Membrane separation device

Abstract

The present application relates to a membrane separation device. According to the separation device of the present application, components to be separated using a separation membrane having a small area size can be separated with high selectivity and consequently processing efficiency and economical efficiency can be superbly improved; and according to a method for producing an expanded polystyrene which includes the membrane separation device, components to be separated using a separation membrane having a small area size, in particular, a volatile organic compound (VOC), can be separated with high selectivity and consequently processing efficiency and economical efficiency can be superbly improved, and also, by separating and recovering VOC, an effect in preventing environmental pollution caused by global warming is exhibited.

Claims

1. A membrane separation device comprising: a first separation membrane, into which a feed stream flows, and in which the feed stream is divided into a first permeate stream which passes through the first separation membrane and a first non-permeate stream which does not pass through the first separation membrane and the first permeate stream and the first non-permeate stream are discharged; a second separation membrane, into which the first non-permeate stream flows, and in which the first non-permeate stream is divided into a second permeate stream which passes through the second separation membrane and a second non-permeate stream which does not pass through the second separation membrane and the second permeate stream and the second non-permeate stream are discharged; a gas-liquid separator coupled to a front end of the first separation membrane and/or coupled between the first separation membrane and the second separation membrane to divide the first permeate stream and the second permeate stream into a gas stream and a liquid stream, discharge the divided gas stream and allow the gas stream to flow into the first separation membrane and/or second separation membrane together with the feed stream or the first non-permeate stream, and a decompression device that decompresses the first non-permeate stream, wherein the gas-liquid separator is coupled so that the gas stream discharged from the gas-liquid separator flows into the second separation membrane together with the first non-permeate stream, and wherein the first separation membrane and the second separation membrane have different selectivities and permeabilities with each other with respect to the at least two components.

2. The membrane separation device of claim 1, wherein the first separation membrane and the second separation membrane satisfy the following Formulas 1 and 2:
?.sup.1.sub.AB??.sup.2.sub.AB>0[Formula 1]
P.sup.2.sub.A?P.sup.1.sub.A>0[Formula 2] wherein ?.sup.1.sub.AB represents a selectivity (P.sup.1.sub.A/P.sup.1.sub.B) of a component A to a component B present in the feed stream flowing into the first separation membrane, ?.sup.2.sub.AB represents a selectivity (P.sup.2.sub.A/P.sup.2.sub.B) of the component A to the component B present in the first non-permeate stream flowing into the second separation membrane, P.sup.1.sub.A and P.sup.1.sub.B represent permeabilities of the component A and the component B present in the feed stream flowing into the first separation membrane, respectively, and P.sup.2.sub.A and P.sup.2.sub.B represent permeabilities of the component A and the component B present in the first non-permeate stream flowing into the second separation membrane, respectively, wherein the component A represents a component to be separated from among components flowing into each separation membrane, and the component B represents the other component with the exception of the component A from among the components flowing into each separation membrane.

3. The membrane separation device of claim 2, wherein the first separation membrane and the second separation membrane satisfy the following Formulas 3 and 4:
?.sup.1.sub.AB>1[Formula 3]
?.sup.2.sub.AB>1[Formula 4] wherein ?.sup.1.sub.AB and ?.sup.2.sub.AB are as defined in claim 2.

4. The membrane separation device of claim 1, further comprising a pressure device configured to apply a pressure to the gas stream before the gas stream discharged from the gas-liquid separator flows into the first separation membrane and/or the second separation membrane.

5. An apparatus for producing an expandable polystyrene, comprising: a reactor, and the membrane separation device defined in claim 1, wherein the reactor is filled with an expandable gas and a portion of the expandable gas is impregnated in polystyrene beads in the reactor, wherein the membrane separation device separates an unimpregnated expandable gas discharged from the reactor.

