Chemical Recycling of Waste Plastics via Hydrothermal Processing

Utilizing a simple, cost effective, feasible and efficient recycling process for waste plastics, which are largely produced from non-renewable sources, is strategically important for a sustainable environment and economy. In Europe, landfilling is still the major waste management method; therefore new routes for recycling are being researched to increase the recycling rates. In this research, hydrothermal processing was used for recycling of waste carbon fibre reinforced plastics (CFRP) and printed circuit boards (PCB) in a batch reactor were investigated. Also, the applicability of the hydrothermal process was tested on refuse derived fuel (RDF), as it is a good representative of municipal solid waste which is a complex waste mixture consisting of plastics, other biodegradable materials and inorganic materials. The ability of supercritical water to degrade the resins and plastics in the composite wastes was largely influenced by the presence of different additives and/or co-solvents. Water at supercritical conditions was able to remove 92.6% of the resin from the CFRP waste in the presence of KOH and 10 wt% H2O2. In the work with PCB, 94% of the resin removal was achieved with alkalis, at zero residence time. The carbon fibre was recovered by preserving 78 % of its tensile strength due to the loss in the mechanical properties as a result of oxidation on the carbon fibre surface. When mixtures of ethylene glycol and water were used as solvent, without any addition of a catalyst, 97.6 % resin removal was achieved at 400oC. The liquid obtained from hydrothermal processing of PCB mainly composed of phenol, and phenolic compounds, which are the precursors of the original thermosetting resin. The liquid effluent from the degradation of CFRP with water and ethylene glycol mixture became too complex for recovery and so was gasified under supercritical water conditions. In the presence of NaOH and ruthenium oxide as catalysts the produced fuel gas consisted of H2, CH4, CO2, CO and C2-4 hydrocarbon gases. The carbon fibres recovered using ethylene glycol co-solvent preserved its mechanical properties and used for the manufacture of new composite materials. The mechanical tests showed that the new composites with recovered carbon fibres had enhanced mechanical properties similar to those made from virgin carbon fibres. Finally RDF was subjected to hydrothermal gasification process to produce fuel gas. Up to 93% carbon gasification efficiency was achieved in the presence of 5 wt% RuO2/γ-Al2O3 catalyst, producing a fuel gas mostly consisting of H2, CH4, and CO2 with a heating value of 22.5 MJ/Nm3. The gross calorific value of the product gas increased to 32.4 MJ/Nm3 in the presence of NaOH, as a result of carbon dioxide fixation as sodium carbonate. Also, high yields of hydrogen were obtained in the presence of both the NaOH and ruthenium catalysts, as both promoted the water-gas shift reaction

Recovery of carbon fibres and production of high quality fuel gas from the chemical recycling of carbon fibre reinforced plastic wastes

A solvolysis process to depolymerize the resin fraction of carbon fibre reinforced plastic waste to recover carbon fibre, followed by hydrothermal gasification of the liquid residual product to produce fuel gas was investigated using batch reactors. The depolymerisation reactions were carried out in ethylene glycol and ethylene glycol/water mixtures at near-critical conditions of the two solvents. With ethylene glycol alone the highest resin removal of 92.1% was achieved at 400 °C. The addition of water to ethylene glycol led to higher resin removals compared to ethylene glycol alone. With an ethylene glycol/water ratio of 5, at 400 °C, resin removal was 97.6%, whereas it was 95.2% when this ratio was 3, at the same temperature. The mechanical properties of the recovered carbon fibre were tested and showed minimal difference in strength compared to the virgin carbon fibre. The product liquid, containing organic resin degradation products was then subjected to catalytic supercritical water gasification at 500 °C and 24 MPa in the presence of NaOH and Ru/AlO as catalysts, respectively. Up to 60 mol.% of H gas was produced with NaOH as catalyst, and 53.7 mol.% CH gas was produced in the presence of Ru/AlO

Supercritical water gasification of wet sludge from biological treatment of textile and leather industrial wastewater

WOS: 000461402600011Activated sludge produced from biological treatment of textile and leather industrial wastewater was processed using hydrothermal gasification in order to produce fuel gas with high calorific value. The gasification experiments were performed in a batch reactor and the effect of temperature (400, 450, 500 and 550 degrees C), additives (KOH and dolomite) and reaction time (0, 30 and 60 min) was investigated. The gas yield increased with the increasing temperature. Hydrogen and methane compositions in the gas was between 42 to 57 vol%, while CO2 was between 30 and 40 vol%. The calorific value of the sludge was determined as around 16 MJ/kg, while after gasification the calorific value of the gas fuel produced was found to be 24.7 MJ/kg (24.3 MJ/Nm(3)) after 30 min. reaction time in the presence of KOH. The addition of dolomite did not affect the gas yield however, addition of KOH promoted the water-gas shift reaction and boosted hydrogen yield in the product gas. Around 70 wt. % of the sludge was converted into either gas or liquid with hydrothermal treatment

