Moderate pretreatment: a practical approach for bioconversion of cellulosic biomass

When pretreating biomass under harsh conditions (extreme pHs and high temperatures), biomass chemical components will degrade into by-products that become inhibitors for the subsequent processing. However, moderate pretreatment can be developed to avoid sugar degradation and toxic compounds formation during pretreatment. As a result, a whole slurry process without inter-stage washing/detoxification can be used, which can significantly reduce capital/operational cost. A moderate pretreatment must remove some lignin but do not break down lignin to simple compounds.It should achieve some defibrillization without much sugar degradation. In a word, It is enough as long as cell wall pores/channels are opened. "Over pretreatment" may improve cellulose accessibility but inevitably cause other chemical components degradation. The right degree of pretreatment is the key. 

The solution to 7 Billion Consuming Resources

On 11/01/2011, the world population hit 7 billion, a warning to the world’s resources: limited food, absolute water scarcity, increasing consumption of non-renewable oil.


One solution: technological advancements and a free market.

• Desalination: to get fresh water from the sea!
• Hybrid and high yield food: Transgenic plants?
• Alternative energy- biofuels,natural power sources like solar and wind may be an alliterative before our fossil fuels run out.

Biomass particle size

It is agreed that biomass feedstock particle sizing can impact the economics of cellulosic ethanol commercialization through its effects on conversion yield and energy cost. Physical size reduction can not always achieve expected effect of biomass enzyme digestibility. For example, the thickness of woody biomass play more critical role in chemical pretreatment of wood chips than its length. Defibrillation of grass biomass is more efficient than size reduction in terms of enzymatic hydrolysis.

Therefore, for practical application, an appropriate size reduction needs to be selected based on the biomass type,what chemicals to be used for pretreatment. The smaller does not mean the best!

Xylooligomers are strong inhibitors of cellulose hydrolysis by enzymes

It has been known that xylooligomers are  the inhibitors to enzymatic hydrolysis. An customized enzyme cocktails have to be developed and applied on specific biomass substrates. Here are two recently published papers reported their research results on this issue.

•  "Supplementation with xylanase and b-xylosidase to reduce xylo-oligomer and xylan inhibition of enzymatic hydrolysis of cellulose and pretreated corn stover".
•  "Hemicellulases and auxiliary enzymes for improved conversion of lignocellulosic biomass to monosaccharides".

The dominating factor for biomass cellulose accessibility to external enzymes:

To improve biomass cellulose accessibility to external enzymes, pretreatment is often required, which seems to plat the following roles depending on the processing conditions:

• lignin or hemicellulose removal
• destroy cellulose crystal structure,
• open channels/cell wall pores
• increase cellulose surface exposure.

Since enzymatic hydrolysis follows the tunneling mechanism: eroding glucose from the inside of cell wall to the outside. Therefore, the pores or channels in cell wall are the dominant factor for the efficiency of enzymatic hydrolysis, i.e. control the rate of diffusion/transport of enzymes and sugar dissolution.

Size reduction by mechanical milling before themo/chemical pretreatment is the worst scenario although the surface area are improved.

Direct one-step conversion of ligninocellulosic biomass to hydrogen-enriched biofuel

The common ways for thermal conversion are fast pyrolysis and hydrothermal liquefaction.

·         The bio-oils obtained by fast pyrolysis are highly oxygenated complex mixtures, which are viscous, corrosive, and relatively unstable. The high contents of water and oxygenated compounds lead to the low HHV and the significant change of the combustion characteristics. They are not miscible with petroleum-based liquids. There is no efficient route for the upgrading needed to produce a motor fuel.

·         The bio-oils obtained by hydrothermal liquefaction are a complex mixture of ketones, aldehydes, phenols, alkenes, fatty acids, esters, aromatics, and nitrogen-containing heterocyclic compounds with high oxygen content and low heating value.

Direct One-Step Conversion of Lignin to Hydrogen-Enriched Biofuel involves in using solvent as the reaction medium and hydrogen donor with/without other catalysts, which can result in gasoline-like hydrocarbon product with high heating value and low char.

