WO2008059208A1

WO2008059208A1 - Process for the conversion of syngas to oxygenates

Info

Publication number: WO2008059208A1
Application number: PCT/GB2007/004243
Authority: WO
Inventors: Qingjie Ge; Andreas Josef Goldbach; Wenzhao Li; Yuchun Ma; Hengyong Xu
Original assignee: Dalian Institute Of Chemical Physics; Bp P.L.C.
Priority date: 2006-11-14
Filing date: 2007-11-08
Publication date: 2008-05-22
Also published as: CN101646641B; CN101646641A; WO2008058425A1

Abstract

A process for the production of oxygenated hydrocarbons from carbon monoxide and hydrogen in the presence of one or more reduced sulphur compounds, in which a reaction composition comprising carbon monoxide, hydrogen and one or more reduced sulphur compounds is contacted with a catalyst comprising a metal active for the production of oxygenated hydrocarbons from carbon monoxide and hydrogen and an inorganic semiconducting oxide support that is capable of catalysing the oxidation of reduced sulphur compounds, in which the concentration of the one or more reduced sulphur compounds in the reaction composition is greater than 0.5 ppm by weight, expressed as elemental sulphur.

Description

PROCESS FOR THE CONVERSION OF SYNGAS TO OXYGENATES

This invention relates to the field of catalysis, more specifically to a catalysed process in which the catalyst is resistant to deactivation by sulphur. Coal is a widely used fuel for power generation. However, it tends to be disfavoured over other fuels, such as crude oil-derived fuels or natural gas, as the energy liberated on its combustion is typically lower on a weight basis. Additionally, coal tends to have relatively larger quantities of sulphur, which can often act as a poison to catalysts in processes which use coal-derived feedstocks, and can reduce catalyst lifetime and activity. Consequently, in many cases, high-sulphur feedstocks have to be pre-treated in order to remove sulphur to below permissible levels. Such feedstock pre-processing requires significant capital expenditure and operating costs. Additionally, as sulphur removal often uses a sacrificial absorbent such as zinc oxide, increased waste is generated by the process. A catalyst that can tolerate relatively high sulphur levels would therefore be advantageous by mitigating or even eliminating the need for such pre-processing.

Methanol is an important high volume commodity chemical, and is typically , manufactured from syngas (a mixture of hydrogen and carbon monoxide). Syngas can be produced from a variety of starting materials, in particular hydrocarbon sources such as natural gas, heavy oils, coal, and also biomass. However, currently used catalysts, such as Cu/ZnO/Al₂θ₃ are highly sensitive to the presence of sulphur in the syngas feedstock, and will typically deactivate even in the presence of sulphur levels of as low as 0.5 ppm. Typical syngas feedstocks, particularly when coal derived, can have sulphur levels in the

1 range of from 10 to 100 ppm. Therefore, a need remains for a process for the conversion of syngas to oxygenates which is tolerant to the presence of sulphur in the feedstock. According to the present invention, there is provided a process for the production of one or more oxygenated hydrocarbons from hydrogen and carbon monoxide, which process comprises contacting a catalyst with a reaction composition comprising carbon monoxide, hydrogen and one or more reduced sulphur compounds under conditions sufficient to produce one or more oxygenated hydrocarbons, which catalyst comprises a metal active for the conversion of hydrogen and carbon monoxide to one or more oxygenated hydrocarbons and a support comprising a semiconducting inorganic oxide that is capable of catalysing the oxidation of reduced sulphur compounds, characterised in that the concentration of the one or more reduced sulphur compounds in the reaction composition is greater than 0.5 ppm by weight expressed as elemental sulphur.

In the present invention, synthesis of oxygenated hydrocarbons from carbon monoxide can be carried out in a relatively high sulphur environment, at concentrations of greater than 0.5 ppm, expressed as elemental sulphur, by using a catalyst with a support that has an inorganic oxide with semiconducting properties, and which is capable of oxidising reduced sulphur compounds to sulphur compounds having sulphur with an increased oxidation state. An example of such a sulphur oxidation reaction would be the oxidation H₂S or COS, both having a sulphur oxidation numbers of -2, to sulphur dioxide or sulphur trioxide, which have oxidation numbers of +4 and +6 respectively.

Conventional methanol synthesis catalysts, typically involving Cu on a ZnOZAl₂O₃ support, tend to deactivate rapidly in the presence of reduced sulphur compounds, such as organosulphide compounds, mercaptans, H₂S, COS and the like which can be present in syngas feedstocks. Deactivation is believed to occur as a result of reaction between the sulphur compounds with either or both of the support and the catalyst metal. This can cause sulphidation of the catalyst metal, resulting in reduced activity or even complete deactivation. Additionally, the reduced sulphur compound can react with the support. In the case of zinc oxide, for example, sulphur is absorbed into the oxide structure, transforming the zinc oxide into zinc sulphide. This acts to increase the concentration of sulphur around the catalyst metal, which exacerbates any deactivation effect. As the zinc oxide is not easily regenerated under reaction conditions, even small quantities of sulphur can cause a build up of sulphide in the structure, with a consequent loss in catalytic activity.

