GB2160542A - Catalytic production of methane - Google Patents

Abstract

Methane is produced by reacting CO or CO2 with hydrogen in the presence of a catalyst in a so-called 'methanation' reaction. To mitigate problems of poisoning and/or ageing of catalytically active material, the catalyst is in the form of one or more discrete catalyst bodies, the or each body having a plurality of internal pathways of pre-determined dimensions and arrangement for reactant(s) and/or product(s) of the reaction and containing the catalytically active material for the reaction uniformly and homogeneously dispersed therethrough. The material may constitute more than 50% by weight and even substantially all of the or each body. The catalytically active material may, for example, be NiO/NiAl2O4.

Description

SPECIFICATION Catalysis The invention relates to a method of producing methane by reaction of CO or CO2 with hydrogen in the presence of a catalyst for the reaction.

Production of methane by reacting CO or CO2 with hydrogen (commonly referred to as 'methanation') is a well-known reaction. See, for example, 'Methanation of Synthesis Gas' by L. Seglin, ACS 146, Washington DC (1975). A known catalyst for the reaction is a combination of Ni and Awl202 in the form of catalyst pellets having a random network of internal spaces, e.g. in the form of channels andior pores, to enhance surface area for catalytic purposes. Pellets of this kind are described, for example in an article by J.J. Carberry in "Chemical and Catalytic Engineering (1976)", published by McGraw-Hill.

A problem associated with the use of catalyst pellets in methanation is that they offer excessive resistance to flow thereby giving rise to an energy-consuming pressure drop. Also, a coated substrate catalyst having ordered internal channels, whilst overcoming the pressure drop problem, would suffer from excessive poisoning and,or ageing of the catalytically active material and employ expensive and bulky inert substrates.

US Patent No 4 337 028 describes a catalyst system in which the catalytic composition comprises a catalytically active material which is homogeneously interspersed throughout a monolith structure of ceramic composition, and the application of such a a system in a combustion process such as in gas turbine combustors. However, combustion processes take place in the presence of large and predominant proportions of air and are not concerned with effecting chemical synthesis to produce a desired product.

The present invention is intended to alleviate one or more of the problems referred to above and provides a method of producing methane by reaction of CO and or CO2 with hydrogen in the presence of a catalyst for the reaction wherein the catalyst is in the form of one or more discrete catalyst bodies, the or each body having a plurality of internal channels of ordered, pre-determined dimensions and arrangement for reactants and products of the reaction and containing catalytically active material for the reaction uniformly and homogeneously dispersed therethrough.

The invention thus provides one or more catalyst bodies having sufficient of a reserve of catalytically active material to combat poisoning and/or ageing problems, and which are of such a configuration as not to offer excessive resistance to flow of reactant(s) and/or product(s) therethrough.

Preferably, catalytically active material constitutes more than 50% by weight of the or each catalyst body and may, for example constitute 75% or more, or 90% or more, or essentially all of the or each catalyst body, where proportions are by weight. Material other than catalytically active material, if present in the or each catalyst body, may be constituted, for example, by one or more of cordierite, alumina, zirconia, clays and ceramic binders. Also, additives may be incorporated for introducing porosity into the catalyst body or bodies or for enhancing the mechanical strength thereof. The catalytically active material is preferably nickel (II) oxide in association with nickel aluminate, wherein the nickel (II) oxide may be wholly or partly reduced.Other examples of catalytically active materials are Ru, Co and Fe, usually in combination with Awl203, although these have the disadvantages of being easily poisoned by sulphur and of giving rise to hydrocarbons other than methane in use with consequent carbonisation problems. Further examples are Mo and!or W in the form of their sulphides which are resistant to sulphur poisoning.

The body or bodies may, for example, be in the form of honeycombs having a plurality of substantially parallel channels extending therethrough constituting the internal channels. Each honeycomb may, for example be in the shape of a right cylinder, the curved surface of which is continuous and is substantially impermeable to the reactant(s) and product(s), and the channels are parallel to the principal axis of the cylinder. The or each honeycomb may conveniently comprise alternate plain and corrugated sheets bonded together to define the channels.

The body or bodies may be made from powdered catalytically active material by methods known in the art for fabricating ceramic bodies. For example, the powdered material may be mixed with binder(s) providing thermoplastic and setting properties (a plasticiser may also be included), shaping the mixture into sheets for defining the body, bonding the sheets together in the desired form of body and firing to give the final body. Alternatively, the body or bodies may be made by extrusion of a suitable mixture using an appropriate die, for example by vacuum extrusion The body or bodies may be in a range of configurations and sizes in accordance with specific requirements, and may also be in a range of arrangements in a container therefor.For example, a plurality of bodies may be arranged randomly or orderly in a container and in the latter case the bodies may be cut to shape to fit tightly into a container thereby minimising 'dead space'. The bodies may be the same or different in external dimensions in a particular container. Alternatively, a single body or small number of bodies may be provided in a container.

