WO2014111310A1

WO2014111310A1 - Process for the preparation of synthesis gas

Info

Publication number: WO2014111310A1
Application number: PCT/EP2014/050377
Authority: WO
Inventors: Yuhan Sun; Tiejun Zhao; Zhiyong Tang; He ZHU; Bin Liu; Yaning XIAO; Dongfei WANG
Original assignee: Shanghai Advanced Research Institute of CAS; Shell Internationale Research Maatschappij BV; Shell Oil Co
Current assignee: Shanghai Advanced Research Institute of CAS; Shell Internationale Research Maatschappij BV; Shell USA Inc
Priority date: 2013-01-17
Filing date: 2014-01-10
Publication date: 2014-07-24
Anticipated expiration: 2015-07-17
Also published as: CN103979492A

Abstract

The invention relates to a process for the preparation of synthesis gas. Process for the preparation of synthesis gas by auto-thermal reforming of carbon dioxide and methane comprising the steps of (a) introducing a methane-comprising feed gas, carbon dioxide and an oxygen-containing gas into a carbon dioxide-methane auto-thermal reforming reactor comprising a bed of reforming catalyst; (b) mixing the methane-comprising feed gas, carbon dioxide and oxygen-containing gas; (c) reacting methane with oxygen in an oxidation reaction; (d) reacting methane with carbon dioxide in a reforming reaction in the presence of the reforming catalyst using the heat released in the oxidation reaction in step (c); and (e) recovering the synthesis gas produced in steps (c) and (d). The process realizes the self-supply of heat in the high temperature reforming reactor by utilizing the heat generated in the exothermic oxidation reaction between methane and oxygen in the endothermic carbon dioxide-methane reforming reaction. The invention, accordingly, not only solves the heating problems of the reforming reactor at high temperatures, but also decreases the energy consumption and operating cost of the system.

Description

PROCESS FOR THE PREPARATION OF SYNTHESIS GAS

Field of technology

The present invention is in the field of CI chemistry and relates to a process for the preparation of synthesis gas, more particularly a process for preparing synthesis gas by auto-thermal reforming of methane and carbon dioxide .

Background

Global warming is an important problem facing the world today. People are, therefore, increasingly

interested in finding ways to reduce the emission of greenhouse gases, such as methane (CH₄) and carbon dioxide ( CO2 ) · As CO2 is an important resource of carbon and oxygen, its conversion to syngas could be an

effective and advantageous way of re-using any CH₄ and

CO2 produced and/or emitted. Syngas or synthesis gas is a commonly used term for a gas comprising carbon monoxide (CO) and hydrogen (¾) and is used in a variety of processes as the starting reaction mixture for producing different chemicals, such as methanol or longer-chain hydrocarbons (via Fischer-Tropsch synthesis).

A catalytic process for converting CO2 at high temperature may turn into a very important direction for CO2 utilization at a large scale. Accordingly, a process for reforming CO2 and CH₄ into syngas not only

effectively uses two greenhouse gases CO2 and CH₄ (which, inter alia, come from coal chemical industry and coal bed gas), but also decreases the emission of these gases. This leads to the cyclic utilization of carbon resources into energy and chemicals which could also have enormous economic benefits. Thus, the reaction of C02~CH₄ reforming could potentially be one of the key

technologies for the efficient (re) utilization of carbon resources in the coal chemical industry for the future.

At this point in time, however, there is no example of CO2-CH₄ reforming to syngas on an industrial scale.

The CO2-CH₄ reforming reaction is a highly endothermic reaction. Based on thermodynamic analysis, it is clear that the temperature has to be increased to at least 600 °C before the C0₂ and CH₄ react into CO and H₂.

Furthermore, the conversion rate, and hence syngas yield, increases with increasing reaction temperature. Providing adequate heat sources which can provide the necessary reaction heat and operate such high temperatures would also be a challenge in any industrial CO2-CH₄ reforming process.

