Process for producing a biocrude employing microalgae

Abstract

This invention refers to a procedure for obtaining a biocrude from greenhouse gases, a procedure which is advantageous industrially and continuous. By means of said procedure it is possible to capture, convert and revalue CO.sub.2, among other greenhouse gases, in an efficient manner, in such a way that a net negative balance is obtained, which in other words means that with this procedure it is possible to capture more CO.sub.2 than is generated which makes it beneficial and sustainable in the environment.

Claims

1. Procedure for obtaining a biocrude from a gas comprising CO.sub.2, procedure which comprises the steps of: a. supply of the gas which comprises CO.sub.2 to a reactor containing a culture which comprises at least one species of microalga which is capable of photosynthesis; b. photosynthesis carried out by the species of microalga using the CO.sub.2 supplied to produce a biomass; c. anaerobic fermentation of the biomass obtained; d. thermochemical decomposition of the biomass fermented at a pressure between 0 and 20 MPa and a temperature between 200 and 420 C. in order to obtain a biocrude mixed with water and gases, and e. separation of the biocrude obtained, characterised in that following the photosynthesis stage, between 5 and 100% of the culture is removed from the reactor which is subsequently separated into a solid fraction which contains biomass, which solid fraction will subsequently be subjected to the stage of anaerobic fermentation, and a liquid fraction containing carbonates and/or bicarbonates, which are separated from the liquid fraction, and which liquid fraction is returned at least partially to the reactor devoid of carbonates and bicarbonates.

2. Procedure according to claim 1, in which in the step of at least partial removal from the reactor, between 5 and 50% of culture is removed.

3. Procedure according to claim 2, in which in the step of at least partial removal from the reactor, approximately 10% of culture is removed.

4. Procedure according to claim 1, wherein prior to the step of supply of a gas comprising CO.sub.2 to the reactor, said gas is pre-treated by at least one of the following treatments: a) substantial elimination of SO.sub.x, NO.sub.x, (b) substantial elimination of humidity and (c) adaptation of the gas temperature to between 30 and 40 C.

5. Procedure according to claim 1, wherein the photosynthesis step is carried out in a turbulent regime and exposed to natural and/or artificial light.

6. Procedure according to claim 1, wherein following the step of at least partial removal of the culture from the reactor, the removed culture is acidified to a pH between 3.5 and 8.

7. Procedure according to claim 6, wherein the removed culture is acidified to a pH between 6 and 8.

8. Procedure according to claim 6, wherein the acidification is carried out by adding to the culture at least one acidifying agent selected from the group consisting of CO.sub.2, mixture of CO.sub.2 and air, strong or weak acids or any combination thereof.

9. Procedure according to claim 8, wherein the acidification is carried out by adding to the culture a mixture of CO.sub.2 and air.

10. Procedure according to claim 1, wherein following the step of at least partial removal of the culture from the reactor, separation of the solid fraction which contains biomass and the liquid fraction which contains carbonates and/or bicarbonates is carried out through at least one technique selected from the group consisting of filtration, centrifugation, flocculation, electro coagulation, ultrasound, evaporation, decantation or any combination thereof.

11. Procedure according to claim 1, wherein the separation of carbonates and/or bicarbonates from the liquid fraction resulting from the at least partial removal of the culture from the reactor is carried out through precipitation of the corresponding carbonated salts deriving from the addition of at least one alkali.

12. Procedure according to claim 1, wherein the anaerobic fermentation step comprises anaerobic fermentation of a biomass in which the concentration of solids is from 1 to 50% and which is carried out at a temperature between 10 and 165 C.

13. Procedure according to claim 12, wherein the biomass has a 5 to 12% concentration of solids and the anaerobic fermentation is carried out at a temperature between 30 and 75 C.

14. Procedure according to claim 13, wherein the anaerobic fermentation is carried out at a temperature of approximately 38 C.

15. Procedure according to claim 1, wherein previously or subsequent to the anaerobic fermentation step, a sub step of homogenisation or cavitation of the biomass is carried out during which it is subjected to pressure between 1 bar and 2,500 bar.

16. Procedure according to claim 15, in which the biomass is subjected to pressure between 250 and 1,200 bar.

17. Procedure according to claim 15, which is repeated between 1 and 5 times.

18. Procedure according to claim 1, wherein the thermo-chemical decomposition step of the fermented biomass is carried out by heating the mass to a temperature between 240 to 340 C. and a pressure of 10 to 20 MPa.

