CN101646641A - Process for the conversion of syngas to oxygenates - Google Patents

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 aninorganic 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 0.5ppm by weight, expressed as elemental sulphur.

Description

Process for converting synthesis gas into oxygenates

The present invention relates to the field of catalysis, and more particularly to a catalytic process in which the catalyst is resistant to deactivation by sulfur.

Coal is a fuel widely used to generate electricity. However, it tends to be unpopular compared with other fuels, such as crude oil derived fuels or natural gas, because of its generally low energy release per unit weight of combustion. In addition, coal tends to contain relatively large amounts of sulfur, which can often act as a catalyst poison in processes using coal-derived feedstocks and can reduce catalyst life and activity.

As a result, high sulfur feedstocks must be pretreated in many cases to remove sulfur below allowable levels. Such raw material pretreatment requires considerable capital outlay and operating costs. Additionally, since desulfurization typically employs sacrificial sorbents such as zinc oxide, the process increases waste generation. Therefore, a catalyst that can tolerate higher levels of sulfur would be advantageous to reduce or even eliminate the need for such pretreatment.

Methanol is an important bulk commercial chemical that is usually produced from synthesis gas (a mixture of hydrogen and carbon monoxide). Syngas can be produced from a variety of raw materials, especially hydrocarbon sources such as natural gas, heavy oil, coal, and biomass. However, currently used catalysts such _as Cu/ZnO/ _Al2O3 are highly sensitive to the presence of sulfur in the syngas feedstock and are often deactivated even in the presence of sulfur in amounts as low as 0.5 ppm. Typical syngas feedstocks, especially when derived from coal, may have sulfur levels in the range of 10-100 ppm. Therefore, there remains a need for a process for converting syngas to oxygenates that is tolerant of the presence of sulfur in the feedstock.

According to the present invention, there is provided a method for producing one or more oxygenated hydrocarbons from hydrogen and carbon monoxide, said method comprising bringing a catalyst and a reaction composition under conditions sufficient to produce one or more oxygenated hydrocarbons contacting, the reaction mixture comprising carbon monoxide, hydrogen and one or more reduced sulfur compounds, the catalyst comprising a metal and a support, the metal being active for converting hydrogen and carbon monoxide into one or more oxygenated hydrocarbons , the support comprising a semiconducting inorganic oxide capable of catalyzing the oxidation of reduced sulfur compounds, characterized in that the concentration of one or more reduced sulfur compounds in the reaction mixture is greater than 0.5ppm.

In the present invention, the synthesis from carbon monoxide to oxygenated hydrocarbons can be carried out in a higher sulfur environment at a concentration greater than 0.5 ppm expressed in terms of elemental sulfur by using a catalyst with a support containing an inorganic oxide with semiconducting properties , and capable of oxidizing reduced sulfur compounds to sulfur compounds with sulfur in an increased oxidation state. An example of such a sulfur oxidation reaction is the oxidation of _H2S or COS, both of which have sulfur oxidation numbers of -2, to sulfur dioxide or sulfur trioxide, which have oxidation numbers of +4 and +6, respectively.

Conventional methanol synthesis catalysts _, usually comprising Cu on ZnO/ _Al2O3 supports, tend to deactivate rapidly in the presence of reduced sulfur compounds such as organosulfides, mercaptans, _H2S , COS, etc. that may be present in the syngas feedstock . This deactivation is believed to occur as a result of a reaction between the sulfur compound and either or both the support and/or catalyst metal. This may cause sulfidation of the catalyst metal, resulting in reduced activity or even complete deactivation. In addition, reduced sulfur compounds are capable of reacting with the support. For example, in the case of zinc oxide, sulfur is adsorbed into the oxide structure, thereby converting the zinc oxide to zinc sulfide. This causes the concentration of sulfur to increase around the catalyst metal, exacerbating any deactivation effects. Since zinc oxide is not easily regenerated under the reaction conditions, even small amounts of sulfur can promote the establishment of sulfur compounds in the structure, resulting in a loss of catalyst activity.

The present invention addresses this problem by providing a support capable of oxidizing reduced sulfur species typically to one or more sulfur oxides, hereinafter collectively referred to as _SOx , such as sulfur dioxide or sulfur trioxide. Without being bound by any theory, it is believed that the inorganic semiconductor oxide is capable of donating framework oxygen to reduced sulfur compounds to oxidize them. This can be achieved by the formation of lattice oxygen vacancies, on which the removed lattice oxygen can then be replaced by oxygen-containing compounds such as oxygen, carbon dioxide or water present in the reaction feed; or alternatively, this This can be achieved by replacing the lattice oxygen with sulfur which can then be catalytically oxidized by the support in the presence of oxygenates in the feedstock, resulting in regeneration of the oxide. In some embodiments of the invention, the activity of _the catalyst is _virtually Can be enhanced by the presence of reduced sulfur.

