JP2000309549A - Production of ethylene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of ethylene capable of much saving cooling energy concerning to a cryogenic separation step, refrigerant and the like and reducing load on equipment. SOLUTION: This method is production of ethylene from a gaseous hydrocarbon including hydrogen, methane, ethane and ethylene and comprises (I) a separating step wherein a gaseous hydrocarbon is fed to a membrane separation device having hydrocarbon permselective membrane to separate a hydrocarbon gas including almost all ethylene (A) and a hydrocarbon gas substantially including no ethylene (B) and (II) a cryogenic separation step for the hydrocarbon gas including almost all ethylene (A). The load of a prefractionator T-1 for demethanization and a demethanizer T-2 can be decrerased. And, if an established cryogenic separation or a deethanizer followed by a demethanizer or the like is used, the throughput can be much increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a separation method for separating and purifying ethylene and propylene from gaseous hydrocarbons containing hydrogen, methane, ethane and ethylene. Specifically, hydrogen and methane are separated from gaseous hydrocarbons containing hydrogen, methane, ethane and ethylene using a membrane separation device, and the load of the cryogenic separation process is reduced to efficiently separate and produce ethylene and propylene. About the method.

[0002]

BACKGROUND OF THE INVENTION As a method for producing ethylene and propylene, hydrogen, methane, ethane, propane, ethylene, and ethylene, which are obtained by pyrolyzing a hydrocarbon oil such as naphtha, are used.
A method of separating and purifying target ethylene and propylene from a gaseous hydrocarbon containing propylene and the like is mainly performed.

Conventionally, when ethylene or propylene is obtained from a gaseous hydrocarbon, many distillation columns such as a demethanizer, a deethanizer, an ethylene rectifier, a depropanizer, a propylene rectifier, and a debutanizer are used. Thus, separation and purification by cryogenic separation are performed. At this time, the gaseous hydrocarbon is highly compressed and cooled, and is introduced into the demethanizer.

[0004] As a method for obtaining ethylene by separating hydrogen and methane from gaseous hydrocarbons in this manner, for example, a process shown in FIG. 3 is mentioned.

In FIG. 3, a gaseous hydrocarbon is converted into a high-pressure gas stream by a compressor, and then heat exchanger (E-1).
In (E-5), cooling is performed sequentially. The hydrocarbon mixture condensed in each temperature zone of each of these heat exchangers is supplied to the corresponding gas-liquid separator (V-
It is separated from the uncondensed gas in 1) to (V-5).

The separated liquid extracted from the bottom of the gas-liquid separator (V-1) is supplied to a pre-fractionator (T-1) for purification. Pre-fractionator (T-
The distillate gas in 1) is withdrawn from the top of the tower, cooled by a heat exchanger (E-6), and then demethanized (T-
2). In addition, the gas-liquid separators (V-2) to (V
The separated liquid extracted from the bottom of -4) is supplied to the demethanizer (T-2).

A methane-based fraction obtained from the top by being purified by the demethanizer (T-2) is cooled by a heat exchanger (E-7), and then cooled by a gas-liquid separator (V). According to -6), it is separated into an uncondensed gas mainly composed of methane and a condensate, and a part of the condensate is returned to the demethanizer (T-2). From the bottom of the demethanizer (T-2), a hydrocarbon mixture containing ethylene and a hydrocarbon having a higher boiling point is obtained.

The uncondensed gas in the gas-liquid separator (V-4) is further cooled by the heat exchanger (E-5), and is not condensed in the gas-liquid separator (V-5). It is separated into condensate mainly composed of gas and methane.

However, in such a method, the gaseous hydrocarbon sent to the cooling step contains a large amount of hydrogen and methane, so that the energy required for compression and cooling is large, and a large load is applied to the pre-demethanizer. There was a problem that it took. In addition, the demethanizer (T-
Since a large amount of methane is contained in the liquid component introduced in 2), there is a problem that the liquid load in the demethanizer (T-2) is large.

