CN102407145A - Catalyst for n-heptane isomerization reaction and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of chemical catalysts, and particularly relates to a catalyst for n-heptane isomerization reaction and a preparation method thereof. The catalyst of the invention is prepared by adopting an oxide M₂O₃(M = In, Fe, Cr) modified Pt/WO₃/ZrO₂Solid acid, and the catalyst comprises the following components in percentage by weight: in terms of molar ratio, the M/Zr ratio is 0.001-0.1; in percent by weight, WO₃The content is 6-30%, and the content of Pt is 0.1-2%. The catalyst has good effect when used for n-heptane isomerization reaction, high n-heptane conversion rate, high isomerization product selectivity and good catalyst stability.

Description

Catalyst for isomerization reaction of n-heptane and preparation method thereof

technical field

The invention belongs to the technical field of chemical catalysts, and in particular relates to a catalyst for isomerization reaction of n-heptane and a preparation method thereof.

Background technique

In order to improve the quality of gasoline and make it more environmentally friendly, people are eager to find a clean fuel chemical process that can produce high-octane without aromatics. n -C ₇₊ (n-alkanes with carbon number 7 and above) hydroisomerization is a solution with great potential. The n -C ₇₊ fraction in crude oil is isomerized into branched alkanes with higher octane number under the action of catalyst, and these isomerized products can be added to gasoline to increase gasoline octane number. Therefore, n -C ₇₊ isomerization has revived great research enthusiasm.

The catalysts used in the isomerization of n-alkanes are mainly metal/carrier bifunctional catalysts in which noble metals (such as Pt, Pd, Ir, etc.) are supported on solid strong acids. In recent years, it has been found that Pt/WO ₃ /ZrO ₂ catalysts have good reactivity for n -C ₇₊ isomerization, and a lot of research has been done on it. Compared with the traditional Pt/zeolite molecular sieve catalyst, Pt/WO ₃ /ZrO ₂ has stronger acidity, so it has higher activity at lower reaction temperature, and compared with Pt/SO ₄ ^2- /ZrO ₂ catalyst, Pt/WO ₃ /ZrO ₂ is slightly less acidic, but shows higher selectivity and better stability in the isomerization reaction, and is insensitive to benzene and sulfide impurities in the reaction raw materials. It has been reported that adding a small amount of Al ₂ O ₃ or Ga ₂ O ₃ to Pt/WO ₃ /ZrO ₂ can improve the activity of the catalyst for n-heptane isomerization, but adding In ₂ O ₃ , Fe ₂ O ₃ , Cr ₂ The use of O ₃ modified Pt/WO ₃ /ZrO ₂ catalysts in the isomerization of n-heptane has not been reported yet.

Contents of the invention

The purpose of the present invention is to provide a new n-heptane isomerization catalyst and a preparation method thereof. The catalyst is used for n-heptane isomerization reaction and has the advantages of high activity and high selectivity of isomerization products.

The n-heptane isomerization catalyst proposed by the present invention is a Pt/WO3 _{/ ZrO2} solid acid catalyst modified with _{M2O3 oxide} , and its composition is as follows:

a) In terms of molar ratio, the M/Zr ratio is 0.001~0.1;

b) In terms of weight percentage, the WO ₃ content is 6-30%, and the Pt content is 0.1-2%.

In the present invention, M in the M ₂ O ₃ oxide may be In, Fe or Cr. That is, the M ₂ O ₃ oxide can be In ₂ O ₃ , Fe ₂ O ₃ or Cr ₂ O ₃ .

In the present invention, in terms of molar ratio, the preferred range of M/Zr ratio is 0.01-0.02; in terms of weight percentage, the preferred range of _WO content is 15-24%, and the preferred range of Pt content is 0.5-1%.

