• Energy Research

Abstract The global presence of plastic debris has become an indisputable environmental issue. While it is useful to recycle used plastic materials, contaminated plastics require a series of pretreatments prior to the process. Here, we offer a viable thermochemical conversion (pyrolysis) platform to directly valorize fishing net waste (FNW). Prior to the pyrolysis of FNW that was collected at a Korean seaport, its chemical composition (polyethylene) was examined using thermogravimetric analysis, ultimate analysis, and Fourier-transform infrared spectroscopy measurements. Pyrolysis of FNW was conducted to produce value-added syngas and C1-2 hydrocarbons (HCs) in both CO2 and N2 environments with a variety of pyrolysis setups. The pyrolysis temperature significantly contributed to the thermal cracking of long-chain liquid HCs into H2 and C1-2 HCs under the N2 and CO2 conditions. In the presence of cobalt-based catalysts, an additional improvement of the reaction kinetics for producing H2 and C1-2 HCs was shown in the N2 environment. However, the synergistic effectiveness of Co-based catalysts and CO2 resulted in CO formation, because CO2 provided additional C and O sources over the Co-based catalysts. Thus, it allowed control of the H2/CO ratio in the CO2 and N2 atmospheres. The compositional matrix of the liquid HCs after pyrolysis also confirmed that CO2 controlled their aromaticity. Thus, the CO2-cofeeding pyrolysis of FNW can be considered a viable platform for the direct treatment of plastic wastes by harvesting energy as a form of syngas.

In this study, wasted mask is chosen as a pyrolysis feedstock whose generation has incredibly increased these days due to COVID-19. We suggest a way to produce value-added chemicals (e.g., aromatic compounds) from the mask with high amounts through catalytic fast pyrolysis (CFP). To this end, the effects of zeolite catalyst properties on the upgradation efficiency of pyrolytic products produced from pyrolysis of wasted mask were investigated. The compositions and yields of pyrolytic gases and oils were characterized as functions of pyrolysis temperature and the type of zeolite catalyst (HBeta, HY, and HZSM-5), including the mesoporous catalyst of Al-MCM-41. The mask was pyrolyzed in a fixed bed reactor, and the pyrolysis gases evolved in the reactor was routed to a secondary reactor inside which the zeolite catalyst was loaded. It was chosen 550 °C as the CFP temperature to compare the catalyst performance for the production of benzene, toluene, ethylbenzene, and xylene (BTEX) because this temperature gave the highest oil yield (80.7 wt%) during the non-catalytic pyrolysis process. The large pore zeolite group of HBeta and HY led to 134% and 67% higher BTEX concentrations than HZSM-5, respectively, likely because they had larger pores, higher surface areas, and higher acid site density than the HZSM-5. This is the first report of the effect of zeolite characteristics on BTEX production via CFP.

Abstract This study valorized a lignocellulosic livestock waste into energy intensive platform chemical, syngas (H2 and CO), and biochar via pyrolysis process as an environmentally sustainable manner for disposal of waste released from livestock industry. To construct a more sustainable valorization platform for the livestock waste, this work also laid stress on the possible use of CO2 as a co-reactant in pyrolysis. In pyrolysis of livestock waste, CO2 itself was reduced into CO, simultaneously oxidizing volatile matters (VMs) from the thermolysis of livestock waste through the gas phase reactions (GPRs). In short, CO2 played a critical role as an additional source of oxygen, and such mechanistic role opens a new opportunity to use CO2 as a raw feedstock during the valorization process of livestock waste. Nonetheless, the temperature window enabling the GPRs in line with CO2 was experimentally determined at ≥510 °C, and the reaction kinetics for the GPRs was not fast to convert the majority of VMs derived from the thermolysis of livestock waste into syngas. In an effort to improve the reaction kinetics of GPRs, this study particularly employed biochar produced from pyrolysis of livestock waste (that was fabricated at 650 °C for 1 h) as a catalyst. In catalytic pyrolysis under the CO2 environment, livestock waste biochar served as a role to expedite the reaction kinetics for GPRs. This led to the significant enhancement of the formation of syngas proportional to the amount of biochar catalyst loading. In reference to non-catalytic pyrolysis, catalytic pyrolysis of livestock waste over its biochar showed 3 times more syngas production.

