NO153131B - PROCEDURE FOR PREPARING PURIFIED SYNTHESIC GAS AND CARBON MONOXIDE - Google Patents

Description

The present invention relates to a partial oxidation process in which synthesis gas is simultaneously produced with a regulated molar ratio H2/CO and either a CO-rich gas or essentially pure CO. Methanol can be produced from the synthesis gas and can then be reacted with the CO-rich gas or with essentially pure CO to produce acetic acid.

Synthesis gas can be produced by partial oxidation of fossil fuel with a gas containing free oxygen, possibly in the presence of a temperature moderator. The waste gas flow from the gas generator is cooled (to below the temperature at which the gas composition approaches equilibrium), e.g. by direct introduction into water in a quench drum as described in US-PS 2,896. 927. In this method for gas cooling, the sensible heat in the waste gas stream is used to produce steam in the product gas.

Alternatively, the waste gas stream from the gas generator can be cooled in a synthesis gas cooler as shown in US-PS 3,920,717. In this method of gas cooling, the waste gas flow becomes

not saturated with water. In US-PS 3,929,429, in order to produce an oil-carbon dispersion and a separate water-carbon dispersion, which are simultaneously fed to a gas generator for the production of fuel gas, a portion of the waste gas stream is cooled in a synthesis gas cooler and then washed with oil; and another stream is quenched in water. Non-catalytic thermal shift is used to adjust the H2/CO molar ratio in a single stream of synthesis gas in US-PS 3,920,717.

The present invention aims to improve the known technique and relates to a method for producing a product stream of purified synthesis gas suitable for conversion to methanol, and a CO-rich product stream, and this method is characterized by the fact that it comprises: 1) conversion of a hydrocarbon-containing or oxygenated hydrocarbon-containing organic material with a free oxygen-containing gas in the reaction zone of a free-flowing non-catalytic partial oxidation gas generator at a temperature within the range of 700-1650°C and at a pressure within the range of 1-250 atm., to produce a waste gas comprising H,,, CO, H,,0, solid particles of carbon and ash and at least one gas from the group consisting of C02, H2S' C0S' CH4' NH3' N2 °^ Ar; • 2) splitting the waste gas stream from (1) into a first and second stream and simultaneously further processing these in separate first and second sequences of steps; 3) cooling the first gas stream from; (2) in the first sequence by indirect heat exchange in a separate heat exchange zone, purification to remove entrained solids and removal of water; 4) purifying at least one part of the off-gas stream from (3) in a first gas purification zone and separating at least one gas from the group CO2/ t^S, COS, CH^ and NH3 to give a purified stream of synthesis gas essentially free for gaseous sulfur compounds; 5) dividing the purified stream of synthesis gas from (4) into two streams and supplying the first of these to a CO separation zone, from which said product stream of CO-rich gas and a separate stream of H2-rich gas are removed; 6) cooling and purifying the second gas stream from (2) by direct contact with water to thereby remove entrained solid particles and to increase the H20/CO molar ratio of the gas stream to a value within the range of 2-5; 7) reacting CO and H 2 O in the gas stream from (6) in a water-gas shift conversion zone to provide an H 2 -rich gas stream; 8 ) removal of H20 and purification of at least a portion of the H2-rich gas stream from (7) in a second gas purification zone and separation from there of at least one gas from the group CO2, H2S, COS, CH4 and NH^ to give a purified H2 ~rich gas stream substantially free of gaseous sulfur compounds; and 9) mixing at least a portion of the second separated stream of purified synthesis gas from (5) with from 0-100% of the H2-rich gas stream from step (5) and at least a portion of the purified H2-rich gas stream from ( 8) to obtain a product stream of purified synthesis gas.

In the present process, the waste gas stream directly from a free-flowing unpackaged synthesis gas generator for non-catalytic partial oxidation and with an H2/C0 molar ratio in the range 0.5-1.9 is thus divided into two gas streams. A gas stream is then first passed through a cycle comprising the following steps: cooling in a gas cooler by indirect heat exchange with boiler feed water, washing with water to remove solid particles present, cooling to below the dew point to separate water and removal of gaseous impurities in a first gas cleaning zone to obtain a stream of clean and purified synthesis gas with an H^/CO molar ratio in the range of 0.5-1.5. A part of this stream of synthesis gas is supplied to a separation zone and separated into a stream of CO-rich product gas, preferably essentially pure CO, as well as an H^-rich gas stream. At the same time, the second part of the gas stream from the gas generator is treated in another sequence comprising the following steps: quenching and washing with water to remove solid particles, catalytic water-gas shift, cooling and condensation of water and removal of gaseous impurities in a second cleaning zone to obtain a stream of pure hydrogen-rich gas.

At least part of the remaining part of the purified stream of synthesis gas from the first sequence is mixed with from 0-100% by volume of the I^-rich gas stream from the first sequence and at least a portion of the I^-rich gas stream from the second sequence to obtain a purified synthesis gas product stream with a mole ratio of H 2 to CO between 2 and 12.

Furthermore, methanol synthesis gas with a molar ratio between

H and CO within the range 2-4 are obtained by the above-mentioned process and catalytically converted into a stream of crude methanol. Pure methanol is obtained by purifying this stream. Optionally, at least part of the pure methanol can be catalytically reacted with at least part of said product stream of essentially carbon monoxide to obtain a crude acetic acid which can then be purified to produce glacial acetic acid.

The invention will be further explained with reference to the accompanying drawings. Fig. 1A schematically shows a preferred embodiment of the method for the simultaneous production of a product stream of pure and purified synthesis gas with a mole ratio H2/CO in the range 2-12 and a separate product stream of CO-rich gas and preferably essentially pure CO. Fig. 1B, as shown to the right of the line A-A, schematically shows another embodiment of the method in which pure methanol is produced from a product stream of methanol synthesis gas produced by the above-mentioned method. Optionally, at least part of said pure methanol can be reacted with at least part of the substantially pure carbon monoxide stream to obtain acetic acid.

In the first step of the process, raw synthesis gas, i

essentially comprising hydrogen and carbon monoxide and with a molar ratio between H2 and CO in the range 0.5-1.9, produced by partial oxidation of a hydrocarbon-containing fuel with essentially pure oxygen, possibly in the presence of a temperature moderator in the reaction zone in a non -packaged, free-flowing non-catalytic partial oxidation gas generator. The weight ratio between steam and fuel in the reaction zone is in the range 0.1-5 and preferably 0.2-0.7. The atomic ratio between free oxygen and carbon in the fuel (the O/C ratio) is in the range 0.6-1.6 and preferably 0.8-1.4. The reaction time is in the range of 1-10 sec. and preferably 2-6 sec.

