JPH055277B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD This invention relates to the reforming of hydrocarbons, and more particularly to a reforming process using a catalyst system consisting of a discrete physical mixture of zinc oxide and a silicalite conversion catalyst. BACKGROUND OF THE INVENTION In the chemical and refining industries, a variety of processes exist that involve converting hydrocarbon feedstocks into corresponding products of high economic value. Reforming operations are carried out on gasoline boiling range petroleum fractions to increase their octane rating. Octane values can be increased from values of about 30-60 octane to values within the range of 70-90 octane. Typical conditions for reforming operations are temperatures of about 400-600°C and
Contains a pressure of 35 bar. Commercial reforming operations are typically carried out using noble metal catalysts, such as platinum, often in combination with other metals, such as rhenium. Reforming reactions that produce products with increased octane ratings include isomerization of linear hydrocarbons, conversion of linear hydrocarbons to cyclic hydrocarbons, aromatization of cyclic naphthenes by dehydrogenation, and heavy Involves hydrogenolysis of paraffin to lighter products. A disadvantage of conventional platinum-type catalysts is their low resistance to catalyst "poisons" such as sulfur and nitrogen compounds. Such catalysts are sensitive to sulfur inhibition and require feedstocks with very low sulfur content, usually less than a few ppm. Reforming operations usually do not substantially affect the substantial change in boiling point. The product boiling range is approximately the same, or perhaps slightly lower than the feedstock boiling range. Reforming processes and other hydrocarbon conversion processes are also carried out in the presence of molecular sieve type catalysts. Such molecular sieves can be used as composites with metal catalysts. For example, US Pat. No. 4,276,151 to Plnk et al. describes a catalytic reforming process in which the catalyst is a composite of a zeolite, i.e., a crystalline aluminosilicate, and a common metal reforming catalyst, e.g., a platinum/rhenium catalyst. is disclosed. No. 4,197,214 to Chen et al. discloses the use of metal-zeolite combinations in various conversion reactions including the production of aromatics from normal hexane. The composite catalysts disclosed in this patent include zeolites with zinc incorporated by wet impregnation, ion exchange, and extrudates formed from zinc oxide and ammonium exchanged ZSM-5 zeolites. The impregnated, ion-exchanged and extruded forms showed substantially increased aromatization activity relative to the ammonium-exchanged zeolite alone. The ion-exchanged composite showed improved water vapor stability and no zinc oxide added by physical mixing. US Pat. No. 4,288,645 [Wagstaff] and US Pat. No. 4,291,182 [Dautzenberg et al.] disclose aromatization processes based primarily on feed streams of propane and butane, respectively. These methods are
It is carried out at conversion conditions of 400-700 DEG C. and 5-10 bar in the presence of crystalline silicates containing zinc as promoter. Zinc is present in an amount ranging from 0.05 to 20% by weight, preferably from 0.1 to 5% by weight, and can be incorporated into the silicate by ion exchange or impregnation. US Pat. No. 4,403,044 to Post et al. discloses a number of conversion procedures using silicate-based catalyst systems. The method disclosed in the US patent to Post et al.
Including improvements in hydrocracking and gasoline octanization. The feed streams for the aromatization process include acyclic organic compounds and aliphatic and/or cycloaliphatic hydrocarbons and mixtures thereof. Silicalite is nickel, copper, zinc, cadmium,
Platinum, palladium, nickel-tungsten, copper-molybdenum, nickel-molybdenum, zinc-palladium, zinc-copper, and zinc-rhenium metals or metal combinations, iron-chromium oxides,
and zinc oxide-chromium oxide. DISCLOSURE OF THE INVENTION In accordance with the present invention, a new and improved process for reforming relatively low octane feedstocks to produce products having substantially high octane ratings is provided. A gasoline range feedstock containing branched and linear aliphatic hydrocarbons is passed through a reaction zone and contacted with a catalyst system, wherein the catalyst system comprises a shape-selective crystalline silica polymorph. It consists of a discrete physical mixture of a silicalite catalyst and a metal or metal oxide dehydrogenation catalyst. Silicalite catalysts are preferentially selective towards linear aliphatic hydrocarbons, but are restrictive towards their branched isomers. Conversion conditions are established within the reaction zone to produce a modified product with increased aromatic content and decreased paraffin content with respect to the aromatic content and paraffin content of the feedstock. In one embodiment of the invention, the catalyst system is in the form of particles consisting of pellets formed from silicalite and crystallites of the dehydrogenation catalyst oxide mixed with a binder. In other embodiments, the catalyst system is in the form of particles consisting of silicalite particles and dehydrogenation catalyst particles mixed together to form a discrete physical mixture. In a preferred embodiment, the dehydrogenation catalyst is zinc oxide. In another aspect of the invention, the feedstock contains sulfur in an amount greater than 2 ppm. BEST MODE OF CARRYING OUT THE INVENTION When carrying out the reforming process of the invention, a hydrocarbon feedstock is injected into a reaction zone containing a catalyst system. The catalyst system consists of a discrete physical mixture of a dehydrogenation catalyst, preferably zinc oxide, and a crystalline silica polymorph silicalite catalyst. In this zone, the feedstock is contacted with a catalyst system under appropriate conditions of temperature, pressure, and residence time to carry out the desired reforming reaction to produce a high octane product. As detailed below, the reaction zone temperature is typically maintained within the range of approximately 400-600°C and the pressure is approximately 38-41°C.
