• Energy Research

Abstract The electrochemical method has emerged as a novel option for bio-oil upgrading due to the advantages of having mild reaction conditions, control convenience and carbon neutrality. Bio-oil is easy to form coke even at low current densities during electrochemical upgrades of bio-oil. Unveiling the coke evolution during the electrochemical processing of bio-oil is essential to enable both oil-to-material and oil-to-fuel strategies. Here, we investigate the coke formation behaviors during the electrochemical processing of bio-oil. The coke comes primarily from the polymerization of aromatic components. The reaction time and current density have a promoting effect on the coke yields. The current density has an accelerating influence on the morphological evolution of the coke. The O-containing groups increases slightly with the increasing reaction time and current density. The large to small ring ratio of the coke is similar under different reaction time and current densities. The potential applications as carbon materials of the coke formed from bio-oil via electrochemical polymerization are discussed based on its physical morphology and chemical structure.

Abstract Sewage sludge, the inevitable by-product of municipal wastewater treatment plant operation, is a key issue in many countries due to its increasing volume and the impacts associated with its disposal. Thermochemical processing offers a new way of managing sewage sludge, not only by providing effective volume reduction, but also enabling transformation of carbon-rich organic fraction into valuable energy and fuel. Owing to some unique properties, sewage sludge differs from other solid fuels such as lignocellulosic biomass and coal, making its thermochemical conversion application somewhat complicated and challenging. This paper reviews the options of converting sewage sludge to energy and fuel via three main thermochemical conversion processes namely pyrolysis, gasification and combustion. The fundamental aspects of sewage sludge and its behaviour in each of thermochemical process are summarised. The challenges in adopting thermochemical conversion technology in sewage sludge management are addressed, and various alternative approaches deserving further consideration, such as the incorporation of pre-processing and co-utilisation, are discussed.

Abstract A study was carried out in both inert and CO2 atmosphere to investigate the interaction mechanism of K2CO3 with graphite and coal char during the catalytic gasification of coal char. The formation of K2CO3 catalytic precursors was identified by using series of different techniques. The results obtained in an inert atmosphere show that the interaction between K2CO3 and carbon readily took place at low temperature. For the K2CO3 loaded graphite, the intermediate of CnK clusters formed by the interactions of K2CO3 with carbon prevented the evaporation of K at low temperature. At temperatures above 800 °C, however, the CnK clusters were unstable, and decomposed to release K through vaporization. On the contrary, for the K2CO3 loaded demineralized coal char, due to the presence of oxygen groups, K was tightly bonded to carbon during heating, forming a complex precursor containing O and K with high thermal stability. The reaction pathway of carbon-K2CO3 interactions in an inert atmosphere are proposed for both char and graphite. The results of DRIFTs experiment suggest that CO2 is chemisorbed by the K- catalytic precursors during CO2 gasification to form potassium phenolate species and a covalently bound carbonate group (dimethyl carbonate). It is believed that these species act as active intermediates in the gasification process.

Abstract The current study aimed to investigate catalytic behaviors of alkali metal salt participating in homogeneous steam-volatile and heterogeneous steam-char reforming reactions in steam gasification of cellulose. The results indicate that the temperature is a key parameter which significantly influenced both yield and composition of gas and tar and catalytic performances of KCl. Externally added steam had negligible effect on cracking/reforming of macromolecules volatiles at the temperature of 700 and 900 °C without KCl, whereas in the presence of KCl, it would be activated and further reacted with low reactivity macromolecules volatiles, leading to an increase in gas yield and a decrease in tar yield. KCl was notably involved in homogeneous steam-volatile reactions, and enhanced the water gas shift reaction and tar reforming reactions. However, KCl had little promotion effect on thermal cracking/reforming of levoglucosan in homogeneous steam-volatile reforming process at 500 °C. Its inhibition effect on levoglucosan formation mainly acted during the primary pyrolysis reactions. KCl could also enhance heterogeneous in situ char-steam reaction resulting in a higher H2 yield. The general pathway of KCl involved in homogeneous/heterogeneous reactions in steam gasification of biomass was eventually proposed.