US3433609A - Process for the production of gases containing methane from hydrocarbons - Google Patents

Description

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l l ,r /Ar Af G. PERCIVAL ET AL Filed March 20. 1964 METHANE FROM HYDROCARBONS March 1.8, 1969 Ffg. 9.

United States Patent Office 3,433,009 Patented Mar. 18, v1969 3,433,609 PROCESS FOR THE PRODUCTION OF GASES CON- TAINING METHANE FROM HYDRO'CARBONS George Percival and Thomas Alan Yarwood, Solihull,

England, assignors to The Gas Council, London, England, a British body corporate Filed Mar. 20, 1964, Ser. No. 353,381 U.S. Cl. 48--214 15 Claims Int. Cl. C07c 3/42; C101 3/00; B01j 9/04 ABSTRACT OF THE DISCLOSURE This invention is directed to a process for the production of gases containing methane by preparing a mixture of paraftinic hydrocarbons containing an average of 4-15 carbon atoms and steam, preheating the mixture to at least 350 C. and passing the mixture at a pressure of at least one atmosphere, at a linear velocity not exceeding 0.3 foot per second and a space velocity of at least 400 volumes per volume per hour through a bed of nickel-alumina catalyst maintained at temperatures of `from 400 C. to 600 C. whereby substantially no carbon is deposited on the catalyst. Optionally, the catalyst may contain an oxide, hydroxide or carbonate of an alkali metal or alkaline earth metal or of magnesium.

In British specification No. 820,257 there is described and lclaimed a process for the production of gasses containing methane from mixtures of predominantly paratlinic hydrocarbons containing an average of 4 to 10 carbon atoms, wherein the vapour of the hydrocarbons and steam are passed through a bed of a nickel catalyst -under atmospheric or superatmospheric pressure, and the hydrocarbon vapour and steam are passed into the catalyst bed at a temperature above 350 C. lsuch that the bed is maintained by the reaction at a temperature within the range of 400 C. to 550 C. The reactions cause different temperatures to be established in different rregions of the catalyst bed, so that the temperature varies throughout the catalyst, but according to the invention of specification No. 820,257, the lowest temperature is 400 C. or above and the highest temperature is 550 C. or below.

The pressure may be up to 50 atmospheres, but may be higher, if desired. Convenient pressures are within the range of to 25 atmospheres.

In order to avoid the deposition of carbon on the catalyst it is necessary that the proportion of steam relatively to hydrocarbons shall be greater than that which enters into reaction. The excess of steam required for this purpose depends on the average molecular weight of the hydrocarbons used and increases with an increase in molecular weight. However, the excess is not great and 2 parts by weight of steam to 1 part by weight of hydrocarbons can be used with all mixtures of hydrocarbons containing an average of 4 to 10 carbon atoms; a larger proportion, up to 5 parts by weight of steam to 1 part by weight of hydrocarbons may be used if desired. With hydrocarbon mixtures containing an average of 4 to 7 carbon `atoms the proportion of steam may be as low as 1.5 parts by weight.

In conjunction with these proportions of steam to hydrocarbon mixture, as described in our prior specification, whereas the lower temperature limit of 400 C. was specified to minimise loss of catalyst activity, the upper limit of 550 C. was specied to avoid deposition of carbon on the catalyst. However, further experimentation has shown that it is possible to carry out the reaction with a part of the catalyst bed at a temperature of above 550 C. for example, 558 C.; temperatures of, for example, up to 575 C. or 600 C. can be established without deposition of carbon on or loss of life of, the catalyst, or other adverse effect. Such temperature conditions are particularly likely to be encountered when preheat temperatures are substantially above 350 C. for example, 500 C. and when the steam to distillate ratio is low. The preheat temperature is always at least 350 C. -to ensure sufficient catalyst activity.

The lower the temperature of the catalyst bed the higher is the content of methane in the gas produced, and the higher the pressure the higher is the methane content. The gas produced, after the removal of carbon dioxide and water vapour therefrom, will generally contain at least 50 percent by volume of methane, and the concentration of methane may exceed percent under a relatively higher pressure, such as 50 atmospheres.

