阅读说明：本技术 一种利用离子液体回收尼龙/聚烯烃复合膜的方法 (Method for recovering nylon/polyolefin composite membrane by using ionic liquid ) 是由 麻一明 徐禄波 吴剑波 王旭 文正健 孙剑 于 2020-05-15 设计创作，主要内容包括：本发明提供一种利用离子液体回收尼龙/聚烯烃复合膜的方法。包括以下步骤：尼龙/聚烯烃复合膜经粉碎、清洗、烘干后,与干燥剂一起置于离子液体中,升温将尼龙/聚烯烃复合膜溶解后,静置,溶液上层浮出物质,收集该物质,洗涤、烘干得再生聚烯烃；将除去上层物质的剩余溶液过滤,以除去干燥剂,得到含有尼龙的离子液体溶液,将溶液加入水中析出尼龙,过滤、洗涤、烘干得再生尼龙。过滤尼龙后的残留溶剂通过真空蒸馏处理,分离离子液体和水,得到可重复利用的离子液体。本发明的回收方法可以将复合膜中的尼龙和聚烯烃完全分离,分别再循环利用,而回收方法中使用的干燥剂和离子液体均能再回收使用,大大降低回收成本,绿色环保。(The invention provides a method for recovering a nylon/polyolefin composite membrane by using ionic liquid. The method comprises the following steps: after being crushed, cleaned and dried, the nylon/polyolefin composite membrane and a drying agent are placed in ionic liquid together, the nylon/polyolefin composite membrane is dissolved by heating, then the mixture is kept stand, substances float out from the upper layer of the solution, and the substances are collected, washed and dried to obtain regenerated polyolefin; and filtering the residual solution from which the upper-layer substances are removed to remove the drying agent to obtain an ionic liquid solution containing nylon, adding the solution into water to separate out the nylon, and filtering, washing and drying to obtain the regenerated nylon. And (3) carrying out vacuum distillation treatment on the residual solvent after nylon filtration to separate the ionic liquid and water, thereby obtaining the recyclable ionic liquid. The recovery method can completely separate the nylon and the polyolefin in the composite membrane and recycle the nylon and the polyolefin respectively, and the drying agent and the ionic liquid used in the recovery method can be recycled, so that the recovery cost is greatly reduced, and the method is green and environment-friendly.)

1. A method for recovering a nylon/polyolefin composite membrane by using ionic liquid is characterized by comprising the following steps:

after being crushed, cleaned and dried, the nylon/polyolefin composite membrane and a drying agent are placed in ionic liquid together, the nylon/polyolefin composite membrane is dissolved by heating, then the mixture is kept stand, substances float out from the upper layer of the solution, and the substances are collected, washed and dried to obtain regenerated polyolefin;

filtering the residual solution from which the upper-layer substances are removed to remove the drying agent to obtain an ionic liquid solution containing nylon, adding the solution into water to separate out the nylon, filtering, washing and drying to obtain regenerated nylon;

and (3) carrying out vacuum distillation treatment on the residual solvent after nylon filtration to separate the ionic liquid and water, thereby obtaining the recyclable ionic liquid.

2. The method for recycling a nylon/polyolefin composite film according to claim 1, wherein the polyolefin is polyethylene and/or polypropylene.

3. The method for recycling a nylon/polyolefin composite membrane according to claim 1, wherein the ionic liquid comprises a cation and an anion, the cation is one or more of 1-alkyl-3-methyl substituted imidazolium, N-alkyl pyridinium, N-alkyl-N-methyl piperidinium, alkyl quaternary ammonium, alkyl quaternary phosphonium, N-alkyl-N-methyl pyrrolidinium, 1, 2-dialkyl pyrrolidinium, N-alkyl thiophenium; the anion is one or more of hexafluorophosphate, tetrafluoroborate, trifluoroacetate, bis (trifluoromethanesulfonyl) imide, triflate, nitrate and halide.

4. The method for recycling a nylon/polyolefin composite membrane according to claim 1 or 3, wherein in the ionic liquid, the cation is 1-alkyl-3-methyl substituted imidazolium and the anion is trifluoromethanesulfonate.

5. The method for recycling a nylon/polyolefin composite membrane according to claim 4, wherein the ionic liquid is 1-butyl-3-methylimidazole trifluoromethanesulfonate.

6. The method of recycling a nylon/polyolefin composite membrane according to claim 1, wherein the desiccant is a neutral desiccant.

