废聚苯乙烯裂解回收苯乙烯研究进展

对近年来国内外废聚苯乙(烯PS)的化学解聚制备苯乙烯单体的方法与工艺研究进展进行了综述,指出催化裂解是废PS裂解回收苯乙烯单体的有效途径,并对碱性中孔分子筛催化PS裂解进行了分析与展望,认为碱性中孔分子筛有望成为废PS裂解回收苯乙烯单体的有效催化剂,建议今后应在改善中孔分子筛催化剂的稳定性及酸碱性方面做进一步研究。     

Catalytic reduction of residual styrene monomer in polystyrene

Styrene monomer has a low taste and odor threshold, and its presence in the polystyrene used in food packaging applications must be as low as possible. Conventional devolatilization technology does not lower styrene contents to desired levels, so special costly devolatilization techniques have to be used. Attempts to employ scavengers for styrene to reduce residual monomer levels have been largely unsuccessful. This article evaluates the possibility that strong acids can be used to induce residual styrene to alkylate styrene units in polystyrene by Friedel–Crafts reactions. The results of studies evaluating this approach indicate its feasibility, but colored products are obtained when sulfonic acids are used and prohibitively high levels of acids must be used to be effective. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1786–1791, 2002     

废旧发泡聚苯乙烯的利用

本文叙述废旧发光聚苯乙烯的几种回收途径，介绍了废旧发泡聚苯乙烯回收用于粘合剂，涂饰剂，密封胶，水泥砖，增塑剂，苯乙烯单体，聚苯乙烯塑料，可发生聚苯乙烯珠粒，建筑除水涂料等的方法。     

Kinetics of styrene removal from polystyrene by thermal treatment in air

The influence of certain factors on the kinetics of styrene mass transfer from polystyrene in air at elevated temperature is investigated. It is established that this process can be simulated by a model including molecular diffusion of styrene to the surface of the solid material and evaporation from that surface. The effective coefficients of molecular diffusion at different temperatures and the evaporation coefficients under different hydrodynamic conditions are determined. The data obtained can be used for estimation of the monomer removal by thermal treatment of the polymer.     

Dehydrohalogenation during pyrolysis of brominated flame retardant containing high impact polystyrene (HIPS-Br) mixed with polyvinylchloride (PVC)

Dehydrohalogenation during pyrolysis of brominated flame retardant containing polystyrene (brominated high impact polystyrene (HIPS-Br)) mixed with polyvinylchloride (PVC) was carried out in a laboratory scale batch process. Thermal and catalytic degradation of HIPS-Br mixed with PVC on carbon composite of iron oxide (TR-00301) catalyst was investigated. The thermal degradation of waste plastics (HIPS-Br/PVC) yielded liquid products with 55,000 ppm bromine and 4300 ppm chlorine content in oil. Catalytic degradation (4 g; TR-00301) of HIPS-Br/PVC waste plastics at 430 °C produced halogen-free clean oil, which can be used as a fuel oil or chemical feedstock. The main liquid products during catalytic degradation were benzene, toluene, styrene, ethyl benzene, α-methyl styrene, butyl benzene, 1,2-dimethyl benzene etc. The average carbon number of the liquid products produced during catalytic degradation (9.3) of waste plastics was less than that of the thermal degradation (10.4) and the density of liquid products was found to be lower during the catalytic degradation than the thermal degradation. The possibility of a single step catalytic process for the conversion of halogenated waste plastics into fuel oil with the simultaneous removal of chlorine and bromine content from the oil was demonstrated.     

Compatibilization of a polystyrene-polyethylene blend through reactive processing in a twin screw extruder

Direct grafting of polystyrene onto polyethylene has been carried out in a twin screw extruder with an organic peroxide and a crosslinking co-agent. The reaction extruded blends exhibited enhancement in impact properties at an optimum level of peroxide and co-agent. Further improvement was achieved by introducing styrene monomer into the system during reactive extrusion. The structure and morphology of the blends were studied using differential scanning calorimetry, scanning electron microscopy, infrared spectroscopy, and size exclusion chromatography.     

