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Rapid And Effective Oxidative Pretreatment Of Woody Biomass At Mild Reaction Conditions And Low Oxidant Loadings
One route for producing cellulosic biofuels is by the fermentation of lignocellulose-derived sugars generated from a pretreatment that can be effectively coupled with an enzymatic hydrolysis of the plant cell wall. While woody biomass exhibits a number of positive agronomic and logistical attributes, these feedstocks are significantly more recalcitrant to chemical pretreatments than herbaceous feedstocks, requiring higher chemical and energy inputs to achieve high sugar yields from enzymatic hydrolysis. We previously discovered that alkaline hydrogen peroxide (AHP) pretreatment catalyzed by copper(II) 2,2 -bipyridine complexes significantly improves subsequent enzymatic glucose and xylose release from hybrid poplar heartwood and sapwood relative to uncatalyzed AHP pretreatment at modest reaction conditions (room temperature and atmospheric pressure). In the present work, the reaction conditions for this catalyzed AHP pretreatment were investigated in more detail with the aim of better characterizing the relationship between pretreatment conditions and subsequent enzymatic sugar release. Results: We found that for a wide range of pretreatment conditions, the catalyzed pretreatment resulted in significantly higher glucose and xylose enzymatic hydrolysis yields (as high as 80% for both glucose and xylose) relative to uncatalyzed pretreatment (up to 40% for glucose and 50% for xylose). We identified that the extent of improvement in glucan and xylan yield using this catalyzed pretreatment approach was a function of pretreatment conditions that included H2O2 loading on biomass, catalyst concentration, solids concentration, and pretreatment duration. Based on these results, several important improvements inpretreatment and hydrolysis conditions were identified that may have a positive economic impact for a process employing a catalyzed oxidative pretreatment. These improvements include identifying that: (1) substantially lower H2O2 loadings can be used that may result in up to a 50-65% decrease in H2O2 application (from 100 mg H2O2/g biomass to 35–50 mg/g) with only minor losses in glucose and xylose yield, (2) a 60% decrease in the catalyst concentration from 5.0 mM to 2.0 mM (corresponding to a catalyst loading of 25 mumol/g biomass to 10 mumol/g biomass) can be achieved without a subsequent loss in glucose yield, (3) an order of magnitude improvement in the time required for pretreatment (minutes versus hours or days) can be realized using the catalyzed pretreatment approach, and (4) enzyme dosage can be reduced to less than 30 mg protein / g glucan and potentially further with only minor losses in glucose and xylose yields. In addition, we established that the reaction rate is improved in both catalyzed and uncatalyzed AHP pretreatment by increased solids concentrations. Conclusions: This work explored the relationship between reaction conditions impacting a catalyzed oxidative pretreatment of woody biomass and identified that significant decreases in the H2O2, catalyst, and enzyme loading on the biomass as well as decreases in the pretreatment time could be realized with only minor losses in the subsequent sugar released enzymatically. Together these changes would have positive implications for the economics of a process based on this pretreatment approach. Author: Zhenglun LiCharles H ChenEric L HeggDavid B Hodge Credits/Source: Biotechnology for Biofuels 2013, 6:119 Continue reading
Seeking Biomass Feedstocks That Can Compete
Biofuels and biobased chemical makers hope to win with cellulosic sugars By Melody M. Bomgardner On the hot, dry agricultural land of California’s Imperial Valley, 17 new varieties of an unusual crop are being tested on a 100-acre plot. If the tests are successful, the valley’s bounty of lettuce, cantaloupes, and broccoli may someday be joined by plants that are converted into fuels and chemicals. The crop, energy cane, is a less sweet cousin of sugarcane. It is a perennial grass that was developed by plant scientists to create a large amount of biomass quickly. Canergy , a biofuels start-up, plans to grow enough energy cane to power one or more commercial-scale fuel ethanol plants starting in 2016. Although the valley is known for producing fruits and vegetables, more than half of its 450,000 acres are actually devoted to crops such as Sudan grass, used for hay. If enough farmers decide to add energy cane to their crop rotation, the region would produce a huge amount of biomass. “It grows extremely well there—we’re expecting phenomenal yields,” says Timothy R. Brummels, Canergy’s chief executive officer. He estimates that 1,800 to 2,200 gal of ethanol per year can be made from 1 acre of energy cane, compared with about 400 gal from 1 acre of corn. Energy cane is a dedicated energy crop, a category of plants that also includes the giant reed Arundo donax, napier grass, switchgrass, and hybrid poplar. Investments in energy crops are one part of a larger push by the biobased