The raw synthesis gas exits the reaction zone at a temperature within the range 704-1650°C, e.g. 1093-1538°C, and at a pressure within the range 1-250 atmospheres, e.g. 40-150 atmospheres.

The composition of the raw synthesis gas from the gas generator is approximately as follows in mol%: H2 60-29; CO 31-57; CO 2 0-5; H 2 O 0-20; CH4 0-25; H 2 S 0-2; COS 0-0.1; NH 3 0-5; N2 0-1 and Ar 0-0.5. Particulate carbon in the range of 0-20% by weight (basic carbon content in the original raw material) may also be present, and ash in an amount of 0-60% by weight of the original hydrocarbon raw material.

The synthesis gas generator comprises a vertical cylindrical shaped steel pressure vessel lined with refractory material, as shown in US-PS 2,809,104. A typical quench drum is also shown in the said patent. A burner as shown in US-PS 2,928,460 can be used for supplying feed streams to the reaction zone.

A wide range of combustible carbonaceous organic substances can be reacted in the gas generator with a gas containing free oxygen, possibly in the presence of a temperature-moderating gas, to produce synthesis gas.

The term hydrocarbon-containing fuel, as used herein to describe various suitable raw materials, is intended to include gaseous, liquid and solid hydrocarbons, carbonaceous substances and mixtures thereof. Thus, essentially any combustible carbonaceous organic material or slurries thereof may be included within the definition of the term "hydrocarbonaceous". For example, there are (1) pumpable slurries of solid carbonaceous fuels, such as coal, particulate carbon, petroleum coke, concentrated sewage sludge, and mixtures thereof, in a vaporizable liquid carrier, such as water, liquid hydrocarbon fuels, and mixtures thereof; (2) gas-solid suspensions, such as finely divided solid carbonaceous fuels, dispersed in either a temperature-moderating gas or a gaseous hydrocarbon; and (3) gas-liquid-solid dispersions, such as atomized liquid hydrocarbon fuel or water and particulate carbon, dispersed in a temperature moderating gas. The hydrocarbon-containing fuel can have a sulfur content in the range 0-10% by weight and an ash content in the range 0-60% by weight.

The term liquid hydrocarbon, as used herein to describe suitable liquid raw materials, is intended to include various substances, such as liquefied petroleum, liquefied natural gas, petroleum distillates and residues, petrol, naphtha, kerosene, crude petroleum, asphalt, gas oil, residue oil, tar sands oil and shale oil, coal-derived oil, aromatic hydrocarbons (such as benzene, toluene and xylene fractions), coal tar, cycle gas oil from fluid catalytic cracking processes, furfural extract of coker gas oil and mixtures thereof.

Gaseous hydrocarbon fuel, as used herein to describe suitable gaseous feedstocks, includes methane, ethane, propane, butane and other unsaturated light hydrocarbon gases, pentane, natural gas, water gas, coke oven gas, refinery gas, acetylene tail gas, ethylene off gas, synthesis gas and mixtures thereof. Solid, gaseous and liquid raw materials can be mixed and used simultaneously, and these can include paraffinic, olefinic, acetylenic, naphthenic and aromatic compounds in any ratio.

Also included within the definition of the term carbonaceous fuel are oxygenated hydrocarbon-containing organic substances including carbohydrates, cellulosic materials, aldehydes, organic acids, alcohols, ketones, oxygenated fuel oil, waste liquids and by-products from chemical processes containing oxygenated hydrocarbon-containing organic substances and mixtures thereof.

The hydrocarbon-containing raw material can be present at room temperature or it can be preheated to a temperature as high as 315-650°C, but preferably below the cracking temperature. The hydrocarbon-containing raw material can be supplied to the gas generator burner in liquid phase or in vaporized mixture with the temperature moderator.

The need for a temperature moderator to regulate the temperature in the reaction zone generally depends on the carbon/hydrogen ratio in the raw material and the oxygen content in the oxidant stream. A temperature moderator need not be necessary with certain gaseous hydrocarbon fuels, however one is generally used with liquid carbon fuels and with essentially pure oxygen. Steam can be added as a preferred temperature moderator in admixture with either one or both reactant streams. Alternatively, the temperature moderator can be supplied to the reaction zone in the gas generator by means of separate pipelines in the burner.

The term free oxygen-containing gas as used herein essentially means pure oxygen, i.e. over 95 mol-% oxygen (with the rest usually consisting of N2 and noble gases). Free oxygen-containing gas can be supplied by means of the partial oxidation burner at a temperature within the range of ambient temperature to 980°C.

The raw synthesis gas from the reaction zone in the gas generator is immediately divided into two streams which are then simultaneously processed in two separate sequences. In the first sequence, no water-gas exchange takes place, while this is carried out in the second sequence.

The division of the raw synthesis gas between the two sequences can be calculated by material and heat balances. The calculated division can then be adjusted, if this should be necessary, after a period of operation. Accordingly, these calculations take into account the compositions of the carbonaceous fuel and raw syngas, the amount and desired composition of the purified syngas product stream, the desired amount of substantially pure carbon monoxide product, the desired amount and efficiency of the catalytic water-gas shift conversion, the efficiency of the C0 separation zone and the desired amount of steam as a by-product.

For example, from 20-80% by volume, preferably 30-50% by volume,

of the raw synthesis gas from the reaction zone in the gas generator is directly supplied to the quench drum containing water in the second sequence. The rest of the raw synthesis gas from the generator can be passed through an isolated transmission line and directly to a synthesis gas cooler in the first sequence, in which the hot gases are passed in

indirect heat exchange with boiling water, which entails cooling of the gas flow to a temperature within the range of 350-750°C while simultaneously producing by-product steam.

The by-product steam can be used elsewhere in the process, if necessary. Furthermore, it can be produced at a pressure greater than that in the gas generator. Parts of the by-product steam can e.g. is used as a temperature moderator in the gas generator, as a carrier for hydrocarbon-containing fuel or as a working fluid in an expansion turbine, i.e. a turbocompressor or a turboelectric generator. The steam can also be used to drive an air separation unit which provides essentially pure oxygen which is used in the gas generator.

The amount of solid particles, i.e. particles selected from particulate carbon, ash and mixtures thereof, entrained in the raw synthesis gas leaving the reaction zone depends on the type of carbonaceous fuel used and the atomic ratio O/C in the reaction zone. A smaller amount of entrained particulate carbon, i.e. 1-2% by weight (the basis weight for C in hydrocarbon-containing feedstock), is recommended to increase the life of the refractory lining in the gas generator.

