AU2005240368B2

AU2005240368B2 - System and process for synthesis of methanol

Info

Publication number: AU2005240368B2
Application number: AU2005240368A
Authority: AU
Inventors: Gregor August Jenzer; Thian Hoey Tio; Pieter Lammert Zuideveld
Original assignee: SHELL INT RESEARCH; Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2004-05-07
Filing date: 2005-05-04
Publication date: 2009-04-02
Anticipated expiration: 2025-05-04
Also published as: WO2005108336A1; RU2006143195A; AU2005240368A1; JP2007536347A; CN1950316A; RU2386611C2; EP1742901A1

Description

WO 2005/108336 PCT/EP2005/052043 1 SYSTEM AND PROCESS FOR SYNTHESIS OF METHANOL Field of the invention The present invention relates to a system and process for synthesising methanol out of a source gas containing light hydrocarbons.

Background of the invention For the purpose of this specification, "light hydrocarbons" is a term used to embrace hydrocarbon molecules containing one, two, or three carbon atoms.

Examples of light hydrocarbons are methane, ethane, and propane.

More in particular, the invention relates to a system and process for synthesising methanol out of natural gas.

Syngas, which is a mixture containing CO, COz, and

H

2 can be reacted into methanol via a known catalytic process.

There are several processes to produce syngas from light hydrocarbons for methanol synthesis. In WO 98/28248 steam reforming of methane is disclosed. The syngas produced by steam reforming contains more H 2 relative to CO and C02 than required for the catalytic methanol reaction. The synthesis gas mixture is separated into a hydrogen-rich stream and a hydrogen-depleted stream containing carbon oxides and methane. The H 2 in the hydrogen-rich stream is burned to provide energy to the steam reforming reaction, and the hydrogen-depleted stream is recycled into the steam reforming zone.

Another known process to form syngas for methanol production is autothermal reforming. The syngas from this process contains more CO and C02 compared to H 2 than required for the catalytic methanol reaction.

WO 2005/108336 PCT/EP2005/052043 2 The known processes produce syngas at pressures of around 25 to 40 bar. The subsequent methanol reaction, however, requires a higher pressure in order to reach a reasonable efficiency.

US-A-5496859 describes a a process to prepare methanol from syngas. The syngas is prepared by a combination of a non-catalyzed partial oxidation of natural gas and a gas heated steam reforming of natural gas. By using this combination the required molar ratio between hydrogen and carbon monoxide as specified in the description is achieved to carry out the methanol synthesis reaction.

EP-A-111376 describes a process to prepare methanol from syngas. The syngas mixture is prepared by a noncatalyzed partial oxidation of methane, ethane or propane or a mixture thereof. From the effluent of the methanol synthesis step methanol is isolated. From the remaining mixture carbon dioxide is partly removed by washing at the methanol synthesis pressure. The gas mixture depleted of carbon dioxide is recycled to the methanol synthesis step. In this manner the required molar ratio between hydrogen and carbon monoxide as specified in the description is achieved to carry out the methanol synthesis reaction. According to the description the process is advantageous because no steam reformer is required.

An advantage of the process of EP-A-111376 is that no steam reformer is required as in the process of US-A- 5496859. Combining a gasification reactor and a steam reformer reactor as in US-A-5496859 is not simple. A disadvantage of the process of EP-A-111376 is that a relatively complex separation process is applied downstream the methanol synthesis. That process is complicated by the use of a washer with recycle.

WO 2005/108336 PCT/EP2005/052043 3 The object of the present invention is to provide a simple process to prepare methanol wherein the disadvantages of the process of EP-A-111376 are overcome.

