WO1994024194A1

WO1994024194A1 - Polystyrene-dissolving agent

Info

Publication number: WO1994024194A1
Application number: PCT/IB1994/000097
Authority: WO
Inventors: Hatai Masanobu
Original assignee: Sekitei America Corporation
Priority date: 1993-04-20
Filing date: 1994-04-19
Publication date: 1994-10-27
Also published as: AU6544294A

Abstract

A process for an efficient and safe recovering of polystyrene from polystyrene resin products (30) using a polystyrene-dissolving agent (20) which is harmless and superior in the dissolving ability and does not cause environmental pollution, which comprises holding the polystyrene resin product (30) under contact with the polystyrene-dissolving agent (20) to dissolve polystyrene therefrom, said dissolving agent (20) containing 100-50 % by weight of terpene and, if necessary, 0-50 % by weight of surfactant, washing out the surfactant and any contaminants from the dissolution liquor containing the polystyrene-dissolving agent (20) and the dissolved polystyrene by mixing with water (21) and subjecting, then, the resultant surfactant-free polystyrene solution to distillation to separate the polystyrene-dissolving agent (20) and the polystyrene.

Description

POLYSTYRENE-DISSOLVING AGENT

TECHNICAL FIELD

The present invention relates to a polystyrene-dissolving agent for dissolving polystyrene resin products including polystyrene foamed articles. More specifically, the invention relates to a polystyrene-dissolving agent adapted for treating waste polystyrene resin products including waste polystyrene foamed products to recover polystyrene therefrom.

BACKGROUND ART

In the past, it has scarcely been attempted to recover polystyrene from wastes of polystyrene resin products including foamed articles. In most cases, these wastes have been disposed by incineration or by burying in the earth at a disposal landfill without seeking any reclamation of resources. When polystyrene resins are burnt, noxious gases are emitted, causing not only atmospheric pollution but also possible harm to the health of the attending workers. Therefore, it has long been expected to develop a safe and effective technique for recovering polystyrene from wastes of polystyrene resin products.

SUMMARY OF THE INVENTION An object of the present invention is to provide a dissolving agent for dissolving polystyrene from polystyrene resin products, which is harmless and superior in the ability of dissolving polystyrene and can afford the use of recovering polystyrene without causing environmental pollution. Another object of the present invention is to provide a process for recovering polystyrene from waste polystyrene resin products in a safe and efficient manner without causing any environmental pollution.

A further object of the present invention is to provide an apparatus for realizing the process for recovering polystyrene from waste polystyrene resin products according to the invention herein.

The dissolving agent for dissolving polystyrene according to the present invention contains terpene and, if necessary, a surfactant.

By contacting waste polystyrene resin products with such a dissolving agent according to the present invention, the polystyrene contained in the resin products will be dissolved out, whereupon the polystyrene can be recovered by separating it from the resulting solution.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic flow diagram of one embodiment of the apparatus for recovering polystyrene according to the present invention, shown in the operation phase of the dissolution of polystyrene.

FIG. 2 is another illustration of the flow diagram in the operation phase of separation of the liquid layers.

FIG. 3 shows the results of Example 3 for dissolution of various waste polystyrene resin products, in bar charts. DETAILED DESCRIPTION OF THE INVENTION

The polystyrene resins capable of being dissolved by the dissolving agent according to the present invention include, in addition to homopolymers of styrene, colopymetic resins of styrene as the principal constituent with other comonomer(s) as subsidiary component(s) , such as impact-resistant polystyrene resins, acrylonitrile-styrene resins (AS resins) , acrylonitrile- butadiene-styrene resins (ABS resins) and so on, and foam products obtained by foaming these polystyrene resins using a propellant (foaming agent) , such as n-pentane, nitrogen gas, carbon dioxide, sodium carbonate, azodicarbonamide and so on.

The terpene to be employed as an essential component of the dissolving agent according to the present invention may preferably include, though there is no limitation, d-limonene, 1-limonene, dipentene (dl-limonene) , d-o-pinene, d-,9-pinene, oc- terpinene, 3-terpinene, r-terpinene, d-2-carene, d-3-carene, 1-2- carene, 1-3-carene and so on. Among them in particular, d- limonene, 1-limonene and dipentene are preferred. These terpene compounds may be used each solely or in combination of two or more of them.