7. The method for recycling a nylon/polyolefin composite membrane according to claim 1 or 6, wherein the drying agent is one or more of anhydrous calcium chloride, anhydrous copper sulfate, anhydrous calcium sulfate, anhydrous magnesium sulfate, alumina and molecular sieve.

8. The method for recycling a nylon/polyolefin composite membrane according to claim 7, wherein the desiccant is anhydrous calcium chloride.

9. The method for recycling a nylon/polyolefin composite membrane according to claim 1, wherein the mass ratio of the nylon/polyolefin composite membrane, the desiccant and the ionic liquid is (5-20): 1: (50-200).

10. The method for recycling a nylon/polyolefin composite membrane according to claim 1, wherein the temperature is raised to 150 ℃ and 200 ℃ to dissolve the nylon/polyolefin composite membrane for 0.5 to 8 hours.

Technical Field

The invention belongs to the technical field of high polymer material recycling and relates to a method for recycling a nylon/polyolefin composite membrane by using an ionic liquid.

Background

The nylon/polyolefin composite film is a multilayer structure film formed by blowing nylon (PA), an ionic resin adhesive, polyolefin and the like by a co-extruder by adopting a special production process. The composite film has the advantages of nylon and polyolefin, has the advantages of high stretching, good moisture resistance, low oxygen permeability, oil resistance, high and low temperature resistance, no toxicity, no odor, easy heat sealing, good air tightness and the like, and is widely applied to the fields of food packaging, medicines, express packaging buffer air cushions and the like. Nylon composite membranes are one of the important sources of recycled PA and recycled polyolefin. Currently, nylon/polyolefin composite particles are directly recycled on the market, for example, a recycled express packaging buffer air cushion film material is composed of three components including LDPE, PA6 and LLDPE, wherein the mass content of the LDPE is within the range of 38% -46%, the mass content of the PA6 is about 17% -23%, and the mass content of the LLDPE is 36% -40%. Because PA and polyolefin in the nylon composite film are difficult to separate and polyolefin and PA are incompatible, the mechanical strength of the polyolefin/PA composite material directly subjected to injection molding is very poor and difficult to directly apply, so that the utilization efficiency of regenerated polyolefin and regenerated PA is low, and the effective recycling of the regenerated polyolefin/PA from the nylon composite film is limited.

If polyolefin and PA are separated, a large amount of manpower and material resources are inevitably consumed, and the product cost is increased. The cost of regrind has long been the core of product competitiveness, driving costs unacceptable to the traditional plastic recycling industry. Therefore, the industry has not been devoting great skill and expense to research the separation and recovery of PA and polyolefin. In recent years, with the increase of environmental protection strength in China, the recycled plastic industry is facing transformation, the demand for recycled plastics is shifting from cost driving to environmental resource protection, and the quality requirement for recycled plastics is higher and higher. The classified recovery of PA and polyolefin of nylon composite films is also one of the important trends in future development.

Ionic liquids are salts that are liquid at or near room temperature and are composed entirely of anions and cations. The ionic liquid is generally composed of organic cations and inorganic or organic anions, common cations include quaternary ammonium salt ions, quaternary phosphonium salt ions, imidazolium salt ions, pyrrole salt ions and the like, and anions include halogen ions, tetrafluoroborate ions, hexafluorophosphate ions and the like. In general, an ionic salt is melted into a liquid state only at a high temperature, and the melting point of an ionic liquid is usually close to room temperature, so that the ionic liquid is also called room-temperature molten salt, room-temperature ionic liquid and the like. Compared with traditional solvents such as water, organic solvents and the like, the ionic liquid has a series of advantages of wide liquid temperature range, difficult volatilization, strong dissolving capacity, high electrochemical stability and the like. More importantly, the functional designability of the ionic liquid enables the physical and chemical properties of the ionic liquid to be adjusted and controlled by modifying or adjusting the structure and the type of the anions and cations. The ionic liquid with unique physical and chemical properties becomes a green functional material and medium with good application prospect, and has been applied to the field of PA recovery.

For example, chinese patent CN102492155A discloses a method for preparing nylon powder by dissolving waste nylon with ionic liquid. Dissolving waste nylon in ionic liquid at high temperature, adding deionized water for precipitation, filtering and drying to obtain nylon powder. However, the invention does not relate to the separation of nylon/polyolefin composites.