6. A membrane separation device comprising: a condenser in which a feed stream including at least two components flows; a first separation membrane, into which an uncondensed stream from the condenser flows, and in which the uncondensed stream is divided into a first permeate stream which passes through the first separation membrane and a first non-permeate stream which does not pass through the first separation membrane and the first permeate stream and the first non-permeate stream are discharged; a second separation membrane into which the first non-permeate stream flows, and in which the first non-permeate stream is divided into a second permeate stream which passes through the second separation membrane and a second non-permeate stream which does not pass through the second separation membrane and the second permeate stream and the second non-permeate stream are discharged; and a gas-liquid separator coupled to a front end of the first separation membrane and/or coupled between the first separation membrane and the second separation membrane to divide the first permeate stream and the second permeate stream into a gas stream and a liquid stream, discharge the divided gas stream and allow the gas stream to flow into the first separation membrane and/or second separation membrane together with the feed stream or the first non-permeate stream; and a decompression device that decompresses the first non-permeate stream, wherein the gas-liquid separator is coupled so that the gas stream discharged from the gas-liquid separator flows into the second separation membrane together with the first non-permeate stream, and wherein the first separation membrane and the second separation membrane have different selectivities and permeabilities with each other with respect to the at least two components.

7. The membrane separation device of claim 6, wherein the first separation membrane and the second separation membrane satisfy the following Formulas 1 and 2:
?.sup.1.sub.AB??.sup.2.sub.AB>0[Formula 1]
P.sup.2.sub.A?P.sup.1.sub.A>0[Formula 2] wherein ?.sup.1.sub.AB represents a selectivity (P.sup.1.sub.A/P.sup.1.sub.B) of a component A to a component B present in the uncondensed stream flowing into the first separation membrane, ?.sup.2.sub.AB represents a selectivity (P.sup.2.sub.A/P.sup.2.sub.B) of the component A to the component B present in the first non-permeate stream flowing into the second separation membrane, P.sup.1.sub.A and P.sup.1.sub.B represent permeabilities of the component A and the component B present in the uncondensed stream flowing into the first separation membrane, respectively, and P.sup.2.sub.A and P.sup.2.sub.B represent permeabilities of the component A and the component B present in the first non-permeate stream flowing into the second separation membrane, respectively, wherein the component A represents a component to be separated from among components flowing into each separation membrane, and the component B represents the other component with the exception of the component A from among the components flowing into each separation membrane.

8. The membrane separation device of claim 7, wherein the first separation membrane and the second separation membrane satisfy the following Formulas 3 and 4:
?.sup.1.sub.AB>1[Formula 3]
?.sup.2.sub.AB>1[Formula 4] wherein ?.sup.1.sub.AB and ?.sup.2.sub.AB are as defined in claim 7.

9. The membrane separation device of claim 6, further comprising a pressure device configured to apply a pressure to the gas stream before the gas stream discharged from the gas-liquid separator flows into the first separation membrane and/or the second separation membrane.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic diagram showing a first embodiment of a membrane separation device according to the present application.

(2) FIGS. 2 to 4 are schematic diagrams showing various embodiments of the membrane separation device according to one exemplary embodiment of the present application.

(3) FIG. 5 is a schematic diagram showing an apparatus for producing an expandable polystyrene according to one exemplary embodiment of the present application.

(4) FIGS. 6 to 8 are schematic diagrams showing various embodiments of the apparatus for producing an expandable polystyrene according to one exemplary embodiment of the present application.

(5) FIG. 9 is a schematic diagram showing a membrane separation device including only a first separation membrane according to one exemplary embodiment of the present application.

(6) FIG. 10 is a schematic diagram showing a membrane separation device including only a second separation membrane according to one exemplary embodiment of the present application.

(7) FIG. 11 is a graph illustrating the content of pentane in a mixed gas of unimpregnated pentane and nitrogen, which is introduced into the apparatus for producing an EPS according to Example 6 of the present application, with the lapse of time.

(8) FIG. 12 is a graph illustrating the content of pentane in a mixed gas of unimpregnated pentane and nitrogen, which is introduced into the apparatus for producing an EPS according to Example 7 of the present application, with the lapse of time.