De-Brominating Flame-Retardant Polystyrene by Utilizing Basic Oxides in Chemical Recycling

Chemical recycling is a method to close the recycling loop for polymers. This is particularly applicable for polystyrene (PS), where the monomer styrene is directly formed by depolymerization and subsequently utilized for the production of new PS. However, some waste sources contain critical additives as legacies, such as brominated flame retardants. There is a profound need to remove these substances from the material, as current thresholds do not allow such additives above certain limits in new products. In this work we present the beneficial use of basic oxides during the thermal depolymerization of a mixture of PS and 1,2,5,6,9,10-hexabromocyclododecane. It was demonstrated that especially barium oxide and calcium oxide allowed the reduction of bromine up to 96 % in the crude styrene oil.     

Conversion of waste polystyrene through catalytic degradation into valuable products

Waste expanded polystyrene (EPS) represents a source of valuable chemical products like styrene and other aromatics. The catalytic degradation was carried out in a batch reactor with a mixture of polystyrene (PS) and catalyst at 450 °C for 30 min in case of Mg and at 400 °C for 2 h both for MgO and MgCO₃ catalysts. At optimum degradation conditions, EPS was degraded into 82.20±3.80 wt%, 91.60±0.20 wt% and 81.80±0.53 wt% liquid with Mg, MgO and MgCO₃ catalysts, respectively. The liquid products obtained were separated into different fractions by fractional distillation. The liquid fractions obtained with three catalysts were compared, and characterized using GC-MS. Maximum conversion of EPS into styrene monomer (66.6 wt%) was achieved with Mg catalyst, and an increase in selectivity of compounds was also observed. The major fraction at 145 °C showed the properties of styrene monomer. The results showed that among the catalysts used, Mg was found to be the most effective catalyst for selective conversion into styrene monomer as value added product.     

乳液法聚苯乙烯纳米微球的制备

采用十二烷基硫酸钠为乳化剂、过硫酸盐为引发剂、苯乙烯为单体,在低水油比的条件下,采用乳液聚合方法合成了聚苯乙烯纳米微球,探讨了乳化剂用量、乳化时间、反应温度、引发剂用量和反应时间对单体转化率及产物分子量的影响.结果表明:在低水油比条件下,反应参数对苯乙烯的转化率和聚苯乙烯的分子量具有一定的影响.在最优条件下苯乙烯的转化率达到98%、聚苯乙烯的分子量达到32万.激光粒度分布测试结果显示,所得产物为单分散纳米微球.     

Co-coking of coal with pitches and waste plastics

Liquid-phase co-thermolysis of waste plastics (e.g. polystyrene, polycarbonate, polyurethane, polyvinyl chloride, tire rubber, unsaturated polyester resin, melamine-phenol formaldehyde resin, polyethylene, polyamide, polyethylene terephthalate, phenol formaldehyde resin) with coal-tar pitch at temperatures up to 400°C yielded gases, pyrolysis oils, and high-melting pitches (reaction pitches). Thermogravimetric analysis of these pitches showed that they were thermally stable up to the plastic temperature range of coals. Hence, the reaction pitches could be used as reactive additives for weak-coking coals to improve their coking properties.     

Production of micron-size monodisperse polymer particles by seeded polymerization utilizing dynamic swelling method with cooling process

Monodisperse polystyrene particles (6.6 μm diameter) were produced by seeded polymerization utilizing the dynamic swelling method with cooling process as follows. Monodisperse polystyrene seed particles (1.8 μm diameter) were dispersed in ethanol/water (3/4 w/w) medium containing styrene monomer, benzoyl peroxide as initiator and poly(vinyl alcohol) as stabilizer at 65d?C. By lowering the temperature to ?5d?C at a speed of ?1d?C/min the polystyrene seed particles were swollen from 1.8 to 7.7 μm by the absorption of styrene monomer, keeping the high monodispersity. An appropriate amount of water was then added to the dispersion at ?5d?C to depress the redissolution of styrene from the swollen particles into the medium. By elevating the temperature the seeded polymerization was carried out at 70d?C. The production of submicron-size polystyrene new particles as a by-product was depressed by the addition of NaNO₂ to the medium.     

