The common method of hydrogen production God help!

Biological hydrogen production can be divided into photolytic water hydrogen production, anaerobic bacterial hydrogen production, photosynthetic bacterial hydrogen production According to the microorganisms used, hydrogen-producing raw materials and hydrogen production mechanism, biological hydrogen production can be divided into photolytic water hydrogen production, anaerobic bacterial hydrogen production, photosynthetic bacterial hydrogen production and so on, three types, and its characteristics are shown in Table 1. Green Algae Water as raw material, high solar energy conversion rate, the process of hydrogen production requires light, the influence of light intensity is large, the system of hydrogen production is unstable, and at the same time, the oxygen produced has an inhibitory effect on the reaction. Cyanobacteria Water as feedstock, hydrogen production is mainly done by nitrogenase, which can fix N2 in the atmosphere Hydrogen production process requires light, low rate of hydrogen production, and the oxygen produced inhibits nitrogenase Anaerobic Bacteria Do not require light, can produce hydrogen continuously, can utilize a variety of organic matter as a substrate, the process of hydrogen production is anaerobic, there is no oxygen limitation, and the system is easy to realize scale-up experiments The reaction needs to be controlled to keep the pH in the acid range, and the product inhibition is not stable, and the system is easy to implement. The reaction needs to control the pH in the acidic range, the utilization rate of raw materials is low, the inhibition of the product is obvious Photosynthetic Bacteria Hydrogen production efficiency is high, a variety of organic wastes can be used as raw materials, a wide range of spectral range can be utilized, there is no oxygen inhibition Hydrogen production process requires light, it is not easy to carry out the amplification of the test (1) photolytic water hydrogen production is a photosynthetic organism in anaerobic conditions, photosynthesis decomposition of water, generating organic matter, and at the same time, the release of hydrogen gas. Its mechanism and green plant photosynthesis mechanism is similar, in some algae and eukaryotic organisms (cyanobacteria) have two photosynthetic centers such as PS Ⅰ, PS Ⅱ, PS Ⅰ to produce reductant used to fix CO2, PS Ⅱ to receive solar energy decomposition of water to produce H +, electrons and O2; PS Ⅱ produced by the electrons, carried by iron redox proteins, through PS Ⅱ and PS Ⅰ to reach the hydrogen enzyme, H + hydrogen enzyme catalyzed by the formation of H2, H+, H+, H+, H+, H+, H+, H+, H+, H+, H+, H+, H+, H+, H+, H+, H+, and H2, H+. Among them, the system that utilizes algae to produce hydrogen by photolysis of water is called direct biophotolysis hydrogen production system, and the system that utilizes cyanobacteria for hydrogen production is called indirect photolysis water hydrogen production system. The hydrogen production reaction of algae is catalyzed by hydrogenase and can utilize water as the original donor of electrons and protons, which is the main advantage of hydrogen production by algae. Cyanobacteria have both nitrogen-fixing and hydrogenase enzymes, and their hydrogen production process is mainly acted by nitrogen-fixing enzymes, while hydrogenase enzymes mainly act in the direction of hydrogen absorption. Cyanobacteria can also utilize water as the ultimate electron donor, and the electrons and protons required for their hydrogen production also come from water cleavage [10]. (2) Anaerobic bacterial hydrogen production utilizes anaerobic hydrogen-producing bacteria to convert organic matter into hydrogen by decomposition under dark, anaerobic conditions. It is currently believed that the process of anaerobic bacterial hydrogen production can be realized through three pathways: the pyruvate hydrogen production pathway, the formate catabolic hydrogen production pathway, and the hydrogen production pathway through the regulation of NADH/NAD+ homeostasis, etc. The pyruvate hydrogen production pathway and the formate catabolic hydrogen production pathway are sometimes also referred to as the direct pathway of hydrogen production [11], i.e., glucose is first fermented through the EMP pathway to form pyruvate, ATP, and NADPH; pyruvate is fermented via the pyruvate ferric oxide reductase is oxidized to acetyl coenzyme A, CO2 and reduced ferric oxide reductase, or through the pyruvate formate lyase and broken down to acetyl coenzyme A and formic acid, the resulting formic acid is again oxidized to CO2, and the ferric oxide reductase; finally, reduced ferric oxide reductase reducts hydrogenase, and the resulting reduced hydrogenase reduces protons when protons are present to Hydrogen is produced. (3) Photosynthetic bacterial hydrogen production is the use of photosynthetic bacteria in anaerobic conditions through the light to decompose organic matter into hydrogen. Photosynthetic bacteria are a class of primitive archaea that can convert organic acids into molecular hydrogen under light conditions. Since the American biologist Gest first proved the hydrogen production phenomenon of photosynthesizing bacteria (Rhodospirillum? rubrum) under light conditions in 1949, a large number of studies have shown that the hydrogen production of photosynthesizing bacteria is produced under the hydrogen release effect of nitrogen-fixing enzymes coupled with photosynthetic phosphorylation. Photosynthetic bacteria contain only one photosynthetic center, and the electron donor is organic matter or reduced sulfide, so the photosynthetic phosphorylation process does not emit oxygen, and only ATP is produced without NAD(P)H. Compared with green algae and cyanobacteria, this characteristic of only producing hydrogen without emitting oxygen can greatly simplify the production process, and there is no problem of separating the product oxygen from the hydrogen and will not cause the inactivation of the enzyme of nitrogen fixation [11]. 