What Plants for Cellulosic Biofuel Production?

In an article titled “Feedstocks for Lignocellulosic Biofuels” published in Science, Chris Somerville of the University of California, Berkeley, and Deputy Director Steve Long of the University of Illinois at Urbana-Champaign with bioenergy analysts Caroline Taylor, Heather Youngs and Sarah Davis at the Energy Biosciences Institute suggest that a diversity of plant species, adaptable to the climate and soil conditions of specific regions of the world, can be used to develop “agroecosystem” for fuel production that are compatible with contemporary environmental goals.

Well, press release and research notes aside, they mean that there can be a set of plant species that could provide substantial amounts of biomass grown widely across the planet without an impact on food and feed production.  The troubled firm BP, well before the Gulf well crisis, funded the study.

The study authors discuss the sustainability of current and future crops that could be used to produce advanced biofuels with emerging technologies that use non-edible parts of plants. Such crops include perennial grasses like Miscanthus grown in the rain-fed areas of the U.S. Midwest, East and South; sugarcane in Brazil and other tropical regions, including the southeastern U.S.; Agave in semiarid regions such as Mexico and the U.S. Southwest; and woody biomass from various sources.

The team takes some assumptive license by making some simplifying assumptions: that technology will become available for converting most of the structural polysaccharides that comprise the bodies of plants to sugars, that all the sugars can be used for fuel production, and that the process energy required for the conversion of the sugars to fuels will be obtained from combustion of the other components of the biomass, mostly the lignin.  That way a sugar-to-ethanol bioconversion process using current technology, a metric ton (MT) of switchgrass or poplar, for example, would be expected to yield about 310 liters of ethanol.

The author’s base is founded on the comparative soil impacts.  Maize or corn plants used completely remove much more soil fertility than a perennial plant.  Perennial plants that use C4 photosynthesis, such as sugarcane, energy cane, elephant grass, switchgrass, and Miscanthus, have intrinsically high light, water, and nitrogen use efficiency as compared with that of C3 species as seen in corn.  Moreover reduced tillage and perennial root systems add carbon to the soil and protect against erosion.

While the team reports that tropical Napier Grass in El Salvador natural stands of Echinochloa polystachya on the Amazon floodplain can respectively reach production of 88 and 100 MT/ha/year, temperate Miscanthus x giganteus produced in England at 52°N a peak biomass of 30 MT/ha/year and harvestable biomass of 20 MT/ha/year. (ha is hectare, 2.47 ha per U.S. acre) Miscanthus also offers an important soil protection effect, seasonality leads to an annual cycle of senescence, in which perennial grasses such as Miscanthus mobilize mineral nutrients from the stem and leaves to the roots at the end of the growing season. Thus, harvest of biomass during the winter results in relatively low rates of removal of minerals.

That could account for the observation that stands grown at Rothamsted, UK showed no response to added nitrogen during a 14-year period during which all biomass was removed each year.  In side-by-side trials in central Illinois, unfertilized M. x giganteus produced 60% more biomass than a well-fertilized highly productive maize crop, and across the state, winter-harvestable yields averaged 30 MT/ha/year.

Miscanthis US Growing Area Map. .

The author’s note in an observation that if Miscanthus were used as the only feedstock, less than half of the 14.2 Mha currently set aside for the U.S. Conservation Reserve Program  (CRP) would be required to deliver the ethanol mandate of the Energy Independence and Security Act of 2007.  Contrary to that readers should be informed that a great chunk of the CRP land area is tiny little headlands, terraces, protective filters along watercourses and the like.  But there are vast amounts of highly erodeable land that could better serve the economy than being used for corn or soybean production.

Its worthwhile to note that as the authors seem to overlook some details they turned up others.  The Global Potential of Bioenergy on Abandoned Agriculture Lands published in 2008 reveals that more than 600 Mha of land worldwide has fallen out of agricultural production, mostly in the last 100 years.

Most readers will know that for tropical production sugarcane isn’t beaten yet and won’t most likely.  Harvested cane arrives with the sugar in liquid form ready for fermentation and the plant remnants can be burned for distillation with power left over for the electric grid.  Many other regions of the world beyond Brazil are also well suited to sugarcane production or formerly produced sugarcane on land that has been abandoned. Thus, “the total amount of fuel that may be produced from sugarcane worldwide could eventually be a very substantial proportion of global transportation fuels.” As the authors seem to be aware – the potential in sugarcane defies calculation in responsible numbers for now.

