Hydrogen from CO2 and H2O
Edward Chesky
Major (Retd) US Army, USA
Mohideen Ibramsha
1968 Alumni of Thiagarajar College of Engineering, Madurai, TN, India
1974 intellectual son of PhD guide Prof. V.Rajaraman & Mrs. Dharma Rajaramn, CS, EE, IIT, Kanpur, UP, India
1991 First HOD of CSE, CEC [now BSAU] Chennai, TN, India
Associate Professor (Retd), Computer Science, Framingham, MA, USA
Consultant R&D, M A M College of Engineering, Trichy, TN, India
Advisor, HyDIGIT Pte Ltd, Singapore
Email: ibramsha7@yahoo.com
Introduction: Global warming is caused by accumulation of CO2 and other greenhouse gases in the atmosphere. From https://en.wikipedia.org/wiki/History_of_coal_mining we find:
Archeological evidence in China indicates surface mining of coal and household usage after approximately 3490 BC. … In Roman Britain, the Romans were exploiting all major coalfields (save those of North and South Staffordshire) by the late 2nd century AD … After the Romans left Britain, in AD 410, there are few records of coal being used in the country until the end of the 12th century. … India: Commercial exploitation began in 1774,
Even though coal was used for centuries, the first recorded concentration of CO2 in the atmosphere was by scientist Charles David Keeling. We quote from https://www.co2.earth/1958-background-co2-and-the-keeling-curve
Keeling's long-term CO2 measurements began in 1957 with the first flask collection at the South Pole. Hawaiian measurements started in March 1958. That air had 316 parts per million of CO2. By March 2007 the comparable value was 384 parts per million. { From a picture in that page: Data: July 5 2018: June 2016 406.81 June 2017 408.84 June 2018 410.79 }
We hope, all would agree that weather was kind and good in 1958 and thus rolling back the atmospheric CO2 to 316 parts per million is a worthy objective.
In https://mohideenibramsha7.wixsite.com/website/single-post/2018/07/25/Hydrogen-Economy-Now-1 we stated:
By building solar power based on the days of minimum sunshine, we hope we would reduce the greenhouse gases to pre-industrial levels soon, hopefully much earlier than 2050.
Once the greenhouse gases are reduced to pre-industrial levels, we could let the fossil fuels stay underground. Such retention of fossil fuels underground
need not result in all the investment in fossil fuel plants being written off. We hope to consider different fossil fuel plants retaining most of the investment by simply replacing the fossil fuel with Hydrogen as fuel. For example, in a coal fired power plant the furnace could be replaced by a Combustor burning Hydrogen and the hot gases from the Combustor could be passed through the boiler to generate steam. Thus simply replacing the furnace retains the rest of the investment. We hope to consider this aspect after completing our analysis to establish the development of the Hydrogen Economy as soon as possible, hopefully now itself.
By the Grace of God, we are happy to show that the fossil fuel power plants could be easily modified to become Hydrogen producers as well. The enzyme Carbonic Anhydrase performs the reversible reaction CO2 + H2O → ← HCO3( - ) + H( + ) using which we could remove CO2 and produce H2. Thus we need to enhance the fossil fuel power plants as indicated below and continue to use fossil fuels also.
Nature or the Second Law(?) of Thermodynamics?: The LHS of the bicarbonate producing equation has CO2 and H2O which have no energy. None of these reacts with Oxygen to produce energy. What about the RHS? The H( + ) does have 120 MJ of energy per Kg that gets released when it burns! The bicarbonate producing equation clearly violates the Second Law(?) of Thermodynamics. Has the Second Law(?) of Thermodynamics stopped nature from violating it in the oceans, in the plants, and indeed in all life forms that contain the enzyme Carbonic Anhydrase? No, nature has subdued the Second Law(?) of Thermodynamics for ages even before the so called law was formulated.
Coral reefs: Among many corals we find that Scleractinia are 1634 species of reef building corals from https://seaworld.org/en/animal-info/animal-infobooks/coral-and-coral-reefs/conservation-and-research . We quote from https://en.wikipedia.org/wiki/Coral now.