Terpene is a naturally occurring ethereal oily mixture contained in, for example, peels of citrus fruits and thus, is safe and harmless and exhibits superior solubility for polystyrene. It brings about no fear of causing environmental pollution, since it is easily biodegradable. Due to a comfortable fragrance peculiar to citrus fruits, it emits no unpleasant smell and is easy in handling. While terpene can be used alone as a dissolving agent for styrene polymers, it can also be used therefore as a mixture with additive(s) , such as a surface active agent and so on. When terpene is used alone as the dissolving agent without any surfactant, the dissolved polystyrene will be maintained in a homogeneous solution. When, on the contrary, terpene is used therefor together with a surfactant, the resulting liquid mixture is subject to a clear phase separation into two liquid layers, namely, a surfactant liquid layer of polystyrene-containing solution and an underlying liquid layer of the dissolving agent, after the mixture as been allowed to stand. Therefore, it is preferable to incorporate the dissolved agent together with a surfactant, so long as gravity recovery of polystyrene is intended. The terpene content in the dissolving agent may preferably be in the range from 50 to 100 %, in particular, from 70 to 90% by weight, with the corresponding surfactant content of 50 to 9 %, in particular, 30 to 10 % by weight.

When the waste polystyrene resin products are stained or contaminated with different types of dirt and foreign matter, such contaminants that have a lower relative density may be entrained into the layer of dissolving agent more easily. In this case, it is also preferable to incorporate a surfactant in the dissolving agent, since the migration of contaminants into water layer upon water wash of the resulting polystyrene solution will be facilitated thereby. For the case where a surfactant is incorporated in the dissolving agent for facilitating removal of the contaminants, and where separation of the phases is not of prime interest, the content of the surfactant may preferably be in the range from 0.25% to 2.5%, by weight, and in particular from 0.30% to 0.95% by weight, based upon the weight of the dissolving agent. A surfactant content in excess of 2.5% may, in average circumstances, bring about no substantial increase in the efficiency of contaminant removal.

Surfactants are available which are able to contribute to the phase separation into a supernatant layer of the polystyrene solution having a high content of polystyrene and an underlying layer of the dissolving agent having a low content of the polystyrene. Such surfactants may be readily enumerated, for example, straight chain alkylbenzenesulfonates, branched or straight chain alcohol ethoxylates, alkyl succinates, dialkyl succinates, fatty acid ethanolamides and ethoxylated alkylphenols having from about five to about twenty ethylene oxide units.

Concrete examples of such surfactants include sodium dioctyl sulfosuccinate, polyethoxynonylphenol, cocos fatty acid ethanolamide, lauric acid diethanolemide and sodium alkyl sulfates. They can be used each alone or in combination of two or more of them.

The dissolving agent according to the present invention may contain, in addition to the above mentioned constituents, further component(s) , such as diethanolamine and so on, in a content not obstructing the purpose of the present invention.

The dissolving agent according to the present invention can continue to dissolve styrene polymers up to a concentration of about 70 parts of the polymers per 100 parts of the dissolving agent on the weight basis at a temperature of from about 10° C to about 150°C. The process for recovering polystyrene from waste polystyrene resin products according to the present invention comprises contacting the resin products with the dissolving agent to dissolve polystyrene contained therein and subsequently subjecting the resulting polystyrene solution to separation of the polystyrene from the dissolving agent by, for example, distillation or other separation technique. When a surface active agent is incorporated in the dissolving agent for facilitating removal of dirts and contaminants for contribution to any easy recovery of polystyrene, it may be preferable to admix water to the resultant polystyrene solution with sufficient agitation, before the resulting mixture is allowed to stand, in order to subject the mixture to a gravity phase separation into a first liquid layer of polystyrene solution having a high concentration of polystyrene, and a second liquid layer of the dissolving agent having a low concentration of polystyrene and a layer in which the contaminants are dispersedly gathered. This phase separation is done in order to effect a phase separation into two liquid layers, namely, a layer of polystyrene solution with a high concentration of polystyrene and a layer of the dissolving agent with a low concentration of polystyrene, usually before the polystyrene solution is subjected to recovery of polystyrene by, for example, distillation.