Approximately 18% of the earth’s surface is semi-arid and prone to drought.  The authors suggest various Agave species that thrive under arid and semi-arid conditions with high efficiencies of water use and drought resistance hold a potential opportunity for production of biomass for fuels.  Agave species that thrive under arid and semi-arid conditions by using a type of photosynthesis called Crassulacean acid metabolism (CAM) that strongly reduces the amount of water transpired by absorbing CO2 during the cold desert night and then internally assimilating this into sugars through photosynthesis during the warmer days.  By opening their stomata at night, they lose far less water than they would during the day.  Much of the land noted in the Global Potential of Bioenergy on Abandoned Agriculture Lands that has fallen out of agricultural production worldwide is semi-arid, and it appears that the amount of land that may be available for cultivation of Agave species is vast.

The research paper points out that about 89 to 107 Mha of land that were formerly in agriculture globally are now in forests and urban areas.  The authors bravely note the biomass that is harvested annually in the Northern Hemisphere for wood products has an energy content equivalent to approximately 107% of the liquid fuel consumption in the United States.  Wood resources provide regionally specific opportunities for sustainably harvested biomass feedstocks.  That explains the Chevron and Weyerhaeuser deal for biomass.

For this summary its important to note one more point the authors took the time to briefly discuss.  It is inevitable that some mineral soil nutrients will be removed when biomass is harvested, it will be essential to recycle mineral nutrients, which are not consumed in the production of biofuels, from biomass-processing facilities back onto the land. That is virtually all of the minerals.  It needs to be a built in cost before soils are degraded further by any new biomass effort.

This writer’s summary leaves a lot out from the published study including the references, the supporting documentation and the available links.  For this article Science has free registration, an opportunity cost well worth the small effort.

The authors did a good job here, but left a lot out.  There are lots more plants to consider, but the local weather and soils are going to decide what farming can accomplish and the profit for production will in the end decide.  This writers main concern is that highly profitable biomass could displace prime food and feedstock land and force food and feedstock production onto the less optimal soils.  Some oversight, as oppressive as it is – is going to be needed to balance the demands with the conditions – something competition isn’t going to get done.


Original post here: New Energy and Fuel

A Local Biofuel Process Development

Purdue University chemical engineers are proposing the creation of mobile processing plants that would rove the Midwest to produce the fuel with a newly developed method to process agricultural waste and other biomass into biofuels.

Rakesh Agrawal, the Winthrop E. Stone Distinguished Professor of Chemical Engineering said,  “What’s important is that you can process all kinds of available biomass  — wood chips, switch grass, corn stover, rice husks, wheat straw …,”

The proposed harvest to production method bypasses a problematic economic barrier for using biofuels: Transporting biomass is expensive because of its bulk volume, whereas liquid fuel from biomass is concentrated and thus far more economical to transport.

Agrawal and his team are making the point, “”Material like corn stover and wood chips has low energy density. It makes more sense to process biomass into liquid fuel with a mobile platform and then take this fuel to a central refinery for further processing before using it in internal combustion engines.”  If they can come up with a low investment processor, they team could have a kind of home run.

The new method is called fast-hydropyrolysis-hydrodeoxygenation, which works by adding hydrogen into the biomass-processing reactor. The hydrogen for the mobile plants would be sourced from natural gas or the biomass itself. However, Agrawal envisions the future use of solar power to produce the hydrogen by splitting water, making the new technology entirely renewable.

The method, which has the shortened moniker of H2Bioil — pronounced H Two Bio Oil — has been studied extensively through modeling, and experiments are under way at Purdue to validate the concept.

Mobile Biomass to Fuel Block Diagram. .

Fast pyrolysis isn’t new, but kicking in an added hydrogen source is and taking the fast pyrolysis on to de oxidizing the product is as well.  It’s a combination of processes that looks innovative.

Singh, who is now a researcher working at Bayer CropScience, said, “Another major thrust of this research is to provide guidelines on the potential liquid-fuel yield from various self-contained processes and augmented processes, where part of the energy comes from non-biomass sources such as solar energy and fossil fuel such as natural gas.”