The preparation method of the normal heptane isomerization catalyst that the present invention proposes, concrete steps are as follows:

1. First, under the condition of constant pH=8~10, use 4~8 mol/L ammonia water to hydrolyze the mixed salt solution of Zr and M to obtain Zr(OH) ₄ -M (OH) ₃ mixed hydroxide; Mixed hydroxides were filtered, washed, and dried at 80-120 ^o C for 10-36 hours;

2. Immerse the required amount of W salt solution on Zr(OH) ₄ -M (OH) ₃ by equal volume impregnation method, and dry at 80~120 ^o C for 10~36 hours;

3. Calcined at 700~850 ^o C for 2~5 hours in air atmosphere to obtain WO ₃ /ZrO ₂ M ₂ O ₃ solid acid;

4. Then, impregnate the required amount of Pt salt solution on WO ₃ /ZrO ₂ -M ₂ O ₃ by equal volume impregnation method, dry at 80~120 ^o C for 10~36 hours, and place in air atmosphere at 400~500 ^o C roasting for 2 to 5 hours to obtain the desired catalyst.

The raw materials used in the catalyst of the present invention are as follows: the raw materials of Zr are selected from ZrOCl ₂ 8H ₂ O or ZrO(NO ₃ ) ₂ 7H ₂ O, the raw materials of W are selected from ammonium metatungstate, and the raw materials of Pt are selected from tetraammonium nitrate Platinum or chloroplatinic acid, the raw material of In is selected from In(NO ₃ ) ₃ 4.5H ₂ O, the raw material of Fe is selected from Fe(NO ₃ ) ₃ 9H ₂ O, the raw material of Cr is selected from Cr(NO ₃ ) _{3.9H2O .}

The ^catalyst of the present invention uses Pt/WO ₃ /ZrO ₂ solid acid modified by M ₂ O ₃ (M = In, Fe, Cr) oxides, and is used for the isomerization reaction of n-heptane. Under the conditions of reaction temperature and normal pressure, the conversion rate of n-heptane can reach 75.2%, and the selectivity of isomerization products can reach more than 95%.

The evaluation conditions of the catalyst obtained in the present invention are: before the reaction, the catalyst is first air-activated at 450 ^° C for 2 hours, then reduced with hydrogen at 250 ^° C for 2 hours, the isomerization reaction is carried out at 200 ^° C, and the mass of n-heptane The space velocity is 0.9 h ^-1 , and the H ₂ / n -C ₇ molar ratio is 27.

Detailed ways

Below by embodiment the present invention will be further elaborated.

Example 1: 34.800 grams of ZrO(NO ₃ ) ₂ 7H ₂ O and 0.394 grams of Fe(NO ₃ ) ₃ 9H ₂ O were dissolved in 400 mL of water, and the above solution was mixed with 6 mol/L ammonia water dropwise while stirring Add to 200 mL of ammonia solution with pH = 9, and control the pH to be constant at 9 throughout the dropping process. After the obtained precipitate was filtered, washed, and dried at 100 ^o C for 24 hours, the ammonium metatungstate solution was impregnated on Zr(OH) ₄ -Fe(OH) ₃ by equal-volume impregnation method, and dried at 100 ^o C for 24 hours, then in Calcined at 800 ^o C for 3 hours in air atmosphere to obtain WO ₃ /ZrO ₂ -Fe ₂ O ₃ solid acid. Then, the tetraammineplatinum nitrate solution was impregnated on WO ₃ /ZrO ₂ -Fe ₂ O ₃ by equal volume impregnation method, dried at 100 ^o C for 24 hours, and then calcined at 450 ^o C in air atmosphere for 3 hours to obtain the desired catalyst. The Fe/Zr molar ratio in the catalyst was 0.01, the WO ₃ content was 18%, and the Pt content was 1%.

Examples 2 to 6: Catalysts were prepared according to the steps and conditions of Example 1. The changed preparation conditions included the type of M, the molar ratio of M/Zr, the content of WO ₃ , and the calcination temperature. See Table 1.

Table 1 Preparation of Pt/WO ₃ /ZrO ₂ -M ₂ O ₃ solid acid catalyst

the m M/Zr molar ratio WO ₃ content (%) Calcination temperature ( ^o C) Example 2 In 0.02 18 800 Example 3 Cr 0.02 18 800 Example 4 Fe 0.02 twenty four 800 Example 5 Fe 0.03 15 850 Example 6 In 0.01 15 750 Example 7 In 0.03 twenty one 800

Comparative Example 1: A non-modified Pt/WO ₃ /ZrO ₂ solid acid catalyst was prepared according to the steps and conditions of Example 1, and no M ₂ O ₃ oxide was doped during the preparation process.

