Patent Description:
These polystyrene based materials comprise flame retardants which are activated under ignition conditions, such as fire or heat, and are intended to prevent or slow the further development of ignition or fire breakthrough. When recycling polystyrene containing a flame retardant it is necessary that the flame retardant is removed in a manner such that it will not enter the environment. This holds in particular for organohalogen flame retardants, examples of which are organobromo flame retardants, such as hexabromocyclododecane (HBCD), tetrabromobisphenol A (<NUM>,<NUM>-Dibromopropyl)ether (BDDP or <CIT>), tris(tribromophenoxy) triazine (<CIT>), Tetrabromobisphenol-A-bis(<NUM>,<NUM>-dibromo-<NUM>-methylpropylether, <NUM>,<NUM>'-(isopropylidene)bis[<NUM>,<NUM>-dibromo-<NUM>-(<NUM>,<NUM>-dibromo-<NUM>-methylpropoxy)benzene] (TBBPA-DBMPE or AP <NUM> SF), a block copolymer of polystyrene and brominated polybutadiene (FR-122P), organochloro flame retardants, such as Tris(<NUM>-chloro-<NUM>-propyl) phosphate (TCPP) and polyvinylchloride (PVC), and organofluoro flame retardant tetradecafluorohexane (TDFH). Expanded polystyrene based materials comprise freonen used as expansion agent. It are organofluoro compounds, such as hydrochlorofluorocarbons (HCFC, such as R-<NUM>, R-<NUM> and R134a).

Several processes are known from the art for the removal of bromine from styrene polymers containing bromated flame retardant. <NPL>, uses a solution of NaOH in ethylene glycol for removing decabromodiphenenyl ethane (DBPE) from high-impact polystyrene. The debromination ratio was <NUM>% at <NUM>. The ratio was decreased to about <NUM> wt% by a mechanical treatment using a ball mill reactor. Ukisu in Chemosphere, <NUM>, pages <NUM>-<NUM>, <NUM>, studied catalytic debromination of HBCD using a silica-supported palladium catalyst in a solution of <NUM>-propanol/methanol containing dissolved NaOH at <NUM>. The reaction product yielded <NUM>% for bromine-free products. <NPL>, studied the removal of tetrabromobisphenol (TBBPA) from brominated plastics, modem Wi-Fi plastics, and printed circuit boards using solvent extraction with isopropanol or toluene followed by pyrolysis. Reportedly the degree of removal of bromated compounds was relatively low. <NPL>) studied the debromination of ABS containing TBBPA. Under supercritical conditions (<NUM>, <NUM> to <NUM> MPa) water, methanol, isopropanol, and acetone have been used. Water showed highest debromination efficacy (<NUM>%). Alkali were added to supercritical isopropanol, and salts formed dissolved in the supercritical alcohol and precipitated under ambient conditions. NaOH and KOH use resulted in a bromine yield in the treated product of about <NUM> wt%. <NPL>, studied the thermal depolymerization of polystyrene in highly aromatic hydrocarbons. At <NUM> the styrene yield was <NUM>% at a polymer conversion of <NUM>%. <NPL> a method/ installation for the pyrolysis of a waste fraction of high impact polystyrene (HIPS) containing brominated flame retardants in a fluidized bed reactor; the effects of various Ca-based additives (CaO, Ca(OH)<NUM> and oyster shells) on the removal of bromine.

The present invention has for its object to recycle polystyrene based material providing styrene of high purity that can be used as virgin or added styrene monomer and other valuable products for sale or reuse in the method, while generating minimal by-products and no formation of halogenated hydrocarbons, such as PCBs and PBBs. Still the dehalogenation treatment is carried out under moderate conditions (mild temperature and atmospheric pressure) in a basic organic environment without a catalyst and common reaction vessel. Thus, the invention aims at providing a method and installation to carry out the method, in which all reactions are carried out in a liquid phase using preferably or predominantly solvents evolving when carrying out the method. The materials used and reaction conditions applied are such that it is not necessary to operate the compaction part of the installation, particularly on location, under ATEX conditions as explosive atmospheres will not occur. And as to transportation of materials and intermediate products (such as compacted polystyrene), they fall in the lowest classification of the ADR (Accord européen relatif au transport international des marchandises Dangereuses par Route).

It is important to appreciate that the present invention is able to recycle a variety of different polystyrene based materials, such as packaging as yogurt cups or bowls. Particularly, for expanded, foamed, and extruded materials, the compaction is not thermal and/or chemical compaction.

According to this objective, the invention provides a method for recycling a polystyrene based material containing organohalogen flame retardant and/or freonen, comprising the steps of:.

