RU2447048C1 - Combined method of producing ethylene and derivatives thereof and electrical energy from natural gas - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing ethylene and electrical energy from natural gas through direct oxidation of natural gas and then feeding the waste gas into an electric power installation. The method involves feeding the initial stream of natural gas to the step for synthesis of ethylene via oxidative condensation of methane, which is carried out in the presence of oxide catalysts at temperature 700°C-950°C, pressure 1-10 atm and molar ratio of methane to oxygen in the interval from 2:1 to 10:1. Further, ethylene, the remaining portion of the gas stream containing unreacted methane and combustible products hydrogen and CO are extracted from the reaction mixture and fed into the electric power installation in which electrical energy and heat are regenerated. Energy, which is released during synthesis of ethylene via oxidative condensation of methane in form of heat content of vapour and other heat carriers, is recycled together with energy generated by the electric power installation, which is powered by natural methane gas which has not reacted in the ethylene synthesis reactor.

EFFECT: method provides economic and technological advantages compared to existing production processes.

5 cl, 1 dwg

Description

The invention relates to the field of energy and the technology of basic organic synthesis, namely to the production technology of ethylene and its derivatives, and can be used in the energy and chemical industries.

Modern processes for the production of many large-tonnage products of basic organic synthesis are accompanied by both large energy expenditures and intense energy release, and are often based on the same hydrocarbon feedstock used for electricity production. Therefore, combined (integrated) energy-chemical processes for the production (cogeneration) of chemical products and energy are becoming more widespread.

A known process for the simultaneous production (cogeneration) of methanol and electricity, including the production of synthesis gas, consisting of H ₂ , CO, CO ₂ and small amounts of methane, is reformed by feeding lower hydrocarbons, incl. natural gas, and steam to the reforming unit, the separation of synthesis gas into two streams, one of which is used as raw material for one or more synthesis reactions of methanol and / or dimethyl ether and / or other oxygenates, while the other stream fed to one or more reactors for the water gas conversion reaction, resulting in the formation of a gas stream consisting mainly of H ₂ and CO ₂ , then subjected to separation into two streams consisting of H ₂ and CO ₂ , respectively, with at least at least 5% containing H ₂ the stream is fed to a methanol synthesis reactor, and the remainder of the H ₂ containing stream is fed to one or more heat generation units or other H ₂ consuming processes. (US Patent No. 6809121, IPC C07C 29/151; C10G 2/00, publ. 10/26/2004)

A combined method of producing electricity and liquid synthetic fuel using gas turbine and combined cycle plants is known.

The method includes partial oxidation of hydrocarbon fuel in a stream of compressed air taken after a high-pressure compressor of a gas turbine unit with subsequent booster, synthesis gas, its cooling and environmental cleaning, supplying the resulting synthesis gas to a single-pass liquid synthetic fuel synthesis reactor with partial conversion of synthesis gas gas to liquid fuel. The energy gas remaining in the liquid synthetic fuel synthesis reactor is discharged into the combustion chamber of the gas turbine installation, while the degree of conversion of the synthesis gas is selected from the condition of maintaining the temperature of the working fluid at the inlet of the gas turbine depending on the type of gas turbine used to generate electricity, and subsequent booster air taken after the high-pressure compressor of a gas turbine installation is carried out using an expander driven by energy gas, heated by cooling the synthesis gas in front of the synthesis reactor. (RF patent No. 2250872, IPC C01B 3/32, C10L 3/10, F01K 23/10, publ. 04/27/2005)

A disadvantage of the known methods is the difficulty of obtaining and further preparing synthesis gas and the associated high technological complexity of the whole process, which excludes the possibility of its use for small-tonnage productions and as a part of power plants of medium and low power.

Known is a combined method of producing electricity and synthetic liquid fuel as part of a combined cycle plant.

