# Patent

## Title
Mo containing catalyst, a preparation method and a method for preparing methyl mercaptan

## Abstract

A method is described to prepare a Mo containing supported catalyst comprising TeO2 as active promoter and a process for preparing methanethiol in the presence of said catalyst.

## Background
INTRODUCTION AND BACKGROUND
The invention relates to a process for the preparation of a Mo and Te containing catalyst, and the catalyst itself, useful for methanethiol synthesis from syngas preferably containing high amounts of H2S.
THE PRIOR ART
As an important chemical educt for the production of methionine, pesticides and medicine, methanethiol is predominantly prepared by the reaction of hydrogen sulfide with methanol. For example, U.S. application Ser. No. 856,232 discloses a methanethiol synthesis method based on the reaction of hydrogen sulfide with methyl alcohol or diethyl ether; FR appl. 93,112,491 discloses a preparation method based on the reaction of methyl thio-ether with hydrogen over a transition metal catalyst; EP167,354 discloses a synthesis pathway with a catalyst based on titanium dioxide support and containing NiO or MoO3 as active components for the reaction of hydrogen sulfide with carbon monoxide; Chinese patent applications CN1207957 and CN98118187.2 disclose two catalysts for methyl mercaptan synthesis from syngas containing high amounts of H2S, in which the active component Mo—S—K is formed from the precursor of K2MoS4 or (NH4)2MoS4 plus one potassium salt; WO 2005/040082 discloses two Mo—O—K/SiO2 catalysts for the methanethiol synthesis, wherein the promoters are chosen from the group consisting of oxides of Co, Ni, Fe, Mn or La and Ce, whereby the active component Mo—O—K is formed from K2MoO4 or (NH4)6Mo7O24.4H2O plus a potassium salt as precursors.
STATEMENT OF THE INVENTION
The object of this invention is the preparation of catalysts with high activity and selectivity for the one-step methanethiol synthesis from syngas, preferably containing high amounts of H2S. This means preferably a content in the range of 50 to 80 Vol. % H2S.



BRIEF DESCRIPTION OF DRAWING
The Invention will be further understood with reference to the drawing which shows x-ray diffractogram of the catalyst TeO2—K2MoO4/SiO2 compared with other catalysts.



DETAILED DESCRIPTION OF THE INVENTION
The catalyst according to the invention comprises active components, active promoters and a support material. It is directed to a supported catalyst comprising

    
    
        a) a Mo containing and a K containing compound as active components, whereby Mo and K can be constituents of the same compound,
        b) a promoter, wherein the promoter comprises TeO2 and
        c) an oxidic carrier.
    
    


Said active component is preferably a Mo—O—K-based active center. Precursors of the Mo and K containing compounds are

    
    
        a) K2MoO4 or
        b) (NH4)6Mo7O24.4H2O denoted by MoO3 plus a potassium salt denoted as a K2O precursor or
        c) MoO3 plus one kind of potassium salt, said potassium compound is at least one chosen from the group comprising K2CO3, KOH and CH3COOK or any other potassium containing compound being known as a K2O precursor.
    
    


Said promoter is a Te-containing compound denoted by TeO2 whereby H6TeO6 (H2TeO4×2 H2O) or any other Te-containing salts or compounds being suitable as TeO2-precursors are used, also a potassium salt of said telluric acid H6TeO6.
Said support is preferably SiO2 or an oxidic carrier such as TiO2, ZrO2, Al2O3, Al2O3—SiO2, zeolites, pure or mixtures of said metal oxides.
For the catalyst TeO2—K2MoO4/SiO2 (prepared from K2MoO4) the weight ratio is TeO2/K2MoO4/SiO2=(1-20)/(1-50)/100, more preferably (3-12)/(15-30)/100, for the catalyst TeO2—MoO3—K2O/SiO2 (prepared for example from (NH4)6Mo7O24.4H2O and a potassium containing salt) the weight ratio is TeO2/MoO3/K2O/SiO2=(1-20)/(1-50)/(1-50)/100, more preferably (3-12)/(15-30)/(8-20)/100.

    
    
        The invention is also directed to a method to prepare a catalyst according to claim 1, comprising the steps:
        a) impregnating said carrier in more than one step with one or more aqueous solutions comprising a Te containing compound which acts as a Teo2 precursor and a K containing compound which acts as a K2O precursor and (NH4)6MO7O24 or MoO3 as Mo containing compounds; or
        b) impregnating said carrier in more than one step with one or more aqueous solutions comprising a Te containing compound which acts as a TeO2 precursor and K2MoO4;
        c) drying the received impregnated carrier; and
        d) optionally treating said impregnated carrier with H2 or syngas (CO+H2) or a syngas and H2S at elevated temperatures, preferably 200 to 450° C.
    
