GB2247465A

GB2247465A - Catalytic process for the production of synthesis gas by means of reforming and combustion reactions

Info

Publication number: GB2247465A
Application number: GB9118116A
Authority: GB
Inventors: Luca Basini; Mario Marchionna; Domenico Sanfilippo; Stefano Rossini
Original assignee: SnamProgetti SpA
Current assignee: SnamProgetti SpA
Priority date: 1990-08-29
Filing date: 1991-08-22
Publication date: 1992-03-04
Anticipated expiration: 2011-08-22
Also published as: CA2050143A1; CN1059318A; NO913360L; GB9118116D0; IT9021326A0; NO913360D0; IT9021326A1; GB2247465B; IT1242994B

Abstract

In a catalytic process for the production of synthesic gas comprising two reaction stages in one or more reactors, the first stage (R1) comprises carrying out exothermic combustion reactions by making a hydrocarbon or hydrocarbon mixture or carbon react with air and/or oxygen, and the second stage (R2) comprises carrying out reforming reactions by making the products of the combustion reaction react with a hydrocarbon or a hydrocarbon mixture, having a number of carbon atoms no higher than 10, with the assistance of a catalytic system comprising: - one or more compounds of metals of the platinum group; and - a support comprising inorganic compounds, in which the percentage by weight of the metal or metals of the platinum group in the catalytic system is between 0.01 and 20%. <IMAGE>

Description

"CATALYTIC PROCESS FOR THE PRODUCTION OF SYNTHETIC GAS BY MEANS OF HYDROCARBON REFORMING AND COMBUSTION REACTIONS The present invention relates to a catalytic process for the production of synthetic gas by means of hydrocarbon reforming and combustion reactions.

Synthetic gas or syngas comprises a gaseous mixture which principally contains carbon monoxide and hydrogen, but which may also contain smaller quantities of CH , CO and N 4 2 2 Synthetic gas is used as a reagent in large-scale chemical processes such as the production of methanol, FISCHER TROPSCH processes and the production of ammonia. The most widespread production processes of synthetic gas include: steam reforming, autothermal reforming and non-catalytic partial oxidation of hydrocarbons.

Steam reforming processes catalytically convert mixtures of hydrocarbons (typically natural gas) and steam into mixtures of CO and H in a H /CO ratio of around 3. The main involved 2 2 reactions are the following:

The catalysts commonly used for these processes are based on Ni supported on Al, Mg and Si oxides with high thermal stability.

The temperature conditions in the two reforming units exceed o 850 C, while the pressure is between 10 and 45 MPa.

(See for example "Catalysis - Science and Technology" - Vol.

5, (1984), 1 - J.R. Rostrup - Nielsen).

The partial oxidation processes are less common and used to convert mixtures of heavy hydrocarbons and oxygen into synthetic gas. The chemistry of the process can be represented by the equation:

The plants so far built (by Texaco and Shell - see Hydrocarbon Processing - April (1990), 99) involve noncatalytic partial oxidation reactions at temperatures of o o between 1250 C and 1500 C and a pressure of between 3 and 12 MPa.

Autothermal reforming processes exploit a combination of exothermic partial oxidation reactions and endothermic steam reforming reactions. In this process hydrocarbons, steam and oxygen are supplied and mixtures of H and CO are 2 obtained in intermediate ratios between those of steam reforming and partial oxidation processes. Autothermal reforming is a catalytic process which uses the same catalysts as steam reforming processes.

O o The temperatures adopted are between 800 C and 1000 C; the pressure is between 2.0 and 4.0 MPa.

A process has now surprisingly been discovered which enables synthetic gas to be produced at temperatures lower than those currently in use by exploiting the products and heat of combustion.

The process for the production of synthetic gas from hydrocarbons, the object of the present invention, is characterised in that it is conducted in one or more reactors in two reaction stages, in the first stage carrying out exothermic combustion reactions, by making a hydrocarbon or hydrocarbon mixture or carbon react with air and/or oxygen, which can generally be represented by the following main reaction

in the second stage by carrying out reforming reactions, exploiting the heat produced by the combustion reactions, by making the products of the combustion reactions react with a hydrocarbon or hydrocarbon mixture, having a number of carbon atoms essentially no higher than 10, which can generally be represented by the following main endothermic reactions

with the assistance of a catalytic system comprising:: - one or more compounds of metals of the platinum group, preferably chosen from rhodium, ruthenium, palladium and platinum; - a support comprising inorganic compounds in which the percentage by weight of the metal or metals of the platinum group in the catalytic system is between 0.01 and 20%, preferably between 0.1 and 3%.