The method of the invention comprises the dissolution of polystyrene containing an organohalogen flame retardant and/or freonen, and possible foreign plastics in the high-boiling reaction solvent from which solution halogen present in the flame retardant compound is released as halogen compound. The halogen compound is captured by a base and removed as the halogen salt. The dehalogenated polystyrene still present in reaction solvent is then pyrolyzed to depolymerize it into at least styrene. The styrene contains minimal amounts of remaining organohalogen flame retardant or freonen and any halogen compounds and suitable for use as virgin monomer or additional styrene monomer. The use of the high-boiling reaction solvent in all method steps allows for operation under non-ATEX conditions during compaction, particularly on location, and handling and routing of products and intermediate products under lowest ADR conditions.

In one embodiment of the invention, the halogen compound released from the flame retardant may be recuperated from the reaction solvent and separate from the solvent contacted with a base in order to form a halogen salt. Under these circumstances practically any base able to form such halogen salt may be used. In a preferred embodiment, the base is added to the reaction solvent so that halogen compound released in step (ii), is contacted in step (iii) with the base so that the halogen salt is formed in the reaction solvent. This means that the base is present in the reaction solvent at the time during heating step that halogen compound is released from the organohalogen containing flame retardant or freon. The released halogen compound is there and then captured and converted into a halogen salt which is easily removed as solid from the reaction solvent. Accordingly, the halogen compound such as in the form a halogen acid which is a corrosive agent, is not or only shortly present in the reaction solvent, so that there is no need for using corrosion resistant material for the installation equipment. Moreover, under the heated conditions of step (ii) and during the subsequent pyrolysis step (v) no halogen compound is present and thereby any side-reactions of halogen compound with solvent or depolymerization products are avoided.

It is particularly preferred that the base added to the apolar, organic reaction solvent is dissolved therein, so that the reaction with halogen proceeds optimally in the liquid phase, which makes the removal of the halogen salt easy. And avoids any side stream such as water and polar (organic) solvent containing the base. Therefore, the base used for forming the halogen salt in the reaction solvent is selected from the group comprises sodium diamine, potassium tert-butoxide (KOtBu), sodium bis(trimethylsilyl)amide, and P(CH3NCH2CH2)3N. These selected bases are soluble in the reaction solvent. Small volatiles formed may be removed and neutralized.

Essentially a versality of different polystyrene based materials may be used, such as polystyrene, high impact polystyrene (HIPS), expanded polystyrene (EPS), extruded polystyrene (XPS), styrene-butadiene rubber (SBR), acrylonitrile-butadiene-styrene (ABS), and polymethylmethacrylaat (PMMA). Several of these materials comprise additional monomers (or polymers) which will have no negative on the performance of the method. This holds for polystyrene based materials comprising up to about <NUM> wt% foreign polymer, such as polyethylene, polypropylene, and/or polyvinylchloride. Examples used are Piocelan a polypropylene-compounded polystyrenic foamed resin and a polyethylene-compounded polystyrenic foamed resin. Also these foreign polymers will not hamper the method and ultimately will end up in a rest-product stream.

The dehalogenation of the flame retardant and/or freonen in step (ii) is generally carried out by heating the reaction solvent containing polystyrene to a temperature in the range of about <NUM> to about <NUM>, preferably about <NUM>° to about <NUM>. The pressure corresponding to these temperatures varies between about <NUM> bar to about <NUM> bar, preferably about <NUM> bar to about <NUM> bar, such as <NUM> to <NUM> bar.

The dehalogenation reaction starts at elevated temperatures, and the higher the temperature the shorter the time to completion of the reaction. Reaction time for the dehalogenation is generally between <NUM> to <NUM>, but halogenation is normally almost complete between <NUM> to <NUM>, such as between <NUM> and <NUM>.

The method of the invention is particularly intended for the recycling of expanded, foamed or extruded polystyrene or mixtures of polystyrene and expanded, foamed or extruded polystyrene, and of their related polystyrene based materials. But due to the relative low density of expanded polystyrene their application is the basic method of the invention is less practical. Therefore, the invention provides in a generally preferred embodiment an additional pre-step in the method in which the expanded polystyrene is compacted and its density substantially increased. In addition, the compacted polystyrene is converted into a semi-solid form stiff material or two-phase system dependent on the type and amount of compaction solvent used. But they can be easily handled and are less or not sticky. But in order to compact the expanded polystyrene properly or optimally it is required to use a solvent or solvent mixture different in properties of the reaction solvent. Thus, the invention provides a pre-step which is a step of compacting expanded polystyrene in a compaction solvent. With this compaction solvent the expanded polystyrene forms a semi-solid material or a two-phase system comprising a semi-solid (dough-like) phase of the polystyrene. This compacted form-stiff polystyrene is separated from the liquid phase by any suitable technique.

This two-phase system or the compacted polystyrene may be subjected to the heating step for dehalogenation. But it is preferred to add the reaction solvent or that the compaction solvent is at least partly replaced by the reaction solvent. And after this replacement the compacted polystyrene enters step (i) of the method of the invention.

