Deplasticization and dechlorination of flexible polyvinyl chloride in NaOH solution by microwave heating

This study investigated the deplasticization and dechlorination of flexible polyvinyl chloride (PVC) containing 59.2% PVC, 29.7% dioctyl phthalate (DOP), and approximately 12% stabilizers. Flexible PVC was treated with NaOH solutions at concentrations in the range 2–16 mol/l and heated by microwaves to temperatures between 100° and 250°C for 0–120 min. DOP was extracted from flexible PVC into the NaOH solution as a phthalic acid salt; the remaining PVC was subsequently dechlorinated by increasing the temperature. On internal heating using microwaves, the plasticizer was 100% extracted during processing at 150°C for 30 min, whereas the chlorides were 100% removed during processing at 235°C for 30 min; the residue was converted into hydrocarbon compounds. The maximum weight loss ratio was 71% compared to the pretreatment state. It was also found that 100% deplasticization and dechlorination was possible using 8 mol/l NaOH solution, which is almost half the concentration employed when using conventional external heating systems.     

Production of hydrogen by steam gasification of dehydrochlorinated poly(vinyl chloride) or activated carbon in the presence of various alkali compounds

Steam gasification of dehydrochlorinated poly(vinyl chloride) (PVC) or activated carbon was carried out in the presence of various alkali compounds at 3.0 MPa and 560°C–660°C in a batch reactor or in a semi-batch reactor with a flow of nitrogen and steam. Hydrogen and sodium carbonate were the main products, and methane and carbon dioxide were the minor products. Yields of hydrogen were high in the presence of sodium hydroxide and potassium hydroxide. The acceleration effect of the alkali compounds on the gasification reaction was as follows: KOH > NaOH > Ca(OH)₂ > Na₂CO₃. The rate of gasification increased with increasing partial steam pressure and NaOH/C molar ratio. However, the rate became saturated at a molar ratio of NaOH/C greater than 2.0.     

Electrodialysis for NaCl/EG solution using ion-exchange membranes

A new concept for the recycling of poly(vinyl chloride) (PVC) has been introduced, including the dehydrochlorination of PVC in ethylene glycol (EG) with NaOH as a reactant, the subsequent separation of NaCl from EG by electrodialysis, and the recovery of chlorine for the synthesis of new PVC. In this work, the separation of NaCl by electrodialysis was investigated. About 98 % of the salt were recovered from EG, with less than 10 % of the EG permeating the membranes after 5 h.     

Viable chemical recycling of poly(carbonate) as a phosgene equivalent illustrated by the coproduction of bisphenol A and carbohydrate carbonates

Chemical recycling of waste poly(carbonate) (PC) to coproduce bisphenol A (BPA) and carbohydrate carbonates was studied by selecting glycerol (Gly) and glucose (Glu) as model carbohydrates (CHs). In advance of the reaction of PC with CHs, reactions with diphenyl carbonate were examined as a model PC. In dioxane at 100°C using NaOH as catalyst, Gly was converted to cyclic carbonate hydroxymethyldioxolane (HMDO) at 98% and Glu was converted to the dicarbonate (Glu-DC) at 46%, in pyridine, in addition to the production of phenol. Similar treatment of PC with Gly using KOH as a catalyst produced HMDO and BPA at very high yields and treatment with Glu produced Glu-DC and BPA in 38%–42% yields. Chemical Feedstock Recycling & Other Innovative Recycling Techniques 6     

Liquefaction process for a hydrothermally treated waste mixture containing plastics

Most landfilled plastic waste is a mixture or is in the form of composites with incombustible wastes such as glass, metals, and ceramics. After hydrothermal treatment, including a steam-explosion process, the separation of mixed waste (MW) into organic and inorganic substances becomes easy. However, the effect of hydrothermal pretreatment on the subsequent liquefaction of organic substances from MW is not obvious. In this study, the effects on the liquefaction of polystyrene and high-density polyethylene are discussed. Moreover, optimum conditions for the liquefaction of organic substances from hydrothermally treated MW are identified. By means of this hydrothermal pretreatment, including the steam-explosion process, polystyrene and high-density polyethylene can be significantly converted to oil by liquefaction at 300°–400°C. In comparison with liquefaction of hydrothermally pretreated mixed waste (HMW) at 300°–400°C with a batch type reactor, the yield of oil increases significantly on liquefaction using a semi-batch type reactor. It is considered that the radical chain and termination reactions among the radicals from HMW were inhibited in the semi-batch type reactor. On liquefaction of HMW in a semi-batch reactor, the conversion of HMW to oil was enhanced on increasing the liquefaction temperature to 350°C and the holding time to 60 min. Chemical Feedstock Recycling & Other Innovative Recycling Techniques 6     

