TREATMENT OF ZEOLITES

Abstract: A method of preparing catalysts which exhibit enhanced hydrocarbon conversion activity which comprises calcining a zeolite such as ZSM-5 at temperatures ranging from about 600 to about 1300°C and subsequently activating it by exposing it to a mixture of ammonia and steam at tempera­ tures ranging from 100 to 1000°C to the extent that at least about 10% crystallinity is preserved in the resulting activated catalyst.

Description: TREATMENT OF ZEOLITES This invention relates to treatment of zeolites to enhance their catalytic activity. Zeolitic materials, both natural and synthetic, have been demonstrated in that past to have catalytic properties for various types of hydrocarbon conversions. Certain zeolitic materials are ordered, porous crystalline aluminosilicates having a definite crystalline structure -containing a large number of channels. These cavities and channels are precisely uniform in size. Since the dimensions of these pores accept molecules of certain dimensions for adsorption while rejecting those of large dimensions, these materials have come to be known as "molecular sieves and are utilized in a variety of ways to take advantage of these properties. The present invention relates particularly to the relatively recently discovered class of such materials which is characterized by possessing a constraint index in the range 1 to 12. Constraint Index (C.I.) values for some typical materials are: Zeolite C.I. ZSM-4 0.5 ZSM-5 8.3 ZSM-11 8.7 ZSM-12 2 ZSM-23 9.1 ZSM-35 4.5 ZSM-38 2 ZSM-48 3.4 TMA Offretite 3.7 Clinoptilolite 3.4 H-Zeolon (mordenite) 0.4 REY 0.4 Amorphous Silica-Alumina 0.6 Erionite 38 Zeolites ZSM-51 -11, -12, -23, -35, -38 and -48 are def ined, respectively by the X-ray data set forth in US-A3,702,886, 3,709,979, 3,832,449, 4,076,842, 4,016,245, 4,046,859 and EP-A-15132. When synthesized in the alkali metal form then zeolite is conveniently converted to the hydrogen form, generally by intermediate formation of the ammonium form as a result of ammonium ion exchange and calcination of the ammonium form to yield the hydrogen form. In addition to the hydrogen form, other forms of the zeolite wherein the original alkali metal has been reduced to less than about 1.5 percent by weight may be used. Thus, the original alkali metal of the zeolite may be replaced by ion exchange with other suitable metal cations of Groups 1 through VIII of the Periodic Table, including, by way of example, nickel, copper, zinc, palladium, calcium or rare earth metals. In spite of the well-known attributes of the ZSM-5 family of zeolites, attempts have been made to improve these materials by further enhancing their hydrocarbon conversion activity. Such enhancement is desirable in order to improve the efficiency of catalysts in hydrocarbon conversion process and is of particular importance where shape selective catalysts are concerned. Shape selective catalysts are extremely useful in such processes as xylene isomerization, toluene disproportionation and p-ethyltoluene synthesis which require relatively high para-selectivity. Enhanced shape-selectivity of a catalyst composition can also improve the efficiency of methanol-to-gasoline (MTG) processes, methanol-to-olefin (MTO) processes, and catalytic dewaxing, as well as petrochemical processes. Efforts to enhance the shape-selectivity of ZSM-5-type materials in sorptive and catalytic applications by calcining at temperatures of 6000C to 1300C have generally met with disappointing results. While such treated catalyst materials may exhibit enhanced shapeselectivity, they can suffer loss in catalytic activity. Exposure of zeolites to high temperatures results in a breakdown of crystalline structure and a corresponding loss in activity. Furthermore, zeolites which are calcined to an activity of about zero, generally prove extremely difficult, if not impossible, to reactivate. There has now been discovered