GB2046779A

GB2046779A - Process for gasification of ethanol

Info

Publication number: GB2046779A
Application number: GB7921685A
Authority: GB
Original assignee: SAO PAULO GAS
Current assignee: SAO PAULO GAS
Priority date: 1979-04-16
Filing date: 1979-06-21
Publication date: 1980-11-19
Also published as: GB2046779B; AU4776479A; AR220381A1; FR2454427A1; JPS55144093A; ZA792841B

Abstract

A mixture of ethanol and steam is passed over a gasification catalyst at 300 to 600 DEG C and 1 to 100 Kg/cm<2> using a steam to ethanol ratio by weight of 0.5:1 to 3.0:1 to produce a mixture of hydrogen, carbon monoxide and dioxide, methane and steam. The catalyst is one which is capable of gasifying hydrocarbons at 350 to 600 DEG C and preferably is nickel-based.

Description

SPECIFICATION Process for gasification of ethanol This invention relates to a catalytic process of making a gaseous mixture composed of H2, CO, CO2, CH4 and H2O(v) from ethanol.

The catalytic gasification at temperatures between 500"C and 800"C with steam of raw materials originating from petroleum and containing mainly paraffinic hydrocarbons having 4 to 20 carbon atoms has been known for some time. This process has been modified in such way that it could operate at lower temperature level, between 350"C and 600"C, in order to obtain a gas mixture rich in methane. Various patents describe such processes which differ from each other mainly in the type of catalyst used. The only prior art catalytic gasification with steam of non-hydrocarbons is methanol gasification.

It has now been found that ethanol can be gasified with steam using a catalyst which is capable of gasifying hydrocarbons at low temperature (350-600"C). Characteristic of the process is the fact that the vaporized ethanol-steam mixture enters the catalytic bed at a temperature not lower than 300"C and the product leaves at a temperature not higher than 600"C. The operating pressure may vary between 1 and 100 kg/cm2, the most convenient level between 10 and 40 kg/cm2.

It has been established that the gasification reaction of ethanol with steam on a nickel based catalyst produces a gaseous mixture in accordance with the general equation: C2H2OH + x.H2O < a.CO + b.CO2 + c.CH4 + d.H2 + e.H2O(v) (1) which occurs in the first levels of the active catalyst bed. The components of the gaseous mixture produced then react amongst themselves through the remainder of the bed according to the reactions: CO + H2OtCO + H2 (2) CH4 + H2OtCO + 3H2 (3) The composition of the gas mixture obeys the thermodynamic equilibrium of reactions (2) and (3) for the pressure and temperature exit conditions of the catalyst bed.As the overall reaction is governed by considerations of thermodynamic equilibrium, the composition of the gas mixture produced depends on the ratio of steam to ethanol fed into the reactor.

Possible other reactions which should be avoided are: 2COtC + CO2 (4) CO + H2tC + H2O (5) CH4C + 2H2 (6) These reactions, if they occur, provoke deposition of carbon on the catalyst followed by the latter's rapid deactivation. They are avoided by operating with a ratio of steam to ethanol fed into the reactor such that the ratio of steam to carbon present in the ethanol is above the minimum thermodynamic ratio which makes these reactions possible.

Any catalyst which promotes the reactions (1), (2) and (3) is adequate for the process of the invention; the principal requirements being: activity in relation to the reaction (1), (2) and (3); large surface area in order to obtain a high reaction rate at the relatively low temperature at which the process operates; resistance to sintering under the conditions at which the process operates; low activity in relation to reaction (4), (5) and (6); high activity in relation to reactions (5) in the sense of carbon removal or in the sense of CO and H2 formation.

Catalysts active in relation to the reactions (2) and (3) have been known for some time, the most common ones being nickel based.

It has been found that the same nickel-based catalyst used in the catalytic gasification of hydrocarbons with steam at low temperature or for methanation of gases containing a high content of carbon oxides are active in relation to reaction (1) and fulfil all the other catalyst requirments mentioned above. Thus the catalysts described in British Patent No.923385, German Patent No. 1545420, Japanese Patent No. 7880/1971 and British Patent No.

1055909, in connection with gasification or hydrocarbons with steam at low temperature, are adequate for the process of the present invention. Similarly, the catalysts for methanation of gases which contain substantial amounts of carbon oxides can be used in the process of the present invention in the same way as these catalysts are used for the gasification of hydrocarbons at low temperature according to British Patent No. 11 52009 and U.S. Patent No, 3912775.