Surface ozonation of polyvinyl chloride for its separation from waste plastic mixture by froth floatation

Selective surface modification of polyvinyl chloride (PVC) by ozonation was evaluated to facilitate the separation of PVC from other heavy plastics with almost the same density as PVC, especially polyethylene terephthalate (PET), by the froth flotation process. The optimum froth flotation conditions were investigated, and it was found that at 40°C, 90% of PVC and PET plastics floated. The bubble size became larger and the area covered with bubbles on the plastic surface was reduced with increasing temperature. Optimum PVC separation was achieved with the flotation solution at 40°C and mixing at 180–200 rpm, even for sheet samples 10 mm in size. Combined treatment by ozonation and froth flotation is a simple, effective, and inexpensive method for PVC separation from waste plastics.     

Effect of microwave irradiation on anaerobic degradability of model kitchen waste

High temperature and pressure microwave (MW) irradiation was investigated as a pre-treatment to enhance anaerobic biodegradability and methane production from a model kitchen waste (KW). Heating rates of 7.8, 3.9 and 1.9 °C/min from room temperature to a final pre-treatment temperature of 175 °C with 1 min temperature holding time were tested. MW irradiation was successful in solubilization of particulate chemical oxygen demand (COD) resulting in higher soluble COD, protein and sugar concentrations in the supernatant phase (<0.45 μm) as well as in the whole fraction of pretreated KW compared to controls (not pretreated). Anaerobic biodegradability of the supernatant and whole fractions of pretreated KW was assessed by using a batch biochemical methane potential assay (BMP) at 33 °C. Although the highest level of solubilization was achieved at a heating rate of 1.9 °C/min, improvement in anaerobic biodegradability was observed only at the fastest heating rate of 7.8 °C/min for whole waste and for all conditions with the supernatant phase. BMP indicated increased biodegradability of between 5% and 16% for the supernatant fraction relative to controls. For the whole fraction, anaerobic biodegradability improved by 9% at a heating rate of 7.8 °C/min.     

Influence of poly(bisphenol A carbonate) and poly(ethylene terephthalate) on poly(vinyl chloride) dehydrochlorination

Recycling of poly(vinyl chloride) (PVC) waste is a serious problem because of its high chlorine content. Dehydrochlorination of PVC-containing polymer waste produces solid residue char, for which conversion to pyrolysis oil in a petrochemical plant seems to be an attractive way of recycling PVC waste. Unfortunately, some polymer admixtures react with HCl and cause formation of chloroorganic compounds in a char. This article describes the influence of polycarbonates and poly(ethylene terephthalate) on thermal feedstock recycling of PVC wastes using a two-stage method. It was found that the presence of polycarbonate causes the formation of small amounts of benzyl chloride and other chloroaryl or chloroalkylaryl compounds. Poly(ethylene terephthalate) interacts with HCl forming significant amounts of various chlorocompounds – mainly chloroethyl esters of terephthalic and benzoic acids, but derivatives possessing chlorine directly connected to the aromatic ring are also formed.     

Pyrolysis of jute dust: effect of reaction parameters and analysis of products

Biowastes are becoming potential feedstocks for direct utilization or conversion to solid, liquid and gaseous fuels via various thermochemical routes. In this regard, jute dust which is a major agro-industrial waste in jute mills was pyrolysed in a fixed-bed reactor with an aim to study the product distribution and their characterization and to identify the optimum condition for bio-oil yield. The investigated process variables were temperature (400–700 °C), heating rate (10 and 40 °C/min) and nitrogen gas flow rate (50–250 ml/min). The yield of bio-oil is found to be maximum at 500 °C with a heating rate of 40 °C/min. However, further increase in temperature leads to decrease in bio-oil yield. Chemical compositions of the bio-oils were investigated using chromatographic and spectroscopic techniques such as ¹H NMR, FTIR and GC–MS. The heating value of the bio-oil is 26.71 MJ/kg. The study shows that jute dust have potential for conversion to bio-oil through the process of pyrolysis to supplement the petro-derived liquid fuel for heating and transportation applications after upgrading. The biochar produced as a co-product of jute dust pyrolysis can be a potential soil amendment with multiple benefits including increased soil fertility and C-sequestration.     