a process for enhancing the hydrocarbon conversion activities of zeolites such as ZSM-5, particularly the hydrogen forms, such as which have been substantially deactivated by calcining. Such catalysts are activated, according to the invention, by exposure to an activating agent comprising a mixture of steam and ammonia, vat temperatures ranging from about 100 to 10000C, preferably 400 to 6000C. Calcining and activation of the zeolite material is allowed to proceed to the extent that the resulting product retains a crystallinity of at least about 10X. The extent of crystallinity remaining within the product as it undergoes reactivation can be determined by conventional X-ray diffraction studies. The activity of the resulting catalyst can be measured in terms of its alpha value. The alpha test is described in the Journal of Catalysis, Vol. VI, pages 278287, 1966. The extent of the activation produced by the present method is notable. Significant increases in the alpha value may be obtained where ZSM-5 type zeolites are activated by the method of the present invention. The activation process of the present invention may be used to produce a catalyst material of enhanced shape-selectivity having relatively high hydrocarbon conversion activity. The zeolites are calcined at temperatures ranging from about 6000 to 13000C, say about 10000C in order to enhance their shape selectivity. The resulting materials, which suffer a loss of activity on calcination, are then activated by exposing the calcined compositions to a mixture of steam and ammonia at temperatures of about 1000 to 10000C. The calcining and activation steps are carried out to the extent that'at least about 10% crystallinity is preserved in the result ing product. The molar ratio of steam to ammonia employed can range from about .01 to 10, preferably about 1. The zeolite particles can be in the form of a powder, a granule, or a molded product, such as an extrud ate having particle size sufficient to pass through a 2 mesh (Tyler) screen and be retained by a 400 mesh (Tyler) screen. In cases where the catalyst is molded, such as by extrusion, the catalyst crystals can be extruded before drying or dried or partially dried and then extruded. The zeolite compositions resulting from the process of the invention can be used as catalysts in a number of Important reactions. In particular, the subject shape-selectivity enhanced catalysts can be advantageously utilized in xylene isomerization, toluene disproportionation and p-ethyltoluene synthesis processes where high para-selectivity is desirable. The enhanced shape-seleciity of these compositions also commends their use in processes such as catalytic dewaxing. In addition these compositions are suitable for methanol conversion processes such as methanol-to-olefin, and methanol-to-gasoline where their use can result in lower durene (1,2,4,5-tetramethylbenzene) yields. The compositions of the present invention can also be used as supports for metals in dual-functional catalytic applications such as syngas reactions. Alkylation of aromatic hydrocarbons, e.g., benzene, with an alkylating agent such as an alkyl halide, an alcohol or an olefin, can be readily effected in the presence of the treated composition as catalyst. Alkylation conditions include a temperature between about 2040C and about 5380C (about 4000F and about 10000F), a pressure between about 25 and about 1000 p.s.i.g. util izing an aromatic hydrocarbon/alkylating agent mole ratio of 2 to 200 and an alkylating agent weight hourly space velocity within the approximate range of 0.5 to 50. Xylene isomerization is another reaction which can be suitably conducted in the presence of the described treated ZSM-5 composition as catalyst. Isomerization conditions include a temperature between about 1490C and about 4820C (about 3000F and about 9000F), a pressure between about 25 and about 1000 p.s.i.g., utilizing a weight hourly space