CN106362756A - Catalyst for preparation of isobutylene from isobutane through fixed bed dehydrogenation and preparation method thereof - Google Patents

Abstract

The invention provides a catalyst for preparing isobutene from isobutane fixed-bed dehydrogenation and a preparation method thereof. The catalyst uses Cr ₂ O ₃ as the active component, Al ₂ O ₃ as the carrier, the additive A is selected from a group VIII element oxide, the additive B is selected from a IVB element oxide, and the final catalyst contains Cr ₂ O The mass fraction of ₃ is 10%~25%, the mass fraction of additive A is 0.1%~1.0%, the mass fraction of additive B is 0.5%~1.5%, and the rest is alumina. The preparation steps of the catalyst include co-precipitation to obtain a precursor, and then forming, drying, and steam roasting to obtain a final catalyst. The catalyst provided by the invention has excellent dehydrogenation activity, mechanical strength and thermal stability.

Description

Catalyst for isobutane fixed-bed dehydrogenation to isobutene and preparation method thereof

technical field

In general terms, the present invention relates to the field of catalysts. Specifically, the invention relates to a catalyst for preparing isobutene by catalytic dehydrogenation of isobutane in a fixed bed and a preparation method thereof.

Background technique

Isobutene is a very important organic chemical intermediate, mainly used in the preparation of methyl tert-butyl ether (MTBE, high-octane clean gasoline blending component), butyl rubber, polyisobutylene, methacrylate, tert-butyl Various organic raw materials and fine chemicals such as phenol, tert-butylamine, 1,4-butanediol, ABS resin, etc. In recent years, with the rapid development of petrochemical and related industries, my country's demand for isobutene is also increasing; my country's low-carbon alkanes are usually used as fuel, which greatly reduces the utilization value of isobutane. The production of isobutene by catalytic dehydrogenation of isobutane with low utilization rate is an effective way to increase isobutene production. The technological development of isobutane catalytic dehydrogenation in my country is relatively late, and domestic isobutane dehydrogenation projects basically adopt foreign technology. The world's low-carbon alkane dehydrogenation patented technologies include: UOP's Oleflex process, ABB Lummus's Catofin process, ConocoPhillips (Uhde)'s Star process, Snamprogetti/Yarsintz's FBD-4 process, Linde/BASF The company's PDH process, etc. Among the devices already built, most of the former Soviet Union adopted the FBD-4 process, while the Catofin and Oleflex processes have become the dominant processes used in new plants. At present, the key to isobutane dehydrogenation to isobutene technology lies in the development of catalysts with high activity, high selectivity and high activity stability. There are two main types of catalyst systems that can be used for this reaction: one is platinum-based noble metal catalysts; One is chromium-based catalysts. Compared with Pt-based catalysts, chromium-based catalysts have the advantages of high activity, low cost, and easy availability, and are widely used in the market.

Patent CN102962054 introduces a chromium-based catalyst with mesoporous carbon as a carrier, the conversion rate of isobutane can reach 25-70%, and the selectivity of isobutene can reach 80-96%;

Patent _{CN201210197241} introduces a chromium _- based catalyst for _isobutane dehydrogenation. _The preparation method is to weigh the nitrates corresponding to various oxides and mix uniform, adding dilute nitric acid aqueous solution, drying, and then roasting in a nitrogen atmosphere to decompose nitrate and achieve solid-state ion exchange to obtain a Cr ₂ O ₃ -CaO-K ₂ O-Al ₂ O ₃ catalyst. The contents of Cr ₂ O ₃ , CaO, K ₂ O and Al ₂ O ₃ in the final catalyst were 60-90%, 3-12%, 0.5-3.0% and 5-36.5% of the mass fraction of the catalyst, respectively. The single-pass conversion rate of isobutane is more than 50%, and the selectivity to the target product isobutene is more than 98%;

Patent CN201210408473 introduces a chromium-based catalyst with La-containing alumina as a carrier. Based on the weight content of oxides, the content of lanthanum oxide in the final catalyst is 0.1-5.0%, and the content of chromium oxide is 5.0%-20.0%. The La in the La alumina carrier is introduced during the gelation during the alumina preparation process. The catalyst has excellent activity and activity stability;

Patent CN96121452 introduces a catalyst for dehydrogenating isobutene to produce isobutene. The catalyst comprises at least one metal element capable of dehydrogenating isobutane, one or more alkaline earth metals and transition metal elements, at least one alkali metal and alumina or aluminum pellets with suitable specific surface area and pore diameter.