Results outlining the process, showing how a portion of the biomass is used as a source of hydrogen to convert the remaining biomass to liquid fuel is detailed in a research paper appearing online in June issue of the journal Environmental Science & Technology. The paper was written by former chemical engineering doctoral student Navneet R. Singh, Agrawal, chemical engineering professor Fabio H. Ribeiro and W. Nicholas Delgass, the Maxine Spencer Nichols Professor of Chemical Engineering.  The abstract says in part:

We have estimated sun-to-fuel yields for the cases when dedicated fuel crops are grown and harvested to produce liquid fuel. The stand-alone biomass to liquid fuel processes, that use biomass as the main source of energy, are estimated to produce one-and-one-half to three times less sun-to-fuel yield than the augmented processes. In an augmented process, solar energy from a fraction of the available land area is used to produce other forms of energy such as H2, heat etc., which are then used to increase biomass carbon recovery in the conversion process. However, even at the highest biomass growth rate of 6.25 kg/m2· per year considered in this study, the much improved augmented processes are estimated to have sun-to-fuel yield of about 2%. We also propose a novel stand-alone H2Bioil-B process, where a portion of the biomass is gasified to provide H2 for the fast-hydropyrolysis/hydrodeoxygenation of the remaining biomass. This process is estimated to be able to produce 125−146 ethanol gallon equivalents (ege)/ton of biomass of high energy density oil but needs experimental development. The augmented version of fast-hydropyrolysis/hydrodeoxygenation, where H2 is generated from a nonbiomass energy source, is estimated to provide liquid fuel yields as high as 215 ege/ton of biomass. These estimated yields provide reasonable targets for the development of efficient biomass conversion processes to provide liquid fuel for a sustainable transport sector.

The Purdue group is also developing reactors and catalysts to experimentally demonstrate the concept. In another paper addressing various biofuels processes, including fast-hydropyrolysis-hydrodeoxygenation, that appeared in June’s Annual Review of Chemical and Biomolecular Engineering.  The full paper is available at this link.

The new method would produce about twice as much biofuel as current technologies when hydrogen is derived from natural gas and 1.5 times the liquid fuel when hydrogen is derived from a portion of the biomass itself.

Biomass along with hydrogen will be fed into a high-pressure reactor and subjected to extremely fast heating, rising to as hot as 500 degrees C, or more than 900 degrees Fahrenheit in less than a second. The hydrogen containing gas is to be produced by “reforming” natural gas, with the hot exhaust directly fed into the biomass reactor.

Agrawal explains, “The biomass will break down into smaller molecules in the presence of hot hydrogen and suitable catalysts. The reaction products will then be subsequently condensed into liquid oil for eventual use as fuel. The uncondensed light gases such as methane, carbon monoxide, hydrogen and carbon dioxide, are separated and recycled back to the biomass reactor and the reformer.”

Purdue has been pioneering the concept of combining biomass and carbon-free hydrogen to increase the liquid fuel yield.  An older design called “hybrid hydrogen-carbon process,” or H2CAR also use additional hydrogen to boost the liquid-fuel yield. However, H2Bioil is more economical and mobile than H2CAR, Singh said.

Singh continues, “H2Bioil requires less hydrogen, making it more economical.  It is also less capital intensive than conventional processes and can be built on a smaller scale, which is one of the prerequisites for the conversion of the low-energy density biomass to liquid fuel. So H2Bioil offers a solution for the interim time period, when crude oil prices might be higher but natural gas and biomass to supply hydrogen to the H2Bioil process might be economically competitive.”

Regular folks have only a slight impression of what say, the planetary daily oil use of 85 million barrels would look like. The equivalent in biomass to be made into fuel would be an awe-inspiring mound, indeed.

Punching up the total fuel produced is likely the main benefit until political and economic types catch on to the transport issue.  By any measure the Purdue effort is getting somewhere worth going and its something that could go worldwide in local areas as modern farming practices reach further into the under developed world.

This is worthy research from Purdue.  The original article was written by Emil Venere.


Original post created by: New Energy and Fuel

Culturing Cyanobacteria for Biofuel

Hyun Woo Kim and Raveender Vannela, researchers at the Biodesign Institute at Arizona State University are perfecting the means to culture cyanobacteria, a potentially rich source of biofuels and biomaterials in greater abundance.  Cyanobacteria are among the oldest organisms in nature, responsible for generating the atmospheric oxygen we breathe today.

The pair’s work is meant to provide a vital foundation for optimizing a device known as a photo bio reactor (PBR), in which these energy-packed photosynthetic organisms can proliferate.

Dr. Kim explains, “Cyanobacteria are much easier to re-engineer because we have a lot of knowledge about them. We can control their growth so that we can produce large amounts of biofuel or biomaterial.

Culturing is akin to ‘farming’ the cyanobacteria, thus the new research indicates that the optimization of cyanobacterial growth requires a delicate interplay of CO2, phosphorus and sufficient light irradiation within the PBR vessel containing the microbial crop. The group’s foundational study provides quantitative tools for evaluating factors limiting production of cyanobacteria within PBRs – a critical step along the path to large-scale biofuel production.  Results appeared recently in the journal Biotechnology and Bioengineering.