Summary of the invention The present invention provides a system for synthesising methanol out of a source gas containing light hydrocarbons, the system comprising a hydrocarbon gas supply for providing the source gas; an oxygen supply for providing an oxygen containing fluid; a syngas reactor, arranged to receive the source gas from the hydrocarbon gas supply and the oxygen containing fluid from the oxygen supply, the syngas reactor being arranged to produce an intermediate reaction product from the source gas and the oxygen containing fluid, and to discharge the intermediate reaction product, the intermediate reaction product comprising syngas; a methanol reactor, arranged to receive at least a fraction of the intermediate reaction product from the syngas reactor, and arranged to let the intermediate reaction product react into at least methanol via a methanol forming reaction, the methanol reactor being provided with a methanol outlet for discharging the formed methanol and an offgas outlet for discharging an offgas; whereby the syngas reactor comprises a gasification reactor, and wherein a gas flow path extends between the hydrocarbon gas supply and the methanol outlet, which gas flow path, in flow direction, passes through at least the hydrocarbon gas supply, the syngas reactor, the methanol reactor and the methanol outlet, and wherein the system further comprises 0- an H 2 supply system for injecting an H 2 containing gas into the gas flow path through an H 2 inlet located upstream the methanol reactor and downstream the Ssyngas reactor; S- a pressure swing absorber as H 2 separator arranged to receive at least a fraction of the offgas discharged through the offgas outlet and to separate H 2 from 0 the received offgas and to discharge separated H 2 into the H 2 supply system.

IN In another aspect, the present invention provides a process of synthesizing methanol Sout of a source gas containing light hydrocarbons, the process comprising steps of: extracting the source gas from a hydrocarbon gas supply; reacting the light hydrocarbons from the source gas with oxygen, in the C absence of added steam, to produce a syngas-containing intermediate reaction product having a pressure higher than 60 bar via a non-catalytic partial oxidation; reacting at least a fraction of the intermediate reaction product into methanol via a methanol forming reaction as performed in a single pass reactor whereby also an H 2 -containing offgas is produced; discharging the methanol and offgas through a methanol outlet and an offgas outlet downstream the methanol forming reaction; separating H 2 from at least part of the offgas by means of a pressure swing absorber process to obtain hydrogen having a purity of greater than 90 mol% and a pressure of above 60 bar; injecting separated H 2 into the syngas-containing intermediate reaction product and before performing the methanol forming reaction to obtain a syngas composition having a SN of whereby expressed in the molar contents [H 2 and [CO 2 SN is equal to ([H 2

[CO

2

[CO

2 wherein the process does not comprise a syngas compressor and wherein the process does not comprise a shift and wherein the process does not involve a steam reforming step.

Gasification is a non-catalytic partial oxidation process that advantageously requires essentially no steam, although steam may be added to amounts of typically less than of the source gas. A AH21(1982340 1):RTK

I

gasification reactor, or gasifier, is a reactor wherein gasification is performed.

An advantage of gasification to produce the syngas as Sthe intermediate reaction product for methanol synthesis 5 is that it can discharge the intermediate reaction product at a pressure of higher than 60 bar, preferably 00 around 80 bar. Consequently, only a light compressor or CC even no compressor is required between the syngas reactor and methanol reactor to bring the syngas to the desired C1 1o pressure for the methanol reactor. Also, gasification produces relatively low amounts of inert components such C-i as methane, nitrogen, and argon, which enhances the methanol reaction efficiency. Moreover, the ratio CO/C02 from the gasifier is very favourable in CO, because only very limited amounts of CO 2 form in the water gas shift equilibrium since no or only little steam is added to the process. A high CO/C02 ratio is advantageous, because the formation of methanol from CO is more efficient than that from CO 2 Brief description of the Figures The invention will be described hereinafter in more detail and by way of example, with reference to the accompanying drawings in which: Fig. 1 schematically shows the system according to an embodiment of the invention; Fig. 2 schematically shows the system according to another embodiment of the invention; Fig. 3 schematically shows a flow diagram of the system and process of the invention.

73 Detailed description of the invention In order to further improve the system, the system can optionally further comprise an H 2 supply system for injecting an H 2 containing gas into a gas flow path through an H 2 inlet located .3 upstream the methanol outlet; AH21(1982340 I K'I'K WO 2005/108336 PCT/EP2005/052043 6 an H2 separator arranged to receive at least a fraction of the offgas discharged through the offgas outlet and to separate H 2 from the received offgas and to discharge separated H 2 into the H2 supply system; whereby said gas flow path extends between the hydrocarbon gas supply and the methanol outlet and, in flow direction, passes through at least the hydrocarbon gas supply, the syngas reactor, the methanol reactor and the methanol outlet.

