ECN is developing processes for biorefining wheat straw and other residual streams such as forestry residues and grass. On a laboratory scale, it is already possible to convert wheat straw into alcohol, phenol compounds, other products and biogas. ECN will scale this process up in the short term and continue its development in collaboration with Dutch companies, says Hans Reith, Coordinator Biorefinery at ECN's Biomass, Coal and Environmental Research unit.
Reith: “Abengo, Nedalco and other producers of bioethanol currently produce so-called ‘first generation’ bioethanol using agricultural raw materials such as wheat or corn starch and cane sugar. These companies are also working hard to realise the production of bioethanol using ‘second generation’ materials such as straw. At ECN, we focus on biorefining these residues. The aim is to co-produce biofuels, chemicals, electricity and heat. This does not conflict with food production and enables all parts of a crop to be put to use.”
Reith explains the steps involved in the biorefining process: “Wheat straw, for example, contains the same substances as wood: cellulose, hemicellulose and lignin. In our process, called Organosolv, we separate these substances in a way comparable to separating oil fractions in a refinery. At ECN, this research is led by Wouter Huijgen. First we pre-treat the straw with an alcohol/water mixture for roughly thirty minutes at a temperature of 200 °C and a pressure of 20 bars. During this step, the lignin and hemicellulose dissolve into the mixture of water and alcohol. The cellulose fibres remain intact and can be filtered out. Subsequently, the lignin is separated in a solid form, while the hemicellulose remains in solution. Thus, we can separate the lignin from the hemicellulose. We intend to make this process continuous, because this is a requirement for using it on an industrial scale.
Challenge
“The cellulose can be converted into glucose with the help of enzymes. In turn, the glucose can be converted into alcohol by yeasts. The hemicellulose can be partially or completely anaerobically digested to produce biogas. Depending on the composition of the hemicellulose fraction, it can also be converted into alcohol using a new generation of enzymes and yeasts,” explains Reith.
“Lignin is a glue-like substance that, together with hemicellulose, connects the cellulose fibres in plants and gives plant stems their strength. It is a sticky substance consisting of a network of phenol compounds. People once said that you can make anything from it except money. This is why it was a challenge for ECN to find a process to convert lignin into valuable products. This can be done using pyrolysis,” explains Reith.
Paul de Wild, who is conducting the pyrolysis research: “Pyrolysis involves heating the lignin without the presence of oxygen in an atmosphere consisting of pure nitrogen or steam at temperatures of 400 °C to 600 °C. Under these conditions, a catalyst helps to break the lignin down into 20% biogas, 55% oil and 25% char (a carbon-containing residual product). The oil produced consists of 75% phenol compounds, water and small quantities of acetic acid and methanol. Breaking down lignin into valuable products is an art in itself, because it melts easily. Before you know it, the whole installation can get clogged up with melted and partially carbonized lignin. We found a solution to these problems, which allows us to pyrolyze lignin effectively to produce valuable products. We are now able to convert more than 50% of the lignin into phenolic oil, a raw material that is quite suitable for producing valuable chemical substances. ECN has a patent pending for this innovative catalytic process. We are going to scale up and optimize this process further in an attempt to produce an even higher yield of phenol compounds,” says De Wild.
The earth's crust isn't the only place to find oil: refined agricultural residues can also be a source (Photos: ECN).
Applications: from glucose to soil improvers
“In brief: biorefining wheat straw using our Organosolv process produces highly purified cellulose and lignin as well as a hemicellulose fraction. We can convert 90% of the cellulose into glucose that can be further converted to a range of products via fermentation. Alternatively, the cellulose can be used in the production of paper. In addition, we can separate out more than 70% of the lignin, which can then be converted into valuable products using pyrolysis. The hemicellulose can be used to produce biogas or ethanol, or chemicals such as furfural. We are still working on optimizing the conversion of hemicellulose," says Reith.
ECN is considering various applications for the phenol compounds produced from lignin, including biobitumen mixed into asphalt, bioresins for chipboard, conversion into monomers for bioplastics and a fuel additive. The char produced is suitable for use as a soil improver. It stimulates the growth of soil bacteria and can result in savings because less fertilizer is needed. Use as active coal is also a possibility. ECN is talking to various companies about the various applications.
Reith outlines the economic perspective of biorefining wheat straw: “Making ethanol from straw is still 50% to 100% more expensive than producing ethanol from wheat grain or sugar cane. For this reason, biorefining of straw is profitable only if sufficient profit can be made on the sale of biogas and, in particular, the phenol compounds. This is why we have invested so much effort into identifying a process that makes the valorisation of lignin an economically feasible option. Reith estimates that the biorefining of wheat straw will be used commercially in five to ten years’ time.
In the field of biorefining, ECN is collaborating with various universities and companies in the Netherlands and Europe, including the European BIOSYNERGY project. Hans Reith is coordinating this project. On November 17 2010 a workshop was held in Reims, France, in which the results of the four year project were presented. ECN is also contributing to the EU BIOCORE biorefining project, which has started recently.
Contact
Hans Reith
Biomass, Coal & Environmental research / Transportation fuels & Chemicals
Tel.: +31 (0)22 456 43 71
Email: Hans Reith
Text: Erik te Roller
Info
European project BIOSYNERGY
European project BIOCORE
ECN-research into biorefining
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