The two reaction stages do not require the presence of steam (apart from that produced by the combustion reactions of the first stage of reactions) the addition of which is therefore optional.

The support preferably comprises inorganic compounds chosen from oxides and/or spinels of aluminium, magnesium, zirconium, silicon, cerium and/or lanthanum, on their own or in combination with each other, if necessary in the presence of alkaline metals.

The support used may comprise aluminium, magnesium, cerium or lanthanum silicified oxides.

The surface areas of the catalytic systems used are 2 preferably varied between 1 and 400m /g, more preferably 2 between 10 and 200m /g, whilst the volume of pores is preferably varied between 0.1 and 3cc/g, more preferably between 0.5 and 2cc/g.

The catalytic system may be obtained either through a process of impregnating the inorganic compounds with a solution of a salt of the metals of the platinum group, followed by thermal drying and calcining treatments, or by dispersing the inorganic compound in an organic solvent, then making them react in an atmosphere of carbon monoxide or in an inert atmosphere with solutions of compounds of metals of the platinum group.

In this second case after the reaction, usually exothermic, which gives rise to coloured materials, filtration, drying and calcining treatments are carried out.

The catalytic system in question may be prepared, more particularly, by a heterogeneous solid/liquid reaction at o o temperatures of between 0 C and 150 C, preferably between o o 20 C and 50 C, between organo-metallic compounds of the metals of the platinum group dissolved in an organic solvent and the above-mentioned inorganic compounds dispersed in the said solvent.

On following this procedure the quantity of metal which fixes on the substrate is determined chiefly by the chemical properties of the inorganic oxide rather that by its characteristics of porosity and surface area.

The latter are however important as regards the properties of integrity and stability of the catalyst during the reforming reaction.

The procedure of preparing the supports comprising aluminium, magnesium, cerium or lanthanum silicified oxides consists essentially in a condensation reaction between the inorganic oxide (of aluminium, magnesium, cerium or lanthanum) and a silicon compound containing hydrolizable organic groups and in the subsequent removal of unhydrolized organic residues by means of a combustion reaction or in the presence of steam.

With these silicification procedures it is possible to obtain materials containing percentages by weight of silicon which range between 0.5 and 15% by weight, preferably between 1 and 10%.

The above-described catalytic system enables conversions close to those of thermodynamic equilibrium to be obtained for the system described by reactions (2) and (3) over a o wide temperature range of between 300 and 1200 C.

This catalytic system also enables reagents with a high H O/C ratio (calculated as moles of steam/moles of carbon 2 contained in the reagents) to be used and if necessary enables synthetic gas to be obtained from light hydrocarbons and CO even in the absence of steam in the mixture of 2 reagents. In particular, the H o/c ratio in the mixture of reagents of the second stage may be reduced to 0.01, however it should preferably be chosen between 0.5 and 4.

Currently in conventional steam reforming plants the H O/C 2 ratio varies between 2.5 and 3 whensthe reagent used is natural gas and between 3 and 5 when the reagents used are LPG or naptha.

The H O/C ratio in the mixtures of reagents affects: 2 a) the carbon formation reactions

b) the H /CO ratio in the mixture of products 2 c) the equilibrium of the water gas shift reactions

d) the technology of reforming processes.

The possibility of using mixtures of reagents with a low H O/C ratio in synthetic gas production processes according 2 to reactions (2) and (3), enables mixtures to be obtained with a high CO content by using just one catalytic reforming reactor. Furthermore, when the catalytic process is dedicated to the production of hydrogen and the reforming reactor is followed by a reactor for the water gas shift catalytic reaction, the use of reagents with a low H O/C 2 ratio enables the production of H per unit of hydrocarbon 2 consumed to be increased.

The catalytic process for the production of synthetic gas in two reaction stages, described in the present invention, also enables all the CO and heat produced by the first 2 stage of combustion reactions (1) to be used in reforming reactions (2) and (3) thus drastically reducing the effects of environmental pollution.