It has been found that if the temperature at any point of the catalyst bed falls below approximately 300"C, the gasification reaction of ethanol degenerates into simultaneous reactions and carbon formation. When this occurs the formation of the gaseous mixture gradually ceases and carbon deposition causes rapid catalyst deactivation. Further, it has been found that if the temperature exceeds approximately 600"C the catalyst life abruptly diminishes due to sintering.

The ranges of operation parameters considered adequate for the process of the present invention are: 1) operating pressure: 1 to 100 Kg/cm2 2) temperature in catalyst bed: 300"C to 600"C 3) steam to ethanol ratio: 0.5 Kg/Kg to 3.0 I < g/l < g.

Generally speaking the overall gasification reaction of ethanol with steam is exothermic in the above ranges. The lower the temperature entering the bed and the lower the steam/ ethanol ratio fed into an adiabatic fixed bed gasifier, the higher will be the exothermicity of the reaction.

If because of sufficiently low inlet temperature and steam/ethanol ratio, the temperature of the catalyst bed is likely to exceed 600"C, then the surplus heat must be absorbed, for example by one or more of the following methods:- a) enclosing the reactor in a jacket of cooling water; b) using a reactor with an internal heat exchanger which will use the surplus reaction heat for steam generation and/or preheating and vaporization of the ethanol; c) recycling part of the reaction product to the inlet of the gasifier; d) carrying out the gasification in two or more stages with cooling of the reaction product between the stages; and e) mixing ethanol vapor with the product gas resulting from a first stage gasification and introducing it into a second catalytic bed which contains the same type of catalyst.

Suitably, the ethanol starting material is anhydrous ethanol or ethanol containing up to 5% by weight water.

The ethanol and water can be simultaneously or separately vaporized and superheated before being introduced into the catalytic bed.

In one embodiment of the invention, additional vaporized ethanol is added to the gaseous reaction product of a first gasification stage and the resultant mixture fed to a second gasification stage.

It is preferred that the gasification process of the invention is carried out under substantially adiabatic conditions.

The present invention also provides in a further aspect, a process of producing a synthetic natural gas which comprises gasifying ethanol with steam by the gasification process of the invention, cooling the gaseous gasification reaction product to a temperature in the range 250 to 350"C, subjecting the cooled gaseous product to catalytic methanation in manner known per se; and removing carbon dioxide from the gaseous methanation product.

In another aspect, the present invention provides a process of producing a town gas which comprises gasifying ethanol with steam by the gasification process of the invention, passing a proportion of the gaseous gasification reaction product together with additional steam through a steam reformer containing a methane reforming catalyst and operating at a temperature in the range 500 to 850"C and combining the reformed gaseous product with the remainder of the gaseous gasification reaction product to provide a town gas having a calorific value in the range 4000 to 6000 Kcal/Nm3.

Another aspect of the present invention provides a process of producing a gas for use in the production of alcohols, ammonia, hydrogen which comprises gasifying ethanol with steam by the gasification process of the invention and passing the gaseous gasification reaction product together with additional steam through a steam reformer containing a methane reforming catalyst and operating at a temperature in the range 500 to 950"C.

Yet another aspect of the present invention provides a process of producing a town gas which comprises gasifying ethanol with steam by a gasification process of the invention and subsequently removing unreacted steam from the gaseous gasification reaction product to provide a town gas having a calorific value in the range 4000 to 5000 Kcal/Nm3.

The following Examples are given to illustrate the process of the present invention. They are however not meant to limit the scope of the invention as defined in the Claims.

The catalyst used in the Example was a nickel catalyst having the approximate composition given in Table I below: Table I - Approximate composition of the nickel catalyst Components Content by weight Ni 56.5 - 59.5% Na + K 0.6 - 0.8% Na 0.2% S 0.04% Awl202 42.66 - 39.546% Example 1 The catalyst (0.3cm X 0.3cm) was placed inside a reactor of a pilot plant which had been constructed exclusively for tests concerning this invention. Initially the catalyst bed was heated in a stream of gaseous nitrogen to a temperature of 400"C under a pressure of 24 kg/cm2.