At this point it is noted that the compaction pre-step is not necessarily to be carried out in time and/or location directly prior to step (i) or step (ii) of the method of the invention. It is equally possible while maintaining all benefits of the invention to perform the pre-step earlier in time and/or even at a different location. Particularly, if the availability and/or presence of polystyrene material to be recycled by time is less than the processing rate of the method. Then expanded polystyrene to be recycled is advantageously compacted at one or more remote locations and transported to a central processing site where the compacted polystyrene of different locations, of different types and/or of different sources is processed. All transport and processing proceeds at general and common conditions as working under ATEX conditions is not required and two-phase system and the compacted polystyrene are materials which fall in the lowest ADR classification.

One of the important finding of the present invention is that the pyrolyzation mixture obtained after pyrolyzation in step (v) comprises an aromatic and/or aliphatic fractions that can be obtained by distillation in step (vi), and have properties of compacting expanded polystyrene present in the polystyrene based material and/or properties of the reaction solvent. They are method-own solvent and distillation fractions.

For the compaction a distilled fraction has such a high boiling point that compaction related processing is carried out at least <NUM> below the flashpoint so that processing is not to be carried out under ATEX conditions. When using for compaction only the aromatic fraction then compaction results in the formation of a polystyrene solution with the consistency of a syrup. Using a mixture of the aromatic fraction and the aliphatic mixture compaction results in the formation of a two-phase system with the consistency of a paste or of a form stiff product with the consistency like camembert cheese. The more aliphatic fraction is used the more the consistency becomes stiffer and the polymer density increased. under liquid conditions. Therefore the method of the invention applies at least partly as the compaction solvent a mixture of an aliphatic solvent and an aromatic compaction solvent, such as a high-boiling distillate fraction obtainable in step (vi) preferably a styrene dimer fraction boiling at about <NUM> to about <NUM>, or boiling at about <NUM> to about <NUM>, such as about <NUM> to about <NUM> at about <NUM> to <NUM> mbar absolute pressure. Alternatively, the dimer fraction may contain up to C16 and has a boiling point of about <NUM> to <NUM>. The aromatic compaction solvent and an aliphatic compaction solvent, are preferably a fraction obtainable in the distillation of step (vi).

The volume ratio of the aromatic solvent and the aliphatic solvent is selected dependent on the composition of the (expanded, foamed or extruded) polystyrene based material. But the percentage of flame retardant present is generally relatively small, so that the solvent mixture is generally present in excess. But as the Some flame retardants such as HBCD dissolves only slightly in the aliphatic solvent and good in the aromatic solvent, whereas any present polyethylene and/or polypropylene dissolves better in the aliphatic solvent. Hence, the volume ratio of the aromatic compaction solvent and the aliphatic compaction solvent selected dependent on the type of polystyrene material to the recycled and in regard of the consistency of the compacted mass. For instance at ><NUM>% aromatic solvent becomes the compacted mass form stiff. Accordingly, the volume ratio may be in the range of about <NUM>:<NUM> (paste consistency), preferably about <NUM>:<NUM>, more preferable about <NUM>:<NUM> (stiff consistency).

Another the important finding of the present invention is that the pyrolyzation mixture obtained after pyrolyzation in step comprises a fraction of that has properties of dissolving the dehalogenated polystyrene and of having a such high boiling point that both the dehalogenation of step (ii) and the pyrolyzation of step (v) can be performed under liquid conditions. This reaction solvent is also a system-own product, and any degradation of it would result in styrene and styrene oligomers which can be used. Therefore the method of the invention applies at least partly a high-boiling apolar organic reaction solvent having a vapor pressure of less than about <NUM> bar at a temperature in the range of about <NUM> to about <NUM>. This reaction solvent is preferably a high-boiling distillate fraction obtainable in step (vi), preferably a styrene trimer fraction boiling at about <NUM> to about <NUM>. Alternatively, the trimer fraction may contain up to C24 and has a boiling point of about <NUM>.

Due to the difference in composition and properties of the compaction solvent and the reaction solvent, is preferred that the compaction solvent is replaced at least partly by the reaction solvent prior to the dehalogenation step (ii), and preferably the compaction solvent is recycled to the compaction step.

When preferably the reaction of the released halogen compound in step (ii) with the base is carried out in the reaction solvent when release of halogen is eminent, then it is preferred that the removal of the halogen salt is carried out on stream from the reaction solvent by solid liquid separation such as filtration, centrifugation, (hydro) cyclonic separation, at a salt particle size of less than about <NUM>, preferably less than about <NUM>, such as less than <NUM>, or less than <NUM>. Such salt removal has the additional advantage that any sand or other particulate material present in the styrene based material to be recycled is removed which is beneficial to processing and reduces the risk for installation damage due to abrasion.

For the practical and sufficient removal of any organohalogen flame retardant or freonen it is preferred that the base is present in slight excess, such that the molar ratio of base to the organohalogen flame retardant and/or freonen is about <NUM> to about <NUM>, such as about <NUM> to about <NUM>, or <NUM> to <NUM>.

