MXPA97008694A - Process for the aromatization of hydrocarb - Google Patents

Abstract

The present invention relates to an aromatization process in which the proportion of coke formation during the aromatization of hydrocarbons having boiling temperatures in the boiling range of gasoline is significantly reduced by contacting with a catalyst. zeolite, by providing a concentration of a silylating agent in the hydrocarbon feed

Description

PROCESS FOR THE HYDROCARBON AROMATIZATION BACKGROUND OF THE INVENTION The invention relates to a process for the conversion of non-aromatic hydrocarbons, in the presence of a zeolite material, to aromatic hydrocarbons. More particularly, the invention relates to the reduction in the proportion of coke formation during aromatization of hydrocarbons in the presence of a zeolite material to thereby improve the stability of such a zeolite material. It is known to catalytic pyrolysis of non-aromatic hydrocarbons, whose boiling temperatures are in the boiling range of gasoline, to lower olefins (such as ethylene and propylene) and aromatic hydrocarbons (such as benzene, toluene and xylenes) in the presence of catalysts which contain a zeolite (such as ZSM-5), as described in a NY article Chen et al. in Industrial & Engineering Chemistry Process Design and Development, Volume 25, 198, pages 151-155. The reaction product of this catalytic pyrolysis process contains a multitude of hydrocarbons: unconverted alkanes, of more than 5 carbon atoms, lower alkanes (methane, ethane, propane), lower alkenes (ethylene and propylene), aromatic hydrocarbons of 6 to 8 carbon atoms (benzene, toluene, xylenes and ethylbenzene) and aromatic hydrocarbons of more than 9 carbon atoms). One concern with the use of zeolite catalysts in the conversion of hydrocarbons, whose boiling temperatures are in the boiling range of gasoline, to aromatic hydrocarbons and lower olefins is the excessive production of coke during the reaction of REF: 26058 conversion. The coke formed during the aromatization of the hydrocarbons, catalyzed by zeolite, tends to deposit on the surface of the zeolite, thereby causing deactivation. It is desirable to improve the process for the aromatization of hydrocarbons by minimizing the amount of coke formed during such an aromatization reaction process.

Brief description of the invention It is an object of this invention to at least partially convert the hydrocarbons contained in the gasoline to ethylene, propylene and aromatic compounds of BTX (benzene, toluene, xylene and ethylbenzene). A further object of this invention is to provide an improved process for the aromatization of hydrocarbons, in which the proportion of coke formation, during such aromatization of hydrocarbons, is reduced to a lower level of the proportion of coke formation in the processes of aromatization of the prior art. The process of the invention provides for the production of lower olefins and aromatics from a hydrocarbon feed stream, with a proportion of coke formation, during the conversion reaction, which is less than that of other similar conversion processes. A feed stream containing hydrocarbons whose boiling temperature is in the boiling range of gasoline undergoes an aromatization step by contacting the feed stream under aromatization reaction conditions with an acid leached zeolite material. A certain concentration of a silylating agent is provided in the feed stream, which is contacted with the acid leached zeolite material. Other objects and advantages of the invention will become apparent from the detailed description and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION Any catalyst containing a zeolite, which is effective for the conversion of non-aromatic compounds to aromatic compounds can be used in the contacting step of the process of the invention. Preferably, the zeolite component of the catalyst has a constraint index (as defined in U.S. Patent No. 4)., 097,367) in the range of about 0.4 to about 12, preferably about 2-9. In general, the molar ratio of SiO2 to AI2O3 in the crystal structure of the zeolite is at least about 5: 1 and can fluctuate to infinite. Preferably, the molar ratio of SiO2 to AI2 3 3 in the structure of the zeolite is from about 8: 1 to about 200: 1, more preferably about 12: 1 to about 60: 1. Preferred zeolites include ZSM-5, ZSM-8, ZS-11, ZSM-12, ZSM-35, ZSM-38 and mixtures thereof. Some of these zeolites are also known as "MFI" or "Pentasil" zeolites. It is within the scope of this invention to use zeolites which contain boron and / or at least one metal selected from the group consisting of Ga, In, Zn, Cr, Ge and Sn. The most preferred zeolite herein is ZSM-5.

