Converting CO2 into Higher Alcohols By Thomas Cleary, Monica Callaghan, and Peiyu Guo

Overview The 2010 Academic Award went to James C. Liao of the University of California for his work on converting carbon dioxide into higher alcohols This was achieved by genetically engineering microorganisms to make higher alcohols from glucose or directly from carbon dioxide Higher alcohols are defined by having more than two carbons in the molecule They have a higher energy content than biofuels such as ethanol so they serve as a better building block for fuel

Higher Alcohols Higher alcohols, especially those with 3-8 carbon atoms, are useful as chemical feedstocks and transportation fuels. Native organisms do not synthesize these alcohols None of these alcohols have been synthesized directly from carbon dioxide before this and alcohols with more than 5 carbon atoms have never been synthesized in nature.

The Original idea that how transfer CO2 to other compound Use the photosynthetic machinery. The initial process in Calvin Cycle of plant cell is that native organism is to produce the sugar If can add or change some chemicals in that cycle, that will change the products eventually and achieve something new. Like longer chain alcohols.

Alternative Pathway to produce alcohols pyruvate Nature can automatically produce only 1-butanol and Iso-propanol, but so far scientists cannot improve that way very much. Other higher alcohols nature hasn’t produced yet. Dr. Liao and his team found an alternative pathway to create those longer chain alcohols. PDC Acetaldehyde Is there a way to produce n-Butanol by Non-CoA pathway? It’s challenge for scientists to build way to create longer chain butanol ADH This is how industry produce Ethanal Ethanol This is traditional way here to produce longer chain

Apply some step to Bio-system. Dr. Liao’s team has already found something new in environment which is Lactococcus lactis KdcA that has same type of reaction, same type of structure with PDC, so they clone this way to bio-system. Furthermore, they have detected different types of long chain alcohols.It proves that it works well. They solved the half of problem, the longer chain Keto-acid can go to longer chain alcohol.

How could elongate the pyruvate The most challengeable step in process of producing longer chain alcohols is how elongate the shortest chain of pyruvate, it has only three carbon atoms. Here is the nature way that make pyruvate longer found by Dr. Liao’s team.

First Steps of the Process Liao and his team first started by trying to find alternatives to a bacteria, Clostridium acetobutylicum, that enables a starch fermentation process that makes a mixture of butanol, acetone and ethanol, called the ABE process. They did this because the Clostridium acetobuylicum is difficult to grow, has poor selectivity for a single product, and is difficult to genetically alter. The team made and re engineered a different strain of the bacteria that led to microbes that produce enzymes that convert sugars into isobutanol and other higher alcohols

The Process Dr. Liao’s process involves leveraging the highly active amino acid biosynthetic pathway, diverting its 2-keto acid intermediates toward alcohols From this process he produced isobutanol from glucose They also transferred the pathway into a photosynthetic microorganism, Synechococcus elongatus PCC7942, in order to produce isobutyraldehyde and isobutanol directly from carbon dioxide

Isobutyraldehyde (C4H8O) Isobutanol (C4H10O)

The Process (contd.) The lithoautotrophic microorganisms produced by Liao are known as Ralstonia eutropha H16. These were used to make isobutanol (3-methyl-1-butanol) in an electro-bioreactor It used CO2 as the only carbon source and the only energy input was electricity Photosynthesis has two reactions, a light and a dark reaction. The light reaction converts light energy into chemical energy, and it must take place in light. The dark reaction converts CO2 into sugar and does not need light to happen. Liao was able to separate the light reaction from the dark. Instead of using biological photosynthesis, they were able to make the sunlight into electricity, then to a chemical intermediate, and then were able to make fuel with the CO2 fixation

Modified microbes turn carbon dioxide to liquid fuel Today, electrical energy generated by various methods is still difficult to store efficiently. Chemical batteries, hydraulic pumping and water splitting suffer from low energy-density storage, but when you store it in liquid fuel, the density could actually be very high Liao and his team genetically engineered a lithoautotrophic microorganism known as Ralstonia eutropha H16 to produce isobutanol and 3-methyl-1-butanol in an electro-bioreactor using electricity as the sole energy input. http://phys.org/news/2012-03-microbes-carbon-dioxide-liquid-fuel.html

Significance This process is more efficient than producing ethanol from corn Higher alcohols are also better than ethanol in several regards, they have a higher energy density, lower hygroscopicity, and lower vapor pressure (which results in better air quality) If 60 billion tons of higher alcohols were used each year as chemical feedstocks and fuel about 500 million tons of carbon dioxide could be eliminated (approximately 8.3 percent of the U.S.’s carbon emissions). Easel Biotechnologies is commercializing the process under exclusive license from UCLA