Method for the synthesis of a ZSM-22 zeolite, a metal containing zeolite and its application in hydromerization of long chain n-paraffins

Abstract

The present invention provides a process for preparing a zeolite by hydrothermal heating of silica precursor and alumina precursor along with a combination of two structure-directing organic templates, N,N-dimethyl formamide and 1,6-diaminohexane in the presence of an alkali. The use of two structure-directing organic templates, not only reduces the crystallization time but also enables the preparation of more catalytically active ZSM-22 of submicron crystallite size. The present invention also provides a process of preparing a noble metal containing zeolite catalyst for hydroisomerization of long chain n-paraffins.

Claims

1. A process for the synthesis of zeolite from a reaction mixture comprising silica and alumina precursors along with a combination of two structure-directing organic templates, N,N-dimethyl formamide and 1,6-diaminohexane in the presence of an alkali and maintaining said reaction mixture at a sufficient temperature to crystallize the zeolite and recovering the zeolite wherein the zeolite is selected from zeolites of the TON framework structure.

2. The process as claimed in claim 1, wherein the zeolite is ZSM-22.

3. The process as claimed in claim 1, wherein said silica precursor is selected from the group consisting of silica sols, tetraalkyl orthosilicates, silicon dioxides such as fumed silicas and precipitated silicas.

4. The process as claimed in claim 1, wherein said alumina precursor is Al.sub.2(SO.sub.4).sub.3.18H.sub.2O.

5. The process as claimed in claim 1, wherein the mole ratio of organic 1,6-diaminohexane and N,N-dimethyl formamide is in the range of 1:0.1 to 1:10.

6. The process as claimed in claim 1, wherein the alkali is sodium hydroxide, potassium hydroxide or combination thereof.

7. The process as claimed in claim 1, wherein the molar ratio of SiO.sub.2/Al.sub.2O.sub.3 in the zeolite is not more than 300.

8. The process as claimed in claim 1, further comprising preparing a noble metal containing zeolite catalyst comprising the steps: (a) calcining the zeolite at sufficient temperature to decompose the organic templates; (b) converting the zeolite to its acidic form by ion-exchanging with ammonium nitrate and followed by calcination at sufficient temperature to decompose ammonium ions; (c) treating the acidic form with a metal by the process of ion-exchange with a metal precursor salt to obtain noble metal loaded acidic form of the zeolite; (d) drying the metal loaded acidic form of the zeolite to obtain a dried material; (e) extruding the dried material with a binder selected from the group consisting of clays, silicas, aluminas, metal oxides, and mixtures thereof to obtain an extruded catalyst; and (f) calcining the extruded catalyst under constant air flow to obtain a metal-containing zeolite catalyst.

9. The process as claimed in claim 8, wherein the acidic form in step (a) is H form which is obtained by exchanging Na+ or K+ or combination of both forms of zeolite with ammonium nitrate and followed by calcination.

10. The process as claimed in claim 9, wherein said acidic H-form has a surface area in the range of 100-320 m.sup.2/gm.

11. The process as claimed in claim 9, wherein said acidic H-form zeolite has a crystal size of <1 micron.

12. The process as claimed in claim 9, wherein said acidic H-form has external surface area in the range of 10-80 m.sup.2/gm.

13. The process as claimed in claim 9, wherein the acidic H-form has acidity in the range of 50-300 mol/gm.

14. The process as claimed in claim 8, wherein the steps (a and b) are carried out at 550 C.

15. The process as claimed in claim 8, wherein said metal containing catalyst has metal dispersion over 10 to 95%.

16. The process as claimed in claim 8, wherein the acidic H-form is loaded with Group-VIII metal by ion-exchange using a precursor salt.

17. The process as claimed in claim 16, wherein said platinum salt used for ion-exchange is tetra-ammonium platinum nitrate complex.

18. The process as claimed in claim 16, wherein the wt % of platinum in the metal containing catalyst is 0.05-3 wt %.

19. The process as claimed in claim 8, wherein said binder is in the percentage of 30 to 70%.

20. The process as claimed in claim 8, wherein in step(e) 30% w/w to 70% w/w of the dried material is extruded with 70% w/w to 30% w/w of binder.

21. The process as claimed in claim 8, wherein in step(f) calcination of the extruded catalyst is at 250-400 C. under constant air flow.