As referred to above, the pyrolysis step (v) is carried out under more stringent conditions than the dehalogenation step (ii). Practically the pyrolysis of step (v) is carried out at atmospheric pressure at a temperature about <NUM> to about <NUM>, preferably at about <NUM> to about <NUM>, or at higher pressure and at correspondingly lower temperatures. Preferably the pressure is about <NUM> bar to <NUM> bar.

The pyrolysis step (v) may be carried out in a meltbed reactor. This is a reactor of common and simple design and can be applied because the pyrolysis is carried out under liquid conditions due to the use of the high-boiling reaction solvent. This liquid state pyrolysis is optimal for heat transfer and substantially avoids pyrolysis to solid materials such as soot.

Processing the method of the invention optimally has the beneficial result that the removal of organohalogen flame retardant and/or freonen present in the polystyrene based material is at least <NUM>%, preferably at least <NUM>%, more preferably at least <NUM>%. Accordingly, the styrene product comprises flame retardant and/or freonen in an amount of less than <NUM> ppm, preferably less than <NUM> ppm, such as less than <NUM> ppm.

Another aspect of the invention relates to an installation for recycling a polystyrene based material containing an organohalogen flame retardant and/or freonen, such as defined and discussed hereinbefore. Such installation comprises:.

As discussed above the installation is suitable for compacting expanded polystyrene and thereto additionally comprises a compaction unit for compacting expanded polystyrene in a compaction solvent, and for preferably replacing the compaction solvent by the reaction solvent.

It is also beneficial that the reaction solvent used for the dehalogenation and pyrolysis at least partly is generated when carrying out the method of the invention, To that extent the installation comprises a distillation unit (f) which distils the depolymerized mixture to a styrene trimer fraction which is recycled and used at least in apart as reaction solvent. For the same reasons, the distillation unit (f) distils the depolymerized mixture to a styrene dimer fraction which is recycled and is used at least in apart as compaction solvent for expanded polystyrene.

As discussed above, the pyrolysis is carried out under liquid conditions due to the use of the high-boiling solvent. This allows for the use of a meltbed reactor. This is a reactor of common and simple design and can be applied because this liquid state pyrolysis is optimal for heat transfer and substantially avoids pyrolysis to solid materials such as soot. Thus, the pyrolyzation unit (e) comprises a meltbed reactor. Additional advantages of the use of a meltbed reactor will be discussed in the description below.

The method and the installation of the invention are suitable for recycling a variety of different polystyrene based materials comprising a great number of different flame retardant and/or freonen. Examples of the polystyrene based materials are polystyrene, expanded polystyrene (EPS), extruded polystyrene (XPS), such as used in packaging foils and containers, styrene-butadiene rubber (SBR), acrylonitrile-butadiene-styrene (ABS). Examples of the organohalogen flame retardants are organobromo flame retardants, such as hexabromocyclododecane (HBCD), tetrabromobisphenol A (<NUM>,<NUM>-Dibromopropyl)ether (BDDP or <CIT>), tris(tribromophenoxy) triazine (<CIT>), Tetrabromobisphenol-A-bis(<NUM>,<NUM>-dibromo-<NUM>-methylpropylether, <NUM>,<NUM>'-(isopropylidene)bis[<NUM>,<NUM>-dibromo-<NUM>-(<NUM>,<NUM>-dibromo-<NUM>-methylpropoxy)benzene] (TBBPA-DBMPE or AP <NUM> SF), a block copolymer of polystyrene and brominated polybutadiene (FR-122P), organochloro flame retardants, such as Tris(<NUM>-chloro-<NUM>-propyl) phosphate (TCPP) and polyvinylchloride (PVC), and organofluoro flame retardant tetradecafluorohexane (TDFH). Expanded polystyrene based materials comprise freonen used as expansion agent. These are organofluoro compounds, such as hydrochlorofluorocarbons (HCFC, such as R-<NUM>, R-<NUM> and R134a).

Mentioned and other characteristic and advantages of the method and installation of the present invention will become apparent from the description given hereafter which is considered to be given for information purposes only and not to limit the invention to any extent. In this respect reference is made to the annexed figures wherein:.

<NUM> gr expanded polystyrene is added to <NUM> gram compaction solvent is added.

The compaction solvent comprises about 20wt%, aromatic hydrocarbons with a boiling point of about <NUM>, and about <NUM> wt% aliphatic hydrocarbons with a boiling point of <NUM>. Compaction was carried out at about <NUM> to <NUM>.

After dissolution in the compaction solvent a relatively hard form-stable product is formed. This high-load polystyrene product has a solid content of about <NUM>%.

An expanded polystyrene product comprising <NUM>,<NUM> gr expanded polystyrene (<NUM>%) and <NUM>,<NUM> gr expanded polyethylene (<NUM>%) is added to <NUM> gram compaction solvent. The compaction solvent comprises about <NUM> wt% aromatic hydrocarbons with a boiling point of about <NUM>, and <NUM> wt% aliphatic hydrocarbons with a boiling point of about <NUM>. The compaction temperature is about <NUM>.

