Patent Application
20160230292
The present invention relates to a method for dissociating an aqueous solution comprising:
Optionally, the pulsed light is a coherent light, i.e. generated by a laser.
Such a method is for example known from document Biochimica et Biophysica Acta 1817 (2012) 1028-1212, of Sheleva and Messinger, which discloses the electrochemical oxidation of water in the presence of light.
This method most particularly finds its application within the scope of producing renewable energy from solar light.
PSII is a photosensitive enzymatic molecular complex comprising pigments (chlorophyll) which is the centre of water hydrolysis in the chloroplasts present in the cytoplasm of plant cells according to the following reaction:
wherein hv corresponds to a light photon, for example of solar light, H2O is water, H+ represents a free proton and e− represents a free electron.
The enzymatic complex PSII, because of its hydrolyzing function, produces from light, oxygen on the one hand, and free electrons and free protons on the other hand, is of a particular interest within the scope of its use for producing, via a cathode, a clean fuel which is hydrogen gas (as a gas under standard temperature and pressure conditions). Indeed, the cathode gives the possibility of recombining the e− and the H+ (reduction reaction of protons) in order to form the hydrogen. With this in mind, this enzymatic complex is a promising actor for producing clean fuel, i.e. the combustion of which is not associated with the production of CO2, from natural energy: light, which furthermore is a quasi-inexhaustible source of energy.
Consequently, hydrogen gas, resulting from the reduction of the free protons which are associated with the free electrons, combines to oxygen resulting from the hydrolysis reaction in order to produce a combustion reaction, which results in production of energy on the one hand and of water on the other hand which may be again hydrolyzed by the PSII complex, so that a water cycle is formed, thereby forming a quasi-inexhaustible source of clean fuel. Further, the oxidation assisted by the PSII complex allows the formation of oxygen and hydrogen in situ, and is an answer to the present problematical question of the conditioning of hydrogen which, when it is formed in situ, no longer requires being stored under limiting packaging forms such as those known presently: large volumes, significant pressures, etc.
According to the document Biochimica et Biophysica Acta 1817 (2012) 1028-1212, there are successive absorptions of photons of light by the pigments of PSII. To each absorption corresponds a chemical oxidation-reduction reaction which takes place in the enzymatic complex PSII. Moreover it is known from the state of the art that the successive absorption of four light photons by the pigments of PSII exclusively allows successive achievement of four oxidation-reduction reactions forming a photochemical cycle (Kok cycle) at the origin of the oxidation of water into oxygen, on the one hand, and into free protons and free electrons on the other hand.
Moreover, it is known from the state of the art that the activity of the PSII complex is inter alia regulated by that of the PSI complex.
The activity of PSII is measured by the production rate of oxygen in the water, the higher this rate, the higher is the yield of the water oxidation reaction by PSII, i.e.
the higher is the amount of produced oxygen.
Indeed it is known that, the presence of the PSI complex, because of its function in the mechanism for producing energy by photosynthesis, consumes the free photons and electrons indirectly intended subsequently for the reaction of synthesis of sugars by polymerization of CO2.
It is therefore advantageous that the PSII complex is insulated from the PSI complex so that the water oxidation reaction increases in yield. In practice, the PSII complex is isolated from the PSI system, the latter being replaced by a sensor (device, product, material) or a group of electron and proton sensors which have the property of not inhibiting the activity of PSII. As an example, the electron and proton sensor may also be a cathode allowing reduction of the protons into hydrogen gas.
By the term of <<isolated>>, is meant in the sense of the invention that the PSI complex is not able to cooperate with the enzymatic complex PSII.
In the aforementioned method, the activity of the PSII is mainly limited by the concentration and the nature of the electron sensors and proton sensors or electron and proton sensors which, for example react with the free protons and the free electrons in order to undergo reduction.
This aspect is moreover underlined in the article of Sheleva and Messinger mentioned at the beginning and wherein the authors demonstrate the efficiency of the turnovers for an enzymatic complex PSII according to the chemical nature of the electron sensors.
By the term of <<turnovers>>, should be understood the number of steps of each looped Kok cycle per unit time, it being understood that a full Kok cycle comprises four successive turnovers since it is associated with consecutive absorption of four protons of light.
During the interaction of light with the enzymatic complex, a first charge separation S0→S1 takes place and is followed by three other charge separations S1→S2, S2→S3, and S3→S4. With each of these charge separations is associated an oxidation-reduction reaction of the Kok cycle with, when the cycle is a closed loop, formation of oxygen and of free protons as well as free electrons, and the return of the complex from the state S4 to the state S0.
In particular, the authors demonstrate that one of the four oxidation-reduction reactions of the Kok cycle: the reduction reaction, governed by the reactivity of the electron sensor, is the limiting step of the Kok cycle.