Continuous production of solid polystyrene in back‐mixed and linear‐flow reactors

A mathematical model has been developed to predict the steady state performance of a continuous bulk styrene polymerization process with catalytic initiation for solid polystyrene. The polymerization section contains one boiling CSTR, followed by multiple linear‐flow reactors. The devolatilization section consists of two polymer pre‐heaters and two high‐solids flashes. The polymer moment equations were solved simultaneously with the reactor modeling equations. The non‐linear algebraic equations were solved by a Newton‐Raphson iteration technique to give the steady‐state styrene monomer weight fraction in a CSTR. The coupled, non‐linear ordinary differential equations were numerically integrated using a single‐step, 4th‐order Runge‐Kutta technique, followed by a multi‐step Adams‐Moulton technique. The resulting computer simulation model is capable of evaluating how the production rate and product quality are affected by feed composition, temperature, initiator type, initiator concentration, and residence time. Several case studies were given for commercially important crystal‐clear and impact‐resistant resins. A binary initiation system gives a good balance of monomer conversion, polymer molecular weights, and rubber grafting compared to a single initiation system. The styrene dimer/trimer occur in low concentrations but can be substantially reduced with a low temperature initiator. The ideal mean residence time is approximately one minute or less in a shell‐and‐tube devolatilization pre‐heater. Low flash chamber vacuum is more effective than high polystyrene melt temperature to reduce the volatile content of the final product. The water injected to the low volatile melt shows promising improvement in the second‐stage polystyrene devolatilization.     

Effect of solvents on radiation‐induced grafting of styrene onto fluorinated polymer films

The effect of solvents on radiation‐induced grafting of styrene onto commercial fluorinated polymer films such as poly(tetrafluoroethylene) (PTFE), poly(tetrafluoroethylene‐co‐hexafluoropropylene) (FEP) and poly(tetrafluoroethylene‐co‐perfluorovinyl ether) (PFA) was investigated by a simultaneous irradiation technique. Three solvents, ie methanol, benzene and dichloromethane, were used to dilute styrene under various irradiation doses, dose rates and monomer concentrations. The effect of addition of mineral and organic acids on the degree of grafting in the presence of the three solvents was also studied. The degree of grafting was found to be strongly dependent upon the type of solvent and composition of the monomer/solvent mixture. Dilution of styrene with dichloromethane in various grafting conditions was found to enhance dramatically the degree of grafting compared with other solvents, and the maximum degree of grafting was achieved at a monomer/solvent mixture having a composition of 60:40 (v/v). The formation of polystyrene grafts in the three fluorinated films was verified using FTIR spectrometry. © 2001 Society of Chemical Industry     

Emissions from the combustion of polystyrene,styrene and ethylbenzene under diverse conditions

This experimental study contrasts the products of incomplete combustion (PIC) of polystyrene, a widespread solid waste, with those from the combustion of its predominant pyrolyzate, styrene. The study also included ethylbenzene, as it has been reported to convert to styrene extensively and extremely fast in combustion conditions. Emissions were compared from: (i) steady-state combustion of vaporized ethylbenzene in premixed flames, (ii) steady-state combustion of polystyrene powders in a drop-tube furnace, (iii) batch combustion of fixed beds of polystyrene in a muffle furnace, and (iv) batch combustion of pools of liquid styrene in a muffle furnace. PICs, sampled in post-combustion zones, included unburned hydrocarbons, with emphasis to polycyclic aromatic hydrocarbons (PAH), particulates, CO₂ and CO. Yields of major PIC were compared to underscore the differences in the underlying physics of premixed and non-premixed (diffusion) flames. Combustion of polystyrene and styrene in diffusion flames generated soot at any nominal global (bulk) equivalence ratio, no matter how fuel-rich or fuel-lean. On the other hand, combustion of ethylbenzene in premixed flames did not generate any soot up to its soot onset limit, which typically occurs well-within the fuel-rich domain. However, conditions that were not conducive to the formation of soot did not preclude the presence of other PIC, such as PAH.     

Decomposition characteristics of residue from the pyrolysis of polystyrene waste in a fluidized-bed reactor

Effective treatment of residue generated from the pyrolysis of polystyrene wastes has been one of the important factors in the recovery of styrene monomer and oil from polystyrene wastes. Depending on the experimental conditions, the yields of oil and styrene monomer are considerably decreased in the presence of residue. Here the residue was decomposed effectively in a catalytic fluidized-bed reactor. Nitrogen and silica sand were used as a fluidizing gas and a bed material, respectively. Effects of catalyst, temperature and gas velocity on the characteristics of decomposition of the residue were examined. It was found that the residue could be decomposed to oil or chemicals effectively by means of a catalytic fluidized-bed reacting system. The yields of oil and individual chemicals and the composition of the products were dependent upon the operating variables such as reaction temperature, catalyst and gas velocity.     