19. Procedure according to claim 1, wherein following the step of anaerobic fermentation and prior to the step of thermo-chemical decomposition, an aqueous fraction containing ammonium salts is separated from the biomass resulting from the anaerobic fermentation, which aqueous fraction is then returned to the reactor again.

20. Procedure according to claim 1, wherein the species of micro alga which carries out the photosynthesis is selected from the group consisting of Chlorophyceae, Bacillariophyceae, Dinophyceae, Cryptophyceae, Chrysophyceae, Haptophyceae, Prasinophyceae, Raphidophyceae, Eustigmatophyceae, or any combination thereof.

21. Procedure according to claim 1, wherein the gas which comprises CO.sub.2 and which is supplied to the reactor proceeds in an exogenous way from the atmosphere or from any industry and/or in an endogenous way from the gases generated in the actual procedure, in any combination thereof.

22. Procedure according to claim 21, in which the exogenous component of the gas containing CO.sub.2 proceeds from a cement works or similar industry.

23. Procedure according to claim 1, wherein the gas comprising CO.sub.2 further comprises other greenhouse gases selected from the group consisting of NO.sub.x CH.sub.4 and mixtures thereof.

24. Procedure according to claim 1, which includes a final step of refining of the biocrude obtained.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1shows a block diagram of the procedure in the present invention. It illustrates each of the stages in the procedure.

(2) FIG. 2shows a diagram representing the energy conversion of CO.sub.2, in accordance with a net negative balance.

(3) FIG. 3shows the balance of CO.sub.2 emission of example 2 in a procedure for energy conversion of CO.sub.2, in accordance with a net negative balance.

(4) FIG. 4refers to the balance of CO.sub.2 emissions of example 3 in a procedure for energy conversion of CO.sub.2, in accordance with a net negative balance.

(5) FIG. 5shows the division of the biocrude into different fractions.

EXAMPLES OF AN EMBODIMENT

(6) Below, a series of examples are given which at any given moment illustrate the synthesis of some specific components of this invention and in order to provide examples of the general procedures. In accordance with the foregoing, the following examples are not intended in any way to restrict the scope of the invention considered in this descriptive report.

(7) In this descriptive report the symbols and conventions used in these procedures, diagrams and examples are consistent with those used in the International System and contemporary scientific literature, for example the Journal of Medicinal Chemistry. Unless indicated to the contrary all the basic materials were obtained from suppliers and were used without any additional purification. Specifically, it is possible to use the following abbreviations throughout this descriptive report: g (grams); mg (milligrams); kg (kilograms); g (micrograms); L (liters); mL (milliliters); L (micro liters); mmol (milimols); mol (mols); C. (degrees Celsius); Hz (hertz); MHz (megahertz); (chemical displacement) s (singlet); d (duplete); t (triplet); q (quadruplet); m (multiplet); NMR (nuclear magnetic resonance); M (molar); Et.sub.3N (triethylamine); DMF (dimethylformamide); DMSO (dimethylsulfoxide); ACN (acetonitryl); PBS (phosphate buffered saline); NCV (net calorific value).

Example no 1: Energy Conversion of CO2, Obtaining a Net Negative Balance

(8) The point of departure in this procedure is the emission gases resulting from the combustion of a cement works and optionally the gases resulting from the combustion of the actual product obtained (from biocrude).

(9) Below Table 2 shows an example of the gases emitted by the cement works:

(10) TABLE-US-00002 TABLE 2 Temperature 420 C. Pressure 1 Bar Density 0.79 kg/m.sup.3 Mass flow 2,000 kg/h Specific heat 0.25 kcal/kg Volumetric flow 2,531.64 m.sup.3/h CO.sub.2 12% V N.sub.2 61% V O.sub.2 1.9% V H.sub.2O 20.7% V CH.sub.4 2,500 ppm NO.sub.x 90 ppm SO.sub.2 50 ppm CO 1.65 ppm

(11) In accordance with the composition of the cement works gas, it was considered that the only treatment to be carried out was the elimination of SO.sub.x and the reduction of temperature. For this purpose an absorption column was installed in countercurrent with NaOH (aqueous dissolution at 10% of NaOH). It is important to point out that in the invention procedure, in addition to the reduction in the net balance of CO.sub.2, a reduction in the concentration of NO.sub.x is also obtained (95% NO and the remainder NO.sub.2) in the end product as a result of the dissolution of water from the NO and NO.sub.2 (particularly the latter). Following this treatment, a gas with the following composition (Table 3) is introduced.