The cooling drum is arranged below the reaction zone in the gas generator, and the split stream of crude synthesis gas which it receives carries with it essentially all the slag, and a significant part of the particulate carbon in the form of soot that comes from the reaction zone in the gas generator. However, in order to prevent clogging of downstream arranged catalyst layers and contamination of liquid absorbents used in a subsequent gas purification step, the process gas streams in both sequences can be further purified by contact with washing fluids in separate purification zones, one in each sequence. In this way, the amount of solid particles in the process gas streams can be reduced to less than approx. 3 ppm and preferably below 1 ppm.

Any suitable device can be used to remove entrained solid particles from the process gas streams. For example, the gas stream from the gas cooler in the first sequence may be contacted with a washing liquid, such as water or liquid hydrocarbon in one or more stages in a gas washing zone, as shown in US-PS 3,544,291. On the other hand, the process gas stream from the cooling drum in the second sequence can be successfully contacted only with water in a separate washing zone. In this way, the molar ratio H 2 /CO in the process gas stream in the second sequence can be increased to a value within the range 2-5, preferably 2.5-3.5, by evaporating water during the described steps. This ratio is appropriate for the next step in the second sequence where the water-gas shift reaction occurs and H20 and CO in the process gas stream react to obtain H2 and CO2. This shift reaction will be described in more detail later.

The solids that are dispersed in the washing liquid from the separation zones can be returned to the gas generator as at least a proportion of the fuel. Thus, if the gas stream is washed with water, the dispersion of particulate carbon and water that is formed can be concentrated or separated in a conventional manner to obtain a purified water. This water can be fed back to an orifice, nozzle or venturi washer in the gas cleaning zone. The carbon concentration can be carried out in any suitable way, e.g. by filtration, centrifugation, gravity settling or by well-known liquid hydrocarbon extraction, such as the processes described in US-PS 2,992,906.

The gas flow from the cleaning zone in the first sequence is optionally cooled to below the dew point and is then led to a separation container in which essentially all water is removed. Then, at least a part of, preferably the entire gas flow, is led to a conventional gas cleaning zone in which any H 2 O and at least a part of gaseous impurities from the group CO 2 , H 2 S, COS, NH 1 and CH 2 are removed. Optionally, part of the gas flow can be led past the gas cleaning zone. The stream of bypassed gas can then be combined downstream with the purified gas stream.

Any suitable conventional process may be used to purify the gas stream. Typical gas cleaning processes may include freezing and physical or chemical absorption with a solvent, such as methanol, N-methylpyrrolidone, triethanolamine, propylene carbonate or alternatively with. hot potassium carbonate.

Advantageously, when methanol is used as a solvent, a proportion of the product methanol can be used as refreshment in the gas cleaning zone. When washing the synthesis gas with methanol at 0°C and 10 atmospheres, 100 volumes of C02 are absorbed per volume of methanol. This concentration is increased to 270 vol/vol at -30 C. At a high partial pressure for C02, e.g. 17.5 kg/cm 2 , methanol has a very high absorption power. Similarly, cold methanol is an excellent selective solvent for the separation of H,,S and COS from CO,,. For example, the gas stream can be washed with cold methanol, and the total sulfur content, H2S + COS, can be reduced to less than 0.1 ppm. By selective absorption of H2S and COS, a very high sulfur concentration is achieved in the exhaust gas, which contributes to economical sulfur recovery.

In physical absorption processes, most of the C02 absorbed in the solvent can be released by simple heating. The rest can be removed by stripping. This can be done best with nitrogen. Nitrogen may be available as an inexpensive by-product when a conventional air separation unit is used to produce substantially pure oxygen (95 mol% O 2 or more) for use as free oxygen gas in the synthesis gas generator. Optionally, a proportion of C02 that is separated in the first gas cleaning zone can be returned to the gas generator. The regenerated solvent is then returned to the absorption column for reuse. If necessary, a final purification can be done by passing the gas stream through iron oxide, zinc oxide or activated carbon to remove residual traces of H2S or organic sulphur. In the same way, H2S- and COS-containing solvent can be regenerated by sudden heating or stripping with nitrogen or alternatively by heating and refluxing under reduced pressure without the use of inert gas. H2S and COS can then be converted to sulfur by a suitable process. For example, the Claus process can be used for the production of elemental sulfur, from H2S, as described in Kirk-Othmer, "Encyclopedia of Chemical Technology<1>," second edition, vol. 19, John Wiley, 1969, page 352. Excess S02 can be removed and disposed of by chemical binding with lime or by means of suitable commercial extraction processes.

In an alternative gas cleaning process that uses self-cooling, from 30-95% carbon dioxide can be removed from the synthesis gas stream together with essentially all H2S in the first gas cleaning zone. Here, reference should be made to US-PS 3,614,872, in which a gas

of the shifted synthesis gas is separated into an enriched hydrogen stream and an enriched carbon dioxide stream by countercurrent cooling with an outgoing stream of liquid CO, which is expanded and evaporated to give low temperature.

The partially purified synthesis gas stream leaves the first gas purification zone at a temperature in the range -6 2-121°C and at a pressure in the range 10-450 atmospheres | (preferably substantially equal to the pressure in the reaction zone of the synthesis gas generator minus normal conduction loss). The composition of this partially purified gas stream of synthesis gas is in mol-i% approximately as follows:

in

H2 70-30; CO 30-60; C02 0-15; H 2 O 0-2; CH 4 0-2; Scar 0-2; N2 0-15; H2S 0 and COS 0.

The aforementioned stream of purified and pure synthesis gas is split into two streams, depending on the amount and composition of the desired carbon monoxide-rich gas and the desired composition of the product stream of synthesis gas. The division can be determined by material balance. Thus, from 5-50% by volume of the flow of synthesis gas from the gas cleaning zone in the first sequence can be supplied to a carbon monoxide separation zone in which the following two gas streams are produced; (1) a CO-rich gas stream (preferably

in

essentially pure carbon monoxide containing 95-99 mol% CO) and (2) a stream of H2-rich gas. The mole ratio H2/CO in the rest of this clean and purified synthesis gas is then increased by mixing at least a part and preferably all of it, at least one stream of H2~-rich gas to obtain a stream of synthesis gas with a mole ratio between H2 and CO within the range 2-12 in a manner to be described later. Optionally, from 0-50% by volume of the aforementioned remaining part of the flow of synthesis gas can be removed from the system and used as a by-product.

Any suitable process may be used to separate carbon monoxide from the remainder of the intermediate product stream of purified and clean synthesis gas. Cryogenic cooling or physical absorption with a liquid solvent, e.g. copper-ammonium acetate or copper aluminum chloride solutions can be used.

