• Energy Research

Abstract This paper studied the catalytic pyrolysis of rice husk (RH) with different K-compounds (i.e., KOH, K2CO3, and K2C2O4) for co-production of biofuels and porous carbons. The decomposition of biomass occurred at lower temperature ranges due to the catalytic performance of K-compounds, following the order of KOH > K2CO3 > K2C2O4. By fast pyrolysis of RH with the K-compounds, the number of organic compounds was significantly reduced. More hydrocarbons (e.g., benzene, long-chain alkanes) were generated due to the in-situ catalytic upgrading (e.g., deoxygenation) of bio-oil. Pyrolysis of biomass with K-compounds could also accelerate the generation of unsaturated aliphatic hydrocarbons. In particular, pyrolysis of RH with K2C2O4 could result in the bio-oil with high-content of hydrocarbons and with low-content of oxygenated compounds (e.g., acids, phenols). Furthermore, the activated char with hierarchically micro-mesoporous structure was applied for toluene sorption. The pristine biochar had a relatively low adsorption time and capacity. By the chemical activation followed by the washing process, the specific surface area (SBET) of the RH-derived chars was significantly increased. The RHC-K2C2O4 had a maximum SBET of 1347 m2/g due to its mild activation process, which further contributed to a highest breakthrough time (1230 min) and capacity (609.38 mg/g) on toluene adsorption.

Abstract The impregnation of sulfuric acid aqueous solution to silica is a traditional method to prepare the solid acid catalyst (SO42−/SiO2) via bonding of the SO42− with surface atoms of silica to generate Bronsted acidic sites and Lewis acidic sites. The results in this study indicated the introduction of sulfuric acid could also impact the interaction between silica and subsequently loaded nickel species. The impregnation of sulfuric acid (i.e. 0.5 M) to Ni/SiO2 catalyst could enhance the dispersion of nickel via reducing nickel particle size, suppress sintering of nickel and increase abundance of the acidic sites with strong strength, which significantly enhanced the catalytic activity, stability and resistivity towards coking in steam reforming of guaiacol. The acidic sites with the strong strength aided the cracking of guaiacol to facilitate the subsequent reforming over metallic nickel sites. After impregnation of appropriate amount of sulfuric acid (i.e. 0.1 M or 0.5 M), the coke formed in amorphous form with low thermal stability was transformed into the coke in form of carbon nanotube with high thermal stability. The former type of coke induced rapid deactivation of the catalyst, while the latter type of coke did not.

To understand the potential origin of char activity responsible for volatile evolution during biomass pyrolysis, the interactions between benzyl phenyl ether (BPE, a typical lignin dimer) and pinewood chars prepared under a series of thermal, acidy, and steamy conditions were investigated. The results showed the activity of low-temperature char on BPE conversion was mainly attributed to the surface O-containing functional groups. The BPE conversion decreased as the temperature for char preparation raised, resulting from the elimination of char surface functional groups to a large degree at high temperature. The low activity of high-temperature char on BPE conversion could be recovered by acid-washing to release metal-occupied carbon based active sites (e.g., small aromatic rings), and further promoted by steam activation to modify the surface property and porous structure, finally achieving a full conversion of BPE and high selectivity to the products of phenol and toluene.

The rapid consumption of fossil energy and the urgent demand for sustainable development have significantly promoted worldwide efforts to explore new technology for energy conversion and storage. Carbon-based supercapacitors have received increasing attention. The use of biomass and waste as a carbon precursor is environmentally friendly and economical. In this study, hydrothermal pretreatment was used to synthetize coke from bio-oil, which can create a honeycomb-like structure that is advantageous for electrolyte transport. Furthermore, hydrothermal pretreatment, which is low in temperature, can create a low graphitization degree which can make heteroatom introduction and activation easier. Then, urea and KOH were used for doping and activation, which can improve conductivity and capacitance. Compared with no heteroatom and activation hydrothermal char (HC) (58.3 F/g at 1 A/g), the prepared carbon material nitrogen doping activated hydrothermal carbon (NAHC1) had a good electrochemical performance of 225.4 F/g at 1 A/g. The specific capacitance of the prepared NAHC1 was improved by 3.8 times compared with that of HC.

Effects of external and internal catalysts on anthracite combustion reactivity and kinetics were investigated using the method of differential thermal analysis (DTA). It was found that the combustion reactivity of both raw and demineralized anthracites was all apparently improved by the introduction of CeO2 and Fe2O3. When CeO2 and Fe2O3 were used in raw anthracite, the combustion starting time from the DTA curve was advanced from 1470 to 1312 and 1325 s, respectively, as compared to the improvements from 1285 to 1089 and 1055 s while adding the same amounts of CeO2 and Fe2O3 into demineralized anthracite. The addition of catalysts has increased the combustion rate for raw anthracite much more significantly than that for demineralized anthracite. Reformed differential thermal analysis (RDTA, change the reference material from Al2O3 to raw anthracite) showed a direct effect of catalysts on its combustion, which broadly agreed with the results of the DTA study. The inherent mineral matter at high contents c...

Abstract Attapulgite (ATTP) is an abundant natural magnesium aluminosilicate mineral that can be used as support for manufacturing cost-effective solid acid catalysts. This study mainly focuses on structural change of ATTP and the formation of Bronsted and Lewis acid sites during sulfonation in H2SO4. The results indicate that the sulfonation leads to the drastic change of the crystal phases as sulfuric acid not only plays the roles of grafting the sulfur species but also reacts with the CaO, MgO, Al2O3 and Fe2O3 or their salts in ATTP to form the sulfates, resulting in the substantial change of the porous structure of ATTP. In such a process, the Bronsted acidic sites, which are the main active sites for the conversion of furfuryl alcohol (FA) to ethyl levulinate (EL), are introduced, while the abundance/strength of the Lewis acid sites are enhanced. The yield of EL up to 95.4% is achieved over the H2SO4/ATTP catalyst. The Fe2(SO4)3 and MgSO4 in the catalyst leaches in ethanol but does not affect the catalytic stability. The formed polymer also does not affect much the catalytic activity after their removal via the calcination in air.

This study investigated the pyrolysis of lignin pyrolysis in a temperature region from 200 to 800 °C, aiming to understand influence of pyrolysis temperature on evolution of structures of the resulting char. The results showed that fusion of the ring structure initiated at 200 °C, where the C/H ratio in the char was equal to that in naphthalene (two fused rings). The C/H ratio in the char obtained at 350 °C corresponded to that in pyrene (four fused rings), while the char produced at 550 °C was equivalent to 20 fused benzene rings in terms of C/H ratio. The increasing pyrolysis temperature also shifted the oxygen-containing functionalities such as the carbonyl, esters, ketones in the bio-oil to the ether functionality that had a higher thermal stability. The DRIFTS study of pyrolysis of lignin showed that drastic changes of the functionalities and the internal structure of the char occurred in a narrow temperature region from 520 to 530 °C. The carbonyl functionality and the aliphatic structure were eliminated, and new conjugated π-bond systems formed.