(12) TABLE-US-00003 TABLE 3 Temperature 40 C. Pressure 1.98 Bar Density 2.22 kg/m.sup.3 Mass flow 1,760 kg/h Specific heat 0.24 kcal/kg Volumetric flow 792.79 m.sup.3/h CO.sub.2 13.5% V N.sub.2 63% V O.sub.2 2.1% V H.sub.2O 3.2% V CH.sub.4 2,300 ppm NO.sub.x 62 ppm SO.sub.2 2 ppm CO 0 ppm

(13) In addition to the gases resulting from the cement work emissions, as mentioned previously once again the gases resulting from combustion of the biocrude obtained in the process are reintroduced to the culture; below the composition of the this gas is presented at the outlet of the treatment system, (using scrubber only for tempering in this case there is no SO.sub.x and therefore NaOH is not introduced):

(14) TABLE-US-00004 TABLE 4 Temperature 40 C. Pressure 1.98 Bar Mass flow CO.sub.2 78 kg/h CO.sub.2 14.9% V N.sub.2 58% V O.sub.2 2.7% V H.sub.2O 1.1% V CH.sub.4 1,100 Ppm NO.sub.x 120 Ppm SO.sub.2 0 Ppm CO 0 ppm

(15) The general diagram is represented in FIG. 2. The gases are mixed in a tank designed for this specific purpose and system. In this mixing tank in addition to mixing these two currents a third air current is mixed to adapt the final mixture to the desired CO.sub.2 concentration; in this specific case the average is 13.5% CO.sub.2. In order to make the mixture, the concentration of CO.sub.2 of the two first currents is measured and an electrovalve is activated to allow more or less air to pass through, thus regulating the final concentration. Therefore, this mixture is that which is introduced into the reactors (continuously agitated photosynthetic reactors which allow light to pass through and which are made of transparent material to this effect) which contain a monospecific culture of microalgae (Nannochloris sp).

(16) In order to study the CO.sub.2 taken up by the system, CO.sub.2 composition is continuously measured at the entrance and outlet. According to this data it is possible to determine the amount of CO.sub.2 captured by the system (biological fixation+chemical fixation); together with the dry weight of the culture and it is possible to determine how much CO.sub.2 has been biologically fixed by the alga depending on its photosynthetic behaviour) and how much has been fixed by the system. Below Table 5 shows the results of the CO.sub.2 monitoring:

(17) TABLE-US-00005 TABLE 5 X CO.sub.2 GAS FLOW % CO.sub.2 entry ENTRY % CO.sub.2 Time t (min) entry (L CO.sub.2/L gas) (l/min) outlet 0:00:00 10 0 600 1.16 128.76 0:10:00 10 0 600 1.1 122.1 1:00:00 50 0 600 0.94 521.7 2:00:00 60 0 600 0.62 412.92 3:00:00 60 0 600 0.36 239.76 4:00:00 60 0 600 0.19 126.54 5:00:00 60 0 600 0.08 53.28 6:00:00 60 0 600 0 0 7:00:00 60 0 600 0 0 8:00:00 60 0 600 0 0 9:00:00 60 13.49 600 0.13 8,897.76 10:00:00 60 13.51 600 1 8,331.66 11:00:00 60 13.51 600 2.25 7,499.16 12:00:00 60 13.51 600 3.2 6,866.46 13:00:00 60 13.5 600 3.69 6,533.46 14:00:00 60 13.5 600 3.86 6,420.24 15:00:00 60 13.5 600 3.89 6,400.26 16:00:00 60 13.5 600 3.87 6,413.58 17:00:00 60 13.5 600 3.89 6,400.26 18:00:00 60 13.52 600 4.2 6,207.12 19:00:00 60 13.5 600 5.1 5,594.4 20:00:00 60 0 600 4 2,664 21:00:00 60 0 600 2.2 1,465.2 22:00:00 60 0 600 1.45 965.7 23:00:00 60 0 600 1.3 865.8 23:50:00 50 0 600 1.18 654.9

(18) In accordance with this Table, production will be 681.11 kg/per day of biocrude for a plant with a total volume of 735 m.sup.3. In order to obtain this production based on the efficacy of CO.sub.2 capture of 69%, calculated on the basis of the previous table, it will be necessary to supply the photobioreactors with 342.49 kg/h of CO.sub.2; 264.44 kg of CO.sub.2/h originating from the cement works and the remaining 78 kg CO.sub.2/h resulting from feedback provided by the combustion emissions of the actual biocrude introduced.

