阅读说明：本技术 回收轻质烯烃的方法 (Process for recovering light olefins ) 是由 赵富英 金洹一 曹在汉 禹在英 廉熙喆 郑端费 赵旼贞 于 2017-07-18 设计创作，主要内容包括：本发明涉及一种用于回收轻质烯烃的方法,该方法可以通过将水蒸气供入五个串联连接的脱氢反应器中来实现丙烯产量的增加和工艺基本单元的减少,并且通过分别收集乙烷和乙烯,即丙烯生产工艺的副产物,并将乙烷转化为乙烯,从而将丙烯单一产物转化为丙烯和乙烯,使丙烷脱氢反应工艺的产物多样化,由此提高了该工艺的经济效率和选择性。(The present invention relates to a method for recovering light olefins, which can achieve an increase in the yield of propylene and a reduction in the basic unit of the process by feeding steam into five dehydrogenation reactors connected in series, and diversify the products of a propane dehydrogenation reaction process by separately collecting ethane and ethylene, i.e., byproducts of a propylene production process, and converting ethane into ethylene, thereby converting a propylene single product into propylene and ethylene, thereby improving the economic efficiency and selectivity of the process.)

1. A process for recovering light olefins, the process comprising: subjecting a propane-containing feedstock to a dehydrogenation reaction in five serially connected dehydrogenation reactors, wherein the dehydrogenation reaction is carried out by feeding the propane-containing feedstock and hydrogen to each dehydrogenation reactor and separately feeding steam to each dehydrogenation reactor, the propane-containing feedstock and hydrogen being preheated by two parallel connected reaction material heaters; cooling and compressing the process stream withdrawn from the last dehydrogenation reactor; quenching the process stream by flowing through an ethylene/propylene chiller such that the hydrogen/propane ratio is 0.4 or less; transferring the quenched process stream to a deethanizer wherein ethane and ethylene are separated from the process stream; separating a process stream comprising propane and propylene separated from the deethanizer by a propane/propylene separator to obtain a propylene product; transferring the process stream rich in ethane and ethylene separated from the deethanizer to a demethanizer, wherein methane is previously separated from the process stream; transferring the process stream from which methane has been separated to an acetylene converter, wherein the acetylene in the process stream is converted to ethane and ethylene; separating the process stream diverted from the acetylene converter into ethane and ethylene by flowing through an acetylene/ethylene separator, thereby obtaining an ethylene product; the ethylene product is obtained by converting the ethane separated from the ethane/ethylene separator to ethylene in an ethane reactor by additional reactions.

2. The method of claim 1, further comprising cooling the process stream that has flowed through the ethane reactor by flowing through a quench tower, compressing the cooled process stream by a compressor, neutralizing the compressed process stream by flowing through a scrubber, and recycling the neutralized process stream to the dehydrogenation process by introducing the neutralized process stream to a back end of a main compressor in the propane dehydrogenation process.

3. The process of claim 1 further comprising removing hydrogen chloride and hydrogen sulfide (H) from the process stream after cooling and compressing the process stream exiting the last dehydrogenation reactor and prior to flowing the process stream through the ethylene/propylene chiller₂S)。

4. The method of claim 1, further comprising adsorbing and removing carbon monoxide (CO) from the process stream exiting the cooling tank after quenching the process stream by flowing through an ethylene/propylene chiller, and then transferring the process stream to a hydrogen purification step.

5. The process of claim 1, further comprising pretreating the propane feed prior to transferring the pretreated propane feed to a depropanizer wherein at least a portion of the C4+ hydrocarbons are separated as a bottoms stream and a first purified propylene containing product comprising C3 or lighter hydrocarbons and hydrogen is separated as an overhead stream.

6. The method of claim 2, further comprising drying the neutralized process stream obtained by neutralizing the compressed process stream in a dryer unit to remove impurities.

7. The method of claim 6, further comprising separately capturing hydrogen from a process stream that has passed through the dryer unit, increasing the purity of the hydrogen in a Pressure Swing Adsorption (PSA) unit, and then recovering the hydrogen.

8. The process of claim 1, further comprising transferring unreacted propane separated from the propane/propylene separator to a front end of the dehydrogenation reactor through a propane recycle line and recycling the transferred unreacted propane as a feed propane gas.

9. The method as set forth in claim 1, wherein the temperature of methane in the step of previously separating methane in the demethanizer is from-20 ℃ to 80 ℃ and the pressure is 0.4kgf/cm²To 8kgf/cm²。

10. The process of claim 1, wherein a heating unit is provided in front of the ethane reactor to provide the heat required for the reaction in the ethane reactor.