The scleractinian corals filled the niche vacated by the extinct rugose and tabulate species. Their fossils may be found in small numbers in rocks from the Triassic period, and became common in the Jurassic and later periods. … At certain times in the geological past, corals were very abundant. Like modern corals, these ancestors built reefs, some of which ended as great structures in sedimentary rocks. … Broader threats are sea temperature rise, sea level rise and pH changes from ocean acidification, all associated with greenhouse gas emissions. In 1998, 16% of the world's reefs died as a result of increased water temperature. … Approximately 10% of the world's coral reefs are dead. About 60% of the world's reefs are at risk due to human-related activities. The threat to reef health is particularly strong in Southeast Asia, where 80% of reefs are endangered. Over 50% of the world's coral reefs may be destroyed by 2030; as a result, most nations protect them through environmental laws.
We find that the coral reefs were built for the last 230 million years. Some information about the extent of the coral reefs follows.
https://www.environment.gov.au/system/files/pages/9bf5beee-6e77-4ef3-ab84-4eecc11898b4/files/qld-coral-submission.pdf
Coral reefs are distributed throughout the tropical and subtropical Western Atlantic and Indo-Pacific oceans, generally within 30º north and 30º south latitudes. After Indonesia, Australia has the largest area of coral reefs of any nation, nearly 50,000 square kilometres, or 19% of the world’s total area of reefs (Spalding et al. 2001). The largest reef complex in the world, the Great Barrier Reef (GBR), extends 2,300km along the northeast coast of Australia from the northern tip of Queensland to just north of Bundaberg, and is listed as a World Heritage Area. … Harriott (2001) calculated that 2 500 reefs across the GBR accumulate more than five million tonnes of calcium carbonate per year, of which only 50 tonnes or 0.001% is presently harvested.
Australia has 50,000 sq Km of corals, which is 19% of the world area of corals. This means the world has 50,000/0.19 = 263158 sq Km. Enzyme Carbonic Anhydrase has helped produce coral in 263,158 sq Km of the ocean. CO2 + H2O → ← HCO3( - ) + H( + ) reaction is performed by Carbonic Anhydrase. Two HCO3( - ) combines with two Ca(2+) to form Ca(HCO3)2 which is a reversible reaction. Under another reversible reaction, Ca(HCO3)2 changes to CaCO3 + H2CO3. The H2CO3 reversibly becomes H2O + CO2.
These steps are described in http://www.columbia.edu/itc/eeeb/baker/N0316/Lecture%202/page5.html Quoting, we have:
Zooxanthellae accelerate skeletal formation in reef-building corals … Exactly how calcification is accelerated is not fully understood. … Alteration of physicochemical conditions so as to favor calcification:
Ca2+ + 2HCO3- <->Ca(HCO3)2 <->CaCO3 + H2CO3 <-> CaCO3 + H2O + CO2 … Removal of water and carbon dioxide by photosynthesis (H2O + CO2 ->CH2O + O2) pushes the equation to the right and favors formation of calcium carbonate.
Carbonic Anhydrase has performed the violation of the Second Law(?) of Thermodynamics for millions of years. We believe nature and ignore the Second Law(?) of Thermodynamics in what follows.
Post-processing or pre-processing for CO2 capture?: ALLAM cycle burns CH4 in pure Oxygen and thus the turbine exhaust is CO2 and H2O only. By retrieving most of the energy of the turbine exhaust to reheat the circulating CO2, the ALLAM cycle spends 10% of the power for the air separator to supply pure Oxygen for combustion. ALLAM cycle has no need for any post processing to collect the CO2. Thus we could conclude that any process requiring more than 10% of the power of the power plant need not be considered for future.
