JPS5842605A - Separation of organic solvent from waste solvent containing low-molecular weight polyolefin - Google Patents

Abstract

PURPOSE:To separate an organic solvent from a waste solvent containing a low- MW polyolefin efficiently at a low energy consumption, by conducting pressure filtration by using an ultrafilter membrane. CONSTITUTION:Use is made of a module (preferably, tubular) comprising an ultrafilter membrane of average pore diameter about 10-1,000Angstrom (e.g., aromatic polyamide type, polysulfone type). Namely, through this membrane is filtered under an elevated pressure (about 1-100kg/cm<2>G) an organic solvent (e.g., hexane) solution containing dissolved low-MW polyolefin (e.g., polyethylene wax, MW about 500-50,000) resulting from a polyolefin production process. The filtrate is purified (if required) by adsorption, dewatering or a like operation, and then reused. On the other hand, the polymer is precipitated and recovered from the concentrated waste solution by repeated ultrafiltration, steam injection or a like operation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for separating a low molecular weight polyolefin and an organic solvent from a waste solvent containing a low molecular weight polyolefin obtained in a polyolefin production process.

Low-molecular-weight polyethylene wax or low-molecular-weight, low-crystalline polypropylene (so-called atactic polypropylene) discharged from the manufacturing process of polypropylene, etc. (hereinafter referred to as low-molecular-weight polyolefin) A method of treating waste solvents such as hydrocarbons or alcohols (hereinafter simply referred to as waste solvents) containing hydrocarbons or alcohols (hereinafter simply referred to as waste solvents) to separate low molecular weight polyolefins from hydrocarbons or solvents such as alcohols (hereinafter referred to as solvents). Steam distillation method, solvent displacement method, and centrifugal thin film evaporation method are known as methods.

In the steam distillation method, waste solvent is placed in a steam distillation pot and steam is blown into it to distill the solvent together with the steam.On the other hand, low molecular weight polyolefin floats on water and remains in the pot, so if a certain amount is This is the way to start. The solvent replacement method is a method in which the solvent in the waste solvent is replaced with a high boiling point inert liquid such as a second solvent, such as kerosene, light oil, heavy oil, or mineral spirit. It is. Although the solvent is recovered in this process, the second solvent and low molecular weight polyolefin are usually treated. Therefore, it is not a suitable method if low molecular weight polyolefins are to be separated and rounded. In the centrifugal thin film evaporation method, the waste solvent is preconcentrated, heated at high temperature under pressure, and then lashed in a centrifugal thin film evaporator under atmospheric pressure for 7 hours to remelt the precipitated molecular weight polyolefin and evaporate the remaining solvent. This is done using a centrifugal thin film evaporator. However, when the organic solvent has a low boiling point below room temperature, such as propylene or isobutane, the disadvantage is that energy is required to recompress it for liquefaction.

Since these methods are based on evaporation or recompression of the solvent, they require Kana Kana of thermal or electrical energy. In recent years, energy conservation has become an important issue.

The present invention is based on a study to solve these problems and arrive at the present invention.

That is, an object of the present invention is to provide an energy-saving method for separating a low molecular weight polyolefin and a solvent from waste solvent discharged from a polyolefin manufacturing process.

The present invention is characterized in that an organic solvent is removed from a waste solvent containing a low molecular weight polyolefin obtained during a polyolefin manufacturing process by pressurizing the waste solvent and filtering it through an ultrafiltration membrane. This is a method of separation.

The pressure applied to the waste solvent in the method of the present invention is 1 to 1
00 Kg/exa"G, and the pressure difference before and after the ultrafiltration membrane is 1~lOO4/cs+"G. Further, although the filtration temperature varies depending on the material of the ultrafiltration membrane, it is necessary to carry out the filtration at a low temperature that does not cause the membrane to swell. On the contrary, increasing the filtration temperature increases the permeation rate of the solvent through the ultrafiltration membrane, so it is preferable.The normal temperature is -20℃~
200°C, preferably 0°C to 150°C, preferably 2
It is 0°C to 100°C.