In order to reduce such a load, a method of compressing a gaseous hydrocarbon as a raw material, separating hydrogen using a hydrogen separator, and then subjecting it to cryogenic separation for separating methane and ethylene. (Japanese Patent Laid-Open No. 10-11)
No. 4502). According to this method, the load in the subsequent separation step can be reduced by the amount of hydrogen separated in advance. However, in this case, the hydrogen separation uses a hydrogen separation membrane capable of selectively permeating and separating hydrogen in gaseous hydrocarbons, and it is necessary to supply gaseous hydrocarbons at a high pressure. The load on the machine and the energy required for compression have not been reduced.

For this reason, there has been a strong demand for a method of separating ethylene and propylene from hydrocarbon gas under the condition of further reducing the load on the gas-liquid separator and the like and saving energy consumption.

The present inventor has conducted intensive studies in view of such circumstances, and as a result, when producing ethylene from a gaseous hydrocarbon containing hydrogen, methane, ethane and ethylene by cryogenic separation, the gaseous hydrocarbon was converted into a gaseous hydrocarbon. By using a membrane separation device having a hydrocarbon selective permeable membrane, hydrocarbon gas (A) containing substantially all ethylene and gas (B) containing substantially no ethylene are separated, and substantially all of the separated ethylene is contained. The present inventors have found that by subjecting only the hydrocarbon gas (A) to the cryogenic separation step, the load of the cryogenic separation step can be reduced and ethylene can be produced with high energy efficiency, and the present invention has been completed.

[0013]

An object of the present invention is to reduce the load of a cryogenic separation process by using a membrane separation device having a hydrocarbon selective permeable membrane in producing ethylene from a gaseous hydrocarbon by cryogenic separation. It is an object of the present invention to efficiently produce ethylene by reducing the energy required for cooling and compression as compared with the related art.

[0014]

SUMMARY OF THE INVENTION The present invention is a process for producing ethylene from a gaseous hydrocarbon containing hydrogen, methane, ethane and ethylene, comprising the steps of: (I) converting the gaseous hydrocarbon into a membrane having a hydrocarbon selective permeable membrane. A step of introducing the mixture into a separation device into a hydrocarbon gas (A) containing substantially all ethylene and a gas (B) containing substantially no ethylene, and (II) a hydrocarbon gas (A) containing substantially all ethylene. ) And a step of cryogenic separation.

[0015]

DETAILED DESCRIPTION OF THE INVENTION In the method of producing ethylene of the present invention, any gaseous hydrocarbon containing hydrogen, methane, ethane and ethylene can be suitably used as a raw material gaseous hydrocarbon. And other gaseous lower hydrocarbons such as propane and propylene. As such gaseous hydrocarbons, those obtained by thermal decomposition such as naphtha and NGL are particularly preferably used.

In the present invention, such a gaseous hydrocarbon is introduced into a membrane separation device having a hydrocarbon selective permeable membrane. This membrane separation device can be suitably used as long as it has a hydrocarbon permselective membrane and can separate hydrogen and hydrocarbons.

The hydrocarbon selective permeable membrane is preferably a membrane that is permeable to gaseous hydrocarbons and hardly permeable to hydrogen, and is preferably a gaseous hydrocarbon compound having 8 or less carbon atoms. It is desirable that the membrane be a polymer hydrocarbon selectively permeable membrane having a larger permeation amount as the value is larger and having a higher affinity for gaseous hydrocarbons than inorganic gas. Further, this hydrocarbon selective permeable membrane is more preferably a hydrocarbon selective permeable membrane having a membrane transmission speed ratio of ethylene to hydrogen gas in the range of 4 to 10, which is determined by the following equation.

