GB2142331A

GB2142331A - A process for producing methanol

Info

Publication number: GB2142331A
Application number: GB08416002A
Authority: GB
Inventors: Toshiyuki Mii; Hiroshi Watanabe; Morihisa Hidaki
Original assignee: Toyo Engineering Corp
Current assignee: Toyo Engineering Corp
Priority date: 1983-06-29
Filing date: 1984-06-22
Publication date: 1985-01-16
Also published as: GB8416002D0

Abstract

The process utilizes a synthesis gas produced by a steam reformer (R) from light hydrocarbons, the synthesis gas being fed after appropriate pressure elevation (in compressor (24)) to a methanol reformer (25) from which unreacted gas is recycled. Methanol production is improved by selective purging of excess hydrogen, from within the methanol process loop, using a pressure swing adsorber (1), and the hydrogen stream therefrom is optionally fed through an expander (2), in which power generated by adiabatic expansion is used to drive an adiabatic compressor (24) which acts on the Co/Co2 stream therefrom. This latter stream is recycled to the methanol reformer (R). <IMAGE>

Description

SPECIFICATION A process for producing methanol This invention relates to improvements in a methanol production process wherein hydrocarbons, such as natural gas, are steam reformed to produce a synthesis gas, and a methanol synthesis is carried out using the synthesis gas thus produced.

The methanol synthesis is performed according to the following equations: CO + 2H2eCH30H CO, + 3H2#CH3OH + H20 The molar relationship between carbon monoxide, carbon dioxide and hydrogen in the methanol synthesis gas is generally expressed by the following index R: R = (H2 - C02)/(CO + CO2) When R = 2, the synthesis gas has a stoichiometric composition as to the combination of both of the foregoing reactions. In a methanol synthesis reaction, it is desirable that R is equal to or slightly greater than 2, that is, the synthesis gas should have a stoichiometric composition or else a slight excess of hydrogen.

An excess of hydrogen in the methanol synthesis gas is generally present when light hydrocarbons, such as natural gas, are subjected to a steam reforming reaction and the resulting reformed gas is used as the starting synthesis gas for the methanol synthesis.

When nonaromatic hydrocarbons are used as the starting material for a steam reforming reaction, the main reforming reactions and the values of the index R are as follows: methane CH4 + H20 oCO + 3H2 R = 3.0 ethane C2H6 + 2H20 #2CO + 5H2 R = 2.5 propane C3H8+3H20 - 3CO + 7H2 R= 2.33 butane C4H,o + 4H20 o4CO + 9H2 R = 2.25 pentane CsHt2 + 5H20 o5CO + 11 H2 R = 2.20 The value of R is higher than 2 for reactions utilizing light hydrocarbons such as the foregoing ones listed, thereby indicating the presence of excess hydrogen.R is generally higher than 2 for light hydrocarbons up to naphtha fractions having about 8 carbon atoms or less. The foregoing reforming reactions are actually accompanied by side reactions which form a considerable amount of carbon dioxide, but the values of R obtained in practice substantially coincide with the valuesgiven above.

The term "light hydrocarbons" in the context of the present invention means naphtha and nonaromatic hydrocarbons lighter than naphtha. Naphtha, or petroleum benzin, refers to the well-known mixture of hydrocarbons comprising the low boiling fractions of petroleum.

The R values discussed above are those of the product gas of the steam reforming process, but they are not necessarily those of the gas that enters a methanol synthesis reactor. In the following discussion of the methanol synthesis reaction, it is natural to refer to the gas entering the methanol synthesis reactor and, thus, the values of R described hereafter refer to the gas entering the methanol synthesis reactor unless otherwise specified.

During the methanol synthesis reaction, hydrogen is consumed in an amount that is stoichiometrically equivalent to the amount of carbon monoxide and carbon dioxide that is consumed. In consequence, the stoichiometric excess of hydrogen produced in the preceding steam reforming process remains unreacted and, repeatedly recycled, further increases the hydrogen excess. In an actual methanol synthesis, it is not unusual that the value of R exceeds 10 in the gas entering the methanol synthesis reactor, including the recirculated gas, even if the value of R is around 2.5 in the product gas of the steam reforming gasification process. In such a case, it is desirable to decrease the value of R to close to 2 by purging excess hydrogen from the reaction system.However, since the hydrogen is mixed with carbon monoxide and carbon dioxide, all three of these gases are purged simultaneously when the synthesis gas containing hydrogen is purged, and the effect of the purging is thus lessened, particularly when the reaction being conducted is approximately stoichiometric. The loss of carbon monoxide and carbon dioxide due to such purging also leads to a lower production of methanol.

For efficient purging, it is desirable to maximize the amount of hydrogen that is removed and to minimize the amount of carbon monoxide and carbon dioxide that are lost in the purging. To accomplish this by the prior art processes, however, the value of R of the gas entering the methanol synthesis reactor must be increased. Consequently, according to the conventional practice, purging is minimized and the reactor is operated at a higher hydrogen concentration, which causes the R value for the gas entering the methanol synthesis reactor to be extremely high, as described above.

When the value of R is excessively high, the excess hydrogen exerts a large partial pressure and requires that the synthesis pressure in the methanol forming reactor be much higher than the synthesis pressure needed for conducting the reaction with a stoichiometric synthesis gas composition. As a further result of minimizing the hydrogen purge, the concentrations of other inert gases, such as methane and nitrogen, increase and thereby further raise the required synthesis pressure to a considerable extent.

Such an accumulation of excess hydrogen and inert gases increases the amount of unreacted gas that is circulated through the methanol synthesis apparatus. If the dimensions and overall size of the equipment and piping employed for the reaction are fixed, the flow resistance of the system is directly proportional to the square of the amount of the circulated gas, so that the power required for effecting the circulation is enormously increased when a large amount of excess hydrogen and inert gases is present. The excess hydrogen and inert gases thus require excessive equipment and piping for their retention within the reaction system, and a large amount of power is wasted for circulating them.

If this situation were compared by analogy with the human body, the state of the methanol synthesis equipment is comparable to that of a corpulent human body in which excess fat and cholesterol are accumulated and which has high blood pressure. The present invention provides a means for solving the problems caused by the presence of excess hydrogen and inert gases in the methanol synthesis system. It is essential that the excess hydrogen be purged from the system because such excess hydrogen is the fundamental cause of all of the foregoing problems. However, as noted previously, the mere purging of a gaseous mixture containing hydrogen, carbon monoxide and carbon dioxide does little to correct the hydrogen excess. To make the purging more efficient, it is necessary to purge only hydrogen and prevent loss of carbon monoxide and carbon dioxide.If this becomes possible, hydrogen can be purged as needed and the methanol synthesis can be performed at a desired value of R without loss of methanol production.