The ultrafiltration membrane used in the present invention is preferably one that has excellent solvent resistance and does not easily swell in organic solvents; Polytetrafluoroethylene, polysulfone, etc. are used. A suitable average pore diameter of the ultrafiltration membrane in the present invention is xoX to xoooX, preferably A to 1
It is 50A. The average pore size is selected depending on the molecular weight of the low molecular weight polyolefin. It is important to select from the molecular weight range to be divided.The ultrafiltration membrane in the present invention is usually used in the form of modules. The shape of the membrane module may be a hollow fiber shape, a pastry shape, a flat plate shape, a tubular shape, or the like. The tubular module has a simple structure, is rounded, and waste solvent Kff
Gels or particles of low molecular weight polyolefins that are insoluble in organic solvents are preferable because they can increase the flow rate at the membrane surface without causing clogging of the membrane module.

First, physical cleaning such as sponge pole cleaning or chemical cleaning using an organic solvent can be performed, which is preferable.

The low molecular weight polyolefin in the present invention refers to ethylene, or α-olefins such as propylene, butene-1, pentene-1, hexene-1s41-tylpentene-1, and aromatic styrene such as styrene or α-methylstyrene. It is a homopolymer or copolymer containing a derivative as a monomer, and has a low molecular weight that dissolves in an organic solvent, and its average molecular weight is usually 50QOOO or less. Specific examples of low molecular weight polyolefins include polyethylene wax and solvent-soluble polypropylene, so-called atactic polyolefin. Billet; Politz. 7 fins polytwo (pu).

(pyrene/ethylene series, propylene/butene-1 series), solvent-soluble polybutene-1 so-called atactic polybutene-1, polybutene-1 copolymer, solvent-soluble ethylene/propylene rubber, solvent-soluble polyhexene-1 so-called atactic polybutene-1 Kuchiku polyhexene-1, polyhexene-
1 copolymer, solvent soluble poly number-methylpentene-1
Examples include so-called atactic poly-4-methylpentene-1, poly-4-methylpentene-1 copolymer, and solvent-soluble polystyrene.

The low molecular weight polyolefin that can be separated from waste solvent by the method of the present invention has an average molecular weight of 500 or more, and if it is less than 500, separation is difficult and separation efficiency is reduced.
If it is less than 0, it easily passes through the ultrafiltration membrane and cannot be separated from the specific solvent.

The waste solvent used in the method of the present invention is a solution in which a low molecular weight polyolefin is dissolved in an organic solvent. The concentration is less than 30 weights, preferably less than 10 weights, more preferably less than 3 weights. The waste solvent includes particles or gels of high molecular weight polyolefins insoluble in organic solvents or fine particles of other inorganic compounds (for example, 100
(μ or less) may be contained, and the amount thereof is less than 5 weights, preferably less than 1 weight, and even more preferably less than 0.1 weight. Further, water may be contained in an amount within a range that does not cause phase separation.

However, it is preferred that insoluble substances be separated by KF before passing through the ultrafiltration membrane.

Examples of waste solvents used in the present invention include polyethylene-normal hexane solution, polyethylene-normal heptane solution, polyethylene-liquefied isobutane solution, polyethylene-cyclohexane solution, polyethylene-normal heptane solution, polypropylene-normal heptane solution 1 polypropylene-liquefied propylene solution, Polyglobylene-liquefied propane solution 1 Polypropylene-ingropanol solution, polypropylene-butanol (iso or noryl) solution, polypropylene-acetone solution, polypropylene-
Examples include methyl acetate solution, polyethylene-impronoquinol solution, polyethylene-butanol (iso or normal) solution, polyethylene-acetone solution, polyethylene-methyl acetate solution, liquefied butene-1-liquefied butene-1 solution, etc. can.