Expanded polyethylene also compacts as expanded polystyrene but a wax-like homogenic end product is obtained. The solids content is about <NUM>%. The expanded polystyrene comprises expanded polyethylene in only a small concentration, therefore expanded polyethylene can be processed in the same manner as expanded polystyrene.

<NUM> gr expanded polystyrene based material comprising about <NUM> wt% polystyrene, <NUM> wt% foamed polypropylene, and <NUM> wt% foamed polyethylene was added to <NUM> of a compaction solvent mixture comprising <NUM> vol% aromatic hydrocarbon with a boiling point in the range of about <NUM> - <NUM> (Solvesso 150ND) and <NUM> vol% aliphatic hydrocarbon with a boiling point of about <NUM> - <NUM> (Vasil <NUM>). The density of the compaction solvent solution obtained was <NUM> gr/l. The compaction was carried out at a temperature of <NUM>.

The expanded polyethylene and expanded polypropylene defoamed in a similar manner as expanded polystyrene. But a jelly like end product is obtained. Thus expanded polystyrene comprise some foreign polyethylene and/or polypropylene can be compacted but at higher compaction temperatures.

Due to the jelly like consistency of the end product a once-through-put-away concept (according to <FIG>) may be applied in which the mixture after being saturated with defoamed expanded polystyrene, expanded polypropylene and some expanded polyethylene may be stored as briquets until further processing.

Polystyrene comprising <NUM> wt% flame retardant was dissolved in Solvesso <NUM> ND™ (boiling point: <NUM> to <NUM>, for ExxonMobil Chemical Series) as aromatic reaction solvent. A base was added to the reaction solvent at a given organohalogen to base molar ratio. The debromination was carried out at a given temperature. The conversion at the given temperature for about <NUM>, was calculated as <NUM>-(mass recovered oil * [Br] in oil)/mass Br added to the reactor).

Polystyrene comprising HBCD flame retardant was dissolved in a styrene trimer fraction used as aromatic solvent. NaNH<NUM> base was added to the reaction solvent at a given organohalogen to base molar ratio of <NUM>. The debromination was carried out at <NUM>. The conversion after <NUM> at the reaction temperature was calculated as <NUM>-(mass recovered oil * [Br] in oil)/mass Br added to the reactor) and was about <NUM>%.

Expanded polystyrene containing <NUM> wt% HBCD was subjected to dehalogenation using a mixture of styrene dimer and styrene trimer (obtained by pyrolyzation of polystyrene beads dissolved in Solvesso <NUM> ND™, at <NUM>, and removal of styrene monomer by fractional distillation at <NUM> at <NUM> mbar) as compaction solvent. The reactor loading was <NUM> wt% EPS, which corresponds to a flame retardant loading of <NUM> wt%. NaNH2 was used as base and the base/Br-ratio was <NUM>. The reaction temperature was <NUM>, and the reaction time <NUM>. The dehalogenation conversion was <NUM>% for the EPS (HBCD) sample.

The compacted polystyrene obtained in Example <NUM> was subjected to pyrolyzation for the production of in particular styrene by depolymerization of polystyrene. The liquid mixture of polystyrene and styrene trimer (obtained after distillation of the dimer/trimer mixture of Example <NUM> at <NUM> at <NUM> mbar absolute pressure) was fed to a pyrolyzation reactor and subjected to pyrolyzation at a temperature of <NUM> for about <NUM> to <NUM> at atmospheric pressure. The pyrolyzed oily liquid obtained was cooled by quenching with cooled reaction solvent to a temperature of about <NUM>. After removal of any solids, such as char and soot, the cooled liquid mixture was subjected to a stripping operation for obtaining a styrene product stream of which styrene as the major component as top distillate. Obtained are further a middle distillate fraction and a bottom fraction.

The styrene product stream was subject to a four-stage distillation units for distilling off an aliphatic fraction that may be used as aliphatic solvent, an light aromatics fraction, and heavy ends as bottom fraction. The top fraction is styrene which boils at between about <NUM>, and has a purity of at least <NUM>% and contains less than <NUM> ppm flame retardant.

The middle distillate fraction was further distilled and provided light nafta and a fraction boiling at between about <NUM> and <NUM>, and represents the dimer fraction used as compaction solvent. The bottom distillate fraction boils at about <NUM> to <NUM> and represent the trimer fraction used as reaction solvent.

<FIG> shows a general process flow diagram of a method and installation <NUM> of the present invention. The installation <NUM> comprises a dissolution unit <NUM> to which are added polystyrene based material <NUM> containing organohalogen flame retardant for dissolution or dispersion in added reaction solvent <NUM>. The mixture <NUM> containing polystyrene in the reaction solvent <NUM> is added to a heating unit <NUM>. In the heating unit <NUM> the polystyrene present in the reaction solvent <NUM> is heated to a temperature for a time period sufficient to release halogen compound from the flame retardant. The heating temperature is preferably about <NUM> to about <NUM>, such as <NUM> for about <NUM> to <NUM>, preferably about <NUM> to about <NUM>, such as <NUM>.