fuel and chemical industry to secure cheap, abundant feedstocks. Chemical companies can use the material to produce acrylic acid and butadiene, for example. Genomatica, Gevo , and Myriant have built their processes to take in sugar from corn or sugarcane. Those sources carry downsides. For instance, prices rise and fall along with other commodities such as petroleum, and the supply of sugar may not be ample enough to meet the needs of high-volume chemical makers. To ensure the viability of their industry, they are eager to replace those food sugars with a cheaper, more stable cellulose-based raw material. Executives say they are watching the growth of the cellulosic ethanol industry closely. Its success would pave the way to securing new cellulosic feedstocks for chemicals, they believe. “Just about every one of our chemical partners is interested in the potential for using biomass feedstocks,” says Christophe Schilling, CEO of Genomatica. “The motivation comes from a couple of different potential advantages—the first one is the potential for lower-cost feedstock. It still needs to be proven, but that is the hope. Then it is the stability of a secure supply of feedstock that doesn’t have the volatility of hydrocarbons or commodity agriculture.” Schilling adds that getting feedstock from nonfood sources is also important. Thanks to a half-decade of effort by the ethanol industry, clues are now emerging about how a cellulosic feedstock supply chain for chemicals would take shape. One thing is certain: The route is more complicated than for fossil-fuel feedstocks. “Part of the challenge is that shale gas is shale gas no matter where on Earth it comes from. But biomass is different with each crop,” says Brian Balmer, chemical industry principal at the consulting firm Frost & Sullivan . For that reason, making inexpensive sugars from plant-based feedstocks has become its own specialty. Canergy, Genomatica, and Gevo have partnered with Beta Renewables , which is a joint venture between the engineering firm Chemtex, owned by Italian chemical maker Mossi & Ghisolfi; private equity firm Texas Pacific; and enzyme maker Novozymes. The biobased chemical makers are interested in Beta Renewables’ process for breaking down cellulose with steam and enzymatic treatment to release sugars. Beta Renewables is already using the process to produce ethanol from wheat straw and A. donax at its commercial-scale biorefinery in Crescentino, Italy. Chemtex plans to build a facility in Clinton, N.C., that will run primarily on a mix of energy crops that includes A. donax and use the Beta Renewables technology. Beta Renewables says its process can deliver sugar from biomass for 10 cents per lb, a substantial discount from today’s corn-derived sugars, which cost around 18–20 cents per lb, notes Michele Rubino, the company’s chief operating officer. That is a price that pleases Gevo’s CEO, Patrick R. Gruber. “I hope he’s right. To make it big we will want cellulosic sugar,” he says. “To get more carbon per unit of land is better for everyone.” Gevo makes isobutyl alcohol from corn-based sugar. The output of Gevo’s first plant, in Luverne, Minn., is being used as a solvent and in jet fuel for the U.S. Air Force, but isobutyl alcohol is also a candidate to be an intermediate for p -xylene in Coca-Cola’s project to make 100% biobased soda bottles. Biobased chemical maker Myriant is working to adapt its organisms to squirt out succinic acid on a diet of cellulosic sugar, which contains both five- and six-carbon molecules. However, Alif Saleh, Myriant’s vice president of sales and marketing, says chemical industry customers have not yet demanded a switch away from corn sugar. Poet-DSM is contracting with farmers to obtain 285,000 tons of corn stover for its 25 million-gal-per-year plant. The companies need lots of local growers, so they have started a major outreach campaign , including advertising on local radio stations . DuPont plans to collect stover from a 30-mile radius for its similarly sized facility in Nevada, Iowa. Neither firm has disclosed its cost to make sugar. An alternative is to grow biomass on purpose by planting energy crops on agricultural land that cannot be economically used for food crops. That so-called marginal land may be ideal for some types of energy crops, particularly perennial grasses. By not shifting land use away from food production, companies can also defuse much of the concern about the impact of biobased fuels and chemicals on the food supply—the crux of the food-versus-fuel debate. “For us, having a base load of a dedicated energy crop is a pretty nice way to set up the supply chain,” Rubino argues. “It gives us high density, high yields, and requires less land. We base the facility off of that and take additional locally available residues from agriculture or mills.” The relatively modest amount of land needed to grow dedicated energy crops is appealing to biobased chemical makers. According to the Environmental Protection Agency, A. donax should produce as much as 15 dry tons of biomass per acre. In contrast, DuPont estimates it will collect 2 tons of corn