velocity within the approx imate range of 0.2 and 100. Aromatics, such as, for example, toluene, may be disproportionated in the presence of the treated compositions at a temperature of from about 2320V to about 5930C (about 4500F to about 11000F), a pressure of from about 50 p.s.i.g. to about 800 p.s.i.g. and a liquid hourly space velocity within the approximate range of about 0.1 to about 20. Aliphatic hydrocarbons may also be disproportionated in the presence of the described treated ZSM-5 compositions, at a temperature of from about 1770C to about 4820C (about 3500F to about 9000F) a pressure between 0 and 3000 p.s.i.g. and a liquid hourly space velocity of between about 0.01 and about 5. Other reactions which can be accomplished employing the catalyst of this invention containing a metal, e.g., platinum, include hydrogenation-dehydrogenation reactions, desulfurization reactions, olefin polymerization (oligomerization) and other organic compound conversions, such as ammoniation of phenol wherein the deactivated catalyst is contacted with ammonia and water in the presence of phenol which activates the the catalyst and produces aniline. EXAMPLES 1-14 Effect of Thermal Treatments in Ambient Atmosphere on HZSM-5 zeolites HZSM-5 samples having a silica to alumina ratio of about 70 were subjected to thermal treatments in ambient atmosphere under varying temperature conditions. Following these treatments, each sample was tested for n-hexane sorption and alpha value. Various samples were also tested for 3-methylpentane sorption, cyclohexane sorption, and crystallinity. HZSM-5 retained good crystallinity for periods in excess of one hour at temperatures below 10000C. Above 10000C the rate of drame- work collapse increased significantly. High temperature treated HZSM-5 samples were crystalline by X-ray and sorbed 7-12% n-hexane at 250C after 20 minutes. The zeolites exhibited increased shape-selectivity as calcination temperatures increased. The HZSM-5 zeolites decreased cracking activity from = 150 for parent materials toC(= 0 for material calcined at 10000C for one hour. Additional data relating to these thermal treatments can be found in Table I. EXAMPLE 15 Reactivation by Contact with Ammonia and Steam The catalyst of Example 5 was used to convert phenol to aniline by ammoniation. Phenol was reacted with excess NH3 (0.5 WHSV) at 5100C, and 28 atm. Steam was produced in situ during the reaction. Conversion of phenol was 94.4X. Selectivity to aniline was 90.2X. The catalyst became activated in situ by exposure to steam and ammonia, with the alpha increasing from 0.3 to 3.5. In a control run, ZSM-5 with SiO2/Al203 26,000 and alpha = 0.3 converted only 1.5X phenol at the same conditions. EXAMPLE 16 Sorption and Activity Determination of Reactivated Catalyst The reactivated catalyst of Example 10 was tested for sorption rates (percent by weight) and activity. n-Hexane sorption was 7.9X, cyclohexane sorption was "slow", toluene sorption was 1Z and o-xylene sorption was less than .05X. n-Hexane and cyclohexane were sorbed for 20 minutes at 250C while toluene and o-xylene sorption were measured at the end of 10 minutes sorption at 250C. While sorption rates changed only slightly if at all upon treatment with ammonia and steam, the activity on reactivation changed from &alpha;=0 to &alpha;= 3.5. TABLE I Effects of thermal treatments on ZSM-5 zeolites n-hexane 3-methyl- cyclo X-ray &alpha; Example Treatment Atmosphere sorption pentane hexane crystallinity Parent HZSM-5 ambient air 11.6% 8.9 8.7 192 100 1* 1 hr &commat; 600 C " 11.6% 113-175 90% 2 1 hr &commat; 700 C " 11.2% 35 90% 3 1 hr &commat; 800 C " 10.7% 12 (CI=1.4) 82% 4 1 hr &commat; 900 C " 9.8% 4 (CI=0.4) 5 1 hr &commat; 1000 C " 8.3% 5.4 slow 0 61% 6 1 hr &commat; 1100 C 25% 7 2 hrs&commat;1100 C " 0 0 0% 8 5 min.&commat; 1000 C " 10.2% .1 9 10 min.&commat;1000 C " 10.0% 10 15 min.&commat; 1000 C " 9.0% 11 3.5 min.