Further concrete examples of waste solvents include: 1) Low-pressure solvent polymerization of ethylene or propylene using an inert hydrocarbon or organic solvent such as n-hexane or n-heptane, followed by deactivation of the catalyst with alcohol, water, etc. 2) A waste solvent obtained by applying the resulting slurry to a centrifuge; 111114 Louis is a waste solvent obtained by processing such as sedimentation separation after countercurrent washing with liquefied propylene, and 3) a polypropylene slurry obtained by bulk liquid pool polymerization using liquefied propylene itself as the polymerization solvent. The dried polypropylene powder sent to the chamber is washed with organic solvents such as alcohols such as isopropanol, ketones such as acetone, or hydrocarbons such as n-hexane, and the slurry after washing is subjected to treatments such as centrifugation. 4) Wash the polyolefin powder obtained by gas phase polymerization in the same manner as in 3).
5) The waste solvent obtained by applying the slurry obtained without deactivation with alcohol, water, etc. in 1) to a centrifuge K 6) In 2), alcohol, Examples include waste solvents obtained by similar treatment of slurry obtained without deactivation with water or the like.

The waste solvents are filtered under pressure through an ultrafiltration membrane module to separate the organic solvent and concentrate the waste solvents.

The concentration of low molecular weight polyolefin in the concentrated waste solvent is 5
~dos is 2 to 30 times the initial concentration of the waste solvent. If the concentration of the low molecular weight polyolefin in the concentrated waste solvent exceeds 60%, the permeation (filtration) rate will drop significantly, which is not preferable.

The concentrated waste solvent can be treated by various methods as necessary to separate or recover the low molecular weight polyolefin. For example, 1) a method of repeating filtration and further concentrating, 2) a method of blowing water vapor to float the low molecular weight polyolefin on water, and 3) a method of recovering the solvent in the concentrated dead solvent to a boiling point higher than the melting point of the low molecular weight polyolefin. 4) A method of pressurizing the low molecular weight polyolefin at a temperature higher than its melting point and then using a centrifugal thin film evaporator to recover the low molecular weight polyolefin; 5)
In cases involving low boiling point solvents such as liquefied propylene,
Examples include flushing under reduced pressure.

The nine organic solvents that pass through the ultrafiltration membrane module are
It is used either directly or after death by adsorption, dehydration, or distillation, and then recycled to the polymerization or washing step.

As the organic solvent related to the waste solvent of the present invention, hydrocarbon water 114
alcohols, ethers, esters, ketones, etc. Hydrocarbons include aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, and aliphatic hydrocarbons include liquefied propane, butane (normal or/and iso), inhentane, nor-1, hexane, and normal. Examples include hebutane, liquefied propylene, liquefied butene-1, pentene-1, and hexene-1,4-methylpentene-1. Examples of alicyclic hydrocarbons include methylcyclopentane, cyclohexane, and methylcyclohexane. Examples of the aromatic 111dJt hydrogen compound include benzene, toluene, 1-xylene, and styrene. Hydrocarbon water
Examples of cords include ligroin, kerosene, and light oil.

Alcohols include monohydric alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, tertiary-butyl alcohol, isoamyl alcohol, and 2-
An example is ethylhexyl alcohol. Polyhydric alcohols include ethylene glycol, fluoropylene gellicol,
Examples include Guriryurin. Ethers have the general formula R1
-(OR,), -OR, (R1, R,, R,: alkyl, allyl, aralkyl group %fi = integer of O-5) - Ethyl ether, isopropyl alcohol, ethylene glycol dimethyl ether, etc. can be exemplified. Esters have the general formula R1C0OR, (R1,R,
==fur+#-7lyl/aralkyl group), examples of which include methyl acetate and ethyl acetate. Ketones have the general formula R, C0(R,C0)llR, (R1%
K,, R1=alkyl/allyl/aralkyl group, n=o
-5 integer), and examples include acetone, methyl, ethyl ketone, and acetylacetone.

These exemplified organic solvents may be used alone or in the form of various mixtures, and in the case of mixtures, it is sufficient as long as phase separation does not occur.

In the method of the present invention, the concentration of the low molecular weight polyolefin in the concentrated solvent is significantly increased by filtering through the ultrafiltration membrane. In other words, the waste solvent of low molecular weight polyolefin with a concentration of 1- becomes 5-10- by filtration,
By repeating filtration, it can reach up to 604 degrees. Most of the solvent in the waste solvent is separated by filtration according to the present invention. Therefore, when separating or recovering a low molecular weight polyolefin from a concentrated dead solvent, the thermal energy of steam etc. can be significantly reduced even if conventional steam distillation methods, solvent displacement methods, and centrifugal thin membranes are used.

