**6. Chemical recycling of poly(vinyl chloride)**

#### **6.1 Introduction**

Poly(vinyl chloride) main applications include food packaging, shoes, flooring ,pipes, clothing (leather-like material), ceiling tiles and multi-layered flooring and windowswindoors frames. It has a lifetime range of 5 years. PVC has the same density as that of PET, a property that made the separation prior to recycling of plastic wastes containing both polymers really difficult. The technique used for the efficient separation is X-ray fluorescence. The chlorine atoms of PVC are detected and the wastes are indicated for separation. Also IR sorting is widely used (Sadat-Shojai and Bakhshandeh, 2011).

In principle, PVC waste can be available in two ways: as a mixed plastic waste (MPW) fraction (with a rather low PVC content), or as a PVC-rich plastics fraction.

Fig. 7. The tonage of recycled PVC in EUROPE (Sadat-Shojai, Bakhshandeh, 2011).

As it is well-known PVC incineration is connected with problems arising from the high chlorine content of this polymer which yields large amounts of hydrochloric acid (HCl) during thermal decomposition, beside the possibility of formation of persistent and toxic compounds such as toxic dioxines and furans (Garcia et al., 2007; Ulutan, 1998; Ali and Siddiqui, 2005). In addition, when PVC wastes are fired in an incinerator, HCl corrodes the boiler tubes of the incinerator and other equipments. Therefore the steam pressure must be kept relatively low to prevent corrosion of the heat recovery boiler (Yoshioka et al., 1998). One of the best solutions to this problem may be neutralization of HCl with calcium carbonate (lime) and/or sodium hydroxide (caustic soda) to convert the released HCl to the salts. Also special filters can also be used to prevent problems related to atmospheric emissions during the combustion process (Machado et al., 2010).

Poly(vinyl chloride) main applications include food packaging, shoes, flooring ,pipes, clothing (leather-like material), ceiling tiles and multi-layered flooring and windowswindoors frames. It has a lifetime range of 5 years. PVC has the same density as that of PET, a property that made the separation prior to recycling of plastic wastes containing both polymers really difficult. The technique used for the efficient separation is X-ray fluorescence. The chlorine atoms of PVC are detected and the wastes are indicated for

In principle, PVC waste can be available in two ways: as a mixed plastic waste (MPW)

separation. Also IR sorting is widely used (Sadat-Shojai and Bakhshandeh, 2011).

Fig. 7. The tonage of recycled PVC in EUROPE (Sadat-Shojai, Bakhshandeh, 2011).

emissions during the combustion process (Machado et al., 2010).

As it is well-known PVC incineration is connected with problems arising from the high chlorine content of this polymer which yields large amounts of hydrochloric acid (HCl) during thermal decomposition, beside the possibility of formation of persistent and toxic compounds such as toxic dioxines and furans (Garcia et al., 2007; Ulutan, 1998; Ali and Siddiqui, 2005). In addition, when PVC wastes are fired in an incinerator, HCl corrodes the boiler tubes of the incinerator and other equipments. Therefore the steam pressure must be kept relatively low to prevent corrosion of the heat recovery boiler (Yoshioka et al., 1998). One of the best solutions to this problem may be neutralization of HCl with calcium carbonate (lime) and/or sodium hydroxide (caustic soda) to convert the released HCl to the salts. Also special filters can also be used to prevent problems related to atmospheric

fraction (with a rather low PVC content), or as a PVC-rich plastics fraction.

**6. Chemical recycling of poly(vinyl chloride)** 

**6.1 Introduction** 

Beside all above problems, net energy recovered by incineration of PVC-rich waste is not high enough to make it highly economic. As most hydrocarbon polymers, the calorific value from incineration of PVC in an ideal conditions is about 64 MJ/kg, compared to, for example, 17 MJ/kg for paper, or 16 MJ/kg for wood. Moreover, PVC is inherently difficult to combust, so that complete combustion of PVC-rich waste occurs at such high temperatures (>1700 K), that it is economically prohibitive (Xiong, 2010).

