**6.3 Mixed PVC wastes World inititives**

Regarding the chemical recycling of mixed plastic wastes with a PVC content of up to several percent, the following initiatives seem to be most realistic for the coming 5 years: **Texaco gasification process** (NL, pilot in the US), Polymer cracking process (consortium project, pilot), **BASF conversion process** (D, pilot but on hold) **Use as reduction agent in blast furnaces** (D, operational), **Veba Combi Cracking process** (D, operational but to be closed by 2000**), Pressurized fixed bed gasification of SVZ** (D, operational). A brief report on these initiatives is presented below (Sadat-Shojai and Bakhshandeh, 2011).

**BP Chemicals** has led promotion of Polymer Cracking technology for feedstock recycling since its beginnings in the early 1990's. Since the challenge of recycling of plastics is industry wide, support has been provided by a Consortium of European companies to develop the

Fig. 9. The BP polymer cracking process (Tukker et al., 1999).

Recent Advances in the Chemical Recycling

Fig. 10. BASF process [Heyde and Kremer, 1999].

leaner than stochiometric amount of CaO.

(DKR/DSD, 1999).

of Polymers (PP, PS, LDPE, HDPE, PVC, PC, Nylon, PMMA) 41

Mixed PVC waste can be used as reduction agent in blast furnaces. For the production of pig iron for steel production, iron ore (Fe2O3) has to be reduced to Fe. This process takes place in a blast furnace. Coke, coal and heavy oil are normally used as reducing agents in this process. Iron and steel companies try to lower the consumption of coke, by partly replacing it with coal, gas or fuel oil (30% in weight seems to be the maximum), via coal injection technology. Recently, new developments have started to replace the conventional reducing agents by plastics waste. Though others like British Steel (UK) have done trials as well, the prominent pioneer in this field is Stahlwerke Bremen, Germany. Stahlwerke Bremen is a large German steel manufacturer which operates two blast furnaces to produce over 7000 t/day, or some 3 Million tpa pig iron. Currently, German is the sole country that blast furnace are the only plants using waste this way

**Veba Combi Cracking process**. The plant configuration includes a depolymerisation section and the VCC section (fig. 11). Depolymerisation is required to allow further processing in the VCC section. In the depolymerisation section the agglomerated plastic waste is kept between 350-400ºC to effect depolymerisation and dechlorination. The overhead product of the depolymerisation is partially condensed. The main part (80 %) of the chlorine introduced with PVC is present as HCl in the light gases. It is washed out in the following gas purification process, yielding technical HCl. The condensate, containing 18 % of the chlorine input, is fed into a hydrotreater. The HCl is eliminated with the formation water. The resulting Cl-free condensate and gas are mixed with the depolymerisate for treatment in the VCC section. The depolymerisate is hydrogenated in the VCC section at 400-450ºC under high pressure (about 100 bar) in a liquid phase reactor with no internals. Separation yields a product which after treatment in a fixed-bed hydrotreater is a synthetic crude oil, a valuable product which may be processed in any refinery. From the separation a hydrogenated residue stream also results, which comprises heavy hydrocarbons contaminated with ashes, metals and inert salts. This hydrogenation bitumen is a byproduct which is blended with the coal for coke production (2 wt%). It is most likely that the major part of any metals present in a PVC formulation end up in this residue flow. Light cracking products end up in off-gas (E-gas), which is sent to a treatment section for H2S and ammonia removal. As indicated above, the main part of the chlorine present in the input (i.e. from PVC) is converted into usable HCl. Some 2% of the chlorine input is bound to CaCl2 in the process by a 4 times

technology – initially including Elf Atochem, DSM, Fina and Enichem. The consortium members at the time of the successful pilot plant trials in 1997 were BP Chemicals, Elf Atochem, EniChem, DSM, CREED and the APME. Some elementary preparation of the waste plastics feed is required, including size reduction and removal of most non-plastics. This prepared feed is fed directly into the heated fluidised bed reactor which forms the heart of the Polymer Cracking process. The reactor operates at approximately 500°C in the absence of air. The plastics crack thermally under these conditions to hydrocarbons which vaporise and leave the bed with the fluidising gas. Solid impurities, including metals from e.g. PVC stabilisers and some coke, are either accumulated in the bed or carried out in the hot gas as fine particles for capture by cyclone. The decomposition of PVC leads to the formation of HCl, which is neutralised by bringing the hot gas into contact with a solid lime absorbent. This results in a CaCl2 fraction that has to be landfilled. The purified gas is cooled, to condense most of the hydrocarbon as valuable distillate feedstock. This is then stored and tested against agreed specifications before transfer to the downstream user plant. The remaining light hydrocarbon gas is compressed, reheated and returned to the reactor as fluidising gas. Part of the stream could be used as fuel gas for heating the cracking reactor, but as it is olefin-rich, recovery options are being considered.