    


Products which are not pre-treated with said gases are also part of the invention.
The formulas of catalysts prepared are expressed as TeO2/K2MoO4/carrier or Teo2/MoO3/K2O/carrier.
Being exposed to a hydrogen sulphide containing atmosphere the oxidic compounds of Mo, K, Te comprised in the catalyst are converted into sulphides in complete or partially. That means that oxides or sulfides or mixtures of both are contained on the catalyst carrier.
XPS-spectra of said sulfided catalysts modified by different amounts of TeO2 show, that there are higher relative concentrations of Mo4+ and Mo5+ on the surface of the TeO2-promoted catalysts as compared to K2MoO4/carrier (especially SiO2), accompanied by lower concentrations of Mo6+ at the same time. The catalyst contains TeO2 in the range from 5 to 20, especially 7 to 12 wt. %, based on the total weight of the catalyst.
In order to achieve a better distribution of the active component and the promoter on the surface of the carrier, at least one chelating reagent is preferably present in the impregnation process. Said chelating reagents are chosen from carboxylic acids such as citric acid, tri-ammonium citrate, L-glutamic acid, tartaric acid and complexing agents such as ethylenediaminetetraacetic acid (EDTA), while the amount of chosen chelating agent added is 0.1-0.6 times by weight as much as that of the carrier and more preferably is 0.3-0.6 by weight. Ammonia should be added to adjust the pH value of the impregnating liquor to 8-10, the preferred operating procedure is an at least two step impregnation method comprising:
(1) when K2MoO4 is chosen as the precursor of the active compound, a given quantity of H6TeO6 according to the desired weight ratio is dissolved in a given quantity of distilled water to produce an aqueous solution, with which an according quantity of carrier is impregnated for 8-10 h, then dried at 100-135° C. for 4-6 h to produce an intermediate product; a given quantity of at least one chelating reagent and K2MoO4 are then dissolved in a given quantity of distilled water to produce an aqueous solution, into which a suitable amount of ammonia water is added to adjust the pH value to 8-10. The intermediate product produced above is impregnated with said solution for 8-10 h, finally said impregnated material is dried at elevated temperatures, especially at 110-135° C. for 4-6 h.
(2) When (NH4)6Mo7O24.4H2O plus one of the above-mentioned potassium compounds are chosen as the precursors of the active compound, the order of preparation is preferably as follows: first) a quantity of chosen potassium compound and a given quantity of H6TeO6 according to the desired weight ratio of Mo and Te are dissolved in a given quantity of distilled water to generate an aqueous solution. An according quantity of carrier is impregnated with said solution for 8-10 h, then dried at elevated temperatures, especially at 100-130° C. for 4-6 h to form a H6TeO6—K/SiO2 intermediate product; a quantity of a chosen chelating reagent and (NH4)6Mo7O24.4H2O are then dissolved in a prescribed amount of distilled water to produce an aqueous solution, the pH value of which is adjusted to 8-10, by adding a suitable amount of ammonia water. Said intermediate product is then impregnated with said solution for 8-10 h, followed by drying it at elevated temperatures, especially at 110-135° C. for 4-6 h.
It is also possible to change the step sequence:
(3) A given quantity of (NH4)6Mo7O24.4H2O and a given quantity of H6TeO6 are dissolved in a given quantity of distilled water to generate an aqueous solution. A given quantity of SiO2 is impregnated for 8-10 h, with said solution then dried at elevated temperatures, especially at 100-130° C. for 4-6 h to form a Mo—O—Te/SiO2 intermediate product; a given quantity of potassium compound is dissolved in a given quantity of distilled water to produce an aqueous solution, into which a given quantity of the chosen chelating agent and ammonia water are added to adjust the pH value of the solution to 8-10, with which the Mo—O—Te/SiO2 produced above is impregnated for 8-10 h, followed by drying at 110-135° C. for 4-6 h.
A continuous process for the manufacture of methyl mercaptan is successfully carried out by reacting a mixture of carbon oxides, sulphur or hydrogen sulphide and hydrogen at elevated temperatures and pressures in the presence of the above described catalysts.
The feed gas has preferable a hydrogen sulphide content in the range of 50-80 Vol. %.
It is preferred to feed the reactants carbon oxide, sulphur, hydrogen sulphide and hydrogen to the reactor in a molar ratio from 1/0/1/0 to 1/10/10/10, preferably from 1/0/2/2 to 1/0/10/10.
The reaction conditions as well as purification of the product and the recycling of non reacted compounds are generally known (U.S. Pat. No. 4,665,245/EP-A-104507; WO 2005/040082).