For another example, chinese patent CN103298869 discloses a method for depolymerizing nylon by using ionic liquid solvent and containing [ HSO₄]^-Or [ HPO ]₄]^2-Hydrophobic ions of ionsThe liquid is a solvent, then 1 equivalent of sulfuric acid and 1 equivalent of water are added into the ionic liquid, and the nylon is hydrolyzed under the high-temperature condition, so that the amine salt and the diacid micromolecules are finally obtained. Chinese patent CN102382052 provides a method for obtaining caprolactam by degrading and recycling waste nylon 6 in an ionic liquid/water mixed system, the method adopts imidazole-halide ionic liquid and water to form a mixed solvent, wherein the molar part of the ionic liquid is 10-20%, the process needs to degrade for 5-10 hours at the temperature of 150-230 ℃, and the mass ratio of the nylon to the mixed solvent is 1: 5-15, the yield of-caprolactam can be more than 50%. Chinese patent 102503890 discloses a method for recovering caprolactam by hydrolyzing waste nylon 6 under catalysis of acidic ionic liquid, which takes the acidic ionic liquid as a solvent, can simultaneously serve as the solvent and a catalyst, nylon is limitedly dissolved in the acidic ionic liquid when nylon is degraded and recovered, then water is added at 100-180 ℃, nylon is further hydrolyzed, and the recovery rate of caprolactam can reach more than 80%. Chinese patent CN102491913 discloses a method for catalyzing alcoholysis of waste nylon 6 by using binuclear ionic liquid and recovering alcoholysis monomers, the method comprises the steps of firstly dissolving the waste nylon 6 by using the binuclear ionic liquid, and then adding alcohol solvents such as methanol and ethanol to carry out alcoholysis on the nylon, so as to obtain methyl 6-aminocaproate or ethyl 6-aminocaproate.

However, the above patents adopt a chemical method to recover nylon monomers, and do not mention how to recover nylon by a physical method.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a novel method for recovering a nylon/polyolefin composite membrane, which completely separates and recovers polyolefin and nylon by utilizing the difference of the dissolubility of the ionic liquid to the nylon and the polyolefin, and adds a drying agent, thereby solving the adverse effect of moisture on the recovery of the nylon and greatly improving the economic benefit.

The invention provides a method for recovering a nylon/polyolefin composite membrane by using ionic liquid, which comprises the following steps:

after being crushed, cleaned and dried, the nylon/polyolefin composite membrane and a drying agent are placed in ionic liquid together, the nylon/polyolefin composite membrane is dissolved by heating, then the mixture is kept stand, substances float out from the upper layer of the solution, and the substances are collected, washed and dried to obtain regenerated polyolefin;

filtering the residual solution from which the upper-layer substances are removed to remove the drying agent to obtain an ionic liquid solution containing nylon, adding the solution into water to separate out the nylon, filtering, washing and drying to obtain regenerated nylon;

and (3) carrying out vacuum distillation treatment on the residual solvent after nylon filtration to separate the ionic liquid and water, thereby obtaining the recyclable ionic liquid.

The ionic liquid has good solubility for PA, but it is difficult to dissolve the polyolefin, so the two polymers can be separated and recovered by the difference in solubility of the two polymers in the ionic liquid. The ionic liquid dissolves PA under high temperature, PA is easy to generate thermo-oxidative aging degradation under high temperature, high temperature hydrolysis can also occur under the condition of water molecules, and the molecular weight of PA can be seriously reduced by the side reactions. In the invention, when the nylon composite membrane is dissolved at high temperature, in order to avoid the situation, the drying agent is added to remove the moisture released into the ionic liquid in the dissolving process of the nylon.

The process schematic diagram of the present invention for recycling nylon/polyolefin composite membrane is shown in FIG. 1. According to the invention, the nylon/polyolefin composite membrane as the recycled raw material is subjected to crushing, cleaning and drying treatment before the ionic liquid is added, the crushed composite membrane is favorable for dissolution, and the moisture in the composite membrane can be removed to the greatest extent by drying. After the ionic liquid is added into the nylon/polyolefin composite membrane, stirring treatment is preferably adopted. During the temperature raising process, the polyolefin on the composite film begins to melt before the PA is dissolved, and is stripped from the composite film under the action of stirring shear force. The density of the ionic liquid is mostly 1.0 to 1.5g/cm³Between the polyolefin and the desiccant. In the standing process of the mixed solution, because the density of the polyolefin is lower than that of the ionic liquid, the stripped polyolefin is gradually gathered and floats on the surface of the ionic liquid, the ionic liquid is re-agglomerated into blocks after being cooled, the blocks are fished out by a filter screen, and the blocks are washed by water and dried to obtain the regenerated polyolefinA hydrocarbon. And the drying agent is settled to the bottom of the solution in the standing process, the drying agent can be separated by filtering, and the drying agent after being washed and dried can be recycled. Adding the solution without the drying agent into water, separating out PA from the ionic liquid, filtering, cleaning and drying to obtain regenerated PA powder. And recovering the ionic liquid by vacuum distillation of the ionic liquid/water mixed solvent.