Pressure Swing Adsorption [PSA] is commonly used to separate CO2 and H2 in Steam Methane
Reformation [SMR]. We consider PSA to separate CO2 and N2 now. The article on “Carbon dioxide capture by pressure swing adsorption” by Rafael M. Siqueira and seven coauthors is available at https://ac.els-cdn.com/S1876610217315382/1-s2.0-S1876610217315382-main.pdf?_tid=596c6b55-5299-4a69-9915-437a5ef95ee1&acdnat=1537990431_be69c421a2a5bef8687e94f06096658d
We quote from this article below:
Adsorption processes rely on the use of highly porous solids such as activated carbons, … One of the most basic configurations procedures comprises four steps: pressurization, feed, blowdown and purge. … This work aims to evaluate the performance of a PSA unit to separate N2/CO2 at a composition similar to those of flue gases (85/15%) using the most basic cyclic process of a PSA process (Skarstrom cycle) and a commercial activated carbon as adsorbent. … For the (pseudo) single component breakthrough curves, CO2 and N2 were diluted in 90% of He. The composition for the runs with He/CO2/N2 was 24/16/60%, which gives a relationship of approximately 21:79 for CO2:N2, all in molar basis. … Column and adsorbent properties - Column - Fixed bed length:0.54 m - Inner diameter:0.028 m - Wall thickness:2.8 x 10-3 m - Wall density:7400 kg m-3 - Adsorbent - Mass:0.136 kg … Four elementary steps of a Skarstrom-type PSA cycle were used to perform the CO2 separation process at a constant temperature of 298.15 K, with upper adsorption pressure of 6 bar and lower desorption pressure of 1 bar. … The PSA cycle started with a co-current pressurization step at the top of the bed, fed with the mixture CO2+N2 in a flow rate of 4.2 L min-1 and composition of 85% N2 and 15% CO2. In the second step, adsorption, the heavy component, CO2 in the case, is removed from the mixture, with the same flow rate and composition at a constant pressure of 6 bar and temperature (298.15 K). Blowdown is the third step; a rapid counter-current depressurization until the bed pressure reaches the lowest pressure of the cycle (1 bar). A part of CO2 is removed in this step. Finally, the cycle ends in the purge step where a flow rate of 0.15 L min-1 of pure N2 flows counter-current through the fixed bed at a constant pressure of 1 bar. This step has the goal of remove a part of CO2 adsorbed. A total number of 33 cycles was investigated. … The time of pressurization step (PR) was set according to the total flow rate; this step ended when the bed reached a pressure tolerance of 0.1 bar from the operational maximum pressure (6 bar). The adsorption step (AD) was set to last 70 seconds. Blowdown (BD) and purge (PG) steps must have the same time as pressurization and adsorption, respectively, in order to synchronize both columns. … The performance of a PSA process is commonly evaluated through the product purity, product recovery and productivity. … In this case, the productivity of nitrogen is determined in mol kg-1 h-1. … The activated carbon sample presented a higher capacity for carbon dioxide in comparison to nitrogen, … The isosteric heat of adsorption is a necessary input parameter for the energy balance, … The obtained heats of adsorption for CO2 and N2 as functions of the amount adsorbed are shown in Figure 4. The variation of the heats of adsorption were neglected and an average value of 26 kJ mol-1 was used for CO2 and 15 kJ mol-1 for N2. … In accordance to the equilibrium data (isotherms) one can notice that N2 leaves the column earlier than CO2, indicating higher retention capacity for the latter. … With a pressurization time of 58 seconds in average, the PSA process was performed in 33 cycles, reaching the cyclic stationary stage (CSS) around the 25th. … According to the results for the tested process configuration and step program, a purity of about 98% and productivity of 15 mol h-1 kg-ads-1 are reached at cyclic steady state. … The objective of this work has been reached, given the accuracy of the predictions obtained with the model. The combination of the simulation tool with and experimental PSA unit is very valuable for a deeper understanding of the involved phenomena and helpful with the design of optimized and efficient CO2 adsorption-based capture processes.
The researchers have concentrated on N2 instead of CO2. Starting with CO2/N2 of 15%/85%, they had achieved 2%/98%. We believe this was done by rejecting the extracted CO2 and retaining the mixture and achieving the final purity of N2. The industry is not interested in rejecting the CO2 to the atmosphere and refining the N2.
