Biofuels, and the Crossing of the Rind

February 17, 2014 |

coffeeNew separation technologies offer a route to massive cuts in the cost of biofuel production, by changing the way we extract useful sugars.

Consider, as you may some time this morning, the cup of coffee.

A/k/a the Hot Java, the joe, the brew, the cuppa, the fix, the morning thunder, the jitter juice, or the bolt of black lightning.

There’s been a whole lot of chopping, cooking and water infusion to get behind the peel, or the rind, and extract the caffeine and flavorings you seek — leaving a pile-up of berry waste and coffee grounds, and a smile on your face from what may be your first genuinely pleasant “ah!” of the morning.

If we were to describe this as a separation technology, you might think that’s a fair way to think about it. What you might not know is that there’s an entire life cycle assessment devoted to the subject of the energy it takes to make your morning joe.

Bottom line, 1.94 megajoules of energy, 28.83 liters of water (about 7 gallons), and 114 grams of CO2 equivalence, per cup.

Which is to say, to provide a blast of morning helper to the global population would require 798,000 metric tons of CO2 emission, 17 trillion gallons of water, and 1,300,000 gigawatt hours of energy, per year.

Which is to say, more energy than California produces, plus the emissions equivalent of putting 150,000 cars on the road each day, and enough water to cover the entire state of Colorado to a depth of one foot.

Which is to say, good enough for coffee, but no way to run a planet. That is, traditional biomass separation technologies could use a technological breakthrough.

The problem of biofuels and separation

Which brings us to the separation of lignin from hemicellulose and cellulose — traditionally accomplished by a combination of chopping and cooking. Much of the cost of making fuels from cellulosic material is simply the cost of getting the cellulose isolated in the first place — from the lignin that gives structure, strength and protection to the plant.

If you’ve been reading about the debilitating effects of “20-cent sugars” on the economics of biofuels — and the relentless search for “10-cent sugars” — well, that’s all about reducing the cost of isolating and capturing those usable sugars through new technology.

The Breakthrough at Eindhoven University of Technology

Which is why it is a big deal that Eindhoven University of Technology (TU/e) signed an agreement last week with 14 European paper producers for the further development of a breakthrough new solvent. This new solvent, developed by TU/e professor Maaike Kroon, will potentially enable the paper industry to make big energy savings in production and to use raw materials more efficiently. The European paper industry has high expectations of the new solvent.

The new process is expected to reduce the energy consumption of paper industry by 40 percent, after Kroon discovered that wood fibers easily dissolve in specific ‘deep eutectic solvents’ (DES).

In the production of paper, the basic vegetable material (lignocellulose), such as wood chips or other biomass, has to be separated into lignin and cellulose.

Dissolving the wood chips has up to now not been an option because lignin is normally insoluble. But the new solvent, which Kroon has patented, makes this possible. As well as that the new solvent is entirely vegetable-based and biodegradable. Another advantage is that the new process produces very pure lignin, which the paper industry can use to develop new applications and markets such as making biodegradable plastics.

“This is a game changer, and it means the paper industry will look very different 20 years from now”, said Henk van Houtum, chairman of VNP, the Royal Netherlands’ paper and board association.

Large-scale applications are expected to be possible in around 15 years. The laboratory research will take another five to ten years, with a similar period being required for optimization in the pilot plant.

Deep eutectic solvents were discovered in 2003 in the UK. They consist of a mixture of two compounds which, once they have been combined, have a much lower melting point than that of the individual components. Kroon believed that DES would make it possible to dissolve biomass, which formed the starting point for her present work. And it has indeed led to a process for dissolving lignin using different mixtures for specific types of wood.

The invention

In a patent app for the proces, the team writes:

“Deep eutectic solvents (DESs) were presented by Abbott et al. (2004) for the first time as suitable alternative solvents compared to conventional ionic liquids (ILs). The main constituents of these eutectic mixtures are solids with high melting points that show strong hydrogen bonding interactions.

Most DESs share some of the promising solvent characteristics of ionic liquids. They often show low volatility, wide liquid range, water-compatibility, non-flammability, non-toxicity, biocompatibility and biodegradability. In addition, they can be prepared from readily available materials at high purities and low cost compared to ionic liquids, and they can be considered as environmentally benign solvents.

In a future bio-economy, finding a suitable solvent for lignocellulosic biomass has become the Achilles’ heel of renewable biofuels processing. Conventional methods for biomass deconstruction into cellulose, hemicelluloses and lignin bioproducts often require extreme and expensive techniques (e.g. steam explosion, high temperatures, addition of strong acids/bases) resulting in degradation and the occurrence of undesired side reactions (e.g. the synthesis of hydroxymethylfurfural).

It is noted that in this invention, we are providing new types of (nature-based) deep eutectic solvents (DESs) or low transition temperature mixtures (LLTMs) and we are dissolving the lignin (and not the cellulose) from the lignin-containing biomass. Examples of a lignin-containing biomass are wood, wood residues, paper, straw, corn, stover, sugarcane, bagasse, saw mill discards, paper mill discards, municipal paper waste, or the like.
In one embodiment, the solvent has two or three renewable components that have a high melting point (60–400 Celsius). The mixture has a much lower melting point (always lower than working temperature, and often even lower than room temperature).

Examples of hydrogen bond acceptors are amino-acids, salts, organic salts or natural salts. Examples of hydrogen bond donors are urea, organic acids, alcohols, polyols, aldehydes, carbohydrates or saccharides. The solvent is able to separate lignin and cellulose in a very energy-efficient way without the occurrence of any degradation.

In another example, the remaining cellulose and hemicellulose can be hydrolyzed in the solvent at elevated temperatures (about 120 degrees Celsius). This is advantageous because of the catalytic activity of the LTTM (acidity) and because of the tolerance of the solvent for enzymes and its renewability. The dissolved lignin can be recovered from the LTTM by addition of water to precipitate the dissolved lignin from the LTTM. The solvent itself can be recovered by separating off water or using an anti-solvent (e.g. acetone).

The Bottom Line

While 15 years might seem an awful long time to wait — consider that the current wave of technologies — based, for example, on supercritical water, such as Renmatix employs, or a synthetic biology approach to building a low-cost sugar, such as Proterro employes, are coming along much sooner — in Renmatix’ case, commercial deployment is imminent.

The importance of reducing the energy foot print in producing a fermentable sugar can not be overemphasized — for virtually every advanced technology that generates fuels and chemicals through advanced fermentation by designer microbes, breakthroughs in the cost of sugars are considered game-changers in opening up the field for low-cost fuels .

For specialty chemicals and nutraceuticals, price points are so high that even current technologies can be cost-feasible. But getting down the cost-curve doesn’t just mean changing the technology by which we convert sugars — in fact, we may well find that the most important breakthroughs are in the production of industrial sugars, themselves.

More on the patent app.

More on the story.

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