Catalyst for selective dehydrogenation / oxidative dehydrogenation reactions and process for the preparation thereof

Abstract

The present invention provides a process and catalyst for the direct and selective conversion of ethane to ethylene. The process provides a direct single step vapor phase selective dehydrogenation/oxidative dehydrogenation of ethane to ethylene over Mo supported nanocrystalline TiO.sub.2. The process provides ethane conversion of 65-96% and selectivity of ethylene up to 100%. The process may be conducted in the presence or absence of oxygen.

Claims

1. A MoTiO.sub.2 nanocrystalline oxide catalyst, wherein Mo is present in the range of 5 wt % to 15 wt % and TiO.sub.2 is present in the range of 85 wt % to 95 wt %, the catalyst having particle size in the range of 80-150 nm, and wherein said catalyst is able to selectively convert ethane to ethylene by vapor phase dehydrogenation/oxidative dehydrogenation in the absence or presence of oxygen, respectively, and wherein the catalyst exhibits a crystal morphology as depicted in the transmission electron microscope image of FIG. 4.

2. The catalyst of claim 1, wherein the catalyst has been prepared according to a process comprising: a. preparing solid TiO.sub.2 from a mixture of titanium isopropoxide Ti(i-Pr).sub.4 and octadecyldimethyl (3-trimethoxy silylpropyl) ammonium chloride, present in the ratio ranging from 50:3500:1 to 100:3500:1, in liquid, wherein the mixture has been heated at a temperature in the range of 70 to 90? C. and then autoclaved at a temperature in the range of 150 to 200? C. to form a liquid containing solid material, wherein the solid material is separated from the liquid and then calcined at a temperature in the range of 300 to 800? C. in air to yield the solid TiO.sub.2; and b. mixing MoCl.sub.3, cetyltrimethylammonium bromide and hydrazine, at a molar ratio of Mo:CTAB:hydrazine ranging from 1:1:0.01 to 1:2:0.01, in a liquid followed by adding the TiO.sub.2, a weight ratio of Mo to TiO.sub.2 in the range of 0.05 to 0.15, to form a mixture comprising a solid material that is separated and then calcined at a temperature in the range of 300 to 800? C. in air to yield the MoTiO.sub.2 nanocrystalline catalyst.

3. The catalyst of claim 1, wherein the catalyst comprises: a. TiO.sub.2 prepared from a mixture of titanium isopropoxide Ti(i-Pr).sub.4 and octadecyldimethyl (3-trimethoxy silylpropyl) ammonium chloride, present in the ratio ranging from 50:3500:1 to 100:3500:1, wherein the TiO.sub.2 has been calcined at a temperature in the range of 300 to 800? C. in air; and b. Mo support prepared from a mixture of MoCl.sub.3, cetyltrimethylammonium bromide and hydrazine, at a molar ratio of Mo:CTAB:hydrazine ranging from 1:1:0.01 to 1:2:0.01, and the TiO.sub.2, wherein the weight ratio of Mo to TiO.sub.2 in the catalyst is in the range of 0.05 to 0.15, and the catalyst has been calcined at a temperature in the range of 300 to 800? C. in air.

4. The catalyst of claim 3, wherein the catalyst comprises: a. TiO.sub.2 prepared from a mixture of titanium isopropoxide Ti(i-Pr).sub.4 and octadecyldimethyl (3-trimethoxy silylpropyl) ammonium chloride, present in the ratio ranging from 50:3500:1 to 100:3500:1, in liquid, wherein the mixture has been heated at a temperature in the range of 70 to 90? C. and then autoclaved at a temperature in the range of 150 to 200? C. to form a liquid containing solid material, wherein the solid material is separated from the liquid and then calcined at a temperature in the range of 300 to 800? C. in air to yield the solid TiO.sub.2; and b. the Mo support has been prepared by from a mixture of MoCl.sub.3, cetyltrimethylammonium bromide and hydrazine, at a molar ratio of Mo:CTAB:hydrazine ranging from 1:1:0.01 to 1:2:0.01, in a liquid followed by addition of the TiO.sub.2 at a weight ratio of Mo to TiO.sub.2 in the range of 0.05 to 0.15, to form a mixture comprising a solid material that is separated and then calcined at a temperature in the range of 300 to 800? C. in air to yield the catalyst.

5. The catalyst of claim 1, wherein the catalyst is able to selectively convert ethane to ethylene by vapor phase dehydrogenation/oxidative dehydrogenation in the absence or presence of oxygen, respectively, and wherein the conversion percentage of ethane is in the range of 65 mol % to 96 mol %, and the selectivity of the ethylene conversion in the range of 88 mol % to 100 mol %.