We try to increase the concentration of CO2 by rejecting the N2. From Figure 5a we understand that after adsorption at 6 bar, the desorption at 1 bar results in the CO2 leaving the activated carbon after 250 seconds. If the adsorption was done at 12 bar, the desorption at 1 bar results in the CO2 emission after 500 seconds. Likewise the adsorption at 20 bar results in the CO2 leaving after 750 seconds at 1 bar. In contrast, N2 exits after 50 seconds, 100 seconds and 200 seconds for adsorption at 6 bar, 12 bar, and 20 bar respectively according to Figure 5b.
As CO2 remains until 250 seconds after reaching 1 bar after adsorption at 6 bar, we could collect the CO2 between 250 seconds and 500 seconds of reaching 1 bar. We could remove more or less all N2 before 150 seconds starting with about 40 seconds after reaching 1 bar. We retain the pressurization time of 70 seconds, and the adsorption time of 70 seconds. We would like to collect the N2 after 40 seconds of reaching 1 bar using air instead of N2. This is because using N2 to collect N2 and finally discard it to the atmosphere would waste precious resources. If we propose to use an air separator to prepare N2, we could as well supply O2 for the combustion as in the ALLAM cycle and collect the full flue gas of CO2.
The mixture of N2 and CO2 would be heavier than air as CO2 has atomic weight of 44 compared to 32 of O2. Thus a purge cycle of the reactor with the air from above to displace the mixture of N2 and CO2 for the right time would replace the mixture of N2 and CO2 with air. We could purge the reactor from 140 seconds to 160 seconds. We feed air at 6 bar from above and collect the leaving flue gas in the flue gas tank. At 160 seconds, the reactor has air at 6 bar in its cavity, surrounded by the activated Carbon with both N2 and CO2 absorbed. The emission of N2 starts only after the reactor has remained for 40 seconds at a pressure of 1 bar. Release the air from the reactor to the atmosphere until the pressure inside the reactor is 1 bar. We assume that this depressurization could be completed in 20 seconds or less. We assume it is done in 20 seconds
to continue the analysis. The cavity is at 1 bar from 180 seconds. After 40 seconds, that is at 220 seconds N2 starts leaving the activated Carbon. The release of N2 from the activated Carbon is more or less complete at 280 seconds. During this period the cavity is in contact with the atmosphere so that there is no increase in pressure inside the cavity due to the released N2. After 250 seconds of remaining at 1 bar CO2 would be released by the activated Carbon. That is at 430 seconds CO2 would start leaving the activated Carbon. From 280 seconds feed the flue gas from below and purge the air maintaining the pressure at 1 bar. We assume that the purge is complete in 20 seconds. At 300 seconds the cavity is filled with the flue gas at 1 bar. From 430 to 530 seconds CO2 leaves the activated Carbon. To maintain the pressure in the cavity at 1 bar withdraw the contents of the cavity and pump into the flue gas tank. Now we are ready to start the next cycle. We do not need the first 70 seconds of filling the cavity with the flue gas. Thus we start with pumping more flue gas for the next 70 seconds. From the second cycle onwards the timings are as below:
1. 0 to 20 seconds to increase the pressure from 1 bar to 6 bar by pumping more flue gas.
2. 21 to 90 seconds at 6 bar to adsorb N2 and CO2.
3. 91 seconds to 110 seconds feed air at 6 bar from above and collect the flue gas in the tank.
4. 111 to 130 seconds: Open the cavity to atmosphere so that at 130 seconds the pressure inside is 1 bar.
5. 131 to 230 seconds: N2 leaves the activated Carbon from 171 seconds and by 230 seconds all N2 is expected to have left the activated Carbon.
6. 231 to 250 seconds: Pump the flue gas from below at 1 bar and reject the air in the cavity to atmosphere and fill the cavity with flue gas at 1 bar.
7. 251 to 380 seconds: Retain the cavity filled with flue gas at 1 bar.
8. 381 to 480 seconds: During this time CO2 leaves the activated Carbon. Maintain the pressure at 1 bar and pump the contents of the cavity into the flue gas tank. The flue gas remains in the cavity at 1 bar.
Now we are ready to repeat the cycle.
At the end of the above process the flue gas tank has CO2 and all the N2 that entered the tank initially has been pushed to the atmosphere. We would like to have a continuous process rather than the above in which the flue gas is collected for sometime and processed, necessitating another tank to collect the flue gas. Further as the concentration of N2 continues to decrease we might require more cycles.