The metal may be any metal that is active for the synthesis of oxygenated hydrocarbons from hydrogen and carbon monoxide. In one embodiment of the present 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 invention may optionally comprise: additional components such as cocatalyst or stabilizer components selected from the group consisting of, for example, alkali metals, alkaline earth metals, Sc, Y, La, Nd, Mn, Zn and Al One or more elements of the group.

The support comprises one or more inorganic semiconducting compounds capable of catalytically oxidizing reduced sulfur-containing compounds to oxidized sulfur compounds, such as SOx, under reaction conditions. Optionally, the semiconducting inorganic oxide is doped to impart or enhance its semiconducting properties or ability to generate oxygen vacancies. Preferably, the inorganic semiconductor oxide is selected from one or more of lanthanide oxides, TiO ₂ , ZrO ₂ and ThO ₂ . Most preferably, the support comprises one or more selected from lanthanide oxides, CeO ₂ and ZrO ₂ , and most preferably, the support is CeO ₂ and/or ZrO ₂ . Optionally, one or more semiconducting compounds can be mixed with one or more non-semiconducting compounds, such as CeO ₂ /Al ₂ O ₃ and ZrO ₂ /Al ₂ O ₃ . The carrier may additionally comprise other components, such as binder materials.

Inorganic oxide supports can be prepared by a precipitation route in which soluble and/or colloidal inorganic oxide precursors are treated to produce solid oxides. If more than one oxide is present in the support, a co-precipitation route can be utilized wherein a mixture of soluble and/or colloidal precursors of each oxide is precipitated together to produce a mixed solid oxide. In another embodiment of the invention, a metal is precipitated with one or more oxide precursor materials to form a supported catalyst. Composite or mixed oxides can be prepared by co-precipitation or by precipitating a precursor of one of the oxides onto the other.

When the catalyst metal loading on semiconducting inorganic oxides is above a certain threshold, the lifetime of the catalyst in the presence of reduced sulfur compounds can be further extended. Typically, the molar ratio of the catalyst metal (or at least one of the catalyst metals if multiple catalyst metals are present) to the non-oxygen element of the semiconducting inorganic oxide is greater than 0.09:1. Typically, the catalyst metal loading on the support exceeds 5% by weight, and more preferably exceeds 8% by weight, and most preferably exceeds 10% by weight. When palladium is present, the molar ratio of palladium to non-oxygen elements of the semiconducting inorganic oxide is preferably greater than 0.09:1, more preferably greater than 0.14:1. The palladium loading on the carrier is preferably greater than 5% by weight, more preferably greater than 8% by weight, and most preferably 10% by weight or more. Where copper is present as the only catalyst metal, the copper molar ratio is preferably in excess of 0.22:1, and more preferably in excess of 0.39:1. Preferably, the amount of copper supported on the carrier is greater than 8% by weight, and more preferably 10% by weight or more.

When used in a process for the conversion of hydrogen and carbon monoxide to one or more oxygenated hydrocarbons, the catalyst can be used without pretreatment, or can be selectively reduced, for example in a hydrogen stream or a mixture of hydrogen and nitrogen In-stream reduction to reduce active catalyst metal components prior to use. The pre-reduction temperature is usually above 100°C to ensure efficient conversion of any catalyst metal to the reduced or possibly hydrogenated structural form. A reduction temperature below 300°C is preferred to increase catalyst activity. The optimum temperature for pre-reduction is usually in the range of 220-260°C.

In the process of the invention, a reaction mixture comprising hydrogen and carbon monoxide is contacted with a catalyst to produce one or more oxygenated hydrocarbons, such as alcohols, esters, carboxylic acids and ethers. In one embodiment, the process produces one or more alcohols from hydrogen and carbon monoxide, and is preferably a process for the production of methanol and/or dimethyl ether. The reaction temperature employed is usually in the range of 100 to 450°C, preferably in the range of 170 to 300°C. In general, increasing the reaction temperature results in increased conversion of carbon monoxide, decreased selectivity to methanol, and increased selectivity to carbon dioxide and light hydrocarbons. Usually in the temperature range of 220-280°C, especially in the range of 240-260°C, the best selectivity and yield of methanol are obtained.

The reaction pressure is usually in the range of 1-100 bar (0.1-10 MPa). Although hydrocarbon yields also increase with pressure, higher pressures tend to result in increased methanol selectivity and carbon monoxide conversion. Carbon dioxide yield tends to decrease with increasing pressure. The pressure is preferably in the range of 10-60 bar (1-6 MPa).

Syngas is a readily available source of carbon monoxide and hydrogen. Syngas can be produced from a variety of substances such as natural gas, liquid hydrocarbons, coal or biomass. The sulfur-tolerant catalysts of the present invention are particularly suitable for syngas containing relatively high levels of sulfur, such as when derived from coal. The catalyst of the present invention can tolerate sulfur amounts exceeding 0.5 ppm (expressed in terms of elemental sulfur), such as above 3 ppm, or above 10 ppm. Preferably, the catalyst is tolerant to sulfur levels up to 100 ppm.

