472.2 filed Nov. 18, 2006.
This invention relates to a process for recovering CO2 from desulfurized natural gas or petroleum gas liberated from C2+ components, which, preheated to a temperature of 45 to 75° C., is autothermally reformed in a first reaction stage by adding gas containing at least [calculated dry] 75 vol-% O2 at a temperature of 900 to 1200° C. and a pressure of 40 to 100 barabs by partial oxidation over a fixed bed of a cracking catalyst to obtain a raw synthesis gas, containing as main components [calculated dry] 55 to 75 vol-% H2, 15 to 30 vol-% CO and 5 to 30 vol-% CO2 with a volume ratio of H2:CO of 1.6 to 4, in a second reaction stage the CO contained in the raw synthesis gas having a temperature of 75 to 110° C. and a pressure of 50 to 75 barabs is converted to H2 and CO2 over at least one fixed-bed catalyst, from the synthesis gas containing at least [calculated dry] 55 vol-% H2 CO2 is washed out in at least one washing stage at a pressure of 15 to 100 barabs with methanol having a temperature of +10 to −80° C., and absorbed CO2 is recovered by expanding the cold methanol to almost atmospheric pressure.
From EP-B-1 337 466, there is known a process for catalytically generating NH3 from an N2—H2 mixture. Natural gas together with a gas stream chiefly consisting of O2, preferably at least 70 vol-%, is autothermally reformed at a temperature of 900 to 1200° C. and a pressure of 40 to 100 barabs in the presence of a cracking catalyst to obtain raw synthesis gas, containing [calculated dry] 55 to 75 vol-% H2, 15 to 30 vol-% CO and 5 to 30 vol-% CO2 at a volume ratio of H2:CO of 1.6 to 4. By catalytic conversion, the CO content of the cooled raw synthesis gas withdrawn from the autothermal reformer is converted to H2, so that the synthesis gas formed contains at least [calculated dry] 50 vol-% H2 and not more than 8 vol-% CO. In a multistage gas wash, CO2, CO and CH4 are removed from the synthesis gas, wherein in at least one of the stages liquid N2 is added for generating an N2—H2 mixture for the catalytic production of ammonia in an ammonia synthesis. In the gas wash, CO2 is removed with methanol having a temperature of −58° C. and in conjunction with the production of NH3 is used for generating urea. In the N2 wash, the synthesis gas is cooled to a temperature of −185° C., so that first CH4 and then CO are condensed and both components are recirculated to the autothermal reformer as fuel gas.
It is the object of the present invention to utilize the process described above for further applications.
The solution of this object consists in that the CO2 recovered is transferred into the critical condition, so that for solvent flooding the CO2 is injected into partially deoiled petroleum deposits or can be stored in pore reservoirs, in cavern reservoirs, in depleted natural gas deposits suitable as reservoir or in saline aquifers or can be used for oxo synthesis.
In accordance with the further aspect of the process, it is possible to wholly or partly supply the H2 recovered as fuel to a gas turbine or another means for generating electrical energy, for instance to a fuel cell, wherein in accordance with a further feature of the invention the H2 can be diluted with up to 70 vol-% N2.
In accordance with a particular feature of the invention, part of the mechanical energy generated by the gas turbine or another means for recovering electrical energy is utilized for driving the compressor of the air separation plant and/or the compression plant for the CO2; the remaining part is available as useful energy.



The invention will subsequently be explained in detail with reference to an embodiment in conjunction with a basic flow diagram illustrated in the drawing.



Via conduit (1), natural gas is supplied to the pretreatment plant (4) with a pressure of 45 to 65 barabs and a temperature of 15 to 35° C., via conduit (2) steam and via conduit (3) CH4 is supplied to the pretreatment plant (4), in which the natural gas is liberated from sulfur compounds and C2+ components on a bed of Co—Mo catalyst with a downstream bed of ZnO and preheated to a temperature of 55 to 75° C. The gas withdrawn from the pretreatment plant (4) via conduit (5) is charged to an autothermal reformer (6) along with high-oxygen gas supplied via conduit (7) with an O2 content of [calculated dry] 92 vol-%, which is generated in an air separation plant (8) into which air is introduced via conduit (9). In the autothermal reformer (6) a bed of commercially available NiO catalyst is disposed, on which the natural gas is reformed by partial oxidation with O2 to obtain raw synthesis gas containing CO, H2 and CO2 at a temperature of 900 to 1200° C. and a pressure of 40 to 100 barabs, preferably 40 to 80 barabs. The raw synthesis gas withdrawn from the autothermal reformer (6) via conduit (10) contains [calculated dry] 55 to 75 vol-% H2, 15 to 30 vol-% CO and 5 to 30 vol-% CO2 at a volume ratio of H2:CO of 1.6 to 4. The raw synthesis gas cooled intermediately in a non-illustrated heat exchanger to a temperature of 25 to 45° C. is passed into a two-stage converter (11) filled with a bed of commercially available Fe—Cr catalyst, in which the CO still contained in the raw synthesis gas stream is converted to CO2 and H2, wherein the volume ratio of H2:CO2 [calculated dry] is 2.5 to 3. Upon traversing a non-illustrated heat exchanger, the synthesis gas stream obtained by conversion and withdrawn via conduit (12), which contains [calculated dry] at least 65 vol-% H2 and not more than 8 vol-% CO, is introduced into a two-stage physical gas washing plant (13). In the first stage (14) of the gas washing plant (13), CO2 is absorbed by means of methanol having a temperature of −20 to −70° C. at a pressure of 40 to 80 barabs. In the second stage (15) of the gas washing plant (13), the impurities CO, CH4 and Ar left in the synthesis gas stream upon removal of CO2 are absorbed by means of liquid nitrogen recovered in the air separation plant (8) and charged to the second stage (15) via conduit (16). For removing absorbed CO2 from the methanol and the absorbed CO, CH4 and Ar from the N2, the methanol and the N2 are expanded to almost atmospheric pressure. Via conduit (17), the CO2 recovered is supplied to a plant (18) in which the CO2 is brought into the supercritical condition by increasing pressure and temperature, and via conduit (19) it is injected into partly deoiled petroleum deposits for solvent flooding. The gas stream containing CO, CH4 and Ar is recirculated to the autothermal reformer (6) as fuel gas via conduit (20). Via conduit (21), the H2 obtained during the absorption of the CO2 in the first stage (14) of the gas washing plant (13) flows as fuel into the combustion chamber of a gas turbine (22).
The data obtained with a concrete embodiment of the process of the invention for substance amounts, temperatures, pressures and composition of the gas streams are listed in the following table with reference to the basic flow diagram illustrated in the drawing.

















