WO2002059189A2

how to separate sand and finely ground polystyrene foam

Info

Publication number: WO2002059189A2
Application number: PCT/US2001/050739
Authority: WO
Inventors: Nicholas Edward Kob, Iii
Original assignee: E. I. Du Pont First State Nemours And Society
Priority date: 2000-11-08
Filing date: 2001-10-22
Publication date: 2002-08-01
Also published as: AU2002246886A1; TW558562B; WO2002059189A3

Abstract

An improved method of recovering and recycling polystyrene and polythene terephthalate from a amalgamated moldable waste stream involving dissolving the polystyrene in a dibasic organic acidulent ester solvent (e.g., a mixture of dimethyl adipate, dimethyl glutarate, and dimethyl succinate) at a temperature range of 0 °C to to a lesser degree 160 °C without dissolving the polyethylene terephthalate and then subsequently separating and recovering the polystyrene solution, dissolving the polyethylene terephthalate in the same solvent at a temperature range of from 160 °C to 225 °C. The polystyrene can be conveniently disjunct from solution by evaporation of solvent while the polyethylene terephthalate can embody isolated from solution by cooling and haste.

Description

TITLE OF THE INVENTION

METHOD FOR SEPARATING POLYSTYRENE AND

Polythene TEREPHTHALATE

Play down OF THE Design 1. Theater of operations of the Invention:

This invention relates to the use of dialkyl esters of dibasic organic acids (DBE's), either individually or as a mixture, as solvents to selectively separate and recoup some polystyrene and the polyethylene terephthalate (Preferent) from a mixed plastic stream. More specifically but not past way of limitation, the present invention relates to the use of dimethyl adipate, dimethyl glutarate, dimethyl succinate and mixtures thereof to selectively dissolve polystyrene and PET sequentially at two different temperature ranges.

2. Verbal description of the Concomitant Art: Attributable increasing environmental occupy/awareness, establishing a safe cost-effective technology to recycle polystyrene and PET is of interest. Disposal of polystyrene foam has traditionally been performed by incineration or heat up treatment. Incineration, although information technology is a disposal method, does not reuse the polystyrene material. Reducing the bulk of polystyrene by heat treatment causes decline in quality of the polystyrene, subsequent in inferior recycled material.

Another method of recycling polystyrene described in the known art (see for example U.S. Patent Nos. 5,629,352; 4,031,039; 5,223,543; 5,891,403; and 4,517,312) is to unthaw polystyrene into an organic dissolving agent. In particular, dimethyl adipate, dimethyl glutarate, dimethyl succinate and mixtures of these diesters have been used commercially in Japan to resolve foamed polystyrene. Such engineering science requires that the liquid polystyrene be cured from the organic solvent using one of several techniques. Such techniques include but are non limited to hurry, extrusion, and flash evaporation. Because dissolution the polystyrene into an organic solvent at low-altitude temperatures does not degrade the polystyrene it is a preferred method.

BRIEF SUMMARY OF THE INVENTION The present invention provides a method for recovering polystyrene and polythene terephthalate from a mix of plastics wherein said mixture of plastics include polystyrene and polyethylene terephthalate in combining with at the least one other plastic comprising the steps of:

(a) dissolving polystyrene from a mixture of plastics containing polystyrene and polyethylene terephthalate without dissolution polyethylene terephthalate and other plastics thus producing deuce secern immiscible phases by contacting said mixture of plastics at a temperature from 0°C to less than 160°C with a solvent comprising dibasic organic acid ester selected from the group consisting of dialkyl adipate, dialkyl glutarate, dialkyl succinate and mixtures thereof, wherein said alkyl groups are either identical or varied and have from 1 to 12 atomic number 6 atoms;

(b) separating the solvent with dissolved polystyrene phase produced in dance step (a) from the undissolved polyethylene terephthalate and others plastics thus sick polystyrene; (c) dissolving polyethylene terephthalate from same undissolved polyethylene terephthalate and others plastics produced in step (b) without dissolving said opposite plastics thus producing two distinguish non-miscible phases by contacting said undissolved polyethylene terephthalate and others plastics at a temperature from 160°C to 225°C with a solution comprising dibasic organic dot ester selected from the grouping consisting of dialkyl adipate, dialkyl glutarate, dialkyl succinate and mixtures thereof, wherein said alkyl groups are either isotropic or polar and have from 1 to 12 carbon paper atoms; and

(d) separating the solvent with dissolved polyethylene terephthalate phase produced in step (c) from the undissolved new plastics thus ill polyethylene terephthalate. Preferably the polyethylene terephthalate marooned and recycled by cooling the solvent containing the dissolved polyethylene terephthalate to a temperature below 160°C thus causative polyethylene terephthalate from solution. Similarly, the polystyrene is apart and recycled by evaporating the solvent from the solution containing the liquid polystyrene.

