RU2596870C1 - Method of controlling activity of catalyst for dehydrogenation of higher n-paraffins - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to organic chemistry, specifically, to processes of dehydrogenation with formation of non-aromatic compounds, containing carbon-carbon double bonds, catalytic method, and can be used in production of raw material, used in production of linear alkylbenzenes. Method of controlling activity of a catalyst for dehydrogenation of higher n-paraffins comprises in molar ratio hydrogen/raw material of 6/1, determining change of concentration of coke on surface of catalyst for dehydrogenation of diolefins and aromatic hydrocarbons using formula

where

is change in concentration of coke on surface of catalyst, mol/(unit volume·unit time); t is process time, s; k₁, k₂, k₃ are constants of rate of coke formation reactions of aromatic hydrocarbons, olefins (alkenes) and diolefins (dienes), (unit time)^-1; k₄ is constant of rate of coke formation reaction of carbon oxide (II), unit volume (mol·unit time);

is concentration of aromatic hydrocarbons, mol/unit volume;

is concentration of olefins, mol/unit volume;

is concentration of diolefins, mol/unit volume;

, C_CO is concentration of H₂ and CO respectively, mol/unit volume, at initial conditions at t=0:

taking into account change in concentration of coke, determining water consumption in reactor for dehydrogenation of raw material based on condition of satisfying next equality, wherein ratio of equilibrium constant when during variation of process temperature (T_i+1) to equilibrium constant at initial temperature (T₁) must be equal to 1:

where K_i+1, K₁ are equilibrium constants at T_i+1 and T₁, Pa²¹;

,

is initial amount of substance H₂O at T_i+1 and T₁, mol; n*_CO(i+1), n*_CO(1) is equilibrium amount of substance CO at T_i+1 and T₁, mol;

,

is equilibrium amount of substance H₂ at T_i+1 and T₁, mol.

EFFECT: increased output of end target product in molar ratio hydrogen/raw material equal to 6/1, and maintaining service life of catalyst.

1 cl, 2 tbl, 3 dwg, 1 ex

Description

The invention relates to organic chemistry, in particular to dehydrogenation processes with the formation of non-aromatic compounds containing carbon-carbon double bonds, by a catalytic method, and can be used in the production of raw materials used in the production of linear alkylbenzenes.

A known method of controlling the activity of the catalyst of the process of dehydrogenation of higher n-paraffins with a given molar ratio of hydrogen / raw material equal to 7/1 [US 7687676 B1, IPC C07C 5/333, publ. March 30, 2010], which provides for control of the flow of water into the dehydrogenation reactor when the temperature in the reactor changes. As the catalyst activity of the dehydrogenation process decreases, a gradual increase in the temperature in the reactor is performed to maintain the process productivity at a relatively constant level, in turn, an increase in temperature leads to an increase in the rate of side reactions. To reduce the rate of side (coke-forming) reactions with increasing temperature, control the flow of water into the reactor.

This method provides high efficiency of the dehydrogenation process, however, it does not allow to take into account the change in technological conditions: the molar ratio of hydrogen / raw materials, pressure and composition of the processed raw materials.

A known method of controlling the activity of a catalyst for the process of dehydrogenation of higher n-paraffins [RU 2486168 C1, IPC С07С 5/333 (2006.01), С07С 11/02 (2006.01), publ. 06.27.2013], selected as a prototype, which consists in regulating the activity of the catalyst by increasing the supply of water to the dehydrogenation reactor. The water flow rate is adjusted depending on the type of catalyst, while the ratio of the equilibrium constant when the process temperature changes to the equilibrium constant at the initial temperature should be equal to unity

where K _{i + 1} , K ₁ is the equilibrium constant at T _{i + 1} and T ₁ , Pa ²¹ ;

,

- начальное количество вещества Н₂О при T_i+1 и Т₁, моль;

,

- the initial amount of substance H ₂ O at T _{i + 1} and T ₁ , mol;

,

- равновесное количество вещества СО при T_i+1 и T₁, моль;

,

- the equilibrium amount of substance CO at T _{i + 1} and T ₁ , mol;

,

- равновесное количество вещества Н₂ при T_i+1 и Т₁, моль.