Effect of Solvent Composition on Porosity,Surface Morphology and Thermal Behavior of Metal Alginate Prepared from Algae (<Emphasis Type="Italic">Undaria pinnatifida</Emphasis>)

Alginates, extracted from algae are linear unbranched polymers containing β-(1→4)-linked d-mannuronic acid (M) and α-(1→4)-linked l-guluronic acid (G) residues. The conversion of alginic acid into the metal alginate is confirmed using FTIR spectroscopy. Asymmetric and symmetric stretching of free carboxyl group present in metal alginate occurs almost at the same position in various solvent compositions. Total intrusion volume of metal alginate prepared in propanol (0.0742 mL/g) is greater compared to those in ethanol (0.0648 mL/g) and methanol (0.0393 mL/g) as solvent. Surface morphology as well as porosity and pore size distribution of metal alginate are greatly influenced by solvent. It can be seen from thermal analysis results that calcium alginate prepared using different solvent compositions started decomposing at 100 °C, but rapid degradation started around 200 °C. The results showed a stepwise weight loss during thermal sweep, indicating different types of reactions during degradation. First and second step of rapid degradation was situated around 200–300 and 300–550 °C, respectively; whereas the final step is situated around 550–650 °C. The trend of degradation was similar for all the solvents, although the amount of final residue varied from one solvent to another. At the same time, lower thermal stability was also observed with higher heating rates. Additionally, a kinetic analysis was performed to fit with TGA data, where the entire degradation process has been considered as three consecutive first order reactions.     

Pore structure and adsorption properties of carbonized material prepared from waste paper

We have already reported the adsorptivity and pore structure of activated carbon made from waste newspaper in order to use the waste paper for purposes other than paper-making stock. However, manufacturing the activated carbon may not necessarily be an advantageous method based on environmental concerns and the effective use of the resource because the reaction during the activating process is endothermic and the amount of carbon consumed is significant. Here, we examine the pore structure and adsorption properties of waste newspaper used as an adsorbent in the form of a carbonized material. Waste newspaper was carbonized for 2 h in the temperature range 400°–1000°C. The specific surface area of the carbonized material obtained, 418 m²/g, was highest for the sample carbonized at 800°C, which was equal to or greater than that of commercially available charcoal. Moreover, the iodine adsorption number of 581 mg/g was the highest and the rate of adsorption was the fastest for the sample carbonized at 800°C. However, the humidity control capability was highest for the material carbonized at 600°–700°C. It has been determined that it is advantageous to carbonize waste paper at 800°C in order to use the carbonized material as an adsorbent, while carbonization at 600°–700°C is more advantageous for use as a humidity control material. Received: June 23, 2000 / Accepted: January 17, 2001     

High efficiency chlorine removal from polyvinyl chloride (PVC) pyrolysis with a gas–liquid fluidized bed reactor

In this research a gas–liquid fluidized bed reactor was developed for removing chlorine (Cl) from polyvinyl chloride (PVC) to favor its pyrolysis treatment. In order to efficiently remove Cl within a limited time before extensive generation of hydrocarbon products, the gas–liquid fluidized bed reactor was running at 280–320 °C, where hot N₂ was used as fluidizing gas to fluidize the molten polymer, letting the molten polymer contact well with N₂ to release Cl in form of HCl. Experimental results showed that dechlorination efficiency is mainly temperature dependent and 300 °C is a proper reaction temperature for efficient dechlorination within a limited time duration and for prevention of extensive pyrolysis; under this temperature 99.5% of Cl removal efficiency can be obtained within reaction time around 1 min after melting is completed as the flow rate of N₂ gas was set around 0.47–0.85 Nm³ kg^?1 for the molten PVC. Larger N₂ flow rate and additives in PVC would enhance HCl release but did not change the final dechlorination efficiency; and excessive N₂ flow rate should be avoided for prevention of polymer entrainment. HCl is emitted from PVC granules or scraps at the mean time they started to melt and the melting stage should be taken into consideration when design the gas–liquid fluidized bed reactor for dechlorination.     