Several documents, both from literature and patents, describe methods for CO2-CH₄ reforming. For example, CN- 10145079-A (application number 200710171938), entitled "Method and apparatus for preparing synthesis gas by natural gas-carbon dioxide reforming", reveals a

reforming method, where natural gas is mixed and

electrically preheated with CO2 after decreasing its sulphur content in a hydro-desulfurization reactor, and subsequently the resulting gas mixture is fed to a reforming reactor containing a nickel-based catalyst.

However, using electric heating to supply energy has disadvantages, such as low thermal efficiency and high energy consumption, which is not attractive for

industrial implementation.

CN-1648034-A (application number 200510012305) entitled "Process for preparing synthetic gas by

reforming carbon dioxide-methane" reveals a reforming method, in which a CH₄-rich feed gas, CO2 , H₂0 and O2 are added and preheated in a pyrolysis section of a thermal conversion reactor and when the temperature rises above 950 °C the reaction takes place to produce hot syngas. This hot syngas is subjected to cooling and heat

exchanging to produce the syngas product. 200510012305 discloses that one advantage of the method described is that the carbon source is not only the reactant, but also the catalyst. However, this process requires a large reactor because of the low catalytic activity of carbon source and low reaction rate. This makes the reactor very expensive and hence economically unattractive. Moreover, the heat generated by the exothermic oxidation reaction of the carbon source is required to provide heat for the endothermic reforming reaction, which in return results in limited availability of carbon source as catalyst.

US-2001237689-A entitled "Method for methanol

synthesis using synthesis gas generated by combined reforming of natural gas with carbon dioxide". In this method synthesis gas is obtained f om steam/carbon dioxide reforming of methane, in which steam reforming of natural gas is carried out simultaneously with carbon dioxide reforming of methane, by using a catalyst

(Ni/Ce/MgA10_x or Ni/Ce-Zr/MgA10_x) and processing

condition capable of maintaining a predetermined ratio of carbon monoxide, carbon dioxide, and hydrogen . Methanol synthesis is subsequently carried out by using the synthesis gas obtained and a catalyst system suitable for methanol synthesis with minimum byproduct formation .

CN-1415531-A (application number 20011033389 entitled "Method for producing synthesis gas by catalyzing and transforming natural gas and methane" reveals a

conversion method, in which natural gas or methane is mixed with water vapour and/or CO₂ and the resulting mixture, together with an oxygen-containing gas, is subsequently passed over a catalyst bed in a fixed bed reactor where the gases react to generate syngas. More than 60% of the oxygen-containing gas progressively enters the catalytic reaction bed to ensure the gradual mixing and reaction between natural gas/CH₄ and oxygen- containing gas. The heat produced in the exothermic oxidation reaction can be controlled by the sectional oxygen supply. However, in reality the catalysts are sintered and hence largely deactivated because of the large amount of heat released when O₂ enters the

catalytic bed layer and reacts with H₂ produced in the reforming reaction.

The process disclosed in CN-1660733-A (application number 200410006002), entitled "Method for the

preparation of methanol from synthesis gas through hydrocarbons and steam conversion" also uses the

principle of providing oxygen in batches to the catalyst beds. CN-1660733-A discloses a process, in which the raw gaseous hydrocarbons and water vapour are introduced into a first furnace where the conversion occurs, then CO₂ and O₂ are added into the output conversion gas and the resulting reaction mixture is sent to the second furnace, where the further reaction of gaseous hydrocarbons with water vapour occurs with the adjustment of H/C ratio at the gas outlet of the second furnace. The process

involves the staged reforming in a two-stage furnace as well as the H₂O-CH₄ reforming, which results in

unattractively high investment and operation costs.

Summary of the invention

The technical problem to be solved by this invention is to provide a process for the preparation of synthesis gas by carbon dioxide-methane auto-thermal reforming, which can be applied on an industrial scale and has advantages, such as low energy consumption, high

efficiency, and no requirement of external heating.