The present invention solves this problem by providing a support which is capable of oxidising the reduced sulphur species, typically into one or more oxides of sulphur such as sulphur dioxide or sulphur trioxide, henceforth referred to collectively as SO_x. Without being bound by any theory, it is believed that the inorganic semiconducting oxide can donate framework oxygen to the reduced sulphur compounds in order to oxidise them. This can be achieved either by the creation of framework oxygen vacancies, in which the removed oxygen can be subsequently replaced by the presence of oxygen-containing compounds such as oxygen, carbon dioxide or water in the reaction feedstock, or alternatively by allowing framework oxygen to be replaced by sulphur, which sulphur can then be catalytically oxidised by the support in the presence of oxygen-containing compounds in the feedstock, which regenerates the oxide as a result. In some embodiments of the invention, activity of the catalyst can actually be enhanced by the presence of reduced sulphur compounds, in contrast to the deactivating effect of sulphur on Cu/ZnO/Al₂θ₃, for example, which deactivates rapidly even in the presence of sulphur concentrations of as low as 0.5ppm.

The metal can be any metal that is active for the synthesis of an oxygenated hydrocarbon from hydrogen and carbon monoxide. In one embodiment of the invention, the metal is selected from one or more of Cu, Cr, Co, Mo, Pt, Pd and Rh, and is preferably Cu and/or Pd.

The catalyst used in the process of the present invention may optionally comprise additional components, such as promoter or stabiliser components, selected for example from one or more elements from the group comprising alkali metals, alkaline earth metals, Sc₅ Ϋ, La, Nd, Mn, Zn and Al. The support comprises one or more inorganic semiconducting compounds that are capable of catalysing the conversion of reduced sulphur-containing compounds into oxidised sulphur compounds such as SO_x under the reaction conditions. Optionally, the semiconducting inorganic oxide is doped to impart or improve its semiconducting properties or ability to create oxygen vacancies. Preferably, the inorganic semiconducting oxide is selected from one or more of lanthanide oxides, TiO₂, ZrO₂ and TI1O2. Most preferably, the support comprises one or more selected from lanthanide oxides, CeO₂ and ZrO₂, and most preferably the supportis CeO₂ and/or ZrO₂- Optionally, the one or more semiconducting compounds can be mixed with one or more non-semiconducting compounds, for example Ceθ₂/Al₂θ₃ and ZrO₂ZAl₂Os. The support may additionally comprise other components, such as binder materials.

An inorganic oxide support may be made by a precipitation route, wherein a soluble and/or colloidal precursor of an inorganic oxide is treated so as to produce a solid oxide. If more than one oxide is present in the support, then a co-precipitation route may be employed, in which a mixture of soluble and/or colloidal precursors of each oxide are precipitated together to produce a solid mixed oxide. In a further embodiment of the invention, the metal is precipitated together with the one or more oxide precursor materials to form the supported catalyst. Composite or mixed oxides may be produced by co-precipitation, or by precipitating a precursor of one of the oxides onto the other oxide.

Catalyst lifetime can be further extended in the presence of reduced sulphur compounds when the catalyst metal loading on the semiconducting inorganic oxide is above a certain threshold value. Typically, the mole ratio of the catalyst metal (or at least one of the catalyst metals if more than one is present) to the non-oxygen element of the semiconducting inorganic oxide is greater than 0.09: 1. Typically, the loading of catalyst metal on the support is in excess of 5wt%, and more preferably greater than 8wt%, and is most preferably 10wt% or more. When palladium is present, the mole ratio of palladium to the non-oxygen element of the semiconducting inorganic oxide is preferably greater than 0.09:1, more preferably greater than 0.14:1. The palladium loading on the support is preferably greater than 5wt%, more preferably greater than 8wt% and most preferably 10wt% or more. Where copper is present as the only catalyst metal, the copper mole ratio is preferably in excess of 0.22:1 and more preferably 0.39:1 or more. Preferably, the loading of copper on the support is greater than 8 wt%, and more preferably 10wt% or more.

The catalyst, when used in a process for the conversion of hydrogen and carbon monoxide into one or more oxygenated hydrocarbons, may be used without pre-treatment, or may alternatively be reduced, for example in a flow of hydrogen gas or a mixture of hydrogen in nitrogen, in order to reduce the active catalyst metal component before use. The pre-reduction temperature is typically above 100⁰C to ensure efficient conversion of any catalyst metals to a reduced^' and possibly hydrogenated form. Temperatures less than 300⁰C are preferred for improved catalytic activity. Optimum temperatures for prereduction are typically in the range of from 220 to 26O⁰C.

In the process of the present invention, a reaction mixture comprising hydrogen and carbon monoxide is contacted with the catalyst to produce one or more oxygenated hydrocarbons, such as alcohols, esters, carboxylic acids and ethers. In one embodiment the process is the production of one or more alcohols from hydrogen and carbon monoxide, and is preferably a process for the production of methanol and/or dimethyl ether. Reaction temperatures typically in the range of from 100 to 45O⁰C, preferably from 170 to 30O⁰C, are employed. Generally, increased reaction temperatures result in higher carbon monoxide conversions, lower selectivity to methanol, and higher selectivity to carbon dioxide and light hydrocarbons. Optimum methanol selectivity and yields sire typically achieved in the temperature range of from 220 to 28O⁰C, and especially in the range of from 240 to 26O⁰C.