The molar ratio of carbon monoxide to hydrogen (CO:H ₂ ) in the reaction mixture is generally in the range of 10:1 to 1:10, and preferably in the range of 5:1 to 1:5, for example in the range of 3:1 to 1:3 range. Preferably, the ratio is in the range of 1:1 to 1:3.

Increases in gas hourly space velocity (GHSV), expressed as the total volume of gas per unit volume of catalyst per hour (at standard temperature and under pressure). However, if the GHSV is too low, it may also result in reduced methanol selectivity. GHSV is preferably maintained at a value within the range of 500 to 5000h ^-1 , more preferably within the range of 500 to 2000h ^-1 .

The reaction mixture may additionally contain a source of oxygen, such as water, oxygen or carbon dioxide. In one embodiment of the invention molecular oxygen is present in the synthesis gas which may be fed to the process system. In an alternative embodiment, oxygen is intentionally added to the reaction mixture. The presence of oxygen in the form of molecular oxygen or oxygen-containing compounds such as water or carbon dioxide is advantageous because it can promote the formation of SOx and also remove oxide vacancies in the support, thereby promoting the sulfur tolerance of the catalyst. Thus, this can benefit catalytic activity and lifetime. An oxygen source may be continuously fed into the process system along with hydrogen and carbon monoxide. Alternatively, when catalytic activity and/or product yield begins to decline, the oxygen source may be supplied intermittently to increase conversion.

Whether present in the feedstock or intentionally added, the concentration of molecular oxygen is generally in the range of up to 1% by weight, for example up to 0.5% by weight. Preferably, the molecular oxygen concentration is >10 ppm.

Carbon dioxide may be present in the reaction mixture as a constituent of one or more of the feedstock components (eg, synthesis gas), or produced during the reaction, or added separately to the reaction mixture. Carbon dioxide can also aid in the conversion of reduced sulfur compounds to oxidized sulfur compounds and in the reoxidation of inorganic oxides. When present, its concentration in the reaction mixture may range from up to 15% by weight, such as up to 10% by weight, and is usually above 10 ppm.

The invention will now be illustrated in the following examples and with reference to the accompanying drawings, in which:

Figure 1 shows one of the proposed reaction schemes to suppress catalyst deactivation in the presence of sulfur.

Figure 2 shows the second of the proposed reaction schemes to suppress catalyst deactivation in the presence of sulfur.

Figure 3 is a graph of the catalytic activity of a Pd/ _Al2O3 catalyst in the production of methanol from hydrogen and carbon monoxide in the presence of 3 ppm _{H2S ;}

Figure 4 is a graph of the catalytic activity of the Pd/ _CeO2 catalyst in the production of methanol from hydrogen and carbon monoxide in the presence of ₃ ppm H2S;

Figure 5 is a graph of the carbon monoxide conversion of Pd/ _CeO2 catalysts with different palladium loadings during the production of methanol from hydrogen and carbon monoxide in the presence of 11 ppm _H2S ;

Figure 6 is a graph 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 11 ppm _H2S ;

Figure 7 is a graph of the catalytic activity of the Pd/ _CeO2 catalyst in the production of methanol from hydrogen and carbon monoxide in the presence of 2.2ppm COS and 0.8ppm _H2S ;

Figure 8 is a graph of the catalytic activity of the Pd/ _CeO2 catalyst in the production of methanol from hydrogen and carbon monoxide in the presence of 30 ppm _H2S ;

Figure 9 is a graph of the catalytic activity of a Pd/ _ZrO2 catalyst in the production of methanol from hydrogen and carbon monoxide in the presence of 36 ppm _H2S ;

Figure 10 is a graph of the catalytic activity of Cu/ZnO catalysts in the production of methanol from hydrogen and carbon monoxide in the presence of 36 ppm _H2S ;

Figure 11 is a graph of the catalytic activity of Cu/ _CeO2 catalysts in the production of methanol from hydrogen and carbon monoxide in the presence of 30 ppm _H2S ;

Figure 12 is a graph of the catalytic activity of Cu/ _ZrO2 catalysts in the production of methanol from hydrogen and carbon monoxide in the presence of 36 ppm _H2S ;

Figure 13 is a graph of carbon monoxide conversion versus copper loading for Cu/ _ZrO2 catalysts in the presence of 36 ppm _H2S ;

Figure 14 is a graph of the catalytic activity of the Pd/ _CeO2 / _Al2O3 catalyst in the production of methanol from hydrogen and carbon _monoxide in the presence of 11 ppm _H2S ;

Figure 15 is a graph of the catalytic activity of the Pd-Cu/ _CeO2 catalyst during the production of methanol from hydrogen and carbon monoxide in the presence of 2.2ppm COS and 0.8ppm _H2S ;

