(10d) Hydrocarbon Transformations Catalyzed By Uzm-35, a Material Containing Both 10MR and 12MR Pores

Synthetic zeolites are widely used in the refining and petrochemical industry. UOP has been very active in inventing and patenting new UOP Zeolitic Materials for use in catalytic and adsorptive processes. Many of these UZM’s have been invented using the charge density mismatch approach to zeolite synthesis as the CDM approach often allows preparation of unique structures or morphologies [1].

Zeolitic materials containing both 10MR and 12MR pores are of interest as catalysts with good conversion and shape selectivity. For example, fluidized catalytic cracking often uses a combination of FAU and MFI catalysts to allow high conversion of VGO while still obtaining high yields of propylene. Several frameworks possess both 10MR and 12MR channels in the same material. One of these is the MSE framework which contains a 12MR straight channel and two zig-zag 10MR channels. The known material of the MSE framework is MCM-68[2] which was synthesized using a complicated bicyclic SDA. Recently, we have discovered the UZM-35 family of materials which are also of the MSE zeotype.

The preferred method to make UZM-35 utilizes the charge density mismatch approach [3] to zeolite synthesis. In the CDM approach, quaternary ammonium hydroxides are used to solubilize aluminosilicate species while crystallization inducing agents such as alkali cations are introduced in a separate step. A typical preparation utilizes dimethyldipropylammonium hydroxide in combination with sodium and potassium hydroxide from gels of about Si/Al=10 to yield UZM-35 after crystallization at 175ºC for 5-10 days [4].

Experimental

An aluminosilicate solution of Si/Al=8.83 was prepared by vigorously mixing 27.17g aluminum hydroxide (27.78 wt% Al) and 1053.58 g dimethyldipropylammonium hydroxide (18.8 mass-% solution).  505.96 g  Ludox^TM AS-40 (40 mass-% SiO₂) was then added.  The reaction mixture was homogenized, sealed in a Teflon bottle, and placed in an oven overnight at 100°C. 

1200 g portion of the aluminosilicate solution was continuously stirred. An aqueous solution containing 28.56 g of KOH and 3.6g of NaOH dissolved in 150 g DI H₂O was added drop-wise to the aluminosilicate solution. The resulting reaction mixture was homogenized, transferred to a 2L Parr stainless steel autoclave and heated to 175°C for 216 hrs.  The solid product was recovered by centrifugation, washed with de-ionized water and dried at 100°C. The product had the following mole ratios:  Si/Al = 7.92, Na/Al = 0.1, K/Al = 0.48. The material was then calcined at 540ºC for 10 hours and ion-exchanged with NH₄NO₃ before calcination at 550ºC to yield the H⁺ form.

The H⁺ form of UZM-35 was pressed and meshed to 20-40 mesh.  For n-heptane cracking tests [5], 250mg of zeolite was loaded into the reactor and contacted with an n-heptane saturated N₂ stream at 125mL/min. For butene cracking tests, 5g of meshed catalyst was loaded into the reactor and a 60/40 isobutane/isobutene mixture contacted with the catalyst bed at 7 psig, 27 to 40 WHSV, 520 to 580ºC. For alkylation of benzene with ethylene or propylene to form ethylbenzene or cumene [6], 15mL of meshed catalyst is mixed with 10mL of gamma alumina of 20-40 mesh and loaded into the reactor. The reactor was pressurized to 500 psig with N₂ and benzene flow was then started. Once the reactor attained the target temperature, the ethylene or propylene was introduced. The ethylene feed consisted of 77% CH₄ and 23% C₂H₄ while the propylene feed was 100% C₃H₆. 

Results and discussion

As UZM-35 contains both 10MR and 12MR channels, a key question throughout catalytic testing was whether the material would give behavior more reminiscent of 10MR (MFI) or 12MR (beta) channels or some mixture of the two. For cracking reactions and also for alkylation of benzene with ethylene, UZM-35 approximates 10MR zeolite behavior.

            Interestingly however, in benzene alkylation with propylene to form cumene, UZM-35 shows behavior similar to beta, a 12MR zeolite. UZM-35 is active and selective to the monoalkylated product at the same conditions as beta zeolite. In addition, UZM-35 gives a low yield of n-propyl benzene, a product which, at higher yields, is indicative of 10MR behavior.

Conclusions

UZM-35 is active in various catalytic transformations including catalytic cracking and benzene alkylation. In these reactions, UZM-35 shows behavior reminiscent of either 10MR or 12MR channels. Data from catalytic cracking and alkylation of benzene with ethylene or propylene will be used to attempt to explain the reasons behind the varied behavior of materials containing both 10MR and 12MR channels.

Acknowledgements

The authors thank D. Mackowiak and M. Munley for performing the alkylation reactions and UOP for permission to publish.

References

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