FR2915404A1 - Reducing carbon dioxide in air using biochemical units, comprises introducing biochemical units, appropriate culture medium and carbon dioxide flow in a reactor, illuminating a reactional mixture, and recuperating a reactional product - Google Patents

Abstract

The process for the reduction of carbon dioxide in air using biochemical units in the presence of a reactional medium and under light effect, comprises introducing the biochemical units, an appropriate culture medium and a carbon dioxide flow originated from an industrial effluent in a reactor (1), illuminating the reactional mixture subjected to temperature and pressure conditions in which the carbon dioxide is in dense state, and recuperating a reactional product in the medium. The process is carried out at a temperature of 40[deg] C and at a pressure of 3-8 MPa.

Description

The invention relates to a method for reducing carbon dioxide.

  reduction of CO2 using biochemical units, in particular chloroplasts and microorganisms in complex fluid medium.

  Limiting the concentration of CO2 in the air is a major issue from the point of view of environmental management. Indeed, it seems now accepted that the increased presence of CO2 in the atmosphere has the effect of increasing the temperature on earth and ultimately affects the climate. The measures envisaged or taken to curb this phenomenon include the imposition of CO2 emission quotas by country. However, these measures seem insufficient for the time being to reverse the current evolution of the presence of CO2 in the atmosphere. Various processes to limit CO2 emissions have been explored. In addition, CO2 isolation processes, for example by sequestration, chemical absorption or cryogenics have been proposed. Moreover, it has already been envisaged to reduce CO2 by a reaction of the type of photosynthesis, including biological treatments. Thus, it has been proposed in application US 2005/0064577 to use photosynthetically active microorganisms such as algae to transform CO2 in the presence of water and light into biomass. The reaction is carried out in a suitable aqueous medium through which the CO2-containing gas passes. The reaction leads to a reduction in CO2, in the presence of water and light, in biomass and oxygen. This process therefore generates organic sludges in large volume, which it is necessary to eliminate and if possible to enhance. US 2005/0064577 proposes a valuation of biomass for the production of hydrogen or heat. However, this technology has not yet reached the industrial level. Moreover, the low reaction rate of the overall process remains a factor limiting the yield of the process described. US Pat. No. 3,303,608 proposes to apply a pressure of about 70 kPa above atmospheric pressure in order to improve the oxygen yield of photosynthesis of algae. According to this document, higher pressures, however, lead to the progressive inhibition of oxygen production.

  The aim of the invention is therefore to propose a process for reducing CO2 by the action of biochemical units and in particular chloroplasts which is faster, has a higher yield and is economically viable, in particular by making it possible to obtain valuable products.

  This object is achieved according to the invention by a process for reducing CO2 using biochemical units under conditions of temperature and pressure in which the CO2 is in the dense state. According to the invention, it is therefore proposed a method for reducing CO2 using biochemical units in the presence of a culture medium and under the effect of light, characterized in that it is carried out under conditions temperature and pressure at which the CO2 is in the dense state. According to one embodiment, the method comprises the steps of: a) introducing into a reactor biochemical units and an appropriate culture medium; b) introduce a stream containing CO2; c) illuminating the reaction mixture subjected to temperature and pressure conditions at which the CO2 is in the dense state; and e) recovering from the reaction medium at least one reaction product. Advantageously, the biochemical units are chloroplasts. In particular chloroplasts are isolated from plants such as algae and embryophytes. In addition, the biochemical units can be unicellular photosynthetic organisms, such as microalgae. Preferably, the process is conducted at a temperature below 40 C. According to one embodiment, the process is conducted at a pressure in the range of 2 to 20 MPa, and most preferably 3 to 8 MPa. The recovered reaction product is a mixture preferably comprising one or more monosaccharides, oligosaccharides and / or polysaccharides or more complex compounds such as carotene. Finally, according to a preferred embodiment, the flow introduced in step b) comes from an industrial effluent.