Therefore mechanical and/or chemical recycling of PVC plastic wastes seems the logical solution One usual approach for chemical recycling of PVC wastes is currently "thermal cracking" via hydrogenation, pyrolysis or gasification (Ryu et al., 2007; Williams and Williams, 1998; DeMarco et al., 2002; Kaminsky and Kim, 1999; Borgianni et al., 2002).

The main intermediate product of the thermal cracking is a polyene material that continues to degrade by evolution of aromatics and converts to a products which their composition will be strongly determined by processing variable such as type of atmosphere, temperature and residence time. In an inert atmosphere, the degradation products will be hydrochloric acid (HCl), gaseous and liquid hydrocarbons, and char, which among them HCl is a main product and can be reused either in vinyl chloride production, or in other chemical processes (Slapak et al., 1999).

In the case of manufacturing process of vinyl chloride, a gas purification unit must also be added to obtain high purity hydrogen chloride gas.

In a steam atmosphere at high temperatures, the hydrocarbon fraction will be converted into the some other products such as carbon monoxide, carbon dioxide and hydrogen. In a reported process bench-scale bubbling fluidized bed to investigate some processing parameters on the product outcome. The choice of type of bed material is essential for the product outcome, so that the use of catalytic inactive solid quartz as bed material results in the production of large amounts of char and tar, whereas the application of catalytic active material such as porous alumina results in a high conversion of PVC into the syngas. Moreover, according to their results, temperature has a large impact on the composition of the products, so that the carbon to gas conversion improved from about 70% at 1150 K to approximately 100% by increasing the reactor temperature to 1250 K. For chemical recycling of PVC, an increase in efficiency of dehydrochlorination process is usually attributed to the successful recycling (Wu et al., 2009).

It has been also reported that the emission of hydrogen chloride changes significantly with the oxides used indicating the chlorine fixing ability of oxides and also that utilization of poly(ethylene glycol) (PEG) can accelerate dehydrochlorination of PVC, so that at 210 °C for 1 h the dehydrochlorination degree was as high as 74% for PVC/PEG, while for PVC only 50%. Moreover, they demonstrated that for PVC/ PEG the decomposition of PVC shifted to lower temperatures compared with that of pure PVC, suggesting some interactions exist between PEG and PVC that caused the faster dehydrochlorination rate. According to their results, during this process, no waste byproducts such as KCl were produced, and satisfactory recyclability of PEG (10 cycles) can be obtained (Wu et al., 2009).

An alternative method to thermal process of dehydrochlorination is the rather easy process of dehydrochlorination under the influence of alkaline media to recover hydrochloric acid

Recent Advances in the Chemical Recycling

rigid PVC particles (Kameda et al., 2010).

electric arc furnace (Lee et al., 2007).

characterized (Matuschek et al., 2000).

**6.2 Mixed plastic recycling processes** 

2008).

of Polymers (PP, PS, LDPE, HDPE, PVC, PC, Nylon, PMMA) 37

A new method consisting of copyrolysis of PVC with nitrogen compounds in biowaste to reduce the corrosive effects of the generated HCl was reported. The researchers studied the pyrolysis conditions between PVC and cattle manure via a statistical method and optimized conditions to provide the highest HCl reduction during PVC pyrolysis. They also applied the optimized conditions to a plastic mixture and then determined the quality of the obtained products. They concluded that the lowest heating rate, the highest reaction temperature (450°C), and the PVC:cattle manure ratio of 1:5 are the suitable conditions which provide the highest HCl reduction. However, according to their results the presence of manure decreases the oil yield of pyrolysis by about 17% (Duangchang,

PVC can also be chemically modified by nucleophilic substitution of chlorine atoms in its structure as it has been described: reactions of rigid PVC with various nucleophiles (Nu) such as iodide, hydroxide, azide, and thiocyanate in ethylene glycol as solvent. Such reactions lead to the substitution of Cl by Nu and finally elimination of HCl, resulting in the dehydrochlorination of the rigid PVC. According to their results, the dehydrochlorination yield increased with an increasing nucleophiles concentration, resulting in a maximum substitution at high nucleophiles amounts. Moreover, when ethylene glycol was replaced by diethylene glycol the dehydrochlorination was found to be accelerated, which may be due to the higher compatibility of diethylene glycol with PVC, making it easier to penetrate the