6. The MoTiO.sub.2 nanocrystalline oxide catalyst of claim 1, wherein the catalyst is an anatase nanocrystalline catalyst.

7. A MoTiO.sub.2 nanocrystalline oxide anatase catalyst, wherein Mo is present in the range of 5 wt % to 15 wt % and TiO.sub.2 is present in the range of 85 wt % to 95 wt %, the catalyst having particle size in the range of 80-150 nm, wherein said catalyst is able to selectively convert ethane to ethylene by vapor phase dehydrogenation/oxidative dehydrogenation in the absence or presence of oxygen, respectively, wherein the conversion percentage of ethane is in the range of 65 mol % to 96 mol %, and the selectivity of the ethylene conversion in the range of 88 mol % to 100 mol %, and wherein the catalyst exhibits a crystal morphology as depicted in the transmission electron microscope image of FIG. 4.

Description

BRIEF DESCRIPTION OF THE INVENTION

(1) FIG. 1 represents the conversion of ethane to ethylene over time on stream for the MoTiO.sub.2 catalyst.

(2) FIG. 2 represents X-ray Diffraction (XRD) pattern of the prepared catalyst.

(3) FIG. 3 represents Scanning Electron Microscope (SEM) images of the prepared MoTiO2 catalysts.

(4) FIG. 4 represents Transmission Electron Microscope (TEM) images of the prepared catalyst.

DETAILED DESCRIPTION OF THE INVENTION

(5) Present invention provides a catalyst consisting of MoTiO.sub.2 prepared hydrothermally and process to produce ethylene from ethane by gas phase dehydrogenation/oxidative dehydrogenation with and without O.sub.2 over MoTiO.sub.2 catalyst at atmospheric pressure, at a temperature range of 550 to 850? C. with a gas hourly space velocity (GHSV) in the range of 5000-70000 ml g.sup.?1 h.sup.?1 in the presence of Mo supported TiO.sub.2 catalyst with Mo to TiO.sub.2 weight ratio varied between 0.03 to 0.2 to obtain desired product ethylene for a period of 1-20 hours.

(6) The present invention provides a process for the production of ethylene from ethane by vapor phase dehydrogenation/oxidative dehydrogenation in absence and presence of oxygen and MoTiO.sub.2 nanocrystalline oxide as the catalyst which involves the following steps: i. Synthesis of TiO.sub.2 oxide using sol composition of Ti(i-Pr).sub.4, octadecyldimethyl (3-trimethoxy silylpropyl) ammonium chloride, 1N NaOH solution to adjust the pH between 3-10; ii. heated at 80? C. and maintained for 1-2 h; iii. Transferring the solution into an closed Teflon line stainless steel autoclave and heating the solution inside the oven in the temperature range between 150-200? C. hydrothermally for 20-30 h; iv. filtered the material by washing with excess water (2 liter) followed by drying the materials in oven at a temperature between 100-130? C. for 10-18 h; v. Calcination of the materials at 300-800? C. for 4-6 h in air to yield solid TiO2; vi. Synthesis of MoTiO.sub.2 catalyst using ethanol medium taking the solution composition of MoCl.sub.3, cetyltrimethylammonium hydrazine, in the molar ratio of Mo:CTAB:Hydrazine=1:1:0.01 and prepared TiO.sub.2; vii. The weight ratio of Mo to TiO.sub.2 varied in the range of 0.05 to 0.15; viii. Stirring the mixture for 2-5 h followed and filtered the material by washing with excess water (2 liter) followed by drying the materials in oven at a temperature between 100-130? C. for 10-18 h; ix. Calcination of the materials at 300-800? C. for 4-6 h in air to yield MoTiO2; x. Dehydrogenation/oxidative dehydrogenation of ethane was carried out in a fixed bed down-flow reactor using ultra-pure ethane and/or molecular oxygen as feeds and helium as carrier for 1-20 h to yield ethylene; xi. The process pressure was kept at 1 atmosphere; xii. The reaction temperature is preferably in the range 650 to 800? C.; xiii. The gas hourly space velocity (GHSV in ml g.sup.?1 h.sup.?1) is preferably in the range 10000 ml g?1 h?1 to 50000 ml g?1 h?1; xiv. The ethane conversion (mol %) of 65-96% is obtained and selectivity (mol %) to ethylene is 78 to 100%.