11. The process of claim 1, wherein the process conditions of the ethane reactor are a reaction temperature of 650 ℃ to 950 ℃ and a pressure of 0.1kgf/cm²To 10kgf/cm²。

12. The process of claim 1, wherein a separate feed gas line is provided before the ethane reactor, and the process further comprises controlling the ratio of ethylene production to propylene production by supplying propane via the feed gas line.

Technical Field

The present invention relates to a method for recovering light olefins, and more particularly, to a method for recovering light olefins, which can increase the yield and reduce the number of basic units in a process for producing propylene through propane dehydrogenation, and can obtain two types of products from a propane dehydrogenation reaction process by separately collecting ethane and ethylene, i.e., byproducts of the propylene production process, and converting the ethane into ethylene, thereby improving the economic efficiency of the process.

Background

In the petrochemical industry, continuous catalytic conversion is carried out. The moving catalyst Dehydrogenation Process (MovingCatalyst Dehydrogenation Process) of hydrocarbons is an important Process in the production of light hydrocarbon components and in the production of ethylene and propylene. In a moving catalyst dehydrogenation process, the catalyst is continuously circulated between the reactor and the regenerator.

Dehydrogenation of propane by catalytic dehydrogenation reactions can lead to a route to propylene. Dehydrogenation catalysts typically comprise a noble metal catalyst on an acidic support, such as an alumina, silica alumina, or zeolite support. However, the dehydrogenation reaction is a strongly endothermic reaction, and a high temperature is required for the reaction to proceed at a satisfactory rate. At the same time, the dehydrogenation reaction needs to be controlled to limit the degradation of propane to methane and ethylene, and ethylene can be hydrogenated by the hydrogen released by dehydrogenation of propane. In addition, the dehydrogenation process deactivates the catalyst by coking the catalyst. Therefore, the catalyst needs to be retained after a relatively short operating time or in the dehydrogenation reactor for periodic regeneration.

In this connection, FIG. 1 shows an Oleflex process, which is a typical conventional method for separating and recovering propylene from a propane dehydrogenation product. In the Oleflex process as shown in fig. 1, a propane-containing feed gas stream is preheated to 600 to 700 ℃ and dehydrogenated in a moving bed dehydrogenation reactor to obtain a product gas stream containing propane, propylene and hydrogen as main components.

Meanwhile, the moving bed reactor has an advantage in that the catalyst can be moved, and thus a continuous catalyst regeneration system can be constructed. As an example of the moving bed reactor, U.S. patent No.6,472,577 discloses a continuous catalyst regeneration system including a catalyst bed. However, such conventional fluidized bed dehydrogenation reactors have limitations in that the residence time of the catalyst is short and the conversion rate is low. Because the conversion rate of dehydrogenation reaction is closely related to the basic unit and economic efficiency of said process, it is urgently required to develop a dehydrogenation reactor capable of raising conversion rate so as to raise the efficiency of continuous catalytic reaction-regeneration system.

Meanwhile, ethylene is produced as a byproduct in the propane dehydrogenation reaction, and ethylene used in the conventional propane dehydrogenation process is mainly used as a fuel for a heating furnace. However, the demand for ethylene has recently increased in the chemical raw material market, and it is economically significantly disadvantageous to use only expensive ethylene as a fuel for a heating furnace. Therefore, it would be advantageous to develop a process that enables ethylene (i.e., a byproduct of the propane dehydrogenation process) to be recovered as expensive ethylene.

Disclosure of Invention

Technical problem

The present invention is conceived to overcome the above problems, and an object of the present invention is to provide a method for recovering light olefins, which can increase the total amount of heat supply by supplying reaction heat to each of a plurality of stages of hydrogenation reactors, respectively, and can be operated in a state where the molar ratio of hydrogen to propane in the feed is 0.4 or less, thereby reducing the basic units of the process due to a decrease in hydrogen partial pressure, and increasing the yield due to an increase in yield.

It is another object of the present invention to provide a method for recovering light olefins, which is capable of obtaining two types of products (propylene and ethylene) from a propane dehydrogenation reaction process by collecting ethane and ethylene discharged from a system in a propane dehydrogenation process and converting the ethane into ethylene to produce expensive ethylene. The method also allows for adjustment of production rates to market conditions so that production equipment can be operated most efficiently.