Several ways of carrying out the invention will now be described as follows by way of example only.

Also included below are comparative experiments A, B and C which are not examples of the invention.

Reference will be made to the accompanying drawings in which Figure 1 shows the relationship between catalytic activity and temperature for a device of the invention and for a comparative device; and Figure 2 shows the effect of ageing on the catalytic activity of a device of the invention at two different temperatures.

Example 1 (a) Preparation of Powder [(NO3)2] (H2O)6 (458.18g; 1.58 moles) was dissolved in distilled water (400 cm3). [Al(NO3)3] (H3O)s (675.00g; 1.80 moles) was dissolved in distilled water (900 cm3) and then mixed into the aqueous nickel nitrate with stirring. The mixture was stirred for 0.25h. The resultant solution was then added dropwise with rapid stirring to a solution of urea (254.47g; 4.27 moles) in distilled water (1100cm3). After the addition was complete the reaction mixture was aged at ca 959C in unstoppered flasks for 74 hrs. The flasks were emptied and the mixture homogenised with rapid stirring for 0.5 h.

The pH of the dispersion was 7.80. The material was further aged in the open beaker (5 1) at 60"C for 17.5 h. The residue was mixed with distilled water (ca. 200 cm3) with rapid stirring over 1.5 h to yield a stable thixotropic dispersion (ca 400 cm3). The dispersion, containing hydrous oxides of Ni and of Al, was dried at ca 80"C and sieved to 250 Fm, and then calcined at 450 C for 1 hour to give a powder compris ing nickel(ll) oxide and nickel aluminate.

(b) Preparation of Catalyst Bodies The resultant powder (409) was then dry mixed with polyvinyl butyral (PVB) (15g). A mixture of methyl ethyl ketone (MEK) (15g) and dibutyl phthalate (DBP) (7.5g) was then mixed into the dry mix using a Hobart mixer. The resultant "paste" was rolled in a two-roller miller (roller steam heated to ca 90"C) to yield a homogeneous "rubberised" sheet ca 0.02-0.03 inch thick. The sheet was then passed through a four roll calendar with rollers heated as follows: rollers 1 to 3, oil heated to ca 40"C, roller 4 ambient temperature. The sheet thus obtained had a thickness of ca 0.006 inch.

Two samples of sheet were then fed through a corrugator to yield a sinusoidally corrugated (1 mm corrugations) sheet bound to a flat sheet. The corrugated composite was then tightly hand rolled to yield corrugated monoliths (1 cm diameter x 2 cm length). The "green" pieces were debonded by heating in air from room temperature to 400"C at 5"C min . The cooled pieces were then calcined at 1150"C for 1 hour after being slowly elevated to this temperature over ca 4-5 hours. It is possible that the calcining temperature ensures that the nickel content of the powder is stable during its subsequent use in the catalysis of a methanation reaction e.g. preventing its loss as nickel carbonyl where one of the reactants is CO.The pieces were cooled in the furnace and cut with a diamond saw to the appropriate length when cool.

(c) Preparation of Catalyst Device Catalyst bodies prepared as in (b) above were randomly assembled as a bed in a regular cylindrical container having an inlet and an outlet. The characteristics of the resulting device were as follows: Depth of bed : 8.5 cm Cross-sectional area of bed : 32.2 cm2 Length of each catylst body 1.03 cm Diameter of each catalyst body 1.01cm Voidage in container : 0.42% Experiment A Catalyst pellets similar to those of a type used commercially consisting of Ni and Awl203 and each having a random network of internal spaces were randomly assembled as a bed in a regular cylindrical container having an inlet and an outlet. The characteristics of the resulting comparative device were as follows: Depth of bed : 10.5 cm Cross-sectional area of bed : 32.2 cm2 Length of each pellet : 1.10 cm Diameter of each pellet : 1.10 cm Voidage : 0 44% Tests of Catalyst Devices of Example 1 and Experiment A The pressure drop characteristics of the devices of Example 1 and Experiment A in relation to flow-rate of air therethrough were respectively determined. The tests were carried out at ambient temperature and pressure and the air density was assumed to be 1.29 kg m--3. The results of the tests are summarised in Table 1 below.