(19) In order to carry out the process of obtaining this biomass, firstly 367.64 m.sup.3 per day is extracted (50% of the culture). Prior to passing to the following phase of centrifugation (1.sup.st extraction stage), it should pass through an acidification stage which takes place in a 500 m.sup.3 tank. The basics of this acidification stage are as follows:

(20) The culture extracted as a result of the continuous bubbling of exhaust gases has a content of CO.sub.2, bicarbonate and carbonate in a high solution. When this CO.sub.2 is left to bubble, the pH in the solution tends to rise, displacing the balance towards the formation of carbonates. If a lot of carbonate is formed it will exceed the point of solubility and this will begin to precipitate. This precipitation could cause a fouling problem and in turn the fouling could cause contamination and further complications in the decanting of water. Therefore as the mechanical separation (1.sup.st separation stage) is unable to process all the volume extracted at once, during this storage phase an acid needs to be added. Specifically in this case a solution of H.sub.2SO.sub.4 (1M) is added in order to keep the pH permanently below 7.5.

(21) Having emptied 367.64 m.sup.3 of culture, the mechanical separation of water from the biomass is effected. For this purpose centrifugation is used and in this way a volume of 1.89 m.sup.3/per day is obtained at a concentration of 15% solids.

(22) In addition to the concentrated fraction (15% solids), an aqueous fraction (permeated) is obtained, amounting to a total volume of 3,657 m.sup.3/per day. This water, due to the fact that it formed part of the culture, is charged with CO.sub.2, bicarbonate and carbonate. In order to release this charge from the water it is made alkaline with NaOH until it reaches a pH 9 in order to displace the balance towards the formation of carbonate, and in this way it exceeds the limit of solubility of the carbonate and causes it to precipitate. Thus CO.sub.2, is chemically captured obtaining water poor in CO.sub.2, bicarbonate and carbonate. This water which is poor in these elements is introduced into the system once more (to the photobioreactors) with a renewed capturing capacity in terms of CO.sub.2. If this water were to be introduced without carrying out a previous stage of chemical capture, the CO.sub.2 assimilation capacity of the water would be minimal as it would be close to saturation.

(23) The concentrate with 15% solids resulting from centrifugation, passes to a stage of anaerobic fermentation at 38 C. During anaerobic fermentation the biomass is transformed by the various microbial communities present (anaerobic bacteria) losing O and N in the form of H.sub.2O, CO.sub.2 and NH.sub.3 and becoming enriched in H and C. As the fermentation process progresses, it is noted how the N and O drops as the H and C content rises. At the same time methane is generated as a consequence of the fragmentation of these molecules, providing energy which is used as a source of thermal energy for the following thermochemical stage. In accordance with the fragmentation of the 54.57 kg/h of dry biomass which could potentially pass to the second stage, only 45.48 kg/per day passes to the following stage as a result of the fragmentation and decomposition.

(24) Subsequently following the anaerobic fermentation stage the resulting product is subjected to centrifugation once more, this time until 23% solids are obtained; this product, produced at a production rate of 967 kg/per day, despite its pasty texture can nevertheless be pumped and it is passed to the following thermochemical transformation stage. The clearer water resulting from this process, (1.6 m.sup.3/per day), is charged with ammonia, and is returned once more to the photobioreactors, with the ammonia serving as a further contribution of nutrients to the micro-organisms.

(25) The thermo-chemical transformation takes place in a reactor at 270 C. and 22 MPa in a continuous process supplied at a rate of 40.32 kg/h, with biocrude production (with transformation of 62.20% with respect to the basic dry biomass) of 28.38 kg/h of biocrude with 3% water following a decantation phase subsequent to the reactor. In addition to obtaining biocrude, a fraction gas is obtained from the thermochemical process (mainly CH.sub.4, CO.sub.2, and CO), which is burned with a view to obtaining thermal energy for this particular stage.

(26) The final product has a PCI of approximately 9300 kcal/kg, which permits electrical energy of 138 kW to be obtained following combustion in an internal combustion engine with transformation efficiency from thermal energy to electrical energy of 45%. The CO.sub.2 resulting from the combustion is reintroduced in the system.