The process step of contacting the waste polystyrene resin products with the dissolving agent according to the present invention may be realized at a temperature of from about 10° C to about 150° C, and preferably at a temperature of from about 30° C to about 38° C. It is preferable that the extent of dissolution of the polystyrene may be in the range from about 5 to 50 parts, preferably from about 10 - 30 parts and especially from about 10 - 20 parts of polystyrene per about 95 - 50 parts, preferably per about 90 - 70 parts and especially per about 90 - 80 parts of the dissolving agent on a weight basis (so as to sum up to 100 parts by weight in each case) . It is especially preferable to employ about 90 parts by weight of the dissolving agent per about 10 parts by weight of polystyrene. The above range of the amount of the dissolving agent is preferable, since the higher the dissolved amount of polystyrene, the higher will be the viscosity of the resulting solution up to an almost gelled consistency.

For the case of using a dissolving agent containing a surfactant, it is preferable to admix water to the resultant polystyrene solution, in order to remove the surfactant from the solution by transferring it into the water layer, before the polystyrene is recovered by, for example, distillation. It is of course permissible to realize the distillation without prior removal of the surfactant; and the removal of the surfactant may be effected by, for example, washing with water, after the distillation.

If the waste polystyrene resin products are contaminated with soils and dirts, they can be removed easily in a manner as follows:

The waste polystyrene resin products are first held in contact with the dissolving agent containing a surfactant to cause the polystyrene in the waste resin product to dissolve in the dissolving agent in the manner as explained above. To the resulting solution of polystyrene, an amount of water is added with agitation, whereupon the mixture is left to stand for a time period usually from about 1 to 3 days, to allow a phase separation to occur. The contaminants, such as dirts and soils, are gathered in the interstitial layer formed between the aqueous layer and the solution layer in a dispersed state. The portion of the contaminants having higher densities will settle to the bottom of the lowermost aqueous layer.

Alternatively, it is also possible to effect the dissolution of the polystyrene with a dissolving agent without containing any surfactant, before the surfactant is added to the resulting polystyrene solution. Here, the waste polystyrene resin products are first held in contact with the surfactant-free dissolving agent to cause the polystyrene in the waste polystyrene resin product to be dissolved in the dissolving agent, in the manner mentioned above. Then, water is admixed to the resulting polystyrene solution together with an adequate surfactant while agitating the mixture, whereupon the mixture is left to stand as explained above.

In this manner, the contaminants can be removed almost completely from the polystyrene-containing solution layer.

The amount of water to be admixed to the solution layer for the removal of the contaminants may preferably be, in both cases mentioned above, in the range from 40 to 100 parts, preferably from 48 to 100 and especially preferably from 70 to 100 parts of water per 100 parts of the terpene, on a weight basis.

The resulting polystyrene solution is then subjected to separation of the polystyrene from the dissolving agent by, for example, distillation. The polystyrene recovered can then be reused as the raw material for the production of foamed or non- foamed polystyrene resin products and even for the production of miscellaneous articles, gasoline, tar and the like.

The apparatus for realizing the process for recovering polystyrene according to the present invention comprises a dissolving unit for effecting dissolution of polystyrene in the dissolving agent, a separation unit for separating the polystyrene from the dissolving agent and, if necessary, a removal unit for removing the surfactant from the polystyrene solution.

The dissolving unit constituting the apparatus according to the present invention is a unit for dissolving polystyrene from polystyrene resin products in the dissolving agent, according to the present invention, by contacting the resin products with the dissolving agent. For the dissolving unit, a vessel capable of sealing the vessel contents against the external atmosphere is preferred.

The separation unit constituting the apparatus according to the present invention is a unit for effecting separation of the polystyrene from the dissolving agent by distilling the polystyrene solution from the dissolving unit.

The removal unit constituting the apparatus according to the present invention is a unit for effecting removal of the surfactant in the dissolving agent, which step may be dispensed with in the case of the use of the dissolving agent according to the present invention, without the use of a surfactant. For treating waste polystyrene resin products which may float on the liquid surface of the dissolving agent due to lower densities, such as foam products, it is preferable that the dissolving unit according to the present invention is furnished with a means for forcing the waste resin product to be immersed in the bulk of the dissolving agent.