22. The process according to claim 1, wherein the crystallization temperature is in the range of 130 to 180 C.

23. The process according to claim 1, wherein the crystallization time is in range between 10-96 hrs.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: Powder X-ray Diffraction pattern of ZSM-22 synthesized by employing method as mentioned in Examples 1 to 4.

(2) FIG. 2: Scanning Electron Microscope of ZSM-22 zeolite A) Prepared in Example-1 and (B-D) described in Examples-(2-4).

DETAILED DESCRIPTION OF INVENTION

(3) The present invention relates to the method of synthesis of a metal containing zeolite using a combination of two organic structure-directing agents wherein one of them is non-selective for TON (theta one) type zeolite. The present invention also relates to the application of prepared ZSM-22 zeolite as a support for the preparation of hydroisomerization catalyst for dewaxing applications.

(4) The present invention provides a method for preparing a containing zeolite, comprising: synthesis of a pore filled material under hydrothermal conditions using two different structure directing agent; removal of the structure directing agent to obtain a zeolite material; converting the zeolite material to its acidic form using a inorganic precursor salt and calcination thereafter at about 550 C.; incorporating the calcined acidic porous material with a metal to obtain a metal loaded acidic porous material; drying the metal loaded acidic porous material to obtain a dried material; extruding 50% w/w to 95% w/w of the dried material with 5% w/w to 50% w/w of a binder material to obtain a extruded catalyst; and calcining the extruded catalyst at about 250-400 C. under constant air flow to obtain a dispersed metal-containing catalyst having dispersion of over 80%. The present invention further relates to a catalyst for hydroisomerization of long chain n-paraffins ranging from C.sub.12-C.sub.40 on the acidic sites loaded at pore mouths.

(5) The present invention describes a method for preparation of a porous material with appropriate number of pore mouths to ensure a good balance of acidic and metallic sites wherein the acidic porous material is selected from the group consisting of zeolite, molecular sieve, amorphous silica-alumina, solid acids and mixtures thereof, preferably selected from the group consisting of ZSM-5, ZSM-22, ZSM-23, ZSM-35, ZSM-48 and SSZ-32. Yet another embodiment of the present invention relates to a method, wherein the acidic porous material is prepared in the manner described herein from a mixture comprising.

(6) (i) a source of silicon

(7) (ii) a source of aluminium;

(8) (iii) a source of monovalent cation; and

(9) (iv) a mixture of organic structure directing agents;

(10) The synthesis is carried out under vigorous stirring in the range of about 100 to 500 rpm.

(11) The present invention relates to a method wherein the organic structure directing agents are removed at high temperature by calcination and then converted to its acidic form by exchanging the alkali metal cation to obtain the ammonium form of the zeolite which when calcined results into corresponding acidic from.

(12) The present invention also relates to method for obtaining metal loaded acidic form of the zeolite by exchanging some of the acidic sites with metal cations by use of certain metal precursor salts. Upon successful loading of metal, the acidic porous material is obtained after filtration and drying. The dried acidic porous material is next combined with the binder material and formed into extrudates.

(13) The present invention further relates to a method, wherein the binder material is selected from the group consisting of clays, silicas, aluminas, metal oxides, and mixtures thereof. The relative proportions of the zeolite and binder material may vary between 50 to 95% of zeolite and about 5 to 50% of binder material. These extrudates are then calcined at 400 C. under constant air or oxygen flow.

(14) The catalyst so obtained has smaller crystal size, higher surface area, external surface area, pore volume and optimum acid/metal balance leading to higher selectivity for isomerisation even at significantly high conversion values when used for hydroisomerization reaction. The catalyst of the present disclosure is used for hydroisomerization of long chain n-paraffins ranging from C.sub.12-C.sub.40. A catalyst with an excellent balance of metal/acidic sites is very much desirable for carrying out hydroisomerization reactions and is of prime importance to refining industry. The hydroisomerization method is responsible for the production of high octane gasoline; dewaxed diesel oil, and high quality lube oil with excellent cold flow properties.

(15) Typically, these isomerization reactions are carried out in presence of hydrogen over a bifunctional catalyst. The bifunctional catalyst has a metal component responsible for dehydrogenation/hydrogenation and an acid function for isomerization/cracking. Herein, the metal component is a Group-VIII metal usually platinum or palladium while the acid function is acidic porous material which could be zeolite, molecular sieve, amorphous, silica-alumina or solid acids selected on the basis of required catalyst activity selectivity and hydrocarbon chain length. Medium pore zeolites (ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZM-57, SSZ-32, SSZ-20, EU-1, EU-13, KZ-1, KZ-2, Theta-1 etc) and molecular sieves (SAPO-11, SAPO-31, SM-3, SM-6 etc) have been widely used for diesel and lube dewaxing applications.

