CA2642395A1 - Propylene via methanol over aluminosilicate catalyst - Google Patents

Abstract

A process for the preparation of high silica HZSM-5 for methanol conversion to light olefins especially propylene, is disclosed. The catalyst based on crystalline aluminosilicates of the pentasil type, having an SiO2/Al2O3 molar ratio at least 270, the BET surface area from 300 to 350 m2/g, total pore volume at least 0.15 and at most 0.4 cm3/g, the average pore diameter at least 2 and at most 20 nm and mean crystallites size at least 1 and at most 12 µm.

Description

PROPYLENE VIA METHANOL OVER ALUMINOSILICATE CATALYST
Field of the invention The invention relates to the synthesis of high silica aluminosilicate catalyst for methanol conversion reaction to light olefins. More particularly, the invention relates to method for synthesis of H-ZSM-5 catalyst for methanol conversion to light olefins especially propylene.

Background of the invention Zeolite molecular sieve catalysts are one of the most versatile catalysts ever found in this technology. Zeolite is three-dimensional, crystalline compounds, which are built from A104 and Si04 tetrahedral. It exhibits such properties as being a shape-selective catalyst with unusual catalytic properties, high thermal stability and high quality of ion-exchanging, so that, zeolites have dedicated numerous technical applications, for example they are used as sorbents, ion-exchangers, separation medias and pollution control agents in the petroleum, chemical and process industries.

Catalysts based on crystalline aluminosilicates which are prepared from a source of aluminum, a source of silicon, a source of alkali, a template and water, Depending on the composition of the starting mixture, the size of the primary crystallites is 1 micron or less. Commercially important zeolites, such as ZSM-5 and beta, can be produced under "hydrothermal" conditions, in which a silicon source, an aluminum source, optionally an organic template and a mineralizer (for example, alkali metal hydroxides or fluorides or HF) I

were converted at more than 100 C. under pressure in the pH range between 4 and 14. Hydrothermal syntheses of zeolites with a Si/Al atomic ratio of more than 20, for example, pentasil, are run in autoclaves at temperatures that are generally higher than 130 C., for example, at 180.degree (Accordance with U.S. Pat. No. 3,702,886, U.S. Pat. No. 6645461 and U.S. Pat. No. 6054113).

Methanol conversion is one of the promising and indirect processes in reducing natural gas resources to valuable products such as polymers. In which, the methanol-to-olefins conversion is noticeable process by scientists in recent years which is performed on an acidic molecular sieve catalyst bed.

Production of methanol conversion catalysts based on crystalline aluminosilicates is known from DE-A-28 22 725. The diameter of the primary crystallites is 1 m and more. According to West German Patent No. DE

2,405,909, the catalysts for hydrocarbon conversion are prepared on the basis of zeolites of the ZSM-5 type, the mean diameters of the primary crystallites being in the range from 0.05 to 0.1 micron.

According to DE-A-29 35 123. ZSM-5 or ZSM-11 zeolites are prepared, using ammonium hydroxide and an alcohol as template, in which the presence of nuclei is characteristic. The zeolites are used as cracking and hydrocracking catalysts and as catalysts for isomerization and dewaxing.

A method for production of large flat-structured crystals of zeolites of the pentasil type from Si02 and a compound of one or more trivalent elements, like Al, B, Fe, Ga, Cr, in amine-containing solutions is known from DE-A-35 37 459, characterized by the fact that highly dispersed Si02, prepared by burning of a silicon chloride compound, is used as starting material. The zeolites are used for conversion of organic compounds, especially for conversion of methanol to hydrocarbons containing lower olefins and aromatics. The obtained zeolites are not agglomerated.

European Patent No. EP- 123,449 describes a process for converting alcohol or ethers into olefins, using steam-treated zeolite catalysts; the latter have a crystal size of less than 1 micron and can be incorporated into a matrix.
Clays, silica and/or metal oxides are mentioned as matrix materials.

U.S. Pat. No. 4,206,085 relates to hydrocarbon conversion catalysts based on zeolites and a matrix material, for increasing the abrasion resistance. The matrix material used is alumina from pseudoboehmite, and Si02 from ammonium polysilicate or silica sol. The preferred zeolite is of the faujasite type. There are no data on the size of the zeolite crystals.