The process shows very good results concerning the removal of elements like chlorine. With an input of 10,000 ppm (or 1%) Cl, the products will contain around 10 ppm Cl. This is somewhat higher than the specifications of 5 ppm typical for refinery use. However, in view of the high dilution likely in any refinery or petrochemical application, BP assumes that this is acceptable.Also, metals like Pb, Cd and Sb can be removed to very low levels in the products. Tests have shown that all the hydrocarbon products can be used for further treatment in refineries (Brophy et al., 1997).

**The BASF feedstock recycling process** was designed to handle the recycling of mixed plastic waste supplied by the DSD collection system. The process is as follows, before the waste plastics can be fed to the process, a pretreatment is necessary (fig. 10). In this pretreatment the plastics are ground, separated from other materials like metals and agglomerated. The conversion of the pretreated mixed plastic into petrochemical raw materials takes place in a multi-stage melting and eduction process. In the first stage the plastic is melted and dehalogenised to preserve the subsequent plant segments from corrosion. The hydrogen chloride separated out in this process is absorbed and processed in the hydrochloric acid production plant. Hence, the major part of the chlorine present in the input (e.g. from PVC) is converted into saleable HCl. Minor amounts come available as NaCl or CaCl2 effluent (Heyde and Kremer, 1999). Gaseous organic products are compressed and can be used as feedstock in a cracker. In the subsequent stages the liquefied plastic waste is heated to over 400 ºC and cracked into components of different chain lengths. About 20-30% of gases and 60-70% of oils are produced and subsequently separated in a distillation column. Naphtha produced by the feedstock process is treated in a steam cracker, and the monomers (e.g. ethylene, propylene) are recovered. These raw materials are used for the production of virgin plastic materials. High boiling oils can be processed into synthesis gas or conversion coke and then be transferred for further use. The residues consist of 5% minerals at most, e.g. pigments or aluminium lids. It seems likely that metals present in PVC-formulations mainly end up in this outlet. The process is carried out under atmospheric pressure in a closed system and, therefore, no other residues or emissions are formed.

technology – initially including Elf Atochem, DSM, Fina and Enichem. The consortium members at the time of the successful pilot plant trials in 1997 were BP Chemicals, Elf Atochem, EniChem, DSM, CREED and the APME. Some elementary preparation of the waste plastics feed is required, including size reduction and removal of most non-plastics. This prepared feed is fed directly into the heated fluidised bed reactor which forms the heart of the Polymer Cracking process. The reactor operates at approximately 500°C in the absence of air. The plastics crack thermally under these conditions to hydrocarbons which vaporise and leave the bed with the fluidising gas. Solid impurities, including metals from e.g. PVC stabilisers and some coke, are either accumulated in the bed or carried out in the hot gas as fine particles for capture by cyclone. The decomposition of PVC leads to the formation of HCl, which is neutralised by bringing the hot gas into contact with a solid lime absorbent. This results in a CaCl2 fraction that has to be landfilled. The purified gas is cooled, to condense most of the hydrocarbon as valuable distillate feedstock. This is then stored and tested against agreed specifications before transfer to the downstream user plant. The remaining light hydrocarbon gas is compressed, reheated and returned to the reactor as fluidising gas. Part of the stream could be used as fuel gas for heating the cracking reactor,

The process shows very good results concerning the removal of elements like chlorine. With an input of 10,000 ppm (or 1%) Cl, the products will contain around 10 ppm Cl. This is somewhat higher than the specifications of 5 ppm typical for refinery use. However, in view of the high dilution likely in any refinery or petrochemical application, BP assumes that this is acceptable.Also, metals like Pb, Cd and Sb can be removed to very low levels in the products. Tests have shown that all the hydrocarbon products can be used for further

