Crystalline silicate catalyst and processes using the catalyst

#The present invention relates to a crystalline silicate reforming catalyst and to processes using the catalyst. More specifically, a combination of process conditions and improvements in the catalyst result in a low fouling rate. The catalyst is also useful for benzene production via dehydrogenation and/or dehydroyolization.

#Catalytic reforming is well known in the petroleum industry and refers to the treatment of naphtha fractions to improve the octane rating by the production of aromatics. The more important hydrocarbon reactions occurring during reforming include dehydrogenation of cyclohexanes to aromatics, dehydroisomerization of alkylcyclopentanes to aromatics, and dehydrocyclization of acyclic hydrocarbons to aromatics. A number of other reactions also occur, including the following: dealkylation of alkylbenzenes, isomerization of paraffins, and hydrocracking reactions which produce light gaseous hydrocarbons, e.g., methane, ethane, propane and butane. Hydrocracking reactions are to be particularly minimized during reforming as they decrease the yield of gasoline boiling products and hydrogen.

#Because of the demand for high octane gasoline for use as motor fuels, etc., and of the demand for benzene as a chemical reactant extensive research is being devoted to the development of improved reforming catalysts, improved catalysts for benzene production, catalytic reforming processes and benzene production processes. Catalysts for successful reforming processes must possess good selectivity. That is, they must be able to produce high yields of liquid products in the gasoline boiling range which contain large concentrations of high octane aromatic hydrocarbons and low concentrations of light gaseous hydrocarbons. Benzene production catalysts must also have good selectivity to produce high yields of benzene and low yields of light gaseous hydrocarbons. Also, the catalysts should possess good activity in order that the temperature required to produce a certain quality product need not be too high. It is also necessary that catalysts either possess good stability in order that the activity and selectivity characteristics can be retained during prolonged periods of operation, or be sufficiently regenerable to allow frequent regeneration without loss of performance.

#FIG. 1 is a graph showing the performance of different catalysts.

#There are operating and economic advantages in obtaining longer, yield-stable run lengths from reforming and from benzene production catalysts. One way to attain this, is by improvements in the catalyst itself. We have found that when platinum is added to a crystalline intermediate pore size silicate, such as silicalite, which has a small crystallite size, and a high degree of crystallinity, longer run lengths can be achieved.

#The preferred catalyst of the present invention contains a crystalline silicate. "Crystalline silicate" as used herein refers to silicates having rigid, three-dimensional network of SiO.sub.4 tetrahedra in which the tetrahedra are crosslinked by the sharing of oxygen atoms. The crystalline silicates are substantially alumina-free, but they may contain minor amounts of alumina resulting from impurities in the starting materials or contamination of the reaction vessels. The preferred crystalline silicate is silicalite, examples of which are disclosed in U.S. Pat. No. 4,061,724 and U.S. Pat. No. 29,948 which are hereby incorporated by reference in their entireties.

#The present invention will be more fully understood by reference to the following examples. They are intended to be purely exemplary and are not intended to limit the scope of the invention in any way.

#A Pt-occluded silicalite catalyst was made as follows: 4.6 grams NaNO.sub.3, 10.0 grams EDTA, and 1.0 grams Pt(NH.sub.3).sub.4 (NO.sub.3).sub.2 were mixed into 20 cc of distilled water. This mixture was added to 200 grams of a 25% aqueous solution of TPA-OH with rapid stirring, and stirred an additional 10 minutes. 160 Grams of Ludox AS-30 were then added with rapid stirring and stirred for an additional 15 minutes. The pH of the mixture was reduced to 11.0 using HCl. The mixture was placed in a Teflon bottle in an autoclave under autogenous pressure at 150.degree. C. for three days. The product was filtered, dried overnight in a vacuum oven at 110.degree. C., and calcined for 8 hours in dry air at 454.degree. C. The sieve was identified as silicalite by X-ray diffraction analysis. The average crystallite size was about 40.times.15.times.15 microns (roughly rectangular) as determined by scanning election microscopy. The percent silicalite was determined by X-ray diffraction (XRD) analysis to be 100%. The Pt content was 0.68 wt.%.

#A Pt-occluded silicalite was prepared as follows: 9.2 grams of NaNO.sub.3, 20 gram of EDTA, and 2.0 grams Pt(NH.sub.3).sub.4 (NO.sub.3).sub.2 were mixed into 40 ml of distilled water in a polyethylene beaker. Four hundred (400) grams of a 25% aqueous solution of TPA-OH were added and the mixture stirred well for 15 minutes. Three hundred twenty (320) grams of Ludox AS-30 were added with rapid stirring and the mixture stirred an additional 15 minutes. The pH of the mixture was 13.2. The mixture was poured into a Teflon bottle and kept at 100.degree. C. for 7 days. The product was filtered, dried overnight in a vacuum oven at 120.degree. C., and then calcined in dry air at 454.degree. C. The average crystallite size was about 0.5 microns in diameter (roughly spherical). The Pt content was 0.6 was wt.%. The Al content was 397 ppm. Na was 0.68 wt.%.