Research and Development

A new study on thermal decomposition of a potential fuel additive has shown that it could make biofuels cleaner and have more efficient combustion.

Scientists have been researching additives made of oxygenated organic compounds that could help reduce the release of pollutants into the atmosphere as well as increase the efficiency of combustion of fuels. Researchers from the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia have learned how these potential additives decompose under combustion.

Diethyl carbonate (DEC), which is 40.6% oxygen by mass, has the potential to facilitate clean combustion of diesel fuels. KAUST scientists evaluated the effects of pressure and temperature on the decomposition of DEC to understand its decomposition. They found that DEC had a significant effect on the decomposition of organic esters, lowering the reaction energy and increasing its reactivity.

These findings will present more knowledge on the application of biodiesel fuels to modern diesel engines and engine hybrids. Furthermore, it will also clarify the blending effect of esters and carbonates with conventional fuels.

Using microbes growing in two diverse climatic conditions, A team of researchers from Delhi's Jawaharlal Nehru University (JNU) have found a way to convert carbon-rich waste materials into biofuel.

Researchers discovered two distinctly different species of bacteria from Aravalli marble mines in India and found that they can, in combination, produce biodiesel from carbon-containing waste materials. The first bacterium, Serratia sp. ISTD04, is capable of harvesting carbon dioxide into organic compounds. Meanwhile, lipase from the bacterium Pseudomonas sp. ISTPL3, can convert these lipids into biodiesel.

The Serratia sp. microbe sequesters carbon dioxide linked to climate change and converts it into lipids. Moreover, 60% of its body weight is made up of lipids that can be converted into biodiesel via transesterification. The scientists were amazed to see the lipase having a very high conversion efficiency. They have also demonstrated that the lipase from Pseudomonas sp. could be recycled several times.

In a previous study, scientists from the US National Renewable Energy Laboratory discovered an enzyme, CeIA from Caldicellulosiruptor bescii, adept at breaking down cellulose fibers regardless of its crystalline structure. According to the research, no other enzyme has shown this ability.

The original research showed that CeIA could convert biomass to sugars faster than competing commercial catalysts. This new study now focuses on how the enzyme could help remove one of the main barriers preventing cellulosic biofuels from becoming a commercial reality: the crystalline structure of cellulose.

The structure of cellulose in cell walls has been a problem for cellulases, with fungal enzymes unable to easily break down fibers with high crystalline content. CeIA however, was found to be unaffected by the level of crystalline content. It is capable of breaking down cellulose regardless of its crystallinity.

Researchers looked at how CeIA performed in breaking down and interacting with the components of cell walls in corn stover. Chemical pretreatments were used on corn stover and silky fibers called cotton linters, leaving behind various amounts of the components and varying degrees of crystallinity.

The only obstacle to CeIA was lignin, the component which gives rigidity to cell walls. With some of the chemical pretreatments, some lignin remained, stopping the enzyme.

Energy Crops and Feedstocks for Biofuels Production

Recalcitrance and plant lodging are two traits associated with plant cell wall features. While genetic modification of cell walls can reduce recalcitrance, it is still a challenge to maintain a normal plant growth with enhanced biomass yield and lodging resistance in rice. Sucrose synthase (SUS) is an enzyme regulating carbon partitioning in plants. Although SUS transgenic plants have exhibited improvement on cellulose and starch based traits, little is known about SUS effects on recalcitrance and lodging resistance.

Chunfen Fan from Huazhong Agricultural University selected the transgenic rice plants that expressed OsSUS3 genes that promote secondary cell wall cellulose synthesis in Arabidopsis. The team then examined biomass saccharification and lodging resistance in the transgenic plants.

Transgenic plants maintained a normal growth with slightly increased biomass yields. The four independent transgenic lines exhibited much higher biomass enzymatic saccharification and bioethanol production under chemical pretreatments compared with the control rice cultivar. Notably, all transgenic lines showed a consistently enhanced lodging resistance.

