Enhanced hydrogen production method using straw dark fermentation hydrogen production solid residues

Abstract

The invention relates to the technical field of biomass hydrogen production, in particular to an enhanced hydrogen production method using straw dark fermentation hydrogen production solid residues. Comprising the following steps: 1) collecting solid residues after hydrogen production by straw fermentation, and drying for later use; 2, molten salt with the same components is arranged in the reactor a and the reactor b, and a gas product generated by the straw fermentation hydrogen production system is introduced into the molten salt of the reactor a to purify H2; (3) after H2 purification is finished, obtained solid residues are put into the molten salt of the reactor a for a reaction, and a pyrolytic carbon product and hydrogen-rich combustible gas are obtained; and 4) introducing the gas product and the hydrogen-rich combustible gas generated in the step 2) and the step 3) into a low-temperature condensation collection device to separate a liquid pyrolysis product and a hydrogen-rich gas product, and collecting the hydrogen-rich gas product. According to the method, secondary hydrogen production can be carried out on solid residues obtained after hydrogen production through straw fermentation, and H2 purification is carried out on gas products obtained after hydrogen production through straw fermentation through a molten salt system.

Description

Technical Field

[0001] The present invention relates to the technical field of biomass hydrogen production, and in particular to an enhanced hydrogen production method utilizing solid residues from hydrogen production by dark fermentation of straw. Background Art

[0002] As the world actively seeks sustainable energy solutions, hydrogen energy, as a clean, efficient, and renewable energy carrier, has attracted considerable attention. Traditional hydrogen production methods, such as reforming fossil fuels, not only consume large amounts of non-renewable resources but also generate significant greenhouse gas emissions, placing a severe burden on the environment. While water electrolysis is a cleaner method, its high energy consumption and high cost limit its large-scale application.

[0003] In this context, hydrogen production from biomass fermentation has become a research hotspot. Among these, using straw as a feedstock for hydrogen production offers significant advantages. As a major agricultural waste product, straw is readily available and inexpensive. Converting straw into hydrogen through fermentation not only recycles waste but also reduces environmental pollution caused by straw burning, aligning with the principles of a circular economy and sustainable development. However, current straw fermentation hydrogen production technology faces numerous challenges. Firstly, the conversion rate of straw fermentation to hydrogen is low, making it difficult to meet actual hydrogen production needs. Secondly, the disposal of the solid residues produced by fermentation is an urgent issue. These residues still contain a certain amount of organic matter and incompletely decomposed lignocellulose. Directly discarding or simply treating them would not only waste resources but also potentially cause secondary environmental pollution. Furthermore, the purity of hydrogen produced from biofermentation is relatively low. Applications in high-purity hydrogen-demanding scenarios, such as fuel cells, require extensive purification, significantly increasing the overall cost of biofermentation hydrogen production.

[0004] Currently, the main ways to utilize straw fermentation residues include fertilizer, feed, and energy. Regarding fertilizer utilization, returning the residues directly to the fields can replenish soil organic matter, but the residual fermentation microbial metabolites may affect the original soil microbial community structure, and the incompletely decomposed cellulose is difficult to be quickly absorbed and utilized by crops, which can easily cause an imbalance in the soil's carbon-nitrogen ratio and reduce soil fertility. Regarding feed utilization, the residues contain residual acidic substances from fermentation, and the cellulose content is high and the nutritional value is low, requiring complex pretreatment and high costs. Energy utilization methods, such as incineration for power generation, have very low added value. None of the above traditional utilization methods have fully tapped the potential value of the remaining organic matter in the residues, and a large amount of organic carbon elements have not been effectively utilized, resulting in a waste of resources. Therefore, there is an urgent need to break through the bottleneck of traditional utilization models and explore innovative paths to achieve high-value development of the remaining organic matter in straw fermentation residues.