Several different technologies based on depolymerization and repolymerization processes have been developed for chemical recycling of PVC, which unfortunately the most of them

PVC waste was used in a research wich carried out for the recycling electric arc furnace dust by heat treatment with PVC. The entire process aimed to recover the zinc, lead, and cadmium from the dust and was adjusted so that the residual dust can be injected into the

There are many reports, where thermoanalytical methods especially coupled methods with gas analysis systems, can deliver suitable information for the recycled PVC that needs to be

Recovinyl-Co (UK) deals with post-consumer PVC to reproduce two grades via mechanical recycling. Due to its structure and composition, PVC can easily be mechanically recycled in order to obtain good quality recycling material. Careful and proper sorting is of crucial

A pyrolytic process which has proven to be successful for plastic solid waste rich in PVC, is the Akzo process (Netherlands). With a capacity of 30 kg/h, this fast pyrolysis process is based on a circulating fluidised bed system (two reactors) with subsequent combustion. Input to the process is shredded mixed waste including a high percentage of PVC waste. The main outputs consist of HCl, CO, H2, CH4 and, depending on the feedstock

are more expensive than the mechanical recycling (LaMantia, 1996).

importance for the optimal recycling of PVC (Recovinyl, 2008).

composition, other hydrocarbons and fly ash (Tukker et al., 1999).

with a possibility that the degradation of PVC by oxygen oxidation in an aqueous alkaline solution to produce various carboxylic acids (Brown, 2002).

Some researchers demonstrated that dehydrochlorination of flexible-PVC occurred first and followed then by oxidation. They reported that the major products were oxalic acid, a mixture of benzenecarboxylic acids, and CO2. However, the chlorine content could also be recovered in the form of HCl by adjusting the reaction conditions such as alkali concentration (Yoshioka et al., 1998).

Among various methods of thermal cracking, pyrolysis is a more well-known procedure in the chemical recycling of PVC. The process of pyrolysis, which takes places at 500-900°C without any oxygen, is a very suitable recycling method especially in the case of mixed plastic wastes (PVC recycling, 2005). In a typical process, a PVC-rich waste can be pyrolysed to hydrocarbons (oil), soot, hydrochloric acid, chlorinated hydrocarbons, etc., which hydrochloric acid needs to be removed from the pyrolysis gas although this removal process can result in the formation of toxic dioxins in some stages. The main end product of pyrolysis is, however, oil industry (Sadat-Shojai and Bakhshandeh, 2011).

One main problem connected with pyrolysis of PVC and mixed plastics containing PVC materials is corrosion of the process equipment (e.g., pyrolysis reactor and piping) mainly by the formation of the acid gas (HCl). Moreover, many petrochemical specifications limit the amounts of halogens (appeared in the forms of hydrogen chloride and chloro organic compounds) to a very low range in the gas and oil derived from plastic waste. Therefore in the case of mixed plastic wastes (uneconomic to separate to a single polymer) with a low PVC content, the conventional chemical recycling is frequently used only for a waste stream in which the PVC content is less than 30% (for example, the multiple material products) (Duangchang, 2008).

So far, several solutions to such problems have been proposed which some of them have already been put into practical use. For example, milling of PVC with CaO can be an effective way to extract Cl from the waste (Tongamp et al., 2008).

An attempt has also been made to develop a process for recovering metals from alloywastes by using a mechanochemical reaction consisting of a co-grinding alloy and PVC waste, followed by washing with water and filtration (Zhang et al., 2007).

