Friday, December 31, 2010

Corn Fractionation

The germ, pericarp fiber, and endosperm fiber can be recovered as coproducts in addition to ethanol and DDGS through dry-grinding ethanol process or a modified dry-grind process (E-Mill)

Removal of the suspended solids improves both the fermentation rate and ethanol productivity because such solids interfere with the enzyme kinetics, heat transfer and mixing of the mash. In addition, other benefits can be obtained as follows:

   • Recovery of germ as valuable coproducts that can increase plant capacity and protein content of DDGS
   • Recovery of coarse fiber as valuable coproducts that can be used for the production of corn fiber oil,corn fiber gum, as well as corn ethanol, resulting in an increase in capacity of plant,protein content of DDGS, and reduction in fiber content of DDGS.
  • In Enzymatic Milling Process, recovery of pericarp and endosperm fiber as valuable coproducts can increase plant capacity and protein content of DDGS as well as reduce significantly fiber content in DDGS. In addition, the use of GSH enzymes during E-milling can results in a synergy effects, i.e. improving the fractionation process and converting starch into dextrins and sugars for fermentation.

Wednesday, December 29, 2010

Granular Starch Hydrolysis

Granular Starch Hydrolysis with external enzymes or corn with expressed enzymes:


• Use granular starch-hydrolyzing (GSH) enzymes (e.g., Stargen from Genencor or BPX from Novozymes) to convert starch into dextrins at temperatures lower than 48 C and hydrolyze dextrins into fermentable sugars during SSF


• Not require heating of the corn slurry to high temperatures for cooking or liquefaction; therefore, GSH enzymes reduce the overall utility requirements of the dry grind process.


• With GSH enzyme, the liquefaction, saccharification, and fermentation steps can all be combined into one single step. Compared to conventional enzyme treatments,
      o No increase in viscosity of the corn slurry that occurs during gelatinization and cooking; Therefore, higher concentrations of solids can be used in corn slurries, which allows the fermentation to reach increased final ethanol concentrations
     o Glucose concentrations with GSH enzymes are typically lower but the final ethanol concentrations and ethanol yields remain similar.
     o glycerol concentrations are lower for GSH treatment so that yeast cells are thus subjected to a low osmotic stress; thus improving the overall productivity by lowering the production of glycerol


• The cost of GSH enzymes is approximately double that of conventional enzymes; but overall material, capital, and operational cost may be advantageous.


In addition, if using enzyme expressed corn seeds as feedstocks, the cost of enzyme will be signifcantly low.

Tuesday, December 28, 2010

High Gravity Fermentation

A high final ethanol concentration during ethanol production will improve the plant profitability by reducing water usage, increasing the plant capacity, and decreasing the downstream processing costs, thereby improving plant efficiency. High final ethanol concentrations (i.e., >14 %) can be achieved by high-gravity fermentation. At a high initial dry solids content (~33 %), it is particularly important to ensure that the nutritional needs of the yeast are appropriately met as a preventive measure to avoid stuck or sluggish fermentations.

It has been found that temperature staging (33 C during early stage and 28 C or lower during later stages) is also important to complete a high-gravity mash; The addition of proteases, urea, Mg2+, yeast extracts, and amino acids, have all been reported to provide useful nutrients to yeasts, thereby increasing fermentation rates and final ethanol concentrations in high-gravity mashes.

Monday, December 27, 2010

Dry-mill corn ethanol process

 In a conventional dry-grind process, corn is ground and mixed with water to produce slurry. The slurry is cooked; starch in the slurry is liquefied, saccharified, and fermented to produce ethanol. The remaining nonfermentables in corn (germ, fiber, and protein) are recovered together at the end of the dry-grind process as an animal food coproduct called distiller dried grains with solubles(DDGS). Due to its lower capital and production investments than wet-mills, it is still the dominant process for corn ethanol production nowadays. Conventionally, the process involves the following steps:

Milling. The feedstock (Corn) passes through a hammer mill to break down the corn kernel into a fine powder.

