new chemistry


Electricity and Carbon Dioxide Used to Generate Alternative Fuel

Producing fuel from CO2 and sunlight. (Credit: Image courtesy of University of California - Los Angeles)

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 or incompatibility with current transportation infrastructure.

In a study published March 30 in the journal Science, James Liao, UCLA's Ralph M. Parsons Foundation Chair in Chemical Engineering, and his team report a method for storing electrical energy as chemical energy in higher alcohols, which can be used as liquid transportation fuels.

"The current way to store electricity is with lithium ion batteries, in which the density is low, but when you store it in liquid fuel, the density could actually be very high," Liao said. "In addition, we have the potential to use electricity as transportation fuel without needing to change current infrastructure."

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 carbon dioxide as the sole carbon source and electricity as the sole energy input.

Photosynthesis is the process of converting light energy to chemical energy and storing it in the bonds of sugar. There are two parts to photosynthesis -- a light reaction and a dark reaction. The light reaction converts light energy to chemical energy and must take place in the light. The dark reaction, which converts CO2 to sugar, doesn't directly need light to occur.

"We've been able to separate the light reaction from the dark reaction and instead of using biological photosynthesis, we are using solar panels to convert the sunlight to electrical energy, then to a chemical intermediate, and using that to power carbon dioxide fixation to produce the fuel," Liao said. "This method could be more efficient than the biological system."

Liao explained that with biological systems, the plants used require large areas of agricultural land. However, because Liao's method does not require the light and dark reactions to take place together, solar panels, for example, can be built in the desert or on rooftops.

Theoretically, the hydrogen generated by solar electricity can drive CO2 conversion in lithoautotrophic microorganisms engineered to synthesize high-energy density liquid fuels. But the low solubility, low mass-transfer rate and the safety issues surrounding hydrogen limit the efficiency and scalability of such processes. Instead Liao's team found formic acid to be a favorable substitute and efficient energy carrier.

"Instead of using hydrogen, we use formic acid as the intermediary," Liao said. "We use electricity to generate formic acid and then use the formic acid to power the CO2 fixation in bacteria in the dark to produce isobutanol and higher alcohols."

The electrochemical formate production and the biological CO2fixation and higher alcohol synthesis now open up the possibility of electricity-driven bioconversion of CO2 to a variety of chemicals. In addition, the transformation of formate into liquid fuel will also play an important role in the biomass refinery process, according to Liao.

"We've demonstrated the principle, and now we think we can scale up," he said. "That's our next step."


Unexpected Behaviour of Microdroplets

Researchers from the Institute of Physical Chemistry of the Polish Academy ofSciences (IPC PAS) in Warsaw discovered a new phenomenon related to the fluid dynamics. It occurs when minute droplets translate through microfluidic channels. "The effect observed by our group is related to changes in swirls inside microdroplets and as yet has not been predicted by existing theoretical models," says Dr Sławomir Jakieła from the IPC PAS. The results of the research pursued thanks to a TEAM grant from the Foundation for Polish Science, have just been published in the journalPhysical Review Letters.

Microfluidic systems are miniature chemical reactors of a credit card in size, or even less. Inside these systems, microchannels with diameters of tenths or hundredths of a milimeter provide a path for laminar flow of a carrier fluid (commonly oil) with floating microdroplets of appropriate chemical compounds.

"Using a single microfluidic system, even today one can carry out as much as a few tens of thousands of different chemical reactions a day. In future, these systems will become for chemistry what integrated circuits turned out to be for electronics. Yet before we build chemical devices as revolutionary as silicon microprocessors, we have to reach a comprehensive understanding of all physical phenomena occurring in flows of microdroplets," continues Dr Jakieła.

The flows that we experience at the macroscale are often dominated by inertia and turbulences. With small volumes that are typical for microfluidic systems, the flow of a liquid is laminar and subject to viscosity-related effects.

The speed of oil flowing in microchannels is not uniform. The layers close to the walls move with the lowest speed, whereas those near the middle of a channel -- with the highest speed. "If a microdroplet is distinctly smaller than the channel diameter, it can find a place in the middle part of the flow, reaching the speed even twice as high as the average oil speed. This is nothing surprising. Similar effect can be observed for instance in rivers: the current near the banks is much slower than in the middle of the river," explains Sylwia Makulska, a PhD student at the IPC PAS.