U.S. Pat. No. 5063187 concerns catalyst based on crystalline aluminosilicates of the pentasil type, having an Si/Al atomic ratio of at least 10, has the structure of primary crystallites of a mean diameter of at least 0.1 micron and at most 0.9 micron.

Summary of the invention The present invention relates to catalysts based on crystalline aluminosilicate of the pentasil type having a Si02/A1z03 molar ratio at least 270. These catalysts have an increased activity and selectivity in methanol conversion process to light olefins, in particular in methanol conversion to propylene (MTP). These catalysts are defined by a structure of crystallites of a mean diameter of at least about 1 m and at most 12 gm, the BET surface area from 300 about to 350 m2/g, total pore volume about to 0.15 to about 0.4cm3/g and the average pore diameter at least 2 and at most 20 nm.

The families of crystalline aluminosilicate zeolite known as the ZSM-5 type are more particularly describe in U.S. Pat. No. 3,702,886, the disclosure of which is incorporated herein by reference. These crystalline aluminosilicates are characterized by a silica/alumina mole ratio of greater than 5 and more precisely in the anhydrous state by the general formula:

0.9 ::L 0.2 M2/õO : A1203 : 5-300 Si02 Where M is selected from the group consisting of a mixture of alkali metal cations and organo ammonium cations, particularly a mixture of sodium and tetraalkylammonium cations, the groups of which preferably contain 2 to 5 carbon atoms. The term "anhydrous" as used in the above context means that molecular water is not include in the formula. In a more specific embodiment, the mole ratio of Si02 to A1203 in the above formula is 5-100 and preferably 15-100.

The original cations can be replaced in accordance with techniques well known in the art, at least in part, by ion exchange with other cations.
Preferred replacing cations include alkylammonium cations, metal ions, ammonium ions, hydrogen ions and mixtures of the same. Particularly preferred cations are those which render the zeolite catalytically active. These include hydrogen, rare earth metals, aluminum, metals of Groups II and VIII of the Periodic Table and manganese. Also desired are zeolites which are thermally treated products of the foregoing, said thermal treatment consisting of heating the ZSM-5 type zeolite in the desired particular cation from at a temperature of at least 700 F.
Members of the family of ZSM-5 zeolites possess a definite distinguishing crystalline structure whose X-ray diffraction pattern shows the following significant lines:

Interplanar spacing d(A): Relative intensity 11.1 0.2 s.
10.0 0.2 s.
7.4 0.15 w.
7.1 0.15 w.
6.3 0.1 w.
6.04 0.1 w.

5.97 0.1 w.
5.56 0.1 w.
5.01 0.1 w.
4.60 0.08 w.
4.25 0.08 w.
3.85 0.07 V.S.
3.71 0.05 s.
3.04 0.03 w.
2.99f0.02 w.
2.94 0.02 w.

The values were determined by standard techniques. The radiation was the K-alpha doublet of copper, and a scintillation counter spectrometer with a strip chart pen recorder was used. The peak heights, I, and the positions as a function of 2 times theta, where theta is the Bragg angle, were read from the spectrometer chart. From these, the relative intensities, 100 I/lo, where I0 is the intensity of the strongest line or peak, and d (obs.), the interplanar spacing in A, corresponding to the recorded lines, were calculated. In the above tabulation, the relative intensities are given in terms of the symbols s=
strong, w= weak and vs = very strong.

Zeolite ZSM-5 as the catalyst for use in the hydrocarbon conversion reactions described herein can be suitably prepared from sodium aluminate as a source of aluminum, silicic acid as a source of silicon and tetrapropylammonium compounds (for example tetrapropylammonium hydroxide) as a source of template and sodium hydroxide.

Detailed description of the Invention In the catalyst of this invention, the crystallites have a mean diameter of at least about 1 micron and at most 12 micron. Preferably, the mean diameter of the crystallites is in the range from 4 to 8 micron. The pure catalyst (without binder) determines the BET surface area from 350 to 400m2/g, the total pore volume between 0.15 and 0.4 cm3/g, and the pore diameter have preferably, a diameter of 2-20 nm.