Let us start with some pure CO2 as well. We modify the process as below. Before the cycle, we fill the reactor with flue gas at 1 bar.
1. 0 to 20 seconds: Increase the pressure from 1 bar to 6 bar by pumping more flue gas from the flue gas tank into the reactor cavity.
2. 21 to 90 seconds: The activated Carbon performs adsorption of N2 and CO2.
3. 91 to 110 seconds: The cavity has flue gas with reduced N2 and CO2 concentration compared to the gas in the flue gas tank. Feed air from above at 6 bar and collect the flue gas in the cavity in the flue gas tank. At 110 seconds the cavity has air at 6 bar.
4. 111 to 130 seconds: Open the cavity to the atmosphere so that at 130th second, the air inside the cavity is at 1 bar.
5. 131 to 230 seconds: The cavity remains open to the atmosphere and as N2 leaves the activated Carbon, some contents of the cavity leave the cavity to the atmosphere keeping the inside pressure at 1 bar. We expect that there is no more N2 in the activated Carbon at 230th second.
6. 231 to 250 seconds: Pump CO2 from below at 1 bar and push the air inside the cavity to the atmosphere. At 250th second, the cavity has CO2 at 1 bar.
7. 251 to 380 seconds: Retain the cavity filled with CO2 at 1 bar.
8. 381 to 480 seconds: During this time CO2 leaves the activated Carbon. Move the CO2 from the cavity to the CO2 tank maintaining the pressure at 1 bar. At the 480th second the activated Carbon has neither N2 nor CO2.
9. 481 to 500 seconds: Push the flue gas from the flue gas tank at the top and collect the CO2 in the cavity in the CO2 tank.At 500th second, the cavity has flue gas at 1 bar.
Repeat the cycle.
The N2 absorbed by the activated Carbon is rejected to the atmosphere. The CO2 absorbed by the activated Carbon is collected in the CO2 tank continuously. If the ratio between the absorbed N2 and the absorbed CO2 matches the ratio in the flue gas, by adjusting the amount of the activated Carbon we might get a continuous process. We cannot assume that all fossil fuels have the same ratio of N2 and CO2 in the flue gas. We are constrained to use two flue gas tanks. While one tank gets processed, we fill the other tank with flue gas.
The above process might remove either the CO2 or the N2 more compared to their presence in the flue gas. If more CO2 is removed, the relative concentration of N2 with CO2 inside the flue gas tank would continue to increase. At some point the recovery of the miniscule amount of CO2 in the flue gas tank would not be economical. Then the contents of the flue gas tank which is mostly N2 is purged to the atmosphere. The purged tank starts collecting the flue gas and the other tank is connected to the process.
If more N2 is removed by the activated Carbon compared to the CO2 in the flue gas, eventually the flue gas tank would have virtually all CO2 and very little N2. Then the contents of the flue gas tank is moved to the CO2 tank.
It is important to notice that there is no repetitive adsorption of the same N2 or CO2 and thus the energy spent is for just single adsorption. The energy used in adsorption of CO2 is 26 KJ per mol, while that for N2 is 15 KJ per mol. For the flue gas with 85% N2 and 15% CO2 the energy used is 0.85 x 15 + 0.15 x 26 = 12.75 + 3.9 = 16.65 KJ per mol of flue gas. To separate 1 mol of CO2 the energy required is 16.65/0.15 = 111 KJ per mol.
To estimate the percentage of the power lost in recovering the CO2 from the flue gas, we consider the following electrochemical approach. The article “Electrochemical Capture and Release of Carbon Dioxide,” by Joseph H. Rheinhardt and coauthors could be found at
https://pubs.acs.org/doi/pdf/10.1021/acsenergylett.6b00608 . We quote from this article now.