Example 8: Apply the above catalyst to the isomerization reaction of n-heptane, the specific reaction conditions are as follows: before the reaction, the catalyst was first activated in the air at 450 ^o C for 2 hours, and then reduced with hydrogen at 250 ^o C for 2 hours, the iso The structuring reaction was carried out at 200 ^o C, the mass space velocity of n-heptane was 0.9 h ^-1 , and the molar ratio of H ₂ / n -C ₇ was 27. The reaction performance and stability of the catalyst are shown in Table 2 and Table 3, respectively.

Table 2 Catalyst n-heptane isomerization reaction performance

the Reaction time (h) Conversion rate(%) selectivity (%) Example 1 2 75.2 95.2 Example 2 2 72.0 95.8 Example 3 2 55.8 97.9 Example 4 2 58.2 98.3 Example 5 2 42.3 98.6 Example 6 2 39.1 98.6 Example 7 2 55.9 98.3 Comparative example 1 2 36.9 97.8

Table 3 The stability performance of embodiment 1 catalyst

Reaction time (h) Conversion rate(%) selectivity (%) 1 75.3 95.1 2 75.2 95.2 10 75.3 95.2 30 75.2 95.2 60 75.2 95.2 100 75.1 95.3

Claims (5)

1. the catalyst of a normal heptane isomerization reaction is characterized in that being M ₂O ₃The Pt/WO of oxide modifying ₃/ ZrO ₂Solid acid, M are In, Fe or Cr, and catalytic component content is following:

(a) with molar ratio computing, the M/Zr ratio is 0.001 ~ 0.1;

(b) by weight percentage, WO ₃Content is 6 ~ 30%, and Pt content is 0.1 ~ 2%.

2. the catalyst of normal heptane isomerization reaction according to claim 1 is characterized in that, with molar ratio computing, the M/Zr ratio is 0.01 ~ 0.02.

3. according to the catalyst of the said normal heptane isomerization reaction of claim 1, it is characterized in that, by weight percentage, WO ₃Content is 15 ~ 24%, and Pt content is 0.5 ~ 1%.

4. like the Preparation of catalysts method of the said normal heptane isomerization reaction of claim 1-3, it is characterized in that concrete steps are following:

(1) at first under the condition of constant pH=8 ~ 10, the mixing salt solution with 4 ~ 8 mol/L ammoniacal liquor hydrolysis Zr and M obtains Zr (OH) ₄~ M (OH) ₃Mixed hydroxides; Above-mentioned mixed hydroxides is filtered washing, 80 ~ 120 ^oDry 10 ~ 36 hours of C;

(2) with equi-volume impregnating with the salt solution impregnation of the W of aequum in Zr (OH) ₄~ M (OH) ₃On, 80 ~ 120 ^oDry 10 ~ 36 hours of C;

(3) in air atmosphere 700 ~ 850 ^oC roasting 2 ~ 5 hours promptly obtains WO ₃/ ZrO ₂~ M ₂O ₃Solid acid;

(4) then, with equi-volume impregnating with the salt solution impregnation of the Pt of aequum in WO ₃/ ZrO ₂~ M ₂O ₃On, 80 ~ 120 ^oDry 10 ~ 36 hours of C is in air atmosphere 400 ~ 500 ^oC roasting 2 ~ 5 hours promptly gets required catalyst.

5. according to the Preparation of catalysts method of the said normal heptane isomerization reaction of claim 4, it is characterized in that the raw material of Zr salt is selected from ZrOCl ₂8H ₂O or ZrO (NO ₃) ₂7H ₂O, the raw material of W salt is selected from ammonium metatungstate, and the raw material of Pt is selected from nitric acid four ammino platinum or chloroplatinic acids, and the raw material of In salt is selected from In (NO ₃) ₃4.5H ₂O, the raw material of Fe salt is selected from Fe (NO ₃) ₃9H ₂O, the raw material of Cr salt is selected from Cr (NO ₃) ₃9H ₂O.