Then the nickel oxide contained in the catalyst was reduced to metallic nickel by a stream of 50% hydrogen and 50% nitrogen, at an initial temperature of 400"C and a final temperature of 550"C. A vaporized ethanol and superheated steam mixture in a proportion of 2.0 mols of H2O/atg of C in ethanol at a temperature of 400"C was fed into the reactor. With an outlet temperature of 480"C, a gas mixture of the following composition on a dry volume basis was obtained: CO: 0.40% CO2: 24.07% CH4: 52.58% H2: 22.95% Maintaining the same inlet conditions, the same outlet conditions were obtained during a period of 827 hours of continuous operation.

Example 2 In a second series of experiments under the same conditions as Example 1 and during a period of 1073 hours of continuous operating, a gas mixture was obtained with the following average composition in dry volume basis: CO: 0.43% CO2: 23.18% CH4: 56.49% H2: 20.48% It was observed in these two series of experiments of Examples 1 and 2 that the ethanol gasification was completed in the first layers of the catalyst bed and, due to the reaction being strongly exotheric, the temperature at this point rapidly reached 510"C. Since the pilot plant reactor was not thermally insulated in an adequate way, the temperature across the catalyst bed gradually fell along the bed until it reached 480"C. The lack of adequate thermal insulation of the reactor was intentional in order to check whether the gas mixture formed in the first layers of the bed would react according to the reactions (2) and (3).This was confirmed by the composition of the gas mixture in the two series of experiments being consistent with the thermodynamic equilibrium of the reactions (2) and (3) at a temperature of 480"C.

The process which is the object of the this invention can be applied to the production of a number of products which now are obtained from fossil raw materials or their derivatives, for example synthetic natural gas, town gas, ammonia and methanol. High capitol costs have made the production of these products from coal and shale oil almost prohibitive and at the same time the production from derivatives of petroleum has been sharply reduced in countries which do not produce petroleum.

The process of this invention presents advantages for countries or places which are confronted by the above mentioned limitations. The capitol costs in a plant using the process of the invention would be substantially lower than said alternative plants with the additional advantage that the ethanol can be obtained from renewable sources such as sugar cane.

The accompanying drawings show schematic flow-sheets that illustrate the present invention.

In the drawings: Figure 1 shows a flowsheet illustrating the production of ammonia from ethanol. Since the ammonia synthesis pressure is about 300 Kg/cm2, it is convenient that the ethanol gasification takes place at high pressure (e.g. 30 Kg/cm2). Item (1) is the gasification reactor in which is disposed a fixed bed of nickel catalyst. Downstream of it is disposed the rest of the plant identified as item (2). The vaporized ethanol plus superheated steam in proportion of approximately 1.5 Kg of stem/Kg of ethanol, under pressure, enters the gasification reactor at 400"C.

The gas mixture formed leaves at 500"C. From this point onwards the process is identical to several other methane steam reforming processes for producing ammonia.

Figure 2 refers to the possibility of producing methanol from ethanol. The stage of ethanol gasification is the same as above. Item (2) is one of several methane steam reforming processes for producing methanol.

Figure 3 shows the possibility of producing synthetic natural gas (SING) from ethanol. Since one of the major applications of SNG is as piped fuel, it is convenient, for economy of storage and transmission over long distances, that the gasification of ethanol occurs at high pressure (e.g. 30 Kg/cm2). The vaporized ethanol is mixed in a proportion of approximately 1.5 Kg of superheated steam/Kg of ethanol and under pressure the mixture enters the gasification reactor (1) at approximately 400 C. The gas mixture formed leaves at 500"C. From this point onwards any of the various routes possible for obtaining SNG from liquid petroleum gas, naphtha steam reforming can be used.

Figure 4 shows a flowsheet illustrating the production of town gas from ethanol. The ethanol is mixed with superheated steam in a proportion of approximately 2.35 Kg of steam/Kg of ethanol and, under pressure, enters the gasifier (1) at a temperature of approximately 540"C.

The gas mixture formed leaves at 560"C with the following composition in dry volume: CO: 1.94% CO2: 23.54% CH4: 33.11% H2: 41.41% Kcal and with a heating value above 4.400 Nm3 The correction to a declared heating value may be achieved through injection, for example, of liquid petroleum gas (3) into the main gas stream. Items (2) and (4) are waste heat boilers used for steam raising.

Claims

1. A process for the gasification of ethanol with steam by passing an ethanol and steam mixture over a catalyst in a catalytic bed, wherein: (a) the ratio by weight of steam to ethanol is in the range 0.5:1 to 3.0:1; (b) the operating pressure in the catalytic bed is in the range 1 to 100 Kg/cm2; (c) the minimum inlet temperature to the catalytic bed is 300"C; (d) the maximum inlet temperature from the catalytic bed is 600"C; (e) the temperature in the catalytic bed does not exceed 600"C; and (f) the catalyst is capable of gasifying hydrocarbons at 350 to 600"C.