  In the context of this disclosure, the term CO2 in the dense state refers to a CO2 having a density greater than 400 kg / m3. The term biochemical units refers to unicellular organisms (prokaryotes or algae) or isolated chloroplasts, capable of binding CO2 through photosynthesis. The invention is based in particular on the observation that the CO2 fixation by photosynthesis of biochemical units can be accelerated when it is conducted under conditions of temperature and pressure corresponding to the dense state of CO2.

  Indeed, under these conditions, on the one hand, the CO2 is dense and therefore present in a high concentration, which promotes the reduction reaction. On the other hand, the carbon dioxide in the dense state has particular properties in terms of solvent. In particular, dense CO2 is able to solubilize some of the compounds synthesized by biochemical units. As a result, the products can then be extracted from the biochemical units and thus from the system, which avoids the phenomena of backward inhibition by accumulation and thus further contributes to favoring the CO2 fixation reaction. Moreover, the products thus extracted from the biochemical units are not available for the production of cellular material and therefore of biomass. This avoids the production of bulky organic sludge, difficult to treat or enhance. Thus, and in particular with the chloroplasts isolated, the process implements only the first stages of photosynthesis. In fact, in nature, the sugars generated within the sheet are converted to participate in the synthesis of resist (for example starch) or of cellular constituents, for example cellulose. Thus in the proposed process, CO2 provides both the reagent function and the solvent function. Quite surprisingly, the photosynthetic activity of the biochemical units is not affected by the pressure conditions applied.

  In contrast to the known processes, the proposed process does not have as main product the biomass resulting from the growth of the biochemical units, but the intermediate compounds extracted from the biochemical units thanks to the particular properties of the CO2 under the conditions of the process.

  According to the Calvin experiment, the first compound formed by photosynthesis, after less than 5 seconds is phosphoglyceric acid (APG). Then products such as carbohydrates, organic acids, amino acids, but also provitamins such as carotene are formed.

  The extraction of the reaction products is carried out as and when they are synthesized by the solvent effect of CO2. Thus, the proposed process allows the reduction of CO2 and generates oxygen as well as low molecular weight carbon compounds. These compounds can be easily separated and purified. They can then be used for example in chemical syntheses and thus constitute valuable products.

  The invention will be described in more detail by means of the appended figure, which shows: FIG. unique schematic diagram of a device adapted for implementing an embodiment of the method according to the invention.

  The operating principle of the method is explained by means of a device for its implementation shown schematically in the single figure.

  The reactor 1 is adapted to operate under pressure and to receive the biochemical units. It may be in particular unicellular organisms (prokaryotes or algae) or isolated chloroplasts. Chloroplasts can in particular be isolated from plants selected from algae, or embryophytes (such as spinach).

  The use of isolated chloroplasts is preferred because the extraction of intermediate products is simpler, which accelerates the photosynthesis reaction. In addition, under these conditions of use with chloroplasts, the device has a density of active sites per unit area exposed to light above the plants by a factor of 2 to 10 or more.

  In one variant of the process, the biochemical units are microorganisms. Microorganisms are particularly interesting because they do not require a step of extraction of the plant and are therefore readily available. Advantageously, one can choose microorganisms capable of producing valuable molecules, for example microalgae capable of generating carotene.

  The reactor 1 also comprises illumination means for exposing the reaction mixture to the light necessary for the photosynthesis reaction. According to a preferred embodiment, the reactor has walls at least partially transparent to the light used, for example in the form of portholes 2. Alternatively, it is possible to envisage the introduction of light into the reactor, for example example by means of light devices provided in the enclosure of the reactor. The light needed for the reaction can come from different sources. Preferably, the spectrum of the light used is close to that of the sun, to which the biochemical units are adapted. Advantageously, the light used is sunlight. However, sunlight does not allow the continuous operation of the process. It is also possible to consider exposure to artificial light sources, such as fluorescent lamps. The intensity of the light is not critical, except that it will have a notable influence on the yield obtained. Illumination with saturation intensity of the biochemical units is preferred because it further improves the efficiency of the reaction. In addition, the reactor 1 has an inlet 3 for the introduction of the flow comprising the CO2.