Dr. Raveender VannelaAssistant Professor Research Overlooks a Cyanobacteria Photobioreactor. Image Credit: Arizona State University/Biodesign Institute.

Photosynthetic cyanobacteria are amazingly productive – able to produce roughly 100 times the amount of clean fuel per acre compared with other biofuel crops.  Because their survival needs are simple – sunlight, water, CO2 and a few nutrients – they do not require arable land to be taken out of food production. Rather, cyanobacteria can be grown in rooftop PBRs or wherever sufficient quantities of sunlight and CO2 can be provided.

Maybe . . .

Vannela notes, “The PBR uses solar photons as an energy source to convert CO2 to reduced forms such as biomass, proteins, lipids, and carbohydrates. It’s a biological reactor, fixing solar energy into very useful forms of energy for human society.”

Cyanobacteria reproduction achieves a high biomass yield and they are tolerant of a wide range of temperatures, salinities and pH conditions. In addition to biofuels, which are extracted from fat-containing lipids in the cyanobacteria, the organisms can also produce many chemically based materials useful for industrial applications, like biopolymers or isoprenes.  Photosynthetic microbes are also valuable for the growing field of neutriceuticals, permitting the manufacture of anti-cancer agents from fatty acids or antioxidants like beta carotene.

The pair used wild type Synechocystis PC6803, cultured in a bench top PBR, and supplied with the customary growth medium, known as BG-11. A series of semi-continuous experiments were conducted, in which three principle variables were manipulated and the resulting growth of cyanobacteria, observed. These were CO2, light irradiance and phosphorus.

Kim explains, “In this study we found that phosphorus is really important.”  The cyanobacteria were unable to make efficient use of carbon dioxide in their growth cycle until the BG-11 medium was supplemented with phosphorus. Augmenting the medium with additional phosphorus allowed higher biomass productivity in the bioreactor. Once the phosphorus limitation was overcome, light irradiance and CO2 became the limiting factors for growth.  That’s the ‘maybe’ coming up.

Organically ready phosphorus isn’t a low cost fertility additive.  Many believe its in short and expensive supply now.

In a series of experiments, the team simulated the natural pattern of light irradiance produced by sunlight, while carefully controlling the levels of CO2  (applied at 2.5, 5.0 and 7.5 percent) and phosphorus.  Results showed that when all essential nutrients are supplied, light irradiance becomes the limiting factor, as the crowding of biomass within the containment vessel increasingly blocks available light to the cyanobacteria. This condition is overcome through periodic harvesting of biomass from the reactor. The advance of the team’s research was in quantifying these factors, in order to obtain optimal values for nutrients, CO2 and light irradiance.  Now it’s known for the Synechocystis PC6803 species.

Vannela and Kim point out that while they supplied CO2 and nutrients including phosphorus to the PBR’s cyanobacteria in their experimental design, ultimately, the nutrient source could come from waste streams or be recycled from the harvested biomass, while the excess CO2 produced by power plants could fulfill the microbe’s respiratory requirements. Thus, a closed loop could be formed, generating useful energy from water contaminants and the CO2 currently contributing to greenhouse warming.

All very politically correct.  The ‘maybe’ rises again as the effort to reduce power plant emissions is going to limit access to concentrated CO2.  Coming up with a CO2 scrubber from the atmosphere is a matter of some concern.  Add that to the phosphorus matter and ‘maybe’ has considerable impact.

People in the media and the politically active like to talk of CO2 sequestration.  They might want to wise up and focus on CO2 concentration so worthy research has real prospects for contributing to fuel and chemical production.

Vannela and Kim prove that cyanobacteria could be very productive in a PBR.  PBRs could be fed a medium with the rich phosphorus needed for cyanobacteria production.  But coming up with cheap a CO2 stream and phosphorus enriched medium looks like quite a challenge.  Cyanobacteria in a PBR offer a huge opportunity with huge challenges as well.

On the other hand, Kim is right that cyanobacteria could be highly engineered. Perhaps the next steps might be finding and designing a species that can grow abundantly in today’s low CO2 atmosphere with a lower phosphorus requirement.


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Making Carbohydrates from Lignin with Ozone

Researchers from North Carolina State University have developed a new way to free the carbohydrates from plant lignin. By exposing the plant matter to gaseous ozone, with very little moisture, the NC team is able to produce a carbohydrate-rich solid with no solid or liquid waste.

This may well be the breakthrough. It’s still early, but the lignin and cellulose problem remains a significant barrier for biofuels with a great deal of effort in finding solutions.