The method includes compressing the air in the main and booster compressors, partial oxidation of the hydrocarbon-containing fuel in the reactor, cooling the reaction mixture, producing methanol, expanding the products of incomplete oxidation with feeding them to the combustion chamber of a gas turbine. In this case, the hydrocarbon-containing fuel undergoes sequential oxidation at a temperature of 380-450 ° C and a pressure of 4.5-10 MPa, followed by cooling of the reaction mixture in a condenser refrigerator with condensate from a steam turbine plant. The separation of methanol from liquid oxidation products is carried out in a distillation column. A predetermined temperature of the gas at the entrance to the gas turbine is provided by the accepted number of methanol synthesis reactor units or by mixing the initial hydrocarbon-containing fuel into the combustion chamber of the gas turbine. (RF patent No. 2356877, IPC C07C 27/12, C07C 31/04, published on 05.27.2009)

The disadvantage of this method is the low degree of conversion of the starting hydrocarbons to the target product is methanol, which does not exceed 1-2% with a selectivity above 70%. At deeper degrees of conversion, methanol selectivity decreases to zero.

The integrated process for the production of Fischer-Tropsch liquid products (synthetic liquid hydrocarbons) and the production of electricity with low CO ₂ emissions is known. An installation that implements the known method includes the production of synthesis gas, air separation, the synthesis of Fischer-Tropsch products, CO extraction and power generation based on the combined steam and gas cycle (US Patent No. 6976362, IPC C01B 3/32, publ. December 20, 2005 )

A disadvantage of the known process is the large number of stages associated with the production and further preparation of synthesis gas, and, as a result, its high metal consumption and technological complexity, which excludes the possibility of application for small-tonnage productions and power plants of medium and low power. In addition, Fischer-Tropsch synthesis products are in fact a synthetic analogue of crude oil and require further processing into fuels or chemical products. In the presence of cheaper natural petroleum products, their production, even taking into account their higher environmental characteristics, can be economically justified only in individual cases.

More promising is the integrated production of electricity and such versatile and energy-intensive products as ethylene and its products (liquid hydrocarbons, ethyl alcohol, polyethylene). Ethylene is one of the main large-scale products of organic synthesis and is the basis for the production of most products of basic and fine organic synthesis. In addition, using the oligomerization process, ethylene can be processed into synthetic fuels and oils similar to traditional fuels and lubricants derived from oil, and “synthetic oil” - a mixture of liquid products that can be easily transported by traditional methods (bulk transport, pipelines) and processed into conventional refineries enterprises. Ethyl alcohol (ethanol) is itself a liquid combustible product and is considered as a promising energy carrier for various applications. Ethylene-based polymers (for example, various types and brands of polyethylene, copolymers with other monomers) are the main types of plastics used universally. For these reasons, the creation of highly efficient and economical technologies for the production of ethylene and its products is one of the main tasks of the modern chemical industry.

According to the technologies existing and implemented in industry, ethylene is obtained mainly by the pyrolysis of various hydrocarbon feedstocks (naphtha, propane-butane fraction, ethane, etc.). This sharply limits the raw material base of ethylene production. In addition, these processes are endothermic, i.e. require for their implementation the supply of a significant amount of energy, which further reduces their efficiency and makes them ineffective with small volumes of production.

Currently, direct interest, bypassing the stage of synthesis gas production, is the process of obtaining various products from natural gas (methane) based on its oxidative transformations. Such processes have several advantages: the simplicity of the technological scheme, the absence of chemical stages that occur with the absorption of energy, the possibility of simultaneous production of the target product of heat generation.

In particular, the process of producing ethylene is known from the oxidative condensation of methane (OKM), which takes place in the presence of oxide catalysts at temperatures of 700-900 ° C with a supply of oxygen (air) below the stoichiometric ratio (0.1-0.3 volume of O ₂ per 1 volume of methane). This process is exothermic, i.e. proceeds with the release of energy, and does not require metal-intensive equipment to carry out the main reaction. (BCArutyunov, O.V. Krylov. Oxidative transformations of methane, Moscow: Nauka, 1998, 361 pp.)

The main disadvantage of this process is the relatively low yield of the target product, ethylene, in one pass of the reaction mixture (not higher than 14-15%) and the high consumption of raw materials (natural gas) to obtain the target product.

The technical problem to which the claimed invention is directed is to create a highly efficient and economical method for producing ethylene and products of its processing by combining their production by direct gas-phase oxidation of natural gas with the generation of electric and thermal energy in a power plant.