To solve this technical problem the present invention provides a process for the preparation of synthesis gas in which methane is first reacted with oxygen and the reaction heat generated in this exothermic reaction is subsequently used to enable the endothermic reforming reaction between methane and carbon dioxide to form synthesis gas.

Detailed description of the invention

Accordingly, the present invention provides a process for the preparation of synthesis gas by auto-thermal reforming of carbon dioxide and methane comprising the steps of

(a) introducing a methane-comprising feed gas, carbon

dioxide and an oxygen-containing gas into a carbon dioxide-methane auto-thermal reforming reactor comprising a bed of reforming catalyst;

(b) mixing the methane-comprising feed gas, carbon

dioxide and oxygen-containing gas;

(c) reacting methane with oxygen in an oxidation

reaction;

(d) reacting methane with carbon dioxide in a reforming reaction in the presence of the reforming catalyst using the heat released in the oxidation reaction in step (c) ; and

(e) recovering the synthesis gas produced in steps (c) and (d) .

In this process the methane-comprising feed gas, carbon dioxide and oxygen-containing gas are fed into the carbon dioxide-methane auto-thermal reforming reactor and are subsequently well mixed in step (b) , so that the methane and oxygen for the oxidation step can react effectively in oxidation step (c) to form a first part of the raw synthesis gas. The heat released by this

exothermic oxidation reaction is subsequently used as heat source to provide the necessary heat for the

endothermic reforming reaction between carbon dioxide and methane in step (d) , thereby forming the remaining part of the raw synthesis gas.

The methane-comprising feed gas is suitably selected from the group consisting of natural gas, coke oven gas, oil gas, refinery gas, coal bed methane, methanol synthesis purge gas, Fischer-Tropsch synthesis vent gas and mixtures of two or more of these. This feed gas is desulphurized before being introduced into the carbon dioxide-methane auto-thermal reforming reactor. If a methane-comprising gas is used which also comprises a substantial amount of carbon dioxide, then a separate carbon dioxide feed gas stream may not be required.

Examples of such methane/carbon dioxide comprising gases are methanol synthesis purge gas and Fischer-Tropsch synthesis vent gas.

The oxygen-comprising gas suitably is pure oxygen or oxygen having a purity of more than 99%.

The carbon dioxide-methane auto-thermal reforming reactor can be any reactor suitable for auto-thermal reactions. Generally such reactor will comprise inlet means for the various feed gases at the top part, an upper section comprising mixing means to effectively mix the feed gases and a combustion zone for subsequently carrying out the oxidation reaction, a lower section comprising the reforming catalyst bed where the carbon dioxide-methane reforming reaction takes place and a gas collection space for the raw syngas formed in the lower part of the reactor which gas collection space is fluidly connected with gas outlet means to remove the raw

synthesis gas from the reactor.

The feed gases methane and carbon dioxide may also be mixed before entering the reactor, in which case the reactor does not need to contain separate mixing means. The reactor may also contain a burner to initiate the reaction between methane and oxygen. In such a

configuration oxygen may also be premixed with methane and carbon dioxide as long as the temperature of the resulting gas mixture is below the auto-ignition point of methane (645 °C) . When the gas mixture is then introduced into the burner flame, the oxidation of methane occurs.

Alternatively, the methane, optionally mixed with carbon dioxide, may be preheated to a temperature

sufficient to initiate the oxidation reaction before being introduced into the reactor. Upon contact with oxygen in the combustion zone the oxidation reaction starts and the temperature will rise to above the auto- ignition point of methane, which will further accelerate the oxidation. In that case no burner is required and the hot methane will instantaneously react with oxygen when contacted with oxygen. In this configuration the oxygen will not be premixed with the methane and carbon dioxide, but will be separately introduced into the combustion zone where the oxidation reaction of methane takes place.

In a preferred embodiment the methane-comprising feed gas and the carbon dioxide are preheated before they are introduced into the auto-thermal reactor. It was found particularly suitable to introduce the methane-comprising gas and carbon dioxide into the auto-thermal reforming reactor at a temperature in the range of from 400 to 700 °C, preferably from 500 to 600 °C.