If the contacting surface of the waste polystyrene resin products with the dissolving agent is large, the period required for the waste resin products to be dissolved in the dissolving agent will be reduced correspondingly, so that the waste resin products may preferably be finely disintegrated using, for example, a crusher.

Since the dissolving agent according to the present invention contains terpene in an essential proportion, it exhibits a superior solubility for polystyrene and is harmless, while avoiding any occurrence of environmental pollution.

If the dissolving agent contains a surfactant, the phase separation of the dissolution mixture into the polystyrene solution layer having a high content of polystyrene and the dissolving agent layer having a low content of the polystyrene will be facilitated.

In the process for treating waste polystyrene resin products according to the present invention, a special dissolving agent as explained above is employed, so that waste polystyrene resin products can be treated in a safe and efficient manner without suffering from the environmental pollution. By the process according to the present invention, polystyrene can efficiently be recovered from even waste resin products contaminated with different types of dirt etc. , by effecting the phase separation with addition of water.

The apparatus for treating waste polystyrene resin products according to the present invention serves to facilitate such efficient and safe treatment without environmental pollution.

PREFERRED EMBODIMENT

Below, the present invention will further be explained by a preferred embodiment with reference to the appended Drawings.

In Figs. 1 and 2, the apparatus for treating waste polystyrene resin products is constituted of a dissolving unit 1, a removal unit 2 and a distillation unit 3.

The dissolving unit is composed of a treating vessel 1 equipped at its bottom with a heater 4, on its side wall with an inspection window 5 and on its top with a closable cover 6 (shown in Figure 2) and is constructed in such a manner that it can be charged with the dissolving agent 20 and the waste polystyrene resin products 30 to keep them in contact with each other to effect dissolution of polystyrene of the waste product 30 in the dissolving agent 20. Above the dissolving unit 1 is a pressing- down means 7 for pressing down to immerse low density waste products, such as foamed articles, into a solution of the dissolving agent 20 by means of pressor 10 located at the end of a piston rod 9 of a hydraulic cylinder 8.

The waste polystyrene resin products may be once crushed through a crusher 31 and the so-disintegrated waste 30 is guided into the dissolving unit 1 via a guide path 32. The dissolving unit 1 communicates with the removal unit 2 through lines 11 and 12 disposed at an upper level and a middle level of the vessel 1 respectively. The vessel 1 may be provided with a feed line 13 for external feeding thereto. These lines are provided each with a valves 14, 15 and 16, respectively.

The removal unit 2 is constructed so as to permit the polystyrene solution drawn from the vessel 1 via the line 11 or 12 to contact with the washing water fed thereto via a line 21 and to cause phase separation to thereby effect removal of the surfactant employed, wherein the washed waste water is discharged out via a line 22. If the polystyrene solution does not contain any surfactant, the removal unit 2 can be omitted.

The distillation unit 3 which constitutes the separation unit according to the present invention is constructed so as to effect distillation of the polystyrene solution after passing through the surfactant removal step by heating it by a heater 24, wherein the terpene vapor is guided into a condenser 26 through a conduit 25, from which the liquified terpene is drawn out via a line 27, and the separated polystyrene is drained from the bottom via line 28.

For recovering polystyrene from a waste polystyrene product, such as polystyrene foam, using a polystyrene treating apparatus as above, the operation may be as follows: The dissolving agent 20 is first fed to the dissolving unit l by opening the valve 16 while the valves 14 and 15 are kept closed. The charged dissolving agent 20 is then heated by the heater 4, whereupon the waste polystyrene product 30 (polystyrene foam) which has been crushed by the crusher 31 is introduced thereto through the guide path 32 to bring it into contact with the heated dissolving agent 20 to dissolve it. Here, the hydraulic cylinder 8 of the pressing-down means is operated to cause the pressor 10 to descend, whereby the crushed polystyrene foam 30 is pressed to submerge into the bulk of the dissolving agent 20. It is most preferable to select a ratio of the amount of the waste polystyrene product to the dissolving agent at 10 parts by weight polystyrene product per 90 parts by weight of the dissolving agent. By setting the temperature of the dissolving agent at a temperature of from about 10° to about 150° C as mentioned previously, a prompt dissolution of polystyrene will be attained. When crushing of the polystyrene product is employed, the dissolution rate can further be increased.