Released halogen compound is converted into a halogen salt with base <NUM> added. The halogen salt is removed with a hydrocyclone or by filtration. Polystyrene <NUM> devoid of halogen and contained in the reaction solvent is added to a pyrolyzation unit <NUM> in which polystyrene <NUM> is pyrolyzed and depolymerized into styrene <NUM>, valuable products <NUM>, and pyrolyzed solids such as soot <NUM>. The pyrolyzation is carried out at about <NUM> to about <NUM>, or at <NUM> to about <NUM>, such as <NUM> to about <NUM>.

The pyrolyzation mixture <NUM> in the reaction solvent is added to a distillation unit <NUM>, where in styrene <NUM> and valuable products <NUM> are distilled off. Other distillation liquids and gas may be used for generation energy. The pyrolyzation solids <NUM> are removed.

<FIG> shows another general process flow diagram of a method and installation <NUM> of the invention. In comparison to the installation <NUM> of <FIG>, installation <NUM> additionally comprises a compaction unit <NUM> in which expanded polystyrene based material <NUM> is compacted with compaction solvent <NUM>. The mixture of compacted polystyrene <NUM> contained in the compaction solvent <NUM> is added to a separation unit <NUM> in which the compacted solvent is at least partly replaced by the reaction solvent <NUM>. The replaced compaction solvent <NUM> is recycled to the compaction unit <NUM>. The reaction solvent <NUM> added to the separation unit <NUM> may be fresh reaction solvent <NUM> and/or may be recycled reaction solvent <NUM> obtained as a valuable product <NUM> in the distillation unit <NUM>.

The mixture of compacted polystyrene and compaction solvent may have the form of a two-phase system with a semi-solid polystyrene phase and a liquid phase, or a single semi-solid phase which can be transported with common means, such as a pump. The type of the compacted form depends on the amount of compaction solvent added and the type of expanded polystyrene based material, and is as desired or needed. If this material also comprises polyethylene and/or polypropylene then another valuable distillation product <NUM> comprises an aliphatic solvent, a mixture of the aliphatic solvent with the reaction of compaction solvent improves the dissolution of the flame retardant and/or freonen contained in the polystyrene based material.

<FIG> shows more in detail a compaction unit <NUM> according to the invention. Expanded polystyrene <NUM> is added to a storage hopper <NUM> and transported with a conveyor screw <NUM> to a compaction mill <NUM>. Here the expanded polystyrene is compacted with compaction fluid <NUM> supplied by sprayer unit <NUM> and impacted with the expanded polystyrene with rotating compaction arms <NUM>. The compacted polystyrene <NUM> formed is transported via a pump <NUM> and cooling unit <NUM> to a storage tank <NUM>. The tank <NUM> comprises a two-phase system comprising a phase of semi-solid compacted polystyrene <NUM> and a phase of liquid compaction fluid. That surplus of compaction fluid <NUM> may be recycled via pump <NUM> to compaction fluid tank <NUM> also provided with fresh compaction fluid from storage <NUM> via pump <NUM>.

The compacted polystyrene <NUM> collected in tank <NUM> may be directly added to the heating unit <NUM> or first transported from a remote location to a central installation <NUM>-<NUM>.

<FIG> shows in more detail another compaction unit <NUM> of the present invention (same reference numbers refer to same elements of the compaction unit <NUM> described in <FIG>. Different from the compaction unit <NUM> of <FIG>, here the compaction unit operates under the once-through-put-away principle by which this compaction unit <NUM> is adapted to compact expanded, foamed or extruded polystyrene that contains higher amounts of polyethylene and/or polypropylene, such as amounts up to about <NUM> to about <NUM> wt%. This implies that compacted polystyrene <NUM> is transported with an extrusion conveyor onto a porous conveyor belt <NUM>, and spray cooled with cooling liquid <NUM> supplied with pump <NUM> and collected on a dripping tray <NUM>. Briquette <NUM> of compacted polystyrene are collected in a bin <NUM>. Compaction solvent <NUM> leaving the compaction unit <NUM> with the briquette <NUM> is compensated for and supplied from tank <NUM> and heater <NUM> and pump <NUM>.

<FIG> shows a non-limiting example of a process flow diagram of another installation <NUM> of the invention for recycling polystyrene based material <NUM> into styrene <NUM> and a trimer fraction <NUM>, aliphatic solvent <NUM>, light aromatics <NUM>, and light nafta <NUM>. Produced is also a dimer fraction <NUM> to be used as compaction solvent when expanded polystyrene is processed. Major unit operations will be discussed and details thereof with be described in the <FIG>.