Cooking. The fine powder flour is mixed with water to obtain ground corn slurry with ~27-37% solids content. The pH of the ground corn slurry can be adjusted with anhydrous ammonia to stabilize within the range 5.5 to 6.5. The slurry is then heated to 85 C (185_F) for 30-45 min, and subsequently cooked with high pressure steam in a jet cooker at 104 C (220 _F). After cooling to 85 C (185 F) and a holding period of 30–45 min, the slurry is reheated and cooked to gelatinize the starch and break down its crystalline structure. The resulting mixture of amorphous starch is called the ‘mash.’

Liquefaction. A unit operation involving an enzymatic digestion of the starch molecules in the mash into imonoeric sugar and oligosaccharides. In this step, alpha-amylase (an endoenzyme ) applied randomly hydrolyzes a-1,4-glucosidic bonds to reduce the viscosity of gelatinized starch, producing soluble dextrins and oligosaccharides.
       • The total alpha-amylase dose:0.2 to 0.4 kg enzyme per metric ton ofvdry solids (0.02–0.04 %, w/w).
       • The common practice: add one-third of the alpha-amylase prior to cooking and the remainder after the jet cooker step. The resulting liquefied corn mash has a typical composition as: maltotetraose and other soluble dextrins 24–35%; maltotriose 1.7–3.3%; maltose 0.4–2.7%; and glucose 0.1–1.3 %; i.e. a starch hydrolysate that has a dextrose equivalent ranging from 10.4 to 19.1 (The dextrose equivalent is a measure of the percentages of glucosidic bonds that are hydrolyzed during liquefaction.)

Saccharification. After the corn mash cools to 32 C, a second enzyme, glucoamylase (,an exoenzyme) is added (0.05–0.08 %, w/w) to catalyze the release of successive glucose units from the non reducing ends of soluble dextrins by hydrolyzing both linear a-1,4-glucosidic and branched a-1,6-glucosidic linkages, resulting in the fermentable sugars, mainly glucose.

Fermentation. The glucose generated by glucoamylase during saccharification step will be fermented into ethanol by yeasts (typically Saccharomyces cerevisiae) and carbondioxide as a by-product. Saccharomyces cerevisiae is the yeast species commonly selected because of its quick, efficient production of alcohol and its ability to withstand heat, osmotic stress and high alcohol concentrations. The fermentation process generally takes about 50 to 60 hours with a final ethanol concentrations of14%- 20% (v/v) depending on the corn slurry solids contents from improved fermentation process. Batch or continuous fermentation systems may be used, although batch processing is more common due to its simple, easily cleaning, and flexibility. Some new fermentation systems are designed to minimize dilution water, which reduces the evaporation requirements in the feed processing stages after fermentation.

Distillation. Distillation is the process of separating the ethanol from the solids and water in the mash. The fermented mash, now called “beer”, is pumped to the continuous flow, multi-column distillation system where the ethanol is removed from the solids and the water. Conventional distillation/rectification methods can produce 95% pure (190 proof) ethanol because the ethanol and water form an azeotrope so that further separation by heat cannot occur. Therefore, the ethanol leaves the top of the final column in the distillation syetem at about 95% concentration, and the residue mash (stillage), is transferred from the base of the column to the co-product processing area.

Dehydration. The ethanol from the top of the column passes through a dehydration system to remove remaining water to obtain anhydrous ethanol (pure, without water, and approximately 200 proof). Most modern dry-grind ethanol plants use a molecular sieve system to produce pure ethanol.