Reaction pressures are typically in the range of from 1 to 100 bara (0.1 to 10 MPa). Higher pressures tend to result in improved methanol selectivity and carbon monoxide conversions, although hydrocarbon yields also increase with pressure. Carbon dioxide yields tend to reduce with increased pressure. The pressure is preferably in the range of from 10 to 60 bara (1 to 6 MPa).

Syngas is a convenient source of hydrogen and carbon monoxide. Syngas can be prepared from a variety of substances, such as natural gas, liquid hydrocarbons, coal or biomass. The catalyst of the present invention, being sulphur-tolerant, is particularly suitable for syngas comprising relatively high sulphur levels, for example when derived from coal. The catalysts of the present invention are tolerant to sulphur levels in excess of 0.5 ppm (expressed as elemental sulphur), for example 3 ppm or more, or 10 ppm or more. Preferably, the catalyst is tolerant to sulphur levels of up to 100 ppm. The carbon monoxide to hydrogen (CO : H₂) molar ratio in the reaction composition is typically in the range of from 10 : 1 to 1 : 10, and is preferably in the range of 5 : 1 to 1 : 5, such as in the range of from 3 : 1 to 1 : 3. Preferably, the ratio is in the range of from 1 : 1 to 1 : 3.

Increased gas hourly space velocity (GHSV), expressed in terms of total volume of gases (corrected to standard temperature and pressure) per volume of catalyst per hour, typically results in reduced methanol and hydrocarbon yields, and reduced carbon monoxide conversions, while carbon dioxide yields tend to increase. However, if the GHSV is too low, then this can also result in reduced methanol selectivity. The GHSV is preferably maintained at a value in the range of from 500 to 5000 h^"1, more preferably in the range of from 500 to 2000 h^"1.

The reaction composition can additionally comprise a source of oxygen, for example water, oxygen or carbon dioxide. In one embodiment of the invention, molecular oxygen • is present in syngas that may be fed to the process. In an alternative embodiment, oxygen is deliberately added to the reaction composition. The presence of oxygen, either as molecular oxygen or in the form of an oxygen-containing compound such as water or carbon dioxide, is advantageous, as it can facilitate the formation of SO_x and can also enable oxide vacancies in the support to be removed, thus facilitating the sulphur tolerance of the catalyst. This can therefore benefit both catalytic activity and lifetime. The source of oxygen can be continuously fed to the process along with the hydrogen and carbon monoxide. Alternatively, it can be fed intermittently, to improve conversions when catalytic activity and/or product yields begin to fall. The concentration of molecular oxygen, whether present in the feedstock or deliberately added, is typically in the range of up to 1 wt%, for example up to 0.5 wt%. Preferably the molecular oxygen concentration is above 10 ppm.

Carbon dioxide can be present in the reaction composition, either as a constituent of one or more of the feedstock components (e.g. syngas), or produced during the reaction, or separately added to the reaction composition. Carbon dioxide can also assist in the conversion of reduced sulphur compounds to oxidised sulphur compounds, and in reoxidising the inorganic oxide. When present, its concentration in the reaction composition may be in the range of up to 15wt%, such as up to 10wt%, and is typically above lOppm. The present invention will now be illustrated in the following examples, and with reference to the Figures in which;

Figure 1 illustrates one proposed reaction scheme by which catalyst deactivation in the presence of sulphur is inhibited;

Figure 2 illustrates a second proposed reaction scheme by which catalyst deactivation in the presence of sulphur is inhibited;

Figure 3 is a plot of catalytic activity of a PdZAl₂O₃ catalyst in the production of methanol from hydrogen and carbon monoxide in the presence of 3 ppm H₂S;

Figure 4 is a plot of catalytic activity of a PoVCeO₂ catalyst in the production of methanol from hydrogen and carbon monoxide in the presence of 3 ppm H₂S; Figure 5 is a plot of the carbon monoxide conversion over Pd/CeO₂ catalysts with different palladium loadings in the production of methanol from hydrogen and carbon monoxide in the presence of 11 ppm H₂S;

Figure 6 is a plot of the methanol selectivity of Pd/CeO₂ catalysts with different palladium loadings in the production of methanol from hydrogen and carbon monoxide in the presence of 1 lppm H₂S;

Figure 7 is a plot of catalytic activity of a PoVCeO₂ catalyst in the production of methanol from hydrogen and carbon monoxide in the presence of 2.2 ppm COS and 0.8 ppm H₂S;

Figure 8 is a plot of catalytic activity of a Pd/CeO₂ catalyst in the production of methanol from hydrogen and carbon monoxide in the presence of 30 ppm H₂S;

Figure 9 is a plot of catalytic activity of a PdZZrO₂ catalyst in the production of methanol from hydrogen and carbon monoxide in the presence of 36 ppm H₂S;

