CN1102441C - Preparation of molybdenum modified molecular sieve catalyst - Google Patents

Abstract

The present invention relates to a preparation method for a molybdenum modified molecular sieve catalyst, which comprises the following steps: firstly, dissolving ammonium molybdate in ammonia water and mixing the compound with an HZSM-5 molecular sieve, then filling the mixed material in a high-pressure still in which pressure is from 3 to 5MPa, heating the mixed material to 240 to 260 DEG C, retaining for 3 to 6 hours, stopping heating, reducing to normal pressure, and roasting; thus, the required catalyst is prepared. The present invention has the characteristics of remarkably enhancing the carbon deposition resistance ability of the catalyst, enhancing the catalytic activity of the HZSM-5 molecular sieve and enhancing the selectivity of aromatic hydrocarbon.

Description

A kind of preparation method of molybdenum modified molecular sieve catalyst

The invention relates to a kind of preparation method of HZSM-5 molecular sieve catalyst, relate to a kind of liquefied petroleum gas, oil field light hydrocarbon and condensate of being applicable to specifically and carry out a kind of method of modifying that aromatization is produced the HZSM-5 molecular sieve catalyst of benzene,toluene,xylene.

The aromatization of low-carbon alkanes is to be undertaken carrying out reaction generation aromatic hydrocarbons such as a series of oligomerisation, cyclisation, dehydroaromatizationof again after cracking or the dehydrogenation activation by raw material.Because the HZSM-5 molecular sieve has good duct and selects shape effect and aromatisation ability, it is maximum to be with it that catalyst carries out the research of aromatization of low carbon hydrocarbon.But because it is acid strong, the raw material cracking is serious, and catalyst activity and selectivity are difficult to further raising, and coking deactivation easily takes place.Therefore how the HZSM-5 molecular sieve is carried out modification and become a hot subject in the aromatisation research to improve catalyst activity and selectivity.After finding afterwards to introduce some metal M ion, can promote the carrying out of dehydrogenation reaction.M/HZSM-5 is as a kind of bifunctional catalyst.On M, carry out the dehydrogenation activation earlier, promote the reactions such as oligomerisation cyclisation of activator again by the strong B of molecular sieve acid site, on metal center, carry out dehydroaromatizationof at last, thereby the activation of reactant and the dehydroaromatizationof of cyclic hydrocarbon intermediate are organically combined, significantly improved the aromatisation performance of catalyst.We can say that the dehydrogenation ability that strengthens raw material is to improve the key of catalyst performance.The Pt that studies at most at present, Zn, Ga modified HZSM-5 molecular sieve catalyst all have very strong dehydrogenation ability and very high aromatization activity, and the patent of a series of relevant aromatization of low carbon hydrocarbon occurred.UOP and BP company finish industrial demonstration experiment aspect the liquefied petroleum gas aromatisation.In these a few class catalyst, the cracking performance of Pt/HZSM-5 catalyst is stronger, and the purpose selectivity of product is lower, and sulfur poisoning easily takes place.Ga/HZSM-5 acidity is stronger, and is very fast by the inactivation that carbon deposit causes, and Zn/HZSM-5 is in course of reaction, part Zn ²⁺Be reduced into volatile Zn °, and cause the slow loss of active component.When on these several catalyst, carrying out aromatization, contain more C in the product ₁+ Product, the purpose selectivity of product is difficult to further raising, and tail gas is difficult to recycling.The Mo oxide also has stronger activity to the dehydrogenation of alkane, and has very strong sulfur poisoning-resistant ability.When adopting Mo that HZSM-5 is carried out modification, because the duct of molecular sieve is less, and MoO ₃Molecular diameter bigger, traditional infusion process and mechanical mixing are difficult to make more Mo to enter in the molecular sieve pore passage, though the Mo species are entered in the molecular sieve pore passage by the ion migration, but its limited amount, if further improve the sintering temperature of catalyst, can cause the further decarboxylation reaction of molecular sieve again, be difficult to make the metal center on the catalyst and the proportioning in strong B acid site to reach optimum value, activity of such catalysts and selectivity also just are difficult to improve.And employing MoCl ₅Carry out mechanical mixture with HZSM-5, though can make more Mo through high-temperature roasting again ⁵⁺Enter in the molecular sieve pore passage by solid phase ion-exchange, but because MoCl ₅Activity to dehydroaromatizationof of alkane is very low, and this method also is difficult to adopt.

Goal of the invention of the present invention provides the preparation method of the Mo/HZSM-5 molecular sieve catalyst that is used for aromatizing low-carbon paraffin that a kind of activity is high, arenes selectivity is good, anti-carbon deposition ability is strong.