The-catalyst is a coarsely particulate, -for example, granulated or pelleted, nickel alumina catalyst that has for example been prepared by coprecipitating nickel and aluminum compounds by treating an aqueous solution of water-soluble salts, for example, the nitrates, of nickel and aluminum with an alkali, such as sodium carbonate, and reducing the nickel compound in the precipitate to metallic nickel.

It has been found that, in carrying out the hydrocarbonsteam reaction by passing the vapour of the hydrocarbons and steam through the bed of the coarsely particulate nickel-alumina catalyst at a rate such that the gaseous mixture passes through the bed -at a reasonably high linear velocity within the range of about 1 to 2 feet per second, the life of the catalyst is somewhat limited, probably owing to the deposition of polymerisation products thereon. The limitation in the life of the catalyst is greater the higher the average molecular weight of the hydrocarbon mixture used. The present invention is based on the observation that the life of the catalyst in that reaction can be considerably increased by lowering the linear velocity at which Ithe -gaseous mixture passes through the catalyst bed. It has also been found that this expedient enables mixtures of hydrocarbons to be treated having higher average molecular weights than those used in the process of the aforesaid specification, Afor example kerosene having an average number of carbon atoms of 11.5, a boiling range of C. to 280 C., and a specific gravity of 0.79 at 20 C.

Accordingly, the present invention provides a process for the production of gases containing methane from mix-tures of predominantly paraflinic hydrocarbons containing an average 4of 4 to l5 carbon atoms, wherein a mixture of the vapour of the hydrocarbons and steam, at a temperature of at least 350 C. is passed under atmosphereic or superatmospheric pressure at a linear velocity not exceeding 0.3 foot per second (as hereinbefore defined) and a space velocity of at least 400 volumes per volume per hour through a bed of a particulate nickel alumina cat-aylst, whereby the bed is maintained at temperatures of from 400 C. to 600 C. or 575 C. or 550 C., when substantially no carbon deposition takes place on the catalyst. Under normal operating conditions no carbon deposition takes place on the catalyst. The linear velocity is advantageously within the range of 0.01 to 0.3 foot per second.

The term linear velocity is used herein to denote a velocity calculated by measuring the volume of the mixture entering the bed in unit time and the volume of the mixture leaving the bed in unit time, correcting the volumes for the dierence in temperature between the ingoing and outgoing mixtures, taking the mean of these volumes, and calculating the linear velocity from the mean volume (regarding the vessel containing the catalyst as being empty for this calculation).

The term space velocity is used herein to denote the total volume of reactants, adjusted to standard temperature and pressure conditions, passed per hour into the catalyst bed per unit of reactor volume that is packed with catalyst.

The average number of carbon atoms in the hydrocarbon mixtures referred to herein is determined by `determining the average molecular weight of the mixture of hydrocarbons by measuring the depression in the freezing point of pure benzene caused by dissolving a given quantity of the mixture therein, and estimating the number of carbon atoms present in the average hydrocarbon molecule by analysing the mixture by powder chromatography to determine the relative proportions by volume of the parafnic olelinic and aromatic hydrocarbons present in the mixture.

An improvement in the process of specification No. 820,257 consists in using a nickel-alumina catalyst of the kind described above, but which contains an addition of an oxide, hydroxide or carbonate of an alkali metal or alkaline earth metal or of magnesium preferably from 0.75 to 8.6 percent calculated as metal on the combined weight of the nickel and alumina. Especially advantageous is an addition of potassium carbonate. The effect of the addition of such alkaline compound is to increase the life of the catalyst. The process of the present invention may be carried out with such a catalyst or with a nickel-alumina catalyst containing no addition of an alkaline compound as aforesaid.