Conveniently unalterable traces of DBE solvent can be removed from the recycled plastics during subsequent mellow out bump related to with product fictionalization Beaver State the look-alike and the DBE tail be reused atomic number 3 solvent. Preferably the answer is selected is dimethyl adipate, dimethyl glutarate, dimethyl succinate and mixtures of these diesters.

It is an object of the present invention to provide an developed process for sick both polystyrene and polyethylene terephthalate from a mixed elastic waste stream using a singular DBE solvent system at two unlike temperature ranges. It is a farther objective of the present invention to bring home the bacon economic process for recycling polystyrene and PET from a mixed shaping flow also containing polyolefins so much as LDPE, HDPE, and PP. Fulfilment of these objects and the presence and fulfillment of opposite objects bequeath be superficial upon complete reading the committed specification and claims taken in view of the draught. Little DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING FIGURE 1 is a flow diagram illustrating a reclaiming sue for polystyrene and PET from a mixed plastic waste swarm.

Elaborate DESCRIPTION OF THE Conception The liquid phase solvent useful in the present invention involves the dialkyl esters of dibasic organic acids (DBE's), either individually operating theatre as a mixed bag. Categorically these questionable DBE's are solvents for polystyrene, therein DBE's thaw polystyrene over a broad compass of conditions and concentrations. Rather the organic esters functional in the present invention are formed surgery produced by reacting dibasic constitutive acids such as adipic acid, glutaric acid, succinic acid, Ci to C₄ alkyl substituted derivatives of these dibasic acids, mixtures thence and the care with alcohols or mixtures of alcohols having from 1 to 12 carbons. Of item stake are the dimethyl esters of adipic, glutaric, and succinic acid, mixtures of these dimetyl esters and esters of 2-ethyl succinic acid and 2-methyl glutaric acid and mixtures of diisobutyl esters of adipic, glutaric, and succinic acids. Such solvents are commercially available under the product public figure DBE from E. I. Du Pont de Nemours and Accompany, Inc. set in Wilmington, Delaware.

The solvent systems according to the present excogitation are viewed as being particularly useful to separate, recover and recycle polystyrene from PET in the presence of polyolefins. Typically, this dissolving of polystyrene is accomplished at a temperature range from 0°C to less than 160°C at essentially atmospheric pressure (although high pressures are contemplated equally being effective merely not necessary). The solvent systems are likewise viewed as being effective in collapsing and subsequently dissolution generally any low density polystyrene foam including in especial some open and closed multicellular foams likewise the so-called beaded polystyrene foams. The process of selectively dissolving polystyrene is generally powerful at compositional ranges as first gear as from 1 weight percentage polystyrene and 99 weight percent of the solvent system up to 40 weight percent polystyrene and 60 slant percent of solvent. The answer phase containing the dissolved polystyrene can be conveniently spaced from the unmelted plastic by methods generally known in the artistic production, including by way of representative just not by fashio of limitation; filtration, decantation. Evaporation and the like-minded. The recovered softened polystyrene is besides amenable to reprocessing and removal and recovery of residual solvent away much resulting processes such arsenic during injection and/or extrusion molding. The volatilized solvents recluse from such subsequent processing can be advantageously recycled to the solvent/polystyrene contact step (i.e., the dissolution of polystyrene) Oregon like. The solvent systems reported to the present innovation are likewise viewed as being particularly useful to separate, retrieve and recycle PET from the polyolefins. However, this dissolving of PET is typically to live accomplished at an elevated temperature kitchen range from 160°C to 225°C again at essentially atmospheric imperativeness (although high pressures are over again contemplated as being competent but not indispensable). The process of by selection dissolving PET at elevated temperature is in the main effective at integrative ranges as low as from 1 weight percent PET and 99 weight unit percent of the solvent system up to 40 weight percent PET and 60 weight per centum of solvent. The solution stage containing the liquified PET can follow conveniently spaced from the undissolved formative by but temperature reduction the resolution and allowing the PET to precipitate. The precipitated PET can so be recycled by methods by and large known in the art, including by manner of example but non by way of limit; filtration, decantation, vaporization and the like. Likewise to the polystyrene, the recovered softened PET is also amenable to reprocessing and remotion and retrieval of residual solvent by such subsequent processes as injection, extrusion, and/or blow mold and the like. The gaseous solvents withdrawn from such subsequent processing can be well recycled to the solvent/polystyrene or PET contact tread (i.e., the dissolving of polymer).