Contents of the invention

Aiming at the shortcomings of existing isobutane dehydrogenation catalysts such as poor activity, poor mechanical strength and insufficient thermal stability, the invention provides a fixed-bed isobutane dehydrogenation catalyst and a preparation method thereof. The catalyst has a simple preparation process, can efficiently convert isobutane into isobutene, and has good industrial application prospects.

Technical scheme of the present invention is as follows:

A catalyst for preparing isobutene from isobutane fixed-bed dehydrogenation, characterized in that: the catalyst uses _Cr2O3 as an active component, _A and B as auxiliary agents, and _Al2O3 as a carrier; auxiliary agent _A It is selected from a group VIII element oxide, and the additive B is selected from a IVB element oxide. The mass fraction of Cr ₂ O ₃ in the catalyst is 10%~25%, and the mass fraction of additive A is 0.1%~1.0%. , the mass fraction of additive B is 0.5%~1.5%, and the rest is alumina. .

Preferably, in the catalyst, the mass fraction _{of Cr2O3} is 17.5% to 19.5%, the mass fraction of auxiliary agent A is 0.35% to 0.55%, the mass fraction of auxiliary agent B is 0.60% to 0.90%, and the rest is alumina.

More preferably, the mass fraction of Cr ₂ O ₃ in the catalyst is 19.0%, the mass fraction of additive A is 0.45%, the mass fraction of additive B is 0.75%, and the rest is alumina.

The auxiliary agent A described in the present invention is NiO, and the auxiliary agent B is TiO ₂ .

The preparation of catalyst of the present invention comprises the following steps:

(1) Dissolve the compounds containing Al, Cr, Ti, Ni in deionized water in proportion, and then stir evenly to obtain a certain concentration of salt solution;

(2) Slowly add the precipitant to the salt solution obtained in step (1) at a certain temperature while fully stirring to control the pH value of the solution. Stop adding the precipitant when the pH of the precipitation end is reached, and then perform ultrasonic treatment on the obtained colloid. aging

(3) Wash the aged colloid obtained in step (2) with deionized water, add a certain amount of binder after washing, extrude and dry;

(4) placing the catalyst obtained in step (3) in a tubular muffle furnace, and roasting under a mixed atmosphere of water vapor and air to obtain the final catalyst;

In the above step (1), the compounds containing Al and Ni are the corresponding nitrates, the compound containing Ti is TiCl ₄ , the compound containing Cr is one of chromium nitrate, chromium chloride, and chromium sulfate. In the salt solution, four The sum of the mass concentrations of the salts is 150g/L~350g/L.

The precipitation temperature in the above step (2) is room temperature, the precipitation agent is Na ₂ CO ₃ solution, the pH value at the end of precipitation is 9-11, the ultrasonic treatment time is 5 minutes, and the aging time is 2 hours.

The concentration of the precipitating agent Na ₂ CO ₃ solution in the above step (2) is 0.25mol/L-0.75mol/L.

The binder in the above step (3) is aluminum sol, wherein the added amount of aluminum sol (based on the alumina contained therein) is 1.5wt%-3wt% of the final catalyst.

The volume ratio of water vapor to air in the mixed atmosphere in the above step (4) is 1:4~3:2, the volume space velocity of the mixed gas is 200h ^-1 ~500h ^-1 , and the calcination temperature is 750°C~950°C, The roasting time is 4h~7h.

The catalyst provided by the present invention is prepared by co-precipitation method, and the research results show that the catalyst active components prepared by co-precipitation method are more uniform, which improves the activity of the catalyst, and the introduction of NiO inhibits the cracking, polymerization, aromatization, accumulation Side reactions such as carbon increase the isobutene selectivity; moreover, the introduction of _TiO2 improves the thermal stability of the catalyst. The catalyst provided by the invention has excellent dehydrogenation activity, mechanical strength and thermal stability.

detailed description

The catalyst of the present invention will be further illustrated below in conjunction with specific examples of implementation. The examples cited are used to illustrate the composition and preparation process of the catalyst, but it does not limit the present invention to have a better catalyst composition and preparation process.

