Microwave pyrolysis coupled with conventional pre-pyrolysis of the stalk for syngas and biochar

Effect of Reaction Conditions on Energy Yield of Pyrolysis Gas from Apple Tree Branches

Although the annual branches of apple trees are substantial, most of them are discarded or incinerated, resulting in a significant waste of resources and environmental pollution concerns. Therefore, it has become necessary and urgent to recycle these branches. Compared with crop straw, apple tree pruning branches exhibit a relatively elevated lignin content, which makes them an optimal feedstock for generating high-quality pyrolysis gases. Energy yield can comprehensively measure the gas production and heat value of the pyrolysis gas. Herein, the effect of reaction conditions on the energy yield of the pyrolysis gas is systematically investigated. The single-factor experimental results show that the optimal conditions are 750 °C reaction temperature, 2 °C/min heating rate, and 120 min holding time. The central composite design test of the response surface establishes that temperature has the most impact, followed by heating rate and holding time. In addition, a regression model is constructed to predict the energy yield of the pyrolysis gas. The analysis of interactions between factors indicates that factors within the lower temperature zones, higher heating rate, and shorter holding time have a more significant influence on the energy yield. These findings provide crucial guidance for the efficient production of pyrolysis gas from apple tree branches.

Catalytically Active Carbon for Oxygen Reduction Reaction in Energy Conversion: Recent Advances and Future Perspectives

The shortage and unevenness of fossil energy sources are affecting the development and progress of human civilization. The technology of efficiently converting material resources into energy for utilization and storage is attracting the attention of researchers. Environmentally friendly biomass materials are a treasure to drive the development of new-generation energy sources. Electrochemical theory is used to efficiently convert the chemical energy of chemical substances into electrical energy. In recent years, significant progress has been made in the development of green and economical electrocatalysts for oxygen reduction reaction (ORR). Although many reviews have been reported around the application of biomass-derived catalytically active carbon (CAC) catalysts in ORR, these reviews have only selected a single/partial topic (including synthesis and preparation of catalysts from different sources, structural optimization, or performance enhancement methods based on CAC catalysts, and application of biomass-derived CACs) for discussion. There is no review that systematically addresses the latest progress in the synthesis, performance enhancement, and applications related to biomass-derived CAC-based oxygen reduction electrocatalysts synchronously. This review fills the gap by providing a timely and comprehensive review and summary from the following sections: the exposition of the basic catalytic principles of ORR, the summary of the chemical composition and structural properties of various types of biomass, the analysis of traditional and the latest popular biomass-derived CAC synthesis methods and optimization strategies, and the summary of the practical applications of biomass-derived CAC-based oxidative reduction electrocatalysts. This review provides a comprehensive summary of the latest advances to provide research directions and design ideas for the development of catalyst synthesis/optimization and contributes to the industrialization of biomass-derived CAC electrocatalysis and electric energy storage.

Low-cost eggshell-fly ash adsorbent for phosphate recovery: A potential slow-release phosphate fertilizer

Fly ash (FA) and eggshells (ES) are common solid wastes with significant potential for the recovery of phosphorus from water. This study focuses on synthesizing a low-cost and environmental-friendly phosphate adsorbent called eggshell-fly ash geopolymer composite (EFG) using eggshells instead of chemicals. The CaO obtained from the high-temperature pyrolysis of eggshells provides active sites for phosphate adsorption, and CO2 serves as a pore-forming agent. The phosphate adsorption performance of EFG varied with the eggshell-fly ash ratios and achieved a maximum of 49.92 mg P/g at an eggshell-fly ash ratio of 40 %. The adsorption process was well described by the pseudo-second-order model and the Langmuir model. EFG also exhibited a good regeneration performance through six-cycle experiments and achieved the highest phosphate desorption at pH 4.0. The results of the column experiment showed that EFG can be used as a filter media for phosphorus removal in a real-scale application with low cost. Soil burial test indicated saturated EFG has a good phosphate slow-release performance (maintained for up to 60 days). Overall, EFG has demonstrated to be a promising adsorbent for phosphorus recovery.

Unveiling the microwave heating performance of biochar as microwave absorber for microwave-assisted pyrolysis technology

Microwave (MW) heating has gained significant attention in food industries and biomass-to-biofuels through pyrolysis over conventional heating. However, constraints for promoting MW heating related to the use of different MW absorbers are still a major concern that needs to be investigated. The present study was conducted to explore the MW heating performance of biochar as a low-cost MW absorber for performing pyrolysis. Experiments were performed on biochar under different biochar dosing (25 g, 37.5 g, 50 g), MW power (400 W, 700 W, 1000 W), and particle sizes (6 mm, 8 mm, 10 mm). Results showed that MW power and biochar dosing significantly impacted average heating rate (AHR) from 17.5 to 65.4 °C/min at 400 W and 1000 W at 50 g. AHR first increased, and then no significant changes were obtained, from 37.5 to 50 g. AHR was examined by full factorial design, with 94.6% fitting actual data with predicted data. The model suggested that the particle size of biochar influenced less on AHR. Furthermore, microwave absorption efficiency and biochar weight loss were investigated, and microwave absorption efficiency decreased as MW power increased, which means 17.16% of microwave absorption efficiency was achieved at 400 W rather than 700 W and 1000 W. Biochar weight loss estimated by employing mass-balance analysis, 2-10.4% change in biochar weight loss was obtained owing to higher heating rates at higher powers and biochar dosing.