Keep within range of crowbar. For operating temperatures and pressures within these ranges, the feedstock is passed through the reaction zone at a rate that provides a weight hourly space velocity (WHSV) within the range of 1-50. As discussed in more detail below, feedstocks suitable for use in the present invention may vary in composition within a wide range.
However, the feedstock can be generally described as consisting primarily of normally liquid hydrocarbons within the boiling range of the gasoline fraction. Although the gasoline range can vary somewhat depending on refining operations and crude feed, it can be characterized as varying from the boiling point of pentane at the lower end to the mid-kerosene range (approximately 220-230°C), and In both cases it is lower than the initial boiling point of the gas oil fraction. The feedstock can contain normal and branched chain aliphatic hydrocarbons, cycloaliphatic hydrocarbons, and aromatic hydrocarbons. Aromatic hydrocarbons can be substituted or unsubstituted and thus include benzene and alkyl aromatics such as toluene, ethylbenzene and xylene. Shape-selective catalysts are crystalline silica materials, in contrast zeolitic materials are defined as silicates of aluminum and sodium or calcium, or both, which exhibit ion exchange capacity. These crystalline silica materials are polymorphs of silica, and their structure has been designated in the art as "silicalite." These materials, in contrast to aluminum silicate zeolites, do not exhibit appreciable ion exchange properties since the AlO ₄ tetrahedra do not form part of the crystalline silica framework. Aluminum can be present in these silicalite catalyst materials. However, its presence is the result of impurities in the silica source used to prepare the material, and silicalites containing such alumina or other metal oxides are in no way metallo silicates. It is impossible to think that it is. Descriptions and methods of preparing silicalite-type catalysts are described in US Pat. No. 4,061,724 to Grose, the entire disclosure of which is incorporated herein by reference. Dehydrogenation catalysts that can be used in the present invention include metals or metal oxides including platinum, rhenium, zinc, iron, copper, gallium, antimony, tin, lead, bismuth, indium, thallium, cadmium, and chromium. . Zinc oxide is a preferred dehydrogenation catalyst, as mentioned above. Other suitable catalysts that preferentially accelerate the dehydrogenation reaction can be used in the practice of this invention as long as they are compatible with the silicalite catalyst. The dehydrogenation catalyst and the silicalite catalyst can be mixed together in any suitable manner so long as the two catalysts retain their discrete physical properties in the final product. The catalyst system is thus in the form of particles consisting of particles of the silicalite and particles of the dehydrogenation catalyst mixed together to constitute the discrete physical mixture. The particles of the granulate usually include the specific catalytic material, usually in a binder matrix, and should be well mixed to form a relatively homogeneous mixture. Alternatively, the catalyst system can be in the form of particles consisting of pellets formed from a mixture of dehydrogenation catalyst crystallites and silicalite crystallites. Such pellets may be formed by any suitable technique, but typically will be in the form of an extrudate. The extrudates are formed by mixing the dehydrogenation catalyst crystallites and the silicalite catalyst crystallites with a binder to form a plastic, which is then passed through a suitable die structure to form pellets of the desired size. can do. When using pelletized products formed by extrusion techniques, the granular material typically has a
It will range in size from 0.5 to 5 mm.