Promising New Accomplishments by Biofuel Vehicles

Written by Alan Parker, an active blogger out of New York City whose writing covers green technology, the environment, and the great outdoors.  You can follow him on Twitter @AGreenParker.

It isn't news to anybody that our oil supplies are disappearing rapidly, forcing car companies to develop new technologies that harness the power of alternative energy sources. Although most companies have been working on electric cars, several have also been dabbling in biofuels like ethanol, as a main fuel source for combustion engines. In order to demonstrate the effectiveness of biofuels and increase support for them, some independent research teams have succeeded in some exceptional feats with biofuel vehicles of their own. These accomplishments are showing that greener forms of energy can be used in a practical and effective way to eliminate our reliance on oil and make the environment a healthier place.

Cross-Continental Journeys
At the end of 2010, the first ever ground-based trans-Antarctic expedition was completed using only biofuels. The vehicle, called the Bio-inspired Ice Vehicle or BIV, was funded by biofuel advocate Winston Wong and is the world's first vehicle to complete a trans-Antarctic expedition using this type of power. The BIV was engineered to not only display the potential of alternative energy, but also to stand up to some of the harshest conditions on the planet while carrying researchers across an entire continent.

Setting Land Speed Records
A man named John Petsche set out to modify a Kawasaki motorcycle, aiming to create a vehicle that ran on an alternative fuel source, wasn't complicated or costly, and was designed for fuel efficiency. His result? A homemade motorcycle powered by biofuel. The bike set a land speed record for the 350cc alternative fuel motorcycles at the Loring Timing Association in Maine. The most astounding thing is that John Petsche's motorcycle was built using parts already in existence. Therefore, it should be a simple task for manufacturers to replicate and possibly improve upon the design for mass manufacture.

Distance Records in the Sky
It isn't only land vehicles that are making use of biofuels. Airlines are now beginning to look for alternative means of powering their planes. In fact, Finnair recently set a record for the longest commercial flight powered by biofuel, over 900 miles. Despite this incredible achievement, the airline openly admits that, since biofuel-powered air travel is still in its infancy, it isn't financially practical to convert biofuel just yet. However, they are continuing to experiment with it in hopes of reducing their impact on the environment.

When speaking of the grounds for creating the BIV to cross Antarctica, Winston Wong said that it was necessary to "do something that people can take notice [of] and say this is the future, the future of human endeavor” in an effort to reduce harm to the planet. The teams involved in the efforts above evidently placed stock in that same way of thinking, selecting rigorous ways to test different forms of alternative power. If we combine each of these cleaner energy forms and forward ideas, it is possible that we could soon see the beneficial impact that biofuels will have on our nation.

What is next of biofeuls and biochemicals?

Recently I have been in AIChE annual meeting at Minneapolis, MN. There I sensed a different atmosphere compared to what I felt last year: Less attendance and pessimistic in biofuels.

Indeed, in the past twenty years, DOE and other government agents spent tons of money to support technology development in biofuel production from biomass. People are expecting a sun-rising industry like IT in the past to boost the economy. Therefore, green technology once became a hot green waves hitting every aspects of people’s life, especially for biofuels. Unfortunately, the current dominant technologies claimed in patents and highlighted for biofuel production from biomass have actually been existing there for hundreds of years; none of them seems to solve the cheap sugar problem. Therefore, some anti-biofuel people even anticipate that there would be no biofuels in the next 20 years.

It is true that at least cellulosic bioethanol will be dead if these technologies continue to control the government funding for 10 years. It really needs game-changing technology. Among all of the highlighted technologies, Agrivida technology recently stands out from nowhere and looks like a real solution for cheap sugar production from if it works as it claims. Therefore, hope is still shining somewhere as long as creativity is alive.