,

- amount of substance equilibrium H ₂ at T _{i + 1} and T ₁ mol.

The catalyst activity of the dehydrogenation process of higher n-paraffins is controlled by feeding the optimal amount of water to the dehydrogenation reactor, depending on the type of catalyst loaded, coke accumulation on its surface and the composition of the processed raw materials. The flow rate of water supplied to the dehydrogenation reactor is controlled at a given value of the molar ratio of hydrogen / feed equal to 7/1. The duration of the feed cycle of the catalyst was 310-320 days at a concentration of the target product (olefins) in the product stream after the dehydrogenation reactor 9.3% of the mass.

However, this method of controlling the activity of a dehydrogenation catalyst cannot be applied with a different molar ratio of hydrogen / feed to the system.

The objective of the invention is to develop a method for controlling the activity of the catalyst of the process of dehydrogenation of higher n-paraffins, which allows to increase the yield of the target product with a molar ratio of hydrogen / raw material equal to 6/1, and to preserve the life of the catalyst.

The problem is solved due to the fact that the method of controlling the activity of the catalyst of the process of dehydrogenation of higher n-paraffins, as in the prototype, is to control the activity of the catalyst by increasing the flow of water into the dehydrogenation reactor, according to the following reaction of the interaction of coke with water:

The water flow rate is adjusted depending on the type of catalyst and the process conditions, while the ratio of the equilibrium constant when the temperature (T _{i + 1} ) of the process changes to the equilibrium constant at the initial temperature (T ₁ ) should be equal to one:

where K _{i + 1} , K ₁ is the equilibrium constant at T _{i + 1} and T ₁ , Pa ²¹ ;

,

- начальное количество вещества Н₂О при T_i+1 и T₁, моль;

,

- the initial amount of substance H ₂ O at T _{i + 1} and T ₁ , mol;

,

- равновесное количество вещества СО при T_i+1 и T₁, моль;

,

- the equilibrium amount of substance CO at T _{i + 1} and T ₁ , mol;

,

- равновесное количество вещества Н₂ при T_i+1 и T₁, моль.

,

- the equilibrium amount of substance H ₂ at T _{i + 1} and T ₁ , mol.

According to the invention, before increasing the water supply to the reactor, the change in the coke concentration on the surface of the dehydrogenation catalyst from diolefins and aromatic hydrocarbons is determined by the formula:

- изменение концентрации кокса на поверхности катализатора, моль/(ед. объема·ед. времени);Where

- change in the concentration of coke on the surface of the catalyst, mol / (unit volume · unit time);

t is the process time, s;

k ₁ , k ₂ , k ₃ are the rate constants of coke formation reactions, respectively, from aromatic hydrocarbons, olefins (alkenes) and diolefins (dienes), (unit time) ^-1 ;

k ₄ is the rate constant of the reaction of coke formation from carbon monoxide (II), unit volume / (mol · unit time);

- концентрация ароматических углеводородов, моль/ед.объема;

- concentration of aromatic hydrocarbons, mol / ed.volume;

- концентрация олефинов, моль/ед.объема;

- concentration of olefins, mol / ed.volume;

- концентрация диолефинов, моль/ед.объема;

- concentration of diolefins, mol / ed.volume;

, C_CO - концентрация Н₂ и СО соответственно, моль/ед.объема.

, C _CO - the concentration of H ₂ and CO, respectively, mol / ed.volume.

Initial conditions at t = 0:

According to the scheme of hydrocarbon conversions in the process of dehydrogenation (Fig. 1), with a decrease in the partial pressure of hydrogen in the system (molar ratio of hydrogen / feed), it is necessary to compensate for the change in the coke concentration on the catalyst by additional supply of water for its oxidation by the reaction:

In the proposed method, the dynamics of the water supply to the reactor differs from the prototype of the feed cycle of the catalyst, since the change in coke concentration during side reactions of coke formation is taken into account under conditions of a decrease in the concentration of hydrogen in the reaction medium.