The catalyst according to the invention is obtainable preferably in the following manner:

(a) In an aqueous reaction batch containing a source of aluminum, sodium hydroxide, a source of tetrapropylammonium template, and a source of silicon alumimosilicate gel is produced at room temperature and converted to a crystalline aluminosilicate under atmospheric pressure in a PTFE lined vessel.
(b) The crystallites are separated from the aqueous reaction medium, dried, washed with ionized water and subjected to an appropriate calcination process.
(c) The product from stage (b) is reacted in an aqueous medium with an ammonium salt on heating in a manner that described in U.S. Pat. No. 4, 447,669 for the purpose of exchanging the sodium ions with hydrogen ions.

(d) The product from stage (c) is mixed with an amorphous silica -alumina binder; and (e) The product from stage (d) is subjected to a final calcination.

The catalyst according to the invention is obtainable is explained in more detail below:

In stage (a), an aqueous reaction batch containing a source of silicon (for example silicic acid), a source of aluminum (for example sodium aluminate), sodium hydroxide and a template of tetrapropylammonium compound (for example tetrapropylammonium hydroxide) is first prepared. The proportions by weight between the source of silicon and the source are aluminum is selected such that the crystalline aluminosilicates having a Si02/A1203 mole ratio of at least 250 to about 500 are obtained. An alkaline alumimosilicate gel (synthesis gel) is produced from the reaction batch at room temperature and is transformed to alumimosilicate crystallites under a mild temperature from 80 to 105 C under atmospheric condition in an stainless steel fitted with a polytetrafluoroethylene (PTFE) inner lining for a duration of 15 days.
Preferred templates are tetrapropylammonium hydroxide and bromide (TPAOH and TPABr). The aqueous reaction batch of stage (a) has preferably by a pH value from 10.5 to 13.5.

In stage (b) the product crystallites are separated by filtration. The intermediate calcination can be completed in an oxidizing atmosphere at about 500 to 550 C.

In stage (c) the product from stage (b) is reacted in an aqueous medium with ammonium nitrate on heating in a manner that described in U.S. Pat. No. 4, 447,669. The Na form of zeolite is added to 1M solution of ammonium nitrate.
The mixture is stirred at a temperature 60 C for 4 hours. The product is recovered by filtration. This operation is renewed third times. The product is then dried and then calcined in air at 650 C for 3 hours.

In stage (d) the product from stage (c) is mixed with the amorphous alumimosilicate binder composed 65% of A1203 and 35% of Si02 in a manner that described in U.S. Pat. No. 4,616,098. The extrudates are dried at I10 C
for 16 hours and calcined at 550 C for 12 hours.

The end product thus obtained can be used in methanol conversion processes for the production of light olefins, especially for propylene.

Example 1 This example illustrates the preparation of zeolite ZSM-5. 5.886 grams NaA1O2 (comp.: 53 wt. percent A1203, 44.5 wt. percent Na20, 2.5 wt. percent H20) partially dissolved in 62.700 ml. 0.178N sodium hydroxide by vigorous stirring. There was slowly added 388.941 grams of TPAOH (tetra-n-propylammonium hydroxide, 40 vol%, Merck) as a template. 527.850 grams silicic acid (Si02Ø5H20) was added to above mixture under vigorous stirring at about 500 rpm. After about 60 minutes with stirring, the pH of reaction mixture was adjusted about 10 values by sulfuric acid addition. The resulted mixture had the following composition: 7.650 mole Si02, 0.0306 mol A1203, 0.260 mole Na20, 0.765 mole (CH3CH2CH2)4NOH, 153 mole H20. The mixture was placed in a PTFE lined vessel and heated at 1050 C, at atmospheric pressure for 5 days under reflux with stirring about 100 rpm. The resultant solid product was cooled to room temperature, removed, washed with 80 liter H20. The product was then dried overnight at 105 C. A portion of this product was subjected to X-ray analysis and identified as ZSM-5 phase with amorphous phase. The product was then calcined in air at 550 C for 10 hours.
Example 2 This example illustrates the preparation of zeolite ZSM-5. 4.264 grams NaAlO2 (comp.: 53 wt. percent A1203, 44.5 wt. percent Na20, 2.5 wt. percent H20) partially dissolved in 2490.140 ml. 0.189 N sodium hydroxide by vigorous stirring. There was slowly added 395.04 grams of TPAOH as a template. 536.130 grams silicic acid was added to above mixture under vigorous stirring at about 500 rpm. After about 60 minutes with stirring, the pH