In order to achieve in the process of this invention a high rate of output of methane-containing gas at a given space velocity, notwithstanding the relatively low linear velocity of the gaseous mixture passing through the catalyst bed, it will generally be desira-ble to increase the volume of gaseous mixture treated in unit time by increasing the cross sectional area of the bed through which the gaseous mixture is passed. To this end the catalyst bed may take the form of a plurality of beds through which the gaseous mixture is passed in parallel. Alternatively, the catalyst bed may be of an elongated, tubular form through which the gaseous mixture is passed in a radial direction from the inner periphery of the bed to the outer periphery thereof or in the reverse direction. If desired, a plurality of such tubular beds may be used through which the gaseous mixture is passed in parallel.

It has also been found that it is of advantage in the process of this invention to use the catalyst in the form of particles having a size within the range of 150 to 1,000 microns, which is considerably smaller than the size generally used with the usual linear velocities, for example, particles of 1A to 1/6 inch at linear velocities of 1 to 2 feet per second. The effect of using catalyst particles of the aforesaid small size is to increase the life of the catalyst, as indicated by the period from the initial introduction of the hydrocarbon-steam mixture into the catalyst bed to the time at which undecomposed hydrocarbon is lirst detected in the issuing gases, as compared with the use of larger particles at velocities not exceeding 0.3 feet per second and at the usual high velocities.

Previously, the preferred proportion of metallic nickel in the catalyst was within the range of 28 to 75 percent calculated on the combined weight of metallic nickel and alumina. Nickel-alumina catalysts having nickel contents higher than 75 percent (calculated on the above basis) are of somewhat lower mechanical strength, so that at the usual linear velocities there is a risk of disintegration of the particles and dust formation and a consequent increase in the resistance of the bed to the flow of gases therethrough. This applies not only to the nickel-alumina catalysts containing an addition of an alkaline compound, but also to nickel-alumina catalysts having no such addition.

It has been found advantageous to use in the process of this invention nickel-alumina catalysts, which have been prepared by coprecipitation followed by reduction of the nickel compound as referred to above, and which contain a proportion of metallic nickel higher than 75 and not more than 90 percent calculatd on the combined weight of the nickel and alumina. These catalysts may or may not contain an addition of an alkaline compound as described above. The proportion of nickel is preferably within the range of 80 to 85 percent calculated on the above basis.

An increase in the nickel content would be expected to increase the life of the catalyst, but it has been found that in the process of this invention the increase in the life of the catalyst is greater than would be expected from the increase in nickel content. Catalysts having the aforesaid higher nickel contents also have the advantage that the cost of recovering the nickel from such catalysts, when they have to be replaced or for any other reason, is lower than for catalysts having lower nickel contents.

Examples of such methods of achieving a high rate of output of methane-containing gas are described below with reference to the accompanying drawings, in which FIGURE l shows in longitudinal section a pressure vessel having a plurality of catalyst beds through which the gaseous mixture is passed in parallel, and

FIGURE 2 shows in longitudinal section a pressure vessel containing a catalyst bed of tubular form through which the gaseous mixture is passed in a radial direction from the interior to the exterior of the bed.

As shown in FIGURE l, a pressure vessel 1 is provided with a centrally arranged tube 2, which is open at the top and closed at the bottom, and is surrounded by a casing 3. Between the outer side of the tube 2 and the inner side of the side wall of the casing 3 are mounted a plurality of catalyst units 4, each of which consists of a perforated tray 5 and a partition 6 above, and a partition 7 below the tray, the partitions being joined to the tube 2 and casing 3 in a gas-tight manner. In the case of the uppermost unit 4 the partition 6 constitutes the top of the casing 3. Each tray 5 supports a catalyst bed 8 of a convenient depth.

The preheated mixture of hydrocarbon vapour and steam is introduced into the tube 2 at 9, and is divided into parallel streams that pass through ports 10 in the tube 2 into the spaces above the catalyst in the units 4. Each gaseous stream passes downwardly through a catalyst bed into the space beneath the latter and emerges through ports 11 in the casing 3 into an annular space 12, where the streams unite and nally issue from the pressure vessel through its outlet 13. The partitions 6 and 7 ensure the flow of the gas along the required path. Instead of providing two partitions between each pair of adjacent units 4, a single partition may be used to serve both as an upper and a lower partition.