When the molar ratio of hydrogen / feed 6/1 in comparison with the prototype increases the concentration of diolefins and aromatic hydrocarbons in the product mixture of the dehydrogenation reactor, therefore, increases the concentration of coke on the surface of the dehydrogenation catalyst. To compensate for the decrease in the activity of the dehydrogenation catalyst at a molar ratio of hydrogen / feedstock 6/1, the water flow to the dehydrogenation reactor is increased, which ensures the maintenance of the catalyst service life and an increase in the olefin yield due to a shift in the equilibrium of the reversible dehydrogenation reaction of higher n-paraffins towards the formation of the target product.

In FIG. 1 shows a diagram of the conversion of hydrocarbons in the process of dehydrogenation.

In FIG. 2 shows the active window of a program for modeling a method for controlling the activity of a catalyst for the process of dehydrogenation of higher n-paraffins.

In FIG. Figure 3 shows the dependence of the coke content on the dehydrogenation catalyst during the process at various molar ratios of hydrogen / feed.

Table 1 shows the dependence of the flow of water into the reactor on the process temperature and the coke concentration on the catalyst surface for a molar ratio of hydrogen / feed 6/1 and 7/1.

Table 2 presents the dependence of the flow of water into the dehydrogenation reactor on the concentration of olefins, diolefins, aromatic hydrocarbons and coke on the surface of the catalyst at different molar ratios of hydrogen / feed and process temperature.

The proposed method for controlling the catalyst activity of the process of dehydrogenation of higher n-paraffins was modeled using a program for calculating the process of dehydrogenation of higher n-paraffins (Fig. 2), developed on the basis of a mathematical model of the process that takes into account the change in the activity of the catalyst with a change in the concentration of coke on its surface, as well as water and hydrogen in the system. This program made it possible to forecast the flow rate of water supplied to the reactor at a given molar hydrogen / feed ratio of 6/1, while varying the process parameters, composition and flow rate of the processed feed. In particular, the dependence of water flow on temperature in the reactor and the coke concentration on the catalyst surface was obtained (Table 1), as well as the dependence of the change in coke concentration on the catalyst surface on the molar ratio of hydrogen / feed (Fig. 3).

When carrying out the process with a molar ratio of hydrogen / raw materials equal to 6/1, ceteris paribus, the highest coke concentration on the catalyst surface is achieved, compared with the operation of the catalyst with a molar ratio in the range from 7/1 to 8/1 (Fig. . 2). At a molar ratio of 6/1, the flow rate of water to the dehydrogenation reactor is increased to maintain the catalyst service life at a level of 310-320 days and increase the yield of olefins by shifting the equilibrium of the reversible dehydrogenation reaction of higher n-paraffins towards the formation of the target product with concentrations of 9.5-10 , 2% of the mass.

The invention is illustrated by examples.

Example 1

The catalyst for the dehydrogenation process (Pt content of 0.92%, the carrier is cordierite with the application of α-Al ₂ O ₃ ) higher n-paraffins (C ₉ -C ₁₄ ) with a working temperature range of 469-486 ° C. The dehydrogenation process was carried out under conditions of different molar ratios of hydrogen / feed - 6/1 and 7/1 during the processing of feedstock composition (% wt.): C ₉ H ₂ O = 0,0-0,01; C ₁₀ H ₂₂ = 13.5-15.5; C ₁₁ H ₂₄ = 28.0-30.0; C ₁₂ H ₂₆ = 29.5-32.0; C ₁₃ H ₂₈ = 20.5-23.0; C ₁₄ H ₃₀ = 0.3-0.4 at a pressure of 0.19-0.20 MPa.

The concentration of olefins, diolefins, aromatic hydrocarbons in the product mixture after the dehydrogenation reactor at a molar ratio of hydrogen / feed 6/1 and 7/1 are presented in table 2.

Using a program for calculating the dehydrogenation process, a simulation was performed and the coke concentration on the surface of the dehydrogenation catalyst of higher n-paraffins was determined. The value of the coke concentration at a molar ratio of hydrogen / raw materials equal to 6/1 and 7/1 is presented in table 2.