A system for recovering CO from the gas stream by physical absorption in cold copper liquid in a CO absorption column will be described in more detail. By applying heat and releasing the pressure on the copper liquid in a copper liquid regeneration column, relatively pure copper monoxide is obtained. The reaction is shown in Equation I:

In the second gas cleaning zone, at least part of the waste gas flow from the first cleaning zone can thus be brought into contact with a conventionally packed column or a column of the dish type with a countercurrent flow of e.g. copper(I) acetate dissolved in a water-ammonia solution. The temperature is preferably kept within the range 0-37°C, and the pressure is preferably within the range 50-600 atmospheres. Preferably, the pressure in the CO separation zone is essentially the same as in the gas generator minus the usual pressure loss in pipelines and equipment. By keeping the pressure in the gas generator high enough, it is possible to avoid connecting a gas compressor between the acid gas absorption column in the first gas purification zone and the CO absorption column in the second gas purification zone.

A typical analysis on a weight % basis of the copper liquid solution may include the following: Cu+ 10; Cu++ 2.2; CO^~ (carbonate) 13.9; HCO~ (bicarbonate) 1.3 and NH<*> 16.5. The acid radical in the aqueous solution can be either carbonate, formate or acetate.

Regeneration of the copper liquid and release of CC^-rich gas stream takes place in a copper liquid regenerator. The pressure difference between washer and regenerator is approx. 68-204 atmospheres, e.g.

109 atmospheres. By reducing the pressure and supplying heat and a free oxygen-containing gas, e.g. air, pure oxygen or mixtures thereof, the direction of equation I can be reversed and carbonate and bicarbonate ions calculated. The usual temperature range in the regenerator is approx. 76-82°C. New added ammonia and e.g. acetic acid can be added to the copper liquor in the regenerator to maintain the correct solution chemistry. Optionally, acetic acid can be produced afterwards in an embodiment of the present process.

The CO-rich gas stream from the first sequence has the following composition in mol%: CO 60-99; N2 0-20; CO 2 2-15; H2 2-8; CH4 0-1; NH^ 0-5 and Ar 0-1. By further purification, essentially pure carbon monoxide with a CO content of 95-99 mol% can be obtained.

The H2-rich gas stream from the first sequence can contain in mol%: H2 98-60; CO 0-5; CO 2 0-5; CH4 0-5; Scars 0-4; N2 0-20 and NH^ 0 to trace amounts.

In the second sequence including the catalytic water-gas shift reaction, the soot-free gas stream is preferably supplied to a conventional catalytic water-gas shift reaction zone at an inlet temperature within the range of 176-371°C. CO and H2O are reacted over a conventional water-gas shift catalyst to produce H2 and CO2. A suitable water-gas shift catalyst can comprise iron oxide mixed with chromium oxide and further 1-15% by weight of an oxide of another metal, such as K, Th, U, Be or Sb. Reaction occurs at 260-565°C. Alternatively, cobalt molybdate or aluminum oxide can be used as a catalyst at a reaction temperature in the range 260-482°C. CO-Mo catalysts comprise in % by weight: CoO 2-5; Mo03 8-16; MgO 0-20 and Al^ 59-85. Another low-temperature shift catalyst consists of a mixture of copper and zinc salts or oxides in a weight ratio of 3 parts zinc to 1 part copper.

Subsequently, substantially all H 2 O is removed from the gas stream in the second sequence. For example, the clean gas stream can be cooled to a temperature below the dew point of water in a conventional manner to condense out and separate the H 2 O. Optionally, the gas stream can be essentially dehydrated by contact with a desiccant, such as aluminum oxide.

At least a portion and preferably all of the clean gas in the second sequence is then led to further purification in a second gas purification step. Optionally, part of this second sequence gas can be passed past the second gas cleaning zone. The stream of bypassed gas can then be combined downstream with the purified gas stream. The second gas cleaning zone may comprise any conventional system. For example, the second gas cleaning zone can correspond to that described earlier in connection with cleaning the gas flow in the first sequence. The second gas cleaning zone can use physical absorption with liquid solvent, e.g. cold methanol, N-methylpyrrolidone and dimethyl ether of polyethylene glycol. Optionally, the purification of the dry gas stream may include cooling to a temperature in the range of -56-(-45)CC to condense out and separate a liquid stream comprising from 0-70% by volume of the CO2, H2S and COS originally present , depending on the pressure

and the amount that was present in the raw gas. • The composition of the flow of hydrogen-rich gas from the purification zone in the second sequence is as follows: H2 98-60; CO 0-5; CO2 0-8; CH4 0-5; H 2 O 0-5; Scars 0-4; N2 0-20 and NH3 0 to trace amounts.

At least a part of and preferably all of the clean and purified synthesis gas stream from the first sequence is mixed with from 0-100% by volume of the I^-rich gas stream from the first sequence and at least a portion of and preferably all of the I^- rich gas stream from the second sequence to obtain a clean and purified synthesis gas stream with a molar ratio of H2 to CO in the range of 2-12. The part of the clean and purified stream of synthesis gas from the first sequence that is not used to produce the product gas can be returned to the synthesis gas generator. In the same way, a proportion of said product gas flow can optionally be returned to the reaction zone in the synthesis gas generator.

With the help of the method according to the invention, a pure methanol synthesis gas can be produced with a molar ratio f^/CO in the range 2-4 in the previously described process steps. In normal catalytic steps, the synthesis gas can be converted to methanol.

The exothermic equilibrium reaction of carbon oxides and hydrogen to produce methanol, as shown in equations II and III below, is favored at low temperatures and high pressure. However, high temperatures may be necessary with certain catalysts to achieve commercially usable reaction rates.

Conventional high-pressure methanol processes work at temperatures in the range 342-400°C at pressures in the range 250-350 atmospheres and with zinc oxide/chromium oxide catalysts.

Conventional low and medium pressure methanol processes work at temperatures in the range 204-350°C, e.g. 225-270°C,

and at a pressure in the range 40-250 atm., such as e.g. 40-150 atm., and with catalysts consisting mainly of copper oxide with a smaller amount of zinc oxide and chromium or aluminum oxide. The proportions of these three oxides are 30-60%, 20-40% respectively. 5-20%. The duration and thermal stability of the catalyst can be improved by adding manganese or vanadium. The methanol catalyst can be prepared by alkaline precipitation from nitric acid solution followed by drying, calcination and pelletisation. Space speeds can range from 10,000-40,000/hour. The contact time is less than 1 sec. This degree of methanol formation is from approx. 0.3-2 kg/l catalyst/ hour.

Optionally, gaseous raw material for the methanol converter may contain 2-12 mol-% CO,,. Furthermore, the mole ratio H2/ (2CO+3C02) can

in the feed gas flow to the methanol converter lie in the range 1.01-1.05. The presence of some CO,, reduces the costs of the previous gas cleaning steps. Furthermore, the larger molar specific heat for C02 in relation to CO and the lower heat of reaction for C02 gives a more

uniform temperature control in the methanol reactor. The presence of CO 2 appears to be beneficial in order to suppress the formation of dimethyl ether.