The catalyst should be pretreated with H2 or syngas(CO+H2) for 8-10 h preferably followed by sulfiding with H2S prior to the catalytic conversion of carbon monoxide, hydrogen and hydrogen sulphide to methanethiol to obtain the TeO2 component of the promoter.
The evaluation of the catalytic performance of the catalyst in the present invention was carried out in a fixed-bed tubular reactor with 0.5 ml of catalyst per pass. The experiments were performed under the reaction conditions of CO/H2/H2S=1/1/2, 300° C., 0.2 MPa and GHSV=2000 h−1. The products were analyzed by GC. All data were obtained after steady state conditions were achieved.
The following examples illustrate the present invention.
Example 1
Under stirring 0.648 g of H6TeO6 were fully dissolved in 10.0 ml of distilled water, the pH value of the aqueous solution of H6TeO6 thus prepared was measured to be 4.1, then 5.000 g of SiO2 were impregnated with the aqueous solution of H6TeO6 at room temperature for 8 h, followed by drying at 120° C. for 5 h to produce a dried intermediate product.
Under stirring 2.068 g of K2MoO4 were fully dissolved in 5.0 ml of distilled water to produce a K2MoO4 aqueous solution, into which 5 ml of NH3.H2O were added, the pH value of the aqueous solution was measured to be 11.40, then, under stirring 3.000 g of citric acid were added to the aqueous solution of K2MoO4 plus NH3.H2O, the pH value of the K2MoO4 plus NH3.H2O solution was measured to be 9.26. Finally, the intermediate product prepared in step (1) was impregnated with the solution containing citric acid K2MoO4 plus NH3.H2O at room temperature for 10 h, followed by drying at 120° C. for 5 h to generate a catalyst comprising TeO2/K2MoO4/SiO2, showing the weight ratio of 9/25/100. The evaluation results of the catalyst thus prepared are shown in table 1.
Example 2
(1) Under fast stirring, 1.468 g of K2CO3 and 0.648 g of H6TeO6 were fully dissolved in 10 ml of distilled water to form an aqueous solution, with which 5.000 g of SiO2 were impregnated at room temperature for 9 h, and finally dried at 125° C. for 4 h to generate an intermediate product.
(2) 1.534 g of (NH4)6Mo7O24.4H2O were fully dissolved in 5.0 ml of distilled water under agitating to form an aqueous solution, to which 2.000 g of tri-ammonium citrate were added. Subsequently, a suitable amount of NH3.H2O was added to adjust the pH of the solution to 9.05. The intermediate product prepared in step (1) was impregnated with said solution at room temperature for 9 h and finally dried at 125° C. for 4 h to produce the catalyst K2O/MoO3/TeO2/SiO2, showing the weight ratio of 20/25/9/100. The evaluation results of the catalyst thus prepared are shown in table 1.
Example 3
The catalyst was prepared according to the method described in Example 1, but 2.000 g of tartaric acid was used as chelating reagent and the carrier SiO2 was replaced by γ-Al2O3. The evaluation results of the catalyst thus prepared are shown in table 1.
Example 4 and 5
The catalyst was prepared according to the method described in Example 1, but the quantity of H6TeO6 was changed to be 0.486 g and 0.432 g respectively, and the chelating reagents used was EDTA in both cases, the weight ratio of the final catalysts thus prepared were TeO2/K2MoO4/SiO2=6.75/25/100 and TeO2/K2MoO4/SiO2=6/25/100 respectively. The evaluation results of the catalysts thus prepared are shown in table 1.
Example 6
The catalyst was prepared according to the method described in Example 1, but 5.000 g of TiO2 was used as the carrier. The amount of H6TeO6 and the amount of K2MoO4 were replaced by 0.142 g and 0.827 g, respectively. The final catalyst prepared was TeO2/K2MoO4/TiO2=2/10/100.The evaluation results of the catalyst thus prepared are shown in table 1.
Example 7
The catalyst was prepared according to the method described in Example 6, but 5.000 g of ZrO2 was used as the carrier. and the amount of H6TeO6 and K2MoO4 was replaced by 0.071 g and 0.414 g respectively. The final catalyst prepared was TeO2/K2MoO4/ZrO2=1/5/100. The evaluation results of the catalyst thus prepared are shown in table 1.
Example 8
The catalyst was prepared according to the method described in Example 2, but 5.000 g of the mesoporous molecular sieve MCM-41 was used as the carrier, and the amount of K2CO3, H6TeO6 and (NH4)6Mo7O24.4H2O was replaced by 1.835 g, 1.080 g and 2.454 g, respectively. The final catalyst prepared was K2O/MoO3/TeO2/MCM-41=25/40/15/100.
The evaluation results of the catalysts modified with different amounts of TeO2 for methanethiol synthesis from high H2S containing feed gas are listed in table 1.
As it can be seen the addition of TeO2 to K2MoO4/SiO2 catalyst increases evidently the activity of the catalysts, which can find expression in the significant change of conversion of CO and the yield of CH3SH. The conversion of CO reaches a maximum with 61.5% and a yield of methanethiol of 0.39 g.mlcat−1.h−1. Obviously, both the conversion of CO and the yield of methanethiol do not correspond linearly or regularly as function of the amount of TeO2 added.