Figure 16 is a graph of the catalytic activity of Pd/ _CeO2 catalysts in the production of methanol from hydrogen and carbon monoxide with and without 30 ppm _H2S ;

Figure 17 is a graph of methanol and dimethyl ether (DME) yields for Pd/ _CeO2 catalysts with and without 30 ppm _H2S ;

Figure 18 is a graph of carbon dioxide yield for Pd/ _CeO2 catalysts with and without 30 ppm _H2S ;

Figure 19 is a graph of light hydrocarbon yields for Pd/ _CeO2 catalysts with and without 30 ppm _H2S ;

Figure 20 is a comparative graph of the conversion of carbon monoxide and the selectivity of methanol, carbon dioxide and light hydrocarbons at different temperatures using a Pd/ _CeO2 catalyst;

Figure 21 is a comparative graph of the conversion of carbon monoxide and the selectivity of methanol, carbon dioxide and light hydrocarbons at different pressures using Pd/ _CeO2 catalyst;

Figure 22 is a graph comparing carbon monoxide conversion and selectivity to methanol, carbon dioxide and light hydrocarbons at different gas hourly space velocities using Pd/ _CeO2 catalyst.

The reaction scheme shown in Figure 1 shows the forward reaction 1, as well as the reverse reaction 2, the catalyst 3 comprising a metal E4 supported on a semiconducting inorganic oxide support 5 called _MOx , which is sensitive to hydrogen and The conversion of carbon monoxide to oxygenated hydrocarbons is active. In the forward reaction, _H2S reacts with the inorganic oxide, resulting in the incorporation of sulfur into the support ( _MOxS ) and the release of water. In the reverse reaction, sulfur is removed by reacting with oxygen present in the reaction mixture, resulting in the release of _SOx and the regeneration of the _MOx carrier.

The reaction scheme in Figure 2 shows the formation of oxygen vacancies (MO _x □) 7 in the oxide rather than the formation of sulfurized inorganic oxides. Therefore, instead of releasing water from the support, oxygen is taken from the support to form _SOx , and vacancies are removed by reaction with oxygen.

Example 1 - Pd/Al ₂ O ₃

The catalyst was prepared by treating 22.5 ml containing palladium(II) chloride (20 mg Pd per ml) and 18.765 g Al(NO ₃ ) ₃ ·9H ₂ O by using a solution of 25 g _{Na 2} CO ₃ in 60 ml water as precipitant of aqueous solution. Maintain a pH value of 8-9 and a temperature of 55°C. The formed precipitate was aged for 2 hours before being filtered, washed with distilled water, dried overnight at 120°C and calcined in air at 360°C for 6 hours. The Pd:Al molar ratio of the catalyst was 0.08:1, resulting in a palladium loading of 15% by weight.

Since alumina is not a semiconducting oxide, methods employing this catalyst are not in accordance with the present invention.

Example 2-4-Pd/CeO ₂

These catalysts were prepared using the same procedure as in Example 1, except that Ce(NO ₃ ) ₃ ·6H ₂ O was used instead of aluminum nitrate. The amounts of materials used are listed in Table 1. A solution of 20 g Na ₂ CO ₃ in 60 ml water was also used for each example. In Example 2, the Pd:Ce molar ratio of the catalyst was 0.29:1. The molar ratios for Examples 3 and 4 were 0.18:1 and 0.09:1, respectively. These resulted in palladium loadings of 15%, 10% and 5% by weight, respectively.

Since palladium is active for the synthesis of syngas to oxygenated hydrocarbons, and ceria is a semiconducting oxide capable of catalyzing the oxidation of reduced sulfur compounds, a process employing either of these catalysts may be consistent with the present invention.

Table 1: Amounts of materials employed in Examples 2-4

Example Amount of Pd solution (ml) Ce(NO ₃ ) ₃ 6H ₂ O(g) 2 22.5 6.450 3 15.0 6.813 4 7.5 7.191

Example 5 - Pd/ZrO ₂

The catalyst was prepared using the same procedure as in _Example 1, except that 30 ml of palladium solution and 20 g of _Na2CO3 in 40 ml of water were used. In addition, 11.846 g of Zr(NO ₃ ) ₄ ·5H ₂ O was used instead of aluminum nitrate. The Pd:Zr molar ratio of the catalyst was 0.20:1, resulting in a palladium loading of 15% by weight.

Since palladium is active for the synthesis of synthesis gas to oxygenated hydrocarbons, and zirconia is a semiconducting oxide capable of catalyzing the oxidation of reduced sulfur compounds, methods employing this catalyst may be in accordance with the invention.

Example 6-Cu/ZnO

13.904 g Cu(NO ₃ ) ₂ .3H ₂ O and 8.559 g Zn(NO ₃ ) ₂ .6H ₂ O were dissolved in 50 ml deionized water and mixed with a solution of 20 g Na ₂ CO ₃ in 50 ml water. The mixture was stirred for 2 hours while maintaining a pH of 8-9 and a temperature of 55°C. The formed precipitate was aged for 2 hours before being filtered, washed with distilled water, dried overnight at 120°C and calcined in air at 360°C for 6 hours. The Cu:Zn molar ratio of the catalyst was 2:1, resulting in a copper loading of 56.6% by weight.