Currently in steam reforming plants it is necessary to add to a first tubular reactor, which operates at temperatures o of around 800 C and in which steam and hydrocarbon mixtures are supplied (primary reforming), a second reactor (secondary reforming) which operates at temperatures of o around 1000 C. This configuration is necessary in order to obtain high conversions of the reagents and mixtures of products at the output of the second reforming stage with H /CO ratios of less than 3.

2 As regards combustion reactions these may be catalytic or not, depending on the composition of the reagents used.

If the combustion reactions are catalytic all the known catalysts for combustion may be used and their characteristics must be chosen on the basis of the composition of the mixtures of reagents.

The known combustion catalysts may be divided into two groups: metallic catalysts and oxide catalysts.

Metallic combustion catalysts typically comprise Pt, Pd, Rh, Cu or Ag supported on silicas and aluminas.

For oxide combustion catalysts the oxides of the Group IV elements may be used such as TiO21V2O3,Cr2O3, MnO , Fe O 2 2 2 23 CO O , NiO, CuO, ZnO.

34 In a borderline case the combustion catalysts may be similar to the catalytic system used for reforming, i.e. they may contain the same metal of the platinum group.

If the combustion reactions are not catalytic, at the entrance to the autothermal reactor there is a burner.

By using a single reactor both for combustion and reforming reactions, if the combustion reactions are catalytic the catalytic beds for the reforming reactions may be separate or adjacent to the catalytic beds for the combustion reactions, if they are not catalytic at the entrance of the autothermal reactor there is a burner.

The process in accordance with the invention also enables synthetic gas to be obtained with a H /CO ratio of between 2 0.5 and 3 in a single reactor.

For example, in a first configuration particularly suited to the use of gaseous hydrocarbon reagents, particularly natural gas, the two reaction stages may be carried out in two different areas of an autothermal reactor in which the combustion reactions take place at the entrance of the reactor and the reforming reactions in a subsequent catalytic bed, operating at temperatures of between 600 and o o 1000 C, preferably between 700 and 850 C. The high conversion that can be obtained, thanks to the use of the above-described catalysts, enable synthetic gas to be obtained using a single autothermal reactor which operates o at temperatures of about 200 C lower than those of the autothermal reforming reactors currently in use (operating o between 850-1000 and 2-4 MPa).

The pressure inside the combustion and reforming reactor may be varied between 0.05 and 6 MPa, preferably between 0.1 and 5 MPa. In a second configuration, by contrast, the two reaction stages are performed in two different reactors.

The first reactor is dedicated to combustion reactions which may be catalytic or not, the second is dedicated to catalytic reforming reactions using the heat and mixture of the products of the combustion reactions obtained in the first reactor with the addition or not of more combustible gas.

If the combustion reaction continues until complete conversion of the reagents into CO and H O the products of 2 2 the combustion reaction will be mixed with light hydrocarbons (having a number of carbon atoms of no more than 10) before reaching the catalytic bed of the reforming reactions.

A few examples shall now be given to better illustrate the invention, although it will be understood that it shall not be limited by or to them.

Example 1 Mixtures of methane and air were supplied in a reactor comprising refractory material at the entrance of which is a burner for gaseous flows. After the combustion area, in which reactions (1) occur, there is an annular catalytic bed in which reforming reactions (2) and (3) occur. In the centre of the catalytic bed a thermocouple was inserted to 3 measure the reaction temperature. 20cm of catalyst were placed in the reactor. The CH /0 ratio in the mixture 42 entering the reactor was equal to 2. The spatial speed of the gas was regulated so that the temperature inside the o catalytic bed for the reforming reactions was 750 C and was -1 11000h . The duration of the catalytic tests was 100h after achieving stationary reaction conditions.

The catalyst used in the reforming reaction was prepared in accordance with the following procedure.