Herewith the composition of the syngas is optimised to meet the ideal stoichiometric ratio for the methanol forming reaction. It is an advantage that the H2 separated from the offgas can be discharged at approximately the same pressure as desired for the methanol reaction in the methanol reactor.

The H 2 inlet is best located downstream the syngas reactor, so that it does not interfere with the reaction in the syngas reactor. Nor does it have to be heated to the reaction temperature. It has been found feasible by reinjecting H2 from the offgas into the syngas to bring the stoichiometric number to between 2.0 and 2.1.

In an embodiment of the invention, the methanol reactor is a single pass reactor. This means that no internal recycle in the methanol synthesis process is employed. An advantage hereof is that accumulation of inert components in the methanol reactor can be minimised.

Detailed description of the Figures In the Figures like reference numerals relate to like components.

Referring to Figs. 1 and 2 there is schematically shown a system for the synthesis of methanol. An oxygen supply is provided in the form of an air separation unit 1. A syngas reactor is provided in the form of gasifier 2, which is arranged to receive the oxygen WO 2005/108336 PCT/EP2005/052043 7 containing output stream of the air separation unit 1.

The 02 content of the output stream can typically be higher than 99 The gasifier 2 also receives a source gas containing light hydrocarbons. The source gas can be provided in the form of a stream 3 of natural gas.

The gasifier can be a refractory lined vessel. It is equipped with a co-annular burner designed to ensure proper mixing of the fuel with the oxygen. A source gas preheater (not shown) can optionally be provided to increase the gasification efficiency. For details on gasification reference is made to a book "Gasification" by Ch. Higman and M. van der Burgt, Elsevier Science, 2003 (ISBN 0-7506-7707-4)pages 128-140.

Still referring to Figs. 1 and 2, the syngas from the gasifier 2 is discharged as an intermediate reaction product via syngas cooler 17 through line 4 and fed, via an optional gas cleaning unit 6, to a methanol reactor for producing methanol. The optional gas cleaning unit 6 can comprise, amongst others, a scrubber, a wet scrubber, a filter or combinations thereof. The methanol reactor can be of any known type, such as either an isothermal type or an adiabatic type. A suitable methanol reactor is available from Johnson Matthey (formerly Synetix) or Lurgi.

Note that a compressor does not have to be provided in line 4 for the syngas.

The syngas discharged from the syngas reactor comprises at least H 2 CO, and CO 2 The suitability of the syngas composition for the methanol forming reaction is expressed as the stoichiometric number SN of the syngas, whereby expressed in the molar contents [H 2 and [CO 2 SN ([H 2 [C0 2 [C0 2 It has been found that the stoichiometric number of the syngas produced by gasification of the source gas is lower than WO 2005/108336 PCT/EP2005/052043 8 2, and typically lies between 1.5 and 1.8. This is lower than an ideal stoichiometric ratio of about 2.05 for forming methanol in the methanol forming reaction. As will be discussed below, a recycle into the synthesis loop of hydrogen separated from methanol synthesis offgas can be provided to increase the SN.

The following Table I gives a comparison of syngas produced by the steam reforming method (SMR), the autothermal reforming method (ATR), and the gasification method (SGP). The numbers are obtained by equilibrium calculations and optimization of oxygen addition. The parameters of the ATR and SMR such temperature and pressure are typical, and reference is made to a conference paper "Syngas Technologies for Mega Methanol plants" presented by Wolfgang Hilsebein at the CMAI World Methanol Conference 2003 in Phoenix AZ.

a, C4 Table 1: natural gas Ethane (mo IMethane (me C02 (mol%) CO (mol%)

H

2 (mol%)

N

2 Ar (mol Steam/carbo Oxygen/carb ratio Temperature Pressure (b Stoichiomet

H

2

/CO

CO/C02

L-_

Typical syngas properties for a sample Natural SMR ATR SGP gas feed o1%) 88 .0 6.3 3.3 0.6 1.0 7.6 4.7 1.1 14.1 27.2 347. 2 70.3 j 62.6 61.8 6.0 1. 2 23 )n ratio 2.7 0.6 0 on 0 0.50 0.59 o C) 870 1020 1350 ar) 27 37 ric number 2.88 1.81 I1.72- 4.98 2.30 1.81 1.85 5.79 32.4 In the table, the steam/carbon ratio is defined as the molar ratio of steam over carbon atoms in the hydrocarbons. Several advantageous properties are apparent from the Table I, including a high CO/CO 2 ratio, SN not far below 2, pressure of greater than 60 bar, low level of inerts including methane, nitrogen and argon.

to The advantageous properties of the syngas produced by gasification of light hydrocarbons are advantageous for the production of methanol using only limited recycling.

