Tatiana Krapivnitckaia

Микроволновый пиролиз древесины дуба: исследование процесса и характеристика продуктов

This work is devoted to developing a microwave complex for thermal processing of peat (pyrolysis). To implement the study, the necessary physical properties of high-moor and low-moor peat were studied. Key parameters characterizing the dielectric characteristics of the research objects were measured. The loss tangent and permittivity for the high-moor peat were 3.4×10-2 and 1.58, and for the low-moor peat 6.5×10-2 and 2.76, respectively. Structural elements for creating a microwave complex that allows processing a large volume of organic material during pyrolysis are proposed. Efficient waveguide rotations, an optimized transition from a rectangular waveguide section to a round one, a non-reflective vacuum barrier window, and an elliptical microwave radiation polarization converter are considered in this study. The 3D numerical modeling and optimization of the proposed waveguide elements of the system are performed to ensure efficient transmission of microwave energy to the reactor with minimal reflection losses, which contributes to reliable and long-term operation of the complex.

The production of polymeric materials is one of the fast-growing sectors in the chemical industry. Improving methods for synthesizing high-molecular compounds and studying their physicochemical characteristics are important tasks of synthetic chemistry. Radical polymerization is currently the main method for producing polymeric materials. Its advantages involve simplicity and low cost, along with the possibility of obtaining a wide range of polymeric materials. The results of measuring the dielectric parameters of various high-molecular compounds (polystyrene, polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol, poly(glycidyl methacrylate)) in the frequency range of 100–200 GHz (refractive index and dielectric loss tangent tgδ) are presented. The compounds under study were both those synthesized by radical polymerization with the participation of the conventional initiator, i.e., azobisisobutyric acid dinitrile, and commercial products. The absorption capacity of polymers at room temperature was compared. Polymers with the highest and lowest absorption capacity were determined. The dependence of tgδ on frequency for all the polymers under study is linear, with absorption in the polymers increasing with frequency. Poly(glycidyl methacrylate) exhibits the highest absorption among the studied macromolecules with tgδ being equal to 0.043 at 200 GHz. The minimum tgδ value of 0.0068 was found for polystyrene. For the polymers under study, the refractive index value varies in the range from 1.09 to 1.39. In addition, dielectric properties of the original vinyl monomers (styrene, vinyl acetate, glycidyl methacrylate) were studied. The results are of interest when developing approaches to obtaining polymeric materials with specified characteristics based on vinyl monomers by the method of radical polymerization.

Peat reserves are of great interest for various industries (energy, fuel, chemical, etc.). It is common practice to use pyrolysis to process such solid carbon-containing resources with the subsequent yield of fuel and valuable products. One of the environmentally and energetically favorable ways to degrade carbon-containing feedstock that is currently under development is microwave-assisted pyrolysis. Microwave radiation provides volumetric heating of the material, which significantly increases heating uniformity across the volume of the irradiated sample, providing greater efficiency of heat transfer and avoiding local overheating on the reactor surface. In the conducted study, a system was designed for the microwave processing of organic materials. The structural elements of the system are described, and a schematic showing pyrolysis product separation is presented. A prototype of the developed reactor was used to conduct experiments on degrading high-moor sphagnum peat of the Greko-Ushakovskoe deposit under mild pyrolysis conditions induced by microwave radiation. The component composition of reaction products was analyzed via chromatography-mass spectrometry and compared with the results of previous experiments using conventional thermal pyrolysis. More advanced processing of peat is performed under the conditions of microwave-assisted mild pyrolysis with a high yield of valuable products due to a more efficient heat transfer, uniform heating of the material, and the optimal reaction rate. The developed technology is shown to produce raw materials for a wide range of high-tech industrial productions. The prospects for the industrial use of the proposed microwave-assisted peat processing technology are discussed, specifically for the production of efficient hydrophobic sorbent.

A series of theoretical and experimental studies was carried out with the aim of a direct comparison of the thermal and microwave destruction of peat during pyrolysis. Different heating mechanisms in these processes were investigated in the framework of simulations conducted using a commercial 3D software package, CST Studio Suite, to define their specific features. Based on these simulations, identical reactors were constructed exploiting an electric element and a microwave complex as a heat source, and an experimental technique was developed that allows these processes to be correctly compared under similar conditions. Using these reactors based on different heat sources, comparative experiments on peat pyrolysis were performed, and the results of the theoretical analysis were confirmed. As a result, the advantages of microwave exposure were demonstrated to achieve a more uniform and deep fragmentation of peat, increase the reaction rate and reduce the processing time, with high energy efficiency accompanying this method. As part of the experiments, the yield of pyrolysis products was analyzed. During the microwave destruction of peat, a high gas output (up to 27%) was obtained, which allows for a further increase in the efficiency of this processing method when burning these gases. The conducted elemental analysis showed an increase in the percentage of carbon from about 50% to 78% after microwave processing, which can become a raw material for obtaining effective environmentally friendly sorbents. The prospects for creating industrial microwave complexes for processing organic materials are discussed.

A facility for conducting experiments on the microwave (MW) pyrolysis of peat at a source operating frequency of 2.45 GHz has been developed. The MW pyrolysis of peat for the production of low-molecular-weight organic components has been experimentally studied. The products of peat MW radiation-induced decomposition were determined, and reaction schemes for the degradation of peat components were proposed. A carbonaceous residue with relative carbon, hydrogen, nitrogen, and sulfur contents of 83–85, 4–5, 2–3, and <0.3 wt %, respectively, was obtained.

The design of a technological complex for microwave processing of organic materials is proposed. The electrodynamic system of an oversized microwave reactor for low-temperature pyrolysis has been developed. The constructive elements of the complex that allow its continuous failure-free operation in conditions of high radiation intensity are described. Based on the prototype of the elaborated reactor, model experiments on microwave pyrolysis of peat were carried out. The elemental composition of the solid fraction was analyzed during the conducted experiments. The possibility of the efficiency enhancement of the proposed processing method and potential applications of the novel technology are discussed.