The stated technical problem is solved by the fact that in the method of producing ethylene and electricity from natural gas by direct oxidation of natural gas, followed by the supply of exhaust gas to the power plant, which consists in the fact that the initial stream of natural gas is sent to the stage of ethylene synthesis by the oxidative condensation of methane, which carried out in the presence of oxide catalysts at a temperature of from 700 ° C to 950 ° C, a pressure of from 1 ATM to 10 ATM and a molar ratio of methane to oxygen in the range from 2: 1 to 10: 1, then in fissioning ethylene from the reaction mixture, the remainder of the gaseous stream comprising unreacted methane and combustible products are hydrogen and CO is directed to power generation in which power generation is carried out and heat; the energy released in the process of ethylene production by the oxidative condensation of methane in the form of the heat content of steam and other heat carriers is utilized together with the energy generated by the power plant, which is fed by natural gas with methane that has not reacted in the ethylene synthesis reactor.

In addition, they carry out the separation of ethane and higher hydrocarbons from the flow of combustible gases, which are sent to a power plant, where they generate electricity and heat; the separated ethane and higher hydrocarbons are sent to the stage of ethylene synthesis by the oxidative condensation of methane.

In addition, the oxide catalyst is selected from the group: oxides of alkaline earth elements Mg, Ca, Sr, Ba, oxides of rare-earth elements La, Ce, Nd, Sm, or mixtures thereof, promoted by additives of alkaline elements (Li, Na, K, Rb, Cs), Sb, Bi and / or Pb supported on Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , HfO ₂ supports, aluminates, alkaline earth element silicates, rare earth silicates.

In addition, the composition of the oxide catalyst is selected in accordance with the empirical formula

M ¹ _a M ² _b M ³ ₂ O _{3 + m} , where

M ¹ is an alkaline earth element selected from the group Mg, Ca, Sr, Ba (or a combination thereof);

M ² is an alkaline element selected from the group Li, Na, K, Rb, Cs (or a combination thereof);

M ³ is a rare earth element selected from the group La, Ce, Nd, Sm (or a combination thereof);

a is the gram-atomic index of the element, the value of which is selected from 0.005 to 250;

b is the gram-atomic index of the element, the value of which is selected from 0 to 20;

m is a stoichiometric coefficient determined by the ratio of the components M ¹ , M ² and M ³ .

In addition, the composition of the oxide catalyst is selected in accordance with the empirical formula

Na _X W _Y M _Z SiO _{2 + n} , where

M is a chemical element of Mn or Ce,

X, Y, Z - gram-atomic ratios of elements, from which the value of X is chosen from 0.01 to 0.4; the value of Y is selected from 0.005 to 0.2; Z value is selected from 0.005 to 0.4.

The technical result, the achievement of which is ensured by the implementation of the entire claimed combination of essential features, is

- in combining the production of valuable compounds by the method of direct gas-phase oxidation of natural gas with the generation of electric and thermal energy at a power plant,

- in reducing the specific consumption of natural gas for the production of ethylene and its derivatives.

Also, given that the exhaust gas from the process for producing ethylene and its derivatives is fully used for energy production, and the steam generated in exothermic oxidation reactions is utilized together with the steam generated by the power plant itself, the total efficiency of the useful use of hydrocarbon raw materials in such an integrated energy-chemical process will be close to as much as possible.

The invention is illustrated in the figure, where figure 1 presents an example of a natural gas-fired power plant, which can be implemented in the inventive method. The presented example does not limit the use of other equipment designed for the same purposes on which the method can be implemented.

Figure 1 contains the following positions:

1 - reactor for oxidative condensation of methane (OKM);

2 - quenching-evaporative heat exchanger (high pressure steam generator);

3 - heat exchanger, in which the gas mixture is cooled to ~ 30 ° C with condensation of the main part of the reaction water;

4 - a compressor of the reaction gas;

5 - site ethanolamine purification;

6 - site alkaline washing, drying and cooling to minus 100 ° C using propylene and ethylene refrigeration cycles;

7 - turboexpander;

8 - a column of low-temperature distillation (separation of ethane-ethylene fraction);

9 - a column of low temperature distillation (separation of raw ethylene);

10 - a column of low-temperature distillation (methane emission);

11 - recuperative heat exchanger gas-gas.