Thus a process is provided which can prepare syngas at or near the required pressure for methanol synthesis and which process does not involve a steam reforming process step.

The methanol reactor 5 can optionally be provided with an internal recycle loop 7 (as depicted in Fig. 1) AH21(19S2340 1:RTK WO 2005/108336 PCT/EP2005/052043 10 comprising a methanol recycle compressor 8 to compensate for the pressure drop across the methanol reactor However, a single pass reactor as depicted in Fig. 2 has the advantage that less inert components will accumulate in the methanol reactor. A single pass reactor or methanol process is preferably defined as a process wherein the content of recycled carbon as carbon monoxide and carbon dioxide calculated on the total of carbon as present in the feed to the methanol synthesis step or methanol reactor is smaller than 15 mol%, more preferably smaller than 2 mol%.

The down stream end of the methanol reactor is connected to a gas-liquid separator 10 via line 9. The gas-liquid separator has a methanol outlet 11 for discharging the methanol that has been formed in the methanol reactor 5, and an offgas outlet 12 for discharging an offgas that emerges from the methanol reactor The offgas outlet 11 is connected to an H 2 separator 14 arranged to receive at least a fraction of the offgas discharged through the offgas outlet and to separate H 2 from the received offgas. Line 15 carries the hydrogen-rich stream from the H 2 separator, and is connected to line 4 via an H 2 inlet. This way, a hydrogen containing gas is injected into the syngas upstream the methanol reactor.

A pressure swing absorber (PSA) forms a suitable H 2 separator. PSA type processes are well known and are for example described in the above referred to textbook "Gasification" by Ch. Higman and M. van der Burgt, Elsevier Science, 2003 (ISBN 0-7506-7707-4) pages 310- 311. An advantage of the PSA is that a pure stream of H 2 can be obtained whereas all the other gases including inert gases are removed from the cycle. This gives a high tolerance on the quality of source gas that can be WO 2005/108336 PCT/EP2005/052043 11 converted into methanol using the system and process of the invention. Moreover, the drop of hydrogen pressure across the PSA is small, so that the H 2 can be fed back into the synthesis loop with only moderate recompression for which compressor 16 is optionally provided.

The purity of the hydrogen as separated from at least part of the offgas of the methanol forming reaction is preferably greater than 90 mol%, more preferably greater than 95 mol% and even more preferably greater than 99 mol%. Separating H 2 from at least part of the offgas is preferably performed by means of a pressure swing absorber process. The pressure at which the hydrogen is obtained in the PSA is preferably above 60 bar. It has been found that the PSA is preferably operated at a higher pressure than typically applied in PSA operations.

The somewhat lower yield and purity of the hydrogen then obtained is then compensated by the fact that an additional recompression can be omitted or that a smaller recompression step can be used for the hydrogen to the methanol synthesis pressure.

A membrane-separator or a cold box separator can also be used, but that would require more recompression of the separated H 2 before injecting into the synthesis loop.

Depending on the quality of the source gas, a shift reactor may be required upstream of the H 2 separator to further increase the H 2 content.

The system is optionally provided with means for further processing the discharged methanol, such as one or more distillation columns 13 for purifying the discharged methanol.

Gasification in gasifier 2 can be performed at a pressure between 60 and 80 bar, preferably close to bar, and a temperature of around 1300-1400 The hot reactor effluent is then cooled down to about 350 °C in the syngas cooler 17. In the syngas cooler, saturated WO 2005/108336 PCT/EP2005/052043 12 steam is produced at pressures up to about 100 bar. The saturated steam is used for preheating of the oxygen and, optionally, for preheating of the source gas.

The methanol forming reaction can be performed at a pressure of between 30 and 150 bar, for example 75 bar and a temperature of between 200 and 320 for example 230 The hydrogen recovery in the PSA can be performed at for example 60 bar.

