Mark Cox and Olushola Ashiru, NEF Advisors, LLC.
Global efforts to reduce greenhouse gases have led to the growth of biofuels and carbon neutrality. In the US, ethanol originates from the corn crop (as well as sugar cane) where the starch in the corn kernels is fermented and distilled. Using corn for fuel in the US absorbs 40% of the annual corn harvest and produces about 15 billion gallons of ethanol. This, initially caused corn prices to climb, affecting food markets globally. The effectiveness and energy balance of corn ethanol is critical. Farmer’s have done their best to optimize the efficiency via innovation and process engineering. Ethanol is blended with gasoline in the US to become approximately 10% of the American gasoline liquid fuel.
Cellulose is composed of sugar and is an ideal alternative to corn or the juice from sugar cane. As a non-food biofuel feedstock, cellulose reduces GHG by 88%, while corn and other precious foods used for fuel offer just a 20% GHG reduction. Cellulose is abundant, carbon neutral and is an existing bi-product of food production in agricultural wastes. Sugar cane bagasse and the corn plant (including the stover) alone produce multiples of the sugar that the food part of those plants currently produces. The staggering promise of cellulosic biofuels has of course brought out the best in innovative capabilities.
The cellulose molecule has defenses that have made it extremely difficult to break down. Scientists call this ‘recalcitrance’. Below are four imperfect techniques to release the underlying plant’s sugars. Various governments of the world and hundreds of companies have invested billions of dollars into researching solutions for this challenge and in June of 2015, decision makers are still unaware of any efficient, economic, scalable solutions.
1. Acid hydrolysis employs the use of dilute acids to bathe the cellulose. You can also use alkali chemicals to reduce the cellulose and the different approaches have different success rates at converting the biomass.
2. Enzymes are nature’s way of accessing the sugars available in biomass. Inevitably they are more like costly drug companies with white coated Ph.D.’s than any elegant solution they pretend to be.
3. Gasification is a way to heat or pyrolyze biomass until it releases its organic molecules as gas, or syngas. Extremophile bacteria consume the syngas and release ethanol.
4. Using the Supercritical water method, the biomass is heated with water, in a pressure cooker. At high temperature and pressure the water and steam become a plasma in which the lignocellulosic material simply falls apart.
Using ‘pretreatment’ used in the first two methods, breaks up the material. Chemicals, steam or solvents persuade the lignin to let go. These methods are rarely cheap, rarely quick and almost never have 100% conversion. The aforementioned qualities however are found with the 145 year old ball mill.
The ball mill is so simple it can hardly be called a technology. An electric motor rotates a metal cylinder with ball bearings inside. These pummel anything that is placed inside into a powder with particle size as small as 5 nanometers with no expensive chemicals or high temperatures. Talcum powder or cement are existing and familiar ball mill products. It achieves consistent residence times of 15 minutes and obtains 100% conversion of any source of lignocellulosic biomass into its constituents; lignin, C5 and C6 sugars even without any liquids. The low input costs suggest the final price of the finished sugar can be lower than 5 cents per lb. compared to $0.12/lb., current global market price. In retrospect, the ball mill is the elegant, convenient, fast, simple and economic solution that the world has been looking for to reduce cellulose.