Processing of flexible plastic packaging waste into pyrolysis oil and multi-walled carbon nanotubes for electrocatalytic oxygen reduction.

Flexible plastic packaging waste causes serious environmental issues due to challenges in recycling. This study investigated the conversion of flexible plastic packaging waste with 11.8 and 27.5 wt.% polyethylene terephthalate (PET) (denoted as PET-12 and PET-28, respectively) into oil and multi-walled carbon nanotubes (MWCNTs). The mixtures were initially pyrolyzed and the produced volatiles were processed over 9.0 wt.% Fe2O3 supported on ZSM-5 (400 °C) to remove oxygenated hydrocarbons (catalytic cracking of terephthalic and benzoic acids) that deteriorate oil quality. The contents of oxygenated hydrocarbons were decreased in oil from 4.6 and 9.4 wt.% per mass of PET-12 and PET-28, respectively, to undetectable levels. After catalytic cracking, the oil samples had similar contents of gasoline, diesel and heavy oil/wax fractions. The non-condensable gas was converted into MWCNTs over 0.9 wt.% Ni supported on CaCO3 (700 °C). The type of plastic packaging influenced the yields (2.4 and 1.5 wt.% per mass of PET-12 and PET-28, respectively) and the properties of MWCNTs due to the differences in gas composition. Regarding the electrocatalytic application, both MWCNTs from PET-12 and PET-28 outperformed commercial MWCNTs and Pt-based electrodes during oxygen evolution reaction, suggesting that MWCNTs from flexible plastic packaging can potentially replace conventional electrode materials.

Environmental impact assessment of converting flexible packaging plastic waste to pyrolysis oil and multi-walled carbon nanotubes.

A solution to low recycling rates of plastic waste is the conversion into multi-walled carbon nanotubes (MWCNTs) that have high value and can create additional revenue for plant operators. The purpose of this study was to perform a life cycle assessment (LCA) of an integrated system that involves flexible packaging plastic waste (FPPW) pyrolysis, oil upgrading, and MWCNTs production. The objectives were to determine the environmental impact of MWCNTs synthesis from non-condensable pyrolysis gases, and to assess the environmental impact of MWCNTs synthesis from different plastic fractions. Integrating MWCNTs synthesis to the plastic pyrolysis process provides various environmental benefits including, reduction of contribution towards climate change, fossil depletion, human toxicity (cancer), and ionizing radiation potentials. Sensitivity analysis of MWCNTs yields provided the range of impacts on the environment and a critical yield of >2% for most impact categories was determined. Comparison of different plastic fractions indicated that using low PET content feedstock had lesser impact on the environment, and demonstrated comparable performance to mixed virgin plastics for most impact categories. The results highlighted the versatility of the integrated pyrolysis process for treating diverse plastic waste fractions with negligible effects from the impurities present in the actual FPPW during thermal processing.

High-quality fuel from food waste - investigation of a stepwise process from the perspective of technology development.

A stepwise process (SP) was developed for sustainable energy production from food waste (FW). The process comprised of hydrothermal treatment followed by oil upgrading. Synthetic food waste was primarily used as feedstock in the hydrothermal reactor under subcritical water conditions. The produced hydrochars were analyzed for calorific value (17.0-33.7 MJ/kg) and elemental composition indicating high-quality fuel comparable to coal. Hydrothermal carbonization (e.g. 180°C) would be efficient for oil recovery (>90%) from FW, as compared to hydrothermal liquefaction (320°C) whereby lipid degradation may take place. The recovered oil was upgraded to biodiesel in a catalytic refinery process. Selected biodiesels, that is, B3 and B4 were characterized for density (872.7 and 895.5 kg/m3), kinematic viscosity (3.115 and 8.243 cSt), flash and pour point (30°C and >126°C), micro carbon (0.03% and 0.04%), sulfur (both <0.0016%), and calorific value (38,917 and 39,584 J/g), suggesting similar quality to commercial biodiesel. Fatty acid methyl ethers content was further analyzed to assess the influence of hydrothermal treatment in biodiesel quality, indicating the limited impacts. Overall, the SP provides a promising alternative for sustainable energy recovery through high-quality biofuel and hydrochar production.

Determination of solubility parameters of ionic liquids and ionic liquid/solvent mixtures from intrinsic viscosity.

The total and partial solubility parameters (dispersion, polar and hydrogen-bonding solubility parameters) of ten ionic liquids were determined. Intrinsic viscosity approaches were used that encompassed a one-dimensional method (1D-Method), and two different three-dimensional methods (3D-Method1 and 3D-Method2). The effect of solvent type, the dimethylacetamide (DMA) fraction in the ionic liquid, and dissolution temperature on solubility parameters were also investigated. For all types of effect, both the 1D-Method and 3D-Method2 present the same trend in the total solubility parameter. The partial solubility parameters are influenced by the cation and anion of the ionic liquid. Considering the effect on partial solubility parameters of the solvent type in the ionic liquid, it was observed that in both 3D methods, the dispersion and polar parameters of a 1-ethyl-3-methylimidazolium acetate/solvent (60:40 vol %) mixture tend to increase as the total solubility parameter of the solvent increases.