(27) FIG. 3 shows the balance of CO.sub.2 emissions.

(28) As per the balance, having obtained the electrical energy, following the introduction of 264.44 kg/h of CO.sub.2 only 113.98 kg/h of CO.sub.2 is emitted, which presupposes a net negative balance of 150.47 kg CO.sub.2/h. As a result, in this process not only is CO.sub.2 not emitted, but more CO.sub.2 is captured than is emitted as per the following balance:

(29) TABLE-US-00006 TABLE 6 Introduced 264.44 kg CO.sub.2/h Emitted 113.98 kg CO.sub.2/h Balance 150.47 kg CO.sub.2/h

Example no 2: Energy Valuation of the CO2

(30) The point of departure is the emission gases resulting from combustion in a cement works with the emissions contained in the following table:

(31) TABLE-US-00007 TABLE 7 Temperature 150 C. Pressure 1 Bar Density 0.77 kg/m3 Mass flow 43,914 kg/h Specific heat 0.25 kcal/kg Volumetric flow 57,377 m3/h CO.sub.2 6% V N.sub.2 67.6% V O.sub.2 2.1% V H.sub.2O 20.7% V CH.sub.4 9,000 Ppm NO.sub.x 50 Ppm SO.sub.x 50 Ppm CO 2.69 Ppm

(32) Given the characteristics of the gas emitted by the cement works it was considered that the only treatment needed was that of eliminating SO.sub.x and the reduction of temperature. For this purpose an absorption column was installed, in countercurrent with NaOH. It is important to point out that, in this invention procedure in addition to a reduction in the net balance of CO.sub.2, a reduction is also obtained in the final concentration of NO.sub.x (95% NO and the remainder NO.sub.2) as a result of the dissolution in water of the I NO and NO.sub.2 (particularly the latter).

(33) As per this treatment, the following gas is introduced in the photosynthetic reactors (photosynthetic reactors which are continuously agitated and which are made of transparent material to let in light) and which contain a plurispecific micro algae culture (Nannochloris sp, Tetraselmis chuii and Isocrisis Galbana).

(34) TABLE-US-00008 TABLE 8 Temperature 40 C. Pressure 1.98 Bar Density 2.22 kg/m3 Mass flow 38,716 kg/h Specific heat 0.24 kcal/kg Volumetric flow 17,473 m3/h CO.sub.2 7.37% V N.sub.2 85.95% V O.sub.2 2.95% V H.sub.2O 3.69% V CH.sub.4 10,502 ppm NO.sub.x 23.2 ppm SO.sub.2 1 ppm CO 0 ppm

(35) In accordance with the composition of these gases and the system efficiency in capturing CO.sub.2, a production of 4,017 kg/day of biomass is achieved, transformation of which into bio-oil permits 1,607.13 kg/day of biocrude to be obtained in plant with 230 photosynthetic reactors for a total plant volume of 4,020 m.sup.3.

(36) In order to obtain this biomass, firstly 1,005 m.sup.3 is extracted daily (25% of the culture). This culture having passed to the following centrifugation stage (1.sup.st extraction stage) is required to pass through an acidification stage which takes place in a tank, the capacity of which is 1,500 m.sup.3. The basis of this acidification stage is as follows:

(37) As a consequence of the continuous bubbling of exhaust gases, the extracted culture has a content of CO2, bicarbonate and carbonate in a high level of dissolution. When this CO.sub.2 is allowed to bubble, the pH in the solution tends to rise, displacing the balance towards the formation of carbonates. If a considerable amount of carbonate is formed, it exceeds the point of solubility and begins to precipitate. This precipitation could cause fouling problems and in turn said fouling could cause pollution along with problems in the decanting of water. Therefore, as the mechanical separation (1.sup.st separation stage) is not able to process all the extracted volume at one time, during this storage period an acid must be added. Specifically, a solution of HCl (1M) is added in order to ensure that the pH is always below 7.

(38) In this way when the 1005 m.sup.3 of culture has been emptied out the water is mechanically separated out from the biomass. This is done through centrifugation, thus obtaining a volume of 36 m.sup.3 of concentrated culture, however it is still liquid; the concentration reached being 10% solids.