Promotion of bio-oil production from the microwave pyrolysis of cow dung using pretreated red mud as a bifunctional additive: Parameter optimization, energy efficiency evaluation, and mechanism analysis

To address the issues of high oxygen content and energy consumption in the microwave-assisted pyrolysis of biomass for biofuel production, this study used high-temperature pretreated red mud (RM) as an additive. The pretreated RM exhibited dual functionalities, namely microwave absorption and catalytic properties, during the microwave-assisted pyrolysis of cow dung (CD). This study also evaluated the optimization potential of energy recovery efficiency. The results showed that the addition of pretreated RM significantly increased the oil yield during the microwave-assisted pyrolysis of CD. The highest oil yield (59.63%) was obtained via the microwave-assisted pyrolysis of CD over catalysis with RM pretreated at 750 °C (RM750). Through the optimization of the RM750-to-CD mixing ratio, optimal oil quality and energy recovery efficiency were achieved. At a mixing ratio of 1:1, the pyrolysis oil featured the highest aromatic hydrocarbon content and lowest acid content. The high-temperature pretreatment of RM increased the Fe2O3 content, which enhanced the dielectric properties and magnetic loss ability of the reactants. This resulted in localized high temperatures and the formation of "hot spots," which can promote the deoxygenation and hydrogenation reactions of oil. Consequently, the lower heating rate of oil increased from 35.12 to 40.11 MJ kg-1. The released oxygen escaped in the form of CO. In addition, pyrolytic char was used as an in situ microwave absorbing material owing to its increased Fe2O3 content and graphitization degree, leading to an increase in energy recovery efficiency from 4.71% to 9.98%. This study provides valuable guidance for the efficient utilization of diversified solid wastes and demonstrates the potential application of microwave-assisted pyrolysis technology in the resource utilization of solid wastes.

Breakdown of biomass for energy applications using microwave pyrolysis: A technological review

The agricultural industry faces a permanent increase in waste generation, which is associated with the fast-growing population. Due to the environmental hazards, there is a paramount demand for generating electricity and value-added products from renewable sources. The selection of the conversion method is crucial to develop an eco-friendly, efficient and economically viable energy application. This manuscript investigates the influencing factors that affect the quality and yield of the biochar, bio-oil and biogas during the microwave pyrolysis process, evaluating the biomass nature and diverse combinations of operating conditions. The by-product yield depends on the intrinsic physicochemical properties of biomass. Feedstock with high lignin content is favourable for biochar production, and the breakdown of cellulose and hemicellulose leads to higher syngas formation. Biomass with high volatile matter concentration promotes the generation of bio-oil and biogas. The pyrolysis system's conditions of input power, microwave heating suspector, vacuum, reaction temperature, and the processing chamber geometry were influence factors for optimising the energy recovery. Increased input power and microwave susceptor addition lead to high heating rates, which were beneficial for biogas production, but the excess pyrolysis temperature induce a reduction of bio-oil yield.

Value-added biochar production from microwave pyrolysis of peanut shell

In order to seek efficient resource utilization, the carbonization of agricultural and forestry wastes through microwave pyrolysis technology is an important research hotspot to develop value-added products. The main objective is to produce value-added biochar through microwave pyrolysis of peanut shell in this study. The product yields, functional groups, and biochar HHVs caused by pyrolysis temperature (400, 450, 500, 550, and 600 °C), microwave power (350, 450, 550, 650, and 750 W), and residence time (10, 20, 30, 40, and 50 min) were investigated, and the energy recovery efficiencies were evaluated. It was obtained that the biochar yield declined monotonously within the range of 45.3–86.0 wt% with the enhancement of pyrolysis temperature, microwave power, or residence time. The pyrolysis temperature of 400 °C, microwave power of 350 W, and residence time of 10 min generated the maximum biochar yield (86.0 wt%). The value-added biochar was obtained with high HHV (20.15–31.02 MJ/kg) and abundant oxygen-contained functional groups (C–O bonds and C=O bonds). The maximum energy recovery efficiency during the whole process reached 97.96%. The results indicated that the peanut shell could reach high biochar yield through microwave pyrolysis, and potentially be transformed into value-added products with high energy recovery efficiency.

Review of biochar production via crop residue pyrolysis: Development and perspectives

Worldwide surge in crop residue generation has necessitated developing strategies for their sustainable disposal. Pyrolysis has been widely adopted to convert crop residue into biochar with bio-oil and gas being two co-products. The review adopts a whole system philosophy and systematically summarises up-to-date knowledge of crop residue pyrolysis processes, influential factors, and biochar applications. Essential process design tools for biochar production e.g., cost-benefit analysis, life cycle assessment, and machine learning methods are also reviewed, which has often been overlooked in prior reviews. Important aspects include (a) correlating techno-economics of biochar production with crop residue compositions, (b) process operating conditions and management strategies, (c) biochar applications including soil amendment, fuel displacement, catalytic usage, etc., (d) data-driven modelling techniques, (e) properties of biochar, and (f) climate change mitigation. Overall, the review will support the development of application-oriented process pipelines for crop residue-based biochar.