2. A process as claimed in Claim 1 wherein the catalyst is a nickel-based catalyst.

3. A process as claimed in Claim 2 wherein the catalyst consists essentially of nickel and aluminium oxide.

4. A process as claimed in Claim 3 wherein the catalyst has substantially the following composition: Ni 56.5-59.5% by weight Na + K 0.6- 0.8% by weight Na 0.2% S 0.04% Awl203 42.66 to 39.546%

5. A process as claimed in any one of the preceding Claims wherein substantially adiabatic conditions are maintained in the catalytic bed.

6. A process as claimed in any one of the preceding Claims wherein ethanol and water are simultaneously vaporized and superheated before being introduced into the catalytic bed.

7. A process as claimed in any one of Claims 1 to 5 wherein ethanol and water are separately vaporized and superheated before being introduced into the catalytic bed.

8. A process as claimed in Claim 7 wherein the ethanol is anhydrous ethanol.

9. A process as claimed in Claim 7 wherein the ethanol contains up to 5% by weight water.

1 0. A process as claimed in any one of the preceding Claims wherein the gaseous reaction product of a first gasification stage is supplied with additional vaporized ethanol to a second gasification stage.

11. A process as claimed in any one of Claims 1 to 9 wherein hydrogen or a proportion of the gaseous gasification reaction product is recycled with additional ethanol and steam through the catalytic bed.

1 2. A process as claimed in any one of the preceding Claims wherein the catalytic bed is cooled by an internal heat exchanger in which the ethanol and/or steam supplied to the bed is preheated.

1 3. A process as claimed in any one of Claims 1 to 11 wherein the catalytic bed is cooled by a cooling water jacket which generates directly or by further heat exchange steam supplied to the bed.

14. A process as claimed in any one of the preceding Claims wherein the gasification is conducted in two or more stages with the gaseous reaction product of each stage being cooled before admission to the next stage.

1 5. A process as claimed in Claim 1 and substantially as hereinbefore described.

1 6. A gaseous mixture of hydrogen, carbon monoxide, carbon dioxide, methane and steam whenever prepared by a process as claimed in any one of the preceding Claims.

1 7. A process of producing a synthetic natural gas which comprises gasifying ethanol with steam by a process as claimed in any one of Claims 1 to 16, cooling the gaseous gasification reaction product to a temperature in the range 250 to 350"C; subjecting the cooled gaseous product to catalytic methanation in manner known per se; and removing carbon dioxide from the gaseous methanation product.

1 8. A process of producing a town gas which comprises gasifying ethanol with steam by a process as claimed in any one of Claims 1 to 16, passing a proportion of the gaseous gasification reaction product together with additional steam through a steam reformer containing a methane reforming catalyst and operating at a temperature in the range 500 to 850'C and combining reformed gaseous product with the remainder of the gaseous gasification reaction product to provide a town gas having a calorific value in the range 4000 to 6000 i < cal/Nm3.

1 9. A process of producing a gas for use in the production of alcohols, ammonia, hydrogen which comprises gasifying ethanol with steam by a process as claimed in any one of Claims 1 to 1 6 and passing the gaseous gasification reaction product together with additional steam through a steam reformer containing a methane reforming catalyst and operating at a temperature in the range 500 to 950"C.

20. A process of producing a town gas which comprises gasifying ethanol with steam by a process as claimed in any one of Claims 1 to 1 6 and subsequently removing unreacted steam from the gaseous gasification reaction product to provide a town gas having a calorific value in the range 4000 to 5000 Kcal/Nm3.

CLAIMS (16 Nov 1979)

1. A process for the gasification of ethanol with steam by passing an ethanol and steam mixture over a catalyst in a catalytic bed, wherein: (a) the ratio by weight of steam to ethanol is in the range 0.5:1 to 3.0:1; (b) the operating pressure in the catalytic bed is in the range 1 to 100 Kg/cm2; (c) the minimum inlet temperature to the catalytic bed is 300"C; (d) the maximum outlet temperature from the catalytic bed is 600"C; (e) the temperature in the catalytic bed does not exceed 600"C; and (f) the catalyst is capable of gasifying hydrocarbons at 350 to 600"C.