From sawdust to petrol

As world governments mull over global emission targets agreed at last December’s United Nations Climate Change Conference (COP 21), attention is turning to which new technologies can help them achieve this.

Researchers at the University of Leuven say they have part of the answer, having devised a way to convert sawdust into valuable chemicals and the building blocks for gasoline. By developing a unique chemical process in their laboratory at the Centre for Surface Chemistry and Catalysis, outside Brussels, they can convert the lignin in sawdust into aromatic chemicals and the cellulose into hydrocarbon chains.

The hydrocarbons can be used either as an additive in gasoline or as a component in plastics.

Cellulose is the main substance in plant matter, present in all non-edible plant parts of wood, straw, grass, cotton and old paper, and containing strong carbon chains. Researcher Beau Op de Beeck developed a new method to derive these hydrocarbon chains from cellulose, while removing the oxygen inside, deemed undesirable in gasoline.

The university has a patent pending for its new type of bio-refining and built a unique chemical reactor.

Researcher Sander Van Den Bosch told Reuters that wood has three main components - lignin and two carbohydrate fractions, cellulose and hemicellulose. The cellulose is the key ingredient of these for making gasoline, but the lignin can also be converted into valuable chemicals for plastics or medicines.

“We add wood to a reactor and then we also need a catalyst, which is a specific material that will do the chemical reactions in the wood so it will selectively depolymerize our lignin material into chemicals; and then last but not least we also need solvent to extract the lignin out of the solid material and there we can use water for or also various kinds of bio-derived alcohols,” Van Den Bosch said.

He added: “There are now already processes on a large scale that use the carbohydrates, such as the production of paper or the production of bioethanol, but lignin is still undervalued, so most of the times it’s just burnt for energy. What we invented in our process now is the simultaneous extraction of the lignin from the carbohydrates in the wood and also at the same time we convert the lignin very selectively into chemicals.”

Then it takes about 12 hours to convert the remaining cellulose in the wood shavings into saturated hydrocarbon chains, say the team, leaving one simple step to becoming fully-distilled gasoline.

Colleague Wouter Schutyser said woods from birch, poplar, and conifer trees work particularly well, and that by converting waste woods the environmental impact is minimized.

“What’s really interesting is that we can also convert waste woods...used for construction, for furniture,” said Schuyser. “These contain not only just wood, but also contain paints and other stuff, so we try to convert this, which is used as a low value energy source at the moment and we try to make high value chemicals and fuels from it.”

The team has produced gasoline that could power a vehicle on its own, but say that in the short and medium term it would be best used as an additive in petroleum to help reduce impending CO2 emissions.

According to researcher Aron Deneyer, “we get the identical structures as we have from crude oil, so we have a very interesting fuel that we can use immediately but we think it’s better to use it as an additive because in the short term you have a lot of targets we get from the European Union and from different governments to tackle problems like climate change and things like that. So we can tackle it by adding some percent(age), small percentage - five percent or something - into gasoline.”

Deneyer told Reuters the CO2 produced by their biomass-produced gasoline was less problematic for the atmosphere than that produced by petrochemicals.

“When we produce our light naphta we burn it in our car and we get some CO2, but this CO2 can be used to build new biomass and so we have a very short cycle, while crude oil will last a very long cycle to replace the crude oil,” Deneyer said.

The researchers reported their findings in the journal Energy & Environmental Science.