Depolymerization of polystyrene at reduced pressure through a microwave assisted pyrolysis

Large amounts of styrene and other important aromatic hydrocarbons were obtained employing microwave assisted pyrolysis for the depolymerization of polystyrene in the presence of carbon as an absorber. Working at a reduced pressure the yield of liquid was increased (higher than 75%) with respect to those obtained at ambient pressure. This liquid was clear and showed a low viscosity and density. On the contrary a dark brown liquid was formed when pyrolysis was carried out in a stream of nitrogen, but the yield was 94.3 wt%. Using a fractionating system and a residual pressure of 21.3 kPa the maximum concentration of styrene in the liquid was reached (71.9 wt%) corresponding to the maximum amount of styrene recovered from the starting PS (60.6 wt%). The substitution of carbon with silicon carbide as MW absorber, gave almost the same amount of liquid but the rate of pyrolysis was strongly reduced. Composition of liquids was affected by residence time into the reactor and some different compounds might be obtained by reaction among intermediates formed in the course of the process. Reverse polymerization of PS through microwave assisted pyrolysis may be a way to solve some environmental problems caused by waste PS. Large amount of valuable chemicals such as styrene, α-methylstyrene and toluene was collected while gas and char, formed in low amount, may be used as fuel

A friendly management of waste/contaminated polymeric materials from differentiated waste collection through microwave pyrolysis

Waste/contaminated polymeric materials are present in a solid municipal waste, and in larger amount in a differentiated waste collection. These polymers can’t be easily disposed through mechanical processes. They still contain a large variety of compounds having different chemical and physical properties, thus they can’t be blended together. The conversion of these waste materials into a gas, a liquid and a solid, through a microwave assisted pyrolysis has been reviewed. The solid may be employed as filler to obtain composites or a solid fuel while the liquid is, usually, the more interesting product, as it may be a source of chemicals or liquid fuel. A study about upgrading of this liquid to a gasoline for automotive engine is also reported. The gas may be used as liquefied petroleum gas or converted into energy. Following a pyrolyis process, a complete recycle of waste polymeric materials may be realized. All the products may be reused, some items as the source of monomers for new polymerizations, as raw materials for new synthesis, or to produce energy: thus realizing the last step of a circular economy

Bio-oil from pyrolysis of wood pellets using a microwave multimode oven and different microwave absorbers

Wood pellets were pyrolyzed using a microwave oven and different microwave power, apparatus set-up and microwave absorbers (none, Fe, and carbon). Pyrolysis was realized in a short time in the presence of Fe or carbon while it was incomplete if the absorber was not present. Furthermore when the absorber was present the shape of the pellets remained unaltered while if the absorber was not employed pellets were disaggregated. Three fractions were collected from each pyrolysis: a gas, a liquid also called bio-oil and a solid called bio-char. The bio-oil contained two phases and they were quantitatively characterized through a GC/MS-FID procedure using an internal standard according to a previously reported method. HPLC/MS, FTIR and 1H NMR spectroscopy were also employed for characterization of these liquids. Cellulose pyrolysis products were present in the upper phase such as water, acetic acid, furans (such as furfural), carbohydrates and their derivatives. Compounds from pyrolysis of lignin such as phenols and veratric acid were present in the bottom phase. The microwave assisted pyrolysis showed the possibility to efficiently convert wood pellets in different products. The main economical important components may be separated and used as chemicals, natural drugs or pesticides, while the remaining components, the solid and the gas may be used for energy production (solid and bio-oil). Solid may be also used for carbon sequestration

A simple procedure for chromatographic analysis of bio-oils from pyrolysis

A simple procedure was suggested for the chromatographic analyses of bio-oils from pyrolysis of various feedstock employing different technologies. An acetonitrile solution of each bio-oil was prepared without any extraction or other sample pretreatments. Preliminary thin layer chromatography showed a large number of compounds having a broad range of retention factors (Rfs) among 0–1. Products having a retention factor over 0.9 were mainly detected by GC while some other compounds were only identified by HPLC. GC/MS-FID analysis was used to identify and quantify compounds using peak areas and relative response factors (RRFs). A new equation was proposed to estimate RRFs of compounds identified via their MS spectra when experimental RRFs were not readily available. The novel procedure was employed to characterize bio-oils from pyrolysis of wood of different source or obtained using different pyrolysis procedure. Using this RRF method guaiacol, furfural, butan-2-one, levoglucosan, acetic acid and many other compounds were quantified in bio-oil samples. Different amount of them were found as a function of the type of wood, and pyrolysis conditions adopted. For instance levoglucosan was the main compound using carbon as MW absorber however acetic acid was prevalent when a MW absorber was not employed and both of them were absent in bio-oils from classical heating. The HPLC/MS of bio-oils showed cyclohexancarboxylic acid, 1,2,4-trimethoxybenzene and 2,6-dimethylphenol among the main products present in all bio-oils. On the contrary 4-hydroxyacetophenone and (3,4,5-trimethoxy) acetophenone were present in bio-oil from pyrolysis of wood using MW oven and 2,5-furandiylmethanol when a MW oven without any absorber was employed. Cyclohexanone was present in bio-oils obtained with a thermal heating or a MW oven without any absorber