Example 1

Weigh 50 grams of Cr(NO ₃ ) ₃ 9H ₂ O, 283.8 grams of Al(NO ₃ ) ₃ 9H ₂ O, 0.876 grams of Ni(NO ₃ ) ₂ 6H ₂ O, and 0.891 grams of TiCl ₄ in 2237 mL of deionized In water, stir evenly; then slowly add 0.25mol/L Na ₂ CO ₃ solution dropwise while stirring until the pH value is 9, continue to stir for 5 minutes, then ultrasonically treat for 5 minutes, then stand and age for 2 hours, then filter, wash, wash After completion, add 6.52 grams of aluminum sol (containing 23wt% Al ₂ O ₃ ) to extrude into a strip, dry it, and finally put the above catalyst in a tubular muffle furnace, and introduce a mixed atmosphere of water vapor and air (the volume ratio is 1:4 ), the calcination temperature was controlled at 850°C, the volume space velocity of the mixed atmosphere was 500h ^-1 , and the catalyst A was obtained by calcination for 4h.

Example 2

Weigh 26.5 grams of Cr ₂ (SO ₄ ) ₃ , 289.3 grams of Al(NO ₃ ) ₃ 9H ₂ O, 0.876 grams of Ni(NO ₃ ) ₂ 6H ₂ O, and 0.891 grams of TiCl ₄ were dissolved in 907 mL of deionized water, and stirred Evenly; then slowly drop in 0.75mol/L Na ₂ CO ₃ solution while stirring until the pH value is 11, continue to stir for 5 minutes, then ultrasonically treat for 5 minutes, then stand and age for 2 hours, then filter, wash, and add 3.26 grams of aluminum sol (containing 23wt% Al ₂ O ₃ ) was extruded and dried, and finally the above catalyst was placed in a tubular muffle furnace, and a mixed atmosphere of water vapor and air (volume ratio 2:3) was introduced to control The calcination temperature was 750°C, the volume space velocity of the mixed atmosphere was 300h ^-1 , and the catalyst B was obtained by calcination for 7 hours.

Example 3

Weigh 33.3 grams of CrCl ₄ •6H ₂ O, 287.4 grams of Al(NO ₃ ) ₃ •9H ₂ O, 0.876 grams of Ni(NO ₃ ) ₂ •6H ₂ O, and 0.891 grams of TiCl ₄ in 1612 mL of deionized water, stir well ; Then slowly drop in 0.50 mol/L Na ₂ CO ₃ solution while stirring until the pH value is 9.8, continue to stir for 5 minutes, then ultrasonically treat for 5 minutes, then stand and age for 2 hours, then filter and wash; after washing, add 4.35 Aluminum sol (containing 23wt% Al ₂ O ₃ ) was extruded and dried, and finally the above catalyst was placed in a tubular muffle furnace, and a mixed atmosphere of water vapor and air (volume ratio of 3:2) was introduced to control the roasting The temperature is 950°C, the volume space velocity of the mixed atmosphere is 200h ^-1 , and the catalyst C is obtained by calcining for 5h.

Comparative example 1

The catalyst preparation process was consistent with that of Example 1, but the calcination atmosphere in the final calcination process was only air, and catalyst D was obtained.

Comparative example 2

Weigh 283.8 g of Al(NO ₃ ) ₃ 9H ₂ O, 0.876 g of Ni(NO ₃ ) ₂ 6H ₂ O, and 0.891 g of TiCl ₄ in 1898 mL of deionized water, stir well; then slowly drop in 0.25 mol/L Na ₂ CO ₃ solution to a pH value of 9, continued to stir for 5 min, then ultrasonically treated for 5 min, then stood and aged for 2 h, then filtered and washed, and 6.52 grams of aluminum sol (containing 23wt% Al ₂ O ₃ ) extruded into strips, dried, and then calcined at 500°C for 4 hours to obtain a carrier, 50 grams of Cr(NO ₃ ) ₃ •9H ₂ O was dissolved in deionized water and impregnated on the above carrier, then dried, and finally the above catalyst Put it in a tubular muffle furnace, feed in a mixed atmosphere of water vapor and air (volume ratio 1:4), control the calcination temperature at 850°C, and the volume space velocity of the mixed atmosphere at 500h ^-1 , and calcine for 4 hours to obtain catalyst E. The mass fraction of each component in E is consistent with that in catalyst A.

Comparative example 3

The catalyst preparation process is the same as in Example 1, but the metal salt Ni(NO ₃ ) ₂ 6H ₂ O is replaced by Co(NO ₃ ) ₂ 6H ₂ O, and the mass fractions of NiO and CoO in the final catalyst are kept the same to obtain Catalyst F.

Comparative example 4

The preparation process of the catalyst was the same as in Example 1, but the metal salt TiCl ₄ was replaced with ZrCl ₄ , and the mass fractions of TiO ₂ and ZrO ₂ in the final catalyst were kept the same to obtain catalyst G.