Radiation-induced grafting of sulfonates on polyethylene

Indirect methods for introducing sulfonate groups into polyethylene, using the preirradiation technique, were studied. One of the methods involved graft polymerization of 2,3-epoxypropyl acrylate into polyethylene followed by sulfonation of the epoxy ring with bisulfite. The hydroxy sulfonate thus obtained was unstable in an acid or base environment and hydrolyzed at the esteric bond. The second method involved hydrophylization of the polyethylene by forming a pregraft of polyacrylic acid or polyvinyl alcohol, followed by preirradiation grafting with sodium styrene sulfonate or, less successfully, with sodium vinyl sulfonate. The sulfonates thus obtained were resistant to acids and bases. The acid capacity, water absorption, and water permeability of the grafted films were determined.     

Process of grafting styrene onto LLDPE by swelling and suspension copolymerization

A technology of swelling and suspension copolymerization was conducted to graft styrene onto linear low‐density polyethylene (LLDPE). The graft mechanism of styrene with LLDPE had been described by ¹H NMR and IR. The mean particle diameter and size distribution of the products with different proportions of LLDPE to styrene monomer were calculated. The morphology and thermal behavior of copolymers were characterized by scanning electron microscopy and differential scanning calorimetry. The glass transition temperature of copolymers increased with the addition of LLDPE, which proved the existence of the polyethylene‐g‐polystyrene copolymer. The grafting efficiency and granulation rate of suspension copolymerization were investigated. It was found that the grafting efficiency increased and the granulation rate decreased with the addition of LLDPE. POLYM. ENG. SCI., 50:1713–1720, 2010. © 2010 Society of Plastics Engineers     

Grafting of styrene onto polyethylene in near critical media

In this work, near critical n‐heptane is used as reaction medium for the copolymerization of polyethylene with styrene monomer, using alkylation reaction with different amounts of aluminum chloride (AlCl₃) as catalyst. In this way, polyethylene chains will be more available to react with the catalyst. The reaction effect on pure reactants, as well as, the catalyst activity was previously investigated. The reaction occurrence was corroborated by analyzing the reaction products before and after careful polystyrene extraction with tetrahydrofuran. The reaction products were characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance, scanning electron microscopy, transmission electron microscopy, differential scanning calorimetry, and size exclusion chromatography. The possible architecture for the copolymer molecule was proposed from the molecular characterization results. On the other hand, the polystyrene grafting modifies final properties of polyethylene, increasing the oxygen barrier properties without deteriorating significantly the mechanical properties of the films. In this sense this reaction seems to be a promising route to modify PE films to increase the barrier properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Unsaturated Polyester Resins Obtained from Glycolysis Products of Waste PET

Abstract

Waste polyethylene terephthalate (PET) flakes were depolymerized by using ethylene glycol (EG), propylene glycol (PG), diethylene glycol (DEG), and triethylene glycol (TEG) in the presence of zinc acetate as catalyst. All glycolysis products were reacted with maleic anhydride and mixed with styrene monomer to get unsaturated polyester (UP) resins. Molecular weights of all synthesized UP resins were determined by end-group analysis. The curing characteristics such as gel time and maximum curing temperatures, and mechanical properties such as hardness, tensile strength, and elastic module of these resins were investigated. The waste PET resins were compared with the reference resins prepared with the same glycols and the properties of the resins were found to be compatible with the properties of the reference resins.     

Preparation of mesoporous MCM-41 from natural sepiolite and its catalytic activity of cracking waste polystyrene plastics

Mesoporous MCM-41 was prepared by leaching of sepiolite and sequent hydrothermal synthesis in NaOH solution with hexadecyltrimethylammonium bromide as template. Small-angle X-ray diffraction patterns, Scanning electron microscopy, transmission electron microscopy and Brunauer–Emmett–Teller were performed to characterize the resulting compounds. The results showed that the crystallinity and pore size of MCM-41 increased with increase of crystallization time, ratios of surfactant to SiO₂ and decrease of Mg content. The experimental results of catalytic cracking of polystyrene waste showed that the MCM-41 with MgO from natural sepiolite had high catalytic activity and good selectivity to monomer styrene for the catalytic cracking of polystyrene when the ratio of waste plastics to MCM-41 was 200. The side reactions yielded ethylbenzene, isopropylbenzene, isopropenylbenzene and secondary cross-linking were suppressed by basic species MgO in MCM-41.