The method of the Mo/HZSM-5 of preparation molecular sieve catalyst of the present invention comprises the steps:

(1) by Mo: HZSM-5=2-15: 100 part by weight takes by weighing ammonium molybdate and HZSM-5 molecular sieve respectively;

(2) ammonium molybdate is dissolved in the 2-4% ammonia spirit, in the autoclave of packing into after molecular sieve mixes, adopts inert gas to blow down air, sealing autoclave afterwards in the still;

(3) speed with 2-3 ℃/min is warming up to 240-260 ℃, and keeping the still internal pressure is 3-5MPa, keeps stopping heating behind the 3-6hr, slowly discharges gas reactor subsequently, adopts inert gas purge after reducing to normal pressure, takes out after being cooled to room temperature;

(4) roasting is carried out in the sample taking-up, obtained required catalyst.

The present invention has the following advantages:

1. more helping the molybdenum species than traditional infusion process enters in the molecular sieve pore passage.

2. can significantly improve the anti-carbon deposition ability of catalyst.

3. can significantly improve the catalytic activity and the arenes selectivity of HZSM-5 molecular sieve.

4. this method for preparing catalyst is simple, and properties of product are stable.

5. adopt preparation method of the present invention to be equally applicable to the introducing of transition metal oxide in other macropore or the mesoporous molecular sieve.

Embodiments of the invention are as follows:

Embodiment 1

(1) under even stirring condition with 2.8g (NH ₄) ₆Mo ₇O ₂₄4H ₂O is dissolved in the ammonia spirit of 100ml3%;

(2) get 10g H-ZSM-5 powder, pack into after mixing in the 1L autoclave with ammonium molybdate solution in (1), and use N ₂Speed with 100ml/min purges 20min;

(3) purge the back sealing autoclave, be warming up to 260 ℃ with the speed of 2 ℃/min, keep-uping pressure is 4MPa, keeps slowly discharging gas reactor behind the 4hr, stops heating, adopts N after waiting to reduce to normal pressure ₂Purge, take out after being cooled to room temperature;

(4) in air in 550 ℃ of roasting 4hr, promptly obtain loading and be 10% Mo/HZSM-5 catalyst A.

Embodiment 2

(1) under even stirring condition with 2.8g (NH ₄) ₆Mo ₇O ₂₄4H ₂O is dissolved in the ammonia spirit of 100ml3%;

(2) get 15g H-ZSM-5 powder, pack into after mixing in the 1L autoclave with ammonium molybdate solution in (1), and use N ₂Speed with 100ml/min purges 20min;

(3) purge the back sealing autoclave, be warming up to 260 ℃ with the speed of 3 ℃/min, keep-uping pressure is 3MPa, keeps slowly discharging gas reactor behind the 3hr, stops heating, adopts N after waiting to reduce to normal pressure ₂Purge, take out after being cooled to room temperature;

(4) with obtained sample at H ₂In 550 ℃ of roasting 4hr, obtain catalyst B in the atmosphere.

Embodiment 3

(1) under even stirring condition with 2.0g (NH ₄) ₆Mo ₇O ₂₄4H ₂O is dissolved in the ammonia spirit of 100ml3%;

(2) get 20g H-ZSM-5 powder, pack into after mixing in the 1L autoclave with ammonium molybdate solution in (1), and use N ₂Speed with 100ml/min purges 20min;

(3) purge the back sealing autoclave, be warming up to 260 ℃ with the speed of 2 ℃/min, keep-uping pressure is 6MPa, keeps slowly discharging gas reactor behind the 5hr, stops heating, adopts N after waiting to reduce to normal pressure ₂Purge, take out after being cooled to room temperature;

(4) with obtained sample at H ₂In 550 ℃ of roasting 4hr, obtain catalyst C in the atmosphere.

Embodiment 4

(1) under even stirring condition with 1.6g (NH ₄) ₆Mo ₇O ₂₄4H ₂O is dissolved in the ammonia spirit of 100ml3%;

(2) get 10g H-ZSM-5 powder, pack into after mixing in the 1L autoclave with ammonium molybdate solution in (1), and use N ₂Speed with 100ml/min purges 20min;

(3) purge the back sealing autoclave, be warming up to 240 ℃ with the speed of 2 ℃/min, keep-uping pressure is 4MPa, keeps slowly discharging gas reactor behind the 4hr, stops heating, adopts N after waiting to reduce to normal pressure ₂Purge, take out after being cooled to room temperature;

(4) with obtained sample at H ₂In 550 ℃ of roasting 4hr, obtain catalyst D in the atmosphere.