(7) The detailed steps of the process are:

(8) The dehydrogenation of ethane was carried out in a fixed-bed down flow reactor at atmospheric pressure. Typically 200 mg of catalyst was placed in between two quartz wool plugged in the centre of the 6 mm quartz reactor and dehydrogenation of ethane was carried out in a temperature range of 650-800? C. The catalyst was reduced using 5% H.sub.2 balance He at 650? C. for 1 h before the reaction. The gas hourly space velocity (GHSV) was varied between 5000 ml g.sup.?1 h.sup.?1 to 50000 ml g.sup.?1 h.sup.?1 with a molar ratio of C.sub.2H.sub.6:O.sub.2:He of 1:1:8. The reaction products were analyzed using an online gas chromatography (Agilent 7890A) fitted with a FID & TCD detector using Al.sub.2O.sub.3/KCl column (to analyse C.sub.2H.sub.6, C.sub.2H.sub.4, CH.sub.4 etc.) and PoraPack-Q (for analyzing O.sub.2 and CO.sub.2).

(9) An improved process for the preparation of MoTiO2 catalyst, wherein the said process comprising the steps of: a) Mixing the chemicals: Ti(i-Pr).sub.4, octadecyldimethyl (3-trimethoxy silylpropyl) ammonium chloride and 1N NaOH solution to adjust the pH between 3-10. b) Heating the solution at 80? C. and maintained for 1-2 h c) Transferring the solution into a closed Teflon line stainless steel autoclave and heating the solution inside the oven in the temperature range between 150-200? C. hydrothermally for 20-30 h. d) filtered the material by washing with excess water (2 liter) followed by drying the materials in oven at a temperature between 100-130? C. for 10-18 h e) Calcination of the materials at 300-800? C. for 4-6 h in air to yield solid TiO.sub.2. f) Synthesis of MoTiO.sub.2 catalyst using ethanol medium taking the solution composition of MoCl.sub.3 cetyltrimethylammonium bromide, hydrazine, in the molar ratio of Mo:CTAB:Hydrazine=1:1:0.01 and prepared TiO.sub.2 g) The weight ratio of Mo to TiO.sub.2 varied in the range of 0.05 to 0.15 h) Stirring the mixture for 2-5 h followed and filtered the material by washing with excess water (2 liter) followed by drying the materials in oven at a temperature between 100-130? C. for 10-18 h i) Calcination of the materials at 300-800? C. for 4-6 h in air to yield MoTiO.sub.2

(10) A process for gas phase dehydrogenation/oxidative dehydrogenation with and without O.sub.2 of ethane to produce ethylene using catalyst comprising the steps of: I. Passing ethane at atmospheric pressure, at a temperature range of 550-850? C. with a gas hourly space velocity (GHSV) in the range of 5000-70000 ml g.sup.?1 h.sup.?1 in the presence of Mo supported TiO.sub.2 catalyst with Mo to TiO.sub.2 weight ratio varied between 0.03 to 0.2 to obtain desired product ethylene for a period of 1-20 hours.

(11) Weight ratio of Mo to TiO.sub.2 of the catalyst varied in the range of 0.05 to 0.15.

(12) Reactor pressure is preferably in the range of 1 atmosphere. Reaction temperature is preferably in the range 650 to 800? C. Gas hourly space velocity (GHSV) is preferably in the range of 1000 g ml.sup.?1 h.sup.?1 to 50000 g ml.sup.?1 h.sup.?1. Reaction time used is preferably in the range 3-20 h. Conversion (mol %) of ethane is in the range of 65 to 96%. Selectivity (mol %) of the ethylene obtained in the range of 78 to 100%.

EXAMPLES

(13) The following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.

Example 1: Synthesis of TiO2

(14) 5 ml titanium isopropoxide was taken in 75 ml chilled ethanol to form a heterogeneous solution. Approximately 0.2 g octadecyldimethyl (3-trimethoxy silylpropyl) ammonium chloride was added drop wise under vigorous stirring. Then, the pH of the mixed solution was adjusted by 1(M) NaOH solution and pH of the mixed solution was fixed at 10. Finally, the mixed solution was heated at 80? C. and maintained for 2 h. The resultant mixture was autoclaved at 180? C. for 24 h for further crystallization. The white precipitate (TiO.sub.2) was collected by filtration, washed thoroughly with distilled water and ethanol and dried at 80? C. for 12 h. To remove the template the as-synthesized material was heated to 750? C. with a temperature ramp of 1.5? C./min under static air and kept at the same temperature for 4 h. This was used as a TiO.sub.2 support material.

Synthesis of MoTiO2

(15) Synthesis of MoTiO.sub.2 catalyst using ethanol (25 ml) medium taking the solution composition of 1.05 g of MoCl.sub.3, 0.5 g of cetyltrimethylammonium bromide, 0.2 g hydrazine (the molar ratio of Mo:CTAB:Hydrazine=1:1:0.01) and prepared 1.0 g of TiO.sub.2 was added to it such a way that the weight ratio of Mo to TiO.sub.2 was 0.05. The mixture was stirred for 3 h and the solid material was filtered out with 2 liter distilled water and it was dried in the oven at 110? C. for 16 h. Finally the calcination of the material was carried out at 750? C. for 6 h in air.