Alternatively, the tube 2 may be open at the bottom and closed at the top, so that the mixture of hydrocarbon vapour and steam is introduced into the bottom of the tube. The product gases may issue from the top or the bottom of the pressure vessel.

As shown in FIGURE 2, a pressure vessel 20 is provided with a centrally arranged catalyst carrier 21 which is formed by two coaxial Iperforated tubular members 22 and 23, which may be right cylinders or frustra of cones. The inner member 22 communicates at its upper end with a gas inlet 24 at the top of the pressure vessel, and is closed at the lower end. The annular space 25 bounded by the members 22 and 23 is closed at the bottom, so that gas 'is constrained to flow radially outwards therethrough. The pressure vessel 20 is provided at its lower end with a gas outlet 26.

The annular space 25 is filled with catalyst, and the preheated mixture of hydrocarbon vapour and steam is introduced through the inlet 24. The mixture passes radially outwards through the catalyst bed into an outer annular space 27 within the pressure vessel, and issues from the latter through the outlet 26. The pressure vessel may be arranged vertically as shown in FIGURE 2, or it may be arranged horizontally or in any other convenient posi- EXAMPLE 1 In this example are described experiments that demonstrate the effect of lowering the linear velocity in accordance with the present invention. In these experiments a granulated nickel-alumina catalyst was used that had been prepared in the manner described in Example 2 without the addition of potassium carbonate. The catalyst had the following composition:

Parts by wt. Ni 75 1203 O Na 0.01 Ca 0.003 Fe 0.003 S04 Nil 'Ihe granulated catalyst was sieved to particle sizes ranging from 500 to 850 microns.

A light petroleum distillate having an average number of carbon atoms of 5.8, a boiling range of 40 C. to 97 C., and specific gravity of `0.67 at 20 C. was used. A mixture of 1 part by weight of the vapour of the distillate and 2 parts by Weight of steam was preheated to 450 C. and passed under 25 atmospheres pressure through a bed of the aforesaid catalyst having a depth of 6 inches. The mixture was passed through the bed at a space velocity of 4,000 volumes per Volume per hour and a linear velocity of 0.075 foot per second.

When it was attempted to determine the life of the catalyst in terms of the period from the initial introduction of the hydrocarbon-steam mixture to the time at which undecomposed hydrocarbon is first detected in the issuing gases, it was found that no undecomposed hydrocarbon could be detected after a period of about 2,500 hours, when the experiment Was stopped. During the experiment a hot reaction zone about 1A inch thick having a temperature of about 480 C. moved upwardly through the bed. When the experiment was stopped this reaction zone Was slightly less than half Way up the bed, which indicated that it might be possible to have continued the experiment for an almost equally long period.

The above experiment was repeated with the same distillate and catalyst under the same conditions, except that the depth of the catalyst bed was 12 inches, the linear velocity was 1.65 feet per second and the space velocity was 44,000 volumes per hour. Undecomposed hydrocarbon was first detected in the issuing gases at the end of a period of 20 hours.

This experiment c-annot properly be compared with the previous experiment, owing to the great difference between the space velo-cities used. However, it is resonable to suppose that, if the space velocity in the latter experiment were decreased to 4,000 by increasing the depth of the catalyst bed to 11 feet, undecomposed hydrocarbon would rst be detected at the end of a period no longer than 220 hours.

EXAMPLE 2 Three experiments A, B, and C were carried out 'with the use of a nickel-alumina catalyst prepared as follows. Nickel and aluminum nitrates are separately dissolved in water, and the two solutions filtered, mixed Iand brought to the Iboil. An aqueous solution of potassium carbonate is brought to the lboil and then -added to the solution of the nitrates. When precipitation is complete, the precipitate is filtered as rapidly and completely as possible using a suction pump. The filter cake is suspended in boiling water and the suspension stirred and then filtered. The operations of suspending the precipitate in lboiling water, stirring and then filtering are repeated until the filtrate has a pH of between 7 and 8. Six washings are usually required. After the final washing, the precipitate is partially dried by suction, and the resulting paste thoroughly mixed with an aqueous solution of 106 grams per litre of potassium carbonate. The mixture is then dried in an oven at 110 C., granulated to the required particle size and then heated in a stream of hydrogen to reduce the nickel compounds to metallic nickel.