To achieve this, carbon monoxide and carbon dioxide in the purge gas must first be separated from the hydrogen, and then be recycled to the synthesis reactor. Since such a separation is difficult to perform industrially by conventional means, the present inventors investigated the possible use of a pressure swing adsorption process for carrying out such a separation. Pressure swing adsorption processes use adsorbents, such as activated carbon, natural or-synthetic zeolites, and silica gels, and they are effective to selectively separate gaseous components from a mixture thereof. Pressure swing adsorption was developed more than twenty years ago and is now in general use as an adsorption process. Equipment for such processes is well known and is accordingly not described in detail herein.In a pressure swing adsorption process, the operating pressure swings, that is, the operating pressure is alternately increased and then decreased, whereby impurities are separated from the gaseous mixture.

More specifically, a pressure swing adsorption process separates gaseous components by alternate steps of adsorption and desorption of a selected components or components of a mixture of gases. The adsorbents are chosen to be selective for the component to be removed.

As employed in the present invention, the pressure swing adsorption process includes a first step of passing a purge gas stream containing gaseous hydrogen, carbon monoxide and carbon dioxide through an adsorbent bed under pressure so that the carbon monoxide and carbon dioxide are adsorbed, thereby producing an effluent stream enriched in hydrogen as a first step.

The, the flow of purge gas is stopped before, or at the same time that the adsorbent bed becomes saturated, and then the adsorbed components, namely, carbon monoxide and carbon dioxide, are desorbed from the adsorbent by lowering the adsorbent bed pressure, thereby producing a stream containing carbon monoxide and carbon dioxide which is flowed from the adsorber separately from the hydrogen stream. The adsorbent bed is then cleaned by any conventional method, such as by purging with pure hydrogen, and then repressurized for treatment of additional purge gas. In a continuous process, a plural of adsorbent beds are used alternately in such a manner that when one bed is being used for adsorption, another bed is being regenerated by effecting desorption of the adsorbate.The term "pressure swing" refers to the step of removing the adsorbed components from the adsorbent bed by lowering the pressure within the adsorber.

Such a process is particularly effective for separating impurities from a gaseous mixture consisting mainly of hydrogen. Such processes are widely used to separate hydrogen from purge gases generated by ammonia amd methanol synthesis reactions, and are further used for separating hydrogen from other gaseous mixtures consisting mainly of hydrogen. However, such prior art uses of pressure swing adsorption have been for the purpose of obtaining substantially pure hydrogen. In the context of the present invention, pressure swing adsorption is used in the opposite way, namely, to remove hydrogen from the system and to recycle the so-called "impurities", carbon monoxide and carbon dioxide, to the methanol synthesis loop.

In practising the process of the present invention, a methanol synthesis reaction is carried out using a synthesis gas having a desired stoichiometric composition. Purge gas from the methanol synthesis loop is separated by pressure swing adsorption into a first gas stream consisting mainly of hydrogen and a second gas stream consisting mainly of carbon monoxide and carbon dioxide. The hydrogen stream is discharged from the methanol synthesis loop, and the stream containing carbon monoxide and carbon dioxide is recycled to the methanol synthesis loop.

The purge gas from the methanol synthesis loop is generally effectively treated by the pressure swing adsorption process utilized in the present invention. In the context of this invention, "purge gas" refers to gas removed at any point along the methanol synthesis loop.

However, since the starting methanol synthesis gas from the stream reformer contains excess hydrogen, at least part of this starting synthesis gas can also be subjected to pressure swing adsorption before being fed to a synthesis gas compressor upstream from the methanol synthesis reactor. In addition, unreacted or purge gas downstream from the outlet of the methanol synthesis reactor can be first reduced in pressure and then treated by the pressure swing adsorption at such a reduced pressure. To prevent hydrogen, methane, nitrogen and other inert gases from accumulating in the synthesis loop, at least a part of this unreacted gas must be continually purged from the methanol synthesis loop.For this reason, if part of the starting synthesis gas is to be subjected to the pressure swing adsorption, then it is subjected to such adsorption together with a part of the unreacted gas, preferably at a lower pressure than the synthesis pressure.

According to the present invention therefore, there is provided a process for producing methanol, including the steps of subjecting light hydrocarbons to steam reforming to produce a methanol synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide, feeding said synthesis gas to a methanol synthesis reactor to produce methanol, then cooling said synthesis gas to condense the methanol, separating the methanol from the unreacted gas, and recycling the unreacted gas together with fresh synthesis gas to said methanol reactor, and wherein the value of R in the equation R = (H2-CO)/(CO + CO2), (H2, CO and CO2 representing the mol percent amounts of hydrogen, carbon monoxide and carbon dioxide, respectively, in the gas field to the methanol synthesis reactor), is adjusted to a selected value by purging a portion of the gas to be fed to or from the methanol synthesis reactor, then separating the purged gas into a first gas stream consisting essentially of hydrogen and a second gas stream consisting essentially of carbon monoxide and carbon dioxide by pressure swing adsorption, discharging said first stream from the methanol synthesis process, and recycling said second stream to said methanol synthesis reactor.

According to another aspect of the invention, there is provided a process for removing hydrogen from a pressurized gaseous mixture containing hydrogen, comprising the steps of: subjecting said gaseous mixture to pressure swing adsorption to thereby separate said gaseous mixture into a first stream consisting essentially of hydrogen and having a pressure substantially the same or slightly less than the pressure of said gaseous mixture, and a second stream consisting essentially of gases adsorbed during said pressure swing adsorption, said second stream having a pressure substantially equal to the desorption pressure; feeding said first stream to an expander wherein said first stream is reduced in pressure under substantially adiabatic conditions and generating power from the expansion of said first stream in said expander;; feeding said second stream to a compressor effective to pressurize said second stream under substantially adiabatic conditions; and operating said compressor with the power generated by said expander.

The invention will now be explained by way of non-limitative example in the following description with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of an apparatus used to carry out a methanol producing reaction according to the present invention.

Figure 2 is a partial schematic diagram of an apparatus used to carry out pressure swing adsorption according to a further embodiment of the invention.