Each mole of fresh methanol synthesis gas can be mixed with 0-10 moles of unconverted return gas from the methanol converter, i.e. 3-8 moles of return gas per moles of fresh methanol synthesis gas. A steam turbine driven circulating compressor can be used to compress and recycle a mixture comprising the fresh methanol synthesis gas and the recycled gas. The working fluid for the turbine, e.g. steam, can be obtained from the main synthesis gas cooler after the gas generator.

The feed gas mixture to the methanol converter is preferably preheated by indirect heat exchange with the gaseous effluent from the methanol converter at a temperature within the range 260-427°C and at a pressure within the range 20-450 atm., preferably at the pressure in the synthesis gas generator minus normal pressure loss in the intermediate pipelines and equipment .

The effluent stream from the methanol reactor can have the following main composition in mol%: CH3OH 5-15; CO 8-25; H2 40-80; CO 2 3-12; H 2 O 0.5-15 and (CH 3 ) 2 O 0.05-0.6. Smaller amounts of other alcohols, aldehydes and ketones may be present.

Further cooling of the waste gas stream in air and water coolers can be effected to condense crude methanol and water. This condensate flows to a separation zone where non-condensed non-reacted gases, i.e. H,,, CO,, CH^, N,, and Ar are separated, e.g. by flash evaporation and is returned to the gas compressor, with the exception of a purge flow. The crude ethanol is purified by fractional distillation. Impurities including low boiling compounds, mainly dimethyl ether and higher alcohols, can be drawn off from the distillation zone and possibly disposed of as waste stream,

or used when returning to the gas generator as part of the raw material. These waste streams contain bound oxygen and thus reduce the free oxygen requirement that is necessary for a

given level of soot production. A proportion of the product methanol can be supplied to one or both gas cleaning zones in the first and second sections as supplementary solvent absorbent.

Based on the present invention

methanol synthesis gas is first produced with a molar ratio between H2 and CO in the range 2-4 by the previously described method, simultaneously with the CO-rich gas stream (or preferably essentially pure carbon monoxide). Crude ethanol is then produced

in the previously described manner, and this is cleaned. Although impure methanol and CO-rich gas stream can be reacted to produce crude acetic acid, it is preferred to react purified methanol with substantially pure carbon monoxide to increase the reaction rate, and to improve selectivity.

Theoretically, one mole of carbon monoxide/mol of methanol is required to produce one mole of acetic acid, as shown in the following equation IV. The reaction is slightly exothermic and in practice excess carbon monoxide is required, namely approx. 22%.

Catalysts are commercially available for carbonylation reactions to produce acetic acid at high or low pressure, either as a liquid or vapor phase reaction.

High pressure carbonylation reactions for the preparation of

raw acetic acid can occur at temperatures within the range 170-320°C, e.g. 200-250°C and at a pressure within the range 15-700 atm., e.g. 150-315 atm.

Suitable commercially available high temperature carbonylation catalysts for the production of acetic acid often comprise two main compounds. A compound is a carbonyl-forming metal of the iron group, i.e. iron, cobalt or nickel in the form of a salt, e.g. acetate. The second compound is a halogen, e.g. iodine, bromine or chlorine as free halogen or as a halogen compound. For example, Col or a mixture of cobalt acetate with an iodine compound are suitable catalysts. A contact time of approx. 2-3 min, may be necessary to achieve 50-6 5% conversion of methanol by vapor phase reaction at high pressure. Liquid-phase reaction at approx. 180°C and 258 atm. can take 3 hours, to achieve 51% conversion. Water is used as a solvent or diluent and it increases the methanol conversion while simultaneously suppressing the production of methyl acetate. For example, approx. 30-40% by weight of water be present in the reaction zone.

Carbonylation reactions for the production of crude acetic acid by reacting methanol and carbon monoxide-rich gas or preferably essentially pure CO can take place at a temperature within the range 150-200°C and a pressure within the range 34-680 atm. when it comes to the liquid phase. For a 50% conversion of methanol, the reaction time is 40-200 min. A temperature in the range of 200-300°C

and a pressure within the range 1-10 atm. can be used for the vapor phase reaction.

Suitable commercially available low temperature carbonylation catalysts for the production of acetic acid include the following combinations of ingredients: (1) noble metal catalysts, (2) catalyst promoters, and (3) dispersants or carriers. Noble metal active catalysts can be chosen from the groups rhodium, palladium, platinum, iridium, osmium or ruthenium in the form of an oxide, an organometallic compound, a salt or a coordination compound, consisting of one of the aforementioned noble metals, CO,

a halide, such as a chloride, bromide or iodide, and a suitable amine, organophosphine, organoarsine or organostibine ligand. The catalyst promoter can consist of a halogen or a halogen compound. The dispersant in a liquid phase process is a solvent for the metal catalyst compound, e.g. one

mixture of acetic acid and water. In vapor phase processes, the same noble metal compounds and promoters as mentioned above are dispersed on a carrier, e.g. alumina, activated carbon, silicon oxide or others.

For example, a typical low-pressure catalytic converter can

-2 -4

the liquid phase process comprise 10 to 10 mol/l chlorocarbonyl

-4

bis-triphenolphosphine rhodium and 10 to 2 mol/l methyl iodide dissolved in a mixture of acetic acid and water. The ratio between halogen atoms in the promoter and noble metal atoms in the catalyst is preferably within the range 3-300.

In the low pressure process for the production of glacial acetic acid by liquid phase carbonylation, at least one portion of the crude methanol, which has previously been prepared, is mixed in a reactor tank with recovered unreacted methanol, catalyst, catalyst promoter, acetic acid solvent for the catalyst, methyl acetate and water. The mixture is then pumped to a carbonylation reactor together with essentially pure carbon monoxide whereby the carbonylation reaction takes place at a temperature of e.g. 200°C and. at a pressure of approx. 35 atm. The gaseous product is cooled and sent to a separation zone in which unreacted gases and condensate are separated. The non-condensed gases can be washed with fresh methanol to recover entrained methanol, butyl acetate and methyl iodide for return to the reactor tank. If necessary, the remaining exhaust gas can be returned to the gas generator or to the water-gas exchange converter or vented. The liquid product from the reactor and the condensate is sent to a separation zone, e.g. distillation zone, where at a pressure of 1-3 atm. the low-boiling components, such as methanol, methyl acetate and methyl iodide, are separated and returned to the reactor tank together with recovered rhodium compound catalyst dissolved in acetic acid, and with water that can be recovered by azeotropic dehydration of acetic acid. Glacial acetic acid is also separated together with a bottom stream comprising propionic acid and heavy fractions.