BEST MODE

(9) Hereinafter, the present application will be described in further detail with reference to Examples according to the present application and Comparative Examples not according to the present application. However, it should be understood that the Examples and Comparative Examples described below are not intended to limit the scope of the present application.

(10) Separation of Pentane Using Membrane Separation Device Including Only One Separation Membrane

Example 1

(11) A membrane separation process was performed by allowing a mixed gas (pentane content: 12.7 mol %) of pentane and nitrogen to flow into the membrane separation device as shown in FIG. 9, which included only a first separation membrane having high selectivity to the pentane gas, at a gauge pressure of 4.0 kgf/cm.sup.2 and a flow rate pf 4.1 kg/hr. The permeabilities of pentane (component A) and nitrogen (component B) in the first separation membrane were P.sup.1.sub.A=56.2 GPU and P.sup.1.sub.B=0.5 GPU, respectively, as calculated by Equation 1. Also, the selectivity of pentane (component A) to nitrogen (component B) in the first separation membrane was ?.sup.1.sub.AB=115, as calculated by Equation 2. In this case, the content of pentane in the first non-permeate stream discharged without passing through the first separation membrane was measured to be 3.9 mol %, and the recovery rate of pentane (component A) in the membrane separation device was calculated to be 72%, as calculated by the following Equation 3.
Recovery rate (%)=flow rate (kg/hr) of recovered component A/flow rate (kg/hr) of introduced component A?100[Equation 3]

Example 2

(12) A membrane separation process was performed in the same manner as in Example 1, except that a mixed gas (pentane content: 12.9 mol %) of pentane and nitrogen was allowed to flow into the membrane separation device as shown in FIG. 10, which included only a second separation membrane having high permeability to the pentane gas, at a gauge pressure of 4.0 kgf/cm.sup.2 and a flow rate of 3.8 kg/hr. The permeabilities of pentane (component A) and nitrogen (component B) in the second separation membrane were P.sup.2.sub.A=244.5 GPU and P.sup.2.sub.B=3.3 GPU, respectively, as calculated by Equation 1. Also, the selectivity of pentane (component A) to nitrogen (component B) in the second separation membrane was ?.sup.2.sub.AB=73.4, as calculated by Equation 2. In this case, the content of pentane in the second non-permeate stream discharged without passing through the second separation membrane was measured to be 0.4 mol %, and the recovery rate of pentane (component A) in the membrane separation device was calculated to be 97%, as calculated by the following Equation 3.

(13) Separation of Pentane Using Membrane Separation Device Including Two Separation Membranes Having Different Selectivity and Permeability

Example 3

(14) A membrane separation process was performed in the same manner as in Example 1, except that a mixed gas (pentane content: 13.4 mol %) of pentane and nitrogen was allowed to flow into a membrane separation device in which the first separation membrane used in Example 1 and the second separation membrane used in Example 2 were coupled as shown in FIG. 1 at a gauge pressure of 4.0 kgf/cm.sup.2 and a flow rate of 4.1 kg/hr. The content of pentane in the second non-permeate stream discharged without passing through the second separation membrane was measured to be 0.2 mol %, and the recovery rate of pentane (component A) in the membrane separation device was calculated to be 99%, as calculated by the following Equation 3.

Example 4

(15) A membrane separation process was performed in the same manner as in Example 3, except that a mixed gas (pentane content: 20.0 mol %, and gas temperature: 51? C.) of pentane and nitrogen was allowed to flow into a condenser at a gauge pressure of 4.0 kgf/cm.sup.2 and a flow rate of 11.2 kg/hr, as shown in FIG. 2, and condensed. A condensed stream F.sub.7 emitted from the condenser was separately separated, and an uncondensed expandable gas stream (pentane content: 13.1 mol %, and gas temperature: 15? C.) was allowed to flow into the membrane separation device in which the first separation membrane and the second separation membrane were coupled as shown in FIG. 2 at a flow rate of 6.4 kg/hr.