Also, Sheleva and Messinger suggest that the yield of the enzymatic complex PSII may be optimized by selecting a predetermined pulse frequency value which is a specific pulse frequency of the pulsed light associated with a predetermined reduction reaction rate which occurs in the immediate environment of the electron capture group of the enzymatic complex PSII.
In this way, to a specific electron sensor corresponds a specific pulse frequency: the question is therefore to optimize the pulsed frequency of the pulsed light according to the reduction reaction rate on the reducing site of the enzymatic complex PSII and therefore according to the chemical nature of the electron sensor in order to have a number of turnovers per unit time as high as possible, and therefore of the number of Kok cycles per unit time.
Unfortunately, if the method of the state of the art puts forward promising conclusions as regards an optimization route of the operation of the enzymatic complex PS II, it remains nevertheless limited to a major constraint in the requirement of having a source of light of constant energy in time and sufficient for saturating the Kok cycle of the enzymatic complex PSII, the energy level of the light source being governed by the physicochemical nature of the enzymatic complex PSII, in particular by the chemical composition of the electron capture and donor groups.
The object of the invention is to overcome this drawback of the state of the art by providing a cost-effective method for dissociating an aqueous solution, while allowing the utilization on an industrial scale of a source of light energy and uncontrolled, such as for example solar energy or electric energy of a renewable origin, and transforming it into hydrogen and oxygen produced in situ so as to be able to have a source of fuel and a source of oxidizer which may be directly used for example on site.
In order to solve this problem, according to the invention a method as indicated initially is provided, characterized in that said light energy has a variable energy value overtime and in that said method further comprises a step for modulating said predetermined pulse frequency value of said pulsed light to a sufficient pulse frequency value in order to obtain a first yield for producing oxygen per unit of light energy which is greater by a factor comprised between 1.01 and 100.00 than a second oxygen production yield per light energy unit obtained for a second electrochemical oxidation in the presence of continuous light, said pulsed lights and continuous lights have an equal predetermined wavelength and an equal predetermined power.
Thus, with the method according to the present invention, for irradiation of the enzymatic complex PSII at said sufficient pulse frequency value, the production of oxygen and hydrogen is easily ensured which, as compared with an application of the method in the presence of a continuous light with equal power, is characterized by a surprisingly much higher yield.
Indeed, although this phenomenon is not yet well understood, it was observed in a quite surprising way that by modulating the amount of variable light energy overtime in the form of pulsed light energy at a pulsed frequency having the sufficient pulse frequency value, the oxygen production rate during the oxidation of water and therefore the activity of the PSII are increased for a given incident total energy value, as demonstrated in the examples of the present application.
A contrario, Sheleva and Messinger, which use different predetermined pulse frequency values for stimulating the enzymatic complex, however have to ensure that a predetermined and constant number of pulses are generated and that each pulse has the same energy, so that the total energy provided to the system is constant overtime. Also, for a predetermined pulse frequency, one skilled in the art who would like to apply this method should then make sure that the enzymatic complex has been well irradiated with the predetermined number of pulses and should therefore adjust the irradiation duration according to the selected pulse frequency in order to ensure a constant incident total energy value.
This aspect of the method of the state of the art is most particularly a constraint as soon as the question is to set into place industrially this method of the state of the art for example, by benefiting from the light of the sun for producing hydrogen and oxygen.
As an illustration, in the example of Table 2 shown in the results relative to the present invention, the maximum oxygen production rate per unit energy measured in the presence of pulsed light is at least 20 times higher than the rate measured during the application of the water hydrolysis method in the presence of continuous light, and this for a same predetermined light power value set to 555 mW.
Indeed, within the scope of the present invention, it was observed that for a sufficiently intense and short pulse (so as to be able to saturate the Kok cycle by providing it with the sufficient minimum energy for the activity to induce electrochemical dissociation of water), a first charge separation (S0→S1) takes place in the enzymatic complex, the number of first charge separations is governed by the sufficient pulsed frequency value of the pulsed light.
The selection of the sufficient pulse frequency value is determined by: (i) the light absorption profile of the enzymatic complex and therefore by the wavelength of the pulsed light; (ii) as well as by the energy value of the energy of the incident light.
Also, when the energy value of the light energy is higher, the sufficient pulse frequency value is higher, conversely, when the energy value of the light energy is smaller, the sufficient pulse frequency value is smaller.
Thus, the number of pulses varies so that the energy value of each pulse is sufficient for generating the first charge separation (S0→S1) in the enzymatic complex. The energy value of each pulse depends on the energy value of the light energy and on the selection of the sufficient pulse frequency value for obtaining the claimed oxygen production yield per light energy unit.
The method according to the invention therefore is an alternative to a simpler application than that of the method disclosed in the state of the art since it does not require both control of the energy applied to the system and the pulse frequency with which this energy is applied but only of the pulse frequency of the pulsed light.