Currently, the NKT-Watech pyrolysis process in Europe uses another two-step pyrolysis of PVC wastes in a stirred vessel. Calcium carbonate and filler are used to react with liberated HCl and produce calcium chloride. Then at the increased temperature, the polymer chains break down which produce a solid coke residue. Finally, the residual calcium chloride can be treated to make it suitable for selling (Scheirs, 2010).

Alternative approach is pre-treatment of mixed plastic waste by removing PVC and other halogenated plastics from the feed. Such pre-treatment consists of a dilution of the wastes having excessive chlorine content with less chlorine-containing or chlorine-free polymer mixture. It is also common to dilute the chlorine-containing hydrocarbon feed with chlorinefree petroleum fractions coming from refineries. Another possibility, as a less expensive and more acceptable process, is thermal dehalogenation which takes place either in a liquid or in a fluidized bed pyrolysis.

with a possibility that the degradation of PVC by oxygen oxidation in an aqueous alkaline

Some researchers demonstrated that dehydrochlorination of flexible-PVC occurred first and followed then by oxidation. They reported that the major products were oxalic acid, a mixture of benzenecarboxylic acids, and CO2. However, the chlorine content could also be recovered in the form of HCl by adjusting the reaction conditions such as alkali

Among various methods of thermal cracking, pyrolysis is a more well-known procedure in the chemical recycling of PVC. The process of pyrolysis, which takes places at 500-900°C without any oxygen, is a very suitable recycling method especially in the case of mixed plastic wastes (PVC recycling, 2005). In a typical process, a PVC-rich waste can be pyrolysed to hydrocarbons (oil), soot, hydrochloric acid, chlorinated hydrocarbons, etc., which hydrochloric acid needs to be removed from the pyrolysis gas although this removal process can result in the formation of toxic dioxins in some stages. The main end product of

One main problem connected with pyrolysis of PVC and mixed plastics containing PVC materials is corrosion of the process equipment (e.g., pyrolysis reactor and piping) mainly by the formation of the acid gas (HCl). Moreover, many petrochemical specifications limit the amounts of halogens (appeared in the forms of hydrogen chloride and chloro organic compounds) to a very low range in the gas and oil derived from plastic waste. Therefore in the case of mixed plastic wastes (uneconomic to separate to a single polymer) with a low PVC content, the conventional chemical recycling is frequently used only for a waste stream in which the PVC content is less than 30% (for example, the multiple material products)

So far, several solutions to such problems have been proposed which some of them have already been put into practical use. For example, milling of PVC with CaO can be an

An attempt has also been made to develop a process for recovering metals from alloywastes by using a mechanochemical reaction consisting of a co-grinding alloy and PVC

Currently, the NKT-Watech pyrolysis process in Europe uses another two-step pyrolysis of PVC wastes in a stirred vessel. Calcium carbonate and filler are used to react with liberated HCl and produce calcium chloride. Then at the increased temperature, the polymer chains break down which produce a solid coke residue. Finally, the residual calcium chloride can

Alternative approach is pre-treatment of mixed plastic waste by removing PVC and other halogenated plastics from the feed. Such pre-treatment consists of a dilution of the wastes having excessive chlorine content with less chlorine-containing or chlorine-free polymer mixture. It is also common to dilute the chlorine-containing hydrocarbon feed with chlorinefree petroleum fractions coming from refineries. Another possibility, as a less expensive and more acceptable process, is thermal dehalogenation which takes place either in a liquid or in

pyrolysis is, however, oil industry (Sadat-Shojai and Bakhshandeh, 2011).

effective way to extract Cl from the waste (Tongamp et al., 2008).

be treated to make it suitable for selling (Scheirs, 2010).

waste, followed by washing with water and filtration (Zhang et al., 2007).

solution to produce various carboxylic acids (Brown, 2002).

concentration (Yoshioka et al., 1998).

(Duangchang, 2008).

a fluidized bed pyrolysis.