Figures 3A, 3B and 3C are partial schematic diagrams of systems according to the invention for balancing power between an expander and compressor.

Figures 4A, 4B and 4C are partial schematic diagrams of further embodiments of the invention wherein inlet gas to the pressure swing adsorber is cooled by outlet gas of an expander.

Figure 5 is a partial schematic diagram showing a system according to the invention wherein a gas stream consisting essentially of desorbed gases is cooled by low temperature gas from the outlet of an expander.

Figure 6 is a schematic diagram of an apparatus for carrying out a further embodiment of the present invention wherein carbon monoxide and carbon dioxide are recycled to a stream reformer.

Small arrows indicate the flow directions in the gas flow lines shown in the drawings.

Almost all prior art pressure swing adsorption processes are designed to separate hydrogen of high purity from a gaseous mixture. The process according to the present invention has a different purpose in that it divides the unreacted purge gas and, optionally, the starting synthesis gas, into a first stream consisting essentially of hydrogen and a second stream consisting essentially of carbon monoxide and carbon dioxide, without requiring either of the streams to be high in purity. The content of impurities in the hydrogen stream need not be reduced to the extent of several parts per million, as is the case in conventional processes.

Preferably, the concentration of carbon monoxide and carbon dioxide in the hydrogen stream is reduced to 1000 parts per million or less, particularly 100-1000 ppm. If the amount of carbon monoxide and carbon dioxide in the hydrogen stream exceeds 1000 ppm, the loss of these gases from the methanol synthesis loop is uneconomically high. The rate of recovery of the adsorbed components is very high when pressure swing adsorption is used, so that the concentration of carbon monoxide and carbon dioxide in the hydrogen stream can readily be reduced to 1000 ppm or less. The process according to the present invention also differs from prior art processes utilizing pressure swing adsorption because in this invention the impurities, carbon monoxide and carbon dioxide, are essential substances required to be recovered.In contrast, the prior art processes are primarily directed to purification of hydrogen as the desired product.

Another important factor in a methanol synthesis reaction of the type described is that the concentration of inert gases, such as methane and nitrogen, should be as low as possible in the stream containing carbon monoxide and carbon dioxide and should be as high as possible in the hydrogen stream. In order to make the concentration of inert gases in the circulating methanol synthesis gas as low as possible, a large amount of such inert gases are desirably purged along with the hydrogen discharged from the methanol synthesis loop. However, the excess hydrogen in the synthesis gas is primarily responsible for the problems with the conventional methanol synthesis reaction as described above, and the presence of the inert gases is only a relatively minor problem.Thus, the presence of a certain amount of inert gas in the stream of carbon monoxide and carbon dioxide will only cause a slight increase in the inert gas concentration in the synthesis gas and will not seriously affect the synthesis conditions. Accordingly, it is preferred, but is not critical, that the greater part of the inert gases in the gas subjected to pressure swing adsorption be expelled from the methanol synthesis loop with the hydrogen stream. This should be taken into account when designing the adsorption equipment and selecting the adsorbents.

The adsorption characteristics of carbon monoxide and carbon dioxide are as follows. With the exception of water, carbon dioxide is the most easily adsorbable molecule. It is adsorbed to a large extent by activated carbons, molecular sieves, silica gels and similar adsorbents, all of which can be used to form an adsorbent bed through which the purge gas passes in the process of the invention. Activated carbon adsorbents are commonly used in the pressure swing adsorption process. Water and methanol are generally adsorbed simultaneously. Carbon monoxide is generally adsorbed to a lesser extent than carbon dioxide and ammonia. Molecular sieves made of crystalline alkali metal aluminosilicates have superior adsorbent properties for carbon monoxide and can be used in the process of the present invention. Carbon monoxide is not well adsorbed by activated carbon adsorbents.

In general, carbon monoxide is better adsorbed by molecular sieves than are methane and nitrogen. Therefore, carbon monoxide is adsorbed preferentially when a mixture of these gases is subjected to pressure swing adsorption. These adsorption characteristics, however, vary greatly with different kinds of molecular sieves. Adsorbents which adsorb carbon monoxide well, but which do not adsorb methane and nitrogen, should be selected, subject to the exception described below regarding methane.

The stream containing carbon monoxide and carbon dioxide recovered from the pressure swing adsorption can be subjected to a reforming reaction in the steam reforming apparatus before it is introduced into the methanol synthesis apparatus. If this is done, methane present in this stream will also be reformed, thus effecting a decrease in the concentration of methane in the circulating methanol synthesis gas.

The concentration of methane in the circulating synthesis gas can be maintained at a low level by admitting methane into the stream of carbon monoxide and carbon dioxide to as great an extent as possible so that the concentration of methane in the reformed gas will increase to a selected level. If this is done, the adsorbents should be selected to adsorb carbon monoxide, carbon dioxide and methane as much as possible and to adsorb as little nitrogen as possible.

Since the nitrogen generally originates from natural gas subjected to the stream reforming process, the nitrogen content of the natural gas used in the steam reforming process prior to the methanol production process should be as low as possible.

A two-layer adsorbent bed comprising an activated carbon layer and a molecular sieve layer can be used in the pressure swing adsorption apparatus for the purposes of the present invention. As noted above, carbon monoxide and carbon dioxide are adsorbed almost com pletely, but the purity of these gases after desorption is not extremely high. This happens because methane and nitrogen are slightly adsorbed by the adsorbents, and gaseous components, such as hydrogen, methane and nitrogen, which permeate voids in the adsorbents, are mixed with the stream of carbon monoxide and carbon dioxide under the reduced pressure employed in the desorption step of the pressure swing adsorption process. In the present invention, however, the purity of the stream containing carbon monoxide and carbon dioxide is not of critical importance.For the purposes of the invention, the goal is only to recover carbon monoxide and carbon dioxide as completely as reasonably possible. As described above, the stream containing carbon monoxide and carbon dioxide can be subjected to steam reforming together with a fresh, starting, natural gas before being subjected to the methanol synthesis reaction. In this case, methane is desirably present in the stream containing the carbon monoxide and carbon dioxide, but nitrogen should be excluded from this stream if possible.

The separation efficiency of the pressure swing adsorption process is increased because of the lower degree of purity required for the separated gases. It is relatively easy to obtain around 80 to 90% hydrogen recovery, using state-of-the-art pressure swing adsorption equipment applied for the separation of hydrogen, because the process of the present invention requires only a relatively low degree of purity of the separated gases.