  The CO2 present in the reaction medium is generally not introduced in pure form but mixed with nitrogen, oxygen, nitrogen oxides, or other compounds. Indeed, one of the advantages of the process according to the invention is the fact that it is not limited to a high CO2 content. The gas stream comprising CO2 may also include liquids or solids. Preferably, it may be gaseous effluents or fumes, in particular of industrial origin. Indeed, most thermal processes that use carbonaceous materials such as oil, gas or coal, generate CO2 at combustion. Thus the energy sectors are among the most important to emit CO2 in the air. The combustion gases thus produced can therefore be treated by the process described. Moreover, the gases contained in the pockets of gas drilled during the exploitation of oil deposits have a high CO2 content that can be interesting to treat.

  The reactor 1 also comprises an inlet 4 for introducing the H 2 O and the culture medium. According to one embodiment of the device, the water supply and culture medium is made separately. The culture medium must have a suitable salinity and pH. It comprises the compounds necessary to ensure the photocatalytic activity of the biochemical units. These include nutritional agents. Their nature and quantity depend largely on the nature of the chosen biochemical units. Suitable culture media for the various biochemical units envisaged are known to those skilled in the art. For marine algae, it is thus possible to use a medium based on buffered reconstituted seawater (slightly alkaline pH) to which are added mineral salts (nitrates, potassium, phosphates) and vitamins such as biotin, folic acid and inositol. For isolated chloroplasts, it is possible to use a medium containing sugar such as sucrose or mannitol, a chelator such as ethylenediamine tetraacetic acid (EDTA) for example, a reducing agent such as DTT (dithiothreitol), a pH regulating agent. such as sodium pyrophosphate, magnesium chloride, bovine albumin (BSA) in a buffer such as Hepes or Tricine. The pH of the culture medium is adjusted to a value compatible with a photosynthetic activity of the biological units chosen. Generally, the pH value is between 5 and 9, preferably between 6 and 8 and most preferably between 7 and 8.

  The reactor further comprises means for thermal regulation and application of pressure (not shown). The temperature of the process is preferably selected to be compatible with the activity of the biochemical units. Also, the process is generally conducted at a temperature in the range of 10 to 80 C, in particular at a temperature below 40 C. Particularly preferred is the ambient temperature, that is to say between 20 and 30 C because at this temperature, the enzymatic activity involved in photosynthesis is generally maximal. The pressure in the reactor can be determined according to the chosen temperature, so that both parameters define a dense state of CO2 (> 400 kglm3). Preferably, the pressure is in the range of 2 to 20 MPa and in particular in the range of 3 to 8 MPa. Generally, no improvement is observed beyond a certain pressure. Also, even more preferably, the process is conducted at a pressure of 2 to 10 MPa.

  The reactor further comprises an outlet 5 is provided to withdraw the biochemical units to be replaced. The reactor finally comprises means for separating, on the one hand, the oxygen formed from the reaction medium and, on the other hand, the synthesized intermediate products dissolved in the CO2. The main advantage of oxygen separation is to limit photorespiration, which reduces the efficiency of photosynthesis. According to the illustrated embodiment, a second outlet 6 is provided for separating the gaseous components, in particular the CO 2 and the oxygen from the reaction mixture. The pressure is adjusted downstream of the outlet 6 by a first expansion valve 7 so as to allow the separation of oxygen from the mixture in the subsequent oxygen separator 8. The separated oxygen is discharged from the system via an outlet 9. The oxygen-free gas stream passes through an outlet 10 downstream of which is placed a second expansion valve 11 allowing the separation of the products that can be upgraded from the mixture through an outlet 13. a suitable separator 12 placed downstream. Depending on the biochemical units used, the recoverable products will generally be different. Thus, for example with chloroplasts extracted from leaves are obtained sugars C3 (glyceraldehyde-3-phosphate). The sugars generated can be recovered in a manner similar to that from beet, possibly after processing, in the food industry and as bio-fuel. An outlet 14 is provided to extend the mixture comprising the CO2 released from the recoverable products to the reactor 1 by means of a circulation pump 15. Thus, the products synthesized by the biochemical units are extracted continuously because of their good solubility in CO2 under the conditions prevailing in the reactor. Also, they are eliminated from the biochemical unit system, which avoids a gradual inhibition of reactions. The process can be conducted in batch mode or in continuous mode. Preferably, it is conducted in continuous mode.