The nylon/polyolefin composite membrane as the recovered raw material is a composite membrane material commonly used in the market, such as a high-pressure nylon composite membrane. The nylon/polyolefin composite film is a multilayer structure film formed by adopting raw materials such as nylon, adhesive, polyolefin and the like through a special production process and blow molding by a co-extruder, and can be a three-layer film structure as shown in figure 2, wherein the three-layer film structure sequentially comprises PA, adhesive and polyolefin, and can also be a five-layer film structure as shown in figure 3, the five-layer film structure sequentially comprises polyolefin, adhesive, PA, adhesive and polyolefin, the structure is not limited, and the nylon/polyolefin composite film can be used as a recycled raw material of the invention as long as the nylon and polyolefin composite film is a film material.

The polyolefin of the recycled raw material nylon/polyolefin composite film is preferably polyethylene and/or polypropylene, the polyethylene and the polypropylene are usually compounded with nylon, and the melting point range of the polyethylene and the polypropylene ensures that the polyethylene and the polypropylene are easy to precipitate and separate from the nylon in the dissolving and standing process. The nylon/polyethylene composite membrane and the nylon/polypropylene composite membrane are more suitable for recycling by using the method of the invention.

Preferably, the ionic liquid comprises a cation and an anion, wherein the cation is one or more of 1-alkyl-3-methyl substituted imidazole cation, N-alkyl pyridine cation, N-alkyl-N-methyl piperidine cation, alkyl quaternary ammonium cation, alkyl quaternary phosphonium cation, N-alkyl-N-methyl pyrrole cation, 1, 2-dialkyl pyrrole cation and N-alkyl thiophene cation; the anion is one or more of hexafluorophosphate, tetrafluoroborate, trifluoroacetate, bis (trifluoromethanesulfonyl) imide, triflate, nitrate and halide.

For example, the ionic liquid may be 1-ethyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium bromide, N-butyl-N-methylpiperidine tetrafluoroborate, N-butyl-N-methylpiperidine bromide, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate or the like.

The melting point of the ionic liquid selected in the present invention must not be too high and must be below the melting point of the polyolefin. If the melting point of the selected ionic liquid is lower than that of the polyolefin, but higher than room temperature, in order to prevent the ionic liquid from solidifying due to gradual temperature reduction in the standing process, the solution needs to be reduced to a range above the melting point of the ionic liquid and below the melting point of the polyolefin, and then the solution is stored at constant temperature to ensure that the polyolefin is separated out and the ionic liquid is not solidified. If the melting point of the selected ionic liquid is lower than the room temperature, the ionic liquid is naturally cooled to the room temperature without keeping higher temperature in the standing process.

In combination with good solubility and low melting point characteristics of the ionic liquid to nylon, the ionic liquid is further preferable, wherein cations in the ionic liquid are 1-alkyl-3-methyl substituted imidazolium ions, and anions in the ionic liquid are trifluoromethanesulfonic acid radicals. Such as 1-ethyl-3-methylimidazole trifluoromethanesulfonate, 1-butyl-3-methylimidazole trifluoromethanesulfonate. The 1-ethyl-3-methylimidazole trifluoromethanesulfonate and the 1-butyl-3-methylimidazole trifluoromethanesulfonate have excellent solubility for nylon and lower melting points, the melting point of the 1-ethyl-3-methylimidazole trifluoromethanesulfonate is about-12 ℃, and the melting point of the 1-butyl-3-methylimidazole trifluoromethanesulfonate is about 16 ℃, so that a higher temperature does not need to be kept in the standing process, and the energy consumption is reduced.

Still more preferably, the ionic liquid is 1-butyl-3-methylimidazolium trifluoromethanesulfonate. The thermal decomposition temperature of the 1-butyl-3-methylimidazole trifluoromethanesulfonate is about 409 ℃ and higher than the decomposition temperature of the 1-ethyl-3-methylimidazole trifluoromethanesulfonate of 340 ℃, and the thermal stability is better in the high-temperature dissolving process of the composite membrane.