The catalyst also generally contains an inorganic binder (also called matrix material) which is preferably selected from the group consisting of alumina, silica, alumina-silica, aluminum phosphate, clays (such as bentonite), and mixtures thereof. Optionally, other metal oxides, such as magnesia, ceria, toria, titania, zirconia, hafnia, zinc oxide and mixtures thereof, which improve the thermal stability of the catalyst, may also be present in the catalyst. Preferably, hydrogenation promoters, such as Ni, Pt, Pd and other noble metals of group Vlll, Ag, Mo, W and the like, must be essentially absent from the catalyst (ie, the total amount of these metals must be less than about 0.1% by weight). In general, the content of the zeolite component in the catalyst is about 1-99 (preferably about 5-80)% by weight and the content of the inorganic binder listed above and the metal oxide materials in the zeolite is about 1-50% by weight. In general, the zeolite component of the catalyst has been compounded with binders and subsequently formed (such as by agglomeration, extrusion or pressing of the granules into tablets). In general, the surface area of the catalyst is about 50-700 m2 / g and its particle size is about 1-10 mm. Any suitable hydrocarbon feed, which comprises paraffins (alkanes) and / or olefins (alkenes) and / or naphthenes (cycloalkanes), wherein each of these hydrocarbons contains 5-16 carbon atoms per molecule, can be used as the feeding in the contacting step of this invention. Often these feedstocks also contain aromatic hydrocarbons. Non-limiting examples of suitable, available feedstocks include gasolines from petroleum catalytic pyrolysis processes (eg FCC), pyrolysis gasolines from catalytic hydrocarbon (eg ethane) thermal pyrolysis processes, naphthas, gasoils, reformed and the like. The preferred feedstock is a hydrocarbon feedstock having boiling temperatures in the boiling range of gasoline, suitable for use at least as a gasoline blending feedstock having generally a boiling range of about 30. -210 ° C. In general, the paraffin content exceeds the combined content of olefins, naphthenes and aromatics (if present). The hydrocarbon feed stream can be contacted by any appropriate means with the solid catalyst containing zeolite, contained in the reaction zone of the invention. The contacting step can be carried out as a step of a batch process or preferably as a step of a continuous process. In the latter operation, a solid catalytic bed or a mobile catalytic bed or a fluidized catalyst bed can be used. Any of these modes of operation has advantages and disadvantages and those skilled in the art can select the most appropriate one for a particular feed and catalyst. It is not required that any significant amount of hydrogen be introduced with the feed into the reaction zone of the contacting step, ie, no H 2 gas or only trace amounts of H 2 (for example, less than about 1 ppm of H2) which do not significantly affect the processes will be introduced to these reactors from an external source. An important aspect of the process of the invention is the provision of a concentration of a silylating agent in the hydrocarbon feed stream that is brought into contact with the zeolite catalyst contained in the aromatization reaction zone of the invention. It has been found that the proportion of coke formation, during the zeolite-catalyzed aromatization of a hydrocarbon feed, it is greatly decreased when a concentration of the silylating agent is present in the feed. What is critical for this invention is that the silylating agent is present in the hydrocarbon feed when it is contacted with the zeolite catalyst under aromatization reaction conditions. The use of a zeolite that has been previously modified by a silylating agent, before its use as an aromatization catalyst, does not provide the kind of reduction in the proportion of coke formation which results in the new process of using a concentration of the silylating agent in the hydrocarbon stream which is contacted with the zeolite catalyst, under aromatization reaction conditions. The silylating agent used in the process of the invention can be any suitable compound containing silicon, which is effective to reduce the rate of coke formation when incorporated into a hydrocarbon feed that is contacted with a zeolite, under appropriate reaction conditions for aromatization of hydrocarbons.