When using a mixture of granular silicalite and granular dehydrogenation catalyst, the individual catalyst particles are typically approximately
It will be in the range of 0.2 to 2 millimeters. The crystallites of the dehydrogenation catalyst can be mixed with the crystallites of silicalite in the absence of bonding; in this case,
The size of the catalyst particles will be very small, on the order of 10 microns or less. The use of a catalyst system consisting of a physical mixture of discrete catalysts offers several advantages over catalyst systems in which the metal catalyst is impregnated into a silicalite base as disclosed in the aforementioned patent to Post et al. provides some important benefits. According to this physical mixture,
It is possible to use relatively large concentrations of zinc oxide or other dehydrogenation catalysts without clogging the pore structure of the silicalite, as can result from the use of too much metal in impregnated catalyst forms. can. Also, the use of particulate catalyst systems does not involve wide fluctuations in catalyst activity. Such variations may occur in the case of metal-impregnated catalysts. because,
This is because metal is lost from the pore structure. The advantages derived from the use of particulate mixtures over impregnated catalyst systems can usually be achieved without increased cost. In fact, in addition to providing greater performance constancy, granular mixtures typically
Easier to formulate and lower cost than impregnated catalyst systems. Irrespective of the form of the discrete physical mixture, the weight ratio of zinc oxide to silicalite will usually be in the range of about 0.1 to 1', but as shown by the experiments described below, larger concentrations of oxide Zinc can be used. For most feedstocks, the preferred zinc oxide/silicalite ratio in the multicomponent catalyst will be within the range of 0.3 to 0.8. The feedstock used in the practice of this invention can be derived from any suitable source. Feedstocks to which the present invention is particularly applicable include raffinate streams from aromatic refining units, temporary reformate feeds, and reformates. Regarding the first alternative, it is common practice to subject the product stream from the aromatization process to solvent purification extraction techniques.
As is understood in the art, aromatic hydrocarbons range from aliphatic hydrocarbons and naphthenes to preferential aromatic solvents, such as Udex.
It can be easily separated by extraction with the ethylene or propylene glycol and water mixture used in the process. The raffinate phase derived from solvent aromatic extraction is relatively rich in linear paraffins and, of course, contains small amounts of aromatic hydrocarbons. Another application of the invention is in post-reforming operations. In this case, the feedstock will be the product effluent (reformate) from the first reforming unit and the feedstock will be relatively high in aromatic content. This application of the invention is particularly advantageous. Because it is a heavy aromatic (C ₉ + aromatic)
This is because it is effective in the dealkylation of hydrocarbons and the conversion of linear aliphatic hydrocarbons. Another use of the invention is in the first reforming unit. In this case, as shown by the experimental data described below,
The use of a composite catalyst system according to the present invention results in higher benzene and toluene yields and lower _C9 + aromatics yields than commercially available palladium-rhenium catalysts. Standards for reforming operations using precious metal reforming catalysts require very low sulfur content, about 1 ppm or less. In many cases, the feed to the first reforming unit contains substantially high amounts of sulfur, for example up to 10-20 ppm sulfur, and sometimes even higher concentrations. thus,
A particularly useful application of the invention relates to feedstocks containing sulfur in concentrations greater than that tolerated by commercially available precious metal catalysts, ie, 2 ppm or higher. It is believed that substantially high sulfur concentrations can be tolerated for extended periods of time without inhibiting the catalyst system. Thus, other applications of the invention relate to feedstocks containing even greater amounts of sulfur, on the order of 10 ppm or more. The reforming process can be carried out using suitable processing equipment including a reactor defining a reaction zone containing a catalyst system therein. The composite zinc oxide-silicalite catalyst can be arranged in a single catalyst bed or multiple catalyst beds within the reaction zone. A reactor, as understood in this field, is
It can be of the fixed bed or movable bed type. In practice, it will usually be desirable to provide multiple reactors to allow regeneration without interrupting the reforming process. Typically, the feedstock is heated before it is introduced into the reaction zone. After the feedstocks are maintained in contact for the desired residence time, the reformed product is withdrawn and subjected to appropriate purification and separation procedures. Experimental studies were carried out to reform the first reforming feed using a zinc oxide-silicalite catalyst mixture according to the present invention. The catalyst system was a homogeneous mixture of particulate zinc oxide and silicalite in an amount where the weight ratio of zinc oxide to silicalite was 1.5. Each of the zinc oxide and silicalite was ground to a particle size of approximately 60-80 mesh. Zinc oxide was a commercial catalyst designated UCI S72D. The silicalite catalyst has a crystalline size of less than 8 microns and at least about
The ratio of silica to alumina in the tetrahedral molecular sieve network was 200. The test was conducted for several hours, during which the temperature was increased from about 490 to about
The temperature was increased to 550°C and then to approximately 590°C. The pressure in the reaction zone was kept constant at 20 bar and the feed rate was kept constant to give a space velocity of about 14.5 LHSV. Collection from the reactor was collected and three samples corresponding to reaction temperatures of 490, 550 and 590°C were collected and analyzed to determine their individual liquid hydrocarbon components. The experimental studies are summarized in the table. The table also describes an analysis of the plant reformate produced from the reformer feed. The plant reformer is 458,
It was a three reactor reformer with first, third and third reaction stages operated at inlet temperatures of 463 and 493°C. The reformer was operated at an average pressure of approximately 17 bar. The catalyst used was a commercial platinum rhenium reforming catalyst, and the reformer feed was approximately 1.2
Supplied by LHSV. In the table, the first column indicates the hydrocarbon component. The second column represents the analytical data for the reformer feed, and the third, fourth and fifth columns represent the 490, 550 and 550, respectively.