In addition, more interests and attention are shifting toward hydrocarbon fuel production from lignocellulosic biomass.  And more value-added biochemicals are being produced from biomass although not heavily funded by government funding.  Although a lot of uncertainty still exists for biofuels and biochemicals, one thing that never changes is that they are from renewable resources. Biodegradable materials and chemicals may become leading green products in the near future.

Corn fiber as a raw material for hemicellulose and ethanol production

Com fiber, a byproduct of the wet milling process, has shown to be a substrate of particular interest due to its abundance, ready availability and low value. Corn fiber is primarily composed of the outer seed covering or pericarp of the kernel, along with adherent starch with typicallyl 20% xylose and 10% arabinose in the form of arabinoxylan, 18-24% cellulose and 20% starch although its apparent composition varies considerably according to its source and the method of analysis. As estimate, ethanol yields from com could be increased by approximately 10% if the constituent sugars of corn fiber could be efficiently utilized. Since the xylan in seed fiber is highly branched with arabinose and may cross-links with phenolic acids, GH 10 xylanase and ferulic acid esterases are suggested to supplement for enzymatic hydrolysis.

The Next Wave: The game-change technology for cheap sugars and biofuels

A news from BiofuelsDigest on Sept. 29,2011.

That’s what Agrivida is up to.

“We are expressing all the cell wall degrading systems in the plant,” explains Agrivida CEO Michael Raab, “as the core part of our technology. We can control the activity of those enzymes so that in the plant we can express all the enzymes in dormant form. After harvest, we activate the enzymes in the material, so you don’t have to pretreat in the same way. It makes the process lower temperature, with a moderate PH, and takes out a lot of capital costs and those high costs of dilute acid pretreatment. Also, we really reduce the enzyme loading.”

Biomass feedstocks with hydrolytic enzymes may enable the industry to lower the cost of both pretreatment and enzyme production/loadings, potentially (hopefully) to solve the problem of producing cheap sugar from the root.

All quotes from U.S. Agriculture Secretary Tom Vilsack Touts Mass. Biofuels Sector

QUOTE from: U.S. Agriculture Secretary Tom Vilsack Touts Mass. Biofuels Sector

Challenges in commercialization of algal fuel

• Optimize stress conditions to obtain the highest possible yields of lipids in the cells because stress conditions can induce spontaneous mutation in cultivated strains.


• Simplify harvesting systems to utilize the separation technologies in existing industry such as food, biopharmaceutical, chemical and waste water treatment sectors.


• Utilize existing biodiesel production processes that requires a lipid material free of both water and free fatty acids


• Develop water tolerant downstream processes to avoid cost intensive drying

$11+ trillion in biofuels production by 2050: Internatio​nal Energy Agency

$11+ trillion in biofuels production by 2050: Internatio​nal Energy Agency

Algae oil content of some microorganisms

Microorganisms	Oil content (% dry wt)
Botryococcus braunii	25–75
Cylindrotheca sp.	16–37
Nitzschia sp.	45–47
Schizochytrium sp.	50–77

Bioconversions of lignocellulosic biomass: the points we cannot overlook

Pretreatment

• If you pretreat biomass at alkaline conditions, be sure to separate lignin before neutralization. Otherwise, the solublized lignin will be precipitated or re-deposited when pH drops.
• If you pretreat biomass at acidic conditions, be sure the temperature does not exceed 165 C. Otherwise, the lignin will condense and re-distribute through cell wall and become gel coat on the surface of pretreated fiber
• If you pretreat biomass with organosolvents, make sure to recycle/re-use the solvents.


Post-pretreatment
• If run detoxification, make sure the methods to be used with fundamental mechanisms. It is cheap and scalable.
• Recover by-products and easily and economically deal with the chemicals if any.

Enzymatic hydrolysis
• Know what biomass you are using and their sugar composition. Woody and non-woody biomass has different chemical (especially lignin and hemicelluloses) composition.
• Know the pretreatment methods you used. The modification of cell wall structure and chemical composition differ under different thermochemical pretreatments.
• Know what substrate the enzyme cocktail development has been based on. Alkaline and acidic pretreated biomass will end up different cocktail characteristics. The enzyme cocktail may need to be customized in terms of the specific pretreated biomass.


