Jeong-Ik Oh

Polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs) mitigation in the pyrolysis process of waste tires using CO2 as a reaction medium

Our work reported the CO2-assisted mitigation of PAHs and VOCs in the thermo-chemical process (i.e., pyrolysis). To investigate the pyrolysis of used tires to recover energy and chemical products, the experiments were conducted using a laboratory-scale batch-type reactor. In particular, to examine the influence of the CO2 in pyrolysis of a tire, the pyrolytic products including C1-5-hydrocarbons (HCs), volatile organic carbons (VOCs), and polycyclic aromatic hydrocarbons (PAHs) were evaluated qualitatively by gas chromatography (GC) with mass spectroscopy (MS) as well as with a thermal conductivity detector (TCD). The mass balance of the pyrolytic products under various pyrolytic conditions was established on the basis of their weight fractions of the pyrolytic products. Our experimental work experimentally validated that the amount of gaseous pyrolytic products increased when using CO2 as a pyrolysis medium, while substantially altering the production of pyrolytic oil in absolute content (7.3-17.2%) and in relative composition (including PAHs and VOCs). Thus, the co-feeding of CO2 in the pyrolysis process can be considered an environmentally benign and energy efficient process.

In-situ pyrogenic production of biodiesel from swine fat.

In-situ production of fatty acid methyl esters from swine fat via thermally induced pseudo-catalytic transesterification on silica was investigated in this study. Instead of methanol, dimethyl carbonate (DMC) was used as acyl acceptor to achieve environmental benefits and economic viability. Thermo-gravimetric analysis of swine fat reveals that swine fat contains 19.57wt.% of water and impurities. Moreover, the fatty acid profiles obtained under various conditions (extracted swine oil+methanol+NaOH, extracted swine oil+DMC+pseudo-catalytic, and swine fat+DMC+pseudo-catalytic) were compared. These profiles were identical, showing that the introduced in-situ transesterification is technically feasible. This also suggests that in-situ pseudo-catalytic transesterification has a high tolerance against impurities. This study also shows that FAME yield via in-situ pseudo-catalytic transesterification of swine fat reached up to 97.2% at 380°C. Therefore, in-situ pseudo-catalytic transesterification can be applicable to biodiesel production of other oil-bearing biomass feedstocks.

Employing CO2 as reaction medium for in-situ suppression of the formation of benzene derivatives and polycyclic aromatic hydrocarbons during pyrolysis of simulated municipal solid waste ☆

This study proposes a strategic principle to enhance the thermal efficiency of pyrolysis of municipal solid waste (MSW). An environmentally sound energy recovery platform was established by suppressing the formation of harmful organic compounds evolved from pyrolysis of MSW. Using CO2 as reaction medium/feedstock, CO generation was enhanced through the following: 1) expediting the thermal cracking of volatile organic carbons (VOCs) evolved from the thermal degradation of the MSWs and 2) directly reacting VOCs with CO2. This particular influence of CO2 on pyrolysis of the MSWs also led to the in-situ mitigation of harmful organic compounds (e.g., benzene derivatives and polycyclic aromatic hydrocarbons (PAHs)) considering that CO2 acted as a carbon scavenger to block reaction pathways toward benzenes and PAHs in pyrolysis. To understand the fundamental influence of CO2, simulated MSWs (i.e., various ratios of biomass to polymer) were used to avoid any complexities arising from the heterogeneous matrix of MSW. All experimental findings in this study suggested the foreseeable environmental application of CO2 to energy recovery from MSW together with disposal of MSW.

Evaluating the effectiveness of various biochars as porous media for biodiesel synthesis via pseudo-catalytic transesterification

This study focuses on investigating the optimized chemical composition of biochar used as porous material for biodiesel synthesis via pseudo-catalytic transesterification. To this end, six biochars from different sources were prepared and biodiesel yield obtained from pseudo-catalytic transesterification of waste cooking oil using six biochars were measured. Biodiesel yield and optimal reaction temperature for pseudo-catalytic transesterification were strongly dependent on the raw material of biochar. For example, biochar generated from maize residue exhibited the best performance, which yield was reached ∼90% at 300°C; however, the maximum biodiesel yield with pine cone biochar was 43% at 380°C. The maximum achievable yield of biodiesel was sensitive to the lignin content of biomass source of biochar but not sensitive to the cellulose and hemicellulose content. This study provides an insight for screening the most effective biochar as pseudo-catalytic porous material, thereby helping develop more sustainable and economically viable biodiesel synthesis process.

Estimating total lipid content of Camelina sativa via pyrolysis assisted in-situ transesterification with dimethyl carbonate

Direct derivatization of C. sativa seed into FAMEs without lipid extraction was conducted for the quantification of lipid analysis via in-situ thermal methylation with dimethyl carbonate as an acyl acceptor on silica (SiO2). The introduced method had an extraordinarily high tolerance against impurities such as pyrolytic products and moisture. To ensure the technical completeness of in-situ methylation, thermal cracking of FAMEs transformed from C. sativa seed was also explored. Thermal cracking of unsaturated FAMEs such as C18:1, C18:2, C18:3 and C20:1 occurred at temperatures higher than 365°C due to their thermal instability. Thus, experimental findings in this study suggests not only that qualitative analysis of fatty acid profile in C. sativa seed via in-situ methylation using SiO2 could be achieve, but also that the total lipid content (42.65wt.%) in C. sativa seed could be accurately estimated.