Technical scheme

One aspect of the present invention for achieving the above object relates to a method for recovering light olefins, the method comprising: subjecting a propane-containing feedstock to a dehydrogenation reaction in five serially connected dehydrogenation reactors, wherein the dehydrogenation reaction is carried out by feeding the propane-containing feedstock and hydrogen to each dehydrogenation reactor and separately feeding steam to each dehydrogenation reactor, the propane-containing feedstock and hydrogen being preheated by two parallel connected reaction material heaters; cooling and compressing the process stream withdrawn from the last dehydrogenation reactor; quenching the process stream by flowing through an ethylene/propylene chiller such that the hydrogen/propane ratio is 0.4 or less; transferring the quenched process stream to a deethanizer wherein ethane and ethylene are separated from the process stream; separating a process stream comprising propane and propylene separated from the deethanizer by a propane/propylene separator to obtain a propylene product; transferring the process stream rich in ethane and ethylene separated from the deethanizer to a demethanizer, wherein methane is previously separated from the process stream; transferring the process stream from which methane has been separated to an acetylene converter, wherein the acetylene in the process stream is converted to ethane and ethylene; separating the process stream diverted from the acetylene converter into ethane and ethylene by flowing through an acetylene/ethylene separator, thereby obtaining an ethylene product; the ethylene product is obtained by converting the ethane separated from the ethane/ethylene separator to ethylene in an ethane reactor by additional reactions.

Advantageous effects

According to the process of the present invention, an increase in propylene production and a reduction in the basic units of the process can be achieved by feeding steam to the dehydrogenation reactor. In addition, by providing the heat of reaction separately to each of the five reactors, a reduction in the basic units of the process and an increase in the total amount of heat provided can be achieved, thereby increasing the yield of propylene.

Further, according to the present invention, an ethylene/propylene chiller is included in the cooling tank, whereby the molar ratio of hydrogen to propane in the feed to the reactor can be adjusted to 0.4 or less, thereby increasing the theoretical yield of the propane dehydrogenation reaction due to a decrease in the hydrogen partial pressure and increasing the propylene yield due to an increase in the yield of the dehydrogenation reactor.

Further, according to the present invention, instead of using ethane and ethylene, which are byproducts of a propane dehydrogenation process, as inexpensive fuels, expensive ethylene can be produced, so that two types of products (propylene and ethylene) can be obtained from the propane dehydrogenation reaction process, and thus the productivity of advantageous products can be improved according to market conditions, thereby maximizing economic efficiency of the process.

Drawings

FIG. 1 is a process flow diagram showing a process for the dehydrogenation of propane to produce propylene according to the prior art; and

fig. 2 is a process flow diagram schematically illustrating a process for producing propylene and ethylene together by a propane dehydrogenation process according to one embodiment of the present invention.

Detailed Description

The invention will be described in more detail below with reference to the accompanying drawings.

Although the terms generally used at present are selected as the terms used herein as much as possible, the terms randomly selected by the applicant are used in specific cases. In this case, the meaning of the term should be determined based on the meaning described and used in the detailed description of the present invention, not simply based on the name of the term. Furthermore, the present invention is not limited to the described embodiments, and may be embodied in other forms. Like reference numerals refer to like elements throughout the specification.

Although the figures depict a particular shape of the dehydrogenation reactor of the present invention, the dehydrogenation reactor can have a variety of shapes suitable for the particular environment in which it is to be used in a particular application. The broad application of the present invention is not limited to the specific embodiments described below. Further, the numbers in the drawings represent a simple schematic of the multistage dehydrogenation reactor of the present invention and only the major components are shown in the drawings. In addition, a heat exchanger, an internal heater, a moving pipe for catalyst transfer, a pump and other similar components are omitted in the drawings. The use of these components to condition the dehydrogenation reactor is known to those skilled in the art and does not depart from the scope and spirit of the appended claims.

It is to be understood that various ranges and/or numerical limitations include iterative ranges of like magnitude falling within the expressly stated ranges or limitations.

The term "process stream" as used herein refers to the reaction product produced by the dehydrogenation reaction. Specifically, it refers to a gas, liquid, gas or liquid containing dispersed solids, or mixtures thereof, which may contain hydrogen, propane, propylene, ethane, ethylene, methane, butane, butylene, butadiene, nitrogen, oxygen, carbon monoxide, or carbon dioxide.

The term "reactor" as used herein refers to a reaction apparatus in which a reactant gas is contacted with a catalyst on a catalyst bed.

The term "overhead stream" as used herein refers to the net overhead stream that is recovered from a particular zone after recycling any portion to that particular zone for recycle or any other reason.