(16) The recovery rate of pentane (component A) recovered from the condenser was measured to be 59%. Also, the content of pentane in the second non-permeate stream discharged without passing through the second separation membrane was measured to be 0.7 mol %, and the recovery rate of pentane (component A) in the membrane separation device was calculated to be 95%, as calculated by Equation 3. As a result, the total recovery rate of pentane using the condenser and the membrane separation device was measured to be 98%.

Example 5

(17) A membrane separation process was performed in the same manner as in Example 3, except that a mixed gas (pentane content: 28.4 mol %, and gas temperature: 53? C.) of pentane and nitrogen was allowed to flow into a condenser at a gauge pressure of 4.5 kgf/cm.sup.2 and a flow rate of 9.7 kg/hr, as shown in FIG. 4, and condensed. A condensed stream F.sub.7 emitted from the condenser was separately separated, and an uncondensed expandable gas stream (pentane content: 12.2 mol %, and gas temperature: 15? C.) was allowed to flow into the membrane separation device in which the first separation membrane, the second separation membrane and the gas-liquid separator were coupled as shown in FIG. 4 at a flow rate of 6.5 kg/hr.

(18) The recovery rate of pentane (component A) recovered from the condenser was calculated to be 66%. Also, the content of pentane in the second non-permeate stream discharged without passing through the second separation membrane was measured to be 0.036 mol %, and the recovery rate of pentane (component A) in the membrane separation device was calculated to be 99.8%, as calculated by Equation 3. As a result, the total recovery rate of pentane using the condenser and the membrane separation device was measured to be 99.9%.

(19) Simulation Test for Pentane Separation Process Using Membrane Separation Device Including Two Separation Membranes Having Different Selectivity and Permeability

Experimental Example 1

(20) A simulation test for the membrane separation process was performed by allowing a mixed gas (pentane content: 15.2 mol %) of pentane and nitrogen to flow into the membrane separation device in which the first and second separation membranes satisfying the following requirements were coupled at a gauge pressure of 3.0 kgf/cm.sup.2 and a flow rate of 1.4 Nm.sup.3/hr. In this case, the recovery rate of pentane (component A) in the membrane separation device was calculated to be 96%, as calculated by Equation 3.

(21) <Requirements for Separation Membranes>

(22) First separation membrane: the permeabilities of pentane (component A) and nitrogen (component B) are P.sup.1.sub.A=50 GPU and P.sup.1.sub.B=0.17 GPU, respectively, as calculated by Equation 1, and the selectivity of pentane (component A) to nitrogen (component B) in the first separation membrane is ?.sup.1.sub.AB=300, as calculated by Equation 2.

(23) Second separation membrane: the permeabilities of pentane (component A) and nitrogen (component B) are P.sup.2.sub.A=300 GPU and P.sup.2.sub.B=6 GPU, respectively, as calculated by Equation 1, and the selectivity of pentane (component A) to nitrogen (component B) in the second separation membrane is ?.sup.2.sub.AB=50, as calculated by Equation 2.

Comparative Experimental Example 1

(24) A simulation test for the membrane separation process was performed in the same manner as in Experimental Example 1, except that a mixed gas (pentane content: 15.2 mol %) of pentane and nitrogen was allowed to flow into the membrane separation device, in which the first separation membrane and the second separation membrane were coupled so that the mixed gas flowed into the second separation membrane used in Experimental Example 1 and a non-permeate stream which did not pass through the second separation membrane flowed into the first separation membrane used in Experimental Example 1. In this case, the recovery rate of pentane (component A) in the membrane separation device was calculated to be 94%, as calculated by Equation 3.

(25) Separation of Pentane Gas in EPS Producing Process Using Separation Membranes

Example 6

(26) A dispersion prepared by mixing 269 kg of a styrene monomer, 4 kg of a polystyrene recycle bead (molecular weight: 200,000 to 300,000), 1.16 kg of benzoyl peroxide, 0.13 kg of t-butyl perbenzoate, 0.8 kg of dicumylperoxide as an initiator, 0.06 kg of divinylbenzene as a molecular weight modifier, and 1.27 kg of hexabromocyclododecane as a flame retardant, was put into a 700-L high-pressure reactor, and stirred. Thereafter, 0.28 kg of tricalcium phosphate was added as a dispersing agent together with 219 L of ionic water, and stirred.