Conduit No.
1
5
10
12
17
20
21






















Amount (t/h)
92
263
336
400
0.044
0.01
49.8


Temperature (° C.)
25
65
95
32
40
40
209


Pressure (barabs)
55
61
60
57
110
58
30-54


Composition Vol-%


[calculated dry]


CH4
91.3
27.0
1.8
2.0
—
2.0
0.8


C2H6
5.8
—
—
—
—
—
—


CO
—
1.6
10.6
1.1
0.1
1.1
1.9


CO2
1.9
0.6
7.1
16.7
99.6
16.7
0.5


Ar
—
—
0.3
0.5
—
0.5
0.9


H2
—
3.2
38.7
47.5
0.2
47.5
92.5


N2
1.0
0.3
0.4
2.3
0.1
2.3
4.2


H2O
—
67.3
41.1
29.9
—
—
—









For the gas wash (13), the known Rectisol® process is used, in which in the first stage (14) CO2 is absorbed with methanol having a temperature of −58° C. In the second stage (15) of the gas wash (13), the temperature of the synthesis gas initially is decreased to a value of −185° C., so that the CH4 is condensed, separated and recirculated into the autothermal reformer (3) as fuel gas together with the likewise separated CO and Ar.
The advantages achievable with the invention in particular consist in that

    
    
        emissions of CO2 are prevented, in particular for ecological reasons,
        the process for recovering supercritical CO2 can be used directly in situ for solvent flooding largely deoiled petroleum deposits in petroleum prospects,
        the petroleum gas obtained in the recovery of petroleum can be processed directly in situ in many petroleum prospects, and the gas components generated can be utilized within the process.

## Claims

1. A process for recovering CO2 from desulfurized natural gas or petroleum gas liberated from C2+ components, said process comprising preheating the natural gas or petroleum gas to a temperature of 45 to 75° C., autothermally reforming the natural gas or petroleum gas by partial oxidation in a first reaction stage by adding gas containing at least 75 vol-% O2 at a temperature of 900 to 1200° C. and a pressure of 40 to 100 barabs over a fixed bed of a cracking catalyst to obtain a raw synthesis gas, said raw synthesis gas comprising 55 to 75 vol-% H2, 15 to 30 vol-% CO and 5 to 30 vol-% CO2 with a volume ratio of H2:CO of 1.6 to 4, converting the CO contained in the raw synthesis gas to H2 and CO2 over at least one fixed-bed catalyst in a second reaction stage, wherein the raw synthesis gas has a temperature of 75 to 110° C. and a pressure of 75 to 50 barabs, washing out the CO2 from the synthesis gas in at least one washing stage at a pressure of 15 to 100 barabs with methanol having a temperature of +10 to −80° C., and recovering absorbed CO2 by expanding the cold methanol to almost atmospheric pressure, and recovering H2, wherein CO, CH4 and Ar are left in the synthesis gas upon removal of CO2, wherein the CO2 recovered is transferred into the supercritical condition and the CO, CH4 and Ar-containing gas is recirculated to the autothermal reformer as fuel gas, the supercritical CO2 being used for solvent flooding of partially deoiled petroleum deposits, subterranean storage, or oxo synthesis.

2. The process according to claim 1, wherein the H2 recovered is supplied as fuel to a gas turbine for generating electrical energy.

3. The process according to claim 2, wherein the H2 recovered is diluted up to 70 vol-% N2.

4. The process according to claim 2, wherein part of the mechanical energy generated by the gas turbine is utilized for driving the compressor of an air separation plant.

5. The process according to claim 2, wherein part of the mechanical energy generated by the gas turbine is utilized for driving the compressor for the CO2.