More bioethanol with yeasts?

 

A great amount of ethanol fuel is currently produced by starch fermentation. This starch comes from grains such as wheat and maize. Fermentation is produced by a yeast culture. The digestion of starch by yeasts is done in two stages: the starch is initially hydrolyzed in sugars by a chemical or enzymatic process then sugars are converted into alcohol and carbon dioxide by yeasts. This operation is effective and extracts the solar energy stored in the starch.

This transformation uses noble agricultural products and competes with their food use. It would be more interesting to use cellulose contained in the stems and the sheets of the cereal plants, in particular maize. This cellulosic material is much more abundant than the grain and does not have a great economic value. However the yeasts are not usable for this operation because they do not have the capacity to hydrolyze cellulose in sugars. Many researches are currently made to industrialize this stage of hydrolysis of cellulose. The realization of this stage will give access to the biofuel of second generation, produced in greater quantity and at lower cost.

A part of bioethanol fuel is produced by a discontinuous process. The digestion of the hydrolyzed starch by yeasts is done in large industrial bioreactors. When the totality of the starch is digested, the bioreactor is emptied. The yeasts are recovered to treat the next batch. Produced alcohol is concentrated by distillation.

It seems to me that this discontinuous process could be used for experimentation with the aim to obtain bioethanol with cellulose. Because of this discontinuous operation, the yeasts are submitted to a food stress when they finish transforming the sugars in the bioreactor. This state of stress is favourable to impose a controlled evolution on yeasts.

The technique of controlled evolution consists, by combining stress and food, to obtain a genetic transformation of a biological culture. This process has already obtained the evolution of bacterial cultures for the digestion of organochlorinated compounds which, normally, are not degraded by the bacteria. The bacterial cultures, put in a state of food stress and in the presence of organochlorinated compounds, developed a capacity to digest these compounds.

The controlled evolution applied to yeasts could consist in adding in an industrial bioreactor producing bioethanol a small quantity of cellulosic material. The food stress that the yeasts endure when they digested the most part of sugars could make them develop a capacity to hydrolyze cellulose.

The hydrolysis of cellulose is made via several enzymes named cellulases. A study published in may 2008 (*) has shown the presence of genes coding several cellulases in the genetic code of Sacchromyces Cerevisiae, the yeast used for the production of bioethanol. The goal of the controlled evolution is to push the expression of these genes coding cellulases.

The great volume of industrial bioreactors should be a favourable factor to the evolution of yeasts. The probability of appearance of a genetic mutation of yeasts is proportional to the number of yeasts submitted to the experimentation, and this number is much greater in industrial bioreactor than in a laboratory bioreactor.

The cost of this experimentation could be moderate because it could be inserted in the normal process of production of bioethanol:
- at the start of fermentation, a small quantity of cellulosic material is added in the bioreactor with the hydrolyzed starch and the yeast culture,
- at the end of fermentation, when the bioreactor is emptied, a filtration permits to recover yeasts and the no digested cellulosic material, whereas a distillation concentrates the produced ethanol,
- the recovered yeasts are used to treat the following batch of starch, the presence of cellulosic material in the culture maintains the evolutive pressure on yeasts.

By this cheap experimentation on the industrial production of bioethanol, we could perhaps obtain a slow evolution of yeasts toward a biofuel based on cellulose.

(*) : Genome sequencing and analysis of the biomass-degrading fungus Trichoderma reesei, Nature Biotechnology, Volume 26, Number 5, May 2008.

pf button More bioethanol with yeasts?

Solar chimneys against tornados

The meteorological conditions of formation of tornados are complex but there is a constant: lower part of atmosphere is particularly hot and humid some hours before the beginning of a tornado. The thermal contrast between low hot atmosphere and upper cold atmosphere is instable and the mixture of these layers starts abruptly. The tornados are generated during this mixture.

Since the years 80, the German scientist Jorg Schlaich and his team propose an original way to convert solar light in electric energy: the solar chimney. A solar chimney works in three steps:
- solar radiation heats the air under an horizontal glass roof (the collector),
- at the centre of the glass roof, emerges the chimney ; the hot air flows to the chimney and rises, due to its lower density ; the cold air enters from the outer perimeter of collector as hot air is drawn in the chimney,
- at the base of the chimney, some turbines convert the kinetic energy of ascending hot air in electric energy.

In his book “Solar Chimney” (*), Jorg Schlaich describes some cases of solar chimneys:
- power 5MW, collector diameter 1110m, chimney diameter 54m, chimney height 445m,
- power 30MW, collector diameter 2200m, chimney diameter 84m, chimney height 750m,
- power 100MW, collector diameter 3600m, chimney diameter 115m, chimney height 950m,
- power 200MW, collector diameter 4000m, chimney diameter 175m, chimney height 1500m.

The case of the highest chimneys is particularly interesting. The data contained in the book show that these tall chimneys propel great amounts of hot air at altitude about 900m or more. At full power, a 100 MW solar chimney injects each second about 150000 cubic meters of air at altitude greater than 900m.