  The method can be implemented as follows. The biochemical units are placed in the reactor, into which a stream containing or consisting of CO2, water and the culture medium is then introduced. The reaction mixture is brought to a temperature and subjected to pressure such that the CO2 is in the dense state. The reaction mixture then forms a complex fluid.

  Advantageously, the CO2 is present in excess with respect to the stoichiometric amount, in order to promote the extraction of the recoverable products from the biochemical units by solubilization. The reaction mixture is then illuminated continuously or intermittently so that the biochemical units can perform photosynthesis. The reaction mixture then comprises the starting materials, namely CO2, water, biochemical units and the culture medium, as well as the products formed by photosynthesis, in particular oxygen and other gases and intermediate products. more complex such as carbohydrates such as monosaccharides, oligosaccharides, polysaccharides, as well as other compounds such as carotene. Intermediates and oxygen are extracted from the reaction mixture, preferably continuously. Certain parameters, such as the solubilities in the medium of the starting and / or formed products, are very sensitive to pressure and temperature conditions. These parameters can be used to control the reaction for a given light intensity.

  The realization of the process under the stated conditions can make it possible to improve the kinetics of the photosynthesis reaction by a factor of 10 to 100. It thus becomes possible to envisage the treatment of large quantities of CO2-containing gases with an acceptable yield. . In addition, the reaction can be economically viable insofar as it allows access to easily recoverable compounds. Also, the particular conditions of the process allow exploitation on an industrial scale. The proposed process therefore responds to major challenges related to our economic development in a logic of respect for the environment. Indeed, it makes it possible to treat a waste, CO2, by generating valuable products, without harmful discharges and by requiring only little energy (other than the luminous energy).

Claims (11)

  A method for reducing CO2 using biochemical units in the presence of a reaction medium and under the effect of light, characterized in that it is carried out under conditions of temperature and pressure at which CO2 is in the dense state.   The process of claim 1, comprising the steps of: a) introducing into a reactor biochemical units and a suitable culture medium; b) introduce a stream containing CO2; c) illuminating the reaction mixture subjected to temperature and pressure conditions at which the CO2 is in the dense state; and e) recovering from the reaction medium at least one reaction product.   The method of claim 1 or 2, wherein the biochemical units are chloroplasts.   The method of claim 1 or 2, wherein the biochemical units are unicellular photosynthetic organisms.   5. Method according to one of claims 1 to 4, wherein the chloroplasts are isolated from plants such as algae and embryophytes.   6. Method according to one of claims 1 to 5, wherein the process is conducted at a temperature below 40 C.   7. The process according to one of claims 1 to 6, wherein the process is conducted at a pressure in the range of 2 to 20 MPa. 30   The process according to one of claims 1 to 7, wherein the process is conducted at a pressure in the range of 3 to 8 MPa.   9. Process according to one of claims 1 to 8, wherein the reaction product is a mixture comprising one or more monosaccharides, oligosaccharides and / or polysaccharides.   The process according to one of claims 1 to 9, wherein the reaction product comprises carotene.   11. Method according to one of claims 2 to 10, wherein the flow introduced in step b) comes from an industrial effluent.10.