Preferably, the bottom effluent stream of propionic acid and heavy fractions, as well as exhaust gases that are not flushed out, can be returned to the gas generator as part of the raw material. In this way, the surroundings are not polluted.

A more complete understanding of the invention is obtained by reference to the accompanying schematic drawings. A preferred embodiment of the method according to the invention is shown by the part of the drawing, fig. IA, which is to the left of the line A-A. Another embodiment is shown in fig. IB to the right of the line A-A. The drawings are not intended to limit the continuous process shown to the particular apparatus and substances described.

With reference to fig. IA has the non-packaged free-flowing and non-catalytic synthesis gas generator 1 with refractory lining, a ring burner 2 mounted in the upper intake 3 along the vertical axis. Feed streams are supplied to the reaction zone 4 of the gas generator by means of the burner 2. These include an oxygen stream which comes through pipe 5 and the central channel of the burner, not shown, a steam stream which is passed through lines 6 and 7 and a stream of hydrocarbon-containing fuel, which is passed through the lines 8 and 7. The two latter streams are mixed together in the pipeline 7. and the mixture is then passed through the not shown annular opening in the burner; 2.

The waste stream of synthesis raw gas leaves the reaction zone and is led through the outlet 12 and directly to an isolated chamber 13 where the waste gas stream is divided into two gas streams. One part of the synthesis raw gas is passed through an insulated transfer line 14 to a first sequence of process steps which ends with the production of a stream of CO-rich gas, or essentially pure CO product gas. in pipeline 15, a stream of clean and purified synthesis gas in pipeline 16 and an I^-rich gas stream in pipeline 17. The second partial stream of synthesis raw gas. is passed directly to a second sequence of processing steps by means of pipeline 20, pipe 21 and tank 22. Water enters the cooling tank 22 via pipeline 23, and a water slurry of solid particles of carbon and ash is periodically removed at the outlet opening 24, the pipeline 25, the valve 26 and pipeline 27 at the bottom of this cooling tank. This cooling removal can be done by means of a binge system not shown. The water slurry is fed to a water separator, which is also not shown, where a stream of clarified water is separated and returned to the tank 22. The second sequence ends with the production of a clean and purified f^-rich gas stream in pipeline 28. The product gas stream of clean and purified synthesis gas> can be produced by mixing streams 16, 17 and 28 in desired proportions in a manner to be explained in more detail below.

Going back to the first partial stream of synthesis raw gas

in the transfer line•14, this gas flow is led through the intake 29 in the gas cooler 30 where it is cooled by indirect heat exchange with a flow of boiler feed water from the pipeline 31. This water is led through the intake 32 and exits as steam through the outlet 33 and the pipeline 34. The cooled synthesis raw gas exits through the outlet 35, the pipeline 36 and is brought into contact with water from the pipeline. 37 in a venturi washer 38. Entrained solids, e.g. particulate. carbon and ash are then washed from the synthesis raw gas and carried with the water through pipeline 39 to the separation vessel 40. A mixture of solid particles and water is removed through pipeline 45 near the bottom of the vessel 40 and is led to a separator (not shown) where the water is clarified. are separated and returned to pipelines 37 and 46. Further gas washing can e.g. is achieved by passing the flow of synthesis gas through a water shower 47 before it leaves the container 40 through the pipeline 48.

The purified synthesis gas is cooled to below the dew point in the heat exchanger 50 by indirect heat exchange with cold water that enters through pipeline 51 and exits through pipeline 52. The cooled stream is led through pipeline 53 to the separation vessel 54 where condensed water is removed at the bottom using pipeline 55 , and the gas leaves the container through the pipeline 56 at the top. The clean synthesis gas stream is then cleaned in the gas cleaning zone 57. Gaseous impurities are separated, and e.g. CO 2 is withdrawn by means of line 58, and a stream of H 2 S + COS is passed through line 59 to a Claus unit, not shown, for conversion to sulphur.

The clean and purified synthesis gas stream in pipeline 60 is then divided into two streams 61 and 16. The stream of synthesis gas in pipeline 61 is subjected to further treatment in the carbon monoxide separation zone 62. At least a proportion and preferably all CO-rich gas or substantially clean carbon monoxide product gas, which emerges through pipelines 15 and 63, can be used in organic syntheses. The rest can be drawn off through pipeline 64, valve 65 and pipeline 66. As previously stated, it leaves the H2-

rich gas stream the CO separation zone 62 via pipeline 17.

Returning to the second sequence, the cooled synthesis raw gas stream, which is substantially saturated with water, after the water cooling, is passed through the outlet 70, the pipeline 71, the orifice or venturi washer 72, and the pipeline 73 to the separation vessel 74. Washing water in pipeline 75 is taken to the washer 72 where further purification of the synthesis gas stream can take place. A mixture of solids, i.e. particulate carbon and ash, as well as water, leaves container 74 near the bottom through conduit 76 and is then supplied to a separation zone not shown where clarified water is obtained.

The clarified water is returned as washing fluid in the pipelines 75

and 77. The gas stream can be showered with water from a shower 78 and leaves the container 74 near the top through pipeline 79.

The purified synthesis gas stream saturated with water is preheated in a heat exchanger 80 by indirect heat exchange with the shifted stream of synthesis gas from the catalytic water-gas shift conversion zone 81 through pipeline 82. The feed steam enters the shift conversion zone 81 through pipeline 83, and CO and H20 in the process gas stream react and give H2 + CC^' The resulting pure H2~rich gas stream is cooled in the heat exchanger 80 and then passed through pipeline 84 to the gas cooler 85 where the temperature in the gas stream is lowered to below the dew point by indirect heat exchange with water. For example, boiler feed water in pipeline 86 can be preheated in the heat exchanger 85, passed through, pipeline 87

and then be supplied to the gas cooler 30 by means of the pipeline 31, where it is converted to darap. The cooled H2~-rich gas stream is led through the pipeline 88 to the condensate separator 89, where condensed water is drawn off at the bottom through the pipeline 95, and pure H2~-rich gas exits through the pipeline 96 at the top. In the gas cleaning zone 97, the H2-rich gas stream is separated from unwanted gaseous impurities. For example, a stream of CO 2 is removed through line 98, and a stream of E 2 S + COS is removed through line 99 and fed to a Claus unit, not shown, for the production of sulfur. A clean H2-rich gas stream is removed from the gas cleaning zone 97 through the pipeline 28. At least a portion and preferably all of the H2-rich gas in the pipeline 28 is passed through the pipeline 100 to the pipeline 101 where it is mixed with at least a portion and preferably all of the stream of clean and purified synthesis gas from pipelines 16 and 102 from the first sequence. Any remaining portion of clean and purified synthesis gas from pipeline 16 can be passed through pipeline 103, valve 104 and pipeline 105 for use elsewhere. Any remaining share of H,,-

rich gas stream from pipeline 28, can be removed in the same way through pipeline 106, valve 107 and pipeline 108. The synthesis gas stream in pipeline 101 is led to pipeline 109 where it can be mixed with 0-100% by volume of H2~rich gas from pipelines 17 . H2 and CO within the range 2-12. At least a proportion of and preferably all of this gas can be passed through pipeline 120 for use in organic syntheses. Remaining portions of synthesis gas flow from pipeline 109 can be passed through pipeline 121, valve 122 and pipeline 123 for use elsewhere, or for return to the gas generator.