By its constant injection of hot air at high altitude, a solar chimney could reduce the thermal contrast between hot lower air layer and cold upper air layer. The reducing of this thermal contrast could diminish the power of the tornados in the region where is located the solar chimney.

Besides its electric production, a solar chimney could perhaps help to control tornados, one the most destructive meteorological phenomenon.

(*) Solar Chimney, Jorg Schlaich, Michael Robinson, 1995, Axel Menges GmbH, ISBN: 3930698692

 

pf button Solar chimneys against tornados

Sonofusion with tritium

Is it possible to test the sonofusion with the deuterium-tritium reaction?

The research on sonofusion tries to obtain nuclear fusion in deuterated liquids. In a typical experiment of sonofusion, a beam of neutrons generates tiny bubbles in the liquid. An ultrasound field expands and contracts these bubbles. The nuclear fusion could occur when the collapse of bubbles is sufficiently fast to generate an intense shock wave. The last experiment of Rusi Taleyarkhan and his team has demonstrated the emission of neutrons in deuterated acetone.

With deuterated products, the possible reactions are:
D + D > He3 + n
D + D > T + H

These reactions are not easy whereas the reaction between deuterium and tritium is the easier reaction of nuclear fusion:
D + T > He4 + n

If we could test the sonofusion with a mix of deuterium and tritium, the signs of fusion could be more evident. But the use of tritium is very expensive because it doesn’t exist in nature. It must be generated by a nuclear reaction:
Li6 + n > He4 + T

So the test of sonofusion with the DT reaction obliges the use of a very small amount of tritium.

A mean to limit the amount of tritium in a sonofusion experiment could be the use of tritiated tensioactive molecules.

These molecules, dissolved in heavy water, could be like for example CH3-(CH2)n-phenyl-SO3 Na (alkyl-phenyl-sulfonate) where one or several hydrogen atoms are replaced by tritium atoms.

When this sort of solution is exposed in sonofusion experiment, the neutron beam generates bubbles. These bubbles grow during the depressive phase of the sonic wave.

What could be the comportment of tensioactive molecules? I propose two hypothesis:
- the tensioactive molecule that encounters the surface of the bubble remains glued on this surface by its apolar part,
- when the compressive phase of sonic wave occurs, the bubble surface drags the tensioactive molecules.

By this way, a mix of deuterated water molecules and tritiated tensioactive molecules could be concentrated on the top of the shock wave in final collapse of bubble.

If this scheme works, it could be possible to study the sonofusion of deuterium and tritium in heavy water.

The synthesis of tritiated molecules is a standard technique, particularly for the biological research. Used as a radioactive marker, the tritium permits the study of chemical or biological reactions.

A very small amount of tritium seems to me sufficient to start D-T reactions. Some calculations and hypothesis suggest that sonofusion with tritium could be tested with a solution of heavy water containing less than 100 micromoles of tritium per liter.

pf button Sonofusion with tritium

Planet detection by natural laser emission

These last years, the search for extrasolar planets has been successful. To date, the astronomers have detected more than 400 extrasolar planets. Among these 300 planets, only ten have been discovered by their own light.

There is perhaps a phenomenon which could facilitate this search for extrasolar planets.

The astronomer Michael Mumma and his team have discovered in 1981 (*) a natural laser emission produced by the Martian upper atmosphere. This very fine emission ray centered on 10,33 µm is due to carbon dioxide, majority component of the Martian atmosphere. This natural laser emission has been not only confirmed by other teams but another natural laser has been discovered in the Venusian upper atmosphere.

In consequence of these discoveries, one can suppose that this phenomenon of stimulated emission generated by a planetary atmosphere is frequent.

This phenomenon of stimulated emission could be used for the search for extrasolar planets. The direct detection of an extrasolar planet conflicts, with current technology, with a considerable obstacle: the difference of brightness between planet and its star companion. If the studied planet has an atmosphere and if this one presents a stimulated emission, the brightness of planet in the emission ray could be amplified considerably. To benefit from this emission, it would be necessary to detect very thin rays. With this condition, the ratio of brightness between star and planet could become more favorable for a direct detection.

A first step in the use of this phenomenon could be the checking of its presence on the extrasolar planets already discovered.

Several ray masers would deserve a detailed attention: the ray at 23.7 GHz emitted by molecule NH3 and the rays at 22 GHz and 1.66 GHz emitted by molecule H2O and radical OH. As the stars emit little in this part of electromagnetic spectrum, one can hope for a ratio of brightness more favorable for the planet detection. The ray maser of ammonia could be a good marker for gas giant planets. The masers of water and radical hydroxyl would be good indices for planets similar to Earth.

(*): “Discovery of Natural Gain Amplification in the 10-Micrometer Carbon Dioxide Laser Bands one Mars: A Natural Laser”; MICHAEL J MUMMA, DAVID BUHL, GORDON CHIN, DRAKE DEMING, FRED ESPENAK, THEODOR KOSTIUK, and DAVID ZIPOY; Science, 3 April 1981, Vol. 212, No 4490, pp. 45  – 49.

pf button Planet detection by natural laser emission