Process
• Avoid or reduce unit operations as much as possible
• Be as simple as possible for process configuration
• Use high solids if possible

Fermentation
• Use cheap nutrients if possible
• Ferment C6 and C5 sugars if possible

Fatty acid composition of microalgal oil

 

Fatty acid	Chain length: no. of double bonds	Oil composition (w/total lipid)
Palmitic acid	16:00	12–21
Palmitoleic acid	16:01	55–57
Stearic acid	18:00	1–2
Oleic acid	18:01	58–60
Linoleic acid	18:02	4–20
Linolenic acid	18:03	14–30

(Meng et al., 2009).

Heating values of diesel and biodiesel

The high heating value

• Petroleum diesel: 42.7 MJ/kg.
• Biodiesel derived from seed oils, such as rapeseed or soybean: 37 MJ/kg.
• Biodiesel derived from algae: 41 MJ/kg.

An informative review paper on the physico-chemical properties of feedstocks for biodiesel production

A summarized information was presented in Tables in this paper on the following aspects:

• Yields of vegetable oils and their fatty acid composition.
• Influence of feedstocks on biodiesel process selection and operating conditions.
• Physico-chemical properties of methyl esters from various bio-oils.
• Physico-chemical properties of methyl esters from various bio-oils.

ARPA-E 2011 Keynote: Secretary Steven Chu

News: Secretary for the US Department of Energy, Steven Chu, discusses the big picture of how the United States uses Energy and why innovation in clean technology is the key to Winning the Future.


http://www.youtube.com/watch?v=8QHVOoUDpN4

Universal or “customized” enzyme cocktail for sugar production

Currently available commercial enzyme preparations are limited in number and composition and have generally been optimized for acid-pretreated stover from maize and other grasses.

However, lignocellulosic feedstocks for sugar production include a variety of biomass: woody biomass such as softwood and hardwood, waste paper; non-wood biomass such as grass stovers (e.g., maize, sorghum, switchgrass or Miscanthus); and other biomass materials such as corn cobs, dried distillers’ grains solubles. All these biomass have different chemical composition, which will response differently to different pretreatments (e. acidic, basic, or oxidation), resulting in pretreated biomass with different chemical composition, even sugar composition. Therefore a general enzyme cocktail may work well for one type biomass or one type of pretreated biomass but not efficiently for other biomass. For example, for grass biomass with branchy arabinose and glucuronic acid, it may need GH10 endo-xylanase, a-arabinosidase, and a-glucuronidase. For woody biomass, in addition to the key endo-and exo-glucanases and endo-xylananse, it may need ferulate esterase and beta-mannanase. For acid pretreatment at a temperature >160 C, some of biomass hemicelluloses will be removed but some lignin may condense or re-deposit on fiber surface; while alkaline pretreatment will delignify but may have hemicelluloses re-deposited on the fiber surface. All of these will impact the efficiency of enzymatic hydrolysis and may require specifically modified enzyme cocktails. Therefore, a modified “customized” enzyme cocktail is more appropriate to adapt the spectrum of biomass and pretreatment combination for target hydrolysis.

A good research paper presents a study on this issue.

In planta expression of highly thermostable enzymes

In planta enzyme expression uses plants instead of microbial bioreactors as a “factory” to produce industrial hydrolytic enzymes for biofuel production. The enzymes that are active at typical and ambient plant growth temperatures will hurt plant normal growth/phenotypes and produce shriveled seeds as reported in the research paper.


However, in planta expression of thermophilic enzymes have been suggested as a method to reduce the detrimental effects on plants as these enzymes have higher temperature optima than encountered during plant growth. As a result, the plant stover can be pretreated at a relatively high temperature to induce their activation during processing.


Since a typical enzyme cocktail will require a combination of different class of enzymes to work together to destroy the cell wall for hydrolysis, is it possible to find all the key enzymes with thermophilibility and express them into a single plant without impacting plant growth?