One of the more well studied chemistries based on this tactic employs an amine reagent such as monoethanolamine (MEA), which acts as a nucleophile, attacking CO2 at the electrophilic carbon center, thereby forming a carbamate. Equation 1 summarizes this process. ,,, As shown, 2 equiv of the amine are required to capture 1 equiv of CO2 in the form of a carbamate (RNHCO2 −). Equation 1 also shows that the reverse process, in which CO2 is released (e.g., for permanent storage, use as a chemical feedstock, enhanced oil recovery, etc.), requires an increase in temperature to break the N−C bond. The amount of thermal energy required is exacerbated by the fact that the MEA process is typically operated under aqueous conditions, meaning that significant energy is also required to heat the aqueous solution in which the capture chemistry is contained. Under these conditions, the energy required for recycling the MEA capture agent can consume between 14 and 30% of the output of a typical power plant, greatly impacting the economics of the capture process. … A solution of diamine is exposed to CO2 in a purge chamber. After the adduct is formed, the fluid is pumped to the anode chamber. Oxidation of a copper anode produces Cu2+, which binds to the diamine, displacing CO2. The cycle is completed by plating Cu2+ in a cathode compartment, regenerating the free diamine for another cycle. The chemistry of this approach relies on the very strong binding of the diamine to the metal center, which facilitates release of CO2 via cleavage of the N−C bond. The process was studied in some detail, with authors arguing that CO2 separation could be achieved at an energy cost of less than 100 kJ mol−1 using this type of approach. This compares favorably with the 170 kJ mol−1 reported from a thorough analysis of the MEA process. … For a typical case of separation from flue gas (e.g., assuming 10% CO2 at 1 atm) and delivery to a pure gas stream at 1 atm, eq 10 gives a minimum energy cost of 5.7 kJ mol−1 …
As 170 KJ per mol consumes 30% of the output of a typical power plant, 111 KJ per mol means the activated Carbon process consumes 111/170 x 30 = 19.59%.
Using an air separator and feeding pure O2 for combustion produces pure CO2 as flue gas and thus uses just 10% of the output of the power plant. We conclude that as of now pre-processing is better for the bottom line. However in future, in case a redox process using just 5.7 kJ per mol is developed, that process would consume 5.7/170 x 30 = 1.01% of the power output of a typical power plant. Once such a redox process is developed post-processing becomes substantially superior to pre-processing. A known devil is better than an unknown angel. To usher in the Hydrogen Economy as soon as possible, we hope all the existing and future fossil fuel plants would adapt pre-processing so that 100% capture of fossil CO2 is easy.
On October 5, 2018 we fortunately accessed the PDF of the article, “A process for capturing CO2 from the atmosphere,” whose abstract is found at https://www.sciencedirect.com/science/article/pii/S2542435118302253 . Figure 1 in the PDF
displays 4 processes indicated below.
1. Air Contractor: CO2(gas) + 2KOH(aqueous) → H2O(liquid) + K2CO3(aqueous) releasing 95.8 kJ per mol
2. Pellet reactor: K2CO3(aqueous) + Ca(OH)2(solid) → 2KOH(aqueous) + CaCO3(solid) releasing 5.8 kJ per mol
3. Calciner: CaCO3(solid) → CaO(solid) + CO2(gas) consuming 178.3 kJ per mol
4. Slacker: CaO(solid) + H2O(liquid) → Ca(OH)2(solid) releasing 63.9 kJ per mol
The total process consumes 178.3 - 95.8 - 5.8 - 63.9 = 12.8 kJ per mol. With 170 kJ per mol consuming 30% of the output of a fossil fuel power plant, 12.8 kJ per mol corresponds to 12.8/170 x 30 = 2.2588 % of the power output.
The Carbon Engineering company is currently involved in CO2 capture from atmosphere. Currently CO2 concentration in atmosphere is more than 400 ppm. A process consuming just 12.8 kJ per mol from a low concentration of 400 ppm would surely work to capture CO2 from the flue gases of fossil fuel power plants with CO2 concentration of 15%.
So, on October 5, 2018, we revise our earlier recommendation that pre-processing using pure Oxygen to burn the fossil fuel requiring modification of the furnace replacing N2 by the required amount of CO2, to use post-processing of CO2 capture using the 4 stage process of Carbon Engineering. We expect that the company Carbon Engineering would enter CCUS [Carbon Capture Use and Storage] of CO2 from the existing fossil fuel power plants all over the world.