(16) During the n-paraffin hydroisomerization method, the n-paraffin first undergoes dehydrogenation to olefin at metallic site followed by isomerization to branched olefin at zeolite pore-mouth and then hydrogenation to form saturated branched paraffin which is desirable. If the number of acidic sites is very high, it would lead to the hydrocracking of multibranched isomers leading to loss in yields of the desirable products. Herein, the effect of optimum metal/acid sites and presence of pore mouths is described, which is again based on the total and external surface areas of the catalyst samples is shown.

(17) Catalyst was loaded into a fixed bed micro-reactor operated in an upflow mode. Hexadecane feed along with hydrogen was feed to the reactor using a peristaltic pump to maintain a specified weight hourly space velocity (WHSV) and hydrogen to hydrocarbon ratio. The product composition analysis was done using GC-FID results to obtain catalyst selectivity at a desired conversion level.

(18) In another embodiment, the selectivity of the catalyst is defined to be ratio of Cu isomer yield to the n-hexadecane conversion.

(19) The following examples are provided to illustrate the invention and are not to be construed as limiting thereof.

EXAMPLES

Example 1

(20) Method of Preparation of ZSM-22 Zeolite ZSM-22 (Molar ratio of Si/Al=45) was synthesized using 1,6-diaminohexane as a structure directing agent. As per the method, the crystallization of ZSM-22 was performed using gel molar composition of 27NH.sub.2 (CH.sub.2).sub.6NH.sub.2/12K.sub.2O/Al.sub.2O.sub.3/90SiO.sub.2/3670 H.sub.2O by employing potassium hydroxide, KOH; aluminum sulfate, Al.sub.2(SO.sub.4).sub.3.18H.sub.2O and precipitated silica as precursors. The hydrothermal crystallization of the gel so prepared was carried out at 160 C. under stirred conditions for 24 h. The crystallized samples were filtered, washed several times with deionized water, dried at 110 C. for 24 h, and finally calcined at 550 C. for 12 h in the presence of air.

Comparative Example 1

(21) Method of Preparation of ZSM-22 Zeolite

(22) The synthesis of ZSM-22 with a composition of 100 SiO.sub.2/1 Al.sub.2O.sub.3/30 HDA/4000 H.sub.2O/11.6 Na.sub.2O using hexamethylenediamine and Fumed silica as template and silica source respectively as per the procedure disclosed in literature (I&EC research, 55, 6069-6078 (2016)). The crystallization time for the synthesis of ZSM-22 was 72 hrs and the crystallization temperature was 160 C. n-Hexadecane hydroisomerization activity of the catalyst (COMPCAT-1) prepared using the above mentioned ZSM-22 zeolite is shown in Table 4.

Comparative Example 2

(23) Method of Preparation of ZSM-22 Zeolite

(24) The synthesis of ZSM-22 with a composition of 27NH.sub.2(CH.sub.2).sub.6NH.sub.2: 13K.sub.2O: 0.82Al.sub.2O.sub.3: 91SiO.sub.2: 3670H.sub.2O using 1,6-diaminohexane and Ludox AS40 (40 wt % silica) as template and silica source respectively, as per the procedure disclosed in literature (RSC advances, 5, 99201-99206, (2015)). The crystallization time for the synthesis of ZSM-22 was 4 days. n-Hexadecane hydroisomerization activity of the catalyst (COMPCAT-2) prepared using the above mentioned ZSM-22 zeolite is shown in Table 4.

Comparative Example 3

(25) Method of Preparation of ZSM-22 Zeolite

(26) The synthesis of ZSM-22 with a composition of 27NH.sub.2(CH.sub.2).sub.6NH.sub.2: 13K.sub.2O: Al.sub.2O.sub.3: 91SiO.sub.2: 3670H.sub.2O using 1,6-diaminohexane and Ludox AS40 (40 wt % silica) as template and silica source, respectively. The crystallization time for the synthesis of ZSM-22 was 2 days and the crystallization temperature was 160 C. Chemical and textural Properties of obtained zeolite are shown in Table 3 and the n-Hexadecane hydroisomerization activity of the catalyst (COMPCAT-3) prepared using the above mentioned ZSM-22 zeolite is shown in Table 4.