[0005] The above content is only used to assist in understanding the technical solution of the present invention and does not mean that the above content is the closest prior art. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an enhanced hydrogen production method using the solid residue of straw dark fermentation hydrogen production. This method can not only utilize lignin, cellulose, etc. that are not completely degraded in the biomass fermentation hydrogen production process to enhance secondary hydrogen production, but also use the same molten salt system to treat the biomass dark fermentation gas products, thereby increasing the proportion of hydrogen in the gas products and saving the cost of gas separation and purification. To achieve the above-mentioned purpose, the technical solution of the present invention is implemented as follows: a method for enhancing hydrogen production using solid residues from dark fermentation of straw for hydrogen production; comprising the following steps: Step 1) collecting the solid residue remaining after hydrogen production by the straw fermentation hydrogen production system, washing the solid residue with water to remove the water-soluble components in the solid residue, and drying it for later use; The water-soluble components in the solid residue mainly include inorganic salts, small molecular organic acids and other water-soluble substances; Step 2) The same molten salt composition is set in reactor a and reactor b. Under the protection of an inert gas atmosphere at a specified reaction temperature, the gas product produced by the straw fermentation hydrogen production system is passed into the molten salt in reactor a to purify the H2; Step 3) After the H2 purification in step 2) is completed, the solid residue obtained in step 1) is wrapped in nickel foam or copper foam and then added to the molten salt in reactor a for reaction. The reaction gas products are mainly H2, CO and methane. After the reaction is completed, the solid residue is removed and washed with dilute acid to obtain a biomass pyrolysis carbon product; In step 4), the gaseous product produced in step 2) and the hydrogen-rich combustible gas produced in step 3) are introduced into a low-temperature condensation collection device to separate the liquid pyrolysis product and the hydrogen-rich gas product, and the hydrogen-rich gas product is further dehydrated and carbon dioxide is captured, and finally the hydrogen-rich gas product is collected.

[0007] The low-temperature condensation collection device includes an ice bath collection device and a CaO packing tower; the ice bath collection device can provide a low-temperature environment to separate the gas product generated in step 2) and the low-temperature liquid pyrolysis product in the hydrogen-rich combustible gas generated in step 3) by condensation.

[0008] Pyrolysis products are usually produced during the pyrolysis of straw. They are a complex mixture containing methoxy organic matter, aldehydes, ketones, phenols, water, and a small amount of acid and ester compounds. The ice bath collection device can re-condense these gaseous substances at high temperatures into liquid form.

[0009] All the separated gas products are then passed through a CaO packed tower to reduce the H2O and CO2 therein, and finally the hydrogen-rich gas products are collected, and the H2 content in the collected hydrogen-rich gas products is monitored online.

[0010] Preferably, the molten salt is obtained by adding a mixture containing Li2O, Li2CO3, Na2CO3, K2CO3 and Na2MoO4 into reactor a and reactor b respectively, and heating to 930°C to melt the mixture into a liquid state.

[0011] Preferably, the molar proportion of Li2CO3 in the mixture is 20%-50%; the total molar proportion of Na2CO3 and K2CO3 is 30%-60%, the molar proportion of Na2MoO4 is 2%-6%; the molar proportion of Li2O is 1%-5%; and the molar ratio of Na2CO3 to K2CO3 is 1:1-2:1.

[0012] Preferably, the gaseous product gas produced by the straw fermentation hydrogen production system in step 2) is introduced into the reactor a at least 2 cm below the molten salt liquid level, and the gas flow rate is about 0.1-1 L / min·kg salt; the ventilation time is 0.5-2.5 h; the inert gas is N2 or Ar.

[0013] Step 2) involves treating the fermentation gas with molten salt to purify H₂. The 0.1-1 L / min·kg value corresponds to the unit mass of the melted salt in the reactor and the gas flow rate entering the molten salt at that point. This represents the flow rate of the input gas (to be absorbed) per kilogram of molten salt.

[0014] Preferably, the reaction time of the solid residue in the molten salt in reactor a in step 3) is 5-180 min.

[0015] Preferably, the specified reaction temperature is 500-700°C.