More particularly, the silylating agent is an organosilicon compound selected from the compounds having the following molecular formulas: SiRyX4-yy (RwX3.wSi) 2-Z wherein: y = 1 to 4, w = 1 to 3, R = alkyl, aryl, H, alkoxy, arylalkyl and wherein R has from 1 to 10 carbon atoms; X = halide; and Z = oxygen or NH or amines or substituted amides. The preferred silylating agent is selected from the group of tetraalkyl orthosilicates (Si (OR) 4) and poly (alkyl) siloxane. The most preferred silylating agents are tetraethyl orthosilicate and poly (phenyl methyl) siloxane. The concentration of the silylating agent, in the hydrocarbon feed which is contacted with the zeolite catalyst, within the aromatization reaction zone, must be sufficient to reduce the proportion of coke formation to a smaller proportion than the proportion of coke formation when no silylating agent is present in the feed. An effective concentration of the silylating agent in the hydrocarbon feed may be such that the amount of silicon present is in the range of up to about 50 weight percent silicon, based on the total weight of the hydrocarbon. Preferably, the silicon concentration may be in the range of about 0.01 weight percent to about 80 weight percent and more preferably 0.1 to 10 weight percent.

The contacting step is carried out within an aromatization reaction zone, where the zeolite catalyst is contained and under reaction conditions such as to suitably promote the aromatization of at least a portion of the hydrocarbons of the hydrocarbon feed. The reaction temperature of the contacting step is more in particular in the range from about 400 ° C to about 800 ° C, preferably from about 450 ° C to about 750 ° C and more preferably from 500 ° C to 700 ° C. The pressure of the contacting can range from atmospheric pressure to about 35.1 kg / cm2 (500 psia (pounds per square inch absolute)), preferably from about 1.4 kg / cm2 (20 psia) to about 31.6 kg / cm2 ( 450 psia) and more preferably from 3.5 Kg / cm2 (50 psia) to 28.1 Kg / cm2 (400 psia). The flow rate at which the hydrocarbon feed is charged to the aromatization reaction is such as to provide a space velocity per hour, by weight ("WHSV") in the range of more than 0 hours "1 to about 1000 hours' 1. The term "space velocity per hour, by weight", as used herein, shall mean the numerical ratio of the rate at which a hydrocarbon feed is charged to a reaction zone in pounds per hour divided by the pounds of the catalyst contained in the reaction zone at which the hydrocarbon is charged The preferred WHSV of the feed to the contacting zone may be in the range of about 0.25 hours'1 to about 250 hours'1 and more than preference, from 0.5 hours "1 to 100 hours'1. A particularly preferred embodiment of the invention is the use of a zeolite catalyst that has been subjected to an acid treatment step before being contacted with the hydrocarbon feed containing a concentration of the silylating agent. Any suitable medium can be used to treat the zeolite catalyst by acid, but it is preferred that the zeolite be rinsed with an acid solution by any appropriate means known in the art to contact the zeolite with such an acid solution. The acid of the acid solution can be any acid that appropriately provides for the leaching of the alumina from the crystalline structure of the zeolite. The acid solution is preferably an aqueous hydrochloric acid. The zeolite is rinsed in the acid solution for a period of about 0.25 hours to about 10 hours. After rinsing, the zeolite is freed from the acid by washing and then dried and optionally calcined. The following examples are presented to further illustrate this invention and should not be unduly interpreted as limiting the scope of this invention.

EXAMPLE I This example describes the two zeolite preparations used in the runs of the aromatization reaction of Example II. A commercially available catalyst ZSM-5 (provided by United Catalysts Inc., Louisville, KY, under the product designation "T-4480") was treated by acid leaching. To subject the catalyst to acid leaching, it was rinsed in an aqueous solution of HCl, which had a concentration of 19 weight percent HCl, for two hours at a constant temperature of about 90 ° C. After rinsing, the catalyst was separated from the acid solution and carefully washed with water and dried. The rinsed, acid washed and dried catalyst was calcined at a temperature of about 500 ° C for four hours. This acid-leached ZSM-5 catalyst was used in runs of the aromatization reaction as described below to determine the proportion of coke formation related to its use. The acid-leached ZSM-5 zeolite, described above, was treated with a silylating agent, by the use of an incipient moisture technique to impregnate it with a 50 weight percent solution of poly (methyl phenyl) siloxane with cyclohexanone. as the solvent. The impregnated acid-leached ZMS-5 zeolite was dried for two hours, followed by calcination at 530 ° C for six hours. This ZSM-5 catalyst leached with acid, calcined and silylated was used in the run of the aromatization reaction as described hereinafter, to determine the proportion of coke formation related to its use.