Example 2

(27) Modified Method of Preparation of ZSM-22 Using Dual Templates

(28) ZSM-22 (Molar ratio of Si/Al=45) was synthesized using the procedure as described in Example 1. In this case the templates used were 1,6-diaminohexane and N,N di-methylformamide. As per the method, the crystallization of ZSM-22 was performed using gel molar composition of 27R/12K.sub.2O/Al.sub.2O.sub.3/90SiO.sub.2/3670H.sub.2O by employing potassium hydroxide, KOH; aluminum sulfate, Al.sub.2(SO.sub.4).sub.3.18H.sub.2O and precipitated silica as precursors. Where R is a mixed template consisting of 1,6-diaminohexane and N,N di-methylformamide in the mole ratio of 2:1 respectively. The hydrothermal crystallization of the gel so prepared was carried out at 160 C. under stirred conditions for 24 h. The crystallized samples were filtered, washed several times with deionized water, dried at 110 C. for 24 h, and finally calcined at 550 C. for 12 h in the presence of air.

Example 3

(29) Modified Method of Preparation of ZSM-22 Using Dual Templates

(30) ZSM-22 (Molar ratio of Si/Al=45) was synthesized using the procedure as described in Example 1. In this case the templates used were 1,6-diaminohexane and N,N di-methylformamide. As per the method, the crystallization of ZSM-22 was performed using gel molar composition of 27R/12K.sub.2O/Al.sub.2O.sub.3/90SiO.sub.2/3670H.sub.2O by employing potassium hydroxide, KOH; aluminum sulfate, Al.sub.2(SO.sub.4).sub.3.18H.sub.2O and precipitated silica as precursors. Where R is a mixed template consisting of 1,6-diaminohexane and N,N di-methylformamide in the mole ratio of 1:1 respectively. The hydrothermal crystallization of the gel so prepared was carried out at 160 C. under stirred conditions for 24 h. The crystallized samples were filtered, washed several times with deionized water, dried at 110 C. for 24 h, and finally calcined at 550 C. for 12 h in the presence of air.

Example 4

(31) Modified Method of Preparation of ZSM-22 Using Dual Templates

(32) ZSM-22 (Molar ratio of Si/Al=45) was synthesized using the procedure as described in Example 1. In this case the templates used were 1,6-diaminohexane and N,N di-methylformamide. As per the method, the crystallization of ZSM-22 was performed using gel molar composition of 27R/12K.sub.2O/Al.sub.2O.sub.3/90SiO.sub.2/3670H.sub.2O by employing potassium hydroxide, KOH; aluminum sulfate, Al.sub.2(SO.sub.4).sub.3.18H.sub.2O and precipitated silica as precursors. Where R is a mixed template consisting of 1,6-diaminohexane and N,N di-methylformamide in the mole ratio of 1:3 respectively. The hydrothermal crystallization of the gel so prepared was carried out at 160 C. under stirred conditions for 24 h. The crystallized samples were filtered, washed several times with deionized water, dried at 110 C. for 24 h, and finally calcined at 550 C. for 12 h in the presence of air.

Example 5

(33) Preparation of Acidic Form of Zeolites

(34) All the crystallized samples were filtered, washed several times with deionized water, dried overnight at 110 C. The sample was calcined in air at 550 C. for 12 h. The proton form of the sample was obtained by exchanging the sample three times with ammonium nitrate under reflux at 90 C. for 3-4 h followed by calcination at 550 C. for 4 h. The ZSM-22 samples prepared in Example 1, Example 2, Example 3, and Example 4, are labelled as Z1, Z2, Z3 and Z4 respectively.

Example 6

(35) Characterisation of Zeolite and its Catalysts Sample

(36) All the four zeolites were characterized by several physiochemical techniques. The values are given the table below.