Figure 10 is a plot of catalytic activity of a Cu/ZnO catalyst in the production of methanol from hydrogen and carbon monoxide in the presence of 36 ppm H₂S;

Figure 11 is a plot of catalytic activity of a CuZCeO₂ catalyst in the production of methanol from hydrogen and carbon monoxide in the presence of 30 ppm H₂S; Figure 12 is a plot of catalytic activity of a CuZZrO₂ catalyst in the production of methanol from hydrogen and carbon monoxide in the presence of 36 ppm H₂S;

Figure 13 is a plot of carbon monoxide conversion against copper loading for CuZZrO₂ catalysts in the presence of 36 ppm H₂S;

Figure 14 is a plot of catalytic activity of a PdZCeO₂ZAl₂Os catalyst in the production of methanol from hydrogen and carbon monoxide in the presence of 11 ppm H₂S;

Figure 15 is a plot of catalytic activity of a Pd-CuZCeO₂ catalyst in the production of methanol from hydrogen and carbon monoxide in the presence of 2.2 ppm COS and,0.8 ppm H₂S.

Figure 16 is a plot of catalytic activity of a PdZCeO₂ catalyst with time in the production of methanol from hydrogen and carbon monoxide in the presence and absence of 30 pρm H₂S.

Figure 17 is a plot of the methanol and dimethyl ether (DME) yield for a PdZCeO₂ catalyst in the presence and absence of 30 ppm H₂S.

Figure 18 is a plot of carbon dioxide yield for a PdZCeO₂ catalyst in the presence and absence of 30 ppm H₂S.

Figure 19 is a plot of light hydrocarbon yield for a PdZCeO₂ catalyst in the presence and absence of 30 ppm H₂S.

Figure 20 is a plot comparing conversion of carbon monoxide and slectivity towards methanol, carbon dioxide and light hydrocarbons at various temperatures using a PdZCeO₂ catalyst.

Figure 21 is a plot comparing conversion of carbon monoxide and selectivity towards methanol, carbon dioxide and light hydrocarbons at various pressures using a PdZCeO₂ catalyst.

Figure 22 is a plot comparing conversion of carbon monoxide and selectivity towards methanol, carbon dioxide and light hydrocarbons at various gas hourly space velocities ^"using a PdZCeO₂ catalyst. ' The reaction scheme illustrated in Figure 1 shows a forward reaction, 1, and reverse reaction, 2, and a catalyst 3 comprising a metal E, 4, active for the conversion of hydrogen and carbon monoxide to oxygenated hydrocarbons supported on a semiconducting inorganic oxide support, 5, referred to as MO_x. In the forward reaction, H₂S reacts with the inorganic oxide, resulting in sulphur being incorporated, 6, into the support (MO_xS) and the release of water. In the reverse reaction, the sulphur is removed by reaction with oxygen present in the reaction composition, resulting in the release of SO_x and the regeneration of the MO_x support.

The reaction scheme of Figure 2 shows the creation of an oxygen vacancy (MO_xG), 7, in the oxide instead of the formation of a sulphided inorganic oxide. Thus, instead of water being released from the support, oxygen is extracted from the support to form SO_x, the vacancy being removed by reaction with oxygen. Example 1 - Pd/AbO^

A catalyst was prepared by treating 22.5 mL of an aqueous solution comprising palladium(II) chloride (having 20 mg palladium per mL) and 18.765g A1(NO₃)₃.9H₂O with a solution of 25 g Na₂CO₃ in 6OmL water as a precipitating agent. A pH of between 8 and 9, and a temperature of 55⁰C were maintained. A precipitate formed which was aged for 2 hours, before being filtered, washed with distilled water, dried overnight at 120 ⁰C, and calcined in air at 360 ⁰C for 6 hours. The Pd:Al mole ratio of the catalyst was 0.08 : 1, giving a palladium loading of 15wt%. Processes using this catalyst are not in accordance with the present invention, as alumina is not a semiconducting oxide. Examples 2 to 4 - PdZCeO₂

These catalysts were prepared using the same procedure as Example 1, except that Ce(NO₃)₃.6H₂O was used in place of the aluminium nitrate. The quantities of materials used are listed in Table 1. A solution of 20 g Na₂CO₃ in 60 mL water was also used for each Example. In Example 2, the Pd:Ce mole ratio of the catalyst was 0.29 : 1. The mole ratios for Examples 3 and 4 were 0.18 : 1 and 0.09 : 1 respectively. These give palladium loadings of, respectively, 15wt%, 10wt% and 5wt% respectively.

Processes using any of these catalysts can be in accordance with the present invention, as palladium is active for the conversion of syngas to oxygenated hydrocarbons, and ceria is a semiconducting oxide capable of catalysing the oxidation of reduced sulphur compounds.

Table 1 : Quantities of Materials Used in Examples 2 to 4.

Example 5 - PdZZrO₂

A catalyst was prepared using the same procedure as Example 1, except that 30 mL of the palladium solution and 20 g Na₂CO₃ in 40 mL water were used. Additionally, 11.846 g Zr(NO₃)₄.5H₂O were used in place of the aluminium nitrate. The Pd:Zr mole ratio of the catalyst was 0.20 : 1, giving a palladium loading of 15wt%.

