MXPA98006055A - Procedure for obtaining light olefins through the dehydrogenation of corrupted paraffins - Google Patents

Abstract

The present invention relates to a process for obtaining light olefins through the dehydrogenation of the corresponding paraffins, which consists of: a) reacting in a reactor, operating at a temperature between 450 to 800 ° C, at a pressure of between 0.1 and 3 absolute Atm and with a GHSV space velocity of between 100 and 10000 h-û said paraffins with a catalytic system containing chromium oxide, tin oxide, at least alkali metal oxide (M) and an alumina carrier, in phase delta or theta or phases delta + teta mixed or theta + alpha or delta + teta + alpha, modified with silica, where: - the chromium, expressed as Cr2O3 is in an amount between 6 and 30% by weight; expressed as SnO, is in an amount of between 0.1 and 3.5% by weight, - the alkali metal, expressed as M2O, is in an amount of between 0.4 and 3% by weight, - the silica is in an amount of between 0.08 and 3% by weight. weight, the complement to 100 being of alumina, b) generates r said catalytic system in a regenerator burning the coke deposited on its surface operating at a temperature of more than 400

Description

* PROCEDURE FOR OBTAINING LIGHT OLEFINS THROUGH THE DEHYDROGENATION OF CORRESPONDING PARAFFINS DESCRIPTION OF THE INVENTION The present invention relates to a process for obtaining light olefins through that of shidrogena tion of the corresponding paraffins, in particular, C2-C20 (paraffins with 2 to 20 carbon atoms). Olefins are important intermediates for the production of chemicals that have a high distribution such as: polypropylene, anti-knock additives (MTBE) fuels with a high octane number, alkylated derivatives and numerous other products. of these derivatives, the expansion of industrial processes for their preparation is usually limited by the restricted availability of olefins, for example isobutylene in the production of MTBE.

This leads to the identification of other sources of olefin supply, together with traditional ones (FCC, installation for catalytic disintegration). Among these, the source that is becoming more and more important is represented by the reaction of shidr ogenation of light paraffins. , although simple from a sistéqueometric point of view, has problems with respect to thermodynamics and kinetics. The reaction is endothermic and is regulated through thermodynamic equilibrium; this leads to the need for temperatures higher than 500 ° C for the dehydrogenation of C2-C4 paraffins with conversions that are economically acceptable ISpCpa s a j e. In addition, it is necessary to supply the system with heat due to the endothermic nature of the reaction. In spite of the high operating temperatures, the dehydrogenation rate is low 20 and consequently it is necessary to operate in the presence of a suitable catalyst. The latter must be thermally adequate and capable of guaranteeing high selectivities towards the desired olefin, a minimized Visomerization, distills catalytic disintegration, coke and lateral aromatization reactions and assures useful inductive conversion values. 5 The inevitable formation of coke opens the catalyst causes a progressive reduction in the? catalytic activity and, therefore, it is essential to perform periodic regenerations. As a result, the formulator must have high stability under the conditions to which it is subjected during the reaction and regeneration phases. Various efforts have been made to identify the catalytic compositions that can. satisfy the demands imposed by the type of procedure. The patent literature actually cites various catalytic compositions based on noble metals and combined with other chemical species (US-20 3531543; US-4786625; US-4886928; EP-35106) and also based on metal oxides in the presence of of promoters, in most of those cases consisting of supported Cr203 (US-2945823; US-2956030; US-2991255; GB-2162082). Both groups of formulations, however, have disadvantages, those based on noble metals require a particular treatment in the regeneration phase (US-4438288) to preserve the dehydrogenation of the species by resorting, for example, to post-treatment with chlorinated substances and subsequent 0 reduction treatment; those based on chromium oxide, supported on alumina, silica, silica-alumina, etc., are characterized because they have a low selectivity to the olefin in terms of their acid nature causes parasitic reactions such as Vr / fc is omer iz ation, catalytic disintegration, coke formation and aromatization, which are typical acid catalyzed reactions. The selectivity to olefins is increased by modifying the formulations with the addition of alkali metal and / or alkaline earth metal oxides to mitigate the acid properties. Literature describes (J. Phys. Chem., Vol 66, 1962) that the loading of high amounts of oxides ^^ to 1 ca 1 ino. , in order to improve the selectivity, it endangers the catalytic performance of the formulations: the strong interactions with the chromium oxide suppress the activity of dehydrogenation, while the residual chromium as an oxidation state of more than -3, which can not be completely reduced since it is 'Mfe stabilized through the highly alkaline charge, reduces the selectivity to the olefin of need Surprisingly it has been found that by using a particular catalyst system mainly consisting of Cr203, supported on alumina modified with silica to which tin oxide is added, the selectivity to the desired olefin is significantly improved. The addition of tin drastically reduces the formation of acid-catalyzed side reaction products with a beneficial effect on olefin selectivity. The process for obtaining light olefins through the dehydrogenation of paraffins > corresponding, the object of the present invention consists of: a) reacting in a reactor, operating at a temperature of between 450 and 800 ° C, at a pressure of between 0.1 and 3 absolute Atm and with a GHSV space velocity between 100 and 10000 h "1 said paraffins with a catalytic system W "containing chromium oxide, tin oxide, at least one alkali metal oxide (M) and a carrier 0 of alumina, in delta or theta phase or in delta + teta phases mixed or teta + alpha or delta + teta + alpha, modified with silica, wherein: - the chromium, expressed as Cr203, is in an amount between 6 and 30% by weight, preferably 3 and 25%, and the tin, expressed as SnO, is in an amount between 0.1 and 3.5% by weight, preferably between 0.2 and 2.8%, the alkali metal, expressed as M20, 20 is in an amount between 0.4 and 3% by weight, preferably between 0.5 and 2.5; in an amount between 0.08 and 3% by weight; the complement to 100 being of alumina, b) regenerating said catalytic system in a regenerator burning the coke deposited on its surface operating at a temperature of more than 5 400 ° C. The alkali metal, preferably potassium, TS used to mitigate the acid properties of the formulations to reduce side reactions such as, for example, catalytic disintegration, coke formation, aromatizations and isomerizations of the skeleton and bond structure . With respect to the surface area of the carrier, this is preferably less than 150 _ ^ - m2 / g, determined through the BET method. The process for preparing the catalytic system described above essentially consists in dispersing a chromium, alkali metal and tin compound in a "carrier consisting of alumina (in the delta or theta phase or in mixed phases of delta + teta or theta + alpha or delta + teta + alpha) and silica.