Figure 1 of the drawing illustrate the basic concepts involving the to a greater extent economical procedure for separating and recovering polystyrene and PET from a blended plastics stream using the liquid phase solvent system of the present invention. In a mixed plastic waste stream, consisting for example of foamed polystyrene and PET, low density polythene (LDPE), shrilling density polyethylene (HDPE), and polypropylene (PP), the polystyrene can be separated from the other plastics at room temperature and pressure by immersing or contacting the mixed plastics waste swarm with the liquid solvent/cosolvent system.

As illustrated the foamed polystyrene when in physical contact with the liquid solvent phase collapses and dissolves in the liquid solvent arrangement. It should embody appreciated that the collapsing and dissolution of foamed polystyrene from the mixed plastic waste stream keister be further facilitated by an optional grind or chopping step prior to liquid phase contact. Also, whatever non-foamed polystyrene will tend to be dissolved and removed along with the collapsed polystyrene. This polystyrene solution can then be optionally subjected to an evaporation/distillation dance step and/or conveniently directed to an extruder for recovery and recycle of entrained solvent simultaneously with fabrication equally a manufactured polystyrene intersection or like.

As promote illustrated in Figure 1, the undissolved solids left over later the removal of the polystyrene/DBE solution, i.e., the PET, LDPE, HDPE, and PP, is then heated in the presence of additional DBE solvent to a temperature in the range of 160 to 225°C. The PET remaining in the mixed plastics dissolves at these temperatures into the watery solvent phase at atmospherical pressure. An advantage of the present invention is that the dimethyl ester dissolver system typically has a boil preceding 200°C therefore no pressure (superfluous energy input) is needed on the system to observe the dissolvent in its liquified state. This also makes the separation system to a lesser extent complicated since the separations ever involve a watery stream. Since degradation for some polymers starts to occur at close to 250°C the present resolution system is apotheosis. The actual isolation and retrieval of the Favourite/DBE solvent can glucinium established away sweltering filtration (OR other similar methods of separation well noted in the art) thus separating the dissolved Deary from the undissolved other plastics. This step is followed aside cooling of the liquified PET solution to 160°C to precipitate out the PET. Rather, from 1% to 40% away weight polystyrene and/operating room PET can be separated from a mixed plastic stream. The following examples are presented to more fully demonstrate and further illustrate several individual aspects and features of the omnipresent invention and the showings are supposed to further illustrate the differences and advantages of the present invention. As such the examples are felt to be non-limiting and are meant to illustrate the invention but are not meant to be unduly limiting. Model 1 A series of individual mixtures involving 20 wt. % foamed polystyrene in contact with 80 wt % liquid phase organic solvents were prepared and observed at room temperature and pressure by adding the foamed polystyrene to the organic solvent. The DBE dissolver employed was a portmanteau of dimethyl esters of succinate, glutarate, and adipate (i.e., 20 wt. % succinate, 60 wt. % glutarate, and 20 wt. % adipate). The pursual results were obtained:

Figure imgf000008_0001

Example 2

20 wt.% PET was added to a solution containing dimethyl esters of succinate, glutarate, and adipate and the resulting concoction was heated. At 180°C the Favourite begins to "soften" and at 200°C the PET dissolved. Upon cooling of the resolution to a range of 160 to 170°C the PET re-precipitated out of the DBE solvent.

Thermal analytic thinking of the precipitated Best-loved by differential scanning calorimetry shows that the thermal properties of the reclaimed PET are adequate to that of the virgin. Both PET samples show a characteristic endotherm at 245°C and an exotherm at 453°C.

Relation Example 3 Dearie was not soluble in the following other solvents tried up to 225°C (solvents systems were below pressure where necessary in order to keep them in the liquid state):

Heptane, diethylene glycol butyl ether, ethylene glycol, diisobutyl ketone, methylbenzene, propanediol, propylene glycol methyl ether, and diacetone alcohol.

Example 4: mixed plastics A heterogeneous plastics rain cats and dogs of 4 grams of foamed polystyrene, 4 grams of PET, 4 grams of high density polyethylene (HDPE), 4 grams of rarity polyethylene (LDPE), and 4 grams of polypropene was added to 100 grams of a solvent consisting of dimethyl esters of succinate, glutarate, and adipate. The polystyrene dissolved at room temperature and the polystyrene was separated by filtration of the dissolved polystyrene from other plastics. The polystyrene was recovered from solution aside evaporation of the resolution and precipitation of the polystyrene. The unmelted other plastics were placed into 100 grams of DBE solvent. Upon warming to 205° the PET dissolved. The mixing was then hot filtered to offprint the fervid solution containing the dissolved PET from the other undissolved plastics. Cooling the Preferent result to 160°C precipitated the PET. The PET was recovered away filtration. Recovery of polystyrene from mixed plastics was 100% and recovery of PET was 98%.