2 Status of biological hydrogen production technology and its barriers Hydrogen has become the focus of support for the energy policies of governments after the two energy crises, and biological hydrogen production technology is recognized as the main technology with the most promising application prospects in the future of alternative energy, and has become the current research hotspot in the field of energy science and technology in the world, which promotes the many advances in biological hydrogen production technology. As the earliest researched hydrogen production pathway in biological hydrogen production technology, algae (cyanobacteria) can directly utilize water and sunlight for hydrogen production, which is considered the most promising hydrogen production pathway and the most researched technology in biological hydrogen production at present. At present, the United States, Japan, the European Union, China and other countries have made breakthroughs in the fields of algal molecular biology, development of oxygen-tolerant algae, accelerators and other technologies, and developed various types of bioreactors, which have completed the transformation of algal hydrogen production from the laboratory to practical gradually [13-16]. However, the process of hydrogen production in algae is accompanied by the production of oxygen, the oxygen produced by the reaction, in addition to reacting with the generated hydrogen, is also an inhibitor of hydrogenase activity, thus affecting the rate of hydrogen production in the system; at the same time, when the light intensity is large, it is mainly CO2 absorption and synthesize the required organic substances. Therefore, hydrogen production by algae is unstable and easily inhibited by its by-product oxygen [17],[18]. Similar to algae, cyanobacteria produce hydrogen along with oxygen, which is an inhibitor of nitrogen fixing enzymes. Altering the genes of algae through genetic engineering to improve their oxygen tolerance is currently the main research content, and some progress has been made [19]. Anaerobic bacterial hydrogen production is not dependent on light, hydrogen production reaction can be carried out under dark conditions, easy to realize the hydrogen production reactor engineering scale-up test, coupled with anaerobic bacteria can use a variety of organic substances as hydrogen production reaction raw materials, can make a variety of industrial and agricultural organic sewage to get clean treatment, and effectively control the environmental pollution, and at the same time also produces clean hydrogen, so that the industrial and agricultural organic wastes to achieve the utilization of resources, but also It is regarded as a more ideal way to produce hydrogen, which has attracted the favor of domestic and foreign hydrogen energy science and technology workers, especially in China in the anaerobic hydrogen-producing bacteria selection and breeding, hydrogen-producing mechanism and engineering technology and other aspects of the research progress has been remarkable. However, it has been found that this pathway has the problems of low hydrogen production and feedstock utilization rate of anaerobic bacteria in the process of hydrogen production by fermentation. The main reasons are: from the perspective of cell survival of anaerobic hydrogen-producing bacteria, pyruvate fermentation is mainly used to synthesize the cell's own substances, rather than for the formation of hydrogen, which is the result of natural evolution; secondly, part of the hydrogen produced in the reaction process is re-decomposed and utilized under the catalytic action of the enzyme hydrogenase, which reduces the hydrogen output rate. Meanwhile, the pH value must be in the acidic range to inhibit the growth of hydrogenotrophic bacteria, such as methanogenic bacteria, in the process of hydrogen production by anaerobic bacterial fermentation, but the growth of hydrogen-producing bacteria and the process of hydrogen production were significantly inhibited when the pH was <4. For the continuous anaerobic bacterial fermentation hydrogen production process system, the metabolic pathway of hydrogen production is sensitive to the hydrogen partial pressure and easily inhibited by the end products, when the hydrogen partial pressure increases, the amount of hydrogen production decreases, and the metabolic pathway is converted to the production of reduced products.The concentration of CO2 also affects the rate of anaerobic bacterial hydrogen production and the amount of hydrogen production, and meanwhile, in the continuous anaerobic bacterial hydrogen production process, the hydrogen-producing bacteria can not utilize small molecules of organic acids such as acetic acid, propionic acid and butyric acid, which results in the accumulation of organic acids. At the same time, in the continuous process of hydrogen production by anaerobic bacteria, hydrogen-producing bacteria cannot utilize small molecules such as acetic acid, propionic acid, butyric acid and other small molecules, which results in the accumulation of organic acids and the formation of inhibition of hydrogen-producing bacteria. Although acetic acid has no toxic effect on hydrogen-producing bacteria, the accumulation of large amounts of acetic acid will limit the improvement of the energy conversion rate, which restricts the further application and development of anaerobic bacterial hydrogen-producing engineering technology [18]. Photosynthetic