The purge gas flows through the adsorber at an elevated pressure, sometimes at the operating pressure of the methanol synthesis loop. When sufficient purge gas has been passed through the adsorbent bed, the flow of purge gas is cut off by suitable means, such as a valve, the flow of the stream consisting essentially of hydrogen ceases, and the outlet for this stream is closed.

The pressure within the enclosed catalyst bed is then relieved by suitable means, and the adsorbent bed is then desorbed by the opening of a second outlet through which passes a stream consisting essentially of carbon monoxide and carbon dioxide. If continuous purging is to be carried out, when one adsorbent bed is being regenerated, the purge gas can be flowed through a second adsorbent bed.

In separating -gaseous components by pressure swing adsorption, the adsorbed components, mainly carbon monoxide and carbon dioxide, are thus discharged at a pressure only slightly greater than atmospheric pressure. The unadsorbed components which pass through the adsorbent bed, mainly hydrogen, are discharged from the pressure swing adsorption equipment at a pressure only slightly less than the pressure at which the gas is fed to the adsorber, which small pressure drop is due to the resistance produced by the passage of the gases through the adsorbent bed.In other words, the stream consisting essentially of carbon monoxide and carbon dioxide is discharged at a pressure which is nearly atmospheric pressure when it is discharged from the pressure swing adsorption equipment, whereas the stream consisting essentially of hydrogen is discharged under almost the same pressure as the pressure of the feed gas that is fed into the pressure swing adsorption equipment.

The desorbed stream containing carbon monoxide and carbon dioxide is fed from the adsorbent bed to the synthesis loop. For this purpose, this stream is preferably first pressurized by a compressor to a pressure suitable for the methanol synthesis. The hydrogen stream is reduced in pressure when it is discharged from the adsorbent system for possible further use because it is rarely used under high pressure. A second important embodiment of the present invention involves feeding the hydrogen stream through an expander, and using the power thus generated to drive the compressor for the desorbed stream containing carbon monoxide and carbon dioxide. Reciprocating or rotary type expanders and compressors can be used as the foregoing expander and compressor.An insufficiency of power for operating the compressor can occur under certain combinations of conditions of the amount of gas treated, pressure, etc. of the expander and compressor. However, power for driving the compressor can be readily supplemented by a steam turbine or electric motor. In addition, the compressor need not always compress the stream containing carbon monoxide and carbon dioxide up to the methanol synthesis pressure. Instead, this stream can be compressed to the suction pressure of the methanol synthesis gas compressor or to the inlet pressure of the reforming apparatus. The stream containing carbon monoxide and carbon dioxide can then be fed to the synthesis gas compressor or reformer, respectively. In general, the system should be designed as economically as possible in accordance with the balance between the power generated and the power required.

The present invention provides another means for improving process efficiency and reducing power consumption. As the temperature of the gas to the expander is increased, the amount of power generated by the expander is increased. Correspondingly, as the inlet temperature of the compressor becomes lower, the amount of power required by the compressor decreases. The outlet temperature of the expander is decreased greatly by adiabatic expansion, whereas the outlet temperature of the compressor is increased to a large extent by adiabatic compression.

Therefore, the amount of power generated can be increased by heating the inlet gas of the expander with the high temperature gas discharged from the compressor, arid the power required by the compressor can be decreased by cooling the inlet gas of the compressor with the lower temperature gas discharged from the expander. The above-described power insufficiency can be effectively eliminated by utilizing the high and low temperature conditions obtained by the expansion and compression processes in this fashion.

Preferred embodiments of the present invention are illustrated in the attached drawings. Fig.

1 illustrates a methanol synthesis process according to the present invention. As shown in Fig.

1, a starting methanol synthesis gas produced by subjecting light hydrocarbons to steam reforming is introduced through a line 31 from a conventional. steam reforming apparatus R having a hydrocarbon feedstock inlet 47. The stream of starting synthesis gas is merged with a stream 41 of recovered carbon monoxide and carbon dioxide, and the mixed stream is fed through a line 32 to a methanol synthesis gas compressor 24. After undergoing compression the synthesis gas is fed through a line 33, which line 33 passes through a heat exchange 26, to a methanol reactor 25. In the heat exchanger 26, the feed gas to the reactor 25 undergoes heat exchange and is heated by outlet gas from the reactor 25.After undergoing the methanol forming reaction in the reactor 25, the synthesis gas passes out of the reactor 25 through a line 34 to be cooled in the heat exchanger 26, as aforementioned, then further cooled in a methanol cooler 27 and then fed to a methanol separator 28. Liquid methanol condenses and is collected from an outlet 35 located at the bottom of the methanol separator 28. Unreacted gas leaves the separator 28 through a line 36. Part of the unreacted gas is continuously or intermittently drawn off, as a purge gas, through a branch line 38 and is fed to the pressure swing adsorption apparatus 1. The remainder of the unreacted gas is drawn through the line 37 and enters the synthesis gas compressor 24, wherein it is compressed and recirculated to the methanol synthesis reactor 25 along with fresh synthesis gas supplied from the line 32.

The purge gas from the line 38 is separated by the pressure swing adsorption apparatus 1.

into a first stream consisting essentially of hydrogen and a second stream consisting essentially of carbon monoxide and carbon dioxide. The second stream is fed through a line 40 to a compressor 3, where it is pressurized and then recirculated to the synthesis loop via the line 41.

Alternatively, the said stream can be recirculated to the steam reforming equipment R via a line 43, or recirculated to both of the synthesis gas compressor 24 and the steam reforming equipment via both of the lines 41 and 43.

The first stream flows from the pressure swing adsorption apparatus 1 through a line 39 to an expander 2. The expander 2 reduces the pressure of the hydrogen stream substantially adiabatically and thereby generates power. Alternatively, the hydrogen stream can be reduced in pressure by simple throttle expansion. It is preferable, however, to generate power by means of the expander 2 and utilize such power to operate the compressor 3.

As noted above, the starting synthesis gas can be treated by pressure swing adsorption according to essentially the same principles as described above, except that the gas to be treated by pressure swing adsorption comprises both the synthesis gas from the line 32 and the unreacted gas from the line 36. The synthesis gas can, for example, be continuously or intermittently connected through a line 46 from line 32 to the adsorber 1.