After completion of the dissolution, the pressor 10 is retracted and the vessel 1 is sealed with the cover 6, whereupon the resultant solution is left to stand for a while until a phase separation occurs to build up a surfactant polystyrene solution layer 20a having a high polystyrene content with an underlying dissolving agent layer 20b having a low polystyrene content, as shown in Fig. 2. Usually, a complete phase separation into the surfactant polystyrene solution layer 20a and the underlying dissolving agent layer 20b will be achieved after about 24 hours. The phase separation can be confirmed visually by the inspection window 5. When no surfactant is employed, such phase separation will not occur, so that the resultant polystyrene solution can be supplied directly to the distillation unit 3.

When the phase separation has been confirmed, the polystyrene solution 20a is drained by making use of the force of gravity via the line 12 located at a level slightly above the interface of the two liquid layers by opening the valve 15. It is also possible to discharge out the polystyrene solution by sucking it out or by displacing it out of the line 11 by introducing fresh dissolving agent 20 from the line 13 by opening the valves 14 and 16.

The possible remainder of the polystyrene solution 20b remaining in the dissolving unit 1 can be reused as such or after replenished with fresh dissolving agent 20 in the next cycle of the treatment.

The drained polystyrene solution 20a having a high polystyrene content is then guided to the removal unit 2, where it is mixed with washing water introduced therein through the line 21. The resulting water mixture of the polystyrene solution is then allowed to stand until a phase separation into an aqueous layer to which most of the surfactant is transferred and the polystyrene solution layer from which most of the surfactant has been deprived will be attained. The resulting surfactant- containing aqueous layer is exhausted via the line 22. The above procedures are repeated several times until the removal of the surfactant is complete. This operation of surfactant removal can be omitted, when no surfactant is incorporated in the dissolving agent. The surfactant-containing aqueous phase taken out from the removal unit 2 is then subjected to a surfactant recovering treatment by an adequate technique, such as distillation, and the so-recovered surfactant may be reused in the subsequent cycles after having been refined.

The resulting surfactant-free polystyrene solution is then introduce into the distillation unit 3 via the line 23, where it is distilled to separate the dissolving agent (terpene) from the polystyrene. The components of the dissolving agent, namely, terpene and other volatile solvent are vaporized in the distillation unit and the vapor formed thereby is then condensed in the condenser 26. In this manner they are recovered from line 27 as the condensate. The distillation can be carried out under a reduced pressure by sucking out the vapor via the line 27. The so-recovered terpene-containing dissolving agent can be reused in the subsequent cycles for dissolving polystyrene. Here, a renewed dissolving agent can be formulated by mixing it with the recovered surfactant.

Within the distillation unit 3, polystyrene becomes concentrated and is taken out via the line 28. The polystyrene solution from the removing unit can be subjected to the distillation directly, though it is permitted to carry out the distillation with addition of water or other dilutent to the polystyrene solution.

The polystyrene can be recovered in a form of massive solid, sludge, powder or so on, depending on the distillation operation or other factors.

The polystyrene recovered in this manner is regenerated as raw polystyrene of high purity for reuse. The other materials, such as the surfactant, left after the recovery of the polystyrene can also be separated and refined for reuse.

While the above description of the polystyrene has been directed only to an apparatus furnished with one single dissolving unit, it is of course possible to employ a plurality of operating dissolving units connected in parallel. Polystyrene can be recovered from non-foaming polystyrene resin produces in a similar manner as above. Here the installation of the pressing-down means and operation of pressing-down of the product to be treated can be dispensed with, so long as sufficient immersion of the product in the dissolving agent is realized merely by introducing the product into the vessel 1. Also the crusher 31 may eventually be omitted.

Example 1

100 grams of a polystyrene foam product were introduced into 1,000 grams of d-limonene and the mixture was heated to 30°C. After about 10 minutes, the polystyrene foam product was found to be completely dissolved, whereby a polystyrene solution in d- limonene was obtained. By distillation of this polystyrene solution, d-limonene was recovered by the vaporization and condensation of the polystyrene was recovered in a concentrated form.