The temperature of the reaction mixture during the oxidation reaction will increase. Overall temperature of the gas mixture in the combustion zone will, however, generally be between 1000 and 1500 °C, more typically between 1100 and 1400 °C. This heat is subsequently used to promote the endothermic reforming reaction between methane and carbon dioxide. Accordingly, the temperature of the gas mixture will decrease when the reforming reaction takes place.

The reforming catalyst used can be any catalyst known to catalyze the reforming reaction between methane and carbon dioxide. Examples include nickel-based refractory oxide catalysts and noble metal-based refractory oxide catalysts. Suitable refractory oxide support materials include alumina (AI₂O₃) , silica (S1O₂), titania (T1O₂) , zirconia (ZrC>₂), cerium oxide (CeC>₂) and chromium oxide (Cr₂C>3) , optionally in combination with a promoter such as calcium oxide (CaO) and/or magnesium oxide (MgO) resulting in a refractory oxide composite catalyst.

Specific examples include Ni-based composite catalysts such as Ni-Al₂0₃, Ni-CaO-Zr0₂, Ni-CaO-Ce0₂, Ni-CaO-Al₂0₃, Ni-CaO-Al₂0₃-Zr0₂, Ni-MgO-Al₂0₃ , Ni-MgO-CaO-Al₂0₃ , Ni-MgO- Cr₂0₃-Al₂0₃, Ni-CaO-Ti0₂-Al₂0₃ , Ni-MgO-Ti0₂-Si0₂. Examples of noble metal-based catalysts are Ru, Rh, Pd and/or Pt supported on one of the refractory oxide supports mentioned above. A specific example is a Pt-Al₂0₃

catalyst. It was, however, found that a catalyst

comprising nickel, calcium and zirconium (i.e. nickel

(Ni) on a calcium-promoted zirconate (CaO-ZrC>2) support, also referred to as Ni-CaO-ZrC>2 composite catalyst) was particularly suitable for the process of the present invention .

Nickel content of the reforming catalyst will

typically be up to 25 wt%, suitable between 5 and 20 wt%, more suitably between 10 and 20 wt%.

Because of the high temperature of the methane oxidation reaction mixture, the reforming catalyst is suitably shielded by a gas permeable, heat absorbing material, such as alumina ball and/or a heat-resistant catalyst layer. Such heat-resistant catalyst layer suitably comprises a relatively small amount of

catalytically active metal (typically up to 10 wt%, suitably between 1 and 8 wt%) supported on a heat

resistant refractory oxide material, such as alumina. Such catalyst promotes some degree of reforming reaction to occur, so that the temperature of the reaction mixture is further decreased when it reaches the actual reforming catalyst. A suitable heat-resistant catalyst would be Ni- A1₂0₃ or Ni-CaO-Al₂0₃.

The synthesis gas to be formed has a target hydrogen- to-carbon monoxide (H₂/CO) molar ratio depending on the envisaged end use of the synthesis gas. Therefore, water vapour is suitably introduced into the carbon dioxide- methane auto-thermal reforming reactor in step (a) in an amount corresponding with the target H₂/CO molar ratio of the synthesis gas. Such water vapour (steam) would suitably be added simultaneously with the other feed gases and be mixed with these gases in the top section of the auto-thermal reforming reactor.

The methane (CH₄) , carbon dioxide (C0₂) , oxygen (0₂) and optionally water vapour (H₂0) feed gases to the auto- thermal reforming reactor in step (a) are added in such amounts that the molar ratios of these gases in the mixed gas in the auto-thermal reforming reactor are suitably as follows: CH 4 / CO2 molar ratio is in the range of from 0.5 to 3, O2 / CH 4 molar ratio is in the range of from 0.1 to 0.4 and H₂0/CH₄ molar ratio is in the range of from 0 to 3.5. Most preferably, these molar ratios are as follows:

CH₄/ CO2 molar ratio is 1.2, O2 / CH 4 molar ratio is 0.2 and H₂0/CH₄ molar ratio is in the range of from 0 to 1.5.

