CN104511369B - Method for waste mixed plastic separation - Google Patents

Abstract

The invention discloses a method for waste mixed plastic separation. The method comprises the following steps: crushing waste mixed plastic into mixed plastic particles, adding the obtained mixed plastic particles into a liquid medium I to perform sinking and floating separation, obtaining light-component plastic particles which are smaller than the liquid medium I in density and heavy-component plastic particles which are larger than that of the liquid medium I in density through the sinking and floating separation, adding the heavy-component plastic particles into a liquid medium II to perform surface treatment at a temperature of 70-100 DEG C and performing flotation separation on the heavy-component plastic particles subjected to surface treatment through a floating agent. According to the method, a variety of plastics in waste plastics can be efficiently and selectively separated. The method is simple to operate, is low in cost and meets the industrial application and production.

Description

A method for separating waste mixed plastics

technical field

The invention relates to a method for separating waste and old mixed plastics, belonging to the technical field of waste and old plastics recycling.

Background technique

The rapid development of the plastics industry, the massive consumption of plastics, and the short life cycle of plastics have led to a sharp increase in the amount of plastic waste. The disposal methods of waste plastics are incineration and landfill, resulting in serious environmental pollution and waste of resources. Therefore, the recycling of waste plastics has been highly valued. For the recycling process of waste plastics, it is necessary to separate different plastics. At present, the separation of plastics is the bottleneck link restricting the recycling process of waste plastics. The mixed plastics separation technologies developed include methods such as manual sorting, gravity separation, flotation, electrostatic separation and selective dissolution. The manual sorting process of plastics is labor-intensive, the working environment is harsh, and the separation efficiency is low. Gravity separation and electrostatic separation have great limitations on the separation of mixed plastics with similar physical properties. Selective solvents are costly and organic solvents are very toxic. In addition, the low profit of plastic recycling and the diversity of waste plastics also limit the development of plastic separation technology. Therefore, it is an important issue in this field to develop a separation technology with low cost, strong adaptability and high separation efficiency.

Contents of the invention

Aiming at the defects existing in the methods for separating waste mixed plastics in the prior art, the purpose of the present invention is to provide a method for efficiently and selectively separating various plastic components in waste plastics by combining floating-sink separation and flotation methods. The method has the advantages of simple operation and low cost, and satisfies industrial application and production.

The invention provides a method for separating waste and old mixed plastics. The waste and old mixed plastics contain at least one light component plastic with relatively low density and at least two heavy component plastics with similar density and relatively high density, wherein , the heavy component plastic contains at least one kind of plastic containing polar groups and plastics without polar groups; the waste mixed plastics are broken into mixed plastic particles, and the obtained mixed plastic particles are added to liquid medium I for sinking and floating separation, Light component plastic particles with a density lower than liquid medium I and plastic particles with a density greater than liquid medium I are obtained by sinking and floating separation, and the obtained heavy component plastic particles are added to liquid medium II for surface treatment at a temperature of 70-100°C. After surface treatment The heavy component plastic particles are separated by flotation by flotation agent, and the plastic particles containing polar groups and the plastic particles without polar groups are separated.

The method for separating waste and old mixed plastics of the present invention also includes the following preferred solutions:

In the preferred solution, the density of the liquid medium I is between 970 and 1200 kg/m ³ , and the liquid medium I with a suitable density is selected according to the density of the waste mixed plastic particles to be separated.

In a further preferred scheme, the liquid medium I is selected from an alcohol-water mixed solution, or at least one of tap water, deionized water, seawater, and distilled water, or sodium chloride, sodium sulfate, calcium chloride, potassium chloride, nitric acid An aqueous solution of at least one of potassium and sodium nitrate.

In the preferred scheme, a suitable liquid medium I is selected according to the average density of the plastic to be separated, and the density of the liquid medium I is higher than that of light component plastics and lower than that of heavy component plastics. The liquid medium I can be selected as at least one of tap water, deionized water, seawater, and distilled water with a density close to 1000kg/ ^m3 ; or an aqueous solution of methanol and/or ethanol with a density of 970～1000kg/ ^m3 , Alternatively, it may be selected as an aqueous solution of at least one of sodium chloride, sodium sulfate, calcium chloride, potassium chloride, potassium nitrate and sodium nitrate with a density between 1000-1200 kg/ ^m3 .