Chemical recycling of polycarbonate in dilute aqueous ammonia solution under hydrothermal conditions

Polycarbonate (PC) pellets were subjected to dilute aqueous ammonia solution under hydrothermal conditions in a semi-batch reactor at temperatures ranging from 433 to 463 K and at a pressure of 10 MPa. The PC pellets were almost completely converted to bisphenol A (BPA). During an initial certain period, referred to as an induction time, neither BPA nor total organic carbon in solution were detected, and the BPA yield increased with time. The monomer yield was well represented by a surface reaction model, two-thirds-order reaction with respect to the mass of unreacted PC. The overall rate constant of the reaction in 0.6 mol/kg aqueous ammonia solution at 433 K was about 15 times greater than that in 0.6 mol/kg NaOH solution. The rate constant at 433 K was proportional to the ammonia or NaOH concentration. There was a correlation between the induction time and temperature, as well as the ammonia or NaOH concentration. By carrying out the reaction in aqueous mixtures of (NH₄)₂SO₄ and NaOH at various concentrations of NaOH, ammonia was confirmed not to function as an alkaline reagent, but as a nucleophile reagent.     

Determination of nitrous oxide, methane, and ammonia emissions from a swine waste composting process

The amounts of harmful gas emissions from the process of composting swine waste were determined using an experimental composting apparatus. Forced aeration (19.2–96.1 l/m³/min) was carried out continuously, and exhaust gases were collected and analyzed periodically. With weekly turning and the addition of a bulking agent in order to decrease the moisture content and increase air permeability, the temperature of most of the contents rose to 70°C and composting was complete within 3–5 weeks. NH₃, CH₄, and N₂O emissions were high in the early stage of composting. About 10%–25% of the nitrogen in the raw material was lost as NH₃ gas during composting. The emission rate of NH₃ mainly depended on the aeration rate, so that as the aeration rate rose, the level of NH₃ emissions increased. The CH₄ and N₂O emissions could be kept lower with adequate treatment at more than 40 l/m³/min aeration. N₂O may be mainly the result of the denitrification of NO _x -N in the additional matured compost used as a composting accelerator. Received: September 11, 1998 / Accepted: November 8, 1999     

Preparation, Thermal Properties and Thermal Reliability of Form-Stable Paraffin/Polypropylene Composite for Thermal Energy Storage

This study is focused on the preparation, characterization, and determination of thermal properties and thermal reliability of paraffin/polypropylene (PP) composite as a novel form-stable phase change material (PCM) for thermal energy storage applications. In the composite, paraffin acts as a PCM when PP is operated as supporting material. The composites prepared at different mass fractions of paraffin (50, 60, 70, 80, and 90 w/w%) by solution casting method were subjected to leakage test by heating the composites over the melting temperature of the PCM. The paraffin/PP composite (70/30 w/w%) is found as the maximum paraffin containing composite and was characterized using Fourier transform infrared spectroscopy, optic microscopy, differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA) techniques. DSC analysis indicated that the form-stable paraffin/PP composite melts at 44.77–45.52 °C and crystallizes at 53.55–54.80 °C. It has latent heats of 136.16 and −136.59 J/g for melting and crystallization, respectively. These thermal properties make it potential PCM for latent heat thermal energy storage (LHTES) purposes such as solar space heating applications. Accelerated thermal cycling tests indicated that the form-stable PCM had good thermal reliability. TGA also showed that the form-stable PCM degrades in two distinguishable steps and had good chemical stability.     

Upgrading of poly(vinyl chloride) by chemical modifications using sodium sulfide

The recycling of poly(vinyl chloride) (PVC) is one of the most important issues in the treatment of waste plastics. To improve PVC recycling, it is necessary to develop new recycling techniques, including new techniques for the dechlorination of chlorine-containing polymers. It has been established that wet dechlorination of PVC in NaOH/ethylene glycol solution is more effective than dry dechlorination. In this study, the wet process was used, and the chemical modification of PVC by nucleophilic substitution was considered for upgrading waste PVC. Chlorine was substituted in solution by several nucleophilic reagents, thus changing the properties of PVC. The reaction of PVC in Na2S/ethylene glycol solution at 170°C resulted in the formation of a mixture comprising 32% elimination and 26% substitution products. The scanning electron microscopy/energy dispersive X-ray spectroscopy mappings and elementary analysis of PVC indicated that this chlorine-substitution process led to cross-linking by sulfur.     

