KR20050083353A - A novel process for recovering olefin monomers from polyolefin off-gases - Google Patents

Abstract

The present invention relates to a method for recovering the olefin monomer from the exhaust gas of the polyolefin manufacturing process, more specifically, using a hydrogen permeable polymer gas separation membrane, a melting point to separate using the difference in the diffusion selectivity of the components contained in the exhaust gas A series of single processes consisting of a siloxane-based polymer gas separation membrane that separates using a cooler and a dissolution selectivity difference, low energy excluding the use of an expensive gas cooling device or a compression pump for concentrated monomer gas recovery used in the conventional process, The present invention relates to a method for recovering an olefin monomer from an exhaust gas of a polyolefin production process capable of efficiently separating and recovering three or more components by an environmentally friendly technique.

Description

A Novel process for recovering olefin monomers from polyolefin off-gases

The present invention relates to a method for recovering the olefin monomer from the exhaust gas of the polyolefin manufacturing process, more specifically, using a hydrogen permeable polymer gas separation membrane, a melting point to separate using the difference in the diffusion selectivity of the components contained in the exhaust gas A series of single processes consisting of a siloxane-based polymer gas separation membrane that separates using a cooler and a dissolution selectivity difference, low energy excluding the use of an expensive gas cooling device or a compression pump for concentrated monomer gas recovery used in the conventional process, The present invention relates to a method for recovering an olefin monomer from an exhaust gas of a polyolefin production process capable of efficiently separating and recovering three or more components by an environmentally friendly technique.

Polyolefin refers to a high molecular compound produced by the polymerization of olefin, a chain-shaped hydrocarbon compound having one double bond, and is widely used as a raw material in various industrial fields.

Korea's polyolefin industry is one of the world's five largest producers by volume. Annual output reaches millions of tonnes per year of production, with total production in excess of 20 million tonnes in 2000.

These polyolefin polymers undergo a polymerization process and then a process for removing unreacted monomers contained in the resin, which is a cleaning process injecting nitrogen with high purity. At this time, the unreacted olefin monomer corresponding to 1 to 2% of the production amount is included in the flue gas and volatilized.

Produce polymer C4 LLDPE MDPE Generation amount (kg / hr) 300 300 Pressure (kgf / cm ² ) 20 20 Temperature (℃) 35 35 Composition (% by volume) Hydrogen 9.0 18.0 ethane 2.0 2.8 Ethylene 49.0 49.0 N-butane 0.5 0.4 1-butene 20.0 10.0 N-pentane - 3.6 1-pentene - 0.4 nitrogen 19.5 15.8

Existing olefin monomer-containing flue-gas treatment methods are known by recovery using a cold condensation method and subsequent incineration processes. This method involves not only burning and releasing a large amount of olefin monomer (100 billion to 200 billion won per year in Korea) but also additional consumption of cleaning nitrogen (40 to 80 billion won per year in Korea), which is required for incineration. It has the disadvantage that it involves the generation of energy and incineration flue-gases.

MTR (Membrane Technology and Research) of the United States has developed a variety of membrane processes to solve this problem, using a silicon-based polymer composite membrane with excellent separation of the olefin / nitrogen mixed gas, the problems caused by the above incineration process Tried to solve. In this process, high-pressure unreacted olefin monomer / nitrogen mixed flue gas is introduced into the condenser to recover the monomer, and then the uncondensed low concentration monomer is concentrated using a separator to recover the expensive monomer to the condenser. It is an energy-saving process that does not emit [US Patent No. 5,769,927 (1998)].

However, the only successful commercialization is the low energy condensation system used to increase the separation selectivity of low siloxane separators below 5 and the process of recovering the concentrated monomer through the membrane. It has the disadvantage of requiring device cost. The gas separation technology using the membrane is being researched at home and abroad, the hollow fiber membrane for oxygen enrichment in Korea was commercialized by Air Lane, Chemicoa.

Meanwhile, various techniques for nitrogen / hydrocarbon separation and nitrogen / VOC separation using separation membranes have been studied. However, the technique of treating olefin flue gas as a separation membrane process using hollow fiber separation membranes has not been empirically applied.

Accordingly, the present inventors have studied to improve the problem of low separation efficiency of the separation membrane used to separate the olefin monomer from the exhaust gas of the polyolefin manufacturing process, hydrogen permeable polymer gas separation membrane to separate the difference in the diffusion selectivity of the components contained in the exhaust gas After passing through the high molecular weight monomer to separate the gas with a small molecular weight and a large gas, the separated olefin vapor by cooling condensation to separate the melting point difference, the remaining gas is separated into siloxane-based polymers by the difference in dissolution selectivity The present invention has been completed by discovering that an effective recovery of olefin monomers from exhaust gas generated in a polyolefin manufacturing process is possible in a single process of recovering low carbon number monomer through a gas separation membrane.