The inventive method is as follows.

Natural gas from the gas pipeline, containing 98% methane and entering the power plant in the amount of 60 thousand m ³ / h, is heated in a recuperative gas-gas heat exchanger 11 by heat of the gases leaving the reactor 1 to 450 ° C and fed to the inlet of the reactor 1, in which a part of methane is converted to ethylene and other products due to the catalytic oxidative condensation of methane with the release of heat.

To increase the heat utilization efficiency of the reaction gases, the source natural gas is supplied to the tube space of the heat exchanger 11, and the hot reaction gases are fed countercurrently into the annulus of the same heat exchanger.

The oxidative condensation reaction of methane in the reactor 1 is carried out in the presence of oxide catalysts at a temperature of from 700 ° C to 950 ° C, preferably from 750 ° C to 900 ° C, a pressure of from 1 atm to 10 atm, preferably from 1 atm to 3 atm, and the molar ratio of methane to oxygen in the range from 2: 1 to 10: 1.

The oxide catalyst is selected from the group: oxides of alkaline earth elements Mg, Ca, Sr, Ba, oxides of rare-earth elements La, Ce, Nd, Sm, or mixtures thereof, promoted by additives of alkaline elements (Li, Na, K, Rb, Cs), Sb, Bi and / or Pb supported on carriers Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , HfO ₂ , aluminates, silicates of alkaline earth elements, silicates of rare earth elements.

The composition of the oxide catalyst is selected in accordance with the empirical formula:

M ¹ _a M ¹ _b M ³ ₂ O _{3 + m} , where

M ¹ is an alkaline earth element selected from the group Mg, Ca, Sr, Ba (or a combination thereof);

M ² is an alkaline element selected from the group Li, Na, K, Rb, Cs (or a combination thereof);

M ³ is a rare earth element selected from the group La, Ce, Nd, Sm (or a combination thereof);

a is the gram-atomic index of the element, the value of which is selected from 0.005 to 250;

b is the gram-atomic index of the element, the value of which is selected from 0 to 20;

m is a stoichiometric coefficient determined by the ratio of the components M ¹ , M ² and M ³ .

In addition, the composition of the oxide catalyst is selected in accordance with the empirical formula

Na _X W _Y M _Z SiO _{2 + n} , where

M is a chemical element of Mn or Ce,

X, Y, Z - gram-atomic ratios of elements, from which the value of X is chosen from 0.01 to 0.4; the value of Y is selected from 0.005 to 0.2; Z value is selected from 0.005 to 0.4.

Catalysts for the process of oxidative condensation of methane to produce ethylene are known from the prior art, in particular the publication BC Arutyunov, O.V. Krylov. Oxidative transformations of methane, Moscow: Nauka, 1998, 361 pages, which describes the catalytic properties of mixed oxides containing cations of rare earth, alkaline earth, and alkali metals in various ratios, and a detailed bibliography is provided (references to patents and scientific publications). The totality of these data shows that the systems containing the first members of a series of lanthanides (La, Nd, Sm and, in certain combinations, also Ce and Pr) are most effective. The best indicators for the yield of OKM products on catalysts of this family (independently confirmed by many authors) reach 18-19% with a selectivity above 60%. On page 245 of the same monograph, oxide catalysts are described that correspond to the empirical formula Na _X W _Y Mn _Z SiO _{2 + n} and were first proposed in [Fang XP, Li SB, Lin JZJ Mol. Catal. (China), v.6, 1992, p.225]. These catalysts (for example, with a composition of 20% Na ₂ WO ₄ + 5% Mn / SiO ₂ ) provide the highest confirmed yield of OKM products (20-22%), but at a higher temperature (850-900 ° C compared to the optimum for systems containing lanthanides - 750-850 ° C).

All parameter ranges of the proposed method are indicated in the maximum permissible values, the choice of method parameters outside the declared ranges of values does not ensure the achievement of the specified technical result.