A commercial magnesium oxide (supplied by Carlo Erba) with a 2 surface area of 210m /g was suspended under agitation in a solution of tetra-ethyl silicate (TES). The temperature was o o kept at between 80 C and 90 C to. assist evaporation of the ethanol formed due to the effect of the condensation reactions. A gaseous flow of anhydrous nitrogen was passed through the reaction environment. Gas 'chromatoghraphic analyses or the output gas showed the formation of ethanol. The condensation reaction was considered over when ethanol was no longer detected in the outgoing gaseous flow. At this o point the temperature was increased to 180 C to distill the unreacted TES. The unreactedethoxy groups bound to silicon atoms in turn fixed to the inorganic solid were then hydrolized by supplying a flow of nitrogen and steam at o 200 C.During this stage too the presence of ethanol was detected in the gaseous flow. An analysis of the infrared spectra of the material thus far obtained showed the presence of numerous hydroxylic bands which were not present in the original material. The solid was then heated to o o 850 C (5 C/min) and kept at this temperature for 10h. After 2 these treatments the surface area reduced to 32m /g and the content by weight of silica was 1.5%. Measurements of differential thermal analysis, thermogravimetry and infrared o spectroscopy made during three thermal cycles between 25 C o and 750 C showed no significant alterations in the chemical and physical properties of the silicified materials thus obtained. 50g of silicified magnesium oxide was at this point suspended in 100ml of 2-methyl pentane in a nitrogen atmosphere. A second solution of 50ml, of the sane solvent, containing 0.0919 of Rh (CO) in a CO atmosphere was 4 12 rapidly dripped into the suspension of the silicified oxide under agitation. The organic solution discoloured rapidly changing from deep red to colourless, at the same time the white solid became coloured. This was filtered in an inert atmosphere and a material was obtained which contained 0.1% by weight of Rh highly dispersed as was evident from an analysis of the carbonyl vibrational bands of the surface complexes.

The gases leaving the reactor were analysed by means of gas chromatography The conversion of oxygen was 100% and that of methane 62%. The H /CO ratio in the gases leaving the 2 reactor was 1.92.

The composition of the products if nitrogen is excluded is shown in Table 1. During the reactions deactivation phenomena of the catalyst were not observed.

Table 1 CH = 8.0 4 CO = 3.1% 2 H O = 2.1% 2 CO = 29.8% H = 57.0% 2 Examples 2-5 Mixtures of CH and air were supplied in an annular quartz 4 reactor, surrounded by refractory material, containing two catalytic beds separated by a porous septum. An electric furnace was used to control the reaction temperature. In the first catalytic bed 5ml of a combustion catalyst were added comprising 0.1t by weight of metallic Rh deposited on silica. In the second catalytic bed lOmi of a catalyst were added comprising 0.15 of metallic Rh, deposited on silicified alumina (prepared as in Ex. 1). Four thermocouples were inserted in the areas where the gases entered and left the catalytic beds to measure the temperatures during the combustion and reforming reactions.

4 catalytic tests were performed by supplying four mixtures with a different CX /0 ratio in a temperature range of o 42 between 500 C and 800 c. The composition of the gases leaving the reactor was determined by gas chromatography and is shown in Figures 1-4. The percentages of conversion of the methane introduced into the reactor, obtained by supplying the four mixtures of CH and air, are shown in 4 Figure 5.

EXAMPLE 6 The exothermic combustion reaction (1) and the steam and C02 reforming endothermic reactions (2) and (3) were carried out in two different reactors.

The experimental apparatus is schematically shown in Figure 6.

In a first reactor(R1) of quartz, the total catalytic combustion reactions were carried out, using 5 g of a catalyst containing 0.5% (wt/wt) of platinum deposited on alumina by impregnation. The catalytic bed had a lenght of 5 cm and the reagents gaseous flow (CH4 and air) passed through it with a spatial speed (GHSV) of 5000 h . The feeding CH4 and air were mixed so that the 02/CH4 ratio was equal to 2.5 (v/v). At the exit of the catalytic bed the temperature was maintained below 550 C. The gaseous flow leaving the first reactor was maintained at a temperature of 3500C, further mixed with CH4 and analysed by gaschromatography, before being sent to the second reactor (R2) in which reforming reactions (2) and (3) occur.

At the entrance of the second reactor, the gaseous composition was: % by volume CH4 18.2 co2 6.1 H20 12.1 02 3.0 N2 60.6 In the second reactor 5g of a catalyst consisting of 0.1% (w/w) of Rh deposited on silicified magnesium oxide (prepared as in Example 1), were contained. The catalytic bed had a lenght of 5 cm. In the second reactor the gaseous flow had a spatial speed (GHSV) of 10000 h . At the exit of the catalytic bed the gaseous flow temperature was maintained at 800QC.

In these conditions at the exit of the second reactor, the gaseous flow composition was: % by volume CH4 1.1 CO 1.0 2 H20 5.5 O2 ---- N2 45.5 Co 16.9 H2 30.0 During catalytic tests of the duration of 1000 h, no deactivation phenomena were observed.