of reaction mixture was adjusted about 10 values by sulfuric acid addition.
The resulted mixture had the following composition: 7.770 mole Si02, .0222 mol A1203, 0.266 mole Na20, 0.777 mole (CH3CH2CH2)4NOH, 155.400 mole H20.
The mixture was placed in a PTFE lined vessel and heated at 105 C, at atmospheric pressure for 10 days under reflux with stirring about 100 rpm.
The resultant solid product was cooled to room temperature, removed, washed with enough distilled water. The product was then dried overnight at 105 C. A
portion of this product was subjected to X-ray analysis and identified pure ZSM-5 phase that had a degree of crystallinity of 100%, the BET surface area 319.86 m2/g, total pore volume 0.167 cm3/g, the average pore radius 10.44 angstrom and crystallite size between 1-12 m.

The product was then calcined in air at 550 C for 10 hours. The analysis results of product are indicated in table I.

Example 3:

This example illustrates the preparation of zeolite ZSM-5. 3.019 grams NaA1O2 (comp.: 53 wt. percent A1203, 44.5 wt. percent Na20, 2.5 wt. percent H20) partially dissolved in 2515.810 ml. 0.195N sodium hydroxide by vigorous stirring. There was slowly added 395.04 grams of TPAOH solution as a template. 541.650 grams silicic acid was added to above mixture under vigorous stirring at about 500 rpm. After about 60 minutes with stirring, the pH
of reaction mixture was adjusted about 10 values by sulfuric acid addition.
The resulted mixture had the following composition: 7.85 mole Si02, 0.0 16 mol A1203, 0.267 mole Na20, 0.785 mole (CH3CH2CH2)4NOH, 157 mole H20. The mixture was placed in a PTFE lined vessel and heated at 105 C, at atmospheric pressure for 15 days under reflux with stirring about 100 rpm. The resultant solid product was cooled to room temperature, removed, washed with 80 liter H20. The product was then dried overnight at 105 C. A portion of this product was subjected to X-ray analysis and identified of ZSM-5 phase and quartz phase. The product was then calcined in air at 550 C for 10 hours. The analysis results of product are indicated in table I.

TABLE I

Example Time (day) 5 10 15 Temperature ( C) 105 105 105 Reaction composition, moles SiO2 250 350 500 A1~O3 1 1 1 NazO 8.50 12 17 (CH3CH2CH2)4NOH 25 35 50 Product, weight percent in the H-form zeolite (calcined 550 C) Na20 0.076 0.067 0.051 A1,03 0.625 0.491 0.313 Si02 99.34 99.50 99.41 Total as oxides 100.04 100.05 99.77 SiO2/A1ZO3 270 344 540 Na2O/A1203 0.200 0.224 0.268 Product phase ZSM-5+Arnorph Pure ZSM-5 ZSM-5+Quartz Application Example:

The catalyst conversion of methanol to light olefins especially propylene over HZSM-5 catalyst (Catalyst of example 2) with Si021A1203 molar ratio of 344 was performed in a fixed-bed stainless steel reactor (1 inch I.D.). For methanol conversion, 300 grams of shaped catalyst was placed between two beds of alumina balls with the same dimension of the catalyst. Prior to introducing methanol feed, the catalyst was heated under flow of nitrogen (100 ml/min) at 550oC during 12 hours. Typical test of catalyst was experienced in condition of a pressure of latm. (1.04 bar), temperature of 460 3oC, WHSV of lh-1, with a feed of 50% methanol in water. The conversion of methanol was defined as:

X= noCH3OH - (nCH3OH+2nDME) x 100%
noCH3OH
Wherein X is the conversion, noCH3OH is the moles of methanol fed to the reactor per unit time, nCH3OH is the moles of unreacted methanol leaving the reactor per unit time, nDME is the moles of dimethyl ether leaving the reactor per unit time. That is, the moles of dimethyl ether are treated as equivalent moles to unreacted methanol, not as a reaction product.
Distribution of hydrocarbons and oxygen products are shown in table II.