(37) TABLE-US-00003 TABLE 3 Textural properties of the all the zeolites samples BET Micropore External surface surface surface Pore area area area volume Acidity Sample (m.sup.2/g) (m.sup.2/g) (m.sup.2/g) (cc/g) (mol/gm) Z1 154 103 51 0.146 218 Z2 230 185 45 0.149 183 Z3 270 222 47 0.179 162 Z4 226 176 50 0.158 131 Cooper- 197 151 46 0.060 171 ative example 3

Example 7

(38) Pt Loading, Binding and Extruding of the ZSM-22 Zeolite Catalyst

(39) The proton form of the above sample was used to make extruded Pt-loaded catalyst. 0.05 g of tetra-ammonium platinum nitrate complex was dissolved in 50 ml of distilled water. This solution was taken into a flask and 3.5 g of H-ZSM-22 was added on to it. The pH of the solution was adjusted to be maintained in the range of 9 to 10 using tetra butyl ammonium hydroxide. The product was filtered and dried at 100 C. 50 parts of Pt/I-ZSM-22 crystal were mixed with 50 parts of pseudoboehmite alumina binder in a muller. Sufficient amount of 5% acetic acid was added to produce an extrudable dough type mass on a 1 diameter extruder. This dough was extruded into 1/16 diameter cylindrical extrudates and then dried in an oven at 130 C. overnight. The dried extrudate was calcined in oxygen at 400 C. Four catalyst samples were prepared and coded as CAT-1 (prepared using zeolite Z1), CAT-2 (prepared using zeolite Z2), CAT-3 (prepared using zeolite Z3) and CAT-4 (prepared using zeolite Z4) respectively and the final catalyst composition is shown below:

(40) TABLE-US-00004 Component Weight % Zeolite 49.85% Binder 49.85% Platinum 0.3%

Example 8

(41) Measurement of Activity and Selectivity for the Prepared Catalyst

(42) All the catalyst recipes were tested for hydroisomerization selectivity using n-hexadecane as the model feed. 5 g of calcined catalyst extrudate diluted with inert material (quartz) was packed in a stainless steel fixed bed reactor. The catalyst was then dried overnight at 130 C. under nitrogen flow and reduced at 320 C. under a constant H.sub.2 flow of 100 ml/min at 60 bar pressure for 5 h. After reduction of the metal, the catalyst was used for hexadecane isomerization reaction. The reaction was carried out at a temperature range of 280-320 C., WHSV of 0.8-1.2 h.sup.1, with H.sub.2/HC ratio of 600 at 60 bar pressure. The activity and selectivity data for different catalysts are tabulated in the Table 4.

(43) TABLE-US-00005 TABLE 4 Comparison of activity and selectivity of different catalysts for n-C.sub.16 hydroisomerization at similar n-C.sub.16 conversion Reaction Hexadecane Isomerization Yield of Temperature Conversion Selectivity isomers Sample ( C.) (%) (%) (%) CAT-1 305 90.9 84.3 76.6 COMPCAT-1 300 20 36 7.20 COMPCAT-2 310 80 65 52 COMPCAT-3 305 89.1 79.3 70.5 CAT-2 307 90.8 84.5 76.7 CAT-3 300 90.8 87.1 79.1 CAT-4 305 90.6 86.3 78.3

(44) Table 4 shows a comparative analysis of CAT-1, CAT-2, CAT-3 and CAT-4 based on their n-C.sub.16 hydroisomerization performance vis--vis prior art catalysts. All the prepared catalyst showed, performance better than the prior art catalysts. CAT-2, CAT-3, and CAT-4, prepared using dual template strategy showed better performance than the catalyst prepared using single template i.e. CAT-1. Out of all dual template catalyst, CAT-3 prepared using 1,6-diaminohexane and N,N di-methylformamide in the mole ratio of 1:1 as template and precipitated as silica source gave better activity and higher yield for isomers. Superior performance of CAT-3 for n-C.sub.16 hydroisomerization is attributed to its smaller zeolite crystal size, better surface area, higher external surface area and moderate acidity. In addition to this, CAT-3 required lower operating temperature to achieve given conversion of n-C.sub.16. Furthermore, a higher requirement of operating temperature during start of run condition is indicative of an overall reduced catalyst life span. These experiments clearly elicit the advantage of using precipitated silica as silica source and dual template strategy for ZSM-22 synthesis.

(45) Although the subject matter has been described herein with reference to certain preferred embodiments thereof, other embodiments are possible. As such, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiment contained therein. Furthermore, precise and systematic details on all above aspects are currently being made. Work is still underway on this invention. It will be obvious to those skilled in the art to make various changes, modifications and alterations to the invention described herein. To the extent that these various changes, modifications and alterations do not depart from the scope of the present invention, they are intended to be encompassed therein.