The catalyst had the following composition, the quantities being by weight:

The granulated catalyst was sieved to the particle size given below.

In each experiment a petroleum distillate having an average number of carbon atoms of 6.1, a boiling range of 26 C. to 140 C., and a specific gravity of 0.68 at 20 C., was used. A mixture of l part by weight of the vapour of the distillate and 2 parts by weight of steam was preheated to 450 C., and passed under a pressure of 350 pounds per square inch (gauge) downwardly through a bed of the catalyst. In experiments A and B the catalyst bed had a depth of 6 inches, and in experiment C a depth of 12 inches. The linear velocities and the space velocities in volumes per volume per hour are given below. The following results were obtained:

Experiments were carried out with the use of a nickelalumina catalyst having the composition given in Example 2 and the ranges of particle size given below. They were Icarried out with a petroleum distillate having an average number of carbon atoms of 6.1, a boiling range of 26 C. to 140 C., and a specific gravity of 0.68 at 20 C. at a space velocity of 8,000 pounds per volume per hour and at the linear velocity given below. In both experiments -a mixture of 1 part lby weight of the vapour of the distillate and 2 parts by weight of steam was preheated to 450 C. and passed under a pressure of 350 pounds per square inch (gauge) through a bed of the catalyst having a depth of 6 inches. The life of the catalyst was taken as the period from the initial introduction of the hydrocarbon/steam mixture to the time at which undecomposed hydrocarbon was first detected in the gases leaving the catalyst bed. The following results were obtained:

In this example there are described experiments that compare the effect of using a nickel-alumina catalyst hav- K Ni A1201 (added Na Ca Fo S04 as KqCOs) Catalyst A 75 25 1.65 0.0l 0003 0.003 Nil. B 82.2 17.8 1.1 0.01 0003 0003 Nil.

The granulated catalysts were sieved to a size range of 500-850 microns.

The petroleum distillate having a boiling range of 26 C. to 140 C., described in Example 3, was used. In each experiment a mixture of 1 part by weight of the vapour of the distillate and 2 parts by weight of steam was preheated to 450 C. and passed through a bed of catalyst A or B under a pressure of 350 pounds per square inch at a linear velocity of 0.15 foot per second and a space velocity of 8,000 volumes per volume per hour. The following re- In this example there are described experiments that demonstr-ate the effect of lowering the linear velocity on the life of the catalyst when treating mixtures of hydrocarbons having a higher average number of carbon atoms than those used in the process of British specification No. 820,257.

Two experiments A and B were carried out with the use of a nickel-alumina catalyst containing potassium (added as K2CO3) and having the composition set out in Example 2. The granulated catalyst was sieved to the particle sizes given in the table below.

In each experiment a petroleum distillate having an average number of carbon atoms of 11.5, a boiling range of 120 C. to 280 C., and a specic gravity of 0.79 at 20 C. was used. A mixture of l part by Weight of the vapour of the distillate and 2 parts by weight of steam was preheated to 450 C., and passed under a pressure of `350 pounds per square inch (gauge) downwardly through a bed of the catalyst. In experiment A the catalyst bed had a depth of 6 inches, and in experiment B the bed had a depth of 12 inches. The linear velocities and the space velocities in volumes per volume per hour are given below. The following results were obtained:

and steam at a temperature of at least 350 C., is passed under a pressure of at least one atmosphere at a linear velocity not exceeding 0.3 foot per second and a space velocity of at least 400 volumes per volume per hour through a bed of a particulate nickel-alumina catalyst having a particle size between about 150 microns and 1A inch and containing 28 to 90% by weight nickel, said bed being maintained at temperatures of from 400 C. to 600 C., whereby substantially no carbon deposition takes place on the catalyst.

