Technical Field

The present invention relates to the preparation of various types of natural zeolite catalysts from natural zeolites such as clinoptilolite and the method of producing dimethyl ether from methyl alcohol using these natural zeolite catalysts.

Prior Art In the known state of the art, the method of producing dimethyl ether by dehydration of methyl alcohol is known. According to this method, one molecule of water is separated from two molecules of methyl alcohol to form dimethyl ether:

2CH ₃ OH CH3OCH3 + H ₂ 0

This method is usually carried out on various solid catalysts with acidic character. Said catalysts are separated into two groups, namely oxide catalysts and artificial zeolite catalysts. Some important studies on the use of these catalysts in the process of dimethyl ether production from methyl alcohol are as follows:

In the article Catalysis Communications 6(2) (2005), 147-152 published by Yaripour, F., Baghaei, F., Schmidt, I. B. Perregaard, J., with name "Catalytic Dehydration of Methanol to Dimethyl Ether (DME) Over Solid- Acid Catalyst", γ- AI2O3 and silica-modified Y-AI2O3 catalyst is used for the dehydration of methyl alcohol. At atmospheric pressure and a temperature of 300 ⁰ C, the efficiency of dimethyl ether reaches 58-75% on this catalyst. United States patent document number US2007078285 refers to the use of γ- alumina, palladium-doped γ-alumina, phosphoric acid modified γ-alumina, and similar acid catalysts or different mixtures thereof as catalysts for the production of dimethyl ether from methyl alcohol. Using these catalysts, 80-90% dimethyl ether yield (in molar basis) is obtained with methyl alcohol dehydration at 200- 500°C.

In the United States patent document number US4595785, the usage of various catalysts composed of titanium oxide and aluminum oxide in varying proportions is mentioned. With the catalysts consisting of 1% titanium and 99% aluminum oxide, the concentration of dimethyl ether in the products obtained at 400 ° C and 1034 kPa pressure is 57.5%.

As can be seen from the aforementioned prior art documents, the oxide catalysts used for the dehydration of methyl alcohol are mainly Y-AI2O3 or mixtures thereof modified with different metals. The most important deficiencies of the said catalysts are the relatively low efficiency of dimethyl ether on them.

In the known state of the art, artificial zeolite catalysts are also widely used for the production of dimethyl ether from methyl alcohol:

In the article named "Study of the Conversion of Methanol to Dimethyl Ether on Zeolite HZSM-5 Using Situ Flow MAS MR" published by Lauren K. Carlson, Paul K. Isbester, Eric J. Munson in the "Solid State Nuclear Magnetic Resonance" journal, 16 (1999), p. 93-102, it is mentioned that the production method for dimethyl ether from methyl alcohol is carried out on artificial zeolite H-ZSM-5 catalyst at 250 ⁰ C.

In the article named "Vapour Phase Dehydration of Crude Methanol of Dimethyl Ether Over Na-modified H-ZSM-5 Catalysts" published by V. Vishwanathan, Ki- Won Yun, Yae-Woo Kim, Hyun-Seog Roh in the Applied Catalysts A: General journal, 276 (2004), p. 251-255, it is mentioned that dimethyl ether is produced from methyl alcohol with 94-97 % selectivity at a temperature of 230-340°C and 1 bar pressure on Na-modified H-ZSM-5 catalyst. In the article named "Dehydration of Methanol to Dimethyl Ether Employing Modified H-ZSM-5 Catalysts" published by Khandan, N., Kazemeini, M., Aghaziarati, M., Ave, A., in the Iranian Journal of Chemical Engineering, 6(1) (2009), it is mentioned that the H-ZSM-5 catalyst modified for Mg, Zr, Zn and similar metals are developed for the dehydration of methyl alcohol. The efficiency of dimethyl ether was measured as 78-94% and selectivity as 68-99% at 350°C and 100 bar pressure on this catalyst.

United States patent document number US8957259 refers to obtaining dimethyl ether from methyl alcohol with 90% efficiency on H-ZSM-5 catalyst at a temperature of 300°C.

United States patent document no US 8541630 refers to the use of artificial zeolite Y and other mesoporous molecular sieves as the dehydration catalyst. The conversion of methyl alcohol on zeolite Y + Beta catalyst was measured as 86% and selectivity to dimethyl was measured as 98%.

As can be seen from the documents known in the prior art, it is possible to obtain dimethyl ether with higher yield and selectivity from methyl alcohol on artificial zeolite catalysts than on oxide catalysts. The highest dimethyl ether efficiency and selectivity are obtained on H-ZSM-5 catalyst modified by different metals at high pressure (100 bar).