bacteria as a class of archaea hydrogen production phenomenon widely exists in nature, can use a variety of organic substances in nature as a growth substrate, has been widely used in the degradation of organic wastewater treatment. Hydrogen production, as a unique physiological feature of photosynthetic bacteria, has only been paid attention by the energy science community in recent years, and has gradually become a research hotspot in the field of energy science and technology. However, the high dependence on light in the process of hydrogen production by photosynthetic bacteria has limited the development of hydrogen production by photosynthetic bacteria. Generally, according to the requirements of light intensity and light continuity for the stability of hydrogen production by photosynthetic bacteria, the artificial light source technology that consumes electricity or other fossil energy is often used in the process of hydrogen production by photosynthetic bacteria, which is technically and economically unreasonable, and the prospect of market application is bleak, and at the same time, due to the secretion of pigment and the turbidity of the reaction solution of photosynthetic bacteria in the process of growth, the light is affected by the uniform distribution of light in the reaction solution, and the efficiency of the utilization of light energy is reduced, and the light energy is increased. At the same time, due to the secretion of pigments during the growth process of photosynthetic bacteria and the color turbidity of the reaction solution itself, the uniform distribution of light in the reaction solution is affected, reducing the efficiency of light energy, increasing the energy consumption of the photosynthetic bacterial hydrogen production process and hydrogen production costs. 3 Development potential of biological hydrogen production technology The hydrogen production capacity of hydrogen-producing bacteria (algae) is an important evaluation index for the conversion of biological hydrogen production technology to practical engineering technology The equations of common biological hydrogen production process of organic matter and the Gibbs free energy change (ΔG) of its reaction are expressed as follows [17,20]: Anaerobic bacterial hydrogen production process: Glucose? C6H12O6+2H2O→2CH3COOH+2CO2+4H2? ΔG = -184 kJ C6H12O6→CH3(CH2)2COOH+2CO2+2H2 ΔG = -257 kJ Photosynthetic bacterial hydrogen production process: glucose C6H12O6+2H2O→6CO2+8H2 ΔG = -34 kJ Acetic acid CH3COOH+2H2O→2CO2+8H2 ΔG = -34 kJ Acetic acid CH3COOH+2H2O→2CO2+8H2 ΔG = -34 kJ 2H2O→2CO2+4H2 ΔG = 75 kJ Hydrogen production by photolysis: 4H2O + light energy→2O2+4H2 ΔG = 1498 kJ Although the Gibbs free energy change law of hydrogen production reaction shows that anaerobic bacterial fermentation is very advantageous for hydrogen production, and they can obtain more free energy from the hydrogen production reaction than the photosynthetic bacterial production of hydrogen, however, anaerobic bacterial decomposition of organic matter is slow and incomplete, which significantly reduces the hydrogen production rate. However, the slow and incomplete decomposition of organic matter by anaerobic bacteria significantly reduces the rate and amount of hydrogen production, and 1 mol of glucose can theoretically produce only 2-4 mol of hydrogen. In terms of the Gibbs' free energy change law of hydrogen production reaction, hydrogen production by photolyzed algae is generally similar to that of anaerobic bacterial fermentation, and it can obtain more free energy from the hydrogen production reaction than that of photosynthesizing bacteria. However, the hydrogen production system of photolyzed water from algae is very unstable due to the mediation of hydrogenase and the inhibitory effect of oxygen, which is not conducive to the effective improvement of the rate and amount of hydrogen production in the photolyzed water process. In the hydrogen production reaction of photosynthetic bacteria, it can be seen from the change rule of Gibbs free energy of the hydrogen production reaction, although only a small amount of free energy can be obtained, or even a large amount of free energy has to be paid, but the photosynthetic bacteria can obtain enough ATP through photosynthetic phosphorylation to make the reaction can be carried out efficiently, and theoretically, the photosynthetic bacteria can convert 1 mol of glucose into 12 mol of hydrogen [21]. Obviously, the key to the development of photosynthetic bacteria hydrogen production technology is the light technology, and the appropriate choice of light source and reduce light energy consumption become two key technologies to solve the photosynthetic bacterial hydrogen production process, the use of solar energy as a light source of photosynthetic bacterial hydrogen production technology because of the fundamental solution to the problem of light energy consumption and the cost of hydrogen production and other issues have attracted the special attention of the energy sector, has a strong technical feasibility and potential development prospects. It has strong technical feasibility and potential development prospects. 