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Researchers Develop New Method for the Direct Liquefaction of Biomass to Biopetroleum

8 August 2008

Deoxy
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.

Resources

  • 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

August 8, 2008 in Biomass, Fuels | Permalink | Comments (12) | TrackBack (0)

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Comments

This sounded very promising until I saw the yield. There's no way this will compete with fast pyrolysis with <20% yields.

I wonder how much they net after all that heating, cooling, and distillation. It wasn't clear to me.

The upgrading could take a lot of effort. If the fuel produced a lot of NOx or unburnt phenol that may not be acceptable. On the other hand the big pluses seem to be local production and natural separation of the water. One of the thermochemical methods has to scale up eventually.

What are the byproducts?

"..transporting enough of it economically to wherever it will be processed..."

That is why I favor biomass gasification to methane right where the crops are grown and putting them synthetic methane right in the natural gas pipes.

Old Neil,
are you thinking bio char?

They aks the right question but I am not sure that they provide the right answer. The tranportaion of huge amount of biomass from field to processing plant is still an unsolved issue to scale cellulosic biofuel. The process reported here looks like very energy intensive so doesn't sound like the right thing to do.

If you have a processing plant every 20 miles across Kansas, Iowa, Nebraska and where ever you grow wheat straw and corn stalks, you do not have to transport the biomass very far and the methane is just pumped through pipelines that exist.

Well, this sounds to me like simple slow pyrolysis. And the product is ehmmm... tar. The rest is hmm charcoal. Sure you can use it as low grade boiler fuel, but not for much else.
Simple chemistry rules tell that if you wanna get hydrocarbons from biomass you are gonna have to hydrogenate it. That has been done, Bergius, the german guy who discovered hydrogenation of coal to liquid alkanes/cycloalkanes, did the experiments with wood and demonstrated that it can be successfully hydrogenated too. There were times when they tried to hydrogenate everything - coal, coal tar, petroleum residues, peat, peat tar etc. Thats possible, there were commercial processes and plants. But the overall effectiveness was poor, and the high-pressure equipment very very expensive.

Pure sugar, a simple biomass material, contains 600 pounds of water per thousand pounds of sugar. Thus 400 pounds of carbon would remain if the water were removed. Cellulose has a similar ratio. Then 1000 pounds of sugar could be converted to a maximum of 534 pounds of hydrocarbon if hydrogen were then used to hydrogenate the carbon to hexane.

Simple rules show that bacteria can convert 1000 pounds of sugar to 733 pounds of CO2(carbon-dioxide) and 267 pounds of H2CH2(methane). Or they can convert 1000 pounds of sugar to 657 pounds of CO2 and 343 pounds of H3CH2COH (ethanol). A 20% yield of hydrocarbons does not look bad compared to 27% methane with no hydrogenation. Bacteria cannot work for free so there is much energy loss. It may be best to directly burn biomass for the most efficient use of its energy. ..HG..

..or gasify biomass. This too will give a quantitative yield of gas that can be turned into liquids with high efficiency.

i have research about gasoline convert to petroleum

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