cobs, leaves, and stems per acre. Of course, that land also produces corn. Obtaining feedstock can be further simplified by contracting with companies that control large amounts of land or biomass. In July, Beta Renewables signed a long-term agreement with Murphy-Brown, a livestock subsidiary of Smithfield Foods that is arranging for energy crops to be grown on land where hog farmers spray animal waste. The high-yielding perennial grass crops will help take up the excess nitrogen in the waste. Similarly, cellulosic sugar firm Renmatix has signed a development agreement with UPM, a pulp and paper firm, to develop sugars from UPM’s woody biomass. Renmatix CEO Mike Hamilton says the most cost-effective biobased chemicals will be manufactured on a site near the feedstock, perhaps at a pulp and paper mill. “If people are planning to ship low-value biomass around the country, that is not an effective process,” Hamilton says. “If you can assemble the end-to-end value chain, that is where the economics are optimized to compete with fossil-fuel chemicals.” Hamilton and other biobased chemical makers know that newly abundant natural gas is challenging the economics of their business. Indeed, the rise of shale gas will create biobased winners and losers, experts say. “What biobased chemical makers should focus on is the higher carbon chain lengths that you don’t get in natural gas,” Frost & Sullivan’s Balmer advises. Two- and three-carbon biobased chemicals, in contrast, will struggle to be competitive because petrochemical versions can be made from natural gas. “The rise of natural gas is a fascinating situation,” Genomatica’s Schilling says. “In our case, we benefit because of the products we make.” The firm has developed sugar-based routes to butadiene, which is used to make synthetic rubber, and to 1,4-butanediol, a raw material for urethanes, plasticizers, and coatings. The petrochemical industry has historically made 1,4-butanediol, butadiene, and other four-carbon chemicals by processing by-products from ethylene facilities that consume crude-oil-based feedstocks. But ethylene plants that run on ethane and propane extracted from natural gas produce a much smaller C 4 stream. In the past few years, experts say, prices for 1,4-butanediol and butadiene have significantly increased, and the trend should continue for the foreseeable future. Still, traditional companies aren’t going to cede territory to biobased chemical makers without a fight. For example, one company, TPC Group, is planning to make butadiene via butane dehydrogenation at a plant it owns in Houston. And the seven giant shale-gas-based petrochemical plants that have been announced for the U.S. are going to flood the market with chemicals of all sorts. At Renmatix, competing with chemicals made from shale gas has been on Hamilton’s mind lately, but he believes he is on the right side. “First, natural gas is not renewable. Second, it is also a volatile commodity, whereas biobased materials are significantly more reliable. Where there is competition, the least volatile, more long-term option will win.” [+]Enlarge Credit: POET-DSM (corn stover), Wikimedia Commons (grain sorghum), Beta Renewables (Giant reed), GreenWood Tree Farm Fund (hybrid poplar), USDA (energy cane, napier grass), Shutterstock (switchgrass) Chemical & Engineering News Continue reading
This Gamble On Carbon And The Climate Could Trigger A New Financial Crisis
There is little evidence that institutional investors have recognised that they are sitting on a carbon-asset timebomb Kevin Watkins theguardian.com , Friday 2 August 2013 Summer 2013: eastern Europe is facing one of the heaviest floodings in the last 50 years (Photograph: Ruben Neugebauer/Corbis If you want to see market irrationality in action, look no further than current stock market valuations for the world’s major oil, gas and coal companies. At a time when governments are supposedly preparing for a global climate change deal that will cut carbon emissions , energy multinationals are investing in carbon assets like there’s no tomorrow. Put bluntly, either we’re heading for a climate catastrophe, or the carbon asset bubble will go the way of sub-prime mortgage stock. Yesterday’s disappointing second-quarter results for Royal Dutch Shell provided a useful guide to the future. Over the past couple of years the company has invested heavily in exploration. It has pumped billions of pounds into fracking for natural gas in Ukraine and Turkey; the development of tar sands in Canada, and drilling in the Arctic. The market verdict, prompted by a dip in prices, reduced profits, and concern over costs: a drop in share prices. You can’t help wondering what will happen when carbon prices are aligned with climate imperatives. We are now just two years away from the crucial 2015 UN climate negotiations. If successful, they will put a price on carbon, driving down returns on fossil-fuel investments by capping carbon emissions. Market reactions will make Shell’s results look positively healthy. Yet there is little evidence that institutional investors have recognised that they are sitting on a