**The BASF feedstock recycling process** was designed to handle the recycling of mixed plastic waste supplied by the DSD collection system. The process is as follows, before the waste plastics can be fed to the process, a pretreatment is necessary (fig. 10). In this pretreatment the plastics are ground, separated from other materials like metals and agglomerated. The conversion of the pretreated mixed plastic into petrochemical raw materials takes place in a multi-stage melting and eduction process. In the first stage the plastic is melted and dehalogenised to preserve the subsequent plant segments from corrosion. The hydrogen chloride separated out in this process is absorbed and processed in the hydrochloric acid production plant. Hence, the major part of the chlorine present in the input (e.g. from PVC) is converted into saleable HCl. Minor amounts come available as NaCl or CaCl2 effluent (Heyde and Kremer, 1999). Gaseous organic products are compressed and can be used as feedstock in a cracker. In the subsequent stages the liquefied plastic waste is heated to over 400 ºC and cracked into components of different chain lengths. About 20-30% of gases and 60-70% of oils are produced and subsequently separated in a distillation column. Naphtha produced by the feedstock process is treated in a steam cracker, and the monomers (e.g. ethylene, propylene) are recovered. These raw materials are used for the production of virgin plastic materials. High boiling oils can be processed into synthesis gas or conversion coke and then be transferred for further use. The residues consist of 5% minerals at most, e.g. pigments or aluminium lids. It seems likely that metals present in PVC-formulations mainly end up in this outlet. The process is carried out under atmospheric

pressure in a closed system and, therefore, no other residues or emissions are formed.

but as it is olefin-rich, recovery options are being considered.

treatment in refineries (Brophy et al., 1997).

Fig. 10. BASF process [Heyde and Kremer, 1999].

Mixed PVC waste can be used as reduction agent in blast furnaces. For the production of pig iron for steel production, iron ore (Fe2O3) has to be reduced to Fe. This process takes place in a blast furnace. Coke, coal and heavy oil are normally used as reducing agents in this process. Iron and steel companies try to lower the consumption of coke, by partly replacing it with coal, gas or fuel oil (30% in weight seems to be the maximum), via coal injection technology. Recently, new developments have started to replace the conventional reducing agents by plastics waste. Though others like British Steel (UK) have done trials as well, the prominent pioneer in this field is Stahlwerke Bremen, Germany. Stahlwerke Bremen is a large German steel manufacturer which operates two blast furnaces to produce over 7000 t/day, or some 3 Million tpa pig iron. Currently, German is the sole country that blast furnace are the only plants using waste this way (DKR/DSD, 1999).

**Veba Combi Cracking process**. The plant configuration includes a depolymerisation section and the VCC section (fig. 11). Depolymerisation is required to allow further processing in the VCC section. In the depolymerisation section the agglomerated plastic waste is kept between 350-400ºC to effect depolymerisation and dechlorination. The overhead product of the depolymerisation is partially condensed. The main part (80 %) of the chlorine introduced with PVC is present as HCl in the light gases. It is washed out in the following gas purification process, yielding technical HCl. The condensate, containing 18 % of the chlorine input, is fed into a hydrotreater. The HCl is eliminated with the formation water. The resulting Cl-free condensate and gas are mixed with the depolymerisate for treatment in the VCC section. The depolymerisate is hydrogenated in the VCC section at 400-450ºC under high pressure (about 100 bar) in a liquid phase reactor with no internals. Separation yields a product which after treatment in a fixed-bed hydrotreater is a synthetic crude oil, a valuable product which may be processed in any refinery. From the separation a hydrogenated residue stream also results, which comprises heavy hydrocarbons contaminated with ashes, metals and inert salts. This hydrogenation bitumen is a byproduct which is blended with the coal for coke production (2 wt%). It is most likely that the major part of any metals present in a PVC formulation end up in this residue flow. Light cracking products end up in off-gas (E-gas), which is sent to a treatment section for H2S and ammonia removal. As indicated above, the main part of the chlorine present in the input (i.e. from PVC) is converted into usable HCl. Some 2% of the chlorine input is bound to CaCl2 in the process by a 4 times leaner than stochiometric amount of CaO.

Recent Advances in the Chemical Recycling

**7.2 Recycling techniques** 

pressures from 2 to 25 MPa.

of Polymers (PP, PS, LDPE, HDPE, PVC, PC, Nylon, PMMA) 43

et al., 2005; Chiu et al., 2006; Achilias et al., 2009], alcoholysis [Oku et al., 2000; Hu et al., 1998] and hydrolysis [Grause et al., 2009; Ikeda et al., 2008]. It is difficult to recover pure BPA using

For the purpose of recycling of polycarbonate (PC), e.g. poly[2,2-bis(4-hydroxyphenyl) propane carbonate], in the form of an essential monomer bisphenol A, there have been reported a number of depolymerization methods.[Hub et al., 1998] Due to the insolubility of PC in water, the aqueous depolymerizations require severe conditions such as long reaction times, high temperatures and pressures. Therefore, instead of using aqueous systems, organic solvent systems such as methylene chloride in combination with ammonia [Fox et al., 1989], a mixed solvent of phenol and methylene chloride in combination with an alkali catalyst [Buysch et al., 1994; Shafer, 1994] have been reported. With organic solvents,