TABLE 1







The evaluation results of the catalysts in examples 1-8.















Conv.


Example
Selectivity (%)
CO2/
Yield (g · mlcat−1 · h−1)
of CO

















(catalyst)
CH4
CH3SH
COS
CO2
CH3SH
CH4
CH3SH
COS
CO2
 (%)




















1, K2MoO4/TeO2/SiO2 = 25/9/100
0.23
55.21
10.70
33.86
0.61
0.0005
0.38
0.09
0.21
59.29


2, K2O/MoO3/TeO2/SiO2 = 15/25/9/100
0.25
55.15
11.30
33.30
0.60
0.0005
0.35
0.09
0.19
57.26


3, K2MoO4/TeO2/γ-Al2O3 = 25/9/100
0.30
48.70
17.91
33.08
0.68
0.0005
0.24
0.09
0.21
56.02


4, K2MoO4/TeO2/SiO2 = 25/6.75/100
0.24
54.74
10.72
34.90
0.60
0.0005
0.35
0.09
0.21
56.02


5, K2MoO4/TeO2/SiO2 = 25/6/100
0.24
54.50
10.50
35.02
0.66
0.0005
0.36
0.09
0.22
57.52


6, K2MoO4/TeO2/TiO2 = 10/2/100
0.08
48.40
14.05
37.47
0.77
0.0005
0.31
0.09
0.24
48.4


7, K2MoO4/TeO2/ZrO2 = 5/1/100
0.09
48.17
17.84
33.90
0.70
0.0005
0.27
0.10
0.19
39.6


8, K2O/MoO3/TeO2/MCM-41 = 25/40/15/100
0.07
51.28
11.83
36.82
0.72
0.0005
0.39
0.09
0.28
61.5









Example 9
FIG. 1 shows X-ray diffractograms of the catalyst TeO2—K2MoO4/SiO2 prepared by drying of the catalyst at 150° C. and calcination at 400° C. as compared to the starting materials and the catalysts K2MoO4/SiO2 and CoO—K2MoO4/SiO2 [A) carrier SiO2; B) H6TeO6; C) K2MoO4/SiO2; D) TeO2—K2MoO4/SiO2 (prepared with citric acid; drying at 150° C.); E) TeO2—K2MoO4/SiO2 (prepared with HNO3 and without chelating reagent); F) CoO—K2MoO4/SiO2; G) TeO2—K2MoO4/SiO2 (calcined at 400° C.); H) CoO—K2MoO4/SiO2 (calcined at 500° C.)]. The diffractograms clearly demonstrate the distinct nature of the Te-containing catalysts as compared to other catalysts prepared on the basis of the system K2MoO4/SiO2

## Claims

1. A supported catalyst for the preparation of methanethiol comprising
a) a Mo and a K compound as active components, whereby Mo and K can be constituents of the same compound,
b) a promoter, wherein the promoter comprises TeO2 and
c) an oxidic carrier
wherein the weight ratios of the components are
TeO2/K2MoO4/carrier=(1-20)/(1-50)/100 or
TeO2/MoO3/K2O/carrier=(1-20)/(1-50)/(1-50)/100.

2. The catalyst according to claim 1, wherein the weight ratios of the components are
(1) TeO2/K2MoO4/carrier=(3-12)/(15-30)/100 or
(2) TeO2/MoO3/K2O/carrier=(3-12)/(15-30)/(8-20)/100.

3. The catalyst according to claim 1, wherein the carrier is selected from the group consisting of SiO2, Al2O3, TiO2, Al2O3—SiO2, ZrO2, zeolites, pure or mixtures of said metal oxides.

4. The catalyst according to claim 1, wherein the catalyst contains an active Mo—O—K center.

5. The catalyst according to claim 1, wherein the catalyst is sulfided by exposing to an hydrogen sulphide containing atmosphere.

6. The catalyst according to claim 1, wherein the TeO2 content is in the range from 1 to 20 wt % of the catalyst.