The most disadvantage of artificial zeolite catalysts commonly used in the process of dehydration of methyl alcohol in the state of the art is that the catalyst costs are very high. Brief Description of the Invention

The aim of this invention is to prepare natural zeolite catalysts which are economically and technologically superior to various types of natural zeolites such as clinoptilolite and have high yield and selectivity and to perform dimethyl ether production by dehydration of methyl alcohol using these catalysts.

Detailed Description of the Invention

An objective of this invention is preparing various types of natural zeolite catalyst such as clinoptilolite comprising the steps of; milling natural zeolite; drying the milled natural zeolite; removal of natural zeolite cations and chemical treatment to increase the ratio of Si0 ₂ :Al ₂ 03; and obtaining a H-natural zeolite catalyst, containing proton as a cation, with a first calcination treatment of the natural zeolite of which cations are removed and has increased ratio of Si0 ₂ :Al ₂ 03; and then followed by a second calcination treatment obtaining cation free D-natural zeolite catalyst. In the preferred application of the invention, the first calcination treatment is carried out at 350 ° C. In the preferred application of the invention, the second calcination is carried out at 550 ° C.

In the preferred application of the invention, chemical processes for removing natural zeolite cations and raising Si0 ₂ :Al ₂ 03 ratio includes the steps of performing two-stage cation exchange by treating the milled and dried natural zeolite with NH ₄ C1 solution, dealumination of the natural zeolite with HC1 solution, and two-stage cation exchange of natural zeolite with NH4CI solution. After each step mentioned above, the chemical processes for removing the natural zeolite cations and raising the Si02:Al ₂ 03 ratio, the natural zeolite is washed and dried. An exemplary application of the invention wherein clinoptilolite is used to prepare the natural zeolite catalyst is as follows. Clinoptilolite is first milled and fractionated with a particle size range of 500-1500 μιη and dried. Clinoptilolite is then subjected to three-step chemical treatments to remove cations such as Na, K in crystal structure of clinoptilolite and to increase the ratio of Si02:Al ₂ 03 in the structure at the same time. In the first step, clinoptilolite is subjected to 2-step cation exchange with NH ₄ C1 solution, then the dealumination process is applied to clinoptilolite with HC1 solution, and finally for removal of Na ⁺ and K ⁺ cations from the clinoptilolite structure at maximum level, the clinoptilolite is again subjected to 2-step cation exchange with the NH4CI solution. As a result of these processes, NH ₄ ⁺ - Clinoptilolite containing ammonium cations (NH ₄ ⁺ ) is obtained. After each step of the chemical treatment, the clinoptilolite is washed and dried. The washed and dried NH ₄ ⁺ -Clinoptilolite is then subjected to two-step calcination and eventually H-Clinoptilolite catalyst containing proton (H ⁺ ) as a cation with high catalytic activity and by subjecting H-Clinoptilolite catalyst to calcination D-Clinoptilolite catalyst which is free of cations is obtained. In an alternative application of the invention, catalysts containing different metal cations can be obtained by subjecting the NH ₄ ⁺ -clinoptilolite to the cation exchange with aqueous solutions of various metal salts.

Table 1, Table 2 and Table 3 below show the element contents of the natural zeolite clinoptilolite and the H-Clinoptilolite catalyst and the D-Clinoptilolite catalyst obtained according to the above-mentioned method, respectively.

Table 1. Elemental content of natural zeolite clinoptilolite Element % Weight % Atomic

OK 44,67 59,39

A1K 4,08 3,21

SiK 47,9 36,28

CuK 3,04 1,02

ZnK 0,31 0,1

Table 2. The element contents of the H-clinoptilolite catalyst obtained by the process subject of the invention

Table 3. The element contents of the D-clinoptilolite catalyst obtained by the process subject of the invention As can be seen from the above tables, when the Si:Al ratio of the natural zeolite clinoptilolite is 4.71, this ratio is 11.74 in the H-clinoptilolite catalyst and 12.28 in the D-Clinoptilolite catalyst that are obtained by the method subject of invention. This, in turn, significantly increases the activity of the acidic sites of natural zeolite.