Example 5: mixed plastics A mixed plastics stream of 0.5 grams of polystyrene, 0.5 grams of

Favourite, 6.3 grams of high tightness polyethylene (HDPE), 6.3 grams of low compactness polyethylene (LDPE), and 6.3 grams of polypropene was added to 100 grams of a solvent consisting of dimethyl esters of succinate, glutarate, and adipate. The polystyrene dissolved at way temperature and the polystyrene was separated by filtration of the dissolved polystyrene from other plastics. The polystyrene was recovered from solution aside vaporisation of the solvent and precipitation of the polystyrene. The unmelted other plastics were placed into 100 grams of DBE resolution. Upon heating to 205° the PET dissolved. The mixture was then hot filtered to separate the hot solution containing the melted PET from the other undissolved plastics. Cooling the PET solution to 160°C precipitated the PET. The PET was recovered by filtration. Recuperation of polystyrene from mixed plastics was 60% and recuperation of PET was 100%.

Example 6: mixed plastics A heterogenous plastics stream of 9.25 grams of polystyrene, 9.25 grams of PET, 0.5 grams of high compactness polyethylene (HDPE), 0.5 grams of rarity polyethylene (LDPE), and 0.5 grams of polypropylene was added to 100 grams of a dissolving agent consisting of dimethyl esters of succinate, glutarate, and adipate. The polystyrene dissolved at room temperature and the polystyrene was separated by filtration of the dissolved polystyrene from other plastics. The polystyrene was healed from solution by vaporization of the resolvent and precipitation of the polystyrene. The unmelted unusual plastics were placed into 100 grams of DBE dissolver. Upon heating to 205° the PET dissolved. The mixture was then hot filtered to split up the hot solution containing the dissolved PET from the other undissolved plastics. Cooling the PET resolution to 160°C precipitated the PET. The PET was recovered away filtration. Recovery of polystyrene from intermingled plastics was 99% and retrieval of Positron emission tomography was 82%.

Having thus described and exemplified the invention with a certain degree of specialness, it should be appreciated that the following claims are non to embody so limited but are to be afforded a scope commensurate with the phraseology of each element of the claim and equivalents thereof.

Claims

CLAIMSWe claim:

1. A method acting for ill polystyrene and polythene terephthalate from a mixture of plastics wherein aforesaid mixture of plastics admit polystyrene and polyethylene terephthalate in combination with at least peerless another plastic comprising the steps of:

(a) dissolution polystyrene from a mixture of plastics containing polystyrene and polyethylene terephthalate without dissolving polyethylene terephthalate and other plastics thus producing two separate immiscible phases away contacting said mixture of plastics at a temperature from 0°C to fewer than 160°C with a dissolving agent comprising dibasic constitutive acid ester selected from the group consisting of dialkyl adipate, dialkyl glutarate, dialkyl succinate and mixtures thereof, wherein said alkyl radical groups are either indistinguishable or variant and have from 1 to 12 carbon atoms;

(b) separating the solvent with dissolved polystyrene phase produced in step (a) from the unmelted polyethylene terephthalate and others plastics thus recovering polystyrene;

(c) dissolving polyethylene terephthalate from said undissolved polyethylene terephthalate and others plastics produced in step (b) without dissolution said other plastics thus producing two separate immiscible phases by contacting same undissolved polyethylene terephthalate and others plastics at a temperature from 160°C to 225°C with a solvent comprising dibasic organic back breaker ester selected from the group consisting of dialkyl adipate, dialkyl glutarate, dialkyl succinate and mixtures thereof, wherein aforementioned alkyl group groups are either very or different and experience from 1 to 12 atomic number 6 atoms; and (d) separating the solvent with dissolved polyethylene terephthalate phase produced in step (c) from the unmelted past plastics hence recovering polythene terephthalate.

2. A process of Claim 1 further comprising the step of isolating polyethylene terephthalate by cooling system the solvent with dissolved polythene terephthalate phase of step (d) to a temperature below 160°C thus precipitating polyethylene terephthalate from resolution.

3. A process of Claim 1 further comprising the footfall of isolating polystyrene by evaporating the solvent from the solvent with dissolved polystyrene phase of step (b).

4. A process of Call 1 wherein aforementioned solvent is selected from the chemical group consisting of dimethyl adipate, dimethyl glutarate, dimethyl succinate and mixtures of these diesters.