In another embodiment shown in fig. IB, pure methanol is produced by catalytic conversion of at least one portion of a pure and purified product stream of methanol synthesis gas from pipeline 120. The process steps are shown to the right of line A-A in the drawings. The process gas flow from pipeline 120 is passed through the valve 200 and pipeline 201 to a steam turbo compressor circulator 202 together with unconverted return gas from pipeline 20 3. Compressed gases in pipeline 204 are then preheated in the heat exchanger 20 5 by indirect heat exchange with hot impure metal vapor entering from the catalytic methanol reactor 206 via pipeline 207. The preheated methanol synthesis gas stream in the pipeline 208 is passed through the methanol reactor 206 where the reaction between H2 and carbon oxides takes place to produce crude methanol. After partial cooling in the heat exchanger 205, the methanol reaction products are led through pipeline 209 to the separation zone 210, where the unreacted gases are separated from the crude methanol. The unreacted gases are passed through pipelines 215 and 203 to the return compressor 202, except for purge gas which is passed through pipeline 216, valve 217 and pipeline 218. The crude methanol in pipeline 219 is fed to the purification zone 220 in which impurities are removed, e.g. by distillation. Dimethyl ether can be removed through pipeline 221, mixed alcohols through pipeline 222 and water through pipeline 223. Pure methanol can be withdrawn through pipelines 224 and 225, valve 226 and pipeline 227. Optionally, by-products, oxygen-containing organic compounds, from pipelines 221 , 222 and 218 are returned to the gas generator as part of the fuel and to reduce the need for free oxygen for a given level of soot production.

In yet another embodiment,

a crude stream of acetic acid prepared by low pressure liquid phase catalytic carbonylation reaction between pure methanol and substantially pure carbon monoxide, which has been previously prepared. In this case, at least a portion of the pure methanol in pipeline 224 is passed through pipeline 240, valve 241 and pipeline 242 to the reactor tank 24 3 and mixed with a mixture of recycled materials from pipeline 244. Recycle stream 244 comprises a mixture of methanol, methyl acetate and methyl iodide from lines 245 and 246 and a rhodium catalyst, i.e. Rh(CO)[P( C^ U^)^]^Cl dissolved in a mixture of acetic acid and water from line 247.

By means of the pump 248, the reactant mixture is pumped in

the tank 243 through the pipelines 249 and 250 to a vertical carbonylation reactor 251. At the same time, at least one part of it in the

substantially clean CO gas stream in pipeline 63 led to the carbonylation reactor 251 via valve 255, pipeline 256, a possible steam turbo compressor 257 and pipeline 258. In reactor 251, methanol and CO react and form acetic acid. A gas stream is led out over the top through pipeline 259, cooled in the heat exchanger

260 and is passed through pipeline 261 to separator 262. Non-condensed gases in pipeline 26 3 are washed with fresh methanol in a tower not shown to recover entrained methanol, methyl acetate and methyl iodide for return to reactor tank 24 3. Remaining off-gas from the scrubber can be returned to the gas generator or vented.

The liquid product from the reactor in pipeline 26 4 and the condensate from pipeline 265 are passed through pipeline 270

to the separation zone 271. For example during distillation, low-boiling components comprising a mixture of methanol, methyl acetate and methyl iodide can be separated, and these exit via pipeline 245; water is removed through conduit 272; recovered rhodium compound catalyst dissolved in acetic acid is removed through conduit 247; and impure acetic acid is removed through pipeline 273 and fed to the separation zone 274. Glacial acetic acid is recovered as a distillate from pipeline 275. Propionic acid and heavier components exit through pipeline 276 and can be returned to the gas generator as part of the fuel.

Example

The following example shows a preferred embodiment

of the method according to the invention as shown in the drawing, which relates to the simultaneous production of a pure purified stream of methanol synthesis gas and a stream of essentially pure carbon monoxide.

While preferred modes of operation are shown, the example is not intended to limit the scope of the invention. The process is continuous, and • the flow rates are specified on an hourly basis for all material flows.

736 50 kg. of a vacuum residue with a gravity of 2.0°

API and a total analysis in wt% as follows: C 83.45; H 10.10;

N 0.35; S 5.50 and 0 0.60,. mixed with 1,255 kg of returned unreacted particulate carbon recovered downstream in the process,

to obtain a pumpable dispersion of particulate carbon and petroleum oil. the 01je-carbon dispersion; in pipeline 8 in the drawing.

specified as hydrocarbon-containing fuel, is pumped through a heating device where it is brought to a temperature of 282°C and a pressure of 81.9 kg/cm 2 man.. The dispersion is then mixed with a flow of 29457 kg of steam at a temperature of 301 °C and a pressure of 81.9 kg/cm 2 man. from pipeline 6.

The carbon vapor mixture is passed through the annulus in the annulus burner which is arranged at the upper end of a conventional vertical refractory lined free-flowing non-catalytic non-packed synthesis gas generator.

At the same time, a flow of 77,580 kg of essentially pure oxygen, i.e. 99.5 mol-% O2/ from pipeline 5, led through the central passage in the burner. The two streams meet, mix, and the partial oxidation and other reactions take place in the reaction zone of the gas generator.

3 3

A flow of 246074 standard m (standard m measured at 1 5.5°C and 1.03 kg/cm^ man.) of synthesis raw gas leaves the reaction zone of the gas generator at a temperature of 1424°C and under a pressure of 73.8 kg/cm 2 man. The composition of the synthesis raw gas at outlet 12 from reaction zone 4 is shown in column 1 of the table. About. 1255 kg of unconverted carbon plus ash is carried away by the synthesis raw gas.

The waste raw gas stream leaves the reaction zone and splits into two streams at 13; 1 59991 standard m 3 synthesis raw gas is processed in a first sequence, and the rest, 86083 standard m 3, is processed simultaneously in the second sequence.