carbon asset timebomb. You don’t have to dig too hard to find the gap between market valuation and real world ecology. Avoiding dangerous climate change, defined as a temperature rise of 2C, will require the global community to operate within a constrained carbon budget. That budget has a ceiling of 545 gigatons in carbon dioxide (GTCO2) emissions to 2050. Today, state energy firms and private companies are sitting on reserves amounting to three times that level. Carbon arithmetic points in only one direction. If governments are serious about reaching a 2015 multilateral agreement that avoids dangerous climate change, fossil fuel reserves need to left where they are. The Grantham Research Institute on Climate Change at the London School of Economics estimates that only 20-40% of oil, gas and coal reserves held by the 200 largest energy companies can be exploited if we are to avoid dangerous climate change. Yet the market valuation of these “unburnable carbon” reserves is over $4tn, to which can be added $1.5tn in company debt. The misalignment between our planet’s ecological boundaries and energy markets is set to worsen. High energy prices and concerns over power shortages in emerging markets are fuelling a global scramble for carbon assets. Collectively, the 200 largest energy companies invested $674bn (£441.4m) on the development of new fossil fuel reserves in 2012. If financial markets are mispricing risk, governments around the world have yet to recognise some basic cost-benefits realities. Companies investing in Arctic oil and gas exploration stand to gain revenue streams that will be counted in billions of dollars. But as highlighted in a recent Cambridge University study, the rapid melting of Arctic sea ice and permafrost threatens to unlock methane emissions that will generate costs of up to $60tn, much of it associated with the impact of floods, droughts and storms in developing countries. In effect these companies are taking what they see as a one-way bet on governments failing to tackle climate change. It’s a dangerous play. If governments fail to act on their climate change commitments, financial exposure to fossil fuel assets could become a systemically destabilising liability. Five of the 10 top companies listed on London’s FTSE 100, accounting for a quarter of the indexes’ capitalisation, are almost exclusively high carbon. The Australian Securities Exchange has a recklessly high exposure to coal. The New York exchange is also sitting on a large carbon bubble. Energy companies are exposing institutional investors, mutual funds and banks to dangerously mispriced assets, yet current regulatory frameworks are failing to address the systemic threat. Unfortunately, governments are actively encouraging energy companies to bet on dangerous climate change. The European Union has driven the world’s largest carbon market into freefall by oversupplying permits, undercutting incentives for investment in renewable energy in the process. As a group, rich countries spend over $800bn annually actively subsiding fossil fuels , creating markets for oil, gas and coal companies. Britain’s recent decision to grant tax concessions to companies involved in fracking is a recent example of a wider failure to align fiscal policy with climate commitments. For every $1 invested in renewable energy support in the OECD another $7 is spent on carbon-intensive fuels. From a climate change perspective, this is the policy equivalent of a government running an antismoking campaign while removing the tax on tobacco and subsidising cigarette consumption. Developing countries are also trapped in a cycle of policy-induced carbon-intensive growth. Currently, they are spending over $1tn annually to subsidise fossil fuel use, according to the IMF. These transfers often dwarf budgets for health and education. As research at the Overseas Development Institute has highlighted, most of the benefits go to industry, large-scale agriculture and middle-class consumers. Eliminating subsidies for fossil fuels could open the door to a win-win scenario. It would cut energy-related CO2 emissions by 13%, slowing the drift towards the dangerous climate-change cliff. Coupled with signals to indicate that carbon prices will rise and early investment in renewables, it would unlock the private investment and spur the technological breakthroughs needed to drive a low-carbon transition. Diverting fossil fuel subsidies into low-carbon energy cooperation would also generate wider benefits. Developing countries such as India and China are already investing heavily in wind and solar power. But if emerging markets are to break their dangerous addiction to coal and other fossil fuels, they need financial support to phase out their carbon-intensive stock. Providing that support through the reallocation of fossil fuel subsidies would help create markets for low-carbon investors – and it would go a long way towards building trust in international climate negotiations that are too important to fail. •Kevin Watkins is executive director of the Overseas Development Institute, a UK development think tank. Continue reading