The installation <NUM> comprises a compaction unit <NUM> for compaction of expanded polystyrene material <NUM> in compaction solvent <NUM>, as described in relation to <FIG> and <FIG>. The volume ratio compaction solvent <NUM> to expanded polystyrene <NUM> is about <NUM>:<NUM>. Compacted polystyrene <NUM> is fed to the dissolution unit <NUM> comprising a mixing tank <NUM>, and dissolved in supplied reaction solvent <NUM> and/or trimer fraction <NUM> (optionally in admixture with aliphatic solvent <NUM>).

The dissolved polystyrene <NUM> is filtered and enters separation unit <NUM> comprising a solvent reclaim section <NUM>, for separating compaction solvent <NUM>. Polystyrene contained in reaction solvent <NUM> is transported into a heating unit <NUM> for the dehalogenation of flame retardant and/or freonen. Released halogen compound reacts with base <NUM> present in the reaction solvent and/or added in the form of a mixture with aliphatic/aromatic solvent mixture from tank <NUM> via pump <NUM>, and halogen salt formed is filtered off. Polystyrene <NUM> devoid of halogen and present in reaction solvent <NUM> is in the form of mixture <NUM> subjected to pyrolyzation in pyrolyzation unit <NUM> at a temperature of about <NUM>. The pyrolyzed mixture is cooled in a quencher unit <NUM> with cooled reaction solvent, i.e., in the trimer fraction <NUM>.

After removal of soot and char by filtration the filtered pyrolyzed mixture <NUM> is subjected in a distillation unit <NUM> to distillation sections <NUM> and <NUM> for providing pure styrene <NUM>, dimer fraction <NUM> to be used a compaction solvent <NUM>, trimer fraction to be used as reaction solvent <NUM>, aliphatic solvent <NUM> to be used in admixture with compaction solvent <NUM>, and light aromatics <NUM> to be used in admixture with reaction solvent <NUM>. Other product streams may be used for generating energy and/or heating.

<FIG> shows in more detail de separation unit <NUM>. A liquid mixture <NUM> of about <NUM> part polystyrene, about <NUM> part compaction solvent <NUM> and about <NUM> parts reaction solvent <NUM> is heated with heater <NUM> and enters a flash drum <NUM> provided with a vacuum pump <NUM> for flashing the mixture <NUM>. Lower boiling compaction solvent <NUM> leaves the flash drum over its top and is conveyed to the solvent reclaim section <NUM>. A liquid mixture <NUM> of about <NUM> parts higher boiling reaction solvent <NUM> and about <NUM> part dissolved polystyrene is bottomed and forwarded to the heating section <NUM>. Temperature of the mixture is controlled with a reboiler <NUM> as to maintain polystyrene in liquid state.

<FIG> shows in more detail the compaction solvent reclaiming section <NUM>. The compaction solvent <NUM> added over the pump <NUM> is stripped in stripper <NUM> and after cooling in condenser <NUM> supplied with pump <NUM> to storage tank <NUM>. The stripped light fraction <NUM> is cooled in condenser <NUM> and applied via pump <NUM> to storage tank <NUM>. The stripper may be operated at subatmospheric pressure by connection of a vacuum line <NUM> connected to vacuum pump <NUM>. If desired the compaction solvent may be mixed with added light aromatics <NUM>.

<FIG> shows in more detail the heating unit <NUM> for the dehalogenation of polystyrene and/or freonen. The heating unit <NUM> comprises a reactor <NUM>, such as a plug flow reactor <NUM>. The mixture <NUM> of polystyrene dissolved in reaction solvent <NUM> (i.e., here the trimer fraction possibly containing some compaction solvent <NUM>) enters the reactor <NUM> and is mixed with base <NUM> supplied over pump <NUM> and heater <NUM>. The reaction solvent <NUM> may comprise some compaction solvent <NUM>. The reactor <NUM> is operated at a dehalogenation temperature of about <NUM> and overpressure of about <NUM> to about <NUM> bar. The residence time depends on the type and concentration of organohalogen flame retardant in the mixture <NUM>. Generally, the residence time is about <NUM> to <NUM>. Halogen compound released by flame retardant or freonen is captured by base <NUM> and halogen salt is formed in the reaction solvent. Any gaseous reaction product formed, such as ammonia may leave the reactor <NUM> via gas blead <NUM>. The mixture <NUM> of polystyrene, halogen salt, reaction solvent, and possible remaining reactant such as base <NUM>, and other reaction products, is filtered in a filtration train <NUM>, filtering the mixture <NUM> at about <NUM>, about <NUM> or <NUM>, and at <NUM> or <NUM>. The solids filtered off are collected in sludge tank <NUM>, and may be purified. That filtered liquid <NUM> enters the pyrolyzation unit <NUM>.