[0018]

(Equation 1)

In the present invention, gaseous hydrocarbons are separated by a membrane separation device having such a hydrocarbon selective permeable membrane. At this time, the temperature at which the gaseous hydrocarbons are introduced into the membrane separation device is from 0 to 60. C. and an introduction pressure of about 10 to 50 kg / cm ² G are preferred.

The number of membrane separators used in the present invention may be one or more. If desired, a plurality of membrane separators may be used in parallel or in series.

The gaseous hydrocarbons introduced into such a membrane separator include a hydrocarbon gas (A) containing substantially all of ethylene, which is a component permeating the hydrocarbon selective permeable membrane in the membrane separator, and a hydrocarbon gas (A). It is separated into a gas (B) which does not pass through the permselective membrane and is substantially free of ethylene. At this time, substantially all of the hydrocarbons having 2 or more carbon atoms permeate the hydrocarbon selective permeable membrane, and the hydrocarbon gas (A)
Is obtained as In addition, hydrogen and methane generally depend on both the hydrocarbon gas (A) containing substantially all of the separated ethylene and the gas (B) containing substantially no ethylene, depending on the properties of the membrane and the conditions for membrane separation. Exists.

In this way, a hydrocarbon gas (A) containing almost all ethylene and from which hydrogen and methane are partially separated is obtained. Further, the gas (B) containing substantially no ethylene can be used in a process such as a hydrogenation process by appropriately performing a process such as increasing the hydrogen concentration.

Subsequently, the hydrocarbon gas (A) obtained from the membrane separation device is subjected to a cryogenic separation process. In the step of cryogenic separation, the hydrocarbon gas (A) is cooled to form a mixed phase of a gas phase and a liquid phase, which is separated into a gaseous component and a liquid component by a gas-liquid separator.

In the present invention, in the step of cryogenic separation, the hydrocarbon gas (A) is preferably separated using a plurality of gas-liquid separators in a plurality of temperature zones in which the hydrocarbon gas (A) is sequentially cooled.

Specifically, the hydrocarbon gas (A) substantially free of hydrogen obtained from the membrane separation device is cooled to form a mixed phase of a gas phase and a liquid phase, and the gas is separated by a gas-liquid separator. Separate into a liquid component and a liquid component. The gaseous component obtained from the gas-liquid separator is further cooled to a mixed phase of a gas phase and a liquid phase, and separated into a gaseous component and a liquid component by a subsequent gas-liquid separator. As described above, it is preferable to sequentially cool the gaseous components and perform gas-liquid separation a plurality of times in a plurality of temperature zones.

In the present invention, ethylene can be produced by further separating the liquid component separated by such a cryogenic separation step.

In order to further separate the liquid component, an apparatus used in a normal ethylene production process, such as a demethanizer prefractionator, a demethanizer or an ethylene rectifier, can be appropriately used.

Hereinafter, the present invention will be described more specifically with reference to FIGS. FIG. 1 is an example of a schematic flowchart showing the method for producing ethylene according to the present invention. The present invention is not limited to the method for producing ethylene according to the flowchart.

The process shown in FIG. 1 includes a membrane separator (M), heat exchangers (E-1) to (E-9), gas-liquid separators (V-1) to (V-5), Shonator (T-
1) and a demethanizer (T-2).

First, a raw material gaseous hydrocarbon containing hydrogen, methane, ethane and ethylene is introduced into a membrane separation device (M) having a hydrocarbon permselective membrane, and ethylene as a component permeating the membrane is removed. It is separated into a hydrocarbon gas (A) containing almost all amount and a gas (B) containing substantially no ethylene which is a component that does not permeate the membrane.