Since zinc oxide does not catalyze the oxidation of reduced sulfur compounds, processes employing this catalyst are not in accordance with the invention.

Example 7 - Cu/CeO ₂

The same procedure as Example 6 was used except that a solution of 9.479 g Cu(NO ₃ ) ₂ ·3H ₂ O and 20 g Na ₂ CO ₃ in 40 ml water was used. In addition, 8.521 g of Ce(NO ₃ ) ₃ ·6H ₂ O was used instead of zinc nitrate. The Cu:Ce molar ratio of the catalyst was 2:1, resulting in a copper loading of 42.5% by weight.

Since copper is active for the synthesis of synthesis gas to oxygenated hydrocarbons, and ceria is a semiconducting oxide capable of catalyzing the oxidation of reduced sulfur compounds, methods employing this catalyst may be in accordance with the present invention.

Example 8 - Cu/ZrO ₂

The same procedure as Example 6 was used except that a solution of 11.580 g Cu(NO ₃ ) ₂ ·3H ₂ O and 25 g Na ₂ CO ₃ in 60 ml water was used. In addition, 10.304 g of Zr(NO ₃ ) ₄ ·5H ₂ O was used instead of zinc nitrate. The Cu:Zr molar ratio of the catalyst was 2:1, resulting in a copper loading of 50.7% by weight.

Since copper is active for the synthesis of synthesis gas to oxygenated hydrocarbons, and zirconia is a semiconducting oxide capable of catalyzing the oxidation of reduced sulfur compounds, methods employing this catalyst may be in accordance with the present invention.

Embodiment 9-15-Cu/ZrO ₂

The same procedure as Example 8 was used except using the amounts of materials listed in Table 2.

As in Example 8, since copper is active for the synthesis of syngas to oxygenated hydrocarbons, and zirconia and copper oxide are semiconductor oxides capable of catalyzing the oxidation of reduced sulfur compounds, the method of using any of these catalysts may conform to the present invention.

Table 2: Amounts of salt employed in Examples 9-15

Example 16 - Pd/CeO ₂ /Al ₂ O ₃

The same procedure as Example 2 was used except that 45 ml palladium solution, 30 g Na ₂ CO ₃ in 50 ml water and 11.206 g Ce(NO ₃ ) ₃ ·6H ₂ O were used. Additionally, 4.841 g of Al(NO ₃ ) ₃ .9H ₂ O was added to the solution. The Pd:Ce:Al molar ratio of the catalyst was 0.33:1:0.5. _This yielded a Pd loading on _CeO2 / _Al2O3 of 15 wt%.

Since palladium is active for the synthesis of synthesis gas to oxygenated hydrocarbons and the support contains ceria as a semiconducting oxide capable of catalyzing the oxidation of reduced sulfur compounds, a process using this catalyst can be in accordance with the invention.

Example 17-Pd-Cu/CeO ₂

The same procedure as Example 2 was used except that 19.6 ml palladium solution, 20 g Na ₂ CO ₃ in 50 ml water and 6.45 g Ce(NO ₃ ) ₃ ·6H ₂ O were used. Additionally, 0.222 g of Cu(NO ₃ ) ₂ ·3H ₂ O was added to the solution. The Pd:Cu:Ce molar ratio of the catalyst was 0.25:0.06:1. This yielded a Pd loading of 13.1 wt% on _CeO2 , and a copper loading of 1.9 wt% on _CeO2 .

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

A summary of all catalyst compositions is listed in Table 3.

Table 3: Catalyst composition

Example catalyst metal Inorganic oxide carrier The molar ratio of Catalyst metal, wt% 1 Pd Al ₂ O ₃ Pd:Al=0.08:1 15.0 2 Pd _CeO2 Pd:Ce=0.29:1 15.0 3 Pd _CeO2 Pd:Ce=0.18:1 10.0 4 Pd _CeO2 Pd:Ce=0.09:1 5.0 5 Pd _ZrO2 Pd:Zr=0.20:1 15.0 6 Cu ZnO Cu:Zn=2.00:1 56.6 7 Cu _CeO2 Cu:Ce=2.00:1 42.5 8 Cu _ZrO2 Cu:Zr=2.00:1 50.7 9 Cu _ZrO2 Cu:Zr=0.39:1 10.3 10 Cu _ZrO2 Cu:Zr=0.85:1 30.6 11 Cu _ZrO2 Cu:Zr=1.33:1 40.7 12 Cu _ZrO2 Cu:Zr=2.99:1 60.7 13 Cu _ZrO2 Cu:Zr=4.65:1 70.6 14 Cu _ZrO2 Cu:Zr=17.95:1 90.3 15 Cu CuO - - 16 Pd CeO ₂ /Al ₂ O ₃ Pd: Ce: Al = 0.33: 1: 0.5 15.1 17 Pd Cu _CeO2 Pd: Cu: Ce = 0.25: 0.06: 1 13.2/1.9a

