Direct liquefaction techniques on lignite coal: A review

Combined conversion of lignocellulosic biomass into high-value products with ultrasonic cavitation and photocatalytic produced reactive oxygen species - A review

The production of high-value products from lignocellulosic biomass is carried out through the selective scission of crosslinked CC/CO bonds. Nowadays, several techniques are applied to optimize biomass conversion into desired products with high yields. Photocatalytic technology has been proven to be a valuable tool for valorizing biomass at mild conditions. The photoproduced reactive oxygen species (ROSs) can initiate the scission of crosslinked bonds and form radical intermediates. However, the low mass transfer of the photocatalytic process could limit the production of a high yield of products. The incorporation of ultrasonic cavitation in the photocatalytic system provides an exceptional condition to boost the fragmentation and transformation of biomass into the desired products within a lesser reaction time. This review critically discusses the main factors governing the application of photocatalysis for biomass valorization and tricks to boost the selectivity for enhancing the yield of desired products. Synergistic effects obtained through the combination of sonolysis and photocatalysis were discussed in depth. Under ultrasonic vibration, hot spots could be produced on the surface of the photocatalysts, improving the mass transfer through the jet phenomenon. In addition, shock waves can assist the dissolution and mixing of biomass particles.

Density functional theory simulation of the deoxygenation of lignite model compounds in the aqueous phase under a CO atmosphere catalyzed by OH− ions

The most probable active H species (H−) in the CO–OH− system and the catalytic cycle of OH− in this process were identified.

Role of FeS Catalyst in the Hydromodification of Lignite in a Subcritical Water-CO System

The impacts of FeS catalysts on the hydromodification and structural evolution of lignite were investigated using Fourier transform infrared spectroscopy, nuclear magnetic resonance, and X-ray photoelectron spectroscopy. The results indicate that the caking property of lignite can be significantly improved in the presence of the FeS catalyst. When 6.0 wt % FeS was added, the maximum caking index (G _RI) of modified coal reached 95. During the hydromodification, FeS has little effect on the intrinsic water gas shift reaction, but it can increase the CO conversion by promoting the decomposition and hydrogenation of coal so that more active hydrogen is generated and introduced into modified coal. FeS is conducive to the rupture of distal aliphatic groups in the extractible solutes, which promotes the entrance of hydrogen into the aromatic nucleus (H_ar) and α positions (H_α) of asphaltenes and β positions (H_β) of preasphaltenes. After the catalytic hydromodification, the longer side chains or bridge bonds break and are hydrogenated to form the aliphatic structures with a shorter chain or a higher branched degree. Meanwhile, more oxygen-containing functional groups were removed along with the reduction of volatiles in the modified coal. The synergistic effect of FeS on these factors is favorable for the generation of plastic materials, which contributes to the development of the caking property of lignite.

Investigation on the Distribution of Yimin Lignite Pyrolysis Products and the Stability of its Char

This paper introduces the utilization of lignite in China and abroad and studies the influence of different process conditions on the pyrolysis products of lignite. The effects of pyrolysis temperature, residence time, and heating rate on the yield and stability of pyrolysis products were studied by standard lattice low-temperature distillation of coal. The results showed that the final pyrolysis temperature of lignite increases gradually, which is a key factor affecting the pyrolysis performance of lignite. At the same time, the combustible gas yield and tar yield were also significantly improved. Semichar yield and semichar volatile content showed a downward trend. From the range of pyrolysis products, the heating rate also has an important influence on the pyrolysis performance of lignite. Through the thermal stability test of lignite, it is concluded that the particle size distribution of carbon black products is not significantly different, and most of the coal particles are mainly distributed in the range of more than 6 mm.

Room-Temperature Solid-State Preparation of CoFe2O4@Coal Composites and Their Catalytic Performance in Direct Coal Liquefaction

Iron-based catalysts are promising catalysts in the direct coal liquefaction (DCL) process as they are inexpensive and environmentally friendly. However, most such iron-based catalysts show relatively low activity in coal conversion and oil yield. Common techniques for the synthesis of these catalysts with excellent catalytic performance remain a substantial challenge. We present a simple solid-state synthesis strategy for preparing CoFe2O4 nanoparticles and CoFe2O4 nanoparticles supported on coal (CoFe2O4@coal) composites for DCL. The obtained bimetallic oxide CoFe2O4 nanoparticles show an enhanced catalytic performance in the DCL compared with monometallic components Fe2O3 and Co(OH)2 nanoparticles. The synergistic effect between Co and Fe of CoFe2O4 nanoparticles promotes the catalytic hydrogenation of coal during the DCL process. Moreover, the catalytic performance of CoFe2O4 nanoparticles is further improved when they are loaded on the coal. The conversion, oil yield, liquefaction degree, and gas yield of Dahuangshan lignite are 99.44, 56.01, 82.18 and 19.30 wt %, respectively, with the CoFe2O4@coal composites involved. The smaller particle size and high dispersion of CoFe2O4 supported on coal are of great benefit to full contact between coal and active components. The in-situ solid-state synthesis with coal as support shows great potential to prepare effective iron-based catalysts toward DCL in practice.

Selective synthesis of α-olefins by dehydration of fatty alcohols over alumina–thoria mixed catalysts

The selective and high-yield production of α-olefins by alcohol dehydration is challenging because the isomerization and polymerization olefin products are more thermodynamically stable.