If a sufficiently large droplet flows in a circular channel, it occupies almost the entire lumen of the channel. The droplet speed is then almost identical as that of the oil flow. The situation gets much more interesting when the droplet translates in rectangular channels that are typical to microfluidic systems. Due to interfacial tension the cross-section of a microdroplet remains rounded leaving the corners of the channel free for the flow of oil.

The team from the IPC PAS produced microdroplets from aqueous solutions of glycerine of different concentrations, and therefore of different viscosities. They translated in oil (hexadecane) through a 10 cm long rectangular channel. The researchers measured the speed of microdroplets relative to the oil as a function of their volume (length in a microchannel), droplet and oil viscosities and the flow speed of the carrier liquid.

When the viscosity of microdroplets was less than or comparable to that of the carrier liquid, their speed relative to the oil turned out to decrease with increasing droplet length, but in a certain range only. The droplets were translating with the lowest speed when their length was two, three times greater than the channel width. "Every time we observed the minimum speed relative to oil. Everything seemed to be in line with what the theoreticians would expect," says Jakieła.

But what was really interesting were things that happened when the researchers started to change the rate of oil flow. It turned out that the minimum of the droplet speed relative to oil was disappearing with increasing flow rate. Further increase in the oil flow rate resulted, however, in reappearance of the minimum -- but this time deeper and wider. "To make the long story short: we discovered that, depending on the oil flow rate, a droplet of specific length can translate under some conditions faster and under other conditions slower relative to oil," concludes Jakieła.

To find out what is the reason for the surprising behaviour of the droplets, the researchers from the IPC PAS introduced to microdroplets fluorescent markers of a few micrometers in size. When the droplets were moving along the microchannel, they were irradiated with laser light to excite fluorescence of the markers, which allowed for observation of fluid movements inside the droplets.

The measurements revealed that the distribution of swirls inside a droplet changes with increasing flow rate of the carrier liquid. "We expected changes, but the existing theories suggested that the number of swirls in microdroplets decreases with increasing oil flow rate. We observed, meanwhile, an opposite phenomenon: the faster was the oil flow, the more swirls were in a droplet. The Nature played again a trick on theoreticians," sums up Prof. Piotr Garstecki (IPC PAS).


Generating First-Ever Controlled Ultrafast Radiation Using a Plasma


Electrochemical oxidation is described as a very efficient polymerization procedure for the heterogenization of metallic chiral catalysts. From chromium chiral complexes based on salen–thiophene ligands, this methodology provided an efficient access to various polymers. Recovered as insoluble powders, these materials were tested in different enantioselective heterogeneous catalytic reactions. Structural modifications were introduced on the salen core in order to evaluate their influence on redox polymer properties and on the enantioselectivity of the catalysis. Electrochemical experiments showed the particular stability of these deposited materials at the electrode surface and SEM analyses suggested the influence of the electropolymerization conditions on their morphology.

Graphical abstract: Electropolymerization of chiral chromium–salen complexes: new materials for heterogeneous asymmetric catalysis
RSC Publishing Logo
The salt metathesis reactions of [(η7-C7H7)ZrCl(tmeda)] (1) with various boratabenzene ligands Li(C5H5B–R) (R = H, CH3, C[triple bond, length as m-dash]C–SiMe3) afford the 16-electron sandwich complexes [(η7-C7H7)Zr(η6-C5H5B–R)] (2: R = H, 3: R = CH3, 4: R = C[triple bond, length as m-dash]C–SiMe3). The molecular structures of 3and 4 were determined by X-ray diffraction analyses; they display distorted η6-coordinated boratabenzene ligands with short Zr–B bonds of 2.683(2) and 2.649(6) Å. The possibility of an η6–η5 hapticity interconversion, accompanied by B–L bond formation, upon addition of a Lewis base L (L = PMe3, 4-(dimethylamino)-pyridine) to 3 was studied. However, Zr–L bond formation was observed instead, leading to [(η7-C7H7)Zr(η6-C5H5B–CH3)(L)] (5: L = PMe3, 6: L = 4-(dimethylamino)-pyridine), even if a large excess of L was used.

Graphical abstract: Boratatrozircenes: cycloheptatrienyl zirconium boratabenzene sandwich complexes – evaluation of potential η6–η5 hapticity interconversions
/ 0 نظر / 50 بازدید