^a Pd(wt%)/Cu(wt%)

Catalyst evaluation

The powdered catalyst sample was pressed into tablets under a pressure of 20 MPa, then crushed, and sieved to obtain a particle size of 20-40 mesh. 0.4 g of the sieved granules were diluted with 1.0 g of quartz sand and packed into a stainless steel fixed bed tubular reactor 140 mm long and 14 mm internal diameter. The resulting catalyst bed height was about 5mm. The catalyst was reduced in 100% hydrogen flow (6.67ml/min) for 8 hours at the indicated temperature. A reaction mixture containing hydrogen and carbon monoxide in a CO: _H molar ratio of 1:2 was then fed to the catalyst at a specified reaction temperature, an absolute pressure of 3.0 MPa, and a GHSV (gas hourly space velocity) of 1000 h ⁻¹ . The feed gas also contained 5 vol% _CO2 and 2.3 vol% _N2 . Sulfur is also present in the feed gas in varying concentrations of _H2S or combinations of COS and _H2S .

The amount of methanol in the product stream from the tubular reactor was determined using an on-line gas chromatograph equipped with a 1.5 m long carbon molecular sieve column and high purity helium carrier gas.

Comparative experiment 1

The Pd/Al ₂ O ₃ catalyst of Example 1 was pre-reduced at 300°C. It was studied at a reaction temperature of 240°C using a feedstock containing 3 ppm _H₂S . _O2 was also added to the feedstock at a concentration of 0.5 vol%. Figure 3 shows the results for CO conversion and methanol selectivity over a period of 100 hours. Both CO conversion and methanol selectivity decreased with time, indicating catalyst deactivation. This is not a method according to the invention, since aluminum oxide is not a semiconducting oxide.

Experiment 2

The Pd/ _CeO2 catalyst of Example 2 was pre-reduced at 300 °C. It was studied at a reaction temperature of 240°C using a feedstock containing 3 ppm _H₂S . _O2 was also added to the feedstock at a concentration of 0.5 vol%. Figure 4 shows the results for CO conversion and methanol selectivity over a period of 100 hours. After an initial unstable period of 20 hours of initial reaction, both parameters leveled off and started to increase with time. This indicates that the Pd catalyst with _CeO2 support is tolerant to the presence of sulfur.

Experiment 3

The Pd/ _CeO2 catalysts of Examples 2-4 were pre-reduced at 240°C and studied at a reaction temperature of 240°C with a feedstock containing 11 ppm _H2S . _O2 was also added to the feedstock at a concentration of 0.5 vol%. The results for CO conversion for Examples 3 and 4 over 100 hours, and Example 2 over 72 hours are shown in FIG. 5 , and methanol selectivity is shown in FIG. 6 . The results show that methanol selectivity is higher compared to Pd/Al ₂ O ₃ catalyst after 100 hours on stream. It also shows that when the molar ratio of palladium and _CeO2 support is greater than 0.09, the carbon monoxide conversion rate is higher and the deactivation rate is lower even though the sulfur concentration in the feedstock is higher. As is evident by comparing this result with that of Example 2 of Experiment 2, this result further shows that, even at higher sulfur contents, the carbon monoxide Conversion rates are also higher.

Experiment 4

The Pd/ _CeO2 catalyst of Example 2 was pre-reduced at 300 °C. It was studied at a reaction temperature of 240°C using a feedstock containing 0.8 ppm _H₂S and 2.2 ppm COS. _O2 was also added to the feedstock at a concentration of 0.5 vol%. Figure 7 shows the results for CO conversion and methanol selectivity over a period of 100 hours. After an initial activity-decreasing period of 20 hours of initial reaction, activity began to increase over time. This experiment shows that the Pd/ _CeO2 catalyst is tolerant of different sulfur compounds present.

Experiment 5

The Pd/ _CeO2 catalyst of Example 2 was pre-reduced at 240 °C. It was studied at a reaction temperature of 240°C using a feedstock containing 30 ppm _H₂S . Molecular oxygen was not added to the reactor. Figure 8 shows the results for CO conversion and methanol selectivity over a 100 hour period. After an initial activity-decreasing period of 20 hours of initial reaction, activity began to increase over time. This experiment shows that the Pd/ _CeO2 catalyst is tolerant to high concentrations of sulfur present in the feedstock.

Experiment 6

The Pd/ _ZrO2 catalyst of Example 5 was pre-reduced at 240 °C. It was studied at a reaction temperature of 240°C using a feedstock containing 36 ppm _H₂S . Molecular oxygen was not added to the reactor. Figure 9 shows the results for CO conversion and methanol selectivity over a 10 hour period. A high CO conversion is shown. This experiment shows that _ZrO2 is also an effective carrier that can tolerate high concentrations of sulfur.