Embodiment 5

(1) under even stirring condition with 3.5g (NH ₄) ₆Mo ₇O ₂₄4H ₂O is dissolved in the ammonia spirit of 100ml3%;

(2) get 20g H-ZSM-5 powder, pack into after mixing in the 1L autoclave with ammonium molybdate solution in (1), and use N ₂Speed with 100ml/min purges 20min;

(3) purge the back sealing autoclave, be warming up to 250 ℃ with the speed of 2 ℃/min, keep-uping pressure is 3.5MPa, keeps slowly discharging gas reactor behind the 5hr, stops heating, adopts N after waiting to reduce to normal pressure ₂Purge, take out after being cooled to room temperature;

(4) with obtained sample at H ₂Roasting under the same terms in the atmosphere obtains catalyst E.

Comparative Examples:

(1) the 2.04g ammonium molybdate is dissolved in the ammoniacal liquor of 20ml 5%, immerses the 10gHZSM-5 molecular sieve and put into baking oven in 110 ℃ of dryings afterwards, insert roasting in the Muffle furnace again, make catalyst F;

(2) with 1.67 MoO ₃After the grinding of 10g HZSM-5 molecular sieve, insert roasting in the Muffle furnace, make catalyst C;

(3) with 0.93g Zn (NO ₃) ₂6H ₂O is dissolved in the 20ml distilled water, immerses 10g HZSM-5 molecular sieve, makes catalyst H after oven dry, the roasting.

The catalyst that adopts above method preparation is at 550 ℃ of reaction temperatures, air speed 600h ^-1The structure of carrying out the propane aromatization reaction under the condition is as shown in table 1.Catalyst A, B, C, D, E all have higher conversion of propane and arenes selectivity.After the 30h reaction, conversion ratio descends about 10%, and arenes selectivity is constant substantially, and anti-coking deactivation ability significantly strengthens, and catalyst aromatization activity after regenerating is constant substantially, has very high stability.More than several indexs all be higher than catalyst F, G, H.

The propane aromatization performance of table 1 catalyst

(reaction temperature=550 ℃ air inlet air speed=600h ^-1)

Catalyst	A	B	C	D	E	F	G	H
									Conversion of propane % arenes selectivity % aromatics yield %	89.17 78.54 70.03	87.24 76.11 66.40	87.96 76.34 67.15	91.32 73.21 66.86	90.64 71.96 65.22	72.08 60.93 43.92	69.35 50.55 35.06	88.40 66.25 58.56
Other aromatic hydrocarbons of the senior aliphatic hydrocarbon benzene toluene of product distribution methane ethylene-ethane propylene dimethylbenzene	8.37 4.27 4.01 1.19 3.61 15.53 34.37 26.13 2.51	8.30 4.61 4.05 2.12 5.22 19.89 31.59 23.74 2.92	8.11 4.34 4.26 2.07 4.86 18.26 32.10 23.25 2.73	9.44 4.59 5.82 1.97 4.97 19.79 30.96 20.28 2.18	9.39 4.83 6.05 2.12 5.65 20.12 33.44 16.41 1.99	9.60 7.88 8.93 6.24 6.42 19.73 28.23 12.03 0.94	14.38 10.64 10.25 6.56 7.61 16.94 22.26 9.76 1.59	9.90 1.44 18.34 3.45 0.64 28.24 24.40 13.18 0.43

Annotate: method of testing adopts isotriacontane chromatographic column, hydrogen flame detector, Tianjin, island GC-TA gas phase look

Spectrometer carries out on-line analysis, calculates conversion of propane and arenes selectivity with carbon balance method.

Claims (1)

1. the preparation method of a Mo/HZSM-5 molecular sieve catalyst is characterized in that comprising the steps:

(1) by Mo: HZSM-5=2-15: 100 part by weight takes by weighing ammonium molybdate and HZSM-5 molecular sieve respectively;

(2) ammonium molybdate is dissolved in the 2-4% ammonia spirit, in the autoclave of packing into after molecular sieve mixes, adopts inert gas to blow down air, sealing autoclave afterwards in the still;

(3) speed with 2-3 ℃/min is warming up to 240-260 ℃, and keeping the still internal pressure is 3-5MPa, keeps stopping heating behind the 3-6hr, slowly discharges gas reactor subsequently, adopts inert gas purge after reducing to normal pressure, takes out after being cooled to room temperature;

(4) sample is taken out in air or hydrogen atmosphere in 550 ℃ and carried out roasting 4 hours, obtain required catalyst.