Advantageously, before said electrochemical oxidation step of said aqueous solution, the method comprises a step for extracting said enzymatic complex PSII from chloroplasts or tylakoids of chloroplasts.
In a particular embodiment, the method according to the invention comprises, after the step for extracting said PSII, a step for purifying said enzymatic complex PSII in order to form an enzymatic composition substantially concentrated with PSII.
Preferably, said chloroplasts or tylakoids of chloroplasts are chloroplasts or tylakoids of chloroplasts of plants from the family of Chenopodiaceae, preferably of the genus Spinacia and from the family of Characeae, preferably prokaryotic or eukaryotic algae.
Alternatively, the PSII complex is a synthesis complex resulting from a step for synthetically manufacturing said enzymatic complex PSII, said manufacturing step being carried out prior to the oxidation step of the aqueous solution.
In a particularly advantageous embodiment of the method according to the invention, said capture of free electrons and of free protons is carried out by an electron transport mediator selected for example from the group consisting of derivatives of quinone, preferably from among 2,6-dimethylbenzoquinone, 2,6-dichloro-p-benzoquinone and 1,4-benzoquinone, or one of their mixtures.
Optionally, said pulsed light is emitted at a pulse frequency comprised between 1 Hz and 100 MHz, preferably comprised between 1 Hz and 3,000 Hz, in a range of wavelengths comprised between 400 nm and 700 nm, preferably between 500 nm and 680 nm, at a power comprised between 1 mW and 800 mW, preferably between 500 and 700 mW.
In a particular embodiment, the method according to the invention is characterized in that said water oxidation is carried out at a pH comprised between 4 and 8, preferably between 6 and 7.
The application of the method according to the invention in a pH range comprised between 6 and 7 ensures optimum enzymatic activity of the PSII complex.
Other embodiments of the method according to the invention are indicated in the appended claims.
The object of the invention is also a use of pulsed light, which pulsed light generated from a first source of light energy at a predetermined pulsed frequency value, for producing electrochemical oxidation of water in the presence of light by means of a photosensitive biochemical system comprising:
characterized in that said light energy has a variable energy value overtime and in that said predetermined pulse frequency value of said pulse light is modulated at a sufficient pulse frequency value in order to obtain a first oxygen production yield per light energy unit which is greater by a factor comprised between 1.01 and 100.00 than a second oxygen production yield per light energy unit obtained for a second electrochemical oxidation in the presence of continuous light, said pulsed lights and continuous lights having an equal predetermined wavelength and an equal predetermined power.
Advantageously, said enzymatic complex PSII is extracted from chloroplasts or tylakoids of chloroplasts
Preferably, said enzymatic complex PSII is purified in order to form an enzymatic composition substantially concentrated with PSII.
In a preferential method of use, the chloroplasts or tylakoids of chloroplasts are chloroplasts or tylakoids of chloroplasts of plants from the family of Chenopodiaceae, preferably of the genus Spinacia or from the family of Characeae, preferably prokaryotic or eukaryotic algae.
In particular, said enzymatic complex PSII is a synthetic enzymatic complex.
Alternatively, said sensor of free electrons and of free protons is an electron transport mediator selected from the group for example consisting of derivatives of quinone, preferably from among 2,6-dimethylbenzoquinone, 2,6-dichloro-p-benzoquinone and 1,4-benzoquinone, or one of their mixtures.
Particularly, said mediator is present in the water at a concentration comprising 1 μM and 1 M. Preferably, the PSII is deposited on a substrate. The PSII concentration in this scenario at least greater than 1 M, said substrate playing then the role of an anode, centre of the oxidation of the water contained in the aqueous solution.
Preferably, said mediator is present in the water at a concentration comprised between 10 μM and 1 mM and wherein said PSII is present in the water at a concentration comprised between 1 μg Chl/ml and 1 g Chl/ml, preferably between 20 μg Chl/ml and 200 μg Chl/ml. In the sense of the invention, the PSII concentrations are traditionally expressed relatively to the total chlorophyll concentration (Chl). By total chlorophyll concentration should be understood in the sense of the invention the concentration of A and B chlorophylls.
Preferentially, said pulsed light is emitted at a pulse frequency comprised between 1 Hz and 100 MHz, preferably comprised between 1 Hz and 3,000 Hz, in a range of wavelengths comprised between 400 nm and 700 nm, preferably between 500 nm and 680 nm, at a power comprised between 1 mW and 800 mW, preferably between 500 and 700 mW.
Advantageously, the use of pulsed light according to the invention is characterized in that said water oxidation is carried out at a pH comprised between 4 and 8, preferably between 6 and 7.
Other embodiments of the use of the pulsed light according to the invention are indicated in the appended claims.