Processes using this catalyst can be in accordance with the present invention, as palladium is active for the conversion of syngas to oxygenated hydrocarbons, and zirconia is a semiconducting oxide capable of catalysing the oxidation of reduced sulphur compounds. Example 6 - Cu/ZnO

13.904 g Cu(NO₃)₂.3H₂O and 8.559 g Zn(NO₃)₂.6H₂O were dissolved in 50 mL deionised water, and mixed with a solution of 20 g Na₂CO₃ in 5OmL water. The mixture was stirred for 2 hours and a pH of 8 and 9 and a temperature of 55 ⁰C were maintained. The resulting precipitate was aged for 2 hours before being filtered, washed with distilled water, dried overnight 120 ⁰C and calcined in air at 360 ⁰C for 6 hours. The Cu:Zn mole ratio of the catalyst was 2 : 1, giving a copper loading of 56.6wt%.

Processes using this catalyst are not in accordance with the present invention, as zinc oxide does not catalyse the oxidation of reduced sulphur compounds. Example 7 - Cu/CeO?

The same procedure as Example 6 was used, except that 9.479 g Cu(NO₃)₂.3H₂O and a solution of 20 g Na₂CO₃ in 40 mL water were used. Additionally, 8.521 g Ce(NO₃)₃.6H₂O were used in place of the zinc nitrate. The Cu:Ce mole ratio of the catalyst was 2 : 1, giving a copper loading of 42.5wt%.

Processes using this catalyst can be in accordance with the present invention, as copper is active for the conversion of syngas to oxygenated hydrocarbons, and ceria is a semiconducting oxide capable of catalysing the oxidation of reduced sulphur compounds. Example 8 - Cu/ZrO?

The same procedure as Example 6 was used, except that 11.58O g Cu(Nθ3)2-3H2θ and a solution of 25 g Na₂Cθ₃ in 60 mL water was used. Additionally, 10.304 g Zr(NO₃)₄.5H₂θ were used in place of the zinc nitrate. The Cu:Zr mole ratio of the catalyst was 2 : 1, giving a copper loading of 50.7wt%.

Processes using this catalyst can be in accordance with the present invention, as copper is active for the conversion of syngas to oxygenated hydrocarbons, and zirconia is a semiconducting oxide capable of catalysing the oxidation of reduced sulphur compounds. Examples 9 to 15 - CuZZrO₂ The same procedure as Example 8 was used, except that the quantities of materials listed in Table 2 were used.

As in Example 8, processes using any of these catalysts can be in accordance with the present invention, as copper is active for the conversion of syngas to oxygenated hydrocarbons, and zirconia and copper oxide are semiconducting oxides capable of catalysing the oxidation of reduced sulphur compounds.

Table 2: Quantities of salts used in Examples 9 to 15 lystno Cu(NO₃)₂-3H₂O(g) Zr(NO₃)₄-5H₂

9 2.281 18.285

10 6.842 14.222

11 9.123 12.190

12 13.684 8.127

13 15.965 6.095

14 20.526 2.032

15 15.000 0

Example 16 - PdVCeO₂ZAl₂O₁ The same procedure as Example 2 was used, except that 45 ml of the palladium solution, a solution of 30 g Na₂CO₃ in 50 mL water, and 11.206 g Ce(NO₃)₃.6H₂O were used. Additionally, 4.841 g A1(NO₃)₃.9H₂O were added to the solution. The Pd:Ce:Al mole ratio of the catalyst was 0.33 : 1 : 0.5. This gives a Pd loading on CeO₂ZAl₂O₃ of 15wt%.

Processes using this catalyst can be in accordance with the present invention, as palladium is active for the conversion of syngas to oxygenated hydrocarbons, and the support comprises ceria, which is a semiconducting oxide capable of catalysing the oxidation of reduced sulphur compounds. Example 17 - Pd-CuZCeO₂

The same procedure as Example 2 was used, except that 19.6 mL of the palladium solution, a solution of 20 g Na₂CO₃ in 5OmL water and 6.45 g Ce(NO₃)₃.6H₂O were used. Additionally, 0.222 g Cu(NO₃)₂.3H₂O were added to the solution. The Pd:Cu:Ce mole ratio of the catalyst was 0.25 : 0.06 : 1. This gives a Pd loading on CeO₂ of 13.1wt%, and a copper loading on CeO₂ of 1.9wt%.

As in Examples 2-4 and 7, processes using this catalyst can be in accordance with the present invention.

A summary of the compositions of all the catalysts is listed in Table 3.