Hemicelluloses for fuel ethanol-A good source of information but what else can we get?

A good summary in this review paper with the following aspects:

• various hemicelluloses structures present in lignocellulosic biomass
•  the range of pre-treatment and hydrolysis options including the enzymatic ones
•  the role of different microbial strains on process integration aiming to reach a meaningful consolidated bioprocessing
• the recent trends, technical barriers and perspectives of future development are highlighted.

So far, all the review paper on biomass pretreatments cover almost the same: list the acid, alkaline, wet oxidation, organosolv, ionic liquids pretreatments and their advantages and disadvantages, based on which comes a conclusion: no ‘‘ideal” pre-treatment.

 Actually there do exist good pretreatments, which are effective under low temperature and less by-products. In addition, a milder pretreatment with an efficient process configuration is able to overcome some drawbacks.

The pretreatment I have is conducted at a temperature lower than 120 C and near neutral alkaline conditions, which significantly reduce up-front capital cost and operational cost as well as the chemicals required for neutralization. In addition, a simple process configuration is used for more practical application, which will make it more economical competitive.

My advice: do not just look at these review papers when developing your own pretreatments. They are good sources and references. Understand the fundamentals first and jump out of the box. Remember: be simple for the process.

The latest MIT Sloan report on "Sustainability: The‘Embracers’ Seize Advantage"

Here is the latest MIT Sloan report on "Sustainability: The‘Embracers’ Seize Advantage"


Is it "W" shape for sustaibable business development and investiment?

The first engineered trait designed for the ethanol industry

The news: A corn called Enogen,  the first crops genetically engineered to contain a hydrolytic trait that has been approved or commercial growing by the Department of Agriculture. The crop with this self-hydrolysis trait will increase ethanol output while reducing the use of water, energy and chemicals in the production process.

The advantages of in planta cell wall degrading enzyme expression

1. Can  produce biomass and hydrolytic enzymes in plant sisimultaneously
2. Since the enzymes are already embedded into cell wall, the resistance of mass transfer for exogenous enzymes for diffusion is removed and non-selective binding of enzymes on lignin is avoided
3. Allow consolidated low temperature pretreatment and enzymatic hydrolysis
4. Similar or more sugar production in plant by overexpression of hydrolyitc enzymes

As a result, low cost sugar production is possible.

Biomass hydrolyzate fermentation performance:

An economically-attractive cellulosic technology usually 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. Many metabolically-engineered ethanologens  have been developed to hit the metrics. A research paper published recently by Lau et al compared the fermentation performance of the three engineered microorganisms such as S. cerevisiae 424A(LNH-ST), Z. mobilis AX101 and E. coli KO11, demonstrating that the difficulty to achieve the targets when fermenting  milled AFEX pretreated corn stover using CSL as nitrogen source. 

In a large  commercial scale with a  un-milled biomass biomass at a solids content >= 15%, it will be much harder to achieve the target fermentation conversion through one-pass hydrolysis and fermentation. To avoid harsh pretreatments at extreme conditions, a process with partial recycling  of solid stream from fermentation might be helpful to achieve the target. Without harsh pretreatments and expensive capital cost, the overall cost will be low if the target metrics are achieve.

Biotechnological strategies for hydrolyzate detoxificarion

A revew paper published recently by Parawira et al (Crit Rev Biotechnol. 2010 May 3) describes the application and/or effect of biological detoxification (removal of inhibitors before fermentation) or use of bioreduction capability of fermenting yeasts on the fermentability of the hydrolysates.

Of course, the better strategy is to produce fermentable sugars with little toxic compounds, which will eable us to use a whole slurry process.

Farmers now delivering biomass to POET's Project LIBERTY storage site

A news from Renewable energy world.com "Farmers now delivering biomass to POET's Project LIBERTY storage site ", indicating Poet is making progress on cellulosic ethanol. Hopefully it is not just a trial or testing!

U.S. EPA approves E15 for 2001 and newer vehicles (news)

One more srep forward, U.S. EPA approves E15 for 2001 and newer vehicles!