Suitable operating conditions for the CO2 -CH 4

reforming reaction are an operating pressure of from 0.1 to 5 MPa, preferably from 1 to 3 MPa, and an operating temperature in the reforming catalyst reaction bed of from 700 to 1250 °C, preferably from 900 to 1100 °C . The gas hourly space velocity of the gas feeds is suitably in the range of from 1000 to 50,000 m³ feed gas (S.T.P.)/ m³ catalyst /hour (m³/ ( m³.h)), preferably from 5000 to

20,000 m³/ ( m³.h) wherein S.T.P. means Standard

Temperature of 15 °C and Pressure of 1 atm abs . The gas hourly space velocity refers to the total feed gas volume (i.e. all different gases taken together) processed per unit volume of catalyst per hour.

The hydrogen to carbon monoxide (H₂/CO) molar ratio in the synthesis gas produced is suitably in the range of from 0.5 to 3 and suitably contains from 0.1 to 2 %vol CH 4 .

Compared with the currently known carbon dioxide- methane reforming processes, the process according to the present invention has a number of advantages and beneficial effects.

Firstly, the process according to the present invention is self-supplying in terms of heat required in the endothermic, high temperature reforming reaction between CO2 and CH₄ by utilizing the heat generated from the exothermic oxidation reaction between O2 and CH₄. This requires less heating of the reforming reactor at high temperature above 700 °C and also decreases the energy consumption and operation cost of the system.

Secondly, if the preferred Ni-CaO-Zr02 reforming catalyst is used, it can be used at high gas hourly space velocities without adding water vapour. This decreases the reactor volume required and amount of catalyst needed, which in return is advantageous in that it decreases the investment and operation cost.

Thirdly, the high temperature of the synthesis gas prepared can be used to preheat different feed gases and can be used to provide heat to a waste heat boiler. This decreases the energy consumption of the whole system.

Finally, the process according to the present invention uses CO₂ as a carbon source, thereby chemically utilizing the carbon in CO₂, which not only decreases the emission of the greenhouse gas CO₂, but also produces valuable resources.

Description of Figure

Figure 1 is the schematic process diagram of one embodiment of the present invention as applied in Example 1 of the invention.

Process in detail

Figure 1 and the Examples below illustrate the present invention in more detail.

In Figure 1 the methane-comprising feed gas (1) is desulphurized in desulphurization reactor (2). The desulphurized methane-comprising feed (3) is subsequently preheated against hot raw syngas (12) in heat exchanger (4). The preheated methane-comprising feed (5), water vapour (6), oxygen-containing feed gas (7) and carbon dioxide feed (8) are fed into carbon dioxide-methane auto-thermal reforming reactor (10), where mixing and oxidation of methane takes place in mixing/combustion zone (11) in the upper part of the reactor. The resulting gas mixture is passed over reforming catalyst bed (12) and hot raw syngas (13) leaves the reactor at the bottom end and is passed through heat exchanger (4) to transfer heat to the desulphurized methane-comprising feed (3) . The cooled raw syngas (14) is then passed through waste heat boiler (15), where steam (17) is generated. Cooled syngas (16) leaves the waste heat boiler (15) and is passed through separation tank (18) to remove any remaining water (20) , resulting in dry syngas (19) .

Example 1

The process as shown in Figure 1 was carried out with the following four gas streams flowing into the CO₂-CH₄ auto-thermal reforming reactor:

(a) desulphurized methane-comprising feed gas (5) at a temperature of 600 °C, flow rate of 100 kmol/hr, pressure of 2.3 MPa and molar composition of 25% CH₄,

58% H₂, 6% CO, 6% C0₂ and 5% N₂.

(b) Water vapour (6) at pressure of 2.5 MPa to protect the nozzles and key equipment of the mixer in mixing zone (11).