Currently, to make ethanol, butanol or other biofuels, producers have used sugarcane, corn, sugar beets or other plant matter that is high in starches or simple sugars. But, those crops are also significant staple foods putting biofuels in competition with animals and people for those crops.

The problem is other forms of biomass – such as switchgrass, inedible corn stalks and cobs, miscanthus, poplar trees and many others – can also be used to make biofuels. But this crop arena poses its own problem: the energy potential is locked away inside the plant’s lignin – the woody, protective material that provides each plant’s structural support. Breaking down that lignin to reach the plant’s component carbohydrates is an essential first step toward making biofuels.

Dr. Ratna Sharma-Shivappa of North Carolina State University. .

Dr. Ratna Sharma-Shivappa, associate professor of biological and agricultural engineering at NC State and co-author of the research says in the NC State University press release, “This technique makes the process more efficient and less expensive. The technique could open the door to making lignin-rich plant matter a commercially viable feedstock for biofuels, curtailing biofuel’s reliance on staple food crops.”

The current technology treats this so-called “woody” plant matter with harsh chemicals that break it down into a carbohydrate-rich substance and a liquid waste stream. The remaining carbohydrates are then exposed to enzymes that turn the carbohydrates into sugars that can be fermented to make ethanol or butanol.  But, this technique often results in a significant portion of the plant’s carbohydrates being siphoned off with the liquid waste stream. Researchers must either incorporate additional processes to retrieve those carbohydrates, or lose them altogether.  Think complex, expensive and wasteful – solutions here are huge opportunities.

Sharma says of the ozone technique, ““This is more efficient because it degrades the lignin very effectively and there is little or no loss of the plant’s carbohydrates. The solid can then go directly to the enzymes to produce the sugars necessary for biofuel production.”

At this stage Sharma-Shivappa notes that the process itself is more expensive than using a bath of harsh chemicals to free the carbohydrates, but is ultimately more cost-effective because it makes more efficient use of the plant matter.  Yet experienced process engineers are just becoming aware of the research.  Commercial scale can have an impressive effect on operating costs.

The North Carolina team has recently received a grant from the Center for Bioenergy Research and Development to fine-tune the process for use with switchgrass and miscanthus grass. “Our eventual goal is to use this technique for any type of feedstock, to produce any biofuel or biochemical that can use these sugars,” Sharma-Shivappa says.

Congratulations!  Using a recyclable gas in the process could well be a huge process improvement and putting much more feedstock into product would improve the economics.

Here’s the official plug – The research, “Effect of Ozonolysis on Bioconversion of Miscanthus to Bioethanol,” was co-authored by Sharma-Shivappa, NC State Ph.D. student Anushadevi Panneerselvam, Dr. Praveen Kolar, an assistant professor of biological and agricultural engineering at NC State, Dr. Thomas Ranney, a professor of horticultural science at NC State, and Dr. Steve Peretti, an associate professor of chemical and biomolecular engineering at NC State. The research is partially funded by the Biofuels Center of North Carolina and was presented June 23 at the 2010 Annual International Meeting of the American Society for Agricultural and Biological Engineers in Pittsburgh, PA.

There isn’t a published paper listed – yet, but the North Carolina press release does include an abstract, “Miscanthus is an energy cane capable of producing high quality lignocellulosic biomass for bioethanol production. However, the conversion of this biomass into fuel ethanol has not been investigated in depth and depends to a great extent on the pretreatment technique.  Ozonolysis is a novel pretreatment method that can enhance biomass digestibility with minimal generation of chemical waste streams and degradation of the carbohydrate components. It employs ozone, a powerful oxidant, which forms highly reactive free hydroxyl ions upon decomposition thus degrading lignin in the absence of inhibitory degradation products such as furfural and HMF. This study investigates the effect of ozonolysis as a pretreatment method under room temperature and pressure.  Ozone concentrations up to 60 ppm at flow rates up to 0.5 l/min are being used to pretreat several varieties of miscanthus for varying times to enhance enzymatic hydrolysis. The efficiency of pretreatment will be determined by measuring the reducing sugars generated after hydrolysis. It is expected that the results of this study will help in the development of a pretreatment process that provides higher specificity towards lignin removal compared than other delignifying agents/pretreatments.”

The main question would be what the technique leaves as a waste material.  Is that a resource or a problem?  Time will tell.

One might hope that the ozone gas treatment would have a major impact.  There’s a lot of lignin and cellulose around left for natural fungus and mold degradation.  Picking that resource up and using it, and raising crops to build the volume are worthwhile.  The technology would put humanity in much closer harmony with the planet’s natural carbon cycle.


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