With the rapid increase of production and consumption of PC, the chemical recycling of waste PC has been gaining greater attention in recent years to obtain valuable products. Methanolysis is one of the most important method to recover pure monomer BPA and dimethyl carbonate (DMC). However, due to the insolubility of PC in methanol, the reported methanolysis methods require high temperature and pressure and in presence of a lot amount of concentrated bases or acids. The acid or base catalysts used in traditional methods cannot be reused and result in other disadvantages such as equipment corrosion, tedious workup procedure and environmental problem. Although supercritical method can overcome some of above-mentioned shortcomings, it has its own disadvantages such as severe conditions, so its application is limited. According to a study polycarbonate could be completely decomposed into its monomer, BPA with high pressure (not atmospheric pressure) high temperature steam (300 °C) in five minutes reaction time. It is known that PC can be decomposed into monomer in alkaline alcohol or aqueous solutions. However, the monomer BPA yield has been reported as to be relatively low due to BPA instability in that condition. To develop a high-effective process of PC recycling, a reactive atmosphere must be provided that preserves the stability of BPA and get has high reactivity for PC. To determine the optimum conditions for recycling PC, it is important to know the stability or

Alkali-catalysed depolymerization of polycarbonate wastes by alcoholysis in supercritical or near critical conditions has been also studied by other researchers in order to recover the essential monomer BPA and DMC as a valuable by-product (Liu et al., 2009). Some works aimed to develop continuous process and possible scale-up for decomposition of both PC plastic wastes using methanol as solvent/reagent and NaOH as alkali catalyst. Total depolymerization of PC has been achieved working at a temperature range of 75–180 °C and

However, due to the insolubility of PC in water, the aqueous depolymerizations require severe conditions such as long reaction times, high temperatures and pressures. Therefore, instead of using aqueous systems, organic solvent systems such as methylene chloride in combination with ammonia, a mixed solvent of phenol and methylene chloride in

thermal pyrolysis, and it can be only obtained using hydrolysis. [Liu et al., 2011].

however, a tedious product separation process is generally required.

reactivity of BPA, as well as the decomposition rate of PC.

Fig. 11. Veba Combi Cracking process (Sas, 1994).

#### **7. Chemical recycling of polycarbonate**

#### **7.1 Introduction**

Polycarbonate plastics, C16H14O3 (Fig. 12) are polyesters known for their excellent mechanical properties. Featuring high‐impact resistance, UV resistance, and flame retardancy as well as excellent electrical resistance, polycarbonates are used in a wide variety of materials. Polycarbonates do not have their own recycling identification code and therefore fall under the #7 "other" classification. Polycarbonates may be made a variety of ways, the most popular of which from Bisphenol‐A (BPA) feedstock. BPA use is highly controversial, and the FDA has recently decided to reopen an inquiry on the safety of BPAs. [Jawad et al., 2009].

This is following an approval in 2008. Nalgene Outdoor Products, the pre-eminent manufacturer of reusable plastic water bottles, is transitioning from polycarbonate bottles to other plastics as well as metal alternatives in the wave of negative consumer perception of BPA.

Fig. 12. Structural unit of polycarbonate.

Due to its excellent properties, polycarbonate (PC) is widely used in the manufacture of compact disks, bullet proof windows, food packaging and soft-drink bottles. With the rapid increase in the production and consumption of PC, the chemical recycling of waste PC to obtain valuable products has received greater attention in recent years. Waste PC can be depolymerised through a chemical treatment to produce monomers that can be used to reproduce virgin PC products. Various methods for the chemical recycling of waste PC to recover raw materials have been reported; these methods include thermal pyrolysis [Yoshioka et al., 2005; Chiu et al., 2006; Achilias et al., 2009], alcoholysis [Oku et al., 2000; Hu et al., 1998] and hydrolysis [Grause et al., 2009; Ikeda et al., 2008]. It is difficult to recover pure BPA using thermal pyrolysis, and it can be only obtained using hydrolysis. [Liu et al., 2011].

For the purpose of recycling of polycarbonate (PC), e.g. poly[2,2-bis(4-hydroxyphenyl) propane carbonate], in the form of an essential monomer bisphenol A, there have been reported a number of depolymerization methods.[Hub et al., 1998] Due to the insolubility of PC in water, the aqueous depolymerizations require severe conditions such as long reaction times, high temperatures and pressures. Therefore, instead of using aqueous systems, organic solvent systems such as methylene chloride in combination with ammonia [Fox et al., 1989], a mixed solvent of phenol and methylene chloride in combination with an alkali catalyst [Buysch et al., 1994; Shafer, 1994] have been reported. With organic solvents, however, a tedious product separation process is generally required.