The liquid analysis of the liquid effluent at a temperature of 590°C is described. The last column contains the analysis of the plant's reformate liquid.

【table】

【table】

[Table] Weight%
*DMB-dimethylbenzene, CP-cyclopentane, MP-methylpentane, MCP-methylcyclopentane, DMP-dimethylpentane, DMCP
-dimethylcyclopentane, CP-ethylpentane, MH-methylhexane, M-CH-methylcyclohexane, EP-ethylpentane, ECP-ethylcyclopentane, TMCP-trimethylcyclopentane, DMH-dimethylhexane or dimethylheptane, TMP-trimethyl pentane,
PRO−CP−propylcyclopentane, TMH−
trimethylhexane or trimethylhapten,
EH-ethylhexane, TMCH-trimethylcyclohexane, MCEH-methylethylcyclohexane. Based on the discussion in column 4, it can be seen that the liquid product profile obtained at an intermediate temperature of 550° C. is similar to that obtained from current reformer operation. However, at this temperature, the composite silicalite zinc oxide catalyst produced less _C9 + product than the conventional reforming catalyst, indicating that some dealkylation of heavy aromatics occurred. It was done. Additionally, the concentrations of normal hexane and normal heptane for the composite catalyst are somewhat lower than for commercial platinum rhenium catalysts. At the higher concentration of 590°C (column 5),
The concentrations of normal hexane and heptane were further reduced, and the concentrations of benzene and toluene were significantly higher than for operating the reformer with commercial catalyst. Furthermore, higher temperatures substantially decreased the concentration of _C9 + compounds. In experimental studies, equal volumetric amounts of granular zinc oxide and silicalite were used to obtain the aforementioned weight ratio of 1.5. In practical operations, it will usually be desirable to use substantially smaller amounts of zinc oxide to obtain zinc oxide-silicalite ratios within the aforementioned ranges.

Claims (1)

Claims: 1. Reforming of a low octane feedstock consisting primarily of normally liquid hydrocarbons within the range of gasoline to a product primarily within the boiling point range of gasoline, but having a high octane rating. passing said feedstock containing branched and linear aliphatic hydrocarbons into a reaction zone and contacting a catalyst system in said reaction zone, said catalyst system containing a metal or a metal oxidizer; comprising a discrete physical mixture of a silica dehydrogenation catalyst and a shaped selective crystalline silica polymorph silicalite catalyst, said silicalite catalyst being preferentially selective towards linear aliphatic hydrocarbons. is limiting for its branched isomers and produces in said reaction zone a modified product with increased aromatic content and decreased normal paraffin content with respect to said feedstock. A method characterized by establishing conversion conditions for. 2. The method of claim 1, wherein said catalyst system is in the form of particles consisting of pellets formed from crystallites of said silicalite and said dehydrogenation catalyst to constitute said discrete physical mixture. 3. The method of claim 1, wherein the catalyst system is in the form of particles consisting of particles of the silicalite and particles of the dehydrogenation catalyst mixed together to constitute the discrete physical mixture. 4. The process of claim 1, wherein the feedstock is a roughinate mixture obtained from solvent purification of the product stream from the aromatization process. 5. The method of claim 1, wherein the feedstock is reformate from a reforming unit, and wherein the aromatic hydrocarbons present in the feedstock are primarily in the form of _C9 + hydrocarbons. 6. The method of claim 1, wherein the feedstock contains sulfur in an amount greater than 2 ppm. 7. The method of claim 1, wherein the feedstock contains sulfur in an amount greater than 10 ppm. 8. The method of claim 1, wherein the dehydrogenation catalyst is zinc oxide. 9. The method of claim 1, wherein the weight ratio of zinc oxide to silicalite in said discrete physical mixing is within the range of 0.1 to 1.