Example 2

An recovery of polystyrene was carried out using the apparatus shown in Figs. 1 and 2. As the dissolving agent, a mixture composed of 85 % by weight of d-limonene, 13 % by weight of a mixed surfactant of cocos fatty acid ethanolamide and sodium alkylsulfate and 2 % by weight of diethanolamine was used. The dissolving unit 1 was charged with 1,000 g of the above-mentioned dissolving agent and 100 g of a polystyrene product and the dissolution of polystyrene was carried out at 20"C. After allowing the mixture to stand overnight, the mixture was found to be separated into a polystyrene solution layer 20a having high polystyrene content and a dissolving agent layer 20b having a low polystyrene content. The polystyrene solution layer was transferred to the removing unit 2 and was washed with water three times to remove the mixed surfactant. The resultant surfactant-free polystyrene solution was then subjected to distillation in the distillation unit 3, whereby d-limonene was recovered by vaporization and subsequent condensation, and the polystyrene was recovered in a concentrated form.

Example 3

An experiment of recovery of polystyrene was carried out for a waste polystyrene foam product contaminated with various dirts using a dissolving agent containing d-limonene and lauric acid diethanolamine (surfactant) in the following manner:

Contaminated polystyrene foam products, in the varying amounts given in Table 1 were introduced in the indicated amount (rows 5 and 6) into the dissolving agent of the corresponding composition (rows 1 - 4) indicated above it in Table 1. The mixture was heated at 30° C to dissolve the polystyrene foam product completely. Then, water was introduced thereto each in an amount indicated in Table 1 and the water mixture was agitated. The resulting mixture was left to stand for a period of 2 hours - 3 days, whereby a phase separation occurred, in which a polystyrene solution layer, a contaminant dispersing layer and an aqueous layer were built up in this sequence of increasing density. The portion of contaminants having higher densities was found to be settled down to the bottom of the contaminant dispersing layer or to the bottom of the aqueous layer. The contaminant dispersing layer was built up between the polystyrene solution layer and the aqueous layer, in which the contaminant particles of dirt were dispersed in the polystyrene solution or in the aqueous medium. By distillation of the so- separated polystyrene solution, d-limonene was recovered by the vaporization and condensation and the polystyrene was recovered in a concentrated form.

Table 1

Test Nc .

1 2 3 4 5 d-limonene 50.8 57.7 66.96 51.67 58.28

(part by wt. ) 5 3

Suxfactant 1) 0.25 0.71 0.62

(part by wt. ) 0.37 0.31

Water 32.79 47.10 41.10

(part by wt. ) 48.7 41.9 8 6

Total 100 100 100

100 100

Polystyr. foam 22.0 24.9 28.8 22.4 25.2 (part by wt. )

Dissol. agent 70/ 70/ 70/ 70/ 70/ proportion 2) 30 30 30 30 30 d-limon./surf. 100/ 100/ 100/ 100/ ratio 100/ 0.54 0.37 1.4 1.1 0.73 d-limon./water 100/ 100/ 100/ 100/ ratio 73 49 92 71

100/ 96

1) Lauric acid diethanolamide

2) Weight portion of dissolving agent/polystyrene foam Table 1 cont.

Test No.

6 7 8 9 d-limonene 67.26 52.44 58.82 67.54 (part by wt. )

Surfactant 1 0.48 1.05 0.91 0.71 (part by wt. )

Water 32.26 46.51 40.27 31.75

(part by wt. )

Total 100 100 100 100

Polystyr. foam 29.0 22.9 25.6 29.2 (part by wt. )

Dissol. agent 70/ 70/ 70/ 70/ proportion 2 30 30 30 30 d-limon./surf. 100/ 100/ 100/ 100/ ratio 0.71 2.0 1.5 1.1 d-limon./water 100/ 100/ 100/ 100/ ratio 48 89 58 47