2. A process as claimed in claim 1 wherein the linear velocity at which the hydrocarbon vapour and steam are passed through the catalyst bed is within the range of 0.01 to 0.3 foot per second.

3. A process as claimed in claim 1 wherein the pressure is from 10 to 25 atmospheres.

4. A process as claimed in claim 1 wherein the mixture of hydrocarbon vapour and steam is passed in parallel into a plurality of catalyst beds.

5. A process as claimed in claim 4 wherein the catalyst beds circumscribe a central supply duct at intervals along its length and are themselves surrounded by an annular exhaust duct, and communication mea-ns being provided between said central supply duct and each of said catalyst beds and between said annular exhaust duct and each of said catalyst beds and said mixture of hydrocarbon vapor and steam passes `from the supply duct through each catalyst bed into the exfhaust duct.

6. A process as claimed in claim 1 wherein the catalyst bed is of an elongated tubular form and the hydrocarbon vapour and steam are passed into the inner periphery of the bed and the gaseous reaction products leave the bed from the outer periphery thereof.

7. A process as claimed in claim 1 wherein the catalyst bed is of elongated tubular form, and the hydrocarbon vapour and steam are passed into the outer periphery of the bed and gaseous reaction products leave the bed from the inner periphery thereof.

8. A process as claimed in claim 1 wherein thc nickelalumina catalyst contains an addition of a compound selected from the group consisting of oxide, hydroxide and carbonate of a metal selected from the group consisting of alkali metals and alkaline earth metals.

9. A process as claimed in claim 8 wherein the compound of the metal is potassium carbonate.

10. A process as claimed in claim 1 wherein the nickelalumina catalyst has a particle size within the range of about 150 microns to about 1,000 microns.

11. A process as claimed in claim 1 wherein the nickelalum'ina catalyst contains vfrom 75 to 90 percent by weight of nickel based on the combined weight of nickel and alumina.

12. A process as claimed in claim 11 wherein the nickel-alumina catalyst contains from 80 to 85 percent by weight of nickel based on the combined weight of nickel and alumina.

13. A process as claimed in claim 1 wherein the maximum temperature maintained in the catalyst bed is 575 C.

14. A process for the production of gases containing methane from mixtures of predominantly paraflinic hydrocarbons containing an average of from 4 to l5 carbon atoms and a boiling range of from not less than about 26 C. to not more than about 280 C., wherein a mixture of the 'vapour of the hydrocarbons, and from 2 to 5 parts by weight of steam per part of hydrocarbons, preheated to a temperature of from 350 C. to 500 C., is passed at a pressure of from 1 to 50 atmospheres pressure at a linear velocity of not more than about 0.15 foot per second and a space velocity of at least 400 volumes per volume per hour through a bed of a nickel-alumina catalyst prepared by coprecipitation followed by reduction of the nickel compounds in the coprecipitate to metallic nickel having a composition of from about 75 to about 90 percent of nickel, from about 25 to about 10 percent of alumina and from 0 to albout 1.1615 percent of potassium, said percentages being by weight, and a particle size of from about 210 microns to about 850 microns, said bed being maintained at temperatures of from 400 C. to 550 C. whereby substantially no carbon deposition takes place on the catalyst.

15. A process as claimed in claim 14 wherein the paranic hydrocarbons contain an average of from 4 to 10 carbon atoms per molecule and the vapour of the hydrocarbons is mixed with from 1.6 to 5 parts by weight of steam per part of hydrocarbons.

References Cited UNITED STATES PATENTS Mather 23--2188 Nebeck 23-2188 Bills 48-11916 X McMahon.

Dwyer et al. 48-1961 X Stiles 252-4626 Fox et al. 48-214 Davies et a1. 48-214 X FOREIGN PATENTS Great Britain.

U.S. C1. X.R.

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