Biofuels from Cellulose-based Waste

The growing demand for biofuels, especially in the wealthy developed countries is putting pressure on food crops such as corn, soy and sorghum. Farmers in both developed and developing countries are replacing food crops with crops for ethanol, as they get higher prices and often incentives for these biofuel crops.

As a result, grain and soy prices are going up, and people in poorer countries are facing food shortages. To relieve this pressure, scientists in Australia and the US are developing ways of converting lignocelluloses from plant waste rather than crops to renewable biofuels.

In Australia, Dr Steven Loffler of the CSIRO’s Energy Transformed division and colleagues from Monash University in Melbourne have created the Furafuel Process which produces a stable bio-crude oil from lignocellulose found in green waste such as waste paper, garden waste, crop residues and forest thinnings. The technology makes it economical to produce this biocrude in local areas for transport to a central biorefinery, rather than transporting the bulky green waste to the refinery.

The biocrude oil can then be further refined to produce high value chemicals and biofuels, including both petrol (gasoline) and diesel replacement fuels.

“By using waste, our Furafuel technology overcomes the food versus fuel debate which surrounds biofuels generated from grains, corn and sugar,” said Dr Loffler.

He said that by making changes to the chemical process of breaking down the constituents of plant-based waste, “we’ve been able to create a concentrated bio-crude which is much more stable than that achieved elsewhere in the world,” “This makes it practical and economical to produce bio-crude in local areas for transport to a central refinery, overcoming the high costs and greenhouse gas emissions otherwise involved in transporting bulky green wastes over long distances.”

While it is not yet ready for commercial production, small-scale experiments have proved that the process is efficient and economical. Once laboratory trials of the biocrude are completed, CSIRO and Monash will patent the Furafuel process.

Lignocellulose Key to Plant-based Ethanol

Both the CSIRO’s Furafuel process and another biofuels process being trialed at the University of Massachusetts Amherst catalyse lignocelluloses from plant waste to produce ethanol.

Lignocelluloses are increasingly favoured around the world as a raw material for the next generation of bio-ethanol, as it’s a renewable energy source that, unlike most, is not based on a food crop.

“Lignocellulose is both renewable and potentially greenhouse gas neutral. It is predominantly found in trees and is made up of cellulose; lignin, a natural plastic; and hemicellulose,” Dr Loffler said.

Wood and grass are the raw ingredients for a new method of producing biofuels called catalytic fast pyrolysis, developed by George Huber of the University of Massachusetts Amherst.

Dr Huber, a professor of chemical engineering, has received a $400,000 grant from the US National Science Foundation to continue his research into the process An initial report was published in the April 2008 issue of ChemSusChem, a publication devoted to environmentally-sound chemistry.

He is recognised in the US as an expert on biofuels. In 2007 he chaired a workshop on ‘Breaking the Chemical & Engineering Barriers to Lignocellulosic Biofuels’ in Washington, D.C., for the National Science Foundation and the US Department of Energy. The workshop was attended by experts from academia, industry and governmental agencies.

“We’ve proven this method on a small scale in the lab,” says Huber, a professor of chemical engineering. “But we need to make further improvements and prove it on a large scale before it’s going to be economically viable.”

Two Approaches to Making Ethanol from Lignocellulose

Ethanol production from cellulosic biomass currently involves multiple steps, including pretreatment, enzymatic or acid hydrolysis, fermentation, and distillation. Other processes for making biofuels are hamstrung by similar multi-step methods.

The two researchers and their teams are approaching the same problem from different angles. For the Australians, it’s to do the all initial stages to the point of a producing a crude oil at a local site, say a forestry plantation, or local green waste repository, and then transport the concentrate to a central distillery for distillation into high value chemicals and biofuels, thus overcoming the high costs and greenhouse gas emissions involved in transporting bulky green wastes over long distances.

Dr Huber claims to have invented a one-step process to create gasoline range hydrocarbons from lignocellulose.

Catalytic Fast Pyrolysis

Solid biomass feedstocks such as wood is placed in a reactor, which is basically a high-tech still for thermal conversion of feedstock to gasoline. The feedstock is heated by a technique known as catalytic fast pyrolysis, heating the biomass rapidly to between 400 and 600 degrees Centigrade, followed by quick cooling. By adding zeolite catalysts to this process, gasoline range hydrocarbons can be directly produced from cellulose within 60 seconds.

“This is a big improvement because it’s all done in one single step, instead of several stages,” Huber said.

“Also, because of the high temperatures we use in the process, the residence time in our reactor is two to 60 seconds. With cellulosic ethanol, your residence time is five to ten days, which means you have to have a huge reactor costing much more money. So we estimate that building a facility to use our process would be much less expensive.”

He offered some comparison figures based on the cost of dry wood in Massachusetts, which he is using as a biomass feedstock. This currently costs $US40 a ton, and he estimated that a gallon of green gasoline could be produced for between $1 and $1.70, depending on how much the catalytic conversion in his process can be improved through standard engineering techniques.

Scaling Up for Commercial Production

Both Dr Huber and Dr Loffler’s methods of producing ethanol from lignocellulose have been shown to work in small scale experiments. Neither has yet produced a commercially viable method.

CSIRO plans too patent the Furafuel method and then work with commercial partners to develop onsite converter equipment for organizations such as local government authorities, forestry bodies and waste recyclers.

Huber has received a $30,000 grant from the UMass Amherst Office of Commercial Ventures and Intellectual Property, to develop a prototype reactor to demonstrate green gasoline production on a large scale.