[0016] Preferably, the process further includes step 5) online monitoring of the H2 content in the collected hydrogen-rich gas product. When the H2 content in the gas product is detected to be lower than 70%, step 2) and step 3) are stopped, and the molten salt in reactor a is extracted into reactor b for electrolysis treatment. The molten salt obtained after the electrolysis in reactor b is refluxed into reactor a for continued use when repeating steps 2) and 3).

[0017] Preferably, the electrolysis treatment adopts constant cell pressure electrolysis, the electrolytic cell pressure is 2.1-2.8V, and the electrolysis time is 0.1-8h; the anode of the electrolysis treatment is a metal molybdenum rod or molybdenum sheet, which serves as a sacrificial anode; the cathode is a rotating disk or rotating cylindrical electrode, and the cathode material is molybdenum or stainless steel; the rotation speed is 100-2000rpm.

[0018] Preferably, the molybdenum carbide and carbon composite solid products deposited on the cathode of the electrolytic treatment are regularly recovered (the molybdenum carbide and carbon composite solid products are formed by co-deposition of molybdate and carbonate, and the lost molybdate ions are replenished by a sacrificial anode), and the cathode surface is polished and reused.

[0019] Preferably, the hydrogen-rich gas product collected in step 4) is introduced into the reactor a again for heating, and then the heated gas product is introduced into the solid-state fuel cell reaction zone for use.

[0020] The beneficial effects of the present invention are embodied in: (1) The method provided by the present invention can effectively improve the purity of hydrogen in the gas products of dark fermentation of biomass, and at the same time absorb water vapor in the fermentation gas to supplement the H source for the subsequent hydrogen production process by pyrolysis of hydrogen production residue. The gas products of dark fermentation of biomass to produce hydrogen are mainly H2 and CO2, which may contain a small amount of H2S, ammonia, etc., and also contain water vapor brought out from the fermentation system. When the fermentation gas is introduced into the molten salt system, a small amount of H2S will be absorbed by the alkaline carbonate, while CO2 and H2O will also be absorbed by the molten salt and combined with oxygen anions to form CO3 2- and OH - melted in the molten salt in the form of CO2+O 2- →CO3 2- ;H2O+O 2- →2OH - This not only reduces the CO2 content in the fermentation gas and improves the purity of H2; but also the water vapor-derived OH - The presence of H also provides a source of H other than biomass for H2 production, which is beneficial to the increase of H2 production in the product, such as: OH - +CO+CO2+C→CO3 2- +3H2.

[0021] (2) The method provided by the present invention can convert the unreacted cellulose, hemicellulose and lignin in the straw hydrogen production residue that are not easily degraded by microorganisms into hydrogen / CO / methane and other products during the molten salt enhanced treatment process, thereby improving the comprehensive utilization rate of biomass.

[0022] (3) The method provided by the present invention can solve the problem that biomass fermentation hydrogen production cannot be directly used in conjunction with solid oxide fuel cells. Existing solid oxide fuel cells (SOFCs) have much lower fuel gas purity requirements than proton exchange membrane fuel cells (PEMFCs), making them more suitable for the utilization of biomass fermentation hydrogen and facilitating the development of distributed biomass dark fermentation hydrogen production systems in the field of building combined heat and power. However, SOFCs operate at relatively high temperatures (usually 600-1000 degrees Celsius), and the feed gas needs to be preheated to a certain temperature before entering the reaction system. Otherwise, the reaction kinetic efficiency may be significantly reduced. The hydrogen directly produced by dark fermentation hydrogen production from biomass has a low temperature, close to room temperature, and does not require preheating when used in PEMFCs, but requires deep purification, which increases the cost of hydrogen production. In the present invention, biological fermentation hydrogen production is coupled with a molten salt-enhanced secondary hydrogen production system. On the one hand, the secondary intensification of biomass conversion is achieved to improve the hydrogen yield; on the other hand, preheating is provided for the low-temperature raw gas so that it can be used in SOFC, saving the cost of the preheating system at the front end of the SOFC. As long as the molten salt system is properly insulated, the use of renewable green electricity is sufficient to maintain the system temperature stability and provide energy consumption for electrolysis. With the development of molten salt technology, its operating costs will also decrease.

