Techno-economic and environmental evaluation of the production of biodiesel from rice-straw in China

Rice straw (RS) is the residue obtained during the rice processing process, and is recognized as one of the most abundant biomass resources in the world. Approximately 800 million to 1 billion tons of rice straw are produced globally every year, and most of them are considered general waste and typically end up in landfills or incineration. This approach wastes resources and can also lead to environmental pollution. In the current study, the RS was used as the source of biodiesel production and a comprehensive process model of the RS valorization process was developed to evaluate the energy flow, production efficiency, production costs, and greenhouse gas emissions in Hunan Province, China. The evaluation results showed that the energy efficiency of biodiesel production from rice straw and the overall energy efficiency of the rice straw valorization process are reported as 52.1% and 56.1%, respectively. The minimum selling price of biodiesel, which is CNY 3.03/kg, is considerably lower than the current market prices for similar products in China. The largest proportion of the production cost of biodiesel is the cost of natural gas, followed by utilities, capital, transportation, plant maintenance and overheads, consumables, labor, and waste disposal. For the current RS valorization plant with a 5000 kg/h RS feed rate, the investment payback times are 8.9 yr and 7.1 yr when the biodiesel is sold at the lowest (CNY 4/kg) and highest (CNY 4.6/kg) market price, respectively. Environmental analysis shows that the greenhouse gas emissions intensity of biodiesel production is 75.8 g CO2eq/MJ, which is only about 52% of traditional fossil diesel and indicating that biodiesel is an environmentally friendly energy source

Density Functional Theory Study on the Mechanism of Biochar Gasification in CO2 Environment

This work presents a comprehensive analysis on the CO2 gasification of miscanthus derived biochar by using combined experimental and computational methods. The empirical formula and the 2D molecular model of the biochar were proposed based on the results from elemental analysis, Fourier infrared spectroscopy, and solid-state 13C NMR spectroscopy. The density functional theory (DFT) method was used to study the conversion of biochar to gaseous products under the CO2 condition at the B3LYP/6-31G(d,p) level. The reactants, intermediates, transition states, and products during the CO2 gasification process were analyzed, and the activation energy (ΔE) of each reaction step and thermodynamic parameters (Gibbs free energy, ΔG, and enthalpy, ΔH) were obtained. By comparison of the kinetic and thermodynamic parameters of different reaction paths, it was found that the proposed path 1 and path 5 could occur spontaneously with the changes in Gibbs free energy (ΔG) being -182.6 and -170.6 kJ/mol, respectively. The order of the reaction path was path 1 < path 5 < path 3 < path 4 < path 2, in terms of the degree of difficulty. It was also found that, for the benzene ring having a ring-opening reaction, when the substituents were located in the 2 and 3 carbon atoms or the 2, 3, and 5 carbon atoms, the C-C bond between the 1 and 6 carbon atoms was more prone to homolytic reaction than that between the 1 and 2 carbon atoms

Fractal Reconstruction of Microscopic Rough Surface for Soot Layer during Ceramic Filtration Based On Weierstrass–Mandelbrot Function

The microscopic surface of soot layer on the external surface of filtration elements is rather hard to reconstruct. In this study, an incinerator–filter setup was designed to mimic the capture of soot particles in flue gas to achieve the samples to construct the rough soot-layer surface. The specific velocities around the ceramic cartridge were determined by particle image velocimetry (PIV) measurement. Resorting to a box-counting method, the fractal dimensions (FDs) were determined by Richardson–Mandelbrot method with binary images of samples. Accordingly, the in situ thickness of soot layer was constructed with consideration of particle deposit and the microscopic rough surfaces were modeled by employing Weierstrass–Mandelbrot (W-M) function. Additionally, a comparison between the constructed surface and real surface achieved from the image taken by atomic force microscopy (AFM) was performed. The results suggest that all roughness deviations of constructed surface from real surface of soot layer not exceed 5%