1) Lauric acid diethanolamide

2) Weight portion of dissolving agent/polystyrene foam

The state of phase separation after having been left to stand for a period of 2 hours - 3 days is shown in the bar charts of Fig. 3. The upper chart (A) indicates each state of phase separation for each Test after having been left to stand for 2 hours, and the lower chart (B) illustrates each state of phase separation for each test after having been left to stand for 3 days. In Fig. 3, 40 represents the polystyrene solution layer, 41 represents the contaminant dispersing layer, 42 indicates the aqueous layer and 43 denotes the contaminant particles. Each bar height corresponds to each layer thickness. The height from the bar bottom to the arrow mark represents each amount of admixed water in volume %. In the Test Nos. 6 and 9, no phase separation was recognized after being left to stand for 2 hours. All other test showed occurrence of phase separation after having been left to stand for 2 hours. After having been left to stand for 3 days, all the test samples showed occurrence of phase separation. Here, it was found that the contaminant particles entrained by the polystyrene foam product are gathered in the contaminant dispersing layer 41 and the portion of the contaminant particles 43 having higher densities were finally settled to the bottom of the aqueous layer.

The Test No. 1 exhibited the best result, since the thickness of the contaminant dispersing layer was found to be thin enough and the proportion of recovery of the polystyrene was the highest. The result for Test No. 2 was the second place in the evaluation.

Claims

1. A dissolving agent (20) for dissolving polystyrene, comprising terpene.

2. A dissolving agent (20) as claimed in Claim 1, which comprises terpene and a surface active agent.

3. A dissolving agent (20) as claimed in Claim 1, wherein the terpene is one or more compounds selected from the group consisting of d-limonene, 1-limonene and dipentene.

4. A dissolving agent (20) as claimed in Claim 2, wherein the surface active agent is one or more compounds selected from the group consisting of straight chain alkylbenzenesulfonates, branched- and straight chain alcohol ethoxylates, branched- and straight chain alcohol ethoxysulfates, alkyl succinates, dialkyl succinates, fatty acid ethanolamides and ethoxylated alkylphenols.

5. A process for treating polystyrene resin products, comprising contacting the resin products with a dissolving agent (20) containing terpene to dissolve polystyrene from the resin products and subjecting the resulting polystyrene solution to a separation step for separating the polystyrene from the dissolving agent.

6. A process as claimed in Claim 5, comprising contacting the resin products with a dissolving agent containing terpene and a surface active agent to dissolve the polystyrene from the resin products (30) , causing a phase separation of the resulting mixture into a polystyrene solution layer having a high content of the polystyrene and a dissolving agent (20) layer having a low content of the polystyrene and subjecting then the polystyrene solution layer to a separation step for separating the polystyrene from the dissolving agent (20) .

7. A process as claimed in Claim 5, comprising contacting the resin products (30) with a dissolving agent (20) containing terpene to dissolve polystyrene from the resin products (30) , admixing water (21) and a surface active agent to the resulting mixture with agitation, causing the resultant water mixture to be separated into (a) a polystyrene solution layer having a high content of the polystyrene, (b) an interstatistical layer in which contaminants are gathered in a dispersed state and (c) an aqueous layer having a low content of the polystyrene and subjecting then the polystyrene solution layer to a separation step for separating the polystyrene from the dissolving agent (20) .

8. A process as claimed in Claim 5, comprising contacting the resin products (30) with a dissolving agent (20) containing terpene and a surface active agent to dissolve the polystyrene from the resin products (30) , admixing water (21) to the resulting mixture with agitation, causing the resultant water mixture to be separated into (a) a polystyrene solution layer having a high content of polystyrene, (b) an interstitial layer in which contaminants are gathered in a dispersed state and (c) an aqueous layer having a low content of the polystyrene, and subjecting then the polystyrene solution layer to a separation step for separating the polystyrene from the dissolving agent (20) .

9. An apparatus for treating polystyrene resin products (30), comprising a dissolving unit for effecting dissolution of styrene polymers in the dissolving agent (20) by contacting the resin products (30) with a dissolving agent (20) containing terpene and a separation unit for separating the polystyrene from the dissolving agent (20) by distillation of the resulting polystyrene solution.

10. An apparatus as claimed in Claim 9, which comprises a dissolving unit (1) for effecting dissolution of polystyrene in the dissolving agent (20) by contacting the resin products (30) with a dissolving agent (20) containing terpene and a surface active agent, a removal unit (2) for removing the surface active agent from the polystyrene solution and a separation unit (3) for separating the polystyrene from the dissolving agent (20) by distillation of the resulting polystyrene solution.

11. An apparatus as claimed in Claim 9, which further comprises a crushing unit (31) for crushing the polystyrene resin products (30).