Accordingly, the present invention effectively recovers the olefin monomer from the exhaust gas of the polyolefin manufacturing process in a series of single processes including a hydrogen permeable polymer gas separation membrane using a diffusion selectivity, a cooler using a melting point and a siloxane polymer gas separation membrane using a dissolution selectivity. The purpose is to provide a way to.

The present invention provides a method for separating and recovering an olefin monomer from exhaust gas of a polyolefin production process by using a polymer membrane.

A first step of separating and recovering the exhaust gas into a mixed concentrated olefin using a hydrogen permeable polymer gas separation membrane;

A second step of separating and recovering the C ₄ to C ₁₀ monomer after cooling and condensing the separated mixed concentrated olefin at a temperature of −20 to 0 ° C .; And

A method for separating and recovering an olefin monomer from a flue gas comprising a third step of separating the C ₁ to C ₃ monomers using a siloxane-based polymer gas separation membrane in the mixed concentrated olefin having the C ₄ to C ₁₀ monomers separated therefrom. Has its features.

Hereinafter, the present invention will be described in more detail.

The present invention is a method for separating and recovering the olefin monomer from the exhaust gas generated in the polyolefin manufacturing process, the existing process of passing the exhaust gas through the polymer membrane has the disadvantage that excessive energy cost or equipment cost is required to improve this A novel separation and recovery process consisting of heterogeneous gas separation membranes and coolers with different properties.

Looking at the method for separating and recovering the olefin monomer from the exhaust gas generated in the polyolefin production process according to the present invention in more detail as follows.

As shown in FIG. 1, first, the generated flue gas is passed through a hydrogen permeable polymer gas separation membrane 1 to use diffusion selectivity for separating gas having a low molecular weight such as hydrogen (A) and a large olefin gas. After cooling and condensing the olefin gas using the cooler (3) to separate and recover the high carbon monomer (B), the remaining gas is passed through the siloxane-based polymer gas separation membrane (2) to obtain nitrogen (C) and low carbon water. It consists of a series of single processes using the dissolution selectivity which separates and collect | recovers with a monomer (D).

Various types of polyolefins can be produced by known methods, and industrially, for example, polyethylene, polypropylene, polypropylene and copolymers thereof are generally manufactured.

The exhaust gas generated in the polyolefin process generally contains a monomer, and has a characteristic that a partial pressure difference between components of a gas which is discharged as a high pressure gas and is a driving force for separation is large. Therefore, there is an advantage that it can be introduced into the membrane process simply without going through an energy consumption process such as a separate gas pressurization operation.

The components contained in these flue gases include hydrogen, nitrogen, ethane, ethylene, N-butane, I-butene, N-pentane and I-pentene, among which ethylene is the main component.

On the other hand, the present invention permeates the exhaust gas generated in the process through a glassy hydrogen permeable polymer gas separation membrane to separate into a gas having a small molecular weight, such as hydrogen and a large molecular weight olefin vapor using a difference in diffusion selectivity according to the molecular weight. Hydrogen permeable polymer gas separation membranes having an excellent effect on the hydrogen permeability of the glass phase, for example, polysulfone (Polysulfone), polyimide (Polyimide), polyethersulfone (Polyethersulfone) membrane can be used. Such a separator may be prepared and used by a known method or may be commercially available. The exhaust gas is usually maintained at a temperature of room temperature to 120 ℃, it is preferable to maintain at a temperature near room temperature when passing through the glassy polymer gas separation membrane.

Next, hydrogen is separated, and the mixed and concentrated olefin is condensed in a cooler, and then a high carbon number monomer is separated through the separator. It is preferable to maintain the temperature of the cooler at -20 to 0 ° C, and at low temperatures below -20 ° C, monomers of low carbon number may also be condensed, and there is a problem in that the consumption of cooling energy is large. In case of exceeding the high temperature, there is a problem that condensation of the high carbon number monomer does not occur properly.

In addition, the high carbon number monomer having 4 to 10 carbon atoms, which has a high molecular weight, when cooled and condensed at a constant temperature, is separated into a liquid phase and recovered.

Finally, the mixed concentrated olefin from which the high carbon number monomer is separated is passed through the siloxane-based polymer gas separation membrane and separated into nitrogen and low carbon number monomers using the difference in solubility.