Establishing a green platform for biodiesel synthesis via strategic utilization of biochar and dimethyl carbonate

To establish a green platform for biodiesel production, this study mainly investigates pseudo-catalytic (non-catalytic) transesterification of olive oil. To this end, biochar from agricultural waste (maize residue) and dimethyl carbonate (DMC) as an acyl acceptor were used for pseudo-catalytic transesterification reaction. Reaction parameters (temperature and molar ratio of DMC to olive oil) were also optimized. The biodiesel yield reached up to 95.4% under the optimal operational conditions (380°C and molar ratio of DMC to olive oil (36:1)). The new sustainable environmentally benign biodiesel production introduced in this study is greener and faster than conventional transesterification reactions.

Carbon dioxide assisted thermal decomposition of cattle excreta

To develop the environmentally benign thermo-chemical process, this study placed great emphasis on the influence of CO2 on pyrolysis of cattle excreta for energy recovery. To this end, this study evaluates the possible enhanced energy recovery from cattle excreta using CO2 as reaction medium/feedstock in the thermal degradation of cattle excreta. The enhanced generation of CO in the presence of CO2 reached up to 15.15mol% (reference value: 0.369mol%) at 690°C, which was equivalent to ~4000 times more generation of CO. In addition to the enhanced generation of CO, the enhanced generation of H2 and CH4 in the thermal degradation of cattle excreta in CO2. Thus, the findings of this study revealed two genuine roles of CO2: 1) enhanced thermal cracking of volatile organic carbons (VOCs) evolved from the thermal degradation of cattle excreta and 2) direct reaction between VOCs and CO2 via gas phase reaction.

Quantification of volatile fatty acids from cattle manure via non-catalytic esterification for odour indication

This report proposes a new approach to evaluate the odour nuisance of cattle manure samples from three different cattle breeds (i.e., native cattle, beef cattle, and milk cow) by means of quantification and speciation of volatile fatty acids (VFAs). To this end, non-catalytic esterification thermally induced in the presence of a porous material (silica) was undertaken, and the optimal operational parameters such as the derivatizing temperature (330°C) for the maximum yield (≥99±0.4%) of volatile fatty acid methyl esters (VFAMEs) were established. Among the VFA species in cattle manure based on quantification of VFAs, the major species were acetic, butyric and valeric acid. Considering the odour threshold of each VFA, our experimental results suggested that the major contributors to odour nuisance were C4-5 VFA species (i.e., butyric and valeric acid). Hydrothermal treatment was performed at 150°C for 0-40min to correlate the formation of VFAs with different types of cattle feed formulations. Our experimental data demonstrated that the formation of total VFAs is linearly proportional to the hydrothermal treatment duration and the total content of VFAs in native cattle, beef cattle, and milk cow manure samples reached up to ~1000, ~3200, and ~2800ppm, respectively. Thus, this study demonstrated that the degree of VFA formation is highly dependent on cattle feed formulations, which rely significantly on the protein content. Furthermore, the hydrothermal treatment provides a favourable condition for generating more VFAs. In this context, producing cattle manure into refused derived fuel (RDF) via a hydrothermal treatment is not a viable option to control odour.

Compositional modification of pyrogenic products using CaCO3 and CO2 from the thermolysis of polyvinyl chloride (PVC)

In this study, we explored the mechanistic features of CO2 in the thermolysis of PVC to modify the pyrogenic products. The mechanistic roles of CO2 in the thermolysis of PVC were varied with the pyrolytic temperature. For example, CO2 participated in unknown reactions to form CO at temperatures higher than 600 °C, where CO2 played a key role as an oxygen donor (new finding). This new thermal behavior induced by CO2 could be a new way to shift carbon from pyrolytic oil to syngas (i.e., H2 and CO) without using catalysts. This identified reaction that formed CO was noticeably enhanced in the presence of CaCO3 by up to 12 times, which was proportional to the loading of CaCO3. The stepwise thermal degradation mechanisms for PVC (i.e., dehydrogenation followed by dechlorination) provided favorable conditions for forming benzene derivatives and PAHs in pyrolytic oil. In the temperature range from 480 to 600 °C, CO2 played a key role in restricting the formation of benzene derivatives, which subsequently lowered the formation of PAHs by blocking the pathway for the gas-phase addition reactions. At the current stage of this study, the operational parameters such as the exact amount of CO2, space velocity for CO2, and other parameters for the thermolysis of PVC were fully optimized. However, all the experimental findings marginally described the possible utilization of CO2 for modifying pyrogenic products, which can be applied in various fields such as air pollutant controls (APCs) and energy applications. As such, further studies need to be conducted in the near future.