Hydrothermal Carbonization Of Corncob And Pinenut Shell And The Adsorption Performance Of Its Product

Hydrothermal carbonization (HTC) is a novel thermochemical conversion process to convert waste biomass into value-added products. The process of HTC was conducted at a certain temperature (150-250℃) and pressure (2-10 MPa) for several hours in water as reaction medium. The biochars are widely used in fuel, soil improvement, contamination removal, preparation of functional nano-materials, fixed CO2 and other areas. Compared with other biomass thermochemical conversion, HTC has many advantages, such as low-cost, mild reaction conditions, easy operation, and broader applications in the treatment of waste biomass.The hydrochars were prepared by HTC of corn cob and pinenut shell under 180-230℃, the influences of temperature on HTC were investigated. The properties and structural of the hydrochars were analyzed by elemental analysis, scanning electron microscope (SEM), fourier transform infrared spectroscopy (FT-IR), etc. The results showed that HTC of biomass through dehydration, methanation, and other dehydroxylation reaction, the carbon content was enriched. With temperature increased, the processes of HTC intensely, the yield of hydrochars decreased, the higher heating (HHV), and energy density improved. At 230℃, the HHV of corncobs and pine nut shells are 22.2 MJ/kg and 23.83 MJ/kg, corresponding to an increase of 35.71% and 38.70% as compared to those for the raw materials, respectively. SEM analysis showed that HTC can debris the biomass structure, there are more carbon microsphere were generated on the surface of hydrochars with temperature increased.The effects of Fe3+, citric acid as an additive on HTC of corn cobs and pinenut shell at 200℃ were studied. The results showed that Fe3+ and citric acid can both promote the HTC process of biomass. The HHV of corn cobs and pine nut shell hydrochar prepared by adding Fe3+ with an increase of 18.91% and 29.47%, respectively, compared with direct HTC. Adding citric acid increases 40.70% and 34.30%, respectively. SEM showed that the amount of carbon microspheres generated significantly, and complete spherical, smooth surface when adding Fe3+. The particle size of the carbon microspheres of corncob is in nm level and showing a dense honeycomb by HTC in the addition of citric acid.As the hydrochars produced by HTC in the addition of citric acid showed good physical and chemical characteristics, the adsorption mechanism of methylene blue and kinetics were studied. The results showed that:in the condition of pH 7.0, carbon dosage of 0.5 g/L, methylene blue at a concentration of 50 mg/L, methylene blue adsorption capacity by corn cob hydrochar and pine nut shell hydrochar were 98.6 mg/g,97.7 mg/g, respectively. The adsorption kinetics of methylene blue of hydrochars can better fit the second-order kinetic model, which corncob hydrochar fitting reaches 0.9998, indicating adsorption of methylene blue by hydrochars conform chemical adsorption. The adsorption isotherm can better meet the Langmuir isotherm model. Correlation coefficients were 0.99797,0.99756, which showed that the adsorption of methylene blue by hydrochars was monolayer adsorption.