The unreacted gas from the methanol synthesis loop 24, 25, 26, 27 and 28 can be reduced in pressure before being subjected to the adsorption process. Fig. 2 illustrates a variation of the process shown in Fig. 1 for this purpose. The pressurized purge gas containing hydrogen enters the pressure swing adsorption apparatus 1 through the line 38. A stream consisting essentially of hydrogen passes through the line 39 and is adiabatically expanded in the expander 2. The stream containing carbon monoxide and carbon dioxide desorbed in the apparatus 1 flows through the line 40 and is compressed in the compressor 3, which is driven by the expander 2.

as depicted by the broken line in Fig. 2. The two streams then pass through the lines 41 and 44, respectively, and are allowed to undergo heat exchange in a heat exchanger 4, whereby the cooling generated by expanding the hydrogen containing stream is utilized.

As means for increasing the power generated by the expander and decreasing the power required for the compressor in order to improve the balance of power between the expander and compressor, an effective measure is to cool the inlet gas of the compressor with the low temperature gas discharged from the expander and to heat the inlet gas of the expander with the high temperature gas discharged from the compressor. Figs. 3A, 3B and 3C show preferred embodiments utilizing this procedure, each of which could be incorporated into the apparatus shown schematically in Fig. 1. Fig. 3A illustrates an apparatus for carrying out both expansion and compression in a single stage. The temperature of the gas discharged from the expander T is lowered considerably by the expansion process, whereas the temperature of the gas discharged from the outlet of the compressor C is increased to a large extent due to adiabatic compression. A heat exchanger El is therefore provided so that the gas discharged from the compressor C undergoes heat exchange with the inlet gas to the expander T. Similarly, the outlet gas of the expander T undergoes heat exchange with the inlet gas of the compressor C in another heat exchange E3. The use of such heat exchangers El and E3 prevents the difference in temperature between the gases discharged from the compressor C and the gases discharged from the expander T from becoming too great.The foregoing method is inferior to the methods described below in connection with Figs. 3B and 3C in balancing the power generated by the expander and the power required by the compressor, but it is nonetheless advantageous in its simple scheme and structure. Although the inlet gas to the compressor contains a slight amount of water, it also contains methanol, and hence there is no problem with icing. A slight amount of the methanol can be recovered.

The reaction scheme illustrated in Fig. 3B illustrates a system wherein expansion is conducted in a single stage and compression is conducted in two stages. The illustrated apparatus is essentially the same as the apparatus shown in Fig. 3A, except that the compressors C1 and C2 are employed in series, and the inlet gas to each of the compressors C1 and C2 undergoes heat exchange with the outlet gas of the expander T in the heat exchanger E3. The inlet gas to the expander T is preferably additionally heated by a supplemental heat exchange E4 which further heats the gas preheated in the heat exchange El. The heat exchanger E4 is downstream from the heat exchange El and upstream of the expander T.

Fig. 3C illustrates an embodiment wherein both expansion and compression are conducted in two stages. In this embodiment, a pair of expanders T1 and T2 and a pair of compressors C1 and C2 are each employed in series. The inlet gas of the expander T1 undergoes heat exchange with the outlet gas of the compressor C2 in the heat exchanger El. The inlet gas to the compressor C1 undergoes heat exchange with the outlet gas from the expander T2 in the heat exchanger E3. In addition, the outlet gas from the expander T1, which is the inlet gas to the expander T2, undergoes heat exchange with the outlet gas of the compressor C1, which is also the inlet gas of the compressor C2, in the intermediate heat exchange E2.A pair of supplemental heat exchangers E4, as described in connection with Fig. 38 above, are used to further heat the inlet gas to each of the expanders T1 and T2. One of the supplemental heat exchangers E4 is located between the heat exchanger El and the expander T1, and the other supplemental heat exchanger E4 is located between the heat exchanger E2 and the expander T2,- as shown in Fig. 3C.

Water and methanol are highly adsorbable to conventionally employed adsorbents. The affinity of these substances to the adsorbents is so great that desorption thereof is considered to be quite difficult. As a means of avoiding the problems of desorbing and recovering methanol completely, it is useful to cool the inlet gas to the pressure swing adsorption apparatus using the low temperature gas discharge from the expander. Under proper conditions, it is possible to adjust the temperature at the inlet of the pressure swing adsorption apparatus to as low as - 20"C, at which temperature almost all of the water and methanol in the gas can be recovered by liquefaction. Such temperature reduction is preferred in conducting the adsorption, since it accelerates the adsorption.

Figs. 4A, 4B and 4C illustrate embodiments wherein the inlet gas to the pressure swing adsorber 1 is precooled utilizing the compressor-expander arrangements shown in Figs. 3A, 3B and 3C respectively. As shown in Fig. 4A, the inlet gas to the adsorber 1 passes through a heat exchanger E5 before entering the adsorber 1. In the heat exchanger E5, the inlet gas to the adsorber 1 undergoes heat exchange with the hydrogen stream from the adsorber 1, before this stream is heated in the heat exchanger El and then fed to the expander T. The inlet gas to the adsorber 1 is also cooled by the outlet gas of the expander T. In the embodiment shown, the heat exchanger E3 is not used, and the stream consisting essentially of carbon monoxide and carbon dioxide from the adsorber 1 goes directly to the compressor C.

Fig. 4B illustrates an embodiment wherein the inlet gas to the adsorber 1 is again routed through the heat exchanger E5 to undergo heat exchange with outlet gas from the expander T and hydrogen stream from the adsorber 1, as described previously in connection with Fig. 4A above. However, the outlet gas from the expander T is branched so that part thereof flows through a heat exchanger E3 and undergoes heat exchange with the gas being fed from the outlet of the compressor C1 to the inlet of the compressor C2. The outlet gas of the compressor C2 undergoes heat exchange with the inlet gas to the expander T in the heat exchanger El, as described previously. Similarly, a supplemental heat exchanger E4 is disposed downstream from the heat exchang#er El to further heat the stream entering the expander T.