A new method consisting of copyrolysis of PVC with nitrogen compounds in biowaste to reduce the corrosive effects of the generated HCl was reported. The researchers studied the pyrolysis conditions between PVC and cattle manure via a statistical method and optimized conditions to provide the highest HCl reduction during PVC pyrolysis. They also applied the optimized conditions to a plastic mixture and then determined the quality of the obtained products. They concluded that the lowest heating rate, the highest reaction temperature (450°C), and the PVC:cattle manure ratio of 1:5 are the suitable conditions which provide the highest HCl reduction. However, according to their results the presence of manure decreases the oil yield of pyrolysis by about 17% (Duangchang, 2008).

PVC can also be chemically modified by nucleophilic substitution of chlorine atoms in its structure as it has been described: reactions of rigid PVC with various nucleophiles (Nu) such as iodide, hydroxide, azide, and thiocyanate in ethylene glycol as solvent. Such reactions lead to the substitution of Cl by Nu and finally elimination of HCl, resulting in the dehydrochlorination of the rigid PVC. According to their results, the dehydrochlorination yield increased with an increasing nucleophiles concentration, resulting in a maximum substitution at high nucleophiles amounts. Moreover, when ethylene glycol was replaced by diethylene glycol the dehydrochlorination was found to be accelerated, which may be due to the higher compatibility of diethylene glycol with PVC, making it easier to penetrate the rigid PVC particles (Kameda et al., 2010).

Several different technologies based on depolymerization and repolymerization processes have been developed for chemical recycling of PVC, which unfortunately the most of them are more expensive than the mechanical recycling (LaMantia, 1996).

PVC waste was used in a research wich carried out for the recycling electric arc furnace dust by heat treatment with PVC. The entire process aimed to recover the zinc, lead, and cadmium from the dust and was adjusted so that the residual dust can be injected into the electric arc furnace (Lee et al., 2007).

There are many reports, where thermoanalytical methods especially coupled methods with gas analysis systems, can deliver suitable information for the recycled PVC that needs to be characterized (Matuschek et al., 2000).

#### **6.2 Mixed plastic recycling processes**

Recovinyl-Co (UK) deals with post-consumer PVC to reproduce two grades via mechanical recycling. Due to its structure and composition, PVC can easily be mechanically recycled in order to obtain good quality recycling material. Careful and proper sorting is of crucial importance for the optimal recycling of PVC (Recovinyl, 2008).

A pyrolytic process which has proven to be successful for plastic solid waste rich in PVC, is the Akzo process (Netherlands). With a capacity of 30 kg/h, this fast pyrolysis process is based on a circulating fluidised bed system (two reactors) with subsequent combustion. Input to the process is shredded mixed waste including a high percentage of PVC waste. The main outputs consist of HCl, CO, H2, CH4 and, depending on the feedstock composition, other hydrocarbons and fly ash (Tukker et al., 1999).

Recent Advances in the Chemical Recycling

**6.3 Mixed PVC wastes World inititives** 

(Shin et al., 1998).

(Yoshioka et al., 2000).

of Polymers (PP, PS, LDPE, HDPE, PVC, PC, Nylon, PMMA) 39

depending on the reaction conditions and the alkali concentration. The maximum yield of oxalic acid was 45%and 42% of the chlorine content could be recovered in the form of HCl

Oxidative degradation of rigid-PVC pellets (R-PVC) with oxygen was carried out in 1-25 mol/kg-H2O (m) NaOH solutions, at 150-260°C and PO2 of 1-10 MPa in order to investigate the chemical recycling of PVC materials. The apparent rate of oxidative degradation of R-PVC progressed as a zero order reaction, and the apparent activation energy was 38.5 kJ/mol. The major products were oxalic acid, a mixture of benzene-carboxylic acids, and CO2. The tin in R-PVC was extracted completely. The possibility of converting PVC materials into raw materials such as carboxylic acids by chemical recycling is reported

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

**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

on these initiatives is presented below (Sadat-Shojai and Bakhshandeh, 2011).

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

The NRC process is another successful pyrolysis scheme. This process is based on the pyrolysis with subsequent metal extraction technology. The aim is to produce purified calcium chloride instead of HCl. The input to the process is PVC waste (cables, flooring, profiles, etc.). No other plastic solid waste type is fed to the processing, which results in calcium chloride, coke, organic condensate (for use as fuels) and heavy metals for metal recycling, as products (Al-Salem et al., 2009).