The composition of the raw gas leaving the gas cooler

30 in a pipeline 36, is shown in column 2 of the table. After

essentially all entrained carbon and ash is washed away

the synthesis raw gas, and the gas stream is cooled to below the dew point to condense out essentially all water, the synthesis raw gas has the composition in pipeline 56 as shown in column 3 of the table.

Gaseous impurities including CO 2 , H 2 S and COS are removed from the purified synthesis raw gas stream to provide 1 34505 standard m"^ of an intermediate purified synthesis gas stream in conduit 60 of the composition shown in column 4 of the table. This stream is divided into the following two streams: (a) a stream of 71075 standard m 3 , which is treated in a CO separation zone, and (b) the residue consisting of a stream of 63430 standard m 3 is mixed with H2~rich gas as

shall be described below.

A current of 32281 standard m" <3> of essentially pure

CO in pipeline 15 is processed in the CO separation zone and has the composition shown in column 5 of the table. Furthermore, a stream of 38,794 standard m 3 H^-rich gas in pipeline 17 is produced in the CO separation zone and with the composition shown in column 6 of the table.

Back to the other part of the synthesis raw gas, this comprises the rest of the synthesis raw gas stream from the reaction zone. By passing all the synthesis gas from the reaction zone through a passage of reduced diameter, the flow rate can be accelerated, and the velocity of solid particles, i.e. carbon and ash, which are entrained in the gas flow, can be increased. According to this, a large proportion of solid particles can be entrained in the second part of the synthesis raw gas which is directly cooled in water contained in a tank arranged below the gas generator. The first partial stream of synthesis raw gas is divided and processed in the first sequence, as described above. The actual division between the two sequences can be regulated by non-return valves in each pipeline.

The stream of 200,200 standard m 3 of synthesis raw gas in pipeline 7 9 is saturated with water during the rapid cooling and washing with water and has the composition shown in column 7 in the table.

200200 standard m <3> waste gas from the catalytic water-gas shift converter in pipeline 82 has the composition shown in column 8 of the table. After cooling by indirect heat exchange to below the dew point, the gas stream in pipeline 96 has the composition shown in column 9 of the table. This gas flow is then cleaned in a gas cleaning zone, and 94,578 standard m 3 of pure purified t^-rich gas is obtained in pipeline 28 with the composition shown in column 10 of the table.

All of the essentially dry intermediate product stream of purified synthesis gas in pipeline 16 in an amount of 36430 standard m 3 is mixed with all of the essentially dry H-rich gas stream in pipeline 28 in an amount of 94578 standard m 3 , to obtain a gas flow in pipeline 101 with the composition shown in column 11 of the table. All of this gas flow in pipeline.101

is then mixed with 3 allH z?-rich gas from pipeline 17 in an amount of 38794 standard m , and an essentially dry product is obtained

duct flow of 196803 standard m^ purified synthesis gas in pipeline 109 with the composition shown in column 12 of the table. This is the suitable gas composition for mixing with unconverted return gas from a catalytic methanol converter to obtain a feed gas for the production of crude methanol. Pure methanol can be produced by purification and reacted in a catalytic carbonylation reactor with at least a portion of that stream of substantially pure carbon monoxide gas from stream 15 to obtain crude acetic acid. Glacial vinegar can then be produced by purification.

Claims (8)

1. Process for producing a product stream of purified synthesis gas suitable for conversion to methanol, and a CO-rich product gas stream, characterized in that it comprises: 1) reaction of a hydrocarbon-containing or oxygenated hydrocarbon-containing organic material with a free oxygen-containing gas in the reaction zone in a free-flowing non-catalytic partial alk-sydas ion gas generator at a temperature in the range 700-1650°C and at a pressure in the range 1-250 atm., to produce a waste gas comprising H2, CO, H20, solid particles of carbon and ash and at least one gas from the group consisting of CO 2 , H 2 S, COS, CH 4 , NH 3 , N 2 and Ar; 2) splitting the waste gas stream from (1) into a first and second stream and simultaneously further processing these in separate first and second sequences of steps; 3) cooling the first gas stream from (2) in the first sequence by indirect heat exchange in a separate heat exchange zone, purification to remove entrained solids and removal of water; 4) purifying at least one part of the gas stream from (3) in a first gas purification zone and separating at least one gas from the group CO,,, H2S, COS, CH^ and NH^ to give a purified stream of synthesis gas essentially free for gaseous sulfur compounds; 5) dividing the purified stream of synthesis gas from (4) into two streams and supplying the first of these to a CO separation zone, from which said product stream of CO-rich gas and a separate stream of H2-rich gas are removed; 6) cooling and purifying the second gas stream from (2) by direct contact with water to thereby remove entrained solid particles and to increase the H20/C0 molar ratio of the gas stream to a value within the range of 2-5; 7) reacting CO and H 2 O in the gas stream from (6) in a water-gas shale void formation sor.e to give an H 2 -rich gas stream; 8) removing H20 and purifying at least a portion of the H2-rich gas stream from (7) in a second gas purification zone and separating therefrom at least one gas from the group CO2, H2S, COS, CH^ and NH^ to give a purified E^-rich gas stream substantially free of gaseous sulfur compounds; and 9) mixing at least a portion of the second separated stream of purified synthesis gas from (5) with from 0-100% of the P^-rich gas stream from step (5) and at least a portion of the purified I^-rich gas stream from (8) to obtain a product stream of purified synthesis gas. 2. Method according to claim 1, characterized in that a product stream of CO-rich gas containing 95-99 mol% CO is separated. 3. Method according to claim 1 or 2, characterized in that the purified flow of synthesis gas "in the first sequence is divided in step (5) so that the first flow contains 5-50% by volume of the purified flow of synthesis gas. 4. Method according to any one of the preceding claims, characterized in that the waste gas stream from the reaction zone in step (1) and the purified synthesis gas stream from step (4) have a mole ratio H 2 /CO within the range 2-12. 5. Method according to claim 4, characterized in that the product flow of purified synthesis gas is set to a molar ratio H 2 /CO within the range 2-4. 6. Method according to any one of the preceding claims, characterized in that the second split stream from step (2) is regulated to contain approx. 20-70% by volume of the waste gas flow from step (1), whereby the rest of this constitutes the aforementioned first separated flow. 7. Method according to any one of the preceding claims, characterized in that a proportion of the gas stream \ from step (3) or a portion of the H^-rich gas stream from step (7) after removal of water, or a portion of each of these gas streams, is passed past the first and second gas cleaning zones in the respective sequences, and each of the bypassed gas streams is mixed with the corresponding purified gas streams. 8. Method according to any one of the preceding claims, characterized in that a portion of the f^-rich gas stream from step (8) or a portion of the product stream of purified synthesis gas from step (9)-, or a part of each of these is fed back to the gas generator in step (1).