Fig. 4C illustrates an embodiment essentially similar to the embodiment of Fig. 48, except that a pair of expanders T1 and T2 are employed. The inlet gas to the adsorber 1 undergoes heat exchange in a heat exchanger E5 with the hydrogen stream from the adsorber 1 and the outlet gas from the expander T2. The hydrogen stream from the adsorber 1 is accordingly cooled in the heat exchanger E5, then sequentially heated in the heat exchangers El and E4 before entering the expander T1. The outlet gas from the expander T1 undergoes heat exchange and is heated by the outlet gas from the compressor C1 in an intermediate heat exchanger E2, and is further heated by a second supplemental heat exchanger E4 before entering the expander T2.Upon leaving the expander T2, the hydrogen stream is sent through the heat exchanger E5, as described above, and then out of the system. The stream consisting essentially of carbon monoxide and carbon dioxide flows directly from the adsorber 1 into the compressor C1. The outlet gas from the compressor C1 is sent through the heat exchanger E2, as described above, and then enters the compressor C2. The outlet gas from the compressor C2 is sent to the expander El, and is then flowed back to the synthesis loop for reuse. In general, the use of more than one expander and/or compressor in series, with corresponding heat exchangers as described above, improves the power generating efficiency of the system overall.

The temperature rise of the hydrogen stream due to adsorption in the adsorber 1 is so slight that its function of cooling the inlet gas of the compressor(s) is not impaired. Moreover, the hydrogen stream can be further heated by heat exchange before entering the expander, as described above. For these reasons, the processes illustrated in Figs. 4A, 4B and 4C can obtain the same effects as the processes illustrated in Figs. 3A, 38 and 3C. If low temperature conditions are required for the treatment in the compressor of the stream consisting essentially of the desorbed components carbon monoxide and carbon dioxide, the hydrogen stream separated therefrom is a preferable source of cooling for the inlet gas to the compressor.

However, this coolant source cannot be achieved by mere throttle expansion of the hydrogen stream. Adiabatic expansion in the expander causes a considerable decrease in the temperature of the hydrogen stream in accordance with the expansion ratio, thereby generating a suitable cooling source.

An embodiment describing a cryogenic temperature treatment of the stream consisting essentially of desorbed components, namely carbon monoxide and carbon dioxide, is illustrated by Fig. 5. The hydrogen stream from the adsorber 1 (not shown) passes consecutively through the heat exchanger 51, the expander 2, the heat exchanger 53, and back again through the heat exchanger 51. The desorbed components comprising the other stream flow consecutively through the heat exchanger 52, heat exchanger 53, and back through the heat exchanger 52 again. The hydrogen stream is cooled in the expander 2, is then warmed by heat exchange with the other stream in the heat exchanger 53, then-further cools the inlet gas to the expander 2 in the heat exchanger 51.The stream consisting essentially of desorbed components is cooled in the heat exchanger 53 and then recirculated to the heat exchanger 52 to cool the same stream before the stream enters the heat exchanger 53. The lower the inlet temperature of the expander and the higher the expansion ratio, the lower will be the temperature obtained for the hydrogen stream. On the other hand, the power generated will be reduced since the power generated by the expander is inversely proportional to the temperature of the hydrogen stream at the outlet of the expander. In general, it is relatively easy to provide an outside power source for the system, particularly for compressors, whereas it is more difficult to obtain a coolant source. Thus, priority should generally be given to obtaining a coolant source, and the embodiment of Fig. 5 was designed for this purpose.

Both rotary and reciprocating types of expanders and compressors can be used in the present invention. A preferred combination of the rotary type consists of an expansion turbine expander, a centrifugal or screw compressor, and an auxiliary driver for the compressor in the form of a steam turbine or electric motor. A combination of reciprocating expanders and compressors can be used when the process is to be carried out on a relatively small scale, and may further include an auxiliary driver, such as an electric motor or turbine. The expander(s) and compressor(s) can be disposed coaxially with each other as shown in Figs. 3A-3C and 4A-4C, but may also be disposed otherwise as shown in Fig. 6 described below.

Example 1 A specific embodiment of the process of the present invention is described in the following and is compared with a conventional process. Example 1 further includes one means according to the present invention for discharging excess hydrogen from the methanol synthesis gas. The Example according to the invention was carried out using the process apparatus shown in Fig.

1. The numerals in parentheses below refer to the corresponding reference numerals in Fig. 1.

Raw material: natural gas Reformed gas (in line 31): conventional present composition process invention CO 18.4 mol% 18.4 mol% C 2 7.4 #1 7.4 H2 72.1 " 72.1 CH4 1.3 " 1.3 N2 0.7 " 0.7 H2O 0.1 " 0.1 pressure 18 kg/cm g 18 kg/cm g flow rate 119,310 Nm3/hr 113,800 Nm3/hr Reactor inlet gas (in line 33): conventional present composition process ~ invention CO 4.8 mol% 16.5 mol% C02 3.0 " 10.3 H2 82.2 " 66.3 CH4 6.3 " 4.3 " N2 3.3 " 2.3 TI H20 0.05 " 0.05 CH3OH 0.33 n 0.3 " R 10.2 " 2.09 pressure 80 kg/cm2g 40 kg/cm2g flow rate 652,670 Nm3/hr 629,240 Nm3/hr Crude methanol (in line 35): conventional present composition process invention ::CO, CO2, H2, 0.3 mol% 0.3 mol% CH4, N2) H20 22.4 " 22.4 CH OH 77.1 " 77.1 TI C4HgOH 0.1 " 0.1 (CH3)20 0.1 " 0.1 TI flow rate 49,500 kg/hr 49,500 kg/hr Unreacted gas (in line 36): conventional present composition process ~ invention CO 1.7 mol% 10.6 mol% C02 2.0 " 12.5 H2 84.5 TI 63.9 CH4 7.4 n 8.1 N2 3.9 " 4.4 " H20 0.05 " 0.05 CH30H 0.42 " 0.42 (CH3)20 0.03 " 0.03 pressure 77.8 kg/cm2g 37 kg/cm2g flow rate 554,000 Nm3/hr 532,860 Nm3/hr Pressure swing adsorption conditions (present invention only) Inlet gas:: flow rate (in line 38) 27,420 Nm3/hr Adsorption pressure: 36 Kg/cm2g Adsorption apparatus: 4 beds pressure swing Each bed consists of upper layer containing activated carbon-supported copper aluminate complex adsorbent 24 m3 and lower layer containing Zeolite CaA 22 m3 which lower layer the inlet gas enters.

Total cycle time: 20 min.