Stillage Processing. The solid and liquid fraction remaining after distillation is referred to as “whole stillage”, which includes fiber, oil and protein components of the grain, and the non-fermented starch.
      The “thin stillage” is first separated from the insoluble solid fraction using centrifuges or presses/extruders and then sent to evaporator units to remove excess water to obtain the thick, viscous syrup, which is mixed back with the solids to create a feed product known as Wet Distillers Grains with Solubles (WDGS) with about 65% moisture.
     Due to its low shelf life and high transportation cost, WDGS is usually dried to 10 to 12% moisture to produce a product known as Dried Distillers Grain with Solubles (DDGS). Although drying distillers grains is energy-intensive, consuming about one-third of the energy requirements of the entire dry-grind plant, , it is essential to produce a uniform, stable, high-quality feed co-product to the profitability of the plant, resulting in most plants producing DDGS rather than WDGS.

Typical Yield from a Bushel of Corn from a Dry-Mill Ethanol Plant

  • 2.7 gallons of ethanol
  • 17.5 pounds of distillers dried grains
  • 17 pounds of carbon dioxide

Tuesday, December 21, 2010

Inhibitors

Inhibitors based on their chemical functional groups can be grouped as aldehydes, ketones, phenols, and organic acids.

  • Aldehyde inhibitors: compounds with one or more functional aldehyde groups, regardless of the base structure of a furan ring, a benzene ring or a phenol-related structure, including
      o furfural and HMF
           Cell walls and membranes of yeast cells grown under furfural and HMF-challenged conditions appear damaged when compared to those of controls grown in the absence of any inhibitor, resulting in the delay of cell growth and reduction of ethanol productivity
           Furfural and HMF inhibit cell growth and ethanol production rates at lower concentrations. Individual strains have been isolated that retain their ability to produce ethanol in the presence of 10 to 79 mM of either furfural or HMF, including strains of these species: Saccharomyces cerevisiae, Pichia stipitis, Candida shehatae, Corynebacterium glutamicum, Zymomonas mobilis, and Escherichia coli.
      o 4-hydroxybenzaldehyde, vanillin, syringaldehyde, isovanillin,ortho-vanillin, Cinnamaldehyde
         more inhibitory than those derived from sugar dehydration

• Ketone inhibitors:4-hydroxyacetopheone, acetovanillone and acetocsyringone
         exert a greater inhibitory effect on bacteria such as Thermoanaerobacter mathranii than on yeasts, in terms of reduced growth and ethanol yield

• Organic acid inhibitors: sharing a common carboxylic acid functional group, all contain a carboxyl functional group such as
       o acetic acid,formic acid, levulinic acid, caproic acid,furoic acid, 4-hydroxybenzoic acid, 3-hydroxybenzoic acid, 2-hydroxybenzoic acid, 2,5-dihydroxybenzoic acid, protocatechic acid, vanillic acid, gallic acid, syringic acid, 4-hydroxycinnamic acid, homovanillic acid, guaiaclyglycolic acid, and sinapic acid. These inhibitors are thought to be exert their inhibitory actions via their carboxyl functional groups.
             more toxic to isolates of bacteria than yeasts at low concentration
             The toxicity has been correlated with their degree of hydrophobicity, suggesting the involvement of a hydrophobic target such as the cell membrane

• phenol-based inhibitors: phenol, benzene-1,2-diol (catechol) etc.
      o cause increased membrane fluidity and affect membrane permeability, which may enhance synergistic inhibition when combined.
      o Phenols such as cathecol, hydroquinone, and coniferyl alcohol almost completely inhibit E. coli , but are relatively less toxic to yeast. However, eugenol and isoeugenol are inhibitory to yeasts at low concentrations.
     o The three main phenol structure building blocks in lignin show the order of inhibitory effects, ranked from strong to weak, as (1) hydroxyphenol, (2) guaiacyl, and (3) syringyl

In general, aldehydes and phenols are more toxic than organic acids.

In addition, some inhibitions will be amplified through process. A typical example is that fermentative microorganisms will be inhibited by concentrated non-volatiles such as lignin derivatives and extractives after concentrating although low initial inhibitor concentration in hydrolyzate.

Monday, December 20, 2010

Van Krevlen diagram: A useful means of comparing biomass and fossil fuels for their heating values



The lower the respective H/C and O/C ratios,  the greater the energy content of the material, because the lower energy contained in carbon–oxygen and carbon–hydrogen bonds, than in carbon–carbon bonds.