Fig. 3 shows a schematic process flow chart. A corresponding Table II is also presented, that shows calculated compositions and flow rates of through the lines that are identified in Fig. 3 by letters a to i.

The calculation is made for a low quality and low cost natural gas as the source gas, having a particularly high concentration of N 2 Comparing columns d and e, it can be seen that SN is enhanced from 1.1 to 2.01 by injection of the hydrogen recycle stream i. It can also be seen that the inerts in stream g are effectively removed from the synthesis loop via stream h since the methanol synthesis process is here taken as a once-through process.

In conclusion, surprisingly, a very attractive methanol production process is obtained by employing partial oxidation by gasification, for the conditions as described above. Neither a syngas compressor nor a shift are required, because the methanol synthesis can be a once through process, and because in the preferred embodiment this system a SN of 2 can be reached just by combining the fresh syngas with recycled hydrogen. It is surprising that this relatively simple system, which is to the knowledge of the inventors unique in gasification, gives exactly the conditions that are needed for methanol synthesis out of a source gas containing light hydrocarbons.

WO 2005/108336 PCT/EP2005/052043 13 The gasification can run at high temperature and pressure and without addition of steam. Addition of a little steam can be beneficial for prevention of possible coking during the heat up phase and soot production, but it also has an adverse effect on the CO/CO 2 ratio in the syngas and on the oxygen consumption of the process since more fuel must be burned to bring the steam up to the gasification temperature.

Claims

1. Process of synthesizing methanol out of a source gas containing light Shydrocarbons, the process comprising steps of: extracting the source gas from a hydrocarbon gas supply; s reacting the light hydrocarbons from the source gas with oxygen, in the 00absence of added steam, to produce a syngas-containing intermediate reaction IDproduct having a pressure higher than 60 bar via a non-catalytic partial oxidation; O reacting at least a fraction of the intermediate reaction product into methanol Svia a methanol forming reaction as performed in a single pass reactor whereby also an H 2 -containing offgas is produced; discharging the methanol and offgas through a methanol outlet and an offgas outlet downstream the methanol forming reaction; separating H 2 from at least part of the offgas by means of a pressure swing absorber process to obtain hydrogen having a purity of greater than 90 mol% and a pressure of above 60 bar; injecting separated H 2 into the syngas-containing intermediate reaction product and before performing the methanol forming reaction to obtain a syngas composition having a SN of whereby expressed in the molar contents [H 2 and [C0 2 SN is equal to ([H 2 [C0 2 [C0 2 wherein the process does not comprise a syngas compressor and wherein the process does not comprise a shift and wherein the process does not involve a steam reforming step.

2. Process according to claim 1, wherein the SN number is between 2.0 and 2.1 after injecting separated H 2

3. Process according to claim 1 or 2, wherein the content of recycled carbon as carbon monoxide and carbon dioxide calculated on the total of carbon as present in the feed to the reactor is smaller than 15 mol%.

4. Process according to claim 3, wherein the content of recycled carbon as carbon monoxide and carbon dioxide calculated on the total of carbon as present in the feed to the reactor is smaller than 2 mol%.

5. Process according to any one of claims 1 to 4, wherein the source gas is natural gas.

6. Process according to any one of claims 1 to 5, wherein the separated hydrogen has a purity of greater than 95 mol%.

7. Process according to claim 6, wherein the separated hydrogen has a purity of greater than 99 mol%. AH21(1982340 I):RTK

08. Process according to any one of claims 1 to 7, wherein the methanol forming reaction is performed at a pressure of between 30 and 150 bar.

9. Process according to claim 8, wherein the methanol forming reaction is Sperformed at a pressure of 75 bar.

10. Process according to any one of claims 1 to 9, wherein the methanol forming 00 reaction is performed at a temperature of between 200 and 320 0 C.

11. Process according to any one of claims 1 to 10, wherein the methanol forming Sreaction is performed at a temperature of 230 0 C. N,

12. Process of synthesizing methanol out of a source gas containing light hydrocarbons as defined in claim 1 and substantially as herein described with reference to N Fig. 3.

13. Methanol prepared according to the process of any one of claims 1 to 12. Dated 24 February, 2009 Shell Internationale Research Maatschappij B.V. Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON AH21(1982340 1):RTK