The term "bottoms stream" as used herein refers to the net bottoms stream from a particular zone that is obtained after any portion of the recycle for purposes of reheating and/or reboiling and/or after any phase separation.

The term "light olefin" as used herein refers to ethylene, propylene, and mixtures thereof.

The term "deethanizer" in this application refers to a column that separates a C1-C2 gas stream containing methane, ethane, ethylene, etc. as an overhead stream, a C3-C4 gas stream containing propane and propylene as a bottoms stream, and sends a C3-C4 gas stream to a propane/propylene separator.

"propane/propylene separator" refers to a column designed to separate propylene from a mixture containing hydrocarbons having three or more carbon atoms.

The term "depropanizer" refers to a column designed to separate hydrocarbons having four or more carbon atoms from a mixture containing hydrocarbons having three or more carbon atoms.

The term "C4 + hydrocarbons" in the present invention mainly refers to hydrocarbons having four or more carbon atoms.

The term "C5 + hydrocarbons" in the present invention mainly refers to hydrocarbons having five or more carbon atoms.

The term "conversion" in this application refers to the ratio of propane-containing hydrocarbon to hydrocarbon of the feed, which is converted in a single pass of the reaction gas through the dehydrogenation reactor.

The term "selectivity" in the present application refers to the number of moles of propylene obtained per mole of propane conversion and is expressed as a mole percentage.

Fig. 2 is a process flow diagram showing a process and apparatus for recovering light olefins according to one embodiment of the present invention.

Referring to fig. 2, in the present invention, a propane-containing raw material is subjected to dehydrogenation reaction in five serially connected dehydrogenation reactors R1 to R5 by feeding the propane-containing raw material and hydrogen, which are preheated by two parallel-connected reaction material heaters, into each dehydrogenation reactor and separately feeding water vapor into each dehydrogenation reactor. The process stream exiting the last dehydrogenation reactor is cooled and compressed and then quenched by flowing through an ethylene/propylene chiller to provide a hydrogen/propane ratio of 0.4 or less. The quenched process stream is transferred to a deethanizer where ethane and ethylene are separated from the process stream. The process stream separated from the deethanizer comprising propane and propylene is separated by a propane/propylene separator to obtain a propylene product. At the same time, the process stream rich in ethane and ethylene, which is separated from the deethanizer, is transferred to a demethanizer, where methane is previously separated from the process stream. The process stream from which methane has been separated is diverted to an acetylene converter where the acetylene in the process stream is converted to ethane and ethylene. The process stream diverted from the acetylene converter is separated into ethane and ethylene by flowing through an ethane/ethylene separator to obtain an ethylene product. The ethylene product is obtained by converting the ethane separated from the ethane/ethylene separator to ethylene in an ethane reactor by additional reactions.

The process for producing propylene and ethylene by the dehydrogenation process of the present invention will be described in more detail below.

The process of the present invention comprises the steps of feeding a propane-containing feedstock, hydrogen and steam to a dehydrogenation reactor, followed by dehydrogenation. The dehydrogenation reaction step is carried out in five dehydrogenation reactors connected in series, and each dehydrogenation reactor includes two heaters connected in parallel configured to heat the feedstock fed into each reactor. Steam was fed separately to each of the five reactors.

A feed gas stream comprising propane is fed to five or more dehydrogenation reactors 101, 102, 103, 104 and 105, where it is subjected to catalytic dehydrogenation. In this process step, propene is produced by partial dehydrogenation of propane over a dehydrogenation-active catalyst in a dehydrogenation reactor. In addition, hydrogen and small amounts of methane, ethane, ethylene and C4+ hydrocarbons (n-butane, isobutane, butenes) are also produced.

In the present invention, the dehydrogenation reaction is sequentially performed in five reactors connected in series, and the process of dehydrogenating propane into propylene is performed by the dehydrogenation reaction in each dehydrogenation reactor. The gas stream having undergone the first dehydrogenation reaction is sequentially introduced into the second, third, fourth and fifth dehydrogenation reactors 102, 103, 104 and 105 connected in sequence to the first reactor 101, and the dehydrogenation reaction is performed again. That is, in the multistage dehydrogenation, the reaction product is introduced into one reactor to perform dehydrogenation, and then the reaction product is introduced into the next-stage reactor according to the number of reactors and the dehydrogenation process is repeated.