In a preferred solution, the heavy component plastic particles are added to the liquid medium II at a temperature of 70-100° C. for 30-180 minutes of surface treatment.

In a further preferred scheme, the liquid medium II is at least one of tap water, deionized water, seawater, distilled water, sodium chloride solution, sodium sulfate solution, calcium chloride solution, potassium chloride solution, potassium nitrate solution, and sodium nitrate solution . The pH of the liquid medium II is around 7.

In the preferred solution, the surface-treated heavy plastic particles are dispersed in the flotation medium, and a flotation agent is added for flotation separation.

In a preferred solution, the flotation agent includes a flotation agent with a bubble effect and/or a flotation agent with a wetting effect.

In a further preferred solution, the flotation agent with bubble effect is at least one of terpineol, methyl isobutyl carbinol, α-terpene alcohol, and polyethylene glycol.

In the further preferred scheme, the flotation agent with wetting effect is at least one of lignosulfonate, tannic acid, gelatin, sparrow bark juice, cellulose, alkyl polyoxyethylene ether, water glass, fatty amine A sort of.

In a further preferred scheme, the flotation agent is added to the flotation medium in an amount of 10-500 mg/L. Most preferably, it is added to the flotation medium in an amount of 20-300 mg/L.

In a further preferred solution, the flotation medium is at least one of tap water, deionized water, seawater, and distilled water.

In a further preferred solution, the flotation separation time is 1 to 15 minutes.

In the preferred scheme, the light component plastics include polyethylene and/or polypropylene, the plastics without polar groups in the heavy component plastics include plastics containing aromatic rings, and the plastics containing polar groups in the heavy component plastics include Plastics containing sulfur, oxygen, and nitrogen heteroatom groups; heavy component plastics account for 1% to 99% of the mass of waste mixed plastics. Plastics without polar groups such as polystyrene, etc. Plastics containing polar groups are polycarbonate, polyamide, etc.

In a preferred solution, the heavy component plastics account for 1% to 99% of the mass of waste mixed plastics.

In a preferred scheme, waste and old mixed plastics are crushed into mixed plastic particles with a particle size of 1-10 mm.

In a preferred solution, crushing is freeze crushing or mechanical crushing.

In a further preferred solution, freeze crushing is to freeze the plastic first and then mechanically crush it immediately.

In a further preferred solution, the mechanical crushing is realized by a crusher, and at the same time, an appropriate amount of water is added to the crusher during the crushing process to ensure that the temperature of the plastic is not greater than 40°C.

The crushing is jaw crusher, gyratory crusher, impact crusher or roller crusher.

In a further preferred solution, the plastic particles are uniformly dispersed in the flotation medium by stirring during the flotation process, and the stirring rate is not greater than 100 r/min.

In a further preferred solution, an appropriate amount of air is introduced into the flotation medium during the flotation process to promote the generation of air bubbles, and the inflation rate is 1-800 mL/min.

In the preferred solution, the waste and old mixed plastics are first cleaned to remove non-plastic pollutants such as surface oil and sediment; an appropriate amount of sodium hydroxide or cleaning agent can be added during the cleaning process to improve the cleaning effect.

In a preferred solution, the surface-treated heavy plastic particles are washed with water before flotation, and can be rinsed and cooled with water, or soaked in water for 5-60 minutes.

The method for separating waste and old mixed plastics of the present invention comprises the following steps:

Step 1: Clean the waste and old mixed plastics; add a small amount of sodium hydroxide or cleaning agent during the cleaning process to promote the cleaning effect;

Step 2: Use freeze crushing or mechanical crushing to crush the waste mixed plastics into mixed plastic particles with a particle size of 1-10mm; freeze the waste mixed plastics first, and then perform mechanical crushing, or directly use mechanical crushing, and the mechanical crushing process will be crushed Add an appropriate amount of water to the machine to ensure that the temperature of the plastic is lower than 40°C; the crushing machinery used is a jaw crusher, a gyratory crusher, an impact crusher or a roller crusher; the waste mixed plastic contains at least one Light component plastics with a relatively low density and at least two heavy component plastics with similar densities and relatively high densities, wherein the heavy component plastics contain at least one type of plastic containing heteropolar groups and plastics without polar groups plastic;