Sunday, December 19, 2010

On the way to green fuels

We need make a sound judgement before making a decision.
Read, listen, consult, think, judge, plan, and act!

Important factors that can not be overlooked by using biomass as renewable energy sources

It is believed that burning biomass will not contribute carbon dioxide to the atmosphere because replanting harvested biomass ensures that CO2 is absorbed and returned for a cycle of new growth, i.e biomass emits roughly the same amount of carbon during conversion as is taken up during plant growth. But people have to realize that there is the time lag between the instantaneous release of CO2 from burning biomass energy and its eventual uptake as biomass, which can take many years. Therefore, there is a need to recognize this time delay and take appropriate action to mitigate against the lag period. Most imortantly, the action of consuming biomass resources for fuel  and replacement planting needs to occur concurrently so that the overall resultant from the use of biomass does not contribute to a build up of CO2 in the atmosphere from a long term.

Unforfunately, not amny people realize the time lag and many countries have not implement a programme of replacement planting when they already started harvesting the biomass.

Sunday, December 12, 2010

Analytical Methods for Mass Balances

Biomass compositional data is essential to beginning any study, especially the carbohydrate contents (both soluble and  structural carbohydrates) that is the base to calculate theoretical ethanol and sugars yields, to close carbohydrate mass balances, to determine the enzyme loadings, and to calculate the process efficiencies.
  1. Waxes and fats are extracted into either ether or hexane using sonication.
  2. The soluble sugars are subsequently extracted in 80% (v/v) ethanol, a concentration which is selective for monosaccharides
  3. Wateris then used to extract any water-soluble polysaccharides (e.g., fructans)
  4. Starch is then removed by using amylase in acetate buffer
The final residual material is essentially pure plant cell walls, which is called "structural carbohydrates", including hemicellulose and cellulose. The structural carbohydrates composition will be analysized following two-step acid hydrolysis using H2SO4.

As a complete compositional analysis is labor-intensive, it is often more practical to measure selected components only. Soluble sugars can be extracted by sonication in water if the samples are not to be processed for determining starch contents. For total carbohydrate analysis (including soluble sugars), a two-stage acid hydrolysis procedure similar to NREL protocol can be directly applied to native samples

Saturday, December 11, 2010

Cellulosic biomass pretreatment reactor

A news from Biorefiningmagazine.com reported that  a bench-scale horizontal reactor designed and manufactured by AdvanceBio Systems LLC will be in use by Penn State University for their cellulosic pretreatment research. This is great! If looking at the reactors that have been used in bench top studies on biomass pretreatment, most of them can not be use to run the large particle size (un-milled biomass) with good high shear mixing at high solids content.

Thursday, December 9, 2010

Structural features lead to two-phase enzymatic hydrolysis for mild pretreated biomass

The limiting factors that affect enzymatic hydrolysis of biomass have been traditionally divided into two groups: substrate-based and enzyme based. The substrate-based factors mainly involve chemical structural features such as the compositions of cellulose, hemicellulose, lignin, and side groups bound to hemicellulose and physical structural features that consist of accessible surface area, crystallinity, the physical distribution of lignin in the biomass matrix, degree of polymerization, pore volume, and biomass particle size.

For mild pretreated biomass, the inital rate of enzymatic hydrolysis will be influenced by the transport of enzymes and the dominant hydrolysis will be on amorphous cellulose. At this phase, the hydrolysis of hemicellulose will correlate with the slow increase of glucose yield. When the hemicellulose removal to some point, say 50% removal, a slight hemicellulose hydrolysis will lead to significant increase in cellulose hydrolysis, i.e. crystal cellulose hydrolysis: A transition point occurs, demonstrating the main or 2nd phase hydrolysis.

