Roles Of Clay Minerals And Reaction Conditions In The Transformation Of Biomass To Kerogen Analogues

The depletion of fossil fuel resources and the resulting adverse effects on the global environment and climate are of major academic, economic and political concern worldwide. Bioenergy is one of the most important components to mitigate greenhouse gas emissions and substitute of fossil fuels. Energy products(gas, char and bio-oil) and chemicals can be obtained by thermal conversion(pyrolysis, gasification, liquefaction, etc.) of biomass. However, the substitution of biomass-derived fuels and chemicals for petroleum-based fuels and chemicals is limited due to the low heating value of bio-oil and high tar content in the gas. Fossil fuels were formed millions of years ago by chemical transformation of organic matter(remains of animals and biomass) in sediment. The original energy stored in fossil fuels comes from solar energy. Therefore, researches on the formation of fossil fuels can provide new ideas to produce biomass-derived fuels and chemicals.Many studies had revealed that naturally-occurring fuels are geologically formed through two stages: ?rstly, geologically degradation of biomass to form kerogen with increased energy density by condensation, cyclization and polymerization reactions; secondly, thermal transformation of kerogen to release petroleum and natural gas or to form coal. Generally, kerogen can be classi?ed into three types(Type I, Type II and Type III). In general, Type I and II kerogen were believed to be oil-prone and Type III kerogen was gas-prone. It is worth noting that the generation of fossil fuels is a complex process, which is affected by temperature, time, pressure and minerals etc.Recently, investigations mainly focused on the following aspects: kinetics of oil and gas generation from kerogen, analysis of the structure of kerogen, the pyrolysis of kerogen, role of clay mineral in kerogen pyrolysis. However, few researches focused on the transformation of biomass into kerogen. The reaction mechanism about the transformation of biomass into kerogen and the role of clay minerals in the formation of kerogen are not very clear.Here, Kerogen analogues and kerogen analogues-montmorillonite composites were prepared by hydrothermal/ solvothermal carbonization of microcrystalline cellulose and that in the presence of montmorillonite. Then, we explored the similarity of kerogen analogues to geological kerogen, and investigated the role of clay minerals and reaction conditions in the transformation of biomass into kerogen analogues. Kerogen analogues and kerogen analogues-montmorillonite composites were characterized by using techniques, such as X-ray diffraction(XRD), Fourier transformation infra-red spectra(FT-IR), scanning electron micrograph(SEM) and thermal analyzer(TG).The main results and conclusion were as follows:(1) Kerogen analogues had some similarities with geological kerogen, especially the chemical structure similarity. Both of their FTIR spectra exhibited aliphatic structures or alkyl chains, the aromatic absorption, carbonyl and carboxyl absorption bands.(2) Kerogen analogues-montmorillonite composites were prepared by hydrothermal carbonization of microcrystalline cellulose in the presence of montmorillonite. Montmorillonite acted as a catalyst, adsorbent and templating agent in the hydrothermal carbonization of microcrystalline cellulose into kerogen analogues.(3) Using ‘A Factor’ and ‘C Factor’ proposed by Ganz and Kalkreuth, kerogen analogues can be catalogued. The ‘A Factor’ and ‘C Factor’ of kerogen analogues obtained by hydrothermal carbonization of cellulose were 0.35 and 0.63, respectively. Besides, the O/C and H/C were 0.37 and 0.84, respectively. These data showed that hydrothermal carbonization of cellulose could obtain Type III kerogen analogues. However, after adding montmorillonite, kerogen analogues transited from Type III kerogen to Type II kerogen. Solvothermal carbonization of a mixture of cellulose and oleic acid at a mass ratio of 1:1 was carried out at 200 °C for 24 h, which can obtain kerogen analogues close to Type I kerogen with the maximum value of ‘A Factor’(0.9) and ‘C Factor’(0.8).(4) The thermal decomposition of kerogen analogues took place in the temperature range 300-600 °C. Pyrolysis of kerogen analogs included two stages: in the first stage(300-380 °C), weaker bond-breaking reactions occurred, which generated an active intermediate; in the second stage(380-500 °C), gas were released from the decomposition of active intermediate. The Coats-Redfern analysis was used to caculated the activation energy of pyrolysis for kerogen analogs. The activation energy is 4~13 kJ/mol for the first stage and 19~36 k J/mol for the second stage. However, based on the Coats-Redfern analysis, the activation energies of pyrolysis for microcrystalline cellulose and oleic acid were 120.6 k J/mol and 97.1 kJ/mol; respectively, which were higher than that of pyrolysis for kerogen analogs.(5) TG-FTIR analysis was employed to investigate the volatile products released from kerogen analogs. Gas released from Type III kerogen analogues mainly contained CH4. While, the FTIR spectra of gas released from Type I kerogen analogues showed strong bands of-CH3 at 2933 cm-1,-CH2 at 2864 cm-1 and weak bands of oxygen-containing functional groups in FTIR spectra, which indicated that the composition of gas released from Type I kerogen analogues could contain alkane compounds.It can be found that the investigatation of the conversion of biomass to kerogen analogues, not only has importantsignificance to reveal the basic research of formation mechanism of fossil fuel, but also of great practical significance to develop the biomass-based energy products and chemicals.