<FIG> shows the pyrolyzation unit <NUM> in some more detail. The pyrolyzation reactor <NUM> is provided with heater <NUM> for heating the liquid mixture <NUM> at about <NUM> to about <NUM> at a pressure of about <NUM> bar to about <NUM> bar, to a pyrolyzed mixture <NUM> comprising depolymerize polystyrene to at least styrene and other depolymerized fractions, such as a dimer fraction and a trimer fraction, and reaction fractions, such as an aliphatic fraction <NUM> and aromatic fraction <NUM>. A preferred embodiment of the pyrolyzation reaction <NUM> will be described in <FIG> below.

<FIG> shows in more detail the quencher section <NUM>. It comprises a quencher <NUM> in which recirculated mixture <NUM> and/or reaction solvent sprayed after cooling and in cooler <NUM> and spray pump <NUM>. This is based on the inventive idea in that by using reaction solvent in the form of trimer fraction originating in the process, so that cooling is accomplished without the use of a system-foreign solvent. By cooling the temperature of the mixture <NUM> is greatly reduced to a temperature at which secondary reactions are substantially avoided or stopped. After quench cooling the mixture passes a filter <NUM> for removing any remaining or newly formed solids, such as soot and char.

<FIG> shows in more detail the crude stripper unit <NUM> of the distillation unit <NUM>. The crude stripper unit <NUM> distils the pyrolyzed mixture <NUM> into a top fraction <NUM>, a middle fraction <NUM> and a bottom fraction <NUM>. Operation is such that the production of top fraction <NUM> is maximal as it comprises predominantly styrene <NUM>. Top fraction <NUM> obtained after distillate at the top is cooled in condenser <NUM> partly recycled and partly cooled in cooler <NUM> providing cooled top faction <NUM>. Middle fraction <NUM> is cooled in cooler <NUM> and further processed in light end stripper unit <NUM>. The bottom fraction <NUM> is heated in reboiler <NUM> and partly recycled and partly cooled in cooler <NUM>. This bottom fraction <NUM> is recycled as the trimer fraction <NUM> to dissolution unit <NUM> or stored in storage tank <NUM> and may be used for generating energy.

<FIG> shows in more detail the light end stripper unit <NUM>. Here the middle fraction <NUM> is stripped in stripper <NUM> to topdistil off via condenser <NUM> and cooler <NUM>, light nafta <NUM> so that at the bottom distils off via reboiler <NUM> and cooler <NUM> dimer fraction <NUM> having the specification of, and/or can be used as compaction solvent <NUM>, and having a flashpoint such that the installation can be safely operated.

Returning to <FIG>, it is shown that top fraction <NUM> is distilled in distillation column <NUM> of which the top distillate provides aliphatic solvent <NUM>. The bottom distillate <NUM> is distilled in distillation column <NUM> of which the bottom fraction <NUM> is recycled to distillation column <NUM>. The top distillate <NUM> is distilled in distillation column <NUM> providing light aromatics as top fraction <NUM>. The bottom fraction <NUM> is applied to a styrene distillation column <NUM> providing high pure styrene <NUM>, and as bottom fraction heavy ends <NUM>.

Finally, <FIG> show in more detail an embodiment of reactor <NUM> in the form of a melt bed reactor <NUM>. The reactor <NUM> comprises a reactor housing <NUM> containing a heat exchanger <NUM> dividing the housing <NUM> in a bottom section <NUM> and a top section <NUM>. The bottom section <NUM> and the top section <NUM> are connected by plurality of heating pipes <NUM> which extend over the height of the heat exchanger <NUM> and are regularly divided over the surface of the heat exchanger. The inlet <NUM> of the reactor <NUM> is connected to a downpipe <NUM> extending coaxially through the heat exchanger <NUM>. The surface area of the downpipe <NUM> is substantially equal to the surface area of the plurality of heating pipes <NUM> together. The down pipe <NUM> opens into the bottom section <NUM>. The top section <NUM> is connected to the outlet <NUM>. The downpipe <NUM> may be provided with propellor means <NUM> for controlling the flow of the mixture <NUM> through the heat exchanger dependent on the degree of pyrolyzation required. The heat exchanger <NUM> is provided with a top inlet <NUM> and a bottom outlet <NUM> for heating medium <NUM> which is in counter-current contact with the mixture in the heating pipes. In this manner liquid mixture <NUM> passes via inlet <NUM> through the melt bed reactor <NUM> while being pyrolyzed and leaves the reactor <NUM> via outlet 121as pyrolyzed mixture <NUM>.

Claim 1:
A method for recycling a polystyrene based material containing organohalogen flame retardant and/or freonen, comprising the steps of:
(i) dissolving the polystyrene based material in a high-boiling, apolar, organic reaction solvent;
(ii) heating the polystyrene contained in the reaction solvent to a temperature so as to release halogen from the flame retardant and/or freonen;
(iii) contacting released halogen with a base so as to form a halogen salt;
(iv) removing the halogen salt;
(v) pyrolyzing polystyrene contained in the reaction solvent at a temperature so as to depolymerize polystyrene; and
(vi) distilling the depolymerized mixture into at least a styrene fraction.