Catalyst activity evaluation and physical parameters

Take 30ml of the obtained catalyst and fill it in a fixed _- bed reactor, then raise the temperature of the catalyst bed to 570°C, and then use N to purge. After the purge is completed, feed the isobutane raw material, and the isobutane flow rate is 140ml/min , start timing, collect the reaction product in 18min and carry out gas chromatography quantitative analysis, the results are shown in Table 1.

At the same time, the physical properties of each catalyst were tested, and the results are shown in Table 2.

Table 1. Catalyst activity test data

Table 2. Catalyst physical parameters

catalyst Intensity/N·cm ^-1 Specific surface area/m ² •g ^-1 Pore volume/cm3•g ^-1 Average pore size/nm A 198 78.1 0.269 10.3 B 125 90.1 0.335 11.9 C 153 93.3 0.356 9.8 D. 186 65.1 0.301 12.6 E. 173 55.9 0.139 7.6 f 190 77.6 0.258 10.4 G 192 77.9 0.263 10.3

Claims (10)

1. a kind of for iso-butane fixed-bed dehydrogenation prepare isobutene. catalyst it is characterised in that: this catalyst is with cr₂o₃For Active component, with a and b as auxiliary agent, al₂o₃For carrier;Auxiliary agent a is selected from an ethnic element oxide, and auxiliary agent b is selected from a kind of b Element oxide, cr in catalyst₂o₃Mass fraction be 10% ~ 25%, the mass fraction of auxiliary agent a is 0.1% ~ 1.0%, auxiliary agent b's Mass fraction be 0.5% ~ 1.5%, remaining for aluminium oxide.

2. catalyst according to claim 1 it is characterised in that: the more excellent composition of described catalyst is cr₂o₃Quality divide Number is 17.5% ~ 19.5%, and the mass fraction of auxiliary agent a is 0.35% ~ 0.55%, and the mass fraction of auxiliary agent b is 0.60% ~ 0.90%, remaining Under for aluminium oxide.

3. the catalyst according to any one of claim 1-2 it is characterised in that: cr in final catalyst₂o₃Mass fraction For 19.0%, the mass fraction of auxiliary agent a is 0.45%, and the mass fraction of auxiliary agent b is 0.75%, remaining for aluminium oxide.

4. the catalyst according to any one of claim 1-3 it is characterised in that: described auxiliary agent a is nio, and auxiliary agent b is tio₂.

5. catalyst according to claim 1 it is characterised in that: the preparation method of described catalyst comprises the following steps:

(1) compound containing al, cr, ti, ni is dissolved in deionized water in proportion, then stirs, obtain finite concentration Saline solution；

(2) the saline solution that step (1) obtains is slowly added to precipitant at a certain temperature when being sufficiently stirred for, controls solution ph Value, precipitation to be achieved terminates stopping during ph adding precipitant, then gained colloid is carried out supersound process, stands after being disposed Ageing；

(3) the colloid deionized water after the ageing obtaining step (2) is washed, and washing adds a certain amount of viscous after finishing Knot agent extruded moulding, drying；

(4) the catalyst obtaining step (3) is placed in tubular type Muffle furnace, and roasting under the mixed atmosphere with air for the vapor Obtain final catalyst.

6. catalyst according to claim 5 it is characterised in that: the compound containing al, ni be respectively corresponding nitrate, Compound containing ti is ticl₄, the compound containing cr is one of chromic nitrate, Chlorizate chromium, chromic sulfate, four kinds of salt in saline solution Mass concentration sum be 150g/l ~ 350g/l.

7. catalyst according to claim 5 it is characterised in that: described precipitation temperature is room temperature, described precipitant For na₂co₃Solution, it is 9 ~ 11 that precipitation terminates ph value, and sonication treatment time is 5min, and digestion time is 2h.

8. the catalyst according to claim 5 or 7 it is characterised in that: described precipitant na₂co₃Solution concentration is 0.25mol/l~0.75mol/l.

9. catalyst according to claim 5 it is characterised in that: described binding agent is Alumina gel, and wherein Alumina gel adds Enter 1.5wt% ~ 3wt% that amount (in terms of aluminium oxide contained therein) is final catalyst.

10. catalyst according to claim 5 it is characterised in that: the body of vapor and air in described mixed atmosphere Long-pending ratio is 1:4 ~ 3:2, and the volume space velocity of gaseous mixture is 200h^-1~500h^-1, sintering temperature is 750 DEG C ~ 950 DEG C, and roasting time is 4h~7h.