Step 3: Add the mixed plastic particles into the liquid medium I for sinking and floating to separate the light component plastic particles and the heavy component plastic particles. The liquid medium I can be selected as tap water with a density close to 1000kg/ ^m3 according to the actual density of the plastic to be separated. At least one of deionized water, seawater, and distilled water; or an aqueous solution of methanol and/or ethanol with a density between 970 and 1000 kg/ ^m3 , or chlorine with a density between 1000 and 1200 kg/ ^m3 An aqueous solution of at least one of sodium chloride, sodium sulfate, calcium chloride, potassium chloride, potassium nitrate, and sodium nitrate;

Step 4: Add the heavy component plastic particles obtained from the sink-float separation into liquid medium II at 70-100°C for surface treatment for 30-180 minutes. The liquid medium II is tap water, deionized water, seawater, distilled water, sodium chloride solution, At least one of sodium sulfate solution, calcium chloride solution, potassium chloride solution, potassium nitrate solution, sodium nitrate solution;

Step 5: Rinse and cool the surface-treated heavy-component plastic particles with tap water, or soak the heavy-component plastic particles in water for 5-60 minutes;

Step 6: Disperse the heavy component plastic particles in the flotation medium, add flotation agent for flotation separation; add flotation agent at a rate of 10-500mg/L, blow air in at a rate of 1-800mL/min, and perform flotation Separation for 1-15 minutes, flotation to produce plastics without polar groups; flotation medium is at least one of tap water, deionized water, sea water, and distilled water; flotation agent is terpineol, methyl isobutyl carbinol , α-terpene alcohol and at least one of polyethylene glycol, lignosulfonate, tannic acid, gelatin, quebracho bark juice, cellulose, alkyl polyoxyethylene ether, water glass, fatty amine.

Compared with the prior art, the beneficial effect of the present invention lies in that: based on the fact that it is difficult to achieve multi-component separation of mixed plastics in the prior art, the present invention combines floating-sink separation and flotation separation methods for the first time to selectively separate mixed plastics, and can multi-component Simultaneous separation of two kinds of plastics, especially for the separation of mixed plastics with similar densities. The invention carries out surface treatment on the plastics with similar densities under appropriate temperature conditions, so that the plastics such as polystyrene can be selectively enriched and separated in combination with the flotation method in the mineral processing field. The solution of the invention has good separation effect on various plastics in waste plastics, and has a high recovery rate; in addition, the process of the invention is simple in operation, low in cost, has good economic feasibility, and satisfies industrial application.

detailed description

The present invention is further illustrated by the following examples, which are not to be construed in any way as imposing limitations on the scope of the present invention. On the contrary, it should be clearly understood that various other embodiments, modifications and their equivalents, which can be seen by those skilled in the art after reading the description herein, can be adopted without departing from the spirit of the invention and/or the spirit of the appended claims. scope.

Example 1

Add mixed plastics containing PC, PS and PP to tap water containing a small amount of cleaning agent for cleaning, and then use a plastic crusher to crush it. During the mechanical crushing process, add an appropriate amount of water to the crusher to ensure that the temperature of the plastic is lower than 40°C. Add 30g of plastic particles with a particle size of 3.2 to 4.0mm (the mass ratio of PC, PS and PP is 1:1:1) into tap water, PP plastic particles are separated from the upper layer of tap water by floating and sinking, and then the PC and PS plastic particles Add it into boiling water at 100°C, treat it for 70 minutes, take it out and cool it with water, and then carry out flotation. The flotation conditions are: 200mg/L terpineol, flotation for 2 minutes, the aeration rate is 7.5mL/min, and the stirring rate is 100r/min. After separation, the purity of PC reached 86.42%, and the recovery rate reached 91.86%; the purity of PS reached 92.34%, and the recovery rate reached 98.04%.

Example 2

Add the mixed plastic containing PC, PS and PE to tap water containing a small amount of cleaning agent to clean, then freeze at -10°C, use a plastic crusher to crush it for conventional crushing, and take 30g of plastic particles with a particle size of 3.2-4.0mm ( The mass ratio of PC, PS and PE is 1:1:1) into tap water, PE plastic particles are separated from the upper layer of tap water by floating and sinking, and then PC and PS plastic particles are added to 100°C salt water for 80 minutes, Take it out and cool it with water, and then carry out flotation. The flotation conditions are: 35.1mg/L methyl isobutyl carbinol, flotation for 4min, the aeration rate is 7.5mL/min, and the stirring rate is 50r/min. After separation, the purity of PC reached 94.86%, and the recovery rate of PS reached 98.04%.