TABLE 1 Pressure Drop (kPA m-1) Flow Rate Mass Flux (1 min 1) (kg m 2s 1) Experiment A Device Example 1 (Comparative) Device 20 0.134 0.05 0.030 30 0.200 0.09 0.050 40 0.267 0.14 0.075 50 0.334 0.19 0.104 60 0.401 0.25 0.131 70 0.467 0.33 0.164 80 0.534 0.42 0.205 90 0.601 0.50 0.242 The devices of Example 1 and Experiment A were, as far as possible, comparable in their characteristics; the results in TABLE 1 indicate that the pressure drop is much lower for the device of Example 1 than for the device of Experiment A.

Example 2 A single catalyst body prepared as as in part (b) of Example 1 above was assembled in a container having an inlet and an outlet to constitute a catalyst device. The body was supported on a gas permeable grille and a SiO2 wool plug for dispersing reactants provided on the inlet side of the catalyst body.

Examples 3 to 5 Further catalyst devices were prepared as in Example 2 except that the calcination temperatures of the catalyst bodies in their preparation were 1250"C (Example 3), 1350"C (Example 4) and 1400on (Example 5) respectively.

Experiment B A catalyst device was made by randomly assembling pellets as used in Experiment A and that had been calcined at 1150C in a container as used in Example 2.

Experiment C A catalyst device was made as described in Experiment B except that the pellets had been calcined at 450"C.

Tests on Catalyst Devices of Examples 2 to 5 and Experiments B and C The above devices were tested for a methanation reaction where the feedstock contained CO and H2 in the molar ratio of 1:4. The product gas contained unreacted H3, a major proportion of CH4 and a minor proportion of CO2. The feed rate was ca. 80 cm3 min , and the Gas Hourly Space Velocity (GHSV) was 1.25 x 104h-'. The volume of catalyst in each device was 0.385 cm3 ignoring voidage. For each device, the lowest temperature at which significant methane was formed was measured. The results are summarised in the table below, where the above temperature is referred to as the "bite" temperature.

TABLE 2 Catalyst Device Mass of Catalyst "Bite" Temperature in Device (g) ( C) Example 2 0.33878 280 Example 3 0.39544 280 - 300 Example 4 0.31918 300 Example 5 0.26441 320 Experiment B 0.35300 360 Experiment C 0.41110 220 The results in Table 2 demonstrate that the devices of Examples 2 to 5 have similar activities in the test conditions to the devices of Experiments B and C. It is a reasonable assumption that a device of Example 1 would exhibit similar activity also.

Tests on Catalyst Device of Example 2 and Experiment B The above devices were each tested for the above-mentioned methanation reaction at various temperatures. The percentage of methane produced by volume (v/o) was measured and the results shown graphically in Figure 1 for each of the two devices. Referring to Figure 1, it will be seen that the device of Example 2 exhibits greater activity than the device of Experiment B.

The device of Example 2 was similarly tested at 280"C and at 600'C after having been subjected to steam ageing at 700"C for varying lengths of time. The results are shown graphically in Figure 2 where the temperatures indicated are the test temperatures. Referring to the figure, it will be seen that the devices are catalytically active at 600cm and that steam deactivation of this high temperature activity is not significant after 48 hours steam ageing at 700oC.

Claims (8)

1. A method of producing methane by reaction of CO and/or CO2 with hydrogen in the presence of a catalyst for the reaction wherein the catalyst is in the form of one or more discrete catalyst bodies, the or each body having a plurality of internal channels of ordered, pre-determined dimensions and arrangement for reactants and products of the reaction and containing catalytically active material for the reaction uniformly and homogeneously dispersed therethrough.

2. A method as claimed in claim 1 wherein the catalytically active material is nickel(ll) oxide in association with nickel aluminate.

3. A method as claimed in claim 1 or claim 2 wherein the catalytically active material constitutes more than 50% by weight of the or each catalyst body.

4. A method as claimed in any of the preceding claims wherein a plurality of the discrete catalyst bodies is randomly assembled in a container having an inlet for supplying reactant(s) thereto and an outlet for the production of the reaction.

5. A method as claimed in any of the preceding claims wherein the or each cataylst body comprises a honeycomb having a plurality of substantially parallel channels extending therethrough constituting the internal channels.

6. A method as claimed in claim 5 wherein the or each honeycomb is in the shape of a right cylinder, the curved surface of which is continuous and is substantially impermeable to the raactant(s) and product(s), and the channels are parallel to the principal axis of the cylinder.

7. A method as claimed in claim 5 or claim 6 wherein the or each honeycomb comprises alternate plain and corrugated sheets bonded together to define the channels.

8. A method of producing methane by reaction of CO or CO2 with hydrogen in the presence of a catalyst for the reaction substantially as described herein with reference to any of Examples 1 to 5.