(c) Pure oxygen stream (7), obtained by air separation and purification. Flow rate is 19 kmol/hr,

temperature is 400 °C and pressure is 2.5 MPa.

(d) C0₂-stream (8) at a temperature of 500 °C, flow rate of 50 kmol/hr and pressure of 2.25 MPa.

The desulphurized, cooled CH₄-rich feed (5) was obtained by compressing the CH₄-rich (or CH₄/CC>₂-rich) feed gas (to a pressure of 5.0 MPa, then feeding the compressed gas (1) into the desulfurization reactor (2), where desulphurization to a sulphur content of less than 5 ppm occurred. The desulphurized CH₄-rich feed gas (3) had a temperature of 380 °C . This feed gas (3) was then passed into heat exchanger (4), where its temperature was increased to 600 °C . The heat exchanger used the hot raw syngas (13) from the CO2-CH₄ auto-thermal reforming reactor (10) as heat source.

Desulfurized and heated CH₄-rich feed gas (5), O2 stream (7) CO2 stream (8) and water vapour (6) were subsequently passed into the CO2-CH₄ auto-thermal reforming reactor (10), where the combustion exothermic reaction of CH₄ and O2 occurred in mixing/combustion zone (11), as well as endothermic reforming reaction of CO2 -

CH₄ in catalyst bed (12), so that hot raw syngas (13) was obtained .

The reaction conditions of the CO2-CH₄ reforming reaction were: Ni-CaO-ZrC>2 catalyst having a Ni-content of 15 wt%, gas hourly space velocity of 50, 000 m³/ ( m³.h), pressure of 2.1 MPa, and catalytic reaction bed temperature of 950 °C.

The hot raw syngas (13) obtained had the following parameters: flow rate of 199 kmol/hr, temperature of 950 °C, pressure of 2.1 MPa, and molar composition of 31.4%

H₂, 29.1% CO, 14.1% C0₂, 0.4% CH₄, and 22.5% H₂0.

The hot raw syngas (13) obtained from the CO2-CH₄ auto-thermal reforming reactor (10) entered heat exchanger (4), increased the temperature of the desulfurized feed gas (3) from 380 °C to 600 °C, and decreased its own temperature to 837 °C . Then the cooled syngas (14) continuously was passed into waste heat boiler (15) to recover the maximal amount of heat. At the last stage, syngas is separated and purified in the separation tank (18), in order to obtain the high quality syngas for downstream utilization. Example 2

Example 1 was repeated except that no water vapour stream was used. The remaining three gas streams were introduced into the CO₂-CH₄ auto-thermal reforming reactor at the following conditions:

(a) desulphurized natural gas (5) at a temperature of

450 °C, flow rate of 110 kmol/hr and pressure of 3.2 MPa.

(b) Oxygen stream (7) of 99% purity. Flow rate is 70

kmol/hr, temperature is 420 °C and pressure is 3.3 MPa.

(c) CC>₂-stream (8) at a temperature of 400 °C, flow rate of 100 kmol/hr and pressure of 3.2 MPa.

The above gases were mixed and reacted in the CO₂- CH₄ auto-thermal reforming reactor at 3.0 MPa pressure, and 991 °C equilibrium temperature. The combustion reaction between CH₄ and O₂ subsequently occurred as well as the CO₂-CH₄ reforming reaction and syngas is formed. Gas hourly space velocity was 1000 m³/ ( m³.h) . The hot raw syngas (13) obtained had the following parameters: flow rate of 424 kmol/hr, temperature of 991 °C, pressure of 3.0 MPa and molar composition of 32.0% H₂, 36.0% CO, 12.7% C0₂, 0.8% CH₄, 18.3% H₂0, and 2% N₂.

Example 3

Example 1 was repeated except that no water vapour stream was used and the methane-comprising feed gas and carbon dioxide feed gas were combined. Accordingly, the following feed gases were used: (a) A Fischer-Tropsch synthesis vent gas having a flow rate of 121 kmol/hr, a temperature of 503 °C, a pressure of 2.2 MPa and a molar composition of 34.27% H₂, 7.19% CO, 20.6% C0₂, 31.2% CH₄, and 6.74% N₂.