Antimonate (Sb(V)) and arsenate (As(V)) pollution frequently occur in aqueous environment and can be absorbed by poorly crystalline Fe minerals (i.e., ferrihydrite). In this study, the adsorption capacity and rate of Sb(V) and As(V) from water with fresh ferrihydrite were compared by establishing adsorption isotherms and kinetics, and the effects of ferrihydrite dosage, solution pH and humic substances on Sb(V) and As(V) adsorption were also investigated. The adsorption isotherms results showed that the equilibrium and maximum adsorption capacities of Sb(V) on ferrihydrite were approximately equal to those of As(V) under different temperatures. The results of adsorption kinetics showed that the adsorption rate of Sb(V) derived from the pseudo-second-order equation was much lower than that of As(V). In addition, the adsorption capacity and rate of Sb(V) and As(V) were greatly affected by various ferrihydrite dosage and solution pHs. The presence of humic acid and fulvic acid (FA) significantly affected the adsorption process of Sb(V) due to competition adsorption, whereas the adsorption properties of As(V) were little affected by FA under this experimental conditions.

This study is aiming at exploring the genuine role of CO2 in pyrolysis of lignocellulosic biomass by investigating the susceptibility of pyrolysis of monosaccharide (e.g., xylose and glucose), disaccharide (e.g., sucrose), and polysaccharide (e.g., woody biomass) to CO2. To do this, the thermal degradation of these four biomass samples was characterized in N2 and CO2. The thermal characterization results reveal that the physical aspects of biomass decomposition (i.e., thermal degradation rate and residual mass difference) associated with CO2 were nearly the same; however, the chemical aspects were significantly different. In other words, CO2 enhanced thermal cracking of volatile organic compounds (VOCs) generated from thermal degradation of biomass. In addition, our experiment results show that xylose (a major constituent of hemicellulose) and lignin exhibited a high sensitivity to CO2 in pyrolysis.

Spent mushroom substrate (SMS) is a recalcitrant lignocellulosic waste. Recycling of SMS through composting has been reported; however, the process is lengthy due to its complex biochemical composition. Although vermitechnology is known for its high efficiency, it has rarely been applied to recycle SMS. In this study, the qualitative value of vermicomposted SMS mediated by three earthworm species (i.e., Eisenia fetida, Eudrilus eugeniae, and Perionyx excavatus) was evaluated on the basis of nutrient availability, microbial activity, phospholipid fatty acid (PLFA) profiles, and seed germination assays. Degradation profiles of the lignocellulosic substrate in the vermireactors were assessed by monitoring the changes in crystallinity and distribution of functional groups using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy, respectively. Total organic carbon decreased by 1.4-3.5 folds with approximately 2.1-2.4 folds increase in nitrogen and phosphorus availability in all vermibeds. Interestingly, pH declined in the Eisenia and Eudrilus systems but increased in the Perionyx-vermibeds. XRD-derived crystallinity index was reduced significantly by 1.37 folds in Perionyx-vermicompost with concurrent microbial enrichment. Further, profuse abundance of vital functional groups (CO, NH, and OH) was clearly observed in the vermicompost with Perionyx followed by that with Eisenia. Moreover, PLFA illustrated significant variations in fatty acid distributions and microbial communities of the three vermicomposting systems. The seed germination assay showed that the germination index and relative root-shoot vigor of Perionyx-vermicompost treated seeds were 1.05-1.30 times greater than those of Eisenia and Eudrilus vermicompost treated ones. The results suggest that SMS degradability was affected by the growth of a healthy microbial community through vermicomposting.

Abstract Peanut shells (i.e., an abundant industrial by-product) were subjected to an innovative hydrothermal pretreatment approach using high-pressure CO2 to enhance their enzymatic hydrolysis conversion into glucose. This pretreatment led to a reduction in hemicellulose content in the pretreated peanut shells from 12.4% to as low as 1.8%, which facilitated subsequent conversion into glucose by enzymatic hydrolysis. This pretreatment approach was assessed within a 170–200 °C temperature range and a 20–60 bar CO2 pressure range, after which the results of these conditions were compared to those of conventional hot water pretreatment. Treatment at 190 °C and a 60-bar CO2 pressure was determined to be optimal, resulting in the highest glucose yield (80.7%) from subsequent enzymatic hydrolysis. Acidic conditions resulting from CO2-derived carbonic acid significantly reduced the hemicellulose content of the peanut shells and weakened the interaction between cellulose, hemicellulose, and lignin, improving enzyme accessibility to the cellulose. Furthermore, high-pressure CO2 increased the pore size and porosity of the resulting pretreated peanut shells, improving their enzyme adsorption capacities, as confirmed by cellulase adsorption and mercury intrusion porosimetry tests. The dual effect from high-pressure CO2 led to significant hemicellulose reduction and improved adsorption of enzymes on the cellulose, which in turn increased glucose yield from the subsequent enzymatic hydrolysis of pretreated peanut shells. Alcoholic fermentation of the hydrolyzed glucose resulted in a 12.4% increase in bio-ethanol production compared to a glucose control, thus highlighting the potential of pre-treated peanut shells as a glucose precursor used in biofuel industry.