Further analysis revealed that the reduced cellulose crystallinity was a major factor for the enhanced biomass saccharification and lodging resistance in transgenic rice. Moreover, cell wall thickenings with the increased cellulose and hemicelluloses levels also contributed to plant lodging resistance.

This study showed that the SUS3 transgenic rice plants exhibited largely improved biomass saccharification and lodging resistance by reducing cellulose crystallinity and increasing cell wall thickness.

Microorganisms such as baker's yeast can be compared to miniature factories. The raw materials, usually sugars, are converted in a multi-stage process with the help of enzymes. Microbes generate desirable products along with many by-products. Various enzymes compete for sugar whereby different building blocks important for the cell's survival are formed.

Thomas Thomik and Dr. Mislav Oreb of Goethe University Frankfurt have succeeded in engineering the metabolism of baker's yeast to use sugar more productively. The team constructed an artificial complex between a sugar transporter and a heterologous xylose isomerase in Saccharomyces cerevisiae. This new mechanism made transport proteins deliver the raw materials directly to the enzymes, resulting in accelerated xylose conversion into ethanol and diminished the production of the by-product, xylitol.

Biofuels Processing

Ethanol, a biofuel additive for gasoline, is traditionally produced from biomass. However, a new research has developed a catalyst that can produce the fuel directly from carbon dioxide.

Scientists from the US Department of Energy's Lawrence Berkeley National Laboratory have developed a new electrocatalyst, made from copper nanoparticles, that directly converts carbon dioxide into multi-carbon fuels and alcohols using lower overpotential than typical electrocatalysts. The new electrocatalyst creates the right conditions needed to break down carbon dioxide to form ethylene, ethanol and propanol.

Overpotential refers to the amount of extra voltage needed to drive a chemical reaction in excess of the thermodynamic potential of the products of that reaction. The lower the overpotential, the more efficient the catalyst is. The team estimated that if the catalyst were incorporated into an electrolyzer as part of a solar fuel system, a material only 10 cm2 could produce about 1.3 grams of ethylene, 0.8 grams of ethanol and 0.2 grams of propanol per day.

Pretreatment of biomass with dilute acid requires high temperatures of higher than 160C to remove xylan. However, it does not remove lignin, the main cause for recalcitrance in lignocellulosic biomass. Hyeong Rae Lee of Seoul National University in South Korea now reports that the addition of peracetic acid, a strong oxidant, to mild dilute acid pretreatment reduces the temperature requirement.

Pretreatment of yellow poplar with peracetic acid (300 mM) and dilute sulfuric acid (100 mM) at 120C for 5 min removed 85.7% of the xylan and 90.4% of the lignin, leaving a solid consisting of 75.6% glucan, 6.0% xylan and 4.7% lignin. The solid was then converted to glucose, with an 84.0% yield. This amount of glucose was 2.5 times higher than with dilute acid-pretreated solid and 13.8 times higher than with untreated yellow poplar.

The addition of peracetic acid, which is easily generated from acetic acid and hydrogen peroxide, significantly increases the effect of dilute acid pretreatment of lignocellulosic biomass.

Scientists from Michigan State University (MSU) are now looking to find new algae-based technologies that could capture power plant emissions and convert them into products, including biofuels and other chemicals.

Previous researches have revealed that photosynthetic green algae is capable of capturing carbon dioxide and other greenhouse gases from the atmosphere. However, it is not enough to match the emissions of a conventional power plant. A 100-megawatt coal-fired power plant releases around 3,000 and 4,000 tons of carbon dioxide per day. It would require thousands of acres of land to culture sufficient amount of algae to match the amount of emissions.

The MSU team is now working to condense this process into something viable. They aim to apply a process called "biomass cascade conversion". This process can fully optimize the components of algae for the production of high-value chemicals and biofuels.

An environment-friendly, high efficiency carbon dioxide absorbent is a key product of cascade conversion, one which absorbs carbon dioxide at a relatively high rate and requires significantly less space. Researchers state that biomass cascade conversion can present significant economic benefits for the environment and the power plant.

Polyurethanes, biofuel, and valuable chemicals can be produced from cascade conversion.