Table 3 : Catalyst Compositions

' Pd(wt%) / Cu(wt%)

Catalyst Evaluation

Samples of powdered catalyst were compressed into a disc at a pressure 20 MPa, and were subsequently crushed and sieved to provide particle sizes of between 20 and 40 mesh. 0.4g of the sieved particles were diluted with 1.Og quartz particles, and charged to a 140mm long stainless steel fixed-bed tube reactor with an inner diameter of 14mm. The resulting height of the catalyst bed was approximately 5mm. The catalyst was reduced in a flow of 100% hydrogen (6.67 mL/min) at a specified temperature for 8 hours. A reaction composition comprising hydrogen and carbon monoxide with a molar CO : H₂ ratio of 1 : 2 was then fed to the catalyst at a specified reaction temperature, a pressure of 3.0 MPa absolute, and a GHSV (gas hourly space velocity) of 1000 h^"1. The feed gases also comprised CO₂ at 5% by volume, and N₂ at 2.3% by volume. Sulphur was also present in the feed gases in the form OfH₂S or a combination of COS and H₂S at various concentrations. The quantity of methanol in the product stream from the tube reactor was determined by on-line gas chromatography equipped with a 1.5m long carbon molecular sieve column using a high purity helium carrier gas. Comparative Experiment 1

The Pd/ Al₂O₃ catalyst of Example 1 was pre-reduced at 300 ⁰C. It was studied at a reaction temperature of 240 ⁰C, with a feedstock comprising 3 ppm H₂S. O₂ was also added to the feedstock at a concentration of 0.5% by volume. Figure 3 shows the results of CO conversion and methanol selectivity over a period of 100 hours. The CO conversion and methanol selectivity both reduce over time, indicating deactivation of the catalyst. This is not a process in accordance with the present invention, as alumina is not a semiconducting oxide. Experiment 2

The PdVCeO₂ catalyst of Example 2 was pre-reduced at 300 ⁰C. It was studied at a reaction temperature of 240 ⁰C, with a feedstock comprising 3 ppm H₂S. O₂ was also added to the feedstock at a concentration of 0.5% by volume. Figure 4 shows the results of CO conversion and methanol selectivity over a period of 100 hours. After an initial period of instability during the first 20 hours of reaction, both parameters level out and begin to increase with time. This indicates that a Pd catalyst with a CeO₂ support is tolerant to the presence of sulphur. Experiment 3 The Pd/CeO₂ catalysts of Examples 2 to 4 were pre-reduced at 240 ⁰C and studied at a reaction temperature of 240⁰C, with a feedstock comprising 11 ppm H₂S. O₂ was also added to the feedstock at a concentration of 0.5% by volume. Figure 5 shows the results of CO conversion and Figure 6 shows methanol selectivity over a period of 100 hours for Examples 3 and 4, and over 72 hours for Example 2. The results show that methanol selectivity is higher after 100 hours on stream compared to the Pd/Al₂θ₃ catalyst. It also shows that carbon monoxide conversions are higher and deactivation rates are reduced when the mole ratio of palladium to the CeO₂ support is greater than 0.09, even at higher concentrations of sulphur in the feedstock. The results further demonstrate that carbon monoxide conversions are higher for catalysts that are pre-treated in hydrogen at the lower temperature of 24O⁰C, even when the sulphur content is higher, as is apparent by comparing the results with those for Example 2 of Experiment 2. Experiment 4

The PaVCeO₂ catalyst of Example 2 was pre-reduced at 300 ⁰C. It was studied at a reaction temperature of 24O⁰C, with a feedstock comprising 0.8 ppm H₂S and 2.2 ppm COS. O₂ was also added to the feedstock at a concentration of 0.5% by volume. Figure 7 shows the results of CO conversion and methanol selectivity over a period of 100 hours. After an initial period of activity reduction over the first 20 hours of reaction, the activity begins to increase with time. This experiment demonstrates that the Pd/CeO₂ catalyst is tolerant to the presence of different sulphur compounds. Experiment 5

The PdVCeO₂ catalyst of Example 2 was pre-reduced at 240 ⁰C. It was studied at a reaction temperature of 24O⁰C, with a feedstock comprising 30 ppm H₂S. No molecular oxygen was added to the reactor. Figure 8 shows the results of CO conversion and methanol selectivity over a period of 100 hours. After an initial period of activity reduction over the first 20 hours of reaction, the activity begins to increase with time. This experiment demonstrates that the Pd/CeO₂ catalyst is tolerant to the presence of large concentrations of sulphur in the feedstock. Experiment 6

The Pd/ZrO₂ catalyst of Example 5 was pre-reduced at 240 ⁰C. It was studied at a reaction temperature of 240 ⁰C, with a feedstock comprising 36 ppm H₂S. No molecular oxygen was added to the reactor. Figure 9 shows the results of CO conversion and methanol selectivity over a period of 10 hours. High CO conversions are exhibited. This experiment demonstrates that ZrO₂ is also an effective support which has tolerance to high concentrations of sulphur. Experiment 7 '

The Cu/ZnO catalyst of Example 6 was pre-reduced at 220 ⁰C. It was studied at a reaction temperature of 22O⁰C, with a feedstock comprising 36ppm H₂S. No molecular oxygen was added to the reactor. Figure 10 shows the results of CO conversion and methanol selectivity over a period of 7 hours. Rapid loss in activity is experienced, showing that Cu/ZnO is not tolerant to high levels of sulphur. Experiment 8