The gas stream leaving the reactor 1 having a high heat content and containing the target product of the chemical conversion, ethylene, is subjected to cooling and separation, and the heat generated during the cooling process is used to heat the initial methane in the apparatus 11 and generate high potential steam in the quenching-evaporative heat exchanger (generator high pressure steam) 2. The heat content of steam generated in the quenching-evaporative heat exchanger 2 is disposed of in a power plant together with heat Obtained by the combustion of methane and unreacted combustible gases formed by the oxidation of methane in the reactor part 1 of oxidative coupling of methane (OCM). The quenching-evaporation heat exchanger 2 passed through the reaction gas stream enters the heat exchanger 3, in which the bulk of the reaction water is cooled and separated in the form of condensate. After cooling to 30 ° C, the reaction mixture is fed through the reaction gas compressor 4 to the ethanolamine treatment unit 5, where most of the CO _{2 is} separated. In node 6, the stream is treated with alkaline washing, drying and cooling to a temperature of minus 100 ° C using propylene and ethylene refrigeration cycles. In node 6, fuel gas is released, into which hydrogen, carbon monoxide, nitrogen, oxygen residues and a small part of methane are emitted. This flow is throttled to a pressure of 0.3-0.5 MPa through a turboexpander 7 and fed to the power plant. In the low temperature distillation column 8, the main part of unreacted methane is isolated, which is also fed to the power plant.

The C ₂₊ fraction is discharged from the bottom of column 8, which enters column 9. The bottom residue from this column, which consists mainly of ethane and C ₃₊ hydrocarbons, is returned to reactor 1. From the upper part of column 9, gas containing mainly ethylene and residual methane. This mixture is separated in column 10 into raw ethylene fed to the processing unit and methane fed to the power plant.

The process of generating electricity in various types of plants using methane (the main component of natural gas) is well known. As a power plant in the claimed integrated process, any known type of power plant that produces heat and / or electricity from natural gas can be used (see, for example, S.V. Tsanev, V.D. Burov, A.N. Remezov. Gas turbine and combined-cycle plants of thermal power plants, edited by S. Tsanev, MPEI Publishing House, 2002, 579 pages).

The ethylene processing unit can be a set of devices in which it is refined and brought to market condition, or a reactor in which ethylene is converted into other target products (liquid hydrocarbons, ethanol, etc.), and devices for the isolation and purification of these products .

In the further chemical processing of ethylene into products of its oligomerization ("synthetic oil", liquid fuel, base oils), or polymerization and copolymerization (polymers and plastics), or hydration (ethanol), or alkylation (styrene, other monomers; fuel additives ), the energy released during the chemical processing of ethylene in the form of the heat content of steam and other heat carriers is disposed of together with the energy generated by the power plant, which is fed by natural gas with unreacted methane ethylene synthesis reactor and the energy obtained ethylene synthesis step of oxidative coupling of methane reaction.

The stages of separation / separation, implemented in the above example in the apparatus 5, 6, 8, 9, 10, can be carried out by chemical, cryogenic, adsorption, absorption processing and / or using membrane devices.

The difference between the proposed method and the known processes is that

(a) the production of ethylene as a primary product is included in the gas treatment scheme for a power plant;

(b) methane that does not react in the ethylene synthesis reactor is not recycled, discharged, or flared, but is sent to a power unit (power plant) to produce heat and electricity;

(c) thermal energy (in the form of the heat content of steam and other coolants) released during the production of ethylene by the oxidative condensation of methane and in the process of sequential processing of ethylene into its derivatives (oligo- or polymerization, hydration to ethanol) is utilized together with energy, a power plant that is powered by natural gas (methane) that has not reacted in an ethylene synthesis reactor.

The inventive method for the production of ethylene and its derivatives in an integrated process based on direct partial oxidation of natural gas with the subsequent supply of exhaust gas to a power plant allows to obtain significant economic and technological advantages compared with the known technological processes of their production.

Reducing the specific consumption of natural gas for the production of ethylene and its derivatives is achieved through the use at the stage of production and separation of ethylene and its derivatives from the heat and electric energy received at the power plant. This eliminates the need to include low-power heat and power generators with lower specific energy efficiency in the technological scheme.