Experiment 7

The Cu/ZnO catalyst of Example 6 was pre-reduced at 220°C. It was studied at a reaction temperature of 220°C using a feedstock containing 36 ppm _H₂S . Molecular oxygen was not added to the reactor. Figure 10 shows the results for CO conversion and methanol selectivity over a 7 hour period. Activity undergoes a rapid loss, indicating that Cu/ZnO cannot tolerate high amounts of sulfur.

Experiment 8

The Cu/ _CeO2 catalyst of Example 7 was pre-reduced at 220°C and tested at a reaction temperature of 220°C for 8 hours followed by 240°C for 7 hours in the presence of a feedstock containing 30 ppm _H2S . Molecular oxygen was not added to the reactor. Figure 11 shows the results for CO conversion and methanol selectivity over a 15 hour period. No loss of activity was observed, and activity increased at higher reaction temperatures. This experiment shows that the Cu/ _CeO2 catalyst is resistant to sulfur-induced deactivation even at high sulfur concentrations.

Experiment 9

The Cu/ _ZrO2 catalyst of Example 8 was pre-reduced at 220°C and tested at a reaction temperature of 240°C in the presence of a feedstock containing 36 ppm _H2S for 100 hours. Molecular oxygen was not added to the reactor. Figure 12 shows the results for CO conversion and methanol selectivity over a 100 hour period. Activity remained stable with only minor inactivation observed. This experiment shows that the Cu/ _ZrO2 catalyst is resistant to sulfur-induced deactivation even at high sulfur concentrations.

Experiment 10

The Cu/ _ZrO2 catalysts of Examples 8-15 were pre-reduced at 220°C and tested at a reaction temperature of 220°C for 10 hours in the presence of a feedstock containing 36 ppm _H2S . Molecular oxygen was not added to the reactor. Figure 13 shows the results for CO conversion after 10 hours for each catalyst (data point labels indicate the example number of the catalyst used). This experiment shows that _ZrO supported catalysts with Cu:Zr molar ratio greater than 1.33 and less than 17.95 exhibit the highest activity, corresponding to Cu loadings greater than 40.7 wt% and less than 90.3 wt%.

Experiment 11

The Pd/CeO ₂ /Al ₂ O ₃ catalyst of Example 16 was pre-reduced at 300° C. and tested in the presence of 11 ppm H ₂ S at a reaction temperature of 240° C. for 27 hours. _O2 was also added to the feedstock at a concentration of 0.5 vol%. Figure 14 shows the results for CO conversion and methanol selectivity over a 27 hour period. This result shows that catalysts with supports containing semiconducting oxides and non-semiconducting oxides are still tolerant to sulfur.

Experiment 12

The Pd-Cu/ _CeO2 catalyst of Example 17 was pre-reduced at 300°C and tested in the presence of 0.8ppm _H2S and 2.2ppm COS at a reaction temperature of 240°C for 29 hours. _O2 was also added to the feedstock at a concentration of 0.5 vol%. Figure 15 shows the results for CO conversion and methanol selectivity over a 29 hour period. This result indicates that catalysts containing both Pd and Cu catalyst metals are also active and resistant to sulfur concentrations greater than 0.5 ppm.

Experiment 13

The Pd/Al ₂ O ₃ and Pd/CeO ₂ catalysts of Examples 1 and 2 were analyzed by X-ray diffraction and X-ray fluorescence before and after 100 hours of reaction in an atmosphere containing 30 ppm H ₂ S. The results are shown in Table 4.

The used alumina-supported catalyst had a significantly higher amount of sulfur than the ceria-supported catalyst, indicating a lower level of catalyst poisoning by sulfur in the ceria-supported catalyst.

Table 4: XRD analysis

^a determined by X-ray diffraction

^b S content of catalyst determined by X-ray fluorescence (0% by weight before use).

Comparative experiment 14

The Pd/ _CeO2 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 feedstock. This is not the method according to the invention, since the sulfur concentration is not greater than 0.5 ppm.

The catalytic activity results over a period of 100 hours are shown in Figures 16, 17, 18 and 19 and compared to the results of Experiment 5.

In the absence of _H2S , the methanol selectivity dropped rapidly within the first 2 hours of the reaction, but gradually increased to 83% after 100 hours. The carbon monoxide conversion decreased 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 was also shown to be produced, with concentrations dropping from a maximum near 4% to about 1.5% after 100 hours. In addition, the yield of light hydrocarbons (C1-C5 hydrocarbons) dropped from a yield of 4-5% to about 1% after 100 hours.

In experiment 5, with 30 ppm sulfur present in the feedstock, the CO conversion was lower but the methanol selectivity was higher, ie the methanol yield was comparable to that in the absence of _H2S . Carbon dioxide production was low, dropping from a maximum of nearly 2% to about 0.5% after 100 hours. Also, a very small amount of C1-C5 hydrocarbons are produced.