The CuZCeO₂ catalyst of Example 7 was pre-reduced at 220 ⁰C, and tested at a reaction temperature of 220 ⁰C for 8 hours, and 240 ⁰C for a further period of 7 hours in the presence of a feedstock comprising 30 ppm H₂S, No molecular oxygen was added to the reactor. Figure 11 shows the results of CO conversion and methanol selectivity over a period of 15 hours. No loss in activity was observed, and activity increased at the higher reaction temperature. The Experiment shows that a Cu/Ceθ₂ catalyst is also resistant to deactivation by sulphur even at high sulphur concentrations. Experiment 9

The Cu/ZrO₂ catalyst of Example 8 was pre-reduced at 220⁰C, and tested at a reaction temperature of 240 ⁰C over a period of 100 hours in the presence of a feedstock comprising 36 ppm H₂S. No molecular oxygen was added to the reactor. Figure 12 shows the results of CO conversion and methanol selectivity over a period of 100 hours. Activity remained steady with only a small degree of deactivation observed. The Experiment shows that a CuZZrO₂ catalyst is also resistant to deactivation by sulphur even at high sulphur concentrations. Experiment 10

CuZZrO₂ catalysts of Examples 8 to 15 were pre-reduced at 220 ⁰C, and tested at a reaction temperature of 220 ⁰C over a period of 10 hours in the presence of a feedstock comprising 36 ppm H₂S. No molecular oxygen was added to the reactor. Figure 13 shows the results of CO conversion after 10 hours for each of the catalysts (the data point labels represent the Example number of the catalyst used). The Experiment shows that ZrO₂- supported catalysts with Cu:Zr mole ratios of greater than 1.33 and less than 17.95 show the highest activity, corresponding to copper loadings of greater than 40.7 wt% and less than 90.3%. Experiment 11

The PdZCeO₂ZAl₂O₃ catalyst of Example 16 was pre-reduced at 300 ⁰C, and tested at a reaction temperature of 240⁰C over a period of 27 hours in the presence of 11 ppm H₂S. O₂ was also added to the feedstock at a concentration of 0.5% by volume. Figure 14 shows the results of CO conversion and methanol selectivity over a period of 27 hours. The results demonstrate that a catalyst with a support comprising a semiconducting oxide and a non-semiconducting oxide can still be sulphur resistant.

Experiment 12

The Pd-CuZCeO₂ catalyst of Example 17 was pre-reduced at 300 ⁰C, and tested at a reaction temperature of 240 ⁰C over a period of 29 hours in the presence of 0.8 ppm H₂S and 2.2 ppm COS. O₂ was also added to the feedstock at a concentration of 0.5% by volume. Figure 15 shows the results of CO conversion and methanol selectivity over a period of 29 hours. The results show that a catalyst comprising both Pd and Cu catalyst metals is also active and resistant to sulphur concentrations of greater than 0.5 ppm.

Experiment 13 The PdMl₂O₃ and Pd/CeO₂ catalysts of Examples 1 and 2 respectively were analysed by X-Ray diffraction and X-ray fluorescence both before and after reaction for 100 hours on stream in an atmosphere comprising 30 ppm H₂S. Results are shown in Table 4.

The alumina-supported catalyst after use has significantly higher levels of sulphur than the ceria-supported catalyst, indicating a lower level of catalyst poisoning by sulphur in the ceria-supported catalyst.

Table 4: XRD Analysis

Crystalline Phases³

Example (Catalyst) Before Use After lOOh S after lOOh (wt%)^b

1 (Pd/Al₂O₃) Pd, Al₂O₃ Pd, Al₂O₃, PdS 0.52 2 (Pd/CeO₂) Pd, CeO₂ Pd, CeO₂ 0.032

As determined from X-Ray Diffraction b Sulphur content of the catalyst as determined by X-Ray Fluorescence (0 wt% before use).

Comparative Experiment 14

The PdZCeO₂ catalyst of Example 2 was contacted with hydrogen and carbon monoxide under the same conditions as described in Experiment 5, except that no H₂S was present in the feed. This is not a process in accordance with the present invention, as the sulphur concentration was not greater than 0.5 ppm.

Results of catalytic activity over a 100 hour period are shown in Figures 16, 17, 18 and 19, and compared with the results of Experiment 5. Methanol selectivity dropped rapidly in the first two hours of reaction in the absence

OfH₂S₅ but gradually increased to 83% after 100 hours. Carbon monoxide conversion reduced from an initial value of 27.5% to 20% after 100 hours, resulting in a methanol yield of 16.6% after 100 hours. Carbon dioxide is shown to be produced, the concentration dropping from a maximum value of just under 4% to a approximately 1.5% after 100 hours. Furthermore, the production of light hydrocarbons (Cl to C5 hydrocarbons) reduced from between 4 and 5% yield down to about 1% after 100 hours. In Experiment 5, where 30 ppm sulphur is present in the feedstock, the CO conversion is lower but the methanol selectivity is higher to the effect that the methanol yield was equivalent to that in the absence OfH₂S. The carbon dioxide production is lower, reducing from a maximum of just under 2% down to approximately 0.5% after 100 hours. Similarly, Cl to C5 hydrocarbons were produced in lower quantities.