^ ""% Here are some methods of dispersing the chromium, potassium and tin oxide (tin and / or stannic) on the carrier, it being understood that the invention is not limited to these. The digestion treatment may consist of the impregnation of said carrier with - a solution containing the chromium, potassium and tin oxide precursors, followed by drying and calcination, or through ionic absorption, followed by separation of the liquid and drying and calcination of the solid. Among the procedures listed above, the preferred one is that of impregnation, according to the "incipient moisture" method of the carrier IaJ with the solution containing all the precursors of the active principles. With respect to tin, other procedures are listed, with which it can be added to the catalytic system: 20 - addition of tin to the carrier before the dispersion of the chromium and potassium oxide precursors; - treatment of the solid containing chromium and potassium oxide by ion exchange, impregnation, etc., with a solution containing a tin compound; - deposition of tin through vapor deposition on the carrier, before the addition of the chromium and potassium oxide precursors, using a volatile compound of the species that will be deposited; - deposition of tin through vapor deposition on the solid containing: alumina, chromium oxide and potassium oxide, using a volatile compound of the species that will be deposited. Among the foregoing procedures, those preferred are co-impregnation of the carrier with the solution contained in the precursors of the active ingredients: chromium oxide, potassium and tin and vapor deposition of the product. Both inorganic and organic tin salts, or organometallic derivatives can be used as precursors of stannous and / or stannic oxide. The inorganic or organic salts not very soluble in water, can be used after controlling the pH of the solution, which is influenced by its solubility. , - ,. The organometallic derivatives are used by depleting organic solvents where they are dissolved to be added to the catalyst system 0 according to the procedures described above. The regeneration is carried out in air and / or oxygen, possibly increasing the temperature of the same catalytic system to suitable values, for example, through the combustion of an appropriate fuel. This regeneration must be followed by the reduction phase of the catalyst to reduce the hexavalent chromium formed during the regeneration phase. 20 The claimed procedure can be applied to any dehydrogenation technology if it is a fixed, fluid or mobile bed.

The process can preferably be carried out in a fluid bed system essentially consisting of a reactor, wherein the dehydrogenation reaction occurs and a regeneration wherein the catalyst is regenerated for combustion of the coke deposited there during the reaction phase. . In the reactivator system, the catalyst in its fluidized state circulates continuously between the reactor and the regenerator, allowing the process to operate in a continuous form and the heat necessary for the reaction is supplied through the regenerated catalyst, which reaches the reactor at a temperature that is higher than the average reaction temperature. The catalyst is maintained in its fluidized state in the reactor through the reactive gas, which enters the catalytic bed from below, through a specific distribution system. The reacted gas leaves the reactor from above, then passes through a cyclone system or other suitable separation system of the powders; subsequently it can be sent to a * heat exchanger to preheat the feed and then to a separation section, where the olefin produced is recovered, while the unreacted paraffin can be recirculated to the synthesis, and the byproducts are separated and can also be used in the regenerator as cpmbus tibie gas. ™ When there is a verification plant, downstream of the dehydrogenation, the separation section 0 serves only to eliminate the sub-steps. In the reactor, the catalyst in its fluidized state moves in a counter current with respect to the gas phase; It enters the catalytic bed I &lfrom above, through a distributor which distributes it equally on the surface of the bed and leaves the reactor from below, passing by gravity towards an area of descent, which is part of the reactor with a diameter less than or equal to the area of The reaction, in which the gas between particles is displaced and displaced, introducing nitrogen or methane from below, so that the displaced or desorbed gas re-enters the reactor avoiding losses in reactants or products. The catalyst, even in its fluidized state, is subsequently sent, pneumatically, to the regenerator. In the fluid bed reactor, it is preferred that it operates: at a maintained temperature, acting on the flow rate of the regenerated catalyst, between 450 and 650 Y, depending on the paraffin or mixture of treated paraffins; - at a pressure that is atmospheric or slightly higher; - at a space velocity of between 100 and 1000 h ~ 1 (Number of gas per hour and per liter of catalyst), most preferably between 150 and 200; with a catalyst residence time varying in the fluid bed zone from 5 to 30 minutes, most preferably from 10 to 15 minutes, in the desorption zone from 0.2 to minutes . Grids with a free area of between 10 and 90%, preferably between 20 and 40%, can be horizontally disposed within the reactor, at a distance of between 20 and 200 cm from each other. The purpose of these grids is to prevent the gas and solid from being mixed again, so that the gas flow inside the reactor resembles an oppressor flow; in this way, JL conversion of the paraffin and selectively to the desired t-lefine is maximized. In particular, the selectivity can be further increased through the axial thermal profile, which is established along the bed with the maximum temperature at the top, where the regenerating catalyst arrives and the minimum temperature at the bottom; y1-l-j-difference in temperature along the bed is referentially between 15 and 65 ° C. In order to optimize the axial thermal profile, it is also possible to distribute the regenerated catalyst at variable heights in the bed catalytic. The pneumatic transport system from the reactor to the regenerator consists of a transport line with at least one zone in which the catalyst has a downward movement, preferably maintained under intermediate conditions between the minimum temperature and the minimum bubble formation, through the entry of adequate amounts of gas at appropriate heights 5 and an area where the catalyst moves with an upward movement until it reaches the upper part of the catalytic bed of the regenerator through the gas inlet At the base it considerably reduces the density of the emulsion. The regenerator preferably has dimensions that are similar to those of the reactor. An appropriate distributor divides the catalyst coming from the reactor onto the JB * surface of the catalytic bed. Regeneration occurs within the bed through the combustion of coke deposited on the catalyst and heating of the catalyst through the combustion of methane or fuel gas with air or oxygen or other fuel gas, at a temperature that is greater than the average temperature of the reactor.

Before being sent to the reactor, the regenerated catalyst is subjected to reduction treatment, at temperatures between 650 and 680 ° C and for a time between 0.2 and 10 minutes, to eliminate hexavalent chromium, then it is desorbed from the combustion and reduction product. ? v Also in the regenerator, the movement of the gas and the solid occurs in a contrary current 0; the air is admitted to the bottom of the catalytic bed while the fuel gas enters the appropriate heights along the bed. The gas leaving the regenerator, consisting of nitrogen and combustion product, can pass through cyclones, or another system, located at the top of the apparatus, to separate the accumulated dust and subsequently, after leaving the regenerator, it can be sent to a heat exchanger for air preheating of combustion. Before being discarded into the atmosphere, these gases can pass through a filter system or other devices to reduce the. powder content a few tenths of mg per Nm of gas. Since the combustion catalytically occurs at a temperature that is less than 700 ° C, the content of carbon monoxide and nitrogen oxides in the discharge gas is such that it does not require a purification treatment " additional . In the regenerator, it is preferred to operate at a pressure that is either atmospheric or slightly higher, at a space speed of between 100 and 1000 h_1 and with a residence time of the solid, ranging from 5 to 60 minutes, most preferably from between 20 and 40 minutes. The regenerated catalyst is transported to the reactor in the same way that the exhaust catalyst is transported to the regenerator. The system of reactivation generated in this way allows the operation and operation parameters for the entire technical life of the plant to be kept constant.

The aliquots of catalyst are periodically discarded from the system and replaced with equal aliquots of fresh catalyst, but without having to interrupt the operation of the plant. The advantages of the use of a reactor-regenerator system of the fluid bed can be ^ without ttet -izad -as as follows: - the optimum temperature profile in the reactor allows the production of olefins to be maximized; the heat is directly transferred to the reaction through the regenerated catalyst; There is no thermal exchange surface and the strong remixing of the fluid bed prevents the formation of high temperature points, which could reduce the selectivity; 0 - the fluid bed procedure does not require recirculation of hydrogen, which is dangerous from the thermodynamic point of view, but necessarily in other configurations to keep the temperature under control; - all the other operations are presented continuously and it is not necessary to modify the operating parameters during the entire life of the plant; -_ - the plant can operate with a wide ? flexibility in terms of present productive capacity with respect to project capacity; 0 - the reaction and regeneration occur in physically separate areas and there is no mixing of hydrocarbon stream with oxygen-containing streams; - the procedure is carried out at an atmospheric pressure P or at a slightly higher pressure; therefore, there is no possibility of external infiltrations of air into the reaction zone; no particular treatment is necessary to reduce emissions of gaseous pollutants. Figure 1 shows a possible application of the or-regenerated reaction scheme r described above.

The hydrocarbon feed (1) enters the reactor (A) through a suitable distributor (not shown in the figure) while the gases after the reaction leave the reactor from line (4) after passing through of the cyclones FA. The regenerated catalyst (5) reaches the upper surface of the catalytic bed and leaves the reactor (A) passing to the orbiter's abs (B), where it is brought into contact with the desorption gas (2). The catalyst subsequently enters the transport line (6), where it is sent to the regenerator (D), and precisely the upper part of the catalytic bed. In this case, an individual line of gas inlet along the transport line is shown in (6). The transport line in this application is characterized in that it has a U-shaped connection between the descending part and the ascending part. The catalyst descends along the regenerator (D), enters the reducer, after the former orbiter (G) and finally to the transport line (C) and is sent to the reactor. The regeneration head (8) enters, the combustion gas (9), which is the same gas used for the reduction of the catalyst in (E) and the desorption gas (10), again through the 5 suitable distributors (not shown in the figure). The gases after passing through the attached "cyclones Fo." Come out through (7) Several examples are provided which should not be considered as limiting of the present invention.

Example 1 (Comparative) A ps eudobohemi was prepared in my oidal sfer to which silica (1.2% by weight), with a particle diameter between 5 -t- 300 microns, was added through spray drying. of a solution of hydrated alumina and Ludox silica. A sample of the p eudobohemi t was subjected to a heat treatment consisting of a first calcination at 450 ° C for 1 hour, followed by another 1030 ° C for 4 hours in a stream of dry air.

"The product obtained has a specific surface area of 100 m2 / g, a porosity of 0.34 cc / g and essentially consists of transitional delta and teta alumina, accompanied by a small amount of 5 alpha alumina (see the XRD spectrum in Figure 2). ). 200 g of this alumina were impregnated, illustrating the incipient humidity procedure, with 68 cc of an aqueous solution containing 67.5 g of Cr03 (99.88% by weight) and 6.4 g of KOH (90% by weight) in deionized water, maintained at a temperature of 85 ° C. The impregnated product was allowed to stand for one hour at room temperature and subsequently dried at 90 ° C for 15 hours. The dried product was finally activated, in a stream of dry air, at 750 ° C for 4 hours. The composition by weight of the formulations proved to be as follows: 20% Cr203, 1.89% K20, 1.25% Si02, A1203, the complement to 100. The catalytic performances in the dehydrogenation reaction of isobutene, measured at the scale temperature of between 540 • - 580 ° C with the procedure already described are as shown in table 1.

Example 2 200 g of microesteroidal alumina, prepared as described in Example 1, were impregnated according to the method described above with 68 cc of an aqueous solution containing: 68.3 g of Cr03 (99.8% p), 6.48 g of KOH (90% p) and 4.13 g of SnC204 (99.9% p) in deionized water, maintained at the same temperature as Example 1. The impregnated product was treated as described in the previous example to give a ? 15 catalyst whose composition weight proves to be the following: 20% Cr203, 1.89% K20, 0.9% SnO, 1.23% Si02, A1203 the complement to 100. The catalytic performances in the dehydrogenation reaction of isobutene are shown in Table 1.

Example 3 200 g of microes feroidal alumina were impregnated, prepared as described in Example 1, according to the method described above with 68 cc of an aqueous solution containing: 68.8 g of Cr03 (99.8% p), 6.52 g of KOH p) and 5.61 g of SnC204 (99.9% p) in clear water, maintained at the same temperatures as Example 1 10 The impregnated product was treated as described in the previous example to give a catalyst whose composition weight proves to be the following: 20% Cr203, 1.89% K20, 1.4% SnO, 1.22% Si2, AI2O3 the complement to 100 .l '^ T, "The catalytic operations in the dehydrogenation reaction of isobutene are shown in table 1.

Example 4 200 g of feroidal microe s alumina, prepared as described in example 1 ', were impregnated according to the method described above with 68 cc of an aqueous solution containing: 67.9 g of Cr03 (99.8% p), 6.44 g of KOH (90% p) and 1.78 g of SnC204 (99.9% p) in deionized water, maintained at the same temperatures as Example 1. The impregnated product was treated as described in the previous example to give a catalyst whose weight of composition is tested as follows: 20% Cr203, 1.89% K20, 0.45 SnO, 1.22% Si02, A1203 the complement to 100. The catalytic performances in the dehydrogenation reaction of isobutene are shown in table 1.

E mplo 5 200 g of alumina mi croe s feroi da 1, prepared as described in Example 1, were impregnated according to the method described above with 68 cc of an aqueous solution containing: 67.7 g of Cr03 (99.8% p), 6.42 g of KOH (90% p) and 0.91 g of SnC20 (99.9% p) maintained at the same temperatures as Example 1. The impregnated product was treated as described in the previous example to give a catalyst whose composition weight proves to be the next: 20% Cr203, 1.89% K20, 0.23% SnO, 1.25% Si0, Al203 the complement to 100. The catalytic operations in the dehydrogenation reaction of isobutene are shown in Table 1. 9. Example 6 '200 g of alumina were impregnated micr oes is feroidal, prepared as described in Example 1, with the incipient humidity procedure, with 44 cc of a methanol solution containing 3.99 g of dime toxidibut the dissolved solution.

(CH30) 2 (Sn (C4H9) 2 r in a nitrogen atmosphere. 1 ^ - impregnated product was allowed to stand for 1 hour at room temperature and subsequently dried 90 ° C until complete removal of methanol. The dried product was finally calcined at 750 ° C for 4 hours in an atmosphere of dry air. The composition by weight of the formulations proved to be the following: 20% Cr203, 1.89% K20, 0.87% SnO, 1.23% Si02, Al203 the complement to 100.

The catalytic operations of the formulations in the isobutene dehydrogenation reaction are shown in Table 1.

Example 7 200 g of the same catalyst used in Example 6 were modified with tin, using the vapor deposition technique. For this purpose, the catalyst sample was charged to a quartz reactor equipped with a thermometer support and a ceramic distributor with a calibrated porosity to obtain homogeneous nitrogen distribution at the bottom of the bed. The reactor with the material was placed in an electric furnace, with partial heating i5, and nitrogen was fed (40 between 45 Nl / h) a. through the porous distributor, which maintained the fluidization of the material. When at the pre-set temperature of 200 ° C for the deposition of tin was reached, the longitudinal thermal profile 20 of the bed was carried out before feeding the tin precursor. Once that was finished, the temperature of the bed was homogeneous within ± 1 ° with respect to the pre-set temperature, 10 between 15 Nl / h of saturated nitrogen with dime tox i dibu ti le year (CH30) 2Sn (C4H9) 2 they were introduced at a temperature between 150 and 170 ° C in the catalytic bed. The saturated stream was fed from the top of the reactor, which through the quartz tube to the catalytic bed and porous distributor was mixed downstream of the septum with the fluidization nitrogen. The flow 10 exiting the reactor was cooled to recover the unreacted toxidbutyl toluene. The amount of tin was dosed by checking the height of the residual precursor in the saturator. _ * When the required amount of the precursor to obtain the theoretical charge of tin was removed, the operation was interrupted. The temperature of the catalytic bed increased until reaching 750 ° C, and it was maintained for 4 hours to activate the material. The activated product was analyzed to determine the composition by weight, which proved to be the following: 20% Cr203, 1.89% K20, 0.33% SnO, 1.24% Si02, A1203, the complement to 100. The workings of the formulations in the reaction of dehydrogenation of isobutene are shown in table 1.

EXAMPLE 8 (Comparative) A sample of 1000 g of a product prepared according to the procedure described in Example 1 was subjected to a heat treatment consisting of a first calcination at 450 ° C for 1 hour, followed or another at 1000 ° C. ° C for 4 hours, in a stream of dry air. The calcined product has a surface area of 130 m2 / g, a porosity of 0.49 cc / g and consists of transitional delta and teta alumina (see the XRD spectrum in Figure 3). 150 g of this alumina were impregnated, using the incipient humidity method, with. 74 cc of an aqueous solution containing 66.8 g of Cr03 (99.8% p) and 5.36 g of potassium carbonate (45 ° w / w of KOH) and was maintained at the same temperature as in example 1. The impregnated product was left To stand for 1 hour at room temperature and subsequently dried at 90 ° C for 15 hours. The dried product was finally activated, in a stream of dry air at 750 ° C for 4 hours. The composition by weight of the formulations proved to be as follows: % Cr203, 1% K20, 1.18% Si02, Al203 the complement to ; s ^ 00. This formulation was proven in the reaction of Yes hydrogenation of propane, within the scale of 560 -. 560 - 600 ° C, obtaining the operations indicated in table 2.

Example 9 150 g of the same alumina "used in" Example 8 were impregnated with 74 cc of a methanol solution containing 3.75 g of dimethyl toxidibutyl s (CH30) 2 Sn (C4H9) 2, with the humidity method incipient. The impregnated product was allowed to stand for 1 hour and subsequently dried at 90 ° C until the methanol removal was complete. The dried product was finally calcined at 600 ° C for 2 hours, in a stream of dry air, the calcined product was impregnated , according to the method described in Example 8 with 74 cc of an aqueous solution containing 67.6 g of Cr03 (99.8% w / w) and 5.42 g of potassium carbonate (45% of solution w / w of KOH), the same temperature as in example 1, to obtain a catalyst with the following composition by weight: 25% Cr203, 1% K20, 0.84% SnO, 1.18% Si02, fi1S * A1203 the complement to 100. Catalytic operations in the The propane dehydrogenation reaction is indicated in Table 2. Example 10 150 g of the same alumina used in Example 9 were impregnated with 74 cc of a methanol solution containing 7.63 g of 5-dimethoxybutyl urea (CH30). 2S n (C4H9) 2, with the same procedure described in Example 9, the calcined product, under the same conditions as in example 9, was impregnated with 74 cc of an aqueous solution with the same procedure as example 8, containing 68.4 g of Cr03 (99.8% w / w) and 5.48 g of potassium carbonate (45% solution w / w of KOH), at the same temperature as in example 1, to obtain a catalyst with the following composition fen weight: 25% Cr203, 1% K20, 1.68% CnO, 1.17% Si02, A1203, the complement to 100. The formulation was tested in the dehydrogenation reaction of propane obtaining the performances indicated in the table 2 temple 11 150 g of the same alumina used in example 9 were impregnated with 74 cc of a methanol solution 0 containing 11.61 g of dime t oxidibut i 1-tin (CH30) 2 Sn (C Hg) 2, with the same procedure described in example 9, the calcined product, under the same conditions as in example 9, was impregnated with 74 cc of an aqueous solution with the same procedure as example 8, containing 69.2 g of Cr03 (99.8% w / w) ) and 5.55 g of potassium carbonate (45% solution w / w KOH), at the same temperature as in example 1, to obtain a catalyst with the following composition in weight: 25% Cr203, 1% K20, 2.52 SnO, 1.14% Si02, A1203 the complement to 100. The catalytic operations of the formulations in the propane dehydrogenation reaction are indicated in the table Example 12 150 g of the same alumina used in Example 8 were impregnated with 74 cc of an aqueous solution f at the same temperature as in Example 1, where the following products were dissolved: 68.4 g of Cr03 (99.8% p / p) and 5.49 g of 0 potassium carbonate (45% solution w / w KOH), and 5.35 g of SnC204 (99.9% w / w) • Drying and activation were carried out with the procedure described in example 1 The composition by weight of the formulations proved to be as follows: 25% Cr203, 1%? K20, 1.68% SnO, Al203 the complement to 100. The catalytic performances in the dehydrogenation of propane are indicated in table 2.

Example 13 150 g of catalyst, prepared with the procedure described in Example 8, were impregnated with 39 cc of a methanol solution containing 3.03 g of (CH 3 -O) 2 S n (C 4 H) 2, according to the procedure described in Example 6. The formulation after activation was analyzed to determine its composition and tested in the propane dehydrogenation reaction. The composition by weight proved to be the following: 24.8% Cr203, 0.99% K20, 0.91% SnO, 1.17% A1203 the complement to 100. The catalytic operations are summarized in Table 2 10 Example 14 235 g of catalyst were prepared with the procedure described in example 2, through the impregnation of 200 g of alumina, the same in the same example, with 68 cc of an aqueous solution containing 37.2 g of Cr03 (99.8% p), 5.87 g of KOH ( 90% p) and 3.26 g of SnC204 (99.9%) maintained at a temperature of 85 ° C, having the following composition by weight: 12% Cr203, 1.36% Si02, 1.89% K20, 0.9% SnO, A1203 complement 100. The catalyst was tested in the dehydrogenation reaction of isobutene obtaining the operations indicated in table 1.

Example 15 200 g of alumina with a specific surface area of 104 m2 / g and a porosity of 0.34 cc / g, obtained through the calcination of a mixture of ps eudobohemi ta obtained according to the procedure described in example 1 but without silica , were impregnated with 68 cc of an aqueous solution having 68.3 g of Cr03 (99.8% p), 6.48 g of KOH (90% p) and 4.13 g of SnC204 (99.9%) to obtain a catalyst having the following composition by weight: 20% Cr203, 1.89% K2), 0.9% SnO, A1203, the complement to 100. The formulation was tested in the dehydrogenation reaction of isobutene, obtaining the performances indicated in table 1.

Example 16 A catalyst sample was prepared with the same procedure and the same alumina used in example 2, having the following composition by weight: 20% Cr203, 3% K20, 0.9% SnO, 1.22% Si02, A1203 the complement to 100 The catalytic operations in the dehydrogenation reaction of isobutene are indicated in table 1 ELein. A catalyst sample was prepared with the same procedure and the same alumina used in Example 2, having the following composition by weight: 20% Cr203, 0.2% K20H, 0.9% SnO, 1.27% Si02, A1203 the complement to 1000. v- The catalytic operations in the dehydrogenation action of isobutene are indicated in table 1.

Catalytic Tests The products prepared in Examples 1-17 were tested in a fluid bed using a quartz reactor equipped with a distributor with a calibrated porosity also made of quartz.

An expansion agent was placed on top of the reactor, which has the function of decelerating the effluent allowing the fine particles to fall into the catalytic bed. The catalytic cycle, which is such that it simulates the behavior in an industrial reactor, consists of a reaction phase in which the hydrocarbon is faulted for a time of 15 minutes, a separation phase, in which nitrogen is passed through releasing the catalyst from the products absorbed during 10 minutes, a regeneration phase, in which the regeneration gas consisting of air is fed in tests carried out during a period of 30 minutes, a ^ washing phase with nitrogen, for a period of At least 10 minutes, a reduction phase wherein the reduction gas consisting of methane is fed over a period of 4 minutes to reduce the hexavalent chromium formed in the reaction phase, a phase of nitrogen washing during at least 10 minutes. followed by the reaction phase for a period of 15 minutes. The requirements of the desrogenation process of the industrial fluid bed suggest that the fregeneration is carried out at temperatures that are higher than the reaction temperatures: in the catalytic tests, the regeneration and reduction were carried out at 650 ° C, while the The reaction was carried out within the temperature range of 560 to 600 ° C in the case of dehydrogenation of topane and within the range of 540 to 580 ° C in the case of dehydrogenation of isobutene. The reagent space velocity has a value of 400 ± Nl / cat.h. In the first catalytic test, each catalyst is reduced according to the procedure already described, before carrying out the dehydrogenation reaction. v- The reagent sent to the reactor was dosed # by weight The effluent from the reactor during the reaction and the separation phases was first passed through a cold trap to stop the heavy products whose weight, percentage of carbon and hydrogen are subsequently determined and then collected in a sample bag of multiple layers that have no affinity with hydrocarbon. The contents of the bag were measured afterwards with a volumetric pump and analyzed by gas chromatography. Finally, at the end of the separation of 'with N2, a sample of catalyst was taken to Determine the amount of coke formed. In this way, the data thus obtained are entered into a personal computer to calculate the material balance, conversion and selectivity to the various products. 10 # '• * ^ É > ------ TABLE 1 ISOBUTANE DEHYDROGENATION GHSV = (400 -i- -5) Hor. Ut. Iso-C .H10 / h /? cat. Fluid bed Example Cr2O3 K2O SiO2 SnO Temperat. Conversion Selectivity Yield * P% p / p% p / p% p / p% ° C (% iso-C4l-HO) (% mol ISSO-C4H0) (% mol iso-C 41 .8) 1 comp. 20 1.89 1.25 absence 560 54 88 47.5 2 20 1.89 1.23 0.90 570 54 94 50.7? T > . 3 20 or 1.89 1.22 1.40 589 54 92 49.7 4 20 1.89 1.25 0.45 565 54 91 49 1 5 20 1.89 1.25 0.23 562 '54 90 48.6 6 20 1.89 1.23 0.87 575 54 92 49.7 7 20 1.89 1.24 0.33 564 54 91 49.1 14 12 1.89 1.36 0.90 573 54 90 48.6 5 comp. 20 1.89 absence 0.90 568 54 89 48.1 16 20 30 1.22 0.9 570 54 87 46 9 17 20 0.20 1.27 0.9 568 54 70 37.8 - • "# TABLE 2 PROPANE DEHYDROGENATION GHSH = (400 H- - - 5) Nl / h / 1 cat. Fluid bed Example Cr203 K2O Si02 SnO Temperat. Conversion Selectivity Yield p / p% p / p% p / p% p / p% ° C (% C31 18) (% mol C3I I6) (% mol C3I I6) 8 comp. 25 1.0 1.18 absence 566 37 78 28.9 9 25 1.0 1.18 0.84 570 37.86 31.8 t-1 25 1.0 1.17 1.68 580 37 88 32.5 1 1 25 1.0 1.14 2.52 588 37 84 31.1 12 25 1.0 1.15 1.68 582 37 87 32.2 13 24.8 0.99 1.17 0.91 590 37 89 32.9

Claims (8)

1. A process for obtaining light olefins through the dehydrogenation of the corresponding paraffins, consisting of: a) reacting in a reactor operating 4S a temperature between 450 and 800 ° C, at a temperature of between 0.1 and 3 Absolute Atm and with a GHSV space velocity between 100 and 10000 h "1, said paraffins with a catalytic system containing chromium oxide, titanium oxide, at least one alkali metal oxide (M) and an alumina carrier, in one phase delta or theta or in mixed phases of delta + teta or theta + alpha or delta + ^ ceta + alpha, modified with silica, where: - the chromium, expressed as Cr203 is in an amount of between 6 and 30% by weight; - Tin, expressed as SnO, is in an amount between 0.1 and 3.5% by weight, - the alkali metal, expressed as M20, is in an amount between 0.4 and 3% by weight, the silica is in an amount of between

0. 08 and 3% by weight, the complement to 100 being alumina. b) regenerate the catalytic system in a regenerator by burning the coke deposited on its surface operating at a temperature of more than 400 ° C.

2. The process according to claim 1, wherein: the chromium, expressed as Cr203, is in an amount between 12 and 25% by weight, - the tin expressed as SnO, is in an amount between 0.2 and 2.6% by weight; the alkali metal, expressed as M20, is in an amount of between 0.5 and 2.5% by weight.

3. The process according to claim 1, wherein the alkali metal is potassium.

4. The process according to claim 1, wherein the carrier has a surface area of less than 150 m2 / g.

5. The process according to claim 1, wherein the rector and the regenerator are of the fluid bed type.

6. The process according to claim 5, wherein the dehydrogenation is beaten at a temperature between 450 and 650 ° C, at a pressure that is atmospheric or slightly higher, at a space velocity of GHSV of between 100 and 1000 h " 1 and with a time of resistance of the catalyst in the area of the fluid bed varying from 5 to 30 minutes.

procedure according to 6, wherein the space velocity is between 150 and 200 h-1 and the residence time of the catalyst varies from 10 to 15 minutes.

8. The process according to the rei indication 5, wherein the regeneration is carried out with air or oxygen or other combustion support gas at a temperature which is higher than the average temperature of the reactor, at a pressure which is atmospheric or slightly higher, at a space speed of between 100 and 1000 h_1 and with a residence time of the solid varying from 5 to 60 minutes.

SUMMARY A procedure is described to obtain light olefins through the dehydrogenation of the corresponding paraffins, which consists of: a) reacting in a reactor, operating at a temperature between 450 and 800 Y, at 0.1 and 3 Absolute Atm and with a space capacity of GHSV between 100 and 10000 h "1 said paraffins with a catalyst system 0 containing chromium oxide, tin oxide, at least one alkali metal oxide () and an alumina carrier, in phase delta or theta or in .fases delta + teta mixed or teta + alpha or delta + teta + alpha, modified with silica, where: l ^ iWT - the chromium, expressed as Cr203 is in an amount between 6 and 30% by weight tin, expressed as SnO, is in an amount of between 0.1 and 3.5% by weight, the alkali metal, expressed as M20, 20 is in an amount of between 0.4 and 3% by weight, - the silica is in an amount between 0.08 and 3% by weight, the complement to 100 being of alumina, b) regen The said catalytic system is generated in a regenerator by burning the coke deposited on its surface operating at a temperature of more than 400 ° C.