At 1st phase, lignin content and side groups in hemicellulose play an important role. Any treatments to remove lignin and peel off side groups and break down hemicellulose will improve enzyme transport though opened channels; At the 2nd phase,cellulose crystallility become the limiting factor, any destruction of cellulose crystallility will speed up the hydrolysis and increase the yield.

Wednesday, December 8, 2010

Whole slurry hydrolysis: an approach to produce cheap sugar

Almost all of currently reported  biomass pretreatments are those reqyiring post- liquor/solid separation or washing,  or nutralization, or even detoxification before further processing (hydrolysis), which will add additional cost due to the more step unit operations. A cost-effective pretreatment should be low demand of post- pretreatment processing. A "whole slurry" processing or hydrolysis will be ideal case. Therefore, the pretreatment should not be to acidic or too basic, or too harsher that generate too much toxic compounds. I am working on a process that really can realize this goal.

Tuesday, December 7, 2010

Ionic liquids pretreatment of biomass

Recently more research are conducted on Ionic liquids (< 140 C) pretreatment of biomass, demonstrating
  • Converts Cellulose I to cellulose II, improving cellulose digestibility
  • Deferulylation of biomass, removal of lignin
  •  Cellulose swelling, destruction of cellulose crystal
  •  Work for mixed feedstocks-flexibility on biomass resources

Recovering sugars from ILs has been alos investigated. More questions remain on IL pretreatment:
  • Is it effective on un-mill biomass such as wood chips and 1-2 inche agricultural residues?
  • What about the moisture of wet biomass (in reality, it is hard to dry the biomass with moisture content < 5%) on IL stability?
  • The recovery yield? Can be great than 99%?
  • Any inhibition or toxic on enzymes and fementation microorganisms?

Benefits from Surfactants (Tween and BSA) During Enzymic Hydrolysis

It appears that Tween improves biomass enaymatic hydrolysis through three effects: enzyme stabilizer, lignocellulose disrupter, and enzyme effector. BSA treatment can improve both cellulase and beta-glucosidase activity due to the non-specific competitive, irreversible adsorption of BSA on lignin.

However, all of the research were based on the current leading pretreatment methods. Scince these pretreatments are really cost non-competitive. Any slight improvements in hydrolysis yield and reduction in enzyme loading is negligible compared with the cost of pretreatment and large scale enzyme production.

A cost effective pretreatment must be developed, which does not require harsher conditions (very acidic and very alkaline, and very high temperature). Is it possible? Yes, if we think the chemistry carefully!

When reading the most recently published review paper on pretreatments, nothing new included. I do not understand that there are so many people working in this field, but most of them just copy the ideas and focus on those so-called leading pretreatments.

I think more education on biomass chemistry is really need to train people/students to develop new approches/solve problems before fundemetal understanding of the problems.

Saturday, November 27, 2010

Xylooligomers: Inhibitiors of cellulases

During 2010 AIChE meeting, a paper by Qing Qing from UC Riverside presented their research on "The Mechanism of Inhibition on Cellulose Hydrolysis by Different Chain Length Xylooligomers”. Their research suggests that xylooligomers are strong inhibitors of cellulases (more than xylose, xylan, glucose and cellobiose) based on the experimental results: A trend of decreasing glucan conversion with increasing DP xylooligomers, which was believed to be due to either obstruction of the cellulose by the oligomers, non-specific binding of the cellulases to the xylan or inhibition by the xylooligomers. Protein adsorption tests demonstrated that the spezyme CP cellulase, multifect xylanase, and β-xylosidase bound to the xylooligomers.

Their solution to reduce inhibition was to add the hemicellulases before cellulases. However, the effect was not as big as what expected, probably a synergistic effect is also needed.

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.

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.

Sunday, July 25, 2010

China Overtakes US as World's Largest Energy User

According to IEA, China Passes U.S. as World's Biggest Energy Consumer.

Good news or bad news?

To the global energy resources, it is bad news because it is a giant engine of global energy-demand growth

To the renewable energy developers, it is good news because it means challenges and opportunities, which may stimulate the technological development under the current cool-down environment for renewable energy.

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