Experiments 14 and 5 demonstrate the conclusion that even when sulfur is present in the feedstock, catalytic activity is maintained for a long time.

The experiments also showed that the production of carbon dioxide and hydrocarbon by-products was lower when sulfur was present in the feedstock.

Experiment 15

The Pd/CeO ₂ catalyst of Example 2 was evaluated at a pressure of 30 bar (3 MPa) and a GHSV of 1000 h ⁻¹ with a feedstock containing 3.3 ppm H ₂ S and 0.4 vol % oxygen. The catalysts were studied at temperatures of 220°C, 240°C, 260°C and 280°C. The results are shown in Figure 20.

Methanol selectivity increases between 220 and 240°C and then decreases. Carbon dioxide selectivity decreases between 220 and 240 °C, and then increases. Carbon monoxide conversion increases with temperature. Selectivity to light hydrocarbons increases with temperature.

Experiment 16

The Pd/ _CeO2 catalyst of Example 2 was evaluated at a temperature of 240 °C at 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. The results are shown in Figure 21.

In general, methanol selectivity and light hydrocarbon selectivity increase with pressure, carbon dioxide selectivity decreases with pressure, and carbon monoxide conversion increases with pressure.

Experiment 17

The Pd/CeO ₂ catalyst of Example 2 was evaluated at a temperature of 240° C. and a pressure of 3 MPa using the same raw materials as in Example 15. A GHSV between 500 and 5000h ^-1 is adopted. The results are shown in Figure 22.

Overall, the selectivity to methanol and light hydrocarbons decreased with the increase of GHSV, while the conversion of carbon monoxide and selectivity to carbon dioxide increased with the increase of GHSV.

Claims (17)

1. A method for producing one or more oxygenated hydrocarbons from hydrogen and carbon monoxide, said method comprising contacting a catalyst with a reaction mixture under conditions sufficient to produce one or more oxygenated hydrocarbons, said reaction The mixture comprises carbon monoxide, hydrogen and one or more reduced sulfur compounds, the catalyst comprising a metal active for converting the hydrogen and carbon monoxide to one or more oxygenated hydrocarbons, the support comprising a Semiconducting inorganic oxides that catalyze the oxidation of reduced sulfur compounds, characterized in that the concentration of said one or more reduced sulfur compounds in said reaction mixture is greater than 0.5 ppm by weight expressed in terms of elemental sulfur. 2. The method of claim 1, wherein said metal active for converting hydrogen and carbon monoxide into one or more oxygenated hydrocarbons is selected from the group consisting of Cu, Cr, Co, Mo, Pt, Pd and Rh one or more. 3. The method of claim 2, wherein the metal is Pd and/or Cu. 4. The method of any one of claims 1 to 3, wherein the molar ratio of at least one catalyst metal to the non-oxygen element of the semiconducting inorganic oxide is greater than 0.09:1. 5. The method according to any one of claims 1 to 4, wherein said semiconductor inorganic oxide capable of catalyzing the oxidation of reduced sulfur compounds is selected from the group consisting of lanthanide oxides, TiO ₂ , ZrO ₂ and ThO ₂ one or more of . 6. The method of claim 5, wherein the semiconducting inorganic oxide is _ZrO2 and/or _CeO2 . 7. The method according to any one of claims 1 to 6, wherein the catalyst further comprises a cocatalyst selected from the group consisting of alkali metals, alkaline earth metals, Sc, Y, La, Nd, Mn, Zn and Al's group. 8. A method as claimed in any one of claims 1 to 7 wherein the reduced sulfur compound is present at a concentration above 3 ppm. 9. The method according to any one of claims 1 to 8, wherein the molar ratio of carbon monoxide/hydrogen (CO: _H2 ) is in the range of 3:1 to 1:3. 10. A method as claimed in any one of claims 1 to 9, wherein the source of carbon monoxide and hydrogen is synthesis gas. 11. The method of claim 10, wherein the synthesis gas is obtained from coal. 12. A process as claimed in any one of claims 1 to 11, wherein the process is used for the production of methanol and/or dimethyl ether. 13. The method of any one of claims 1 to 12, wherein a source of oxygen in the form of one or more of molecular oxygen, carbon dioxide and water is present in the reaction mixture. 14. The method of claim 13, wherein oxygen is present in the reaction mixture in a concentration of at most 1% by weight. 15. A method as claimed in claim 13 or claim 14, wherein carbon dioxide is present in the reaction mixture in a concentration of up to 15% by weight. 16. A process as claimed in any one of claims 1 to 15, wherein the reaction temperature is in the range of 100 to 450°C and the reaction pressure is in the range of 1 to 100 bar (0.1 to 10 MPa). 17. A method as claimed in any one of claims 1 to 16, wherein the gas hourly space velocity is maintained at a value in the range of 500 to 5000 h ^-1 .

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