(39) In addition to the concentrated fraction of 10% solids, an aqueous fraction is obtained (permeated) which amounts to a total of 9,680 m.sup.3/per day. This water, due to the fact that it was part of the culture, is charged with CO.sub.2, bicarbonate and carbonate. In order to release the water from this charge it is made alkaline with NaOH until it reaches a pH of 9.5 in order to displace the balance towards the formation of carbonate, thus exceeding the limits of the solubility of the carbonate, and causing it to precipitate. In this way CO2 is chemically captured, obtaining a water poor in CO2, bicarbonate and carbonate. The water poor in these elements is introduced into the system again (to the photobioreactors) with a renewed capturing capacity in terms of CO.sub.2. If this water is introduced without a previous chemical capture stage, the water's CO.sub.2 assimilation capacity would be minimal, as it would be close to saturation.

(40) The concentrate, at 10% solids (36 m.sup.3/dia), resulting from centrifugation, passes to a cavitation stage which consists of two steps each at 750 bar; and in this way the cells are fragmented which facilitates the following phase of anaerobic fermentation. This anaerobic fermentation is carried out at 40 C., and in this way the biomass is transformed by the various microbial communities present (anaerobic bacteria) losing O and N in the form of H.sub.2O, CO.sub.2 y NH.sub.3 and becoming enriched in H and C. As the fermentation advances it is noted how the content of N and O begins to drop as the H and C content increases. At the same time methane is generated as a result of the fragmentation of these molecules, energy which is used as a source of thermal energy for the following thermochemical stage. As a result of this fragmentation, of the 4,017 kg of dry biomass which could potentially pass to the next phase, only 2,800 kg/per day pass to the following stage as a result of said fragmentation and decomposition.

(41) Subsequently, following the anaerobic fermentation stage, the resulting product is centrifuged once more, this time until it achieves 23% solids; this product, with a production of 10.7 m.sup.3/per day which is already a pasty textured product although one which can be pumped, passes to the following stage of thermochemical transformation. The water resulting from this separation, (19.8 m.sup.3 per day), charged with ammonia, is returned to the photobioreactors once more; the ammonia charge serves as a further source of nutrients for the micro-organisms.

(42) The thermo-chemical transformation takes place in a reactor at 300 C. and 15 MPa in a continuous supply process carried out at a rate of 485.24 kg/h of concentrate at 23%, with biocrude being produced (as per a transformation of 60% with respect to the initial dry biomass) at a rate of 1,607.13 kg/per day of biocrude with 7% water following a decantation phase after the reactor.

(43) The final product with an approximate PCI of 8,100 kcal/kg, is burnt in a turbine thus obtaining 284 kW of installed power with a conversion efficiency of thermal energy to electricity of 45%.

(44) In accordance with all the foregoing the CO.sub.2 balance is shown in FIG. 4.

(45) In accordance with this diagram 24,724.98 kg/per day of CO.sub.2 is introduced and 441.96+8,653.74+4,419.61=13,515.31 kg/per day are emitted. Therefore, the net balance is: 11,209.67 kg CO.sub.2 per day with more CO.sub.2 being captured than emitted.

Example no 3: Biocrude Based on CO2 from a Cement Works

(46) The point of departure is emission gases resulting from combustion in a cement works, with the emissions indicated in the table below:

(47) TABLE-US-00009 TABLE 9 Temperature 170 C. Pressure 1 bar Density 0.81 kg/m.sup.3 Mass flow 22,000 kg/h Specific heat 0.25 kcal/kg Volumetric flow 27,160.49 m.sup.3/h CO.sub.2 7% V N.sub.2 66.8% V O.sub.2 1.9% V H.sub.2O 17.3% V CH.sub.4 8,000 ppm NOx 40 ppm SO.sub.2 70 ppm CO 3.69 ppm

(48) Given the characteristics of the gases it was considered that the only treatment required was the elimination of SOx and a reduction in temperature. For this purpose an absorption column was installed in counter current with NaOH.

(49) Following this treatment the following gases were introduced into the photosynthetic columns:

(50) TABLE-US-00010 TABLE 10 Temperature 40 C. Pressure 1.98 bar Density 2.22 kg/m3 Mass flow 19,360 kg/h Temperature 40 C. Specific heat 0.24 kcal/kg Volumetric flow 8,720.72 m.sup.3/h CO.sub.2 7.5% V N.sub.2 87% V O.sub.2 2.1% V H.sub.2O 3.32% V CH.sub.4 9,600 ppm NOx 45 ppm SO.sub.2 1 ppm CO 0 ppm

(51) The gases indicated in the above table resulting from the treatment are introduced into the reactors (photosynthetic reactors which are continuously agitated and which are made of transparent material to let in light) and which contain a monospecific microalgae culture (Isocrisis Galbana). As a result of this procedure a production of 170 kg/h of biomass is obtained for a 2,041 m.sup.3 plant.