( In Figure 6 are schematically shown: a cooler A a condenser B a burner C GAS ANALYSIS D)

Claims

1. A process for the production of synthetic gas from hydrocarbon, the process being conducted in one or more reactors in two reaction stages, in the first stage of which one or more than one exothermic combustion reaction is effected by causing a hydrocarbon or hydrocarbon mixture or carbon to react with air and/or oxygen, and in the second stage of which one or more than one reforming reaction, exploiting the heat produced by the exothermic combustion reaction(s), is effected by causing the product of the exothermic combustion reaction(s) to react with a hydrocarbon or hydrocarbon mixture in the presence of a catalytic system comprising (a) one or more compounds of metals of the platinum group, and (b) a support comprising inorganic compound, wherein the percentage by weight of the metal or metals of the platinum group in the catalytic system is from 0.01 to 20%.

2. A process according to claim 1, wherein the exothermic combustion reaction(s) include the following reaction: CnHm + (n+m/2)02 Cb nCO2 + m/2 H20.

3. A process according to claim 1 or 2, wherein the reforming reaction(s) include the following reactions: CnHm + nH2O =T > nCO + (m/2 + n)H2 CnHm + nCO2 Cr=r 2nCO + (m/2 + n)H2.

4. A process according to any of claims 1 to 3, wherein the hydrocarbon or hydrocarbon mixture used in the second stage is one wherein the hydrocarbon, or the hydrocarbons of the hydrocarbon mixture, contain no more than 10 carbon atoms.

5. A process according to any of claims 1 to 4, wherein the percentage by weight of the metal or metals of the platinum group is from 0.05 to 3%.

6. A process according to any of claims 1 to 5, wherein the metal of the platinum group is chosen from rhodium, ruthenium, palladium and platinum.

7. A process according to any of claims 1 to 6, wherein the surface area of the catalytic system is from 1 to 400m2/g and the volume of the pores thereof is from 0.1 to 3cc/g.

8. A process according to claim 7, wherein the surface area of the catalytic system is from 10 to 200m2/g and the volume of the pores thereof is from 0.5 to 2cc/g.

9. A process according to any of claims 1 to 8, wherein the inorganic compound comprising the support is chosen from oxides and/or spinels of aluminium, magnesium, zirconium, silicon, cerium and/or lanthanum, on their own or in combination with each other.

10. A process according to claim 9, wherein the oxides of aluminum, magnesium, cerium or lanthanum are silicified.

11. A process according to claim 9 or 10, wherein the support contains one or more alkaline metals.

12. A process according to any of claims 1 to 11, wherein the combustion reaction is performed in the presence of one of more catalysts.

13. A process according to claim 12, wherein the catalyst is chosen from Pt, Pd, Rh, Cu and/or Ag supported on silica and/or alumina.

14. A process according to claim 12, wherein the catalyst is chosen from Tit2, V203, Cur203, MnO2, Fe203, Co304, NiO, CuO and ZnO.

15. A process according to claim 12, wherein the catalyst is similar to the catalytic system used for the reforming reaction(s).

16. A process according to any of claims 1 to 15, wherein the combustion and reforming reactions are effected in a single reactor.

17. A process according to claim 16, wherein the single reactor used operates at a temperature of from 600 to 1000"C and at a pressure of from 0.05 to 6 MPa.

18. A process according to claim 17, wherein the temperature is from 700 to 850"C and the pressure is from 0.1 to 5 MPa.

19. A process according to any of claims 1 to 15, wherein the reforming reaction(s) are effected in a single reactor.

20. A process according to claim 19, wherein the combustion and reforming reactions are performed in two reactors.

21. A process according to any of claims 1 to 20, wherein the exothermic combustion reaction(s) are effected until complete conversion of the reagents into CO2 and H20.

22. A process according to claim 21, wherein the product of the exothermic combustion reaction(s) is mixed with light hydrocarbon before contacting the catalytic system used in the reforming reaction.

23. A process according to any of claims 1 to 22, wherein the synthetic gas comprises carbon monoxide and hydrogen.

24. A process according to claim 23, wherein the synthetic gas further comprises methane and/or carbon dioxide and/or nitrogen.

25. A process according to claim 1, substantially as described in any of the foregoing Examples.

26. Synthetic gas when produced by a process according to any of claims 1 to 25.