The low carbon number monomer has a carbon number of 1 to 3, so that the siloxane-based polymer gas separation membrane has a dissolution selectivity to nitrogen, so that it can be separated and recovered. This coating is made. For example, the poly (dimethylsiloxane) polymer in the present invention is dissolved in Sylgard 184 resin of Dow Corning in normal hexane (n-hexane) and applied to polyetherimide, and then dried at room temperature for 12 hours or more. The membrane is then heated in an oven for at least 110 ° C. for 2 hours to induce complete crosslinking reaction of poly (dimethylsiloxane). Such composite membranes exhibit excellent performance in separating hydrocarbon vapors and permanent gases.

In addition, among the low carbon water monomers recovered by the siloxane-based polymer gas separation membrane, the low purity water is pressurized by a compressor, and then mixed with the mixed concentrated olefin and recycled to obtain a low carbon water monomer having high purity.

It consists of a series of single processes using the above-mentioned glassy polymer gas separation membrane, a cooler, and a siloxane-based polymer gas separation membrane, and each gas separation membrane used in each step comprises one or two or more separation membranes for the purpose of improving efficiency. It can be used in series, in parallel, or a mixture of these. This process is carried out continuously at room temperature or lower temperature, the yield of the olefin monomer separated from the flue gas is more than 90%, showing a high yield comparable to the conventional MTR process, the separation and recovery efficiency of the olefin monomer is significantly increased. In addition, the energy consumption and the device cost are reduced. In addition, the separation and recovery of hydrogen, which has not been dealt with in the conventional process, is realized by the present invention, thereby raising the efficiency and usefulness of the process to the next level.

The present invention as described above will be described in more detail based on the following examples, but the present invention is not limited thereto.

Reference Example 1: Performance of Glassy Polymer Gas Separators

In order to determine the performance of the glassy polymer gas separation membrane used in the present invention, the permeability characteristics of the polyisulfone polymer and the selectivity of the polyimide polymer were measured and shown in Tables 2 and 3, respectively.

Permeability (GPU) Hydrogen carbon dioxide Oxygen nitrogen Ethylene Butene Temperature (℃) 25 60 22 4.8 0.8 One 0.01 50 80 30 6.8 1.1 1.5 0.01 75 96 32 9.2 1.6 2.1 0.01

Selectivity Hydrogen / nitrogen Oxygen / nitrogen Ethylene / nitrogen Butene / Nitrogen Temperature (℃) 25 79 6.3 1.3 0.013 50 71 6.1 1.3 0.0089 75 62 5.9 1.3 0.0064

As shown in Tables 2 and 3, the transmittance and selectivity are shown. In particular, as the temperature increases, the permeability and selectivity of hydrogen are greatly improved.

Reference Example 2: Preparation of siloxane-based polymer gas separation membrane

The poly (dimethylsiloxane) polymer (Dow Corning, Sylgard 184 resin) was dissolved in normal hexane (n-hexane) and evenly applied to the polyetherimilar hollow fiber surface, and dried at room temperature for about 12 hours. The membrane was then heated in an oven for at least 110 ° C. for 2 hours to induce complete crosslinking reaction of poly (dimethylsiloxane).

The hollow yarn made by the above method was cut to an appropriate length and then inserted into a cylindrical stainless hollow fiber module, and both ends were fixed with an adhesive. Both ends of the module were covered with a cap made of the same stainless material and used as the inlet and outlet of the mixed gas.

Permeability and selectivity for nitrogen and ethylene of the siloxane-based polymer gas separation membrane prepared above are shown in Table 4 below.

Penetration (kgf / ㎠) One 5 10 20 Nitrogen Permeability (GPU) 9.12 8.28 8.06 7.89 Ethylene Permeability (GPU) 54.6 63.9 71.54 94.88 Selectivity 5.99 7.72 8.88 12.03

As shown in Table 4, it can be seen that as permeation pressure increases, permeability and selectivity improve.

Example 1

 As shown in FIG. 1, the exhaust gas generated at a high pressure was directly introduced into the glassy polymer gas separation membrane 1 without a separate pressurization process. After the hydrogen was effectively separated, the olefin-concentrated flue gas passed through the cooler 3 to be converted to -20 to 0 ° C. low temperature, and then passed through the separator 4. At this time, the appropriate temperature and pressure conditions adjusted according to the characteristics of the process can separate the various types of olefins, paraffinic hydrocarbons present in the mixed gas according to the number of carbon, the exhaust gas used in the present invention is a small amount of butane, a large amount The butene content was high and -10 degreeC was maintained. In addition, the cold exhaust gas passing through the cooler has an advantage that the siloxane-based polymer gas separation membrane (2) shows a much higher separation efficiency than the high temperature exhaust gas. The exhaust gas introduced into the second stage gas separation membrane 2 without condensation was separated into a nitrogen enrichment gas on the unpermeable side and an olefin monomer enrichment gas on the permeate side. The process was performed insulated from the pipe and the membrane module so as to maintain the conditions below room temperature after passing through the condenser.