Experiments 14 and 5 confirm the conclusion that catalytic activity is maintained over extended periods of time, even when sulphur is present in the feedstock. The Experiments also demonstrate that production of carbon dioxide and hydrocarbon by-products are lower when sulphur is present in the feedstock.

Experiment 15

The Pd/Ceθ₂ catalyst of Example 2 was evaluated at a pressure of 30 bara (3 MPa),

1000 h^"1 GHSV, using a feedstock comprising 3.3 ppm H₂S and 0.4% oxygen by volume. The catalyst was studied at temperatures of 220, 240, 260 and 280 ⁰C. Results are shown in Figure 20.

Methanol selectivity improved between 220 and 240 ⁰C, but reduced thereafter.

Carbon dioxide selectivity dropped between 220 and 240 ⁰C, but increased thereafter.

Carbon monoxide conversion increased with increasing temperature. Light hydrocarbon selectivity increased with increasing temperature.

Experiment 16

The Pd/CeO₂ catalyst of Example 2 was evaluated at a temperature of 240 ⁰C, a

GHSV of 1000 h^"1 using the same feedstock as described in Experiment 15. Pressures of 1,

2, 3, 4 and 5 MPa were used. Results are shown in Figure 21. Generally, methanol selectivity and light hydrocarbon selectivity increased with increasing pressure, carbon dioxide selectivity reduced with increasing pressure and carbon monoxide conversion increased with increasing pressure. Experiment 17

The Pd/CeO₂ catalyst of Example 2 was evaluated at a temperature of 240⁰C, a pressure of 3 MPa, using the same feedstock as Example 15. GHSVs between 500 and 5000 h^'1 were used. Results are shown in Figure 22.

Generally, selectivity towards methanol and light hydrocarbons reduced with increased GHSV, while carbon monoxide conversion and carbon dioxide selectivity increased with increased GHSV.

Claims

1. A process for the production of one or more oxygenated hydrocarbons from hydrogen and carbon monoxide, which process comprises contacting a catalyst with a reaction composition comprising carbon monoxide, hydrogen and one or more reduced sulphur compounds under conditions sufficient to produce one or more oxygenated hydrocarbons, which catalyst comprises a metal active for the conversion of hydrogen and carbon monoxide to one or more oxygenated hydrocarbons and a support comprising a semiconducting inorganic oxide that is capable of catalysing the oxidation of reduced sulphur compounds, characterised in that the concentration of the one or more reduced sulphur compounds in the reaction composition is greater than 0.5 ppm by weight expressed as elemental sulphur.

2. A process as claimed in claim I₅ in which the metal active for the conversion of hydrogen and carbon monoxide to one or more oxygenated hydrocarbons is selected from one or more of Cu, Cr, Co, Mo, Pt, Pd and Rh.

3. A process as claimed in claim 2, in which the metal is Pd and/or Cu.

4. A process as claimed in any one of claims 1 to 3, in which the mole ratio of at least one catalyst metal to the non oxygen element of the inorganic semiconducting oxide is greater than 0.09 : 1.

5. A process as claimed in any one of claims 1 to 4, in which the semiconducting inorganic oxide capable of catalysing the oxidation of reduced sulphur compounds is selected from one or more of a lanthanide oxide, TiO₂, ZrO₂ and ThO₂.

6. A process as claimed in claim 5, in which the semiconducting inorganic oxide is ZrO₂ and/or CeO₂.

7. A process as claimed in any one of claims 1 to 6, in which the catalyst also comprises a promoter selected from the group comprising alkali metals, alkaline earth metals, Sc,

Y, La, Nd, Mn, Zn and Al.

8. A process as claimed in any one of claims 1 to 7, in which reduced sulphur compounds are present at concentrations of 3 ppm or more.

9. A process as claimed in any one of claims 1 to 8, in which the carbon monoxide to hydrogen (CO : H₂) molar ratio is in the range of from 3 : 1 to 1 : 3.

10. A process as claimed in any one of claims 1 to 9, in which the source of carbon monoxide and hydrogen is syngas.

11. A process as claimed in claim 10, in which the syngas is derived from coal.

12. A process as claimed in any one of claims 1 to 11, in which the process is for the production of methanol and/or dimethyl ether.

13.^' A process as claimed in any one of claims 1 to 12, in which a source of oxygen in the form of one or more of molecular oxygen, carbon dioxide and water is present in the reaction composition.

14. A process as claimed in claim 13, in which oxygen is present in the reaction- composition at a concentration of up to lwt%.

15. A process as claimed in claim 13 or claim 14, in which carbon dioxide is present in the reaction composition at a concentration of up to 15wt%.

16. A process as claimed in any one of claims 1 to 15, in which the reaction temperature is in the range of from 100 to 450 ⁰C, and the reaction pressure is in the range of from 1 to 100 bara (0.1 to 10 MPa).

17. A process as claimed in any one of claims 1 to 16, in which the gas hourly space velocity is maintained at a value in the range of from 500 to 5000 h^"1.