In addition, due to the exclusion of unreacted methane from the recirculation stage from the scheme and the possibility of oxidizing the feedstock with air rather than oxygen, the overall energy consumption at the ethylene production stage decreases, which also leads to an increase in the specific efficiency of the process in terms of the feedstock natural gas (methane), which in this process, it can be considered as raw material and energy carrier at the same time.

The combination of the production of valuable compounds with high added value with the generation of electric and thermal energy at a power plant can almost completely eliminate the negative impact on the economic indicators of the processes of producing ethylene and its derivatives by direct oxidation of natural gas, its main disadvantages - high methane consumption for the production of the target product and low economic process efficiency. At the same time, their attractive qualities, such as technological simplicity, low capital and operating costs, and the possibility of using air as an oxidizing agent, are fully preserved. The inclusion of the production of chemical products (ethylene and its derivatives) in the technological scheme of a power plant allows to obtain a significant economic effect.

Unlike well-known technologies that require the creation of large energy chemical complexes based on powerful power plants, the integrated process for the production of chemical products (ethylene and its derivatives) by direct oxidation and electricity can be implemented in dozens of medium and low power plants using natural gas. According to technical and economic estimates, the cost of ethylene and its derivatives and specific capital costs will be significantly lower than those that characterize specialized plants for the production of these chemical products.

Claims (5)

1. The method of production of ethylene and electricity from natural gas by direct oxidation of natural gas followed by the supply of exhaust gas to the power plant, which consists in the fact that the initial stream of natural gas is sent to the stage of ethylene synthesis by the oxidative condensation of methane, which is carried out in the presence of oxide catalysts at temperature from 700 ° C to 950 ° C, pressure from 1 atm to 10 atm and a molar ratio of methane to oxygen in the range from 2: 1 to 10: 1, then ethylene is isolated from the reaction mixture, the rest is gaseous stream comprising unreacted methane and combustible products are hydrogen and CO is directed to power generation in which power generation is carried out and heat; the energy released in the process of ethylene production by the oxidative condensation of methane in the form of the heat content of steam and other heat carriers is utilized together with the energy generated by the power plant, which is fed by natural gas with methane that has not reacted in the ethylene synthesis reactor.

2. The method according to claim 1, characterized in that the separation of ethane and higher hydrocarbons from the flow of combustible gases is carried out, which is sent to a power plant, where electricity and heat are generated; the separated ethane and higher hydrocarbons are sent to the stage of ethylene synthesis by the oxidative condensation of methane.

3. The method according to claim 1, characterized in that the oxide catalyst is selected from the group: oxides of alkaline earth elements Mg, Ca, Sr, Ba, oxides of rare-earth elements La, Ce, Nd, Sm, or mixtures thereof, promoted by additives of alkaline elements (Li, Na, K, Rb, Cs), Sb, Bi and / or Pb supported on Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , HfO ₂ supports, aluminates, alkaline earth element silicates, rare earth silicates.

4. The method according to claim 1, characterized in that the composition of the oxide catalyst is selected in accordance with the empirical formula
M ¹ _a M ¹ _b M ³ ₂ O _{3 + m} ,
where M ¹ is an alkaline earth element selected from the group Mg, Ca, Sr, Ba (or a combination thereof);
M ² is an alkaline element selected from the group Li, Na, K, Rb, Cs (or a combination thereof);
M ³ is a rare earth element selected from the group La, Ce, Nd, Sm (or a combination thereof);
a is the gram-atomic index of the element, the value of which is selected from 0.005 to 250;
b is the gram-atomic index of the element, the value of which is selected from 0 to 20;
m is a stoichiometric coefficient determined by the ratio of the components M ¹ , M ² and M ³ .

5. The method according to claim 1, characterized in that the composition of the oxide catalyst is selected in accordance with the empirical formula
Na _X W _Y M _Z SiO _{2 + n} ,
where M is a chemical element of Mn or Ce,
X, Y, Z - gram-atomic ratios of elements, from which the value of X is chosen from 0.01 to 0.4; the value of Y is selected from 0.005 to 0.2; Z value is selected from 0.005 to 0.4.