Next we consider the disposal of the CO2. In fact, we show that CO2 could become a source for H2 itself.
Enzyme carbonic anhydrase: This enzyme performs the reversible balanced reaction CO2 + H2O ← → HCO3( - ) + H ( + ). As a balanced reaction, adding more and more CO2 to the water with the carbonic anhydrase would result in continued production of HCO3( - ) which would precipitate when its concentration in water increases beyond its maximum solubility in water. Once HCO3( - ) precipitates, the H( + ) leaves the water, becomes H2 and could be collected for the Hydrogen Economy.
We look at a few articles on carbonic anhydrase to design a bioreactor to feed CO2 and collect H2.
The abstract of the article on “Carbonic anhydrases in anthozoan corals—A review” by Anthony Bertucci and coauthors is found at https://www.sciencedirect.com/science/article/pii/S0968089612008395
We quote from this article.
Sixteen different a-CA isozymes have been identified in mammals: four cytosolic isozymes (CA I–III, CA VII and XIII), five membrane-bound isozymes (CA IV, CA IX, CA XII, CA XIV and CA XV), two mitochondrial isozymes (CA VA and VB), and one secreted CA isozyme, CA VI. … So far, two models, based either on an external CA activity to dehydrate HCO 3 and/or an intracellular CA activity to convert CO2 are accepted. … As found in other studies,93,94 the phylogenetic tree reveals three main clusters: (1) the membranebound or secreted proteins, (2) the cytosolic and mitochondrial proteins, (3) and the CARPs, which suggests that these 3 families evolved from a common ancestor prior to the separation between Cnidaria and Bilateria. … The a-CA from S. pistillata, referred to as STPCA (ACA53457), consists of 324 amino acids and contains a complete CA catalytic site, as predicted for functional CAs.93 Similarly to FCA a and b, the presence of a signal peptide indicates that STPCA protein is not cytosolic but secreted or membrane-bound. However, the protein does not contain a predictive GPI anchor site or transmembrane domain, suggesting that it is secreted rather than membrane-bound. … Furthermore, Moya et al.14 demonstrated, using real-time PCR, that expression of this secreted CA isoform increased two-fold in the dark relative to the light. This result lead the authors to hypothesize that up-regulation of this CA gene allows the coral to cope with night acidosis and reinforces the pharmacological experiments of Goreau12 that suggested an additional role of CA at night. … With the increase CO2 emission through human activities, a detailed study of enzymes dealing with this gas in organisms such as the corals, may help not only basic knowledge but probably also finding an environmentally friendly way of resolving this problem.
The enzyme STPCA (ACA53457) is a secreted enzyme and could be collected for the bioreactor. In https://mohideenibramsha7.wixsite.com/website/single-post/2018/09/25/Hydrogen-Economy-Now-12 we found that Methanosarcina acetivorans consumes CO and CH3COOH and grows. It has Cam enzyme that converts the CO2 emitted by the microbe to HCO3( - ) so that the CO2 does not reenter the microbe. Quoting from https://pubs.acs.org/doi/abs/10.1021/bi802246s we have:
A recombinant protein overproduction system was developed in Methanosarcina acetivorans to facilitate biochemical characterization of oxygen-sensitive metalloenzymes from strictly anaerobic species in the Archaea domain. The system was used to overproduce the archetype of the independently evolved γ-class carbonic anhydrase. The overproduced enzyme was oxygen sensitive and had full incorporation of iron instead of zinc observed when overproduced in Escherichia coli.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2818130/
Carbonic anhydrases are metalloenzymes catalyzing the reversible hydration of carbon dioxide to bicarbonate (CO2 + H2O ⇆ HCO3−+ H+). … Cam is the γ class archetype isolated from Methanosarcina thermophila, an anaerobic methane-producing species from the Archaea domain … Cam has been characterized biochemically and shown to have carbonic anhydrase activity. … Cam has 3-fold greater carbonic anhydrase activity and contains Fe2+ in the active site (Fe-Cam) when purified anaerobically from E. coli or overproduced in the closely related species M. acetivorans and purified anaerobically establishing Fe2+ as the physiologically relevant metal … Soluble Fe2+ is abundant in oxygen-free environments and available to anaerobic microbes that utilize this metal in a host of enzymes. Thus, it is paramount that the purification and characterization of carbonic anhydrases from anaerobes is performed under oxygen-free conditions.