The dehydrogenation reactors 101, 102, 103, 104, and 105 used in the present invention may be any type of reactor known in the art. For example, the dehydrogenation reactor may be a tubular reactor, a stirred tank reactor, or a fluidized bed reactor. As another example, the reactor may also be a fixed bed reactor, a tubular fixed bed reactor, or a plate reactor.

Referring to fig. 2, the dehydrogenation reactor in the light olefin recovery apparatus of the present invention includes a first reactor 101, a second reactor 102, a third reactor 103, a fourth reactor 104, and a fifth reactor 105. The solid arrows indicate the reactant streams, which are the hydrocarbon gas feeds. The first reactor 101 is supplied with a feed gas stream containing a hydrocarbon to be dehydrogenated, such as propane, or hydrogen, or steam, wherein the gas stream fed into the first reactor 101 is fed after being heated by two parallel-connected reaction material heaters 11 and 12. The feed gas stream is fed directly to the first reactor 101 and the dehydrogenation reaction is carried out in the first reactor and a first product stream is recovered. Thereafter, the first product stream, steam and catalyst for the reaction in the first reactor 101 are fed into the second reactor 112 having two reaction material heaters 21 and 22 connected in parallel, and the dehydrogenation reaction is carried out in the second reactor 102. A second product stream is then recovered from the second reactor 102.

The second product stream, water vapor and catalyst stream for the reaction in the second reactor 102 are then fed to a third reactor 103 having two parallel-connected reactant material heaters 31 and 32 and the dehydrogenation reaction is carried out in the third reactor 103, and then the third product stream is recovered from the third reactor 103. The third product stream, the steam and the catalyst stream for the reaction in the third reactor 103 are fed to a fourth reactor 104 having two reaction material heaters 41 and 42 connected in parallel, and the dehydrogenation reaction is carried out in the fourth reactor 104. The fourth product stream, the water vapor and the catalyst stream for the reaction in the fourth reactor 104 are fed to a fifth reactor 105 having two reaction material heaters 51 and 52 connected in parallel, and the dehydrogenation reaction is carried out in the fifth reactor 105, and the fifth product stream is recovered from the fifth reactor 105 to a product splitter 111, the "process stream" produced in each reactor referring to the reaction products produced by the dehydrogenation process. Specifically, a process stream refers to a gas, liquid, gas or liquid containing dispersed solids, or mixtures thereof, which may contain hydrogen, propane, propylene, ethane, ethylene, methane, butane, butylene, butadiene, nitrogen, oxygen, water vapor, carbon monoxide, or carbon dioxide.

As described above, since the dehydrogenation reaction is repeatedly performed in five dehydrogenation reactors connected in series, the reaction heat provided to each reactor can be reduced, and the load of the reaction material heater can be reduced, thereby improving the reaction selectivity, thereby reducing the process basic unit. In addition, since all the dehydrogenation reactors are adiabatic reactors, additional reaction can be performed by heat supplied from a reaction material heater disposed in front of one additional reactor, thereby increasing the yield of propylene.

In the present invention, since two reaction materials connected in parallel for supplying reaction heat are disposed in front of each stage reactor, the load of the reaction material heater is reduced by half, the temperature uniformity is maintained, the operating temperature is adjusted downward, and the number of process basic units is reduced.

In the present invention, to prevent catalyst coking, steam is fed separately to each of the reactors 101, 102, 103, 104 and 105. In the process of the invention, steam is introduced and reacted with the hydrocarbon during the dehydrogenation reaction, whereby the steam removes coke formed on the catalyst by decomposing the coke into carbon monoxide and hydrogen. Since coke is removed by steam as described above, it is possible to prevent the performance of the catalyst active site from being lowered due to the formation of coke, thereby improving the long-term performance of the catalyst. In addition, propane can selectively bind to active sites formed on the catalyst surface by-products (such as ethane, ethylene, and methane), thereby increasing the productivity of the main reaction (in which propane generates propylene and hydrogen), and thus increasing the amount of propylene generated and the reaction selectivity.

After the dehydrogenation reaction is complete, the product gas stream produced in the fifth reactor 105 is cooled and compressed and then quenched by flowing through a cooling box so that the hydrogen/alkane ratio ahead of the first reactor 101 is down-regulated by using an ethylene/propylene chiller.

The reaction product discharged from the fifth reactor 105 is heat-exchanged by a heat exchanger 111, then transferred to a suction drum 112 and separated by boiling point, and "C5 + hydrocarbons" are separated as a bottom stream.