Debromination of flame-retarded TV housing plastic waste

The thermal stability and degradation kinetics of TV housing plastic and brominated flame retardants were studied by means of thermogravimetry. The effects of the treatment temperature on the removal rate of Br were investigated using a tube furnace reactor under isothermal and vacuum conditions. The results showed that the weight loss of TV housing plastic was divided into two stages: the thermal degradation of brominated flame retardants mainly occurred at 290°–350°C, and the degradation of the high-impact polystyrene resin mainly occurred at 350°–455°C. Nearly 90% of Br can be removed from TV housing plastic when the treatment temperature exceeds 280°C.     

Processing plastics from ASR/ESR waste: separation of poly vinyl chloride (PVC) by froth flotation after microwave-assisted surface modification

The feasibility of the selective surface hydrophilization of poly vinyl chloride (PVC) using microwave treatment to facilitate the separation of PVC via froth flotation from automobile shredder residue (ASR) and electronic waste shredder residue (ESR) was evaluated. In the presence of powder-activated carbon (PAC), 60-s microwave treatment selectively enhanced the hydrophilicity of the PVC surface (i.e., the PVC contact angle decreased from 86.8° to 69.9°). The scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) results are consistent with increased hydrophilic functional groups (i.e., ether, hydroxyl, and carboxyl), amounting to significant changes in the morphology and roughness of the PVC surface after treatment. After only 60 s of microwave treatment, 20 % of the PVC was separated in virgin and ASR/ESR plastics with 33 and 29 % purity, respectively, as settled fractions by froth flotation at a 150 rpm mixing speed. The microwave treatment with the addition of PAC had a synergetic effect with the froth flotation, which brought about 100 and 90 % selective separation of PVC from the other virgin and ASR/ESR plastics, with 91 and 82 % purity. The use of the combined froth flotation and microwave treatments is an effective technology for separating PVC from hazardous waste plastics.     

A study on torrefaction characteristics of waste sawdust in an auger type pyrolyzer

Torrefaction is thermo-chemical process which can improve solid fuel quality as well as grindability. In previous studies, torrefaction has been studied mainly for removal of moisture and for improving grindability. In this experiment, the characteristics of torrefied waste sawdust were studied especially for its energy yield. Hence, torrefaction was performed on varying reaction temperatures (200, 220, 240, 260, 280, 300 °C) and solid residence time (10, 30, 60 min). The results indicated that the yield of torrefaction decreases with increasing temperature and residence time. It was found that above 280 °C, the yield got remarkably decreased. The lowest yield was obtained at the residence time of 60 min. It was also noticed that the HHV of torrefied samples increases with increasing temperature. The highest HHV was found to be 26.09 MJ/kg which was obtained at 60 min and 300 °C. However, the highest energy yield was obtained to be 104.17 % which was noticed at 30 min and 260 °C.     

Mechanical treatment of automobile shredder residue for its application as a fuel

Enforcement of the Automobile Recycling Law in Japan requires utilization of automobile shredder residue (ASR). However, the high contents of copper (∼5%) and chlorine (∼1%) in ASR stand in the way of practical application. We studied methods for the removal of copper and chlorine from ASR so that it could be utilized as a fuel. By compression of the ASR for solidification with an extruder, the polyvinylchloride (PVC) that covered electrical cables was softened and stripped from the copper wire. The solidified ASR was comminuted with cutter mills and classified by dry density separation. The copper content of the obtained light products was 0.2%–0.5%. Furthermore, we studied the possibility of dechlorination of the ASR by mechanochemical (MC) activation. The light product of the ASR was milled with CaO or CaCO₃. The chlorine content decreased to about one-tenth of the original value after MC activation over 8 h. Therefore, the combined processing of softening–stripping and comminution liberated the PVC-covered cables and decreased the copper content of the ASR. In addition, dechlorination of the ASR was also possible by MC activation with the addition of calcium compounds.