|Schematic diagram of the deoxy-liquefaction reactor. Click to enlarge. Credit: ACS|
Researchers at the Chinese Academy of Sciences (CAS) have developed a new method for the direct liquefaction of biomass to a bio-oil with an attractive heating value (HHV 46.9 MJ/kg) and consisting mainly of alkanes (C7-C19) and benzene and phenolic derivatives. The product has low oxygen content and an elemental analysis similar to that of petroleum. The product, which they term “biopetroleum”, can then be upgraded for use in transportation fuels or chemicals. A paper describing their work was published online 8 August as an ASAP article in the journal Energy & Fuels.
One of the challenges in using biomass efficiently to produce fuels is transporting enough of it economically to wherever it will be processed. As a result, direct liquefaction technologies such as pyrolysis are of increasing interest. The concept is that the biomass can be liquefied close to the source and then transported more efficiently in its more energy-dense liquid form for further processing.
Fast pyrolysis is an effective conversion method with high liquid yield. However, notes the CAS team, the oil obtained from fast pyrolysis consists mainly of oxygenous compounds, such as aldehydes, ketones, esters, and ethers, and has a low heating value (20-25 MJ/kg). It thus requires significant upgrading before use as a transport fuel. Furthermore, while easier to transport, the acidity and corrosive aspects of pyrolysis oil make it hard to store.
In contrast, the new CAS process yields product with only 2.9 wt% oxygen. Because of the low oxygen content, the CAS team termed their process “deoxy-liquefaction”.
The CAS researchers used an experimental tubular stainless-steel reactor into which they placed dry sunflower shells with only 10 wt % distilled water as a medium. The reactor was heated to different final temperatures of 350, 400, 450 and 500°C at a rate of 80°C/minute; the final temperature was maintained for 20 minutes.
The initial atmosphere of the airtight reactor was vacuum, while the final pressure of the system can reach 12-20 MPa after heating. The final pressure, which increased with final temperature, has nearly no effect on the results.
After cooling to room temperature, the residue was further distilled from room temperature to 400 °C at normal pressure to obtain water and biopetroleum, which floated on the water.
The liquid oil yield increased from 18% (350°C) to the maximum yield of 19.2% (450 °C) and then decreased to 5.25% (500°C). Although the oil yield is a little lower than that referred in other literature, the oil contains more alkanes with a HHV. Therefore, it has more potential to be a substitute for petroleum fuels.
The researchers are currently exploring upgrading the biopetroleum.
Shipeng Guo, Libin Wu, Chao Wang, Jinhua Li, and Zhengyu Yang (2008) Direct Conversion of Sunflower Shells to Alkanes and Aromatic Compounds, ASAP Energy Fuels doi: 10.1021/ef800283k 10.1021/ef800283k