Next, in the gas-liquid separators (V-1) to (V-4) and the heat exchangers (E-1) to (E-4), ethylene, which is a component permeated through the membrane, is almost completely removed. Cryogenic separation of the contained hydrocarbon gas (A). The hydrocarbon gas (A) obtained from the membrane separation device (M) is cooled by the heat exchanger (E-1) and introduced into the gas-liquid separator (V-1) in a mixed state of a gas phase and a liquid phase. I do. The liquid component obtained from the gas-liquid separator (V-1) is further cooled by a pre-fractionator (T-1), and the gaseous component is further cooled by a heat exchanger (E-2). −2). The liquid component obtained in the gas-liquid separator (V-2) is further cooled in a demethanizer (T-2), and the gaseous component is further cooled in a heat exchanger (E-3). Introduce in 3). Subsequently, the liquid component obtained in the gas-liquid separator (V-3) is further cooled in a demethanizer (T-2), and the gaseous component is further cooled in a heat exchanger (E-4). V-4). Further, the liquid component obtained in the gas-liquid separator (V-4) is introduced into a demethanizer (T-2).

In FIG. 1, in the cryogenic separation step,
Almost all of ethylene is gas-liquid separator (V-1)-(V-4)
And the gaseous component obtained in (V-4) is substantially free of ethylene. The gaseous component obtained in (V-4) may be used as it is as a fuel gas, and may be used as a heat exchanger (E-
The mixture may be further cooled in 5) and introduced into a gas-liquid separator (V-5) to be separated into a gaseous component and a liquid component, each of which may be used as a fuel gas.

In such a cryogenic separation process, the hydrocarbon gas (A) supplied from the membrane separation device (M) is preferably 10 to 45 kg / cm ² , more preferably ^{20 to} 40 k / cm ² .
It is desirably about g / cm ² . In the present invention, if desired, the hydrocarbon gas (A) may be supplied to the cryogenic separation step after being pressurized using a compressor or the like.

In such a cryogenic separation step,
The cooling temperature in the heat exchangers (E-1) to (E-4) is
It depends on conditions such as the composition and pressure of the hydrocarbon gas (A) to be introduced, and is not particularly limited as long as it is a temperature at which a part of the gaseous component is sequentially cooled and liquefied. -30 at the exit of the heat exchanger (E-1)
° C, -65 ° C at the outlet of the heat exchanger (E-2), -100 ° C at the outlet of the heat exchanger (E-3).
At the outlet of 4), the temperature can be about -120 ° C.

As shown schematically in FIG. 2, the ethylene-containing liquid component obtained in the cryogenic separation step is a demethanizer (T-2) or a deethanizer (T-column).
3) It can be subjected to a subsequent ordinary ethylene production process comprising an ethylene rectification column and the like. Usually, this ethylene-containing liquid component is introduced into a demethanizer to separate the contained methane, but among the liquid components obtained in the cryogenic separation process, gas-liquid separation containing a particularly large amount of heavy hydrocarbons The liquid component obtained from the vessel (V-1) is separated into relatively heavy hydrocarbons containing no methane as a liquid component by a pre-fractionator (T-1) and directly introduced into a deethanizer, It is preferable to cool and liquefy only the gaseous component containing methane and introduce it into the demethanizer, but the liquid component obtained from the gas-liquid separator (V-1) is used without using a prefractionator. The entire amount may be introduced into the demethanizer (T-2). In the demethanizer, it is separated into methane obtained as a gaseous component and hydrocarbons having 2 or more carbon atoms obtained as a liquid component. The liquid component containing ethylene obtained from the demethanizer (T-2) is introduced into the deethanizer (T-3).

In the deethanizer (T-3), hydrocarbons mainly containing ethylene and having 2 carbon atoms are separated as gaseous components, and hydrocarbons having 3 or more carbon atoms are separated as liquid components. After cooling and liquefaction, the obtained gaseous component hydrocarbon having 2 carbon atoms is introduced into an ethylene rectification column, where it is separated into ethylene and other gaseous components. Thus, ethylene can be fractionated and produced.

From the hydrocarbon having 3 or more carbon atoms obtained in the deethanizer, components such as propane can be fractionated by further separating in the same manner.

