Wednesday, October 20, 2010

One step liquefaction,saccharification and fermentation in dry-mill corn ethanol process

    In the typical dry-grind process corn ethanol production, high sugar concentration often occurs at SHF process as well as the initial phase of SSF process, which cause the mash to have a high osmotic pressure resulted in the production during the fermentation process of higher concentrations of glycerol as glycerol aids yeast with osmoadaptation. As a result, the osmotic stress negatively affects yeast performance. One of the technological improvements is to use granular starch-hydrolyzing enzymes during corn liquefaction and saccharification.

Granular starch-hydrolyzing (GSH) enzymes can convert starch into dextrins at temperatures lower than 48 C and hydrolyze dextrins into fermentable sugars during SSF. Therefore, there is no need to heat corn slurry to a higher temperature for liquefaction in the dry-grind process, which allows liquefaction, saccharification, and fermentation steps to be combined into one single step. The advantages are found as follows:
  • avoid the increase in viscosity of the corn slurry that occurs during gelatinization and cooking in the conventional process because the rate of glucose production by GSH enzymes parallels the rate of glucose fermentation by yeast
  •  yeast cells are subjected to a low osmotic stress due to the low production of glycerol 
  •  Low glucose concentration but similar final ethanol concentrations and ethanol yields 

Sunday, October 17, 2010

Pretreatment: the last rice straw to knock down the camel?

As a crucial step in the biological conversion to ethanol, biomass pretreatment is often regarded as one of the main economic costs in the process,even described as the second most expensive unit cost in the conversion of lignocellulose. But what pretreatment does it refer to? Sream explosion? Dilute acid? AFEX? Lime? Hot water? organosolv? alkaline? or Ionic liquids? Why not others?

Idealy, a cost effective pretreatment should be the one that uses less chemical at low temperature with little or no inhibitory products. Is it possible? Why not?  For all the pretreatments reported, Soaking Aqueous Ammonia (SAA) is relatively a decent pretreatment method that performed at lower temperature with both glucan and xylan retained in the solids and lower amount of inhibitory compounds released form sugar degradation. After fundemental understanding of linocellulosic chemistry (rather just read the review papers), I believe that a better or improved technology can be potentially developed.

E15 ethanol approved in US for year 2007 and newer cars and light trucks: A clear message!

On Octorber 13, the U.S. Environmental Protection Agency (EPA) announced to waiver a limitation on selling fuel that contains more than 10 percent ethanol for model year 2007 and newer cars and light trucks.  Although the initial impact of the ruling is likely to be minimal and it will take several more steps for federal, state and industry towards commercialization of E15 gasoline blends, no doubt, it sent out a clear massage under the current cool-down atmosphere for biofuels and renewable energy:

1. Clean and renewable is the direction of future energy supported by US government
2. The new rule creates additional demand on fuel ethanol that will open up more market
3. An incentive to create green job opportunities and drive green economy

To avoid the impact on food prices in the future, the advanced biofuel, i.e cellulosic ethanol is still the ultimate solution.

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