(52) In order to obtain this biomass, firstly extraction takes place at the rate of 714 m.sup.3 per day (35% of the culture). This extracted culture passes to a decantation tank with a maximum capacity of 1,000 m.sup.3, where it is subjected to a stage in which it is separated from the algae (1.sup.st phase of extraction) by means of a coagulation-flocculation process. It is coagulated with aluminium, neutralising in this way the charge of microalgae, and it is flocculated with a polyelectrolyte polymer (ZETAG). In this way following 10 minutes of decantation, the biomass is left in the bottom of the tank, obtaining a product with a concentration of 15% solids, which is discharged to the next phase of fermentation.

(53) In addition to the concentrated fraction (15% solids), an aqueous fraction is obtained (leftover in the decantation tank) which amounts to a total volume of 7,026 m.sup.3/per day. This water due to the fact that it was part of the culture, is charged with CO.sub.2, bicarbonate and carbonate. In order to release water from this load, it is made alkaline with KOH until it reaches pH 9 in order to displace the balance towards the formation of carbonate and in this way exceeds the limit of solubility of the carbonate, causing it to precipitate. In this way the CO.sub.2 is captured chemically, obtaining a water poor in CO.sub.2, bicarbonate and carbonate. The water which is poor in these elements is introduced in the system again (to the photo reactors) with a capacity for renewed capture in respect of CO.sub.2. If this water were introduced without proceeding to a prior phase of chemical capture, the water's capacity of CO2 assimilation would be minimal, as it would be close to saturation.

(54) The concentrate, which is 15% solids (11.56 m.sup.3/per day), resulting from centrifugation, passes to an anaerobic fermentation phase at 33 C. During the anaerobic fermentation the biomass is transformed by the different microbial communities present (anaerobic bacteria) losing O and N in the form of H.sub.2O, CO.sub.2 and NH.sub.3 and becoming enriched in H and C. As the fermentation progresses, it is possible to note how the N and O content drops as the H and C increases. At the same time methane is generated as a result of the fragmentation of these molecules, which is used as a source of thermal energy for the subsequent thermochemical stage. In accordance with this fragmentation of 2,040.65 kg of dry biomass per day which could potentially pass to the next stage, only 1,360 kg per day pass to the following phase as a result of said fragmentation and decomposition.

(55) Table 9 below shows the development of the C, N, O and H in accordance with the fermentation process:

(56) TABLE-US-00011 TABLE 11 Prior to fermentation (%) Following fermentation (%) C 50.3 60 N 7.3 2 O 26.82 17.7 H 7.58 12.3

(57) Subsequently, following the anaerobic fermentation stage the resulting product is subjected to a pressed filtration process in order to increase the solid content. The cake resulting from this phase is a wet product with a 30% concentrate of solids. This product in product ion of 4,534,77 kg per day has a pasty texture, however, it can be pumped and passes to the next stage of thermochemical transformation. The resulting clearer water (11.47 m.sup.3 per day), is charged with ammonia and is returned to the photoreactors once more; the ammonia charge serves as a further provision of nutrients for the micro-organisms.

(58) The thermochemical transformation takes place in a reactor at 320 C. and 20 MPa in a continuous process, supplied at a rate of 189 kg/h, with bio-oil production (in accordance with a transformation of 52% with respect to the basic dry biomass) of 29.47 kg/h with 5% water following a phase of decantation subsequent to the reactor.

(59) The final product has a PCI of approximately 8,400 kcal/kg, which, following a stage of water removal through vacuum evaporation, is refined in order to obtain different fractions as shown in the following figure with the process described as follows: the biocrude is preheated, subsequently passing to a furnace where the biocrude is partially vaporised. Subsequently it passes to the distillation or rectification column and is separated into different fractions based on the boiling temperature. The percentages are as follows: 5.6%.fwdarw.Gases 11%.fwdarw.light naphtha 23.8%.fwdarw.heavy naphtha 18%.fwdarw.Kerosene 29.6%.fwdarw.Diesel 12%.fwdarw.Heavy gas-oil.