TABLE II

TOS(h) 100 200 300 400 500 Hydrocarbon Distribution (mole %) CH4 0.69 1.24 0.83 1.31 1.42 C2H4 15.11 12.94 14.57 9.00 8.78 C2H6 0.25 0.18 0.26 0.12 0.12 C3H6 37.54 41.47 43.02 44.30 43.07 CzHg 3.17 2.00 2.80 1.07 0.96 DME 0.01 0.00 0.27 0.00 0.01 TOTAL C4= 25.55 26.56 26.49 27.82 24.50 n-Butane 2.20 2.46 1.93 2.93 1.43 iso-Butane 2.03 2.42 2.03 2.65 3.25 C5 hydrocarbons 3.66 2.24 2.56 3.17 3.79 C6 hydrocarbons 1.87 1.54 0.94 1.78 3.13 C7 hydrocarbons 1.12 1.05 0.59 1.07 1.91 Benzene 0.20 0.12 0.04 0.05 0.12 Toluene 1.49 1.09 0.40 0.54 1.07 p,m,o-Xyelenes 3.01 2.32 0.96 1.75 3.11 Tri methyl benzene 0.50 0.55 0.32 0.50 1.10 C8 hydrocarbons 0.47 0.46 0.28 0.48 0.81 C9+ hydrocarbons 0.58 0.69 0.42 0.41 0.48 CO2 0.22 0.44 0.98 0.50 0.03 CO 0.09 0.09 0.09 0.08 0.08 MeOH (unreacted) 0.09 0.00 0.03 0.12 0.38 Acetone 0.15 0.15 0.06 0.10 0.19 1-Propanol 0.00 0.00 0.01 0.02 0.03 Oxygenates 0.00 0.00 0.11 0.22 0.24 Total 100.00 100.00 100.00 100.00 100.00 %Conversion 99.90 100.00 99.20 99.93 99.73

Claims (14)

1. A crystalline aluminosilicate zeolite which can be identified in term of mole ratios of oxides in synthesis gel as follow:

xNa2O:Al2O3:yR2O:zSiO2:wH2O (where R is tetrapropyl ammonium cation)

2. Catalyst according claim 1, wherein the formation of the primary aluminosilicate crystallites takes place with stirring about 80° C. to about 105°
C under reflux condition.

3. Catalyst according claim 1, wherein the formation of the primary aluminosilicate crystallites takes place with stirring at atmospheric pressure.

4. Catalyst according claim 1, wherein the formation of the primary aluminosilicate crystallites takes place with stirring during 5 to 15 days.

5. Catalyst according claim 1, wherein x is from 8.5 to 17.

6. Catalyst according claim 1, wherein y is from 12.5 to 25.

7. Catalyst of claims 1 which has SiO2/Al2O3 mole ratio of about 100 to 700, preferably about 250-600, especially about 250 to 500.

8. Catalyst according claim 1, wherein the template is tetra-n-propylammonium salt (TPAM, where M= Br or OH).

9. A crystalline zeolite according to claims 1 to 5 wherein the average diameter of the crystallites lies in the range from 1 to 12 µm, especially from 4 to 8 µm.

10. A crystalline zeolite according to one of the preceding claims, wherein the total pore volume lies between 0.15 and 0.4cm3/g.

11. A crystalline zeolite according to one of the preceding claims, wherein the BET surface area lies between 300 and 400 m2/g.

12.Catalyst according to one of the preceding claims, characterized by the fact that the final calcining is conducted at a temperature between 500 to 800°
C. for 6 to 28 hours.

13.Use of the catalyst according to one of the claims 1 to 9 in an MTP or MTO
process.

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