[0038]

According to the present invention, almost all of the hydrogen contained in the gaseous hydrocarbons is introduced by the membrane separation apparatus having the hydrocarbon selective permeable membrane before the gaseous hydrocarbons are introduced into the cryogenic separation step. And a part of methane can be separated, so that the cryogenic separation process is compared with a normal ethylene production method without a membrane separation device and an ethylene production method using a membrane separation device having a hydrogen permeable membrane. The amount of hydrocarbon gas supplied to the fuel cell is small. Therefore, it is possible to greatly save the cooling energy, the refrigerant, and the like related to the cryogenic separation process, and to reduce the load on the device. In addition, the load on the prefractionator and the demethanizer for demethanization can be reduced.

When an existing cryogenic separation and subsequent ethylene separation unit such as a demethanizer is used, the throughput can be greatly increased.

[0040]

EXAMPLES Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited to these examples.

[0041]

Example 1 A simulation for producing ethylene from gaseous hydrocarbons was performed in the steps described below with reference to the schematic flow chart around the demethanizer shown in FIG. The simulation is PRO / II (SIMULATION SCIENCES IN
C.).

The raw material gaseous hydrocarbon is hydrogen 16
Mol%, methane 32 mol%, ethylene 34 mol%, ethane 4 mol%, propylene 9 mol%, other hydrocarbons 5
A model was a pyrolysis gas of naphtha having a mole% composition.

In the following separation operation, the heat exchangers (E-1), (E-6) and (E-8) use the propylene refrigerant and the heat exchangers (E-2) and (E-3). , (E-7) and (E
-9) uses ethylene refrigerant.

After the pressure of the pyrolysis gas is increased to 36 kg / cm ² G, it is cooled to 15 ° C. and a membrane separation having a hydrocarbon permselective membrane having a membrane permeation rate ratio of ethylene to hydrogen gas of 4 to 10 is performed. Supply to device (M). In the membrane separation device (M), 60% of hydrogen in the source gas and 50% of methane in the source gas
% Is separated as gas (B) that does not permeate the hydrocarbon permselective membrane.

Next, the hydrocarbon gas (A) obtained from the membrane separation device (M) is cooled to -30 ° C. in the heat exchanger (E-1), and the gas-liquid separator (V-1) To separate into condensate and gaseous components. The condensate obtained from the gas-liquid separator (V-1) is introduced into a pre-fractionator (T-1).

In the prefractionator (T-1),
A gaseous component containing almost all methane contained in the condensate;
Separates into liquid components that are substantially free of methane. The liquid component substantially free of methane obtained from the bottom of the prefractionator (T-1) is supplied to the deethanizer, and the gaseous component containing almost all methane obtained from the top of the column is subjected to heat exchange. The mixture is cooled to -20 ° C in the heat exchanger (E-6), and partly recycled to the prefractionator (T-1), while being cooled to -47 ° C in the heat exchangers (E-8) and (E-9). Cool and feed to demethanizer.

The gaseous components obtained from the gas-liquid separator (V-1) are cooled to -65 ° C. in the heat exchanger (E-2) and introduced into the gas-liquid separator (V-2). , Separated into condensate and gaseous components. The condensate obtained from the gas-liquid separator (V-2) is introduced into a demethanizer (T-2).

Subsequently, the gaseous component obtained from the gas-liquid separator (V-2) is cooled to -100 ° C. in the heat exchanger (E-3), and the gas-liquid separator (V-3) Into a condensate and gaseous components, and the condensate is removed from the demethanizer (T-2).
To be introduced. The gaseous component obtained from the gas-liquid separator (V-3) is cooled to −120 ° C. in the heat exchanger (E-4), and introduced into the gas-liquid separator (V-4), and condensed liquid and The condensate is separated into gaseous components and introduced into the demethanizer (T-2).

In the demethanizer (T-2), gaseous components containing methane as a main component and containing substantially no ethylene are obtained from the top of the column, and liquid components containing substantially no methane are obtained from the lower portion of the column. Can be The obtained liquid component is supplied to a deethanizer.