(16) The X-ray diffraction pattern, Scanning Electron Microscope (SEM) images and Transmission Electron Microscope (TEM) images of this material are given below.

Example 2

(17) This example describes the dehydrogenation of ethane by gas phase reaction in He using MoTiO.sub.2 nanocrystalline oxide as the catalyst. (Table-1)

(18) The dehydrogenation of ethane to ethylene was carried out in a fixed-bed down flow quartz reactor at atmospheric pressure. Typically 200 mg of catalyst was placed in between two quartz wool plugged in the center of the 6 mm quartz reactor and dehydrogenation of ethane was carried out in a temperature range of 650-800? C. The gas hourly space velocity (GHSV) was varied between 10000 ml g.sup.?1 h.sup.?1 to 30000 ml g.sup.?1 h.sup.?1 with a molar ratio of C.sub.2H.sub.6:He of 1:9.

(19) Process Conditions

(20) Catalyst: 0.2 g

(21) Mo: TiO.sub.2 wt % in the catalyst=5%

(22) Pressure: 1 atmosphere

(23) Total flow=33.3 ml/min (GHSV=10000)

(24) Reaction time: 1 h

(25) TABLE-US-00001 TABLE 1 Ethane Ethylene Catalyst Temperature Conversion Selectivity Yield (5% MoTiO.sub.2) (? C.) (mol %) (mol %) (%) Oxidative 750 91 84 76 dehydrogenation (With O.sub.2) dehydrogenation 750 86 95 82 (Without O.sub.2)

Example 3

(26) The example describes the effect of temperature on yield and selectivity ethylene. The product analysis presented in Table-2.

(27) Process Conditions:

(28) Catalyst: 0.2 g

(29) Mo: TiO.sub.2 wt % in the catalyst=5%

(30) Pressure: 1 atmosphere

(31) Total flow=33.3 ml/min (GHSV=10000)

(32) Reaction time: 1 h

(33) TABLE-US-00002 TABLE 2 Effect of temperature on ethane conversion, ethylene yield and selectivity Ethane Ethylene Temperature Conversion Selectivity (mol Yield (? C.) (mol %) %) (%) Oxidative 650 65 89 58 dehydrogenation 700 82 87 71 (With O.sub.2) 750 91 84 76 800 96 78 74 dehydrogenation 650 10 100 10 (Without 700 56 97 54 O.sub.2) 750 86 95 82 800 94 89 84

Example 4

(34) The example describes the effect of time on stream on yield and selectivity of ethylene. The product analysis presented in Table 3

(35) Process Conditions:

(36) Catalyst: 0.2 g, Mo: TiO.sub.2 wt % in the catalyst=5%

(37) Pressure: 1 atmosphere

(38) Total flow=33.3 ml/min (GHSV=10000)

(39) Reaction temperature: 750? C.

Example 5

(40) The example describes the effect of gas hourly space velocity (GHSV) on yield and selectivity of ethylene. The product analysis presented in Table-3.

(41) Process Conditions:

(42) Catalyst: 0.2 g

(43) Mo: TiO.sub.2 wt % in the catalyst=5%

(44) Pressure: 1 atmosphere

(45) Reaction temperature: 750? C.

(46) Reaction time: 1 h

(47) TABLE-US-00003 TABLE 3 Effect of gas hourly space velocity (GHSV) on ethane conversion, ethylene yield and selectivity Ethane Ethylene GHSV Conversion Selectivity (mol Yield (ml g.sup.?1 h.sup.?1) (mol %) %) (%) Oxidative 10000 91 84 76 dehydrogenation 15000 76 84 64 (With O.sub.2) 20000 63 86 54 25000 54 87 47 30000 48 89 43 dehydrogenation 10000 86 95 82 (Without 15000 79 96 76 O.sub.2) 20000 63 97 61 25000 52 98 51 30000 41 100 41

Advantages of the Invention

(48) The main advantages of the present invention are: 1. The process of the present invention converts ethane to ethylene in a single step with a single catalyst. 2. The process provides not only good conversion but also good selectivity for ethylene. 3. The process produce nominal by-product in the form of methane which is also a major advantage of this process. 4. The process does not need any addition reagent (such as chlorine, bromine etc.) to generate active species. 5. The catalyst is used in very low amounts. 6. The catalyst does not deactivate till 20 h with the reaction stream.