Separated gases: composition CO and C02 stream H2 stream (in line 40) (in line 39) CO 28.4 mol% - mol% co 33.8 " s H2 25.6 " 86.8 CH4 7.2 " 8.6 N2 3.8 TI 4.6 flow rate 10,170 Nm3/hr 17,250 Nm3/hr pressure 0.4 kg/crti2g 36 kg/cm2g Separated methanol: about 160 kg/hr When the apparatus shown in Fig. 3C is used in the above embodiment, the conditions are as follows: compressor condition expander (H2) (cho, C02) gas flow rate 17,250 Nm3/hr 10,170 Nm3/hr pressure change 35#l 1 kg/cm2g 0.4#l8 18 kg/cm2g number of stages two stage two stage expansion compression inlet tempera- 1200C 0 C ture theoretical 2510 PS 1340 PS power efficiency (n) 80% 70% actual power 2010 PS 1910 PS If the inlet temperature of the compressor is 50 C, the actual power required for the compressor will be 2460 PS.This demonstrates that cooling the inlet gas to the compressor to -0 C causes the expander to supply sufficient power to drive the compressor, as indicated by the theoretical power values given above. In Example 1, the stream containing carbon monoxide and carbon dioxide was recycled to the methanol synthesis loop. However, this stream can instead be recycled to the stream reformer and then passed to the methanol synthesis loop as part of the starting synthesis gas. An example of such a process is as follows.

Example 2 In this Example, the reaction conditions in the steam reformer are kept moderate so as to permit methane to leak and be present at some concentration throughout the reformer. The inert gas content of the recycled gas in the methanol synthesis loop is kept comparatively high, and part of the recycled gas is treated by pressure swing adsorption. In contrast with Example 1, an increased amount of the recycled gas is treated in the adsorption apparatus and the synthesis pressure is increased. Fig. 6 schematically shows the apparatus used to carry out this process.

Part of the unreacted gas mixture from the methanol separator 28 is flowed through a line 38 to an expander T1. This mixture is reduced in pressure by the expander T1 and then is passed to the pressure swing adsorber 1. The pressure in the methanol synthesis loop is too high to allow the purge gas to be directly fed to the adsorber 1. An economical pressure level for the adsorber 1 should generally be selected. The adiabatic expansion of the purge gas causes almost all of the methanol present therein to be condensed, separated and passed to the adsorber 1. The amount of adsorbent used can be decreased because of the low temperature of the inlet gas to the adsorber 1.

The stream consisting essentially of carbon monoxide and carbon dioxide is fed from the adsorber 1 through a line 40 to a compressor C3. then sequentially through heat exchanger E3, compressor C2. heat exchanger El, heat exchanger E2, and compressor C1. After final compression in the compressor C1, the stream containing carbon monoxide and carbon dioxide is fed through the line 41 to a line 45 containing a feed gas comprising light hydrocarbons, and the resulting mixture is fed to the steam reformer R.

The stream consisting essentially of hydrogen is fed from the adsorber 1 through a line 39 sequentially through heat exchanger El, heat exchanger E4, expander T2, heat exchanger E2, and heat exchanger E3. The hydrogen stream then leaves the heat exchanger E3 and is discharged from the system. Heat exchange occurs between the two streams in the heat exchangers El, E2 and E3. The additional compressor C3 need only be used if the compressors C1 and C2 are not capable of fully compressing the stream containing carbon monoxide and carbon dioxide. The compressor C3 is powered by an external power source 48, such as a turbine. The power generated by the expanders T1 and T2 is fairly high because the gas mixture to be treated in the adsorber 1 is first passed through the expander T1, and the expansion ratio of the gas passing through expander T2 can be kept high.The gas composition at important stages of this embodiment of the invention is as follows: Reformed gas (at line 32): composition CO 20.1 mol% CO, 8.1 n H2 65.7 CH4 5.0 N 1.1 TI pressure 18 kg/cm g flow rate 139,290 Nm3/hr Reactor inlet gas (at line 33): Unreacted gas (at line 36): composition CO 11.4 molE 9.1 mol% C02 10.7 " 11.4 H2 56.9 " 54.4 88 CH4 17.2 TI 20.6 TI N2 3.8 n 4.5 II R = 2.09 pressure 50 kg/cm2g 47 kg/cm 2g flow rate 649,290 Nm3/hr 543,800 Nm3/hr Pressure swing adsorotion equipment inlet (at line 38!: Gas flow rate: 33,750 Nmjihr Adsorption pressure: 17 Kg/cm2g Adsorption apparatus: 5 beds pressure swing Each bed consists of upper layer containing activated carbon 85 m3 and lower layer containing Zeolite CaX 25 m3 which lower layer the inlet gas enters.

Total recycle time: 25 min.

Separated gases: composition CO and C02 stream H2 stream CO 19.3 mol% - mol% CO, 24.2 TI H2 17.2 " 87.6 '1 CH4 35.2 TI 7.6 N2 4.1 " 4.9 pressure 0.4 kg/cm2g 16 kg/cm2g flow rate 15,900 Nm3/hr 17,850 Nm3/hr The thermal efficiency of the steam reformer is remarkably increased by employing moderate operating conditions in the steam reformer. This reduces the costs of the reforming operation. In this example, the synthesis pressure was raised to 50 kg/cm2g because of the inert gas present in the synthesis loop.

As has been described above, the present invention provides a process for purging excess hydrogen from a methanol synthesis loop when needed, thereby allowing the index R to be adjusted at a desired level. Excess hydrogen in the methanol synthesis gas is not strictly an inert gas and affects the equilibrium of the reaction to some degree. Therefore, some excess hydrogen is preferred, and particularly a gas composition wherein R is in the range of 2.0 to 2.5 at the inlet of the methanol synthesis reactor is most desirable.

The advantages of the present invention are extremely remarkable and are summarized as follows: (1) The synthesis pressure can be greatly reduced according to the present invention, as compared to the currently employed pressures of 60-80 kg/cm2g. According to the invention, the methanol synthesis pressure is preferably in the range of 25-100 kg/cm2g, and the most preferable pressure range is 30-50 kg/cm2g.

(2) As a result of the lower synthesis pressure, the power required for compressing the synthesis gas can be greatly reduced. Although there is a need for increased power required for compressing the recovered carbon monoxide and carbon dioxide stream, the extent of this increase is slight. The power used for circulating the unreacted gas is also reduced so that the overall power requirements are remarkably reduced as compared to conventional processes.

(3) According to the invention, it is possible to reduce the amount of gas that is purged from the system by recovering and recycling carbon monoxide and carbon dioxide which are generally lost with the purge gas according to conventional processes. The overall yield of methanol can accordingly be increased.