Effects of solubility properties of solvents and biomass on biomass pretreatment.

Hildebrand solubility parameters of biomasses and pretreatment solvents were examined by a method of intrinsic viscosity. This is to be used as basic information in selecting a suitable solvent for biomass pretreatment processes. The effects of mixing1-ethyl-3-methylimidazolium acetate (EMIM-AC) and different solvents, lignin content in a pretreatment solvent, and biomass type on the Hildebrand solubility parameter and thermodynamic properties were carried out and calculated in this work. The Hildebrand solubility parameters of the mixtures are according to those of organic solvents: δH[EMIM-AC/DMA]=25.07<δH[EMIM-AC/DMF]=25.48<δH[EMIM-AC/DMSO]=26.10<δH[EMIM-AC/Ethanolamine]=26.95. The Hildebrand solubility parameters of biomass compositions (microcrystalline cellulose, xylan and alkali lignin) and biomasses (cassava pulp residue and rice straw) vary in the ranges of 25.14-26.13. The increases of lignin content in the pretreatment solvents lead to the Hildebrand solubility parameter becoming closer to that of lignin.

Recyclability of an ionic liquid for biomass pretreatment.

This study investigated the possibility of reusing an ionic liquid for the pretreatment of biomass. The effects of lignin and water content in a pretreatment solvent on pretreatment products were examined, along with the recyclability of an ionic liquid for pretreatment. It was discovered that the presence of lignin and water within a pretreatment solvent resulted in a far less effective pretreatment process. 1-Ethyl-3-methylimidazolium acetate/ethanolamine (60/40 vol%) presents more promising properties than EMIM-AC, providing a small decrease in sugar conversion and also a small increase of lignin deposition with an increasing lignin amount in the pretreatment solvent. Deteriorations of the ionic liquid were observed from considerably low sugar conversions and lignin extraction after using the 5th and 7th batch, respectively. Furthermore, the changes of ionic liquid properties and lignin accumulation in ionic liquid were determined by analyzing their thermal decomposition behavior (TGA) and chemical functional groups (FTIR and (1)H NMR).

Influence of organic solvent on the separation of an ionic liquid from a lignin-ionic liquid mixture.

Sixteen solvents added in lignin-ionic liquid mixture provide four types of solubility characteristics. The distinct characteristics can be classified by considering solubility parameters including ET Scale, Kamlet-Taft parameters and solubility parameters. Group 1 solvent shows promising solvents for lignin-ionic liquid separation, contributing full dissolution of ionic liquid with lignin precipitation. Isopropanol, the most potential solvent has solubility properties as following normalized molar electronic transition energies (ET(N))=0.57, hydrogen-bond acidity (α)=0.76 and Hildebrand solubility parameter (δT)=23.58. This study examines potential solvents for ionic recovery, provides simple method of separation and leads to the feasibility of using ionic liquids in industrial applications.

Improvement of biomass properties by pretreatment with ionic liquids for bioconversion process.

Cassava pulp residue and rice straw were used as a precursor for pretreatment with ionic liquids to study the effects of pretreatment conditions on product yield and properties. Cassava pulp residue is a potential biomass in the bioconversion process due to it requiring mild pretreatment conditions while providing a high sugar conversion. The maximum sugar conversion and lignin extraction are attained from pretreatment of biomasses with particle size of <38 µm and ionic liquid of 1-Ethyl-3-methylimidazolium acetate at 120°C for 24h. The effectiveness of ionic liquid for biomass pretreatment process follows the sequence: 1-Ethyl-3-methylimidazolium acetate>1-Ethyl-3-methylimidazolium diethyl phosphate>1,3-Dimethylimidazolium methyl sulfate. The increase of pretreatment temperature from 25 to 120°C and decrease of biomass particle size renders higher sugar conversion, lignin extraction and lower crystallinity index. However, pretreatment at temperatures higher than 120°C shows a sharp decline of regenerated biomass yield, sugar conversion and lignin extraction and giving higher crystallinity index at pretreatment temperature of 180°C.

Effects of gasifying conditions and bed materials on fluidized bed steam gasification of wood biomass.

The effect of steam gasification conditions on products properties was investigated in a bubbling fluidized bed reactor, using larch wood as the starting material. For bed material effect, calcined limestone and calcined waste concrete gave high content of H(2) and CO(2), while silica sand provided the high content of CO. At 650 degrees C, calcined limestone proved to be most effective for tar adsorption and showed high ability to adsorb CO(2) in bed. At 750 degrees C it could not capture CO(2) but still gave the highest cold gas efficiency (% LHV) of 79.61%. Steam gasification gave higher amount of gas product and higher H(2)/CO ratio than those obtained with N(2) pyrolysis. The combined use of calcined limestone and calcined waste concrete with equal proportion contributed relatively the same gas composition, gas yield and cold gas efficiency as those of calcined limestone, but showed less attrition, sintering, and agglomeration propensities similar to the use of calcined waste concrete alone.