The NTK process, depicted below (fig. 8), is a very successful recycling process. The process is based on an initial pre-treatment step that involves separating light plastics (PP, PE, etc.) and other materials, e.g. wood, sand, iron, steel, brass, copper and other metallic pollutants. The PSW waste is then fed to a reactor at a low pressure (2–3 bars) and a moderate temperature (375°C). The process emits neither dioxins, chlorine, metals nor plasticizers. Also, there are no liquid waste streams in the process since all streams are recycled within the system. There is a small volume of carbon-dioxide gas formed by the reaction between lime/limestone and hydrogen chloride. Mixed PVC building waste containing metals, sand, soil, PE, PP, wood and rubber waste have been successfully treated (Al-Salem et al., 2009).

The gasification into high calorific value fuel gas obtained from PVC was also reported by Borgianni et al., 2002.

Fig. 8. NTK process diagram (Tukker et al., 1999).

Chemical recycling of PVC has been also attempted. Most of the proposed processes use the rather easy dehydrochlorination of PVC either under the influence of heat of alkaline media. The oxidative degradation of PVC by molecular oxygen in aqueous alkaline solution at temperatures between 150 and 260 oC with oxygen pressures of 1–10 MPa has been reported. The main products are oxalic acid and carbon dioxide, their yield

The NRC process is another successful pyrolysis scheme. This process is based on the pyrolysis with subsequent metal extraction technology. The aim is to produce purified calcium chloride instead of HCl. The input to the process is PVC waste (cables, flooring, profiles, etc.). No other plastic solid waste type is fed to the processing, which results in calcium chloride, coke, organic condensate (for use as fuels) and heavy metals for metal

The NTK process, depicted below (fig. 8), is a very successful recycling process. The process is based on an initial pre-treatment step that involves separating light plastics (PP, PE, etc.) and other materials, e.g. wood, sand, iron, steel, brass, copper and other metallic pollutants. The PSW waste is then fed to a reactor at a low pressure (2–3 bars) and a moderate temperature (375°C). The process emits neither dioxins, chlorine, metals nor plasticizers. Also, there are no liquid waste streams in the process since all streams are recycled within the system. There is a small volume of carbon-dioxide gas formed by the reaction between lime/limestone and hydrogen chloride. Mixed PVC building waste containing metals, sand, soil, PE, PP, wood and rubber waste have been successfully treated (Al-Salem et al., 2009).

The gasification into high calorific value fuel gas obtained from PVC was also reported by

Chemical recycling of PVC has been also attempted. Most of the proposed processes use the rather easy dehydrochlorination of PVC either under the influence of heat of alkaline media. The oxidative degradation of PVC by molecular oxygen in aqueous alkaline solution at temperatures between 150 and 260 oC with oxygen pressures of 1–10 MPa has been reported. The main products are oxalic acid and carbon dioxide, their yield

recycling, as products (Al-Salem et al., 2009).

Fig. 8. NTK process diagram (Tukker et al., 1999).

Borgianni et al., 2002.

depending on the reaction conditions and the alkali concentration. The maximum yield of oxalic acid was 45%and 42% of the chlorine content could be recovered in the form of HCl (Shin et al., 1998).

Oxidative degradation of rigid-PVC pellets (R-PVC) with oxygen was carried out in 1-25 mol/kg-H2O (m) NaOH solutions, at 150-260°C and PO2 of 1-10 MPa in order to investigate the chemical recycling of PVC materials. The apparent rate of oxidative degradation of R-PVC progressed as a zero order reaction, and the apparent activation energy was 38.5 kJ/mol. The major products were oxalic acid, a mixture of benzene-carboxylic acids, and CO2. The tin in R-PVC was extracted completely. The possibility of converting PVC materials into raw materials such as carboxylic acids by chemical recycling is reported (Yoshioka et al., 2000).