The present invention also relates to a device for applying the method according to the invention, said device comprises:
Other embodiments of the device according to the invention are indicated in the appended claims.
Other features and advantages of the invention will emerge from the description given hereafter, in a non-limiting way and with reference to the examples described below.
The device used for applying the method according to the present invention, for which the performances are illustrated in the following examples, comprises:
During operation, the pulsed light is generated at a first predetermined pulse frequency and the pulsed light source is oriented so that the pulsed light irradiates the photo-enzymes in the aqueous solution.
The irradiation of the enzymatic complex in suspension in the solution induces an oxidation reaction of the water contained in the reactor via the PSII enzymatic complex with production of oxygen which is captured by the first capture means which is for example an electrode of the Clark type immersed in the aqueous phase, the free electrons and the free protons are as for them captured by the second capture means which is a sensor of electrons, for example dimethylbenzoquinone (DMBQ) or 2,5-dichloro-p-benzoquinone (DCBQ).
As the energy value of the light energy varies over time, the modulator of the pulse frequency of the pulsed light, which pulsed light is associated with this variable light energy, gives the possibility when it operates of modulating the predetermined pulse frequency value of this pulsed light at a sufficient pulse frequency value for obtaining a first oxygen production yield per unit of light energy which is greater by a factor comprised between 1.01 and 100.00 at a second oxygen production yield per unit of light energy obtained for a second electrochemical oxidation in the presence of continuous light, which pulsed light and continuous lights have an equal predetermined wavelength and an equal predetermined power.
Preferably, the first oxygen production yield per unit of light energy which is greater by a factor comprised between 1.01 and 80.00 than a second oxygen production yield per unit of light energy obtained for a second electrochemical oxidation in the presence of continuous light, which pulsed lights and continuous lights have an equal predetermined wavelength and an equal predetermined power.
By the terms of <<pulse frequency>>, should be understood in the present invention the frequency with which is modulated the energy value of the light energy emitted at a predetermined wavelength or in a predetermined range of wavelengths.
As mentioned earlier, the PSI complex which inhibits the activity of the PSII complex and which therefore limits the formation of oxygen should be removed.
Chloroplasts from spinach (Spinacia oleracea) are extracted in accordance with the procedure developed by Barthelemy et al. (Journal of Photochemistry and Photobiology B: Biology, 1997, volume 39, pages 213-218), and then extracted from thylakoid membranes and dissociated from the PSI complex present in these membranes, the PSII complex according to the method of Berthold and al., see Febs Letters, 1981, volume 134, number 2, pages 231-234.
As compared with the Barthelemy procedure, in the method according to the invention, mention is made of the following modifications:
The PSII obtained by the modified Bertold and al. method, as described above is then kept at −80° C. after freezing in liquid nitrogen at a temperature of −196° C. (77K) for a period of 10 s.
According to the modified extraction method described above, the PSII of the spinach is isolated from the PSI complex present in the chloroplast. Indeed, as shown by
A photohydrolysis system consisting of a cell, with a volume of 2.5 ml, the walls of which are provided with glass windows, in which a PSII suspension is placed in an aqueous solution at a buffer pH of 6.5, containing dimethylbenzoquinone (DMBQ) or 2.5-dichloro-p-benzoquinone (DCBQ).
The cell is illuminated with a laser light beam at 673 nm, in a continuous mode or in a pulsed mode. The characteristics of the laser are repeated in Tables 1a (DMBQ) and 1b (DCBQ).
By the terms of <<pulsed light>> or <<pulsed mode>>, is meant in the sense of the invention an intermittent light, i.e. for which the energy value alternately assumes a first zero value and a second non-zero predetermined value at a predetermined pulse frequency, for example 800 Hz, which means that the energy value passes 800 times per second from the zero value to the predetermined non-zero value by the power of the light.
The rate of the increase in oxygen concentration under illumination was measured at 25° C. by using an electrode of the Clark type in an aqueous buffer solution with a concentration of 25 mM MES-NaOH (pH=6.5) and 1 mM of DMBQ.
The analysis of
In the presence of pulsed light, at a power of 500 mW, emitted at a pulse frequency of 100 Hz, i.e. an energy of 5 mJ/s, corresponds an oxygen production rate K(O2) (per energy) of 0.01535 μmoles/(25 μg Chl ml min) per 500 mJ/s, i.e. an increase by a factor 21.9 of the energy yield, as compared with the rate measured in the presence of continuous light. The results of the experimental confirmation of this analysis are repeated in Table 2 below.
The analysis of
The results of
It should be understood that the present invention is by no means limited to the embodiments described above and that many modifications may be brought thereto within the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| BE 2013/0598 | Sep 2013 | BE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/069418 | 9/11/2014 | WO | 00 |