Example II This example illustrates the benefit of the reduced coke formation ratio, which results from the process of the invention of contacting a hydrocarbon feed containing a concentration of a silylating agent with a zeolite. The two zeolite preparations of Example I were used in three aromatization reaction runs, the results of which are summarized in Table I. The acid-leached zeolite and the acid-leached zeolite, silylated, are the zeolite catalysts of the base case with which the results of the process of the invention are compared.

For each of the aromatization test runs, a sample of 5 g of the particular zeolite catalyst preparation, mixed with approximately 50 ce of 10-20 mesh alumina was placed in a stainless steel tube reactor (length: approximately 45.7 cm (18 inches), internal diameter: approximately 1.27 cm (0.5 inches)). Gasoline from a refinery catalytic pyrolysis unit was passed through the reactor at a flow rate of about 14 ml / hour, at a temperature of about 600 ° C, and at atmospheric pressure (about 0 Kg / cm2 (0 psig) )). The reaction product formed exits the reactor tube and is passed through several ice-cooled traps. The liquid portion remained in these traps and was weighed, while the volume of the gaseous portion, which came out of the traps, was measured in a "wet test meter". Liquid and gaseous product samples were collected periodically and analyzed by means of gas chromatography. After the reaction runs were completed, the rate of coke formation was determined by measuring the amount of coke deposited on the surface of the catalyst. In the course of the invention, the acid leached zeolite catalyst was used. The initial feed charged to the reactor contained 5 parts by volume of the gasoline feed by 2 parts by volume of tetra methyl orthosilicate (TEOS) and was fed at a rate of about 12 ml / hour for 2 hours. Subsequently, the gasoline feed without TEOS was charged to the reactor at a rate of 14 ml / hour for 6 hours.

As can be seen from the data on the proportion of coke formation presented in Table I, the use of a silylated acid leached zeolite in aromatization of hydrocarbons results in a lower coke formation rate than that of the zeolite leached by acid. In addition, the addition of a silylating agent to the hydrocarbon feedstock that is contacted with the acid leached zeolite during aromatization provides an even more significant reduction in the rate of coke formation, when compared to the use of a acid leached zeolite, leached. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (5)

1. Claims 1. A process for the aromatization of hydrocarbons of a feed stream containing non-aromatic hydrocarbons, characterized by the provision of a silylating agent in the feed stream and the contacting of the feed stream, which has a concentration resulting from the silylating agent, with an acid leached zeolite, under aromatization reaction conditions.
2. 2. The process of approval in the field 1, characterized perqué the raigo fe boiling of hydrocarbons in the feed stream is from about 30 ° C to about 210 ° C.
3. 3. The process of use of the substance in reaction 1 or 2, characterized in that the concentration of the silylating agent in the feed stream is effective in reducing the rate of coke formation during the aromatization of the hydrocarbons in the feed stream.
4. If the recess of the silicone in the feed stream is such that the amount of silicon present is in the range of up to about 50 percent, the recess of the silicon present in any of the reagents is 1-3. by weight of the hydrocarbons in the feed stream.
5. 5. A process in accordance with any of the preceding claims will characterize why the ajaite ds to the lanen is a "xgaxsilicon" label. g The registration process with the re virriifTC? 5, characterized CC-CCJLE the organosilicon cxppuestD is a tetra-alkyl orthosis compound or a poly (alky1) siloxane The process of catchability with the reagent 6 is characterized by the fact that the tetraalkylorthosilicate consists of tetraethyl orthosilicate and the poly (alkylene) if loxane consists of poly (phenylmethyl) siloxane.