&commat; 1100 C " 7.5% 12 10 min.&commat; 1100 C " 3.7% 13 7.5 min.&commat; 1200 C " 4.1% 0 14 5 min.&commat; 1200 C " 0% 0 * note change w/time EXAMPLES 17 to 19 Three HZSM-5 zeolite samples were calcined at 10000C for one hour under ambient conditions. Their activities were measured as = 1.2. The samples were then treated at 400 p.s.i.g. and 510 C in a nitrogen atmosphere with, respectively, ammonia, steam, and a mixture of ammonia and steam. After such treatments the HZSM-5 samples were again measured for activity. The ammoniatreated catalyst was slightly increased in activity to 5 < = 1.5. The steam-treatment yielded a catalyst of de creased activity, = 1, while exposure to the ammonia/ water mixture resulted in a significant increase in activity to 6. Data for the three runs is given in Table III. The results of these runs show that activity of a calcined zeolite catalyst is significantly enhanced when contacted with a mixture of ammonia and steam. TABLE III Effects of Exposure of Calcined HZSM-5 to Ammonia, Steam and a Mixture of Ammonia and Steam on Catalyst Activity Example 17 Example 18 Example 19 Treatment NH3/N2 H20/N2 NH3/H20/N2 mixture tO:1 mole 2:1 mole 1.11:2.67:1.0 ratio ratio (NH3/H20) (0.45:1) Temperature 5100C 5100C 5100C Pressure 400 p.s.i.g. 400 p.s.i.g. 400 p.s.i.g. Exposure time 7.5 hours 4 hours 8 hours 1.5 1 6

Claims: WHAT IS CLAIMED IS: 1. A method for activating a deactivated catalyst comprising a zeolite having a constraint index in the range 1 to 12 which comprises contacting said catalyst with an activating agent comprising ammonia and steam at a temperature from 100 to 10000C to the extent that at least about 10X crystallinity is preserved in the activated product. 2. A method according to claim 1 in which before said contacting the catalyst is calcined at a temperature of 600 to 13000C. 3. The method of claim 1 or 2 wherein the zeolite is ZSM-5, ZSM-11, ZSM-5/ZSM-11 intermediate, ZSM-12, ZSM-23, ZSM-35, ZSM-38 or ZSM-48. 4. The method of any preceding claim wherein the zeolite is in the hydrogen form. 5. The method of any preceding claim wherein the molar ratio of ammonia to steam ranges from about 0.01 to 10. 6. The method of claim 5 wherein the molar ratio of ammonia to steam is 0.75 to 1.25. 7. The method of any preceding claim wherein the zeolite is contacted with said activating agent at a temperature of 400 to 6000C. 8. The method of claim 1 or 2 wherein the deactivated catalyst, in the presence of phenol, is contacted with ammonia and water which activates the catalyst and produces aniline. WHAT IS CLAIMED IS: 1. A method for activating a catalyst deactivated by calcination at a temperature of 1000 to 13000C, said catalyst comprising a zeolite having a constraint index in the range 1 to 12, which comprises contacting said catalyst with an activating agent comprising ammonia and steam at a temperature from 100 to 10000C to the extent that at least about 10% crystallinity is preserved in the activated product. 2. The method of claim 1 wherein the zeolite is ZSM-5, ZSM-ll, ZSM-5/ZSM-ll intermediate, ZSM-12, ZSM23, ZSM-35, ZSM-38 or ZSM-48. 3. The method of any preceding claim wherein the zeolite is in the hydrogen form. 4. The method of any preceding claim wherein the molar ratio of ammonia to steam ranges from about 0.01 to 10. 5. The method of claim 4 wherein the molar ratio of ammonia to steam is 0.75 to 1.25. 6. The method of any preceding claim wherein the zeolite is contacted with said activating agent at a temperature of 400 to 6000C. 7. The method of claim 1 wherein the deactivated catalyst, in the presence of phenol, is contacted with ammonia and water which activates the catalyst and produces aniline.

Inventors: CALVERT, ROBERT BRUCE, CHANG, CLARENCE DAYTON, PERKINS, PATRICK DANFORD
Applicants: MOBIL OIL CORPORATION
Application year: 1983
Main classification: B01J29
IPC codes: B01J29, C07C1, C07C15, C07C2, C07C5, C07C67, C07C209, C10G49, C01B39