Example 3

Add plastics containing ABS, PS and PP to tap water containing a small amount of sodium hydroxide for cleaning, and then use a plastic crusher to crush them. During the mechanical crushing process, add an appropriate amount of water to the crusher to ensure that the temperature of the plastics is lower than 40°C. Add 30g of plastic particles with a particle size of 3.2-4.0mm (the mass ratio of ABS, PS and PP is 1:1:1) into seawater, and the PP plastic particles are separated from the upper layer of seawater by floating and sinking, and then the ABS and PS plastic particles Add it into the water medium at 80°C, treat it for 110 minutes, take it out and soak it in water for 10 minutes to cool it down, and then carry out flotation. , the stirring rate is 50r/min. After separation, the purity of ABS reached 95.16%, the purity of PS reached 91.37%, and the recovery rate of the two plastics reached 91%.

Example 4

Add plastics containing ABS, PS and PE to tap water containing a small amount of sodium hydroxide for cleaning, and then use a plastic crusher to crush them. During the mechanical crushing process, add an appropriate amount of water to the crusher to ensure that the temperature of the plastics is lower than 40°C. Add 30g of plastic particles with a particle size of 2.0-2.5mm (the mass ratio of ABS, PS and PE is 5:1:1) into tap water, PE plastic particles are separated from the upper layer of tap water by floating and sinking, and then the ABS and PS plastic particles Add it into boiling water at 75°C, treat it for 170min, take it out and cool it, and then carry out flotation. . After separation, the purity of ABS reached 90.46%, the purity of PS reached 92.57%, and the recovery rate of the two plastics reached 89%.

Claims (8)

1. A method for separating waste and old mixed plastics, characterized in that the waste and old mixed plastics contain at least one light component plastic with relatively low density and at least two heavy component plastics with similar density and relatively high density , wherein the heavy component plastics contain at least one plastic containing polar groups and plastics without polar groups; the waste mixed plastics are frozen and crushed into mixed plastic particles, and the resulting mixed plastic particles are added to the liquid medium I for Separation by sinking and floating to obtain light component plastic particles with a density lower than that of liquid medium I and heavy component plastic particles with a density greater than that of liquid medium I. The resulting heavy component plastic particles are added to liquid medium II for surface treatment at a temperature of 70-100°C After 30-180 minutes, the heavy component plastic particles after surface treatment are separated by flotation with a flotation agent to obtain plastic particles containing polar groups and plastic particles without polar groups; the liquid medium II is At least one of tap water, deionized water, seawater, distilled water, sodium chloride solution, sodium sulfate solution, calcium chloride solution, potassium chloride solution, potassium nitrate solution, and sodium nitrate solution. 2. The method according to claim 1, characterized in that the density of the liquid medium I is between 970 and 1200kg/m ³ , and the liquid medium I with a suitable density is selected according to the density of the waste mixed plastic particles to be separated . 3. method according to claim 2, is characterized in that, described liquid medium I is selected from alcohol-water mixed solution, or is at least one in tap water, deionized water, seawater, distilled water, or is sodium chloride , sodium sulfate, calcium chloride, potassium chloride, potassium nitrate, sodium nitrate at least one aqueous solution. 4. The method according to claim 1, characterized in that the surface-treated heavy component plastic particles are dispersed in the flotation medium, and a flotation agent is added for flotation separation. 5. method according to claim 4, is characterized in that, described flotation agent is terpineol, methyl isobutyl carbinol, alpha-terpene alcohol, polyethylene glycol, lignosulfonate, At least one of tannic acid, gelatin, sparrow bark juice, cellulose, alkyl polyoxyethylene ether, water glass, and fatty amine; the flotation agent is added to the floating Select media. 6. The method according to claim 4, wherein the flotation medium is at least one of tap water, deionized water, seawater, and distilled water. 7. The method according to claim 4, characterized in that the flotation separation time is 1 to 15 minutes. 8. The method according to any one of claims 1 to 7, wherein the light component plastics include polyethylene and/or polypropylene, and the plastics without polar groups in the heavy component plastics include aromatic ring-containing plastics. Plastics containing polar groups in heavy component plastics include plastics containing sulfur, oxygen or nitrogen heteroatom groups; heavy component plastics account for 1% to 99% of the mass of waste mixed plastics.