In the deethanizer, hydrocarbons having 2 carbon atoms mainly composed of ethylene are separated as gaseous components, and hydrocarbons having 3 or more carbon atoms are separated as liquid components. The obtained gaseous component hydrocarbon having 2 carbon atoms and having ethylene as a main component, after cooling and liquefaction, is introduced into an ethylene rectification column, separated into ethylene and other gaseous components, and To manufacture.

Results of this simulation (material balance)
Are shown in Table 1. In the table, the amount of each component is indicated by kmol / hr, and the total amount is indicated by unit: ton / hr.

In the range shown in FIG. 1, the total power consumption of the ethylene refrigeration system and the propylene refrigeration system compressor is 12,110 KW.

[0053]

【table 1】

[0054]

Comparative Example 1 In Example 1, except that the membrane separator (M) and the heat exchangers (E-8) and (E-9) were not used,
A simulation for producing ethylene from gaseous hydrocarbons was performed along a schematic flow diagram around the demethanizer shown in FIG. 3, which has the same apparatus configuration.

As the raw material gaseous hydrocarbon, the same naphtha pyrolysis gas as used in Example 1 was used, and the pressure of the pyrolysis gas was increased to 35.5 kg / cm ² G, and the heat exchanger (E-
The prefractionator (T-1)
Separation was carried out in the same manner as in Example 1 except that the gaseous component obtained from the top was introduced into the demethanizer (T-1) at a temperature of -20 ° C cooled by a heat exchanger (E-6). I do.

Results of this simulation (material balance)
Are shown in Table 2. In the table, the amount of each component is indicated by kmol / hr, and the total amount is indicated by unit: ton / hr.

In the range shown in FIG. 3, the total power consumption of the ethylene refrigeration system and propylene refrigeration system compressors is 14,554 KW.

[0058]

[Table 2]

When the total power consumption of the ethylene refrigeration system and the propylene refrigeration system compressor of Example 1 and Comparative Example 1 is compared, the total power consumption used in Example 1 is about 83% of Comparative Example 1, Power consumption can be significantly reduced. Further, in the first embodiment using the membrane separation device, since the amount of cryogenic separation is smaller than when the same amount of raw material gaseous hydrocarbon is treated, the load on the cryogenic separation device can be reduced. .

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a schematic flow around a demethanizer used in the method for producing ethylene of the present invention.

FIG. 2 is a diagram showing an example of a separation sequence in the method for producing ethylene of the present invention.

FIG. 3 is a diagram showing an example of a schematic flow around a demethanizer in a conventional ethylene production method.

[Explanation of symbols]

 (M) ... Membrane separation device (E-1)-(E-9) ... Heat exchanger (V-1)-(V-6) ... Gas-liquid separator (T-1) ... Pre-fractionator (T −2)… Demethane tower (T-3)… Deethane tower

Claims (3)

[Claims] 1. A method for producing ethylene from a gaseous hydrocarbon containing hydrogen, methane, ethane and ethylene, comprising: (I) introducing a gaseous hydrocarbon into a membrane separation device having a hydrocarbon selective permeable membrane. And separating into a hydrocarbon gas (A) containing substantially all ethylene and a gas (B) containing substantially no ethylene; and (II) cryogenically cooling the hydrocarbon gas (A) containing substantially all ethylene. Separating ethylene. 2. The method for producing ethylene according to claim 1, wherein the hydrocarbon permselective membrane is a hydrocarbon permselective membrane having a membrane permeation speed ratio of ethylene to hydrogen gas in the range of 4 to 10. . 3. The step (I) of cryogenically separating a hydrocarbon gas (A).
I) has a plurality of temperature zones where gaseous components are sequentially cooled,
3. The method for producing ethylene according to claim 1, which is a step of separating using a plurality of gas-liquid separators.