[0023] (4) In addition to the deep utilization of biomass to produce hydrogen, the method provided by the present invention can simultaneously produce a variety of by-products. For example, biomass pyrolysis carbon can be used as activated carbon or capacitor carbon, and the molybdenum carbide / carbon composite material generated in the molten salt electrolysis reset can be used for electrochemical energy storage or other catalytic fields, thereby optimizing the economic properties of the process.

[0024] (5) The method provided by the present invention sets molten salts of the same composition in reactors a and b. After the molten salts in reactors a and b melt, the temperature of reactors a and b is simultaneously controlled to facilitate the flow of the molten liquid molten salt in reactors a and b. As the reaction proceeds, the molten salt in reactor a undergoes long-term pyrolysis and CO2 absorption, leaving impurities. After the catalytic hydrogen production effect of the molten salt in reactor a weakens, since the temperatures of reactors a and b are the same, the molten salt in reactor a can be quickly transferred to reactor b for electrolytic reforming and then returned to reactor a for continued use, thereby improving work efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a processing schematic diagram of the method of the present invention during the production process; Figure 2 is a schematic diagram of the cathode of the electrolytic treatment of the present invention; Figure 3 This is an analysis chart of the H2 production ratio in pyrolysis gas at different temperatures in Example 1 of the present invention; Figure 4 This is an analysis chart of the H2 production ratio in the molten salt of Example 1 of the present invention without adding sodium molybdate and with adding sodium molybdate. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. In the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] like Figure 1-4 As shown: The present invention provides an enhanced hydrogen production method using solid residues from dark fermentation of straw to produce hydrogen, which is suitable for coupling with a dark fermentation hydrogen production process of straw biomass. The specific steps include: like Figure 1 As shown: 1) Collect the solid residue after enzymatic saccharification of straw biomass or the solid residue remaining after direct anaerobic fermentation to produce hydrogen in the fermentation hydrogen production tank, wash it with water to remove water-soluble components, and then dry it for later use.

[0028] 2) Li2O, Li2CO3, Na2CO3, K2CO3, and Na2MoO4 are weighed in specific proportions in reactors a and b. The heating unit in reactor a heats the mixture to 930°C, melting it into a liquid molten salt. The molten salt system is then cooled to the desired reaction temperature, maintaining the same salt composition ratio in reactors a and b. The molar proportion of each salt component, Li2CO3, ranges from 20% to 50%; the combined molar proportion of Na2CO3 and K2CO3 is 30% to 60%, with the molar ratio of Na2CO3 to K2CO3 ranging from 1:1 to 2:1; the molar proportion of Na2MoO4 ranges from 2% to 6%; and the molar proportion of Li2O ranges from 1% to 5%. The reaction temperature is 500-700°C.

[0029] 3) Under Ar atmosphere, the mixed gas product from the dark fermentation reaction in the hydrogen production tank is introduced into reactor a. The gas should be introduced directly into reactor a to a depth of at least 2 cm below the molten salt surface, at a flow rate of approximately 0.1-1 L / min·kg salt. The aeration time should be 0.5-2.5 h.

[0030] 4) At the same time, in reactor a, the solid residue obtained in step 1) is wrapped in nickel foam or copper foam and quickly put into molten salt for a reaction time of 5-180 min. After the reaction is completed, the solid residue is taken out and washed with dilute acid to obtain a biomass pyrolysis carbon product.

[0031] During specific use, please note that steps 3) and 4) should not be performed at the same time, and should normally be performed alternately.

[0032] 5) The gas generated in steps 3) and 4) is collected by a low-temperature condensation device (i.e. Figure 1 The condenser) separates the pyrolysