RU2159676C1 - Method of regenerating catalysts for dehydrocyclodimerization of aliphatic hydrocarbons - Google Patents

Abstract

FIELD: dehydrogenation catalysts. SUBSTANCE: invention relates to regeneration of catalysts containing Pentasil-type zeolite deactivated by coking during dehydrocyclodimerization of aliphatic hydrocarbons. Regeneration is accomplished by treating catalyst at 300-500 C and pressure 0.1-2.0 MPa with nitrogen-oxygen mixture, in which oxygen content is gradually raised from 0.1 to 21 mol %, after which catalyst is kept in mixture with attained oxygen content. In latter step, gas mixture is circulated over closed circuit thereby removing moisture and partially burning products from catalyst while nitrogen is continuously replenished. Required volume of the replenishment nitrogen Q(r) is determined from condition: Q(r) > Q(ox), where Q(r) is volume of removed components under working conditions in reactor. EFFECT: reduced power consumption due to reuse of regeneration spent gas. 1 dwg, 2 ex

Description

 The invention relates to processes for the regeneration of catalysts containing pentasil type zeolite deactivated as a result of coke deposition during the dehydrocyclodimerization reaction of aliphatic hydrocarbons.

A known method of regeneration of a dehydrocyclodimerization catalyst (US Patent N 4795845 IPC G 7 C 12/02, 1989). According to this method, the coked catalyst is regenerated with a gas containing from 0.1 to 23% molar oxygen, at a temperature of 300 - 700 ^o C and above, with a pressure of 0.1 - 2 MPa. The coke content of the lost activity catalyst may be 20%, typically 0.5-7%.

 During the regeneration, the oxygen content in the gas is increased, based on the temperature of the end of the catalyst bed, in order to quickly change the process conditions and avoid thermal deactivation of the catalyst.

 According to the description, the regeneration is carried out in two stages: the main burnout and the final removal of coke. At the first stage, the oxygen content in the gas at the inlet to the reactor is maintained at about 1% molar. The end of this stage corresponds to a "slip" of oxygen, i.e. equality of oxygen concentrations in the gas at the inlet to the reactor and at the outlet of it. At the stage of final coke burning, the oxygen content is slowly increased to 7% molar or more. The end of the second stage is evidenced by a decrease in temperature at the outlet of the reactor and temperature equalization along the height of the catalyst layer. Then carry out a control burn of coke in a stream of air.

The dehydrocyclodimerization process is carried out in the presence of a catalytic composition comprising phosphorus-containing alumina, gallium and crystalline aluminosilicate zeolite with a ratio of SiO ₂ / Al ₂ O _{3 of} at least 12. Preference is given to pentasil zeolites: ZSM-5, ZSM-8, ZSM-11, ZSM -15, ZSM-35.

The regeneration temperature under the conditions of this method can reach 700 ^o C and above.

Such an increase in temperature can be spasmodic and uncontrollable in nature and can occur at a high initial coke content (more than 7%) and any, even low (less than 1%) oxygen content in the regenerating gas. (R. Hughes. Deactivation of catalysts, M. Chemistry, 1959, 280 p.)
The disadvantage of this method is the high regeneration temperature at any initial coke content on the catalyst, which reduces the activity and the service life of the catalyst.

A known method of regeneration of zeolite catalysts for the dehydrocyclodimerization of aliphatic hydrocarbons containing a crystalline aluminosilicate of the pentasil type with a ratio of SiO ₂ / Al ₂ O _{3 of} not less than 12, by treating the catalyst at an elevated temperature of 300 - 550 ^o C and a pressure of 0.1 - 2.0 MPa with a nitrogen-oxygen mixture with increasing oxygen content in the mixture from 0.1 to 21 mol. % and subsequent exposure of the catalyst in this environment. The change in the oxygen content in the nitrogen-oxygen mixture is carried out by pulses with a period from 0.2 to 8 hours and an amplitude from 0.1 to 10 mol.% Until the coke is completely removed from the catalyst. In this case, from the regeneration it is used on the "Channel", i.e. thrown onto a candle (into the atmosphere) (see Patent N 2079361 IPC B 01 J 29/90, 38/14 publ. 08.20.97).

This method is taken by us as a prototype. According to this method, a stepwise regeneration of the catalyst is carried out on the “Protok” nitrogen pre-heated in the furnace with a normalized oxygen content. The regeneration process includes the following stages:
hydrocarbon purging while cooling the reactors;
burn coke with a content of O ₂ = 0.5%,
burn coke with a content of O ₂ = 1.2%,
burning coke with a content of O ₂ = 5.0%;
exposure to air;
purging reactors with nitrogen to an O ₂ content of 0.5%.

 The duration of the regeneration stages depends on the degree of coking of the catalyst and is controlled by the composition of the regeneration exhaust gas and the temperature in the reactor.

 In the said method, regeneration gas is used on the "Flow", i.e. To continue the regeneration process, a continuous supply of nitrogen is required, which entails the need for continuous operation of the nitrogen production unit and, therefore, requires additional energy costs for air separation.

 The objective of the invention is to reduce energy costs through the secondary use of exhaust gas regeneration.

The problem is solved in that in the method for the regeneration of zeolite catalysts for the dehydrocyclodimerization of hydrocarbons containing a crystalline aluminosilicate of the pentasil type with a SiO ₂ / Al ₂ O ₃ ratio of at least 12, by pre-purging the reactor system with nitrogen from hydrocarbons to the afterburner to a fuel content of <0.5 %, treatment of the catalyst at an elevated temperature of 300 - 550 ^o C and a pressure of 0.1 - 2.0 MPa azotnokislorodnoy mixture with increasing oxygen content in the mixture of from 0.1 to 21 mol%, and then maintaining the catalyst in this media. by pumping the mixture in a closed circuit with a tap formed during moisture of combustion and the combustion products with continuous replenishment of fresh nitrogen, while the amount corresponding to nitrogen recharge (Q _n) is determined from the condition that Q _n> Q _c, where Q _c - number of allocated components in m ³ under operating thermobaric conditions in the reactor.

An essential distinguishing feature of the claimed invention is that the exposure of the catalyst in a nitrogen-oxygen mixture is carried out by pumping this mixture in a closed circuit with the removal of moisture formed during the combustion process and part of the combustion products continuously fed with fresh nitrogen, while the volume of the corresponding nitrogen feed (Q _p ) is determined from the conditions that Q _p > Q _ok , where Q _ok - the number of components removed in m ³ under operating thermobaric conditions in the reactor.

 The above significant distinguishing features were unknown to us from patent and scientific and technical information, which allows us to conclude that they meet the criterion of "Novelty."

 Since the essential distinguishing features are not obvious to the average specialist in our industry, we believe that they meet the criterion of "Inventive step".

 The method for the regeneration of zeolite catalysts for the dehydrocyclodimerization of hydrocarbons has successfully passed the test at the zeoforming unit of the Sosnogorsk gas processing plant, which allows us to talk about the compliance of the claimed invention with the criterion of "Industrial applicability".

 In the process of regeneration, the content of oxygen in the regeneration gas mixture is of great importance. At a high oxygen content, an uncontrolled increase in temperature in the reactor occurs, due to the increased intensity of coke burning, which leads to overheating and, as a consequence, destruction of the catalyst. With the burning of coke and residual hydrocarbons in the presence of oxygen, the formation of water vapor, nitrogen oxides and carbon, which are no longer involved in the combustion process. In the second use of the regeneration gas, the combustion products are components inert to the combustion process. Thus, the regeneration gas can be used according to the recirculation scheme.

 The method of regeneration of zeolite catalysts for the dehydrocyclodimerization of hydrocarbons will be explained using the schematic diagram shown in the drawing.

 A schematic diagram of the regeneration of zeolite catalysts contains a nitrogen accumulation receiver 1, a compressor 2, a heating furnace 3, a reactor 4, a afterburner 5, an air cooling apparatus 6, a separator for separating moisture and dissolved combustion products from the regeneration gas 7.

 Initially, the reactor system is purged with nitrogen from hydrocarbons to the afterburner 5 (to a fuel content of <0.5%). The supply of nitrogen is carried out from the receiver of nitrogen storage 1. Before feeding from the receiver 4, the regeneration gas is heated in a heating furnace 3.

 After purging the system, the release of regeneration gas to the candle is stopped and then regeneration is carried out by pumping the nitrogen-oxygen mixture in a closed loop.

To prevent significant accumulation in the gas of regeneration of the combustion products, a part of the gas leaving the reactor is continuously removed and the system is fed with fresh nitrogen. The required volume of exhaust gas and related recharge is about 10%. In the general case, the feed amount (Q _p ) is determined by the conditions of regeneration and the degree of coking of the catalyst, in any case, the feed amount of the circuit should be not less than the volume of moisture removed and the combustion products dissolved in it (Q _ok ) in terms of operating thermobaric conditions in the reactor, t .e. the condition Q _n > Q _approx . Technologically, the amount of recharge is determined by the flow rate of the regeneration gas after the furnace.

 The regeneration gas leaving the reactor block is cooled in air coolers 6 and passed through a separator 7 to remove condensed moisture and dissolved part of the combustion products, then the gas is compressed in the compressor 2 and again sent to the reactor block 4. To reduce the amount of nitrogen needed to feed the process schemes, it is possible to use an intermediate technological scheme for gas purification (not shown), including absorption absorption of combustion products and adsorption drying.

As coke is burned, air is dosed into the technological scheme to a normalized oxygen concentration. In the final stage of the regeneration cycle, the technological scheme is purged with pure nitrogen from oxygen (up to O ₂ content <0.5%) with emission into the atmosphere.

 After the regeneration cycle is completed, the receiver of nitrogen accumulation 1 is filled.

Example 1 (Prototype)
Purge the system of receivers 4 from hydrocarbons while cooling the reactors from 450 ^o C to 250 ^o C, the purge was carried out for 12 hours. Then, coke was burned at a content of O ₂ = 0.5% for 60 hours. After that, coke was burned at a content of O ₂ = 1.2% for 60 hours. Next, coke was burned at an O ₂ content of 5.0% for a duration of 25 hours. Then made exposure in air, lasting 15 hours. Finally, the reactors were purged with nitrogen to an O ₂ content of 0.5% for 1 hour.

In total, the regeneration time of the zeolite catalyst was 158 hours with a nitrogen flow of 400 m ³ / h, i.e. the consumed volume of nitrogen was 63,200 m ³ .

Example 2
Purge the receiver system with 4 nitrogen from hydrocarbons lasting 2 hours with a nitrogen flow of 400 m ³ / h.

Next, burn at a content of O ₂ = 0.5% for a duration of 60 hours with a nitrogen flow rate of 40 m ³ / h to replenish the technological scheme, then burn coke at a content of O ₂ = 1.2%, a duration of 60 hours, with a nitrogen flow rate of replenishment of the technological scheme 40 m ³ / h. After that, coke is burned at a content of O ₂ = 5.0%, lasting 25 hours, with a nitrogen flow rate of 40 m ³ / h for replenishing the technological scheme, and then holding in air for 15 hours. Finally, the receiver system is purged with 4 nitrogen to an O ₂ content of 0.5% for 1 hour with a nitrogen flow of 400 m ³ / h.

In total, the regeneration time of zeolite catalysts is 3 hours with a nitrogen flow rate of 400 m ³ / h, i.e. the consumed volume of nitrogen is 1200 m ³ and 145 hours with a nitrogen flow of 40 m ³ / h to replenish the technological scheme, i.e. the consumed volume of nitrogen will be 5800 m ^{3; the} total amount of nitrogen consumed will be 7000 m ³ .

 Thus, when using the claimed technical solution, during regeneration of the zeolite catalyst, the latter is aged in a nitrogen-oxygen mixture by pumping this mixture in a closed loop, where the maximum nitrogen consumption occurs during preliminary purging of the system from hydrocarbons and final purging from oxygen, and the rest of the time only replenishment of the technological mixture in the amount of up to 10%. Given that the purge of the technological scheme is 2–3% of the total regeneration time, the nitrogen consumption for the regeneration cycle is reduced by 8–10 times. The claimed invention in comparison with the prototype can significantly reduce energy costs.

Claims (1)

The method of regeneration of zeolite catalysts for the dehydrocyclodimerization of hydrocarbons containing a crystalline aluminosilicate of the pentasil type with a ratio of SiO ₂ / Al ₂ O _{3 of} at least 12, by treating the catalyst at an elevated temperature of 300 - 550 ^o C and a pressure of 0.1 - 2 MPa with an oxygen-nitrogen mixture with an increase in oxygen content in a mixture of 0.1 to 21 mol.% and subsequent exposure of the catalyst in this medium, characterized in that the regeneration of the catalyst in a nitrogen-oxygen mixture is carried out by pumping this mixture in a closed circuit with a tap forming during combustion of moisture and part of the products of combustion with continuous replenishment with fresh nitrogen, while the volume of the corresponding replenishment with nitrogen (Q _n ) is determined from the conditions that Q _n > Q _ok , where Q _ok is the number of components removed in m ³ under operating conditions in the reactor.