Heterogeneous azeotropic distillation with n-hexane

Heterogeneous azeotropic distillation is a widely used technique for separating binary azeotropic mixtures into their components. To produce pure ethanol,  heterogeneous azeotropic distillation using hexane instead of benzen as the entrainer has been developed recently because  n-hexane is a common compound found in gasoline and any trace amount of hexane in the anhydrous ethanol will not be a problem for its subsequent use as a fuel. The composition of the ternary azeotrope determined by numerical interpolation was reported as  0.105, 0.236 and 0.658 mole fraction of water, ethanol, and n-hexane, respectively, and the temperature is 329.21 K.

The heterogeneous azeotropic distillation with n-hexane can produce pure ethano with relatively low energy input.

The opportunities of enzyme expressed grain

Successful expression of enzymes in corn grains will bring the following opportunities for bioethanol production in low cost:

1. Recover suars from DDGs corn fibers by enzymatic hydrolysis using extracted proteins from exzyme expressed corn grains.

2. Mix exzyme expressed grains with pretreated biomass to reduce external hydrolytic enzymes.

Currently, the technology for such a expression is avaible; therefore it is expected such cost effective applications will integrate into bioethanol production.

Vacuum fermentation and distillation

It is known that high ethanol concentrations (10% v/v) were inhibitory to the industrial yeast strains and would reduce the yeast growth and cell density in the high solids mash. However, high slurry solids saccharification and fermentation are right direction for cost effective production of fuel ethanol. To overecome the challenge, vacuum feremtation and vacuum distillation can be applied to remove ethanol produced during SSF. As a result,the ethanol concentration was maintained as negligible during the entire fermentation process, which can lead to high ethanol productivity.Combining hydrolytic enzyme hydrolysis and SSF under a vacuum allows the integration of all four unit operations (liquefaction, saccharification, fermentation and distillation) into one single step, which eliminates both substrate (glucose) and product (ethanol) inhibition of the yeast and allow very high slurry solids (~40%) ssacharification and fermentation.

The higher slurry solids and removal of water during vacuum distillation will also result in higher percentage of stillage solids at the end of the fermentation, which can be sold directly as wet grains without any need for centrifugation and thin stillage evaporation to remove water, therefore to reduce operational cost to a great extent.

In planta expression of biomass cell-degrading enzymes: the solution to cheap sugar for biorefinery

One of the approaches to utilize lignocellulosic biomass as feedstocks for biorefibery is through biological conversion. Currently, an efficient, rapid, and complete enzymatic hydrolysis of biomass using low enzyme loadings is still one of the major technical and economical bottlenecks in this process because of the lack of low cost pretreatment technology as well as high cost of enzymes. Since lignocellulosic biomass is composed of a matrix with multiple intertwined biopolymers (cellulose, hemicelluloses, lignin and extractives), it requires several different classes of enzymes in large quantities to efficiently release fermentable sugars. As a result, it is necessary to produce different classes of enzymes individually in a large scale and then make cocktails for biomass hydrolysis. Because of the high cost and limited capacity for producing these enzymes through fermentation, today, it is still a big challenge to develop an efficient enzyme production system for rapid and less expensive biomass depolymerization.

However, all these enzymes required for biomass enzymatic hydrolysis are produced naturally by a range of microbial species including bacteria and fungi. Many cell wall-degrading enzymes have been isolated and characterized and more are still not uncovered. Availability of genome sequences of Trichoderma reesei and other organisms have increased inventory of enzymes for biomass utilization.

Plants have already been used as a “factory” in industry to produce enzymes and other proteins, carbohydrates, lipids, industrial polymers and pharmaceuticals. Successful technology is available for plant genetic transformation, farming of transgenic crops and harvesting, transporting and processing the plant matter. Therefore, expression of all different classes of cell wall-degrading enzymes  into plants provides great opportunity for developing biomass-specific enzyme cocktails, which will create a low sugar platform for biorefinery.