Given the change in the coke concentration, we determined the water flow in the dehydrogenation reactor of higher n-paraffins, checking that the ratio of the equilibrium constant when the process temperature changes to the equilibrium constant at the initial temperature, which should be equal to 1.

The flow rate of water to the dehydrogenation reactor was increased at a hydrogen / feed molar ratio of 6/1 to 4.5 l / h at 470.6 ° C, to 6.0 l / h at 471.5 ° C, to 8.0 l / h at 473.4 ° C, up to 9.0 l / h at 474.7 ° C, up to 10.0 l / h at 476.2 ° C, up to 12.0 l / h at 479.6 ° C, up to 13.0 l / h at 481.5 ° С, up to 13.5 l / h at 483.2 ° С, up to 14.0 l / h at 486.0 ° С.

With an increased supply of water to the dehydrogenation reactor at a molar ratio of hydrogen / feed to 6/1, an increase in the concentration of olefins in the product stream is observed compared to carrying out the process at a molar ratio of hydrogen / feed to 7/1, an average of 0.32% by weight.

The recommendations obtained using the program for modeling the process of dehydrogenation of higher n-paraffins were used during the process at an industrial plant for the production of olefins in the city of Kirishi. The proposed mode for water supply from 4 to 9-12 l / h, depending on the temperature of the process and the composition of the feed, allowed to reduce the coke concentration on the catalyst surface with a molar ratio of hydrogen / feed to 6/1 and to increase the yield of olefins by 3-5%.

Comparison of different modes of water supply at different molar ratios of hydrogen / feed showed that the duration of the feed cycle of the dehydrogenation catalyst remained at the level of 340-360 days at a concentration of olefins in the product stream after the dehydrogenation reactor at a molar ratio of hydrogen / feed to 6/1, at about 9.5-10.2% of the mass. instead of 8.8-9.3% by weight, with a molar ratio of hydrogen / feed equal to 7/1. The ratio of the concentration of olefins to the concentration of diolefins in the product stream of the dehydrogenation process increased with a decrease in the molar ratio of hydrogen / feed from 7/1 (17.9 at 470.5 ° C) to 6/1 (19.8 at 470.5 °), which indicates an increase in the selectivity of the process over the feed cycle of the catalyst by 7.0-10.0%.

Claims (1)

A method for controlling the activity of a catalyst for the process of dehydrogenation of higher n-paraffins, which consists in the fact that when the molar ratio of hydrogen / feedstock is 6/1, the change in the concentration of coke on the surface of the dehydrogenation catalyst from diolefins and aromatic hydrocarbons is determined by the formula:

Where

- change in the concentration of coke on the surface of the catalyst, mol / (unit volume · unit time);
t is the process time, s;
k ₁ , k ₂ , k ₃ are the rate constants of coke formation reactions, respectively, from aromatic hydrocarbons, olefins (alkenes) and diolefins (dienes), (unit time) ^-1 ;
k ₄ - rate constant of the reaction of coke formation from carbon monoxide (II), units volume / (mol · unit of time);

- concentration of aromatic hydrocarbons, mol / unit volume;

- concentration of olefins, mol / unit volume;

- concentration of diolefins, mol / unit volume;

- the concentration of H ₂ and CO, respectively, mol / unit. volume, under initial conditions at t = 0:

taking into account the change in the coke concentration, the water flow in the dehydrogenation reactor is determined based on the condition for the following equality to be fulfilled, in which the ratio of the equilibrium constant when the temperature (T _{i + 1} ) of the process changes to the equilibrium constant at the initial temperature (T ₁ ) is 1:

where K _{i + 1} , K ₁ is the equilibrium constant at T _{i + 1} and T ₁ , Pa ²¹ ;

- the initial amount of substance H ₂ O at T _{i + 1} and T ₁ , mol;

- the equilibrium amount of substance CO at T _{i + 1} and T ₁ , mol;

- the equilibrium amount of substance H ₂ at T _{i + 1} and T ₁ , mol.

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