(4) Methanol present in the purge gas, which is lost in conventional processes, can be mostly recovered according to the present invention by either cooling the purge gas before it is introduced into the pressure swing adsorber or cooling the desorbed carbon monoxide and carbon dioxide stream using the low temperature hydrogen stream from the expander.

(5) The steam reforming equipment used in a conventional methanol plant employs high temperatures for reducing the residual methane content to the greatest possible extent, and for correcting carbon shortage (or hydrogen excess) in the synthesis gas. Fresh synthesis gas for methanol synthesis usually contains about 1 % methane. However, the concentration of methane in the circulating synthesis gas is fairly high because the amount of the hydrogen purge is extremely limited in conventional processes.

In the present invention, the problem of synthesis pressure is almost completely solved by correcting the hydrogen excess, so that a high methane concentration in the circulating gas, up to certain level, becomes permissible. As noted previously, the stream containing carbon monoxide and carbon dioxide can be fed to the steam reformer to reform methane therein and lower the concentration thereof, with the result that a methane concentration as high as 2 to 3% is allowable in the fresh synthesis gas. This advantage will allow design simplification and cost reduction of the reforming reactor.

The correction of the hydrogen excess also lowers the steam-to-carbon ratio (S/C) in the steam.reforming reaction, thus conserving the energy required for that reaction. If the stream containing carbon monoxide and carbon dioxide is recycled to the steam reformer, it is important that the pressure swing adsorber be designed to adsorb methane as well as carbon dioxide and carbon monoxide, but to not adsorb much nitrogen.

(6) The foregoing advantages (1) to (5) allow cost reduction. Decreasing the overall synthesis pressure lowers the design pressure of pressure vessels, pipings, and equipment such as compressors. The reduction of compression power will reduce the cost of the power plant, while the decrease in the amount of synthesis gas needed and the recovery of methanol will also reduce the overall cost of the plant. The permissibility of a fairly high concentration of residual methane in the reformed gas will also lower the cost of the reforming equipment. On the other hand, the preferred embodiments of the present invention require pressure swing adsorption equipment, a hydrogen expander, a compressor for the carbon monoxide and carbon dioxide stream, and related accessory parts. However, the additional cost of such equipment is more than outweighed by the savings achieved as described above. Thus, efficient methanol production can be accomplished less expensively according to the process of the present invention.

Claims

1. A process for producing methanol, including the steps of subjecting light hydrocarbons to steam reforming to produce a methanol synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide, feeding said synthesis gas to a methanol synthesis reactor to produce methanol, then cooling said synthesis gas to condense the methanol, separating the methanol from the unreacted gas, and recycling the unreacted gas together with fresh synthesis gas to said methanol reactor, and wherein the value of R in the equation R = (H2402)/(CO + CO2), (H2, CO and CO2 representing the mol percent amounts of hydrogen, carbon monoxide and carbon dioxide, respectively, in the gas field to the methanol synthesis reactor), is adjusted to a selected value by purging a portion of the gas to be fed to or from the methanol synthesis reactor, then separating the purged gas into a first gas stream consisting essentially of hydrogen and a second gas stream consisting essentially of carbon monoxide and carbon dioxide by pressure swing adsorption, discharging said first stream from the methanol synthesis process, and recycling said second stream to said methanol synthesis reactor.

2. A process as claimed in claim 1, comprising the additional steps of pressurizing said second gas stream in a compressor before recycling said second stream to the methanol synthesis reactor, expanding said first stream in an expander and thereby generating power, e.g.

electrical power, and powering said compressor using the power generated by said expander.

3. A process as claimed in claim 2, comprising the additional steps of heating said first stream before said first stream is fed to said expander by flowing said first stream in indirect heat exchange relationship with said second stream after said second stream has been discharged from said compressor, and cooling said second stream before said second stream is fed to said compressor by flowing said second stream in indirect heat exchange relationship with said first stream after said first stream has been discharged from said expander.

4. A process as claimed in claim 2 or claim 3, comprising the further step of cooling said purged gas, before said purged gas enters said pressure swing adsorber, by flowing said purged gas in indirect heat exchange relationship with said first stream after said first stream has been discharged from said expander.

5. A process as claimed in any of claims 1 to 4, comprising the further step of substantially adiabatically expanding said purged gas in an expander to reduce the pressure thereof and lower the temperature thereof before feeding said purged gas into said pressure swing adsorber.

6. A process for removing hydrogen from a pressurized gaseous mixture containing hydrogen, comprising the steps of: subjecting said gaseous mixture to pressure swing adsorption to thereby separate said gaseous mixture into a first stream consisting essentially of hydrogen and having a pressure substantially the same or slightly less than the pressure of said gaseous mixture, and a second stream consisting essentially of gases adsorbed during said pressure swing adsorption, said second stream having a pressure substantially equal to the desorption pressure; feeding said first stream to an expander wherein said first stream is reduced in pressure under substantially adiabatic conditions and generating power from the expansion of said first stream in said expander;; feeding said second stream to a compressor effective to pressurize said second stream under substantially adiabatic conditions; and operating said compressor with the power generated by said expander.

7. A process as claimed in claim 6, comprising the further step of cooling said second stream before said second stream is fed to said compressor by flowing said second stream in indirect heat exchange relationship with said first stream after said first stream has left said expander.

8. A process as claimed in claim 6 or claim 7, comprising the further step of heating said first stream, before said first stream is fed to said expander, by flowing said first stream in indirect heat exchange relationship with said second stream after said second stream has left said compressor.

9. A process as claimed in claim 6, 7 or 8, comprising the further step of cooling at least one of (1) said second stream before said second stream is fed to said compressor, and (2) said gaseous mixture before said gaseous mixture is subjected to pressure swing adsorption, by means of indirect heat exchange with said first stream after said first stream has left said expander.

10. A process as claimed in any of claims 6 to 9, wherein said gaseous mixture consists essentially of hydrogen, carbon monoxide, and carbon dioxide, and said second stream consists essentially of carbon monoxide and carbon dioxide.

11. A process according to claim 1 and substantially as hereinbefore set out in Example 1 or Example 2.

12. A process according to claim 1 or claim 6 and substantially as herein described with reference to the accompanying drawings.

13. Methanol synthesis plant for performing the process of claim 1, substantially as herein described with reference to any of the accompanying Figs. 1 to 6.