Friday, February 29, 2008

New Carbon Capture Pilot Plant in Wisconsin

ALSTOM, The Electric Power Research Institute (EPRI) and We Energies just announced a CO2 capture demonstration power plant in Wisconsin using a chilled ammonia process to remove the CO2 from the flue gas. The plant aims to capture about 90% of the CO2 emitted by the power plant. The size of the power plant is ~1210 MW (electric) [actually 2 x 617 MW]. According to this presentation on the web, ALSTOM clearly is seeking to take the lead on making conventional pc fired plants ready for a carbon constrained environment by retrofitting the plant.

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Saturday, February 16, 2008

Energy saving initiatives across the world

The Wall Street Journal describes energy saving initiatives that cities across the world have adopted, either in response to mandated targets (Amsterdam), or external pressure (Beijing) or better reasons. Reading about Chicago's green buildings reminded me of the LEED certification of buildings at Penn State and the Green Design Institute at Carnegie Mellon. More info after the jump.

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Sunday, February 10, 2008

Can biofuels cause global warming ?

A recent biofuels study published in Science points that the use of natural lands for growing biofuels leads to more CO2 emissions compared to the case where no forest lands are cleared. In an interview about a related topic, another scientist points out that using biofuels over fossil fuels actually increases CO2 emissions because the soil carbon released to the atmosphere. There however are are some ppl who disagree with the study's findings, citing uncertanities in modeling the soil carbon cycle arising out of land use changes (tilling, fertilizer use etc..) as one of the study's main weaknesses. Soil carbon turnover rates in the tropics are be much higher than those in temperate climates. I guess that this is one of the key issues the Science study tried to address; they used a global agricultural model to estimate these emissions. The use of waste biomass (ex: from forests) and producing biofuels without converting additional natural habitats to farmland, will not cause additional CO2 emissions.

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Thursday, February 7, 2008

Dow Methane Challenge

Dow Chemical recently announced that academic teams led by Northwestern University and Cardiff University, Wales were selected for $6.4 million in grants over 3 years to fund research on the direct conversion of methane to olefins and olefin precursors. Currently, these compounds are made via the syngas (CO+H2) route. The need to utilize stranded gas reserves and provide alternate sources of petrochemical precursors drives this research. Methane is a tough nut to crack, because of the stability provided by the C-H bonds. Low temperature methane oxidation is therefore considered a "grand challenge".

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Saturday, February 2, 2008

Bioethanol: gasification and biofermentation

A recent USA Today article points out that Coskata, a bioethanol startup company has been backed by GM. Their ethanol production differs from others in that, they combine an initial biomass gasification step to produce syngas (carbon monoxide + hydrogen) and subsequent microbial production of ethanol. Some industry analysts believe that this represents an innovative combination of gasification and biofermentation technologies.

The reaction of carbon monoxide (CO) and hydrogen (H2) to produce ethanol (C2H5OH) is exergonic at standard temperature and pressure (STP). This reaction, however, suffers from problems of selectivity. Among the direct syntheses of alcohols from syngas, only methanol synthesis is 99% selective and also has high product formation rates. Ethanol formation is represented as:

3CO + 3H2 ---> C2H5OH + CO2 [Free energy of reaction at STP ~ -157 kJ/mol EtOH]

CO/H2 ratios of 1:1 are needed to produce ethanol. Each mole of ethanol produced generates a mole of CO2. Biomass (lignin-wood-cellulose) has atomic O/C ratios from 0.5-0.8 and H/C ratios from 1.1 to 1.8. Gasification of various feedstocks will result in different syngas compositions. The need for CO:H2 ratios of 1:1 necessitates water-gas shift reactions to convert some of the CO to CO2 to adjust the CO:H2 ratio in the feed.

CO + H2O ---> CO2 + H2

According to Coskata's website, the advantages of their biological process for ethanol conversion are the selectivity towards ethanol (lower separation costs), higher impurity tolerance of their microbes vis a vis chemical catalysts, lower operating pressures, and most significantly, IMO, variable CO:H2 ratios.

The use of gasification to produce a syngas stream makes it possible to process a variety of biomass feedstocks. A distinguishing feature of the biofermentation might be the use of bacteria to drive similar water-gas shift reactions in the culture medium itself. For example, recently researchers have found microbes (Carboxydothermus hydrogenoformans) which can convert carbon monoxide and water to hydrogen (and CO2).

The advantages of the process are that by regulating the concentration of the CO metabolizing bacteria, one can theoretically produce varied CO:H2 ratios (in the fermentor) for ethanol production. In this scenario, the use of bacteria like Carboxydothermus hydrogenoformans to shift CO and water to H2 is critical to the success of this process.

It therefore appears that this novel combination of gasification and biofermentation may have definite advantages in product selectivity, operating conditions, and also raises interesting questions of process design for other reforming processes in general. For example, one can think of methane reforming, bacteria producing methanol. I think the next big step in biocatalyst design will be the use of enzymes to drive reactions such as the conversion of CO2 to specific chemicals like ethanol or methanol upon reaction with hydrogen or through electrochemical reduction. Typically, reactions involving CO2 (and many other compounds) need specific metal catalysts for product specificity and yield. The aforementioned Carboxydothermus hydrogenoformans bacteria contains a collection of enzymes (CO dehydrogenases) , one of which has been shown to activate CO2 at electrodes. It all comes full circle at some point, after all.

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