When the H-clinoptilolite catalyst and the D-clinoptilolite catalyst that are obtained by the process subject of the invention are compared with the artificial zeolite catalysts, one of their important advantages is that no binder is required for pelletization and in this way the catalyst particles prepared on the basis of natural zeolite have high mechanical resistance. This advantage is achieved by grinding the natural zeolite at the beginning of the process subject of invention and separating the fraction having the desired particle size. The process of the present invention for the production of dimethyl ether by dehydration of methyl alcohol is carried out in an inert gas atmosphere at atmospheric pressure and a temperature range of 250-300 ° C using the natural zeolite catalyst obtained by the process having the abovementioned steps. The conversion of methyl alcohol in these conditions varies between 68.3-96.5% and the selectivity to dimethyl ether is -100% (in moles).

A few examples of the method of obtaining dimethyl ether by dehydration of methyl alcohol are described below:

EXAMPLE 1

H-Clinoptilolite catalyst and D-Clinoptilolite catalyst were prepared according to the method described above for the production of dimethyl ether by dehydration of methyl alcohol. For this purpose; 10 g of clinoptilolite having particle sizes of 500-1000 μιη were dried for 6 to 8 hours at 110-130° C in the air environment. The clinoptilolite was then subjected to 2-step cation exchange with NH ₄ C1 aqueous solution. Both cation exchange steps were carried out for 6 to 8 hours in a continuous mixing environment at a temperature range of 80-90° C. After the second-stage cation exchange, the clinoptilolite was washed with water and air- dried for 2 to 4 hours at a temperature of 110 to 130° C. Clinoptilolite was then subjected to dealumination treatment in the HC1 aqueous solution at a temperature of 70° C to 90° C for 4 to 6 hours in a continuous mixing environment. The clinoptilolite was then washed with water and dried in the air at a temperature of 110 to 130° C for 2 to 4 hours. Later the clinoptilolite was subjected to 2-step cation exchange with NH4CI aqueous solution for 2 to 4 hours in a continuous mixing environment at a temperature range of 80-90° C. After that the clinoptilolite was washed with water and dried at 120° C for 2 to 4 hours in air. Finally, H-clinoptilolite catalyst is obtained by subjecting clinoptilolite to calcination treatment at 350° C for 2 to 4 hours. And D-clinoptilolite catalyst is obtained by subjecting a certain amount of the H-clinoptilolite catalyst to calcination at 550° C for 2 to 4 hours in air. 3 g (~ 3cm ³ ) of the prepared H-Clinoptilolite catalyst was taken and was used in the dehydration process of methyl alcohol. The said dehydration process was carried out in a continuous laboratory experimental system, having tubular fixed bed steel reactor with a diameter of 10 mm and a length of 200 mm under a nitrogen atmosphere. For this purpose, the H-Clinoptilolite catalyst was activated with N ₂ gas for 2 hours at 300° C in atmospheric pressure.

Dehydration was carried out at atmospheric pressure, at a temperature of 300 ° C, at a flow rate of 0.25 cm ³ / min (5 hours ^"1 ) with respect to liquid methyl alcohol and at a flow rate of approximately 11500 hours ^"1 with respect to nitrogen gas. The results are as follows:

CH ₃ OH conversion: %94, 5

Selectivity according to dimethyl ether: %99, 6 (in moles)

EXAMPLE 2

The catalyst used for the dehydration process and other conditions were the same as in Example 1 at a temperature of 250 ⁰ C and results are as follows:

CH3OH conversion: %68, 5

Selectivity according to dimethyl ether: %99, 9 (in moles)

EXAMPLE 3

Dehydration was carried out at 350°C using the D-Clinoptilolite catalyst with the other conditions being the same as in Examples 1 and 2 and results are as follows: CH3OH conversion: %90, 7

Selectivity according to dimethyl ether: %99, 3 (in moles)

EXAMPLE 4

Dehydration was carried out in the same manner as in Example 2 except that the raw material flow rate was 0,125 cm ³ /min (2,5 hours ^"1 ) and results are as follows: CH3OH conversion: %84, 7 Selectivity according to dimethyl ether: %99, 4 (in moles)

EXAMPLE 5

The dehydration process was carried out at 350 ° C so that the raw material flow rate was 0.50 cm ³ / min (10 hours ^"1 ), the same as in Example 3 and results are as follows:

CH ₃ OH conversion: %78, 7

Selectivity according to dimethyl ether: %99, 8 (in moles)

Around these basic concepts, it is possible to develop a wide variety of applications relating to the invention "The Preparation Of Natural Zeolite Catalyst And The Method Of Producing Dimethyl Ether From Methyl Alcohol Using This Catalyst" and the invention cannot be limited to the examples mentioned herein, it is exactly as specified in the claims.