(27) The reactor was hermetically sealed, and the inside of the reactor was heated to a temperature of 90? C. for 90 minutes. After heating for an hour, 0.03 kg of an aqueous potassium persulfate having 1% TSC was added as a dispersing aid. When the inner temperature of the reactor reached 90? C., the inside of the reactor was maintained at 90? C. for 210 minutes. Meanwhile, 0.3 kg of tricalcium phosphate as a pH control agent, and 0.007 kg of polyoxyethylene sorbitan monolaurate as a surfactant, were put into the reactor. After the inner temperature of the reactor was maintained at 90? C. for 260 minutes, 25 kg of pentane as a foaming agent, was added, the inside of the reactor was heated to a temperature of 100? C. for 50 minutes, and the inner temperature of the reactor was maintained for 40 minutes. Then, the inside of the reactor was heated to a temperature of 125? C. for 50 minutes, the inner temperature of the reactor was maintained for 150 minutes, and the reactor was then cooled. The inner pressure of the reactor decreased as the reactor was cooled. When the inner gauge pressure of the reactor reached 3.1 kgf/cm.sup.2, nitrogen having a gauge pressure of 4.8 kgf/cm.sup.2 was fed to the reactor. Subsequently, when the inner gauge pressure of the reactor was kept constant at 3.5 kgf/cm.sup.2, the mixed gas of unimpregnated pentane and nitrogen was discharged from the reactor by means of the discharge device, and put into a condenser whose gauge pressure was set at 3.5 kgf/cm.sup.2 and which was cooled to 15? C. at a flow rate of 6.0 kg/hr, and a portion of pentane was condensed. A condensed stream F.sub.7 emitted from the condenser was separately separated, and the mixed stream of uncondensed pentane gas and nitrogen gas was allowed to flow into the membrane separation device including only the first separation membrane used in Example 1 at a flow rate of 5.4 kg/hr.

(28) The content of pentane in the first non-permeate stream discharged without passing through the first separation membrane was measured to be less than 4 mol %. FIG. 11 is a graph illustrating the content of pentane in a mixed gas of unimpregnated pentane and nitrogen with the lapse of time.

Example 7

(29) An expandable polystyrene was produced in the same manner as in Example 6, except that nitrogen having a gauge pressure of 4.8 kgf/cm.sup.2 was fed to the reactor when the inner gauge pressure of the reactor reached 3.8 kgf/cm.sup.2 as the reactor was cooled, a mixed gas of unimpregnated pentane and nitrogen was emitted from the reactor by means of the discharge device when the inner gauge pressure of the reactor was kept constant at 4.0 kgf/cm.sup.2, and the mixed gas was put into a condenser whose gauge pressure was set at 4.0 kgf/cm.sup.2 and which was cooled to 15? C. at a flow rate of 6.6 kg/hr and a portion of pentane was condensed, as shown in FIG. 8. A condensed stream F.sub.7 emitted from the condenser was separately separated, and the mixed stream of uncondensed pentane gas and nitrogen gas was allowed to flow into the membrane separation device, in which the first separation membrane, the second separation membrane and the gas-liquid separator used in Example 1 were coupled as shown in FIG. 8, at a flow rate of 5.6 kg/hr. In this case, the mixed stream was allowed to flow into the second separation membrane with controlling the non-permeate stream of the first separation membrane to a normal pressure, and the separated gas stream in the gas-liquid separator was circulated to the second separation membrane.

(30) The content of pentane in the second non-permeate stream discharged without passing through the second separation membrane was measured to be less than 1 mol %. FIG. 12 is a graph illustrating the content of pentane in a mixed gas of unimpregnated pentane and nitrogen, which is introduced into the apparatus for producing an EPS shown in FIG. 8, with the lapse of time.