The components separated and recovered by the above process were analyzed by gas chromatography, and the results are shown in Table 5 below. At this time, the total amount of flue gas injected is 1000 m ³ / day.

Comparative Example 1

The final results of the result report data of the olefin monomer separation and recovery membrane process developed by MTR, the exhaust gas of the same component used in Example 1 is shown in Table 5 below.

Example 2

The same procedure as in Example 1 was carried out, but as shown in FIG. 2, a low carbon water monomer was pressurized with a compressor to recycle, and the results are shown in Table 5 below.

division Hydrogen nitrogen ethane Ethylene N-butane 1-butene N-pentane 1-pentene Input flue gas (% by weight) [Total amount of flue gas injected: 1000 m ³ / day] 9.0 19.5 - 51.0 - 20.5 - - Example 1 Recovery (m ³ / day) 82.89 160.3 - 348.8 - 204.4 - - % Recovery 92.1 82.2 - 68.4 - 99.7 - - Example 2 Recovery (m ³ / day) 83.1 1616 - 438.1 - 204.4 - - % Recovery 92.3 82.9 - 85.9 - 99.7 - - Comparative Example 1 Recovery (m ³ / day) - detection - 283.6 - - - - % Recovery - - - 55.6 - - - -

As shown in Table 5, it can be seen that Examples 1 and 2 using different kinds of gas separation membranes according to the present invention have significantly improved recovery compared to Comparative Example 1 using the conventional gas separation membrane.

In addition, it can be seen that the recovery rate of the recovered Example 2 was further improved after the low carbon number monomer was compressed.

As described above, as a series of single processes using the above-mentioned glassy polymer gas separation membrane, a cooler, and a siloxane-based polymer gas separation membrane, the recovery rate is not only improved, but also an expensive gas cooling device or a concentrated monomer gas used in the existing process. It is a low energy and environmentally friendly technology that eliminates the use of recovery compression pumps. In addition, it is a process that can more effectively separate three-component or higher flue gas using two kinds of membrane materials, each having greatly different permeation characteristics, and recover nitrogen and hydrogen, which were previously discarded together in the existing process, to recycle high-purity hydrogen. have.

1 shows a schematic diagram of a process for recovering an olefin monomer from exhaust gas according to the present invention.

Figure 2 shows a schematic diagram of a process for recovering the olefin monomer from the flue gas to add the step of recycling the pressurized low-carbon water monomer according to the present invention.

[Description of Reference Signs for Main Parts of Process Design Diagrams in FIGS. 1 and 2]

1: hydrogen permeable polymer gas separation membrane 2: siloxane-based polymer gas separation membrane

3: cooler 4: separator 5: compressor

A: hydrogen B: high carbon number monomer C: nitrogen D: low carbon number monomer

Claims (5)

In the method for separating and recovering the olefin monomer from the exhaust gas of the polyolefin production process using a polymer separation membrane, A first step of separating and recovering the exhaust gas into a mixed concentrated olefin using a hydrogen permeable polymer gas separation membrane; A second step of separating and recovering the C ₄ to C ₁₀ monomer after cooling and condensing the separated mixed concentrated olefin at a temperature of −20 to 0 ° C .; And The C ₄ ~ C in a third step the siloxane-based monomer is ₁₀ separating a mixture enriched olefin polymer using a gas separation membrane for separating monomers of C ₁ ~ C ₃ Method for separating and recovering the olefin monomer from the exhaust gas comprising a. The method of claim 1, wherein the hydrogen permeable polymer gas separation membrane is a glassy polymer gas separation membrane selected from polysulfone, polyimide, and polysulfone separation membrane. 2. The method of claim 1, wherein the siloxane-based polymer gas separation membrane is formed by coating poly (dimethylsiloxane) on polyetherimide. The method of claim 1, wherein the glassy-phase gas separation membrane and the siloxane-based polymer gas separation membrane each have one, two or more kinds arranged in series, in parallel, or a mixture thereof. . The method of claim 1, wherein the C ₁ to C ₃ monomers separated in the third step is pressurized by using a compressor, and then mixed with the mixed concentrated olefin and recycled to the olefin from the exhaust gas, characterized in that consisting of Method of separating and recovering monomers.