By directly linking the separation method of the present invention to a medium-low pressure method or a process for producing high-density to low-density polyethylene or polypropylene, the production cost of the polyolefin can be significantly reduced.

The polytetrapyrene production process proposed by the present inventor in Japanese Patent Application No. 55-1"07487 (a copolymer production process with a significantly high production rate of hydrocarbon-insoluble polymers) It is possible to complete a complete circulation process in which the polymerization solvent is recycled to the polymerization process without purification.

Examples are shown below.

Examples 1 to 23 The indicated waste solvents were continuously fed under the indicated conditions to a device in which the indicated ultrafiltration membranes were modularized, and the waste solvents were permeated through the ultrafiltration membranes to form a permeated solution and a discharged waste solvent. separated. The discharged waste solvent was continuously recycled to the module. Finally, the feed and dead solvent is separated into permeation solvent and discharged concentrated waste solvent.

To explain Example 1, a charged waste solvent with a polymer concentration of 1.2 weight was passed through an ultrafiltration membrane module, and a permeated solvent with a significantly low polymer concentration (0.04 weight 9G) and an extremely high polymer concentration ( 11.0 weight 9G) was separated into a concentrated waste solvent.

Therefore, the concentration ratio of the solvent is. On the other hand, when comparing the pre-concentration operation, which is a preliminary step of the conventional centrifugal thin film evaporation method, with the conventional method using steam heating, it was found that the method using the ultrafiltration membrane of the present invention is suitable for pressurizing and circulating waste solvent. Since only a small amount of electricity is needed to power the pump, this is a significant energy savings compared to conventional methods.

An explanation of the table is given below.

L ultrafiltration membrane polyhydride system - Nitto Denko N'l'U-4200 series Boria 5-d system - BIrghof polyvinylisoy-7-fluoride system - PINnwalt YNA
B Polytetrafluoroethylene system - Pomaflon polysulfone system manufactured by Sumitomo Electric Industries Ltd. - Ud manufactured by UCC Company P-1 F A low molecular weight, low crystalline copolymer produced as a by-product during the production of .0 to 5.5 weight-).

*2) Low molecular weight, low crystallinity copolymer produced as a by-product during the production of propylene ethylene block copolymer (ethylene content: 8 to 13 weight).

& Polymer concentration The solvent in the sample was evaporated to dryness and the remaining amount was calculated.

Table Average Molecular Weight My WatIr association's G@lPsrm
Obtained from satioachromatography K.

a Operating conditions Pressure - Average value of pressure at module inlet and outlet Temperature - Temperature of charged waste solvent d Permeation rate limit r Amount of permeated solvent per hour per membrane IS (/II I Division molecular weight Monodispersed polyethylene glycol 0.511) The toluene solution was passed through a filter membrane, and the G・lp@rm・1 was
Molecular weight to obtain 96% solute removal rate using kroosatography.

Claims (1)

[Scope of Claims] l) A low-molecular-weight product characterized by concentrating a waste solvent containing a low-molecular-weight polyolefin obtained in a polyolefin manufacturing process by passing it through an ultrafiltration membrane under pressure. A method for separating organic solvents from waste solvents containing polyoleain. 2) AI of the patent claim in which the concentrated waste solution is further filtered through an ultraf filter membrane to further concentrate it! ! No. (1)
The method described in section. 3) A method according to claim 1 or (rumored claim) in which the low molecular weight polyolefin is separated by blowing water vapor into the concentrated 90% solvent. 4) The method described in claim 1 or 4 (purported claim) of blowing steam into the concentrated 90% solvent to separate the low molecular weight polyolefin. The method according to claim (1) or claim 12), wherein the low molecular weight polyolefin is separated by replacing the solvent with a solvent having a boiling point higher than that. 5) The concentrated waste solvent is pressurized at a temperature higher than the melting point of the low-molecular-weight polyolefin and sent to a centrifugal thin film evaporator for 72 hours to separate the low-molecular-weight polyolefin.
The method described in item 1) or item 12).