We could use the overproduced Cam alone in our bioreactor with water. As we bubble CO2 through the water, the Cam converts the CO2 to HCO3( - ) following the reaction
CO2 + H2O → HCO3( - ) + H( + )
Even though this is a reversible reaction, as we bubble more and more CO2 the HCO3( - ) would exceed the soluble amount and start precipitating. We collect the precipitated HCO3( - ) for storage. We also collect the H( + ) that bubbles up and become H2.
In case the Cam from the microbe Methanosarcina acetivorans or the STPCA (ACA53457) is not voluminous enough, we could use the microbe to grow using CO without bubbling CO2 as the microbe itself produces 5 CO2 molecules for every CH4 molecule. However in the reactor while the microbe is consuming CH3COOH and producing CH4, we bubble CO2 in the reactor. As only one CO2 molecule is produced for every CH4 molecule in contrast to the 5 CO2 molecules while consuming CO, we expect the bubbled CO2 also to be converted to HCO3( - ) by the Cam of the microbe.
Now we have a method to convert CO2 to HCO3( - ) using Carbonic Anhydrase. Thus the fossil fuel plants also become producers of Hydrogen for the Hydrogen economy. We call this production of Hydrogen from CO2 as Plan C.
Conclusion: We have detailed Plan A at https://mohideenibramsha7.wixsite.com/website/single-post/2018/09/16/Hydrogen-Economy-Now-11 ; Plan B at https://mohideenibramsha7.wixsite.com/website/single-post/2018/09/25/Hydrogen-Economy-Now-12 ; and Plan C above. Use these plans to produce Hydrogen. For the existing fossil fuel plants install Carbon Capture and produce Hydrogen also using Plan C.
For the new power plants use Hydrogen as fuel using the CAM ALLAM cycle. If it is desired to use the available fossil fuel, use the process of company Carbon Engineering to collect CO2 from the flue gas. Use the CO2 generated by burning the fossil fuel to produce Hydrogen using Plan C.
Use Hydrogen for transportation.
Under the suggested scheme, we reduce the CO2 in the atmosphere by Plan B; convert the fossil fuel to behave as a renewable fuel and do not emit CO2 to the atmosphere by Plan C.
We have the technologies to switch to the Hydrogen Economy as soon as possible and start
reducing the CO2 content of the atmosphere so that we could achieve life without exceeding the 1.5 C limit.
Previous posts in this series:
https://mohideenibramsha7.wixsite.com/website/single-post/2018/07/25/Hydrogen-Economy-Now-1
https://mohideenibramsha7.wixsite.com/website/single-post/2018/08/02/Hydrogen-Economy-2
https://mohideenibramsha7.wixsite.com/website/single-post/2018/08/06/Hydrogen-Economy-Now-3
https://mohideenibramsha7.wixsite.com/website/single-post/2018/08/07/Hydrogen-Economy-Now-4
https://mohideenibramsha7.wixsite.com/website/single-post/2018/08/07/Hydrogen-Economy-Now-5
https://mohideenibramsha7.wixsite.com/website/single-post/2018/08/08/Hydrogen-Economy-Now-6
https://mohideenibramsha7.wixsite.com/website/single-post/2018/08/09/Hydrogen-Economy-Now-7
https://mohideenibramsha7.wixsite.com/website/single-post/2018/08/09/Hydrogen-Economy-Now-8
https://mohideenibramsha7.wixsite.com/website/single-post/2018/08/24/Hydrogen-Economy-Now-9
https://mohideenibramsha7.wixsite.com/website/single-post/2018/09/10/Hydrogen-Economy-Now-10
https://mohideenibramsha7.wixsite.com/website/single-post/2018/09/16/Hydrogen-Economy-Now-11
https://mohideenibramsha7.wixsite.com/website/single-post/2018/09/25/Hydrogen-Economy-Now-12
A