4 Photosynthetic biological hydrogen production technology research progress in recent years at home and abroad has begun to improve the light conversion efficiency of photosynthetic bacteria from the photosynthetic biological hydrogen production experimental research, which is most representative of the research progress of the Ministry of Agriculture of Henan Agricultural University Renewable Energy Key Open Laboratory. Funded by the National Natural Science Foundation of China, the National 863 Program, the Doctoral Funds of the Ministry of Education and international cooperation projects, we have conducted systematic and in-depth researches on key theoretical and technological issues such as the screening and cultivation of highly efficient photosynthetic hydrogen-producing bacteria using fecal wastewater as the raw material, the conditions of hydrogen-producing process, the method of immobilization, the automatic tracking of the sun and the light-guiding system of photoconducting fibers, and the spectral coupling characteristics of solar photosynthetic hydrogen-producing bacteria, and have made some important achievements. In-depth research has been carried out, and some important progress has been made [22-27]. (1) Important progress has been made in the selection and breeding of photosynthetic hydrogen-producing bacterial strains using livestock and poultry manure as raw materials. Twenty-four typical samples were obtained from six representative locations, and according to the growth conditions and nutritional requirements of various types of photosynthetic bacteria, the corresponding media and culture conditions were designed from several aspects, including media composition, pH, light time and period, incubation temperature, and anaerobic state , and the photosynthetic bacteria were extensively enriched and isolated, and 33 strains of photosynthetic bacteria were obtained, and in accordance with the compositional characteristics of swine manure, the According to the characteristics of swine manure, related small molecular organic acids and hydrogen-producing ability, 7 photosynthetic hydrogen-producing bacterial strains with extremely high raw material conversion efficiency were screened out. (2) Successfully developed a solar energy efficient focusing collection system with automatic tracking of the sun and adjustable filtering, and carried out research on the optimization of the optical transmission and spectral coupling performance of the system. In order to improve the utilization of solar energy, a Fresnel lens concentrating type solar light-guide light harvesting system has been developed, which adopts the Fresnel lens concentrating method to gather the sunlight in the focal point, and puts the light-guide fibers on the focal point, which is selectively filtered by the adjustable filter, and then fed into the photosynthetic bioreactor through the light-guide fibers to achieve the high efficiency transmission of the sunlight. At the same time, seven strains of photosynthesizing bacteria screened were subjected to experimental studies on solar light absorption spectra, and the correlation between growth characteristics in different solar light bands and hydrogen production characteristics with pig manure effluent as the substrate was proposed, which explored the coupling performance of light transmission and spectra in the process of solar photosynthesis and biological hydrogen production, as well as the way to further improve the efficiency of solar photosynthesis and biological hydrogen production. (3)A new type of annular flow tank type photosynthetic biohydrogen production reactor with high surface area and volume ratio was successfully developed, and the attenuation characteristics of light transmission process in the reactor were systematically studied. Based on the growth and metabolic characteristics of photosynthetic hydrogen-producing bacteria, the developed circulating tank type photosynthetic biological hydrogen production reactor has the characteristics of being able to utilize high surface area and volume ratio of light to reduce the mutual shading effect of photosynthetic bacterial cells and livestock and poultry wastewater, to produce the "scintillation effect" around the bacteria by controlling the flow rate of the reaction liquid, and to improve the pathway and quality of light propagation effectively. It can automatically control the reaction conditions of photosynthetic hydrogen production, so that the photosynthetic bacteria are under the best growth and metabolic conditions, and the photoconversion efficiency and hydrogen yield can be optimized through the optimal control of temperature, illumination, pH, substrate concentration, different inoculum quantities, and dissolved oxygen level, and so on. (4) We have systematically studied the thermodynamic characteristics of the solar photosynthetic hydrogen production process, revealed the influence of the thermodynamic characteristics of the biological hydrogen production process on the activity of photosynthetic bacterial hydrogenase and the rate of hydrogen production, analyzed the heat production law of the growth and metabolism process of photosynthetic hydrogen-producing bacteria by the method of thermodynamics, obtained the thermodynamic information of the growth and metabolism of solar photosynthetic hydrogen-producing bacteria, and studied the temperature field distribution of the photosynthetic hydrogen-producing system, and established a system to characterize the solar energy conversion efficiency and the rate of hydrogen production. The study of the temperature field distribution of the photosynthetic hydrogen production system, the establishment of a model to characterize the thermodynamic characteristics of the solar photosynthetic hydrogen production process, and the optimization of the optimal growth and metabolic temperature of photosynthetic hydrogen-producing bacteria and the process conditions of the energy flow, provide scientific references and theoretical basis for the further development of the design of the photosynthetic bioreactor and the experimental study of the large-scale production and operation. Tel：86-20-23361169 This article is from: Guangzhou Linglong Electronics Technology Co., Ltd, Hydrogen Production, Hydrogen Fuel Cell ( www.liongon.com )