Monday, September 20, 2010

"climate change”: "J-O-K-E" or "J-O-B-S"?

It was the hottest topic sevral years ago, but why not now?
It is crucial to the survival of the world with the investment on energy; but why is it cooling down?


"Aren’t We Clever?" The author gets it but whoelse not?

Sunday, September 19, 2010

Hemicellulose removal on enzymatic hydrolysis

It has been reported (Grohmann et al., 1985, 1986) that hemicellulose removal substantially enhances cellulose digestion despite of high lignin content. It is believed  that hemicellulose in biomass blocks the contact of cellulase with cellulose by adsorbing enzyme and by physically blocking access of the cellulase to the cellulose surface. As a result, hemicellulose removal alone can increase the surface area and pore volume and makes cellulose more accessible to cellulase. It is suggested to remove at least 50% of hemicellulose to significantly increase cellulose digestibility.

Thursday, September 9, 2010

Lignin, its effect on enzymatic hydrolysis

Biomass lignin is an important factor in enzymatic hydrolysis and sugar yields. Several mechanisms have been suggested about how lignin limits enzymatic hydrolysis:


1. toxic to the enzymes for simple phenolic compounds

2. steric hindrance caused by lignin-polysaccharide linkages that limit access of fibrolytic enzymes to specific carbohydrate moieties. For example, the degradation rate of xylan is said to depend on the number and location of side branches and their lignin associations

3. Lignin as hydrophobic filler that displaces water in the cell wall matrix. As a result of the hydrophobicity of lignin, water cannot enter internal polymers of the cell wall. Hence, the action of hydrophilic enzymes may be limited by this hydrophobic environment

4. Adsorption of enzymes, which increases the loading but decreases the effects

Sunday, September 5, 2010

Non-structural carbohydrate in biomass

In extractives, a fraction of chemical components are those containing sugars, referred to as either water-soluble-carbohydrate, or non-structural carbohydrate, or free sugars, which is mostly composed of the monosaccharide of D-fructose, the disaccharide of sucrose, the trisaccharide of raffinose, and tetrasaccharide of stachyose as well as the group of polysaccharides known as fructans. In addition, arabinogalactan can be classified as among the extractives.

These non-structural sugars tend to be intermediates and primary products of photosynthesis and serve functions in storage, translocation, and metabolic utilization of carbon as well as protection against abiotic stresses. They also play an important role in the dynamics of piles of stored biomass.

The non-structural sugars tend to be present in much higher concentrations in grassy than woody feedstocks. As reported (Chen et at, 2007 and 2010),carbohydrates (primarily sucrose, glucose, and fructose) were found to be the predominant water-soluble components of corn stover and switchgrass, accounting for 18-27% of the dry weight of switchgrass extractives and 30−46% of the dry weight of corn stover extractives (4−12% of the dry weight of feedstocks). The actual level of free sugars in harvestable biomass depends on CO2 assimilation and demand for these assimilates, mainly for respiration and the production of protein and structural carbohydrates (White, 1973). Given that such needs vary greatly with growth cycle, nutritional state, tissue, season, and management regimes, the non-structural sugar concentrations tend to be much more dynamic than those of the structural polysaccharides (Wulfes et al., 1999).

Whether or not these sugars add to sugar yields in fractionation procedures will depend on whether or not they are retarded by process conditions.

Saturday, September 4, 2010

What are cooling down the biofuels?

Not long ago, biofuels became a hot topic, formed a wave, and would replace fossil fuels as an alternative energy, which attracted too much attention from scientists, politicians, policy makers, investors, and common people. And eventually
Congress passed the Renewable Fuels Standard in 2007, which by 2022 would require 16 billion gallons of these fuels every year.

However, only a few years, U.S. EPA will drastically cut the amount of cellulosic biofuels that oil companies are required to blend into their fuel stocks under its Renewable Fuels Standard.

What causes biofuels cooling down? It looks like the money holds it back. But government and private investors already poured tons of money into the areas in the past. Where and when do they get paid off?

Actually the cooling down of biofuels demonstrates the loss of confidence and patience. Recently people always want to get payback as short as possible for their investment. However, biofuels production is a sunrising industry and still in its infancy although many "experts" claimed their technology advanced and can blabla....In reality, real professionals know the truth.

When biofuels became hot, almost overnight, thousands of people stood out to be biofuel experts. Some of them are truly biofuel professionals. Unfortunately, quite a lot of them are not! Those who are not experts but have capability to impact people mis-leaded the direction of the money invested. Just looking at the some projects that have been supported, they are really out of date and not practical even with some common sense. But they were funded. Meanwhile, some game-players started raising money for their start-up companies. As a result, those technologies are still in the lab or published on paper because of not practical, the money has been used. To be worse, an impression has been given to people: Biofuels are not successful! Bankers are therefore holding the money. The development is losing momentum to move forward. From this point of view, fake experts are really killing biofuels!

It is true that biofuels are the right direction for future energy no matter people admit it or not now. But it will take time to have the viable technology to be developed. It needs more people's patience and more consistent support. Hopefully, the correct voice can be heard by money managers, consultants, financial planners, speculators, and environmentalists and their continuous support are sustainable. If so, it will be fortunate for biofuels and of course for our grandchildren.

Enzymatic deconstruction of xylan for biofuel production


A review paper by DODD et al titled "Enzymatic deconstruction of xylan for biofuel production" summarizs current understanding of the molecular basis for substrate specificity and catalysis by enzymes involved in xylan deconstruction.

Xylan is the dominant hemicellulose in hardwood and non-woody biomass. Its deconstruction to monomer sugar not only contributes to the source of sugars but also enhances the exposure of cell wall to enzyme/chemical hydrolysis.
production.

Xylan is known a heteropolymeric substrate consisting of a repeating β-1,4-linked xylose backbone branched with acetyl, arabinofuranosyl, and 4-O-methyl glucuronyl groups (Figure 1).In addition, xylan may be cross linked to lignin by aromatic esters. In order to efficiently depolymerize xylan to the component monosaccharides, a mixture of different enzymatic functionalities are required, including endo-1,4-β-xylanases (EC 3.2.1.8), β-D-xylosidases (EC 3.2.1.37), α-L-arabinofuranosidases (AFs) (EC 3.2.1.55), α-glucuronidases (EC 3.2.1.139),acetyl xylan esterases (EC 3.1.1.72), and ferulic/coumaric acid esterases (EC 3.1.1.73).



A better understanding of the structural diversity in xylan and the corresponding enzymatic strategies employed by microbes will be critical to hydrolyze the linkages within this complex heteropolymer.

Ethanol yield and titer

An economically-attractive cellulosic technology almost certainly requires the strain to achieve ethanol yield, titer and rate higher than 90%, 40 g/L (5.1%v/v),1.0 g/L/h, respectively.

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