(b) Pure oxygen having a flow rate of 15 kmol/hr, a

temperature of 420 °C and a pressure of 2.2 MPa.

Both gas feed streams were introduced into the C0₂- CH₄ auto-thermal reforming reactor (10) and mixed in mixing/reaction zone (11) at 22.0 MPa pressure and 850 °C equilibrium temperature. The combustion reaction between CH₄ and 0₂ subsequently occurred as well as the C0₂-CH₄ reforming reaction and syngas is formed. Gas hourly space velocity was 20, 000 m³/ ( m³.h).

The hot raw syngas (13) obtained had the following parameters: flow rate of 163 kmol/hr, temperature of 850 °C and molar composition of 38.6% H₂, 25.8% CO, 7.8% C0₂, 10.0% CH₄, 12.8% H₂0, and 5.0% N₂.

Claims

C L A I M S

1. Process for the preparation of synthesis gas by auto- thermal reforming of carbon dioxide and methane

comprising the steps of

(a) introducing a methane-comprising feed gas, carbon

(b) mixing the methane-comprising feed gas, carbon

dioxide and oxygen-containing gas;

(c) reacting methane with oxygen in an oxidation

reaction;

(e) recovering the synthesis gas produced in steps (c) and (d) .

2. Process according to claim 1, wherein the methane- comprising feed gas is selected from the group consisting of natural gas, coke oven gas, oil gas, refinery gas, coal bed methane, methanol synthesis purge gas, Fischer- Tropsch synthesis vent gas and mixtures of two or more of these and is desulphurized before being introduced into the auto-thermal reforming reactor.

3. Process according to claim 1 or 2, wherein the oxygen-containing gas is pure oxygen or oxygen having a purity of more than 99%.

4. Process according to any one of claims 1-3, wherein water vapour is introduced into the auto-thermal

reforming reactor in step (a) in an amount corresponding with the target hydrogen-to-carbon monoxide molar ratio of the synthesis gas.

5. Process according to claim 4, wherein the feed gases introduced into the auto-thermal reactor in step (a) are added in such amounts that the molar ratios of the gases in the auto-thermal reforming reactor are as follows: CH₄/ CO2 molar ratio is in the range of from 0.5 to 3, O2/CH₄ molar ratio is in the range of from 0.1 to 0.4 and H₂0/CH₄ molar ratio is in the range of from 0 to 3.5.

6. Process according to claim 5, wherein the molar ratios of the reactant gases are: CH₄/ CO2 molar ratio is 1.2, O2/CH₄ molar ratio is 0.2 and H₂0/CH₄ molar ratio is in the range of from 0 to 1.5.

7. Process according to any one of claims 1-6, wherein the methane-comprising gas and carbon dioxide are

introduced into the auto-thermal reforming reactor at a temperature in the range of from 400 to 700 °C.

8. Process according to claim 7, wherein the methane- comprising gas and carbon dioxide are introduced into the auto-thermal reforming reactor at a temperature in the range of from 500 to 600 °C.

9. Process according to any one of claims 1-8, wherein the reforming catalyst is a Ni-CaO-ZrC>2 composite

catalyst .

10. Process according to any one of claims 1-9, wherein the operating pressure in the auto-thermal reforming reactor is in the range of from 0.1 to 5 MPa and the operating temperature during the CO2-CH₄ reforming reaction in the range of from 700 to 1250 °C.

11. Process according to claim 10, wherein the operating pressure in the auto-thermal reforming reactor is in the range of from 1 to 3 MPa, the operating temperature during the CO2-CH₄ reforming reaction in the range of from 900 to 1100 °C and the gas hourly space velocity of the gas feeds is suitably in the range of from 1000 to 50, 000 m³/ ( m³.h) .