Preferably, the desiccant is a neutral desiccant.

Further preferably, the drying agent is one or more of anhydrous calcium chloride, anhydrous copper sulfate, anhydrous calcium sulfate, anhydrous magnesium sulfate, alumina and a molecular sieve.

The desiccant cannot remain in the PA as an impurity, and therefore the desiccant should be easily separable from the PA. It is necessary to use a desiccant that is insoluble in the ionic liquid so that the desiccant after absorption of water can be removed from the solution by simple filtration without affecting the purity of the PA. The anhydrous calcium chloride, anhydrous copper sulfate, anhydrous calcium sulfate and anhydrous magnesium sulfate absorb water molecules by forming crystal water with the water molecules, and do not form strong interaction with the ionic liquid.

And the anhydrous calcium chloride absorbs water and then loses crystal water completely when heated at about 260 ℃, so the anhydrous calcium chloride is more preferable.

Preferably, the mass ratio of the nylon/polyolefin composite membrane, the drying agent and the ionic liquid is (5-20): 1: (50-200).

The ionic liquid needs to dissolve nylon under high temperature conditions, and the temperature range is between 100 ℃ and 300 ℃. The temperature rise temperature of the invention needs to be selected in consideration of the high-temperature solubility of the polyolefin and the stability of the drying agent. The melting point of polyethylene is below 150 ℃, high density polyethylene is about 130 ℃, low density polyethylene is about 110 ℃, polypropylene has a melting point of about 165 ℃, and the dissolution temperature needs to be higher than that of polyolefin. But the dissolution temperature cannot be too high, and the high temperature can dehydrate the crystal water of the drying agent. Therefore, the temperature rise temperature of the present invention is preferably 150-. After the ionic liquid is added into the nylon/polyolefin composite membrane, the temperature is preferably raised to 150-200 ℃, and the nylon/polyolefin composite membrane is dissolved for 0.5-8 hours at 150-200 ℃.

Preferably, the standing time is 0.5 to 5 hours.

Compared with the prior art, the invention has the following beneficial effects:

1) the ionic liquid is selected as the solvent, the solvent is not easy to volatilize, is non-toxic and environment-friendly, has good dissolving performance on PA, but can not dissolve polyolefin, and PA and polyolefin can be effectively separated;

2) before the nylon/polyolefin composite membrane is dissolved, drying treatment is carried out, and a drying agent is added into the ionic liquid to absorb the water released in the dissolving process of the nylon, so that the hydrolysis of the nylon in the high-temperature dissolving process is avoided to the greatest extent;

3) the invention utilizes the different densities of the ionic liquid, the polyolefin and the drying agent to realize the material separation: after the ionic liquid dissolves the composite membrane, the drying agent with higher density is precipitated at the bottom of the solution, the polyolefin with lower density floats on the surface of the solution, and after the polyolefin floating on the surface is taken out, the drying agent and the solution are filtered and separated, so that the polyolefin, the drying agent and the solution containing PA can be respectively obtained; the separation process is simple and easy to realize industrialization;

4) the recovery method can completely separate the nylon and the polyolefin in the composite membrane and recycle the nylon and the polyolefin respectively, and the drying agent and the ionic liquid used in the recovery method can be recycled, so that the recovery cost is greatly reduced, and the recovery method is green and environment-friendly;

5) the melting points of the 1-ethyl-3-methylimidazole trifluoromethanesulfonate and the 1-butyl-3-methylimidazole trifluoromethanesulfonate further selected by the invention are lower, and the energy consumption is effectively reduced without keeping higher temperature in the standing process;

6) the anhydrous calcium chloride of the drying agent further selected by the invention has high-temperature stability and is beneficial to reducing the degradation effect of moisture on nylon.

Drawings

FIG. 1 is a schematic view of a process for recycling a nylon/polyolefin composite film according to the present invention;

FIG. 2 is a three-layer nylon/polyolefin composite membrane structure;

FIG. 3 is a five-layer nylon/polyolefin composite membrane structure.

Detailed Description

Hereinafter, the technical solution of the present invention will be further described and illustrated by specific examples. The raw materials used in the examples of the present invention are those commonly used in the art, and the methods used in the examples are those conventional in the art, unless otherwise specified.