Improvement in hydrogen production from hard-shell nut residues by catalytic hydrothermal gasification

WOS: 000347360800039The hydrothermal gasification of some hard-shell nut residues (hazelnut, walnut and almond shells) was performed in a batch type reactor at temperature and pressure ranges of 300-600 degrees C and 88-405 bar, respectively. The biomass samples were converted into gaseous product (hydrogen, carbon dioxide, methane, carbon monoxide and C-2-C-4 compounds), aqueous product (carboxylic acids, furfurals, phenols, aldehydes and ketones) and solid products after hydrothermal gasification. Hydrogen production was improved by using natural mineral catalysts (Trona, Dolomite and Borax). The activity of selected natural mineral catalysts in hydrothermal gasification can be ordered as being Trona [Na-3(CO3)(HCO3)center dot 2H(2)O] > Borax [Na2B4O7 center dot 10H(2)O] > Dolomite [CaMg(CO3)(2)]. The most effective catalyst was found to be Trona at 600 degrees C leading enhancement in hydrogen yields (mol H-2/kgC in biomass) for hazelnut, walnut and almond shells as 82.4%, 74.1% and 42.4%, respectively. (C) 2014 Elsevier B.V. All rights reserved.Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [106T748]; Ege University Science and Technology Centre-Technology Transfer Office (EBILTEM-TTO)Ege University [2008BIL017]We gratefully acknowledge the financial support provided by The Scientific and Technological Research Council of Turkey (TUBITAK) (Project No: 106T748) and Ege University Science and Technology Centre-Technology Transfer Office (EBILTEM-TTO) (Project No: 2008BIL017). We would like to thank Mr. Gursel Serin for the assistance during the experiments

Valorisation of vegetable market wastes to gas fuel via catalytic hydrothermal processing

Yildirir, Eyup/0000-0003-1292-1926WOS:000590677900005Residues of leek, cabbage and cauliflower from the market places as representatives of lignocellulosic biomass were processed via hydrothermal gasification to produce energy fuel. The experiments were carried out in a batch reactor at temperatures 300, 400, 500 and 600 degrees C and corresponding pressures varying in the range of 7.5-43 MPa. Natural mineral additives trona, dolomite and borax were used as homogenous catalysts to determine their effects on the gasification. More than 70 wt% of carbon in vegetable residue samples were detected in the gas phase after the hydrothermal gasification process at 600 degrees C. The addition of trona mineral further promoted the gasification reactions and as a result, less than 5 wt% carbon remained in the solid residue at the same temperature, degrading the biomass samples into gas and liquid products. The fuel gas with the highest calorific value was recorded to be 25.6 MJ/Nm(3), from the hydrothermal gasification of cabbage at 600 degrees C, when dolomite was used as the ho-mogeneous catalyst. The liquid products obtained in the aqueous phase were detected as organic acids, aldehydes, ketones, furfurals and phenols. The gas products were consisted of hydrogen, carbon dioxide, methane, and as minors; carbon monoxide and low molecular weight hydrocarbons (ethane, propane, etc.). Above 500 degrees C, all biomass samples yielded 50-55 vol% of CH4 and H-2 while the CO2 composition was around 40 vol% as the gas product. (C) 2020 Energy Institute. Published by Elsevier Ltd. All rights reserved.Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [106T748]; Ege University-EBILTEMEge University [2008BIL017]We sincerely appreciate and give thanks for the financial support of The Scientific and Technological Research Council of Turkey (TUBITAK) (Project No: 106T748) and Ege University-EBILTEM (Project No: 2008BIL017). We also thank Mr. G. Serin for his support in the pre-treatment of the biomasses and his help during the experimental study

Hydrogen and methane production from tomato processing plant waste by hydrothermal gasification

Hydrothermal gasification of tomato processing plant waste was examined in batch autoclaves at temperatures of 300-600 C and pressures of 20.0-42.5 MPa. The catalytic effects of KOH and K2CO3 at the aforementioned temperatures and pressures were also investigated. While increasing the pressure enhanced methane yield, alkali addition improved both hydrogen and methane yields. The highest yields for H2 and CH4 were recorded as 27.4 and 21.8 moles kg-1 C at 600 C and with KOH. In addition, carbon gasification efficiency (CGE) obtained was up to 86% while carbon liquefaction efficiency (CLE) was reduced to 3.5% with KOH at 600 C and 20 MPa. A product gas with a calorific value of 24.9 MJ/Nm3 was obtained during hydrothermal gasification at 500 C and 42.5 MPa, in the presence of KOH.Ege UniversityWe gratefully appreciate the financial support of Ege University. We thank Mr. G. Serin for his support in the pre-treatment step of the bio-masses and the help during the experimental studies and analysis