The overhead stream (gas phase product) from the suction drum 112 is liquefied by pressurization and cooling process in the main compressor 113, and then passes through the hydrogen chloride removal unit 114 and the hydrogen sulfide removal unit 115 in order. The overhead stream is additionally subjected to cooling and compression by flowing through a cooling box, i.e., refrigeration system, and at the same time, hydrogen containing carbon monoxide is sent to carbon monoxide removal unit 118 and a hydrocarbon gas stream containing propane and propylene is diverted to deethanizer 117.

A hydrogen chloride removal unit 114 for removing hydrogen chloride (HCl) generated during the dehydrogenation reaction and the catalyst regeneration, and a hydrogen sulfide removal unit 115 for removing sulfide contaminants discharged from the compressor are disposed downstream of the main compressor 113. The hydrogen chloride removal unit 104 and the hydrogen sulfide removal unit 105 may remove contaminants by an adsorbent or an adsorbent substance.

The product obtained from the reactor after the dehydrogenation reaction contains a mixture of C4 containing propylene, as well as carbon monoxide, unreacted propane, nitrogen, oxygen, water vapor, and carbon dioxide. In particular, in the process of the invention, steam is introduced into the feedstock to remove coke, thus coke formed on the catalyst in the reactor with steam (H)₂O) to produce carbon monoxide and hydrogen (H)₂). These byproducts should be separated and vented out of the system to avoid constant build up in the process. Therefore, in the present invention, the carbon monoxide removal unit 108 configured to remove carbon monoxide is disposed in close proximity to the cooling tank 106, and the gas stream from which carbon monoxide has been removed is sent to the hydrogen purification unit 119.

The carbon monoxide removal unit 108 may include a hopcalite (hopcalite), which is a mixed oxide of copper-manganese that is highly reactive to the reaction between carbon monoxide and oxygen. In the presence of hopcalite, the highly toxic hydrogen monoxide reacts with oxygen to form carbon monoxide. In addition, carbon monoxide can be removed by adsorption with an adsorbent composition comprising copper oxide, zinc oxide and aluminum oxide.

The process stream obtained from the dehydrogenation reactor may be further subjected to a post-treatment process to obtain a product of high purity. In the cooling tank 116, the high-temperature hydrocarbon stream supplied from the hydrogen sulfide removal unit 115 is subjected to cooling and compression processes, and separated into hydrogen containing carbon monoxide and a hydrocarbon stream, which are then transferred to the carbon monoxide removal unit 118 and the deethanizer 117, respectively.

The ethylene/propylene chiller 106, which may be used in the cooling tank 116, may use a propylene-based or ethylene-based solvent as the refrigerant, or may perform the same function using another refrigerant, if desired. For example, the refrigerant may be one selected from methane, ethylene and propylene, or a mixture of two or more thereof. It is understood that propylene-based solvents refer to propylene or propylene-containing compounds, while ethylene-based solvents refer to ethylene or ethylene-containing compounds.

The molar ratio of hydrogen to hydrocarbon (propane) in the feed gas mixture used in the dehydrogenation process according to the present invention is 0.4 or less. In the present invention, in order to carry out the reaction process such that the molar ratio of hydrogen to propane in the feed composition is adjusted down to the range of 0.4 or lower to 0 as described above, an ethylene/propylene chiller 106 is used in the cooling tank to satisfy the energy balance corresponding to the decrease in the hydrogen ratio. Due to this feature, the ratio of hydrogen to propane can be down-regulated, so that the reaction yield can be increased by about 5% to 10% and the reaction selectivity can be increased by 2% to 5% as compared with the conventional method.

Prior to the process of the deethanizer 101, components having the lowest boiling points in the entire process, such as hydrogen and carbon monoxide, are separated from the cooling tank 116, pressurized, and then recovered as hydrogen from the hydrogen purification unit 118. Meanwhile, the process stream containing propylene flowing through the cooling tank 116 and the deethanizer 117 is separated into a mixture of propane and C4 in the propane/propylene separator 120, and propylene is purified and recovered.

In the propane pretreatment unit 1, impurities such as water, metal impurities and carbon monoxide are removed from the propane feed and a propane gas stream containing a very small amount of a mixture of C4 is transferred to the depropanizer 10. In the depropanizer 10, butane, butene, butadiene, etc. which cause coke formation by polymerization reaction on a catalyst in the reactor are removed before components contained in the reaction gas are fed into the first dehydrogenation reactor 101. The high purity propane stream supplied to the depropanizer column 10 is mixed with hydrogen supplied from the hydrogen purification unit 119, then heated by low temperature heat exchange in the cooling tank 116, and sent to the heat exchanger 111 where it is heated by heat exchange. The heated stream is further heated by the reaction material heaters 11 and 12 and is reintroduced into the first reactor 101.

The process stream from which impurities have been removed in the hydrogen chloride removal unit 114 and the hydrogen sulfide removal unit 115 is further liquefied by compression in a cooling tank 116. The cooling box 116 may include a heat removal unit (not shown) configured to add heat generated during compression so that the process stream may be operated in a subsequent deethanizer 117. The heat removal unit may also remove heat by heat exchange with: hydrogen recovered from the hydrogen chloride removal unit 114 and the hydrogen sulfide removal unit 115 in this process, or a cryogenic gas (such as liquefied propane) separated from the depropanizer 10, or a liquid reactant. The liquefied process stream is separated in the deethanizer 17, and methane, ethane, and ethylene as byproducts are introduced into the demethanizer 210, and the remaining process stream from which the byproducts have been removed is introduced into the propane/propylene separator 120. In the propane/propylene separator 120, propylene is separated as an overhead stream and a propane-containing C3-C4 gas stream is separated as a bottoms stream and sent to the depropanizer 10. Unreacted propane, butanes and butenes in the process stream introduced into the propane/propylene separator 120 are separated by a column to yield a pure propylene product.

The separated unreacted propane is supplied to the front end of the first dehydrogenation reactor 101 through a propane circulation line as an inert circulation line and recycled as a raw material propane gas. At this time, the following process may also be performed: hydrogen is separately captured from the process streams flowing through the hydrogen chloride removal unit 114 and the hydrogen sulfide removal unit 115 and the hydrogen purity is increased in a Pressure Swing Adsorption (PSA) unit (not shown). The hydrogen gas having an increased purity may be sold commercially or sent to the first dehydrogenation reactor 101 and recycled as a reaction gas. The unreacted propane separated from the propane/propylene separator 120 is transferred to the front end of the depropanizer 10 through a propane recycle line and recycled as a feed propane gas.

The process of the present invention can produce propylene and hydrogen by dehydrogenation of propane, and at the same time, can produce expensive ethylene using by-products of ethane and ethylene. In the present invention, the process for recovering ethylene in the propane dehydrogenation process may include passing a process stream containing methane, ethane, and ethylene, which are byproducts generated in the deethanizer 117, through the demethanizer 210 to first separate out methane, transferring the process stream from which methane has been separated out into the acetylene converter 220 to convert acetylene in the process stream into ethane and ethylene, passing the process stream separated out from the acetylene converter 220 through the ethane/ethylene separator 230 to separate ethane from ethylene, converting the separated ethane into ethylene through an additional reaction in the ethane reactor 240, cooling the process stream flowing through the ethane reactor 240 by flowing through the quench tower 250, compressing the cooled process stream by the compressor 260, neutralizing the compressed process stream by the scrubber 270, and then injecting the neutralized process stream between the main compressor of the existing dehydrogenation process and the hydrogen chloride removal unit 114, thereby continuously performing the dehydrogenation process.

After the neutralization step, a step of removing impurities such as water, hydrogen chloride and hydrogen sulfide by dehydration in the dryer unit 280 may be further included. That is, in the method of the present invention, the process for recovering ethylene is configured such that ethylene produced in the ethane reactor 240 is separated again after passing through the deethanizer, demethanizer 120, and ethane/ethylene separator 230. When ethane collected through the ethane/ethylene separator 230 is additionally reacted in the ethane reactor 240, the ethane separated after the propane dehydrogenation reaction may be converted into ethylene, thereby generating additional ethylene.

The process for recovering ethylene in a propane dehydrogenation process will be described in more detail below.

First, the process stream flowing through deethanizer 117 contains methane, ethane, and ethylene as reaction byproducts. This reaction by-product is passed through the demethanizer 210 and the methane is pre-separated by the column. The process conditions are that the temperature is-129 ℃ to 52 ℃ and the pressure is 5kgf/cm²To 50kgf/cm². The separated methane gas has, for example, a temperature of 40 ℃ and a pressure of 3.2kgf/cm²The pressure of (a). Methane separated by the demethanizer 210 may be used as a heating fuel.

The process stream from which methane has been separated is contacted with hydrogen in acetylene converter 220, wherein the acetylene in the process stream is converted to ethane and ethylene, thereby forming a process stream that is depleted or substantially free of acetylene. The acetylene-depleted process stream immediately flows through an ethane/ethylene separator 230 where it is separated into an ethane overhead stream and an ethylene bottoms stream. The process conditions are that the temperature is-60 ℃ to 40 ℃ and the pressure is 10kgf/cm²To 80kgf/cm². For example, the separated ethylene gas has a temperature of 25 ℃ and a pressure of 40kgf/cm²。

The ethane separated from the ethane/ethylene separator 230 is additionally reacted in the ethane reactor 240, thereby converting the ethane into ethylene. The reaction to convert ethane to ethylene in ethane reactor 240 does not particularly require a catalyst. Alternatively, a catalyst may be used to convert ethane to ethylene. The catalyst used in this case is not particularly limited, and may be, for example, a platinum catalyst. The process conditions for ethane reactor 240 are transThe temperature is 650 ℃ to 950 ℃ and the pressure is 0.1kgf/cm²To 10kgf/cm². In one embodiment, the ethane gas introduced into the ethane reactor 240 may have a temperature of-30 ℃ and 1.2kgf/cm²The pressure of (a). In addition, a heater unit (not shown) configured to provide the heat required for the reaction occurring in the ethane reactor 240 may be provided directly in front of the ethane reactor 240. Further, before the ethane reactor 240, an additional feed gas line configured to supply propane may be provided to control the ratio of ethylene production to propylene production.

The process stream, which is raised in temperature by the reaction of converting ethane to ethylene in ethane reactor 240, is cooled in quench column 250. The reaction product obtained from ethane reactor 240 may be in the form of a high temperature gas and therefore requires cooling before being reintroduced into the main dehydrogenation process equipment. The cooling method used in the cooling step is not particularly limited. For example, a cooling method in which a cooling solvent is brought into direct contact with the reaction product may be used, or a cooling method in which a cooling solvent is brought into indirect contact with the reaction product may be used.

Thereafter, the cooled process stream is compressed in compressor 260 and flows through scrubber 270, where the catalyst and additional gases are neutralized. The compressor 260 reduces the pressure difference from the pressure at the supply location so that the reactant stream generated in the ethane reactor 240 can be smoothly supplied to the rear end of the main compressor 113 through the scrubber 270 and the dryer unit 280. The reactant stream flowing through compressor 260 is then neutralized by a caustic wash treatment in scrubber 270 to remove Cl generated by the Cl-containing catalyst during process recycle₂A gas.

Thereafter, the neutralized process stream flows through a dryer unit 280, where impurities, such as water, hydrogen chloride, and hydrogen sulfide, are removed from the process stream. The process conditions are that the temperature is-40 ℃ to 100 ℃ and the pressure is 0.01kgf/cm²To 60kgf/cm². After the neutralization step or the drying step, between the main compressor 113 and the hydrogen chloride removal unit 114 in the existing dehydrogenation processA process stream is injected. The process stream supplied to the rear end of the main compressor 113 may include propane, propylene, ethane, ethylene, methane, and hydrogen, and in one embodiment, the process stream may have a temperature of 30 ℃ and a pressure of 0.1kgf/cm²。

According to the present invention, the ethane reactor 240 is disposed at the rear of the ethane/ethylene separator 230, so that the concentration of ethylene introduced into the deethanizer 117 during the recycle production is increased. Therefore, the produced ethylene may be separated in advance, so that the catalyst coking in the ethane reactor 240 may be prevented, and the loss of ethylene due to the ethylene side reaction may be prevented. In addition, since ethylene flowing through the ethane/ethylene separator 230 and ethylene generated in the ethane reactor 240 are separated again, ethane, which is a byproduct of the propane dehydrogenation process, may be mostly converted into ethylene without being used as an inexpensive fuel, so that expensive ethylene may be produced, thereby increasing economic efficiency of the process. As a result, the product of propane dehydrogenation can be diversified into propylene and ethylene from a single product of propylene, so that the operating conditions of the propylene dehydrogenation reactor and the operating conditions of the deethanizer can be adjusted according to market conditions.

Although the present invention has been described in detail with reference to the preferred embodiments thereof, the scope of the present invention is not limited to the above-described embodiments, and it is apparent that many modifications can be made by those skilled in the art without departing from the technical spirit of the present invention. Therefore, the true scope of the invention should be defined based on the following claims and their equivalents. For example, although a propane dehydrogenation reaction for producing propylene has been described above mainly in detail, as understood by those skilled in the art from the disclosure of the present application, the disclosure of the present application can be applied to a dehydrogenation reaction that converts alkanes containing two or more carbon atoms, such as ethane, n-butane, isobutane, and pentane, into corresponding alkenes.