Analysis And Upgrading Of Bio-petroleum From Biomass By Deoxy-liquefaction

With the depletion of fossil fuels and the growing greenhouse effect, more attention has been paid to the exploitation of biomass energy. Biomass, containing carbon and hydrogen, has proved to be a potential resource of renewable energy due to the advantages on its renewal and better quality exhaust emissions etc., which may ultimately be used as the alternative fuels. The conversion processes of biomass can be divided into physical conversion, chemical conversion and biological conversion. Among the many procedures, the thermochemical process of converting biomass into liquid fuels through pyrolysis is a promising one. The liquid oils obtained from biomass pyrolysis are usually called pyrolysis oil or bio-oil, which are mainly composed of acids, alcohols, aldehydes, esters, ketones, furans, ethers, phenols, guaiacols and other compounds containing multi-functional groups. Furthermore, the bio-oil is limited as a substitute of transport fuels due to its high oxidation, viscosity, corrosion, instability and hydroscopic properties and the difficulties in upgrading. So it is important to explore new method to realize the effective transition and utilization of biomass. Our research group has developed an innovative technological route in which biomass can be converted into the carbon-hydrogen liquid fuel with high heating value by direct deoxy-liquefaction at the absence of hydrogen. The bio-petroleum, which is the preferred liquid fuel as a substitute of transport fuels, was prepared and close to fossil petroleum not only in composition but also in H/C molar ratio and the heating value. It is worthy to note that the innovative upgrading method used is quite different from that in other bio-oils according to its chemical characteristics of the bio-petroleum. Therefore, the high-quality oil, close to diesel oil in composition, was obtained and the chemical feedstocks with high value like phenols were separated simultaneously. The detailed studies are as follows: The bio-petroleum was obtained from soybean stalk and cotton stalk respectively by deoxy-liquefaction and the chemical compositions were analyzed by using elemental analysis, FTIR and GC-MS. The results indicated that the bio-petroleum from the two kinds of biomass was both mainly composed of long-chain alkanes, phenol derivatives and benzene derivatives. What makes the minor difference is the content of each component, which may be due to the different contents of cellulose, hemicellulose and lignin in the biomass. The H/C molar ratios are 1.90 and 1.85; O/C molar ratios are 0.06 and 0.05; the higher heating values are 44.22 MJ/kg and 44.24 MJ/kg, respectively. These values are all in the range of petroleum (H/C>1.5, heating value 43-48 MJ/kg). Compared with that of the biomass, the oxygen content of the bio-petroleum has been decreased greatly and the heating value has been increased. Thus, the aim to deoxygenate has been realized.As the chemical analysis showed, phenol derivatives are the main oxygenous compounds in the bio-petroleum. So, the method of bathing with NaOH solution was used to remove the phenol derivatives. The bio-petroleum bathed with 1% NaOH solution makes further decrease in O/C molar ratio and obvious increase in H/C molar ratio. As a result, the bathed bio-petroleum is mainly composed of benzene derivatives and long-chain alkanes, which are also the main compositions of diesel oil. Then, the bio-petroleum was distilled and the distillation fractions at different boiling points (<120oC, 120-180oC, 180-240oC, 240-350oC) were obtained, among which the fraction of 240-350oC was much close to diesel oil in composition. However, this fraction has been observed to change color, from a clear transport hue when when it is just produced to dark brown after several days of storage. Thus, acid activated bentonite was selected to remove the colored pigments arising from the unsaturated carbonyl groups, polycyclic aromatic hydrocarbons, quinines and nitrous compounds, etc. which were analyzed by using GC-MS and different from those in the fossil petroleum (the compounds containing sulfur, nitrogen and oxygen). As expected, the color of the decolorized fraction is almost the same with that of diesel oil. The bio-petroleum which is rich in phenol derivatives was obtained from cotton stalk by deoxy-liquefaction under certain conditions. Then, the bio-petroleum was rectified and the fraction (180-260oC) was obtained, in which the content of phenol derivatives was as high as 78.84%. When the fraction was bathed with NaOH solution, the oil phase and water phase were separated. The phenol derivatives in water phase were separated by adsorption with the organobentonite and extraction with the organic solvent. The results showed that the latter was better in separating more pure phenol derivatives.In a word, the liquid fuel which is similar to diesel oil both in composition and in quality is obtained through upgrading of bio-petroleum and can be used as transport fuel. In addition, the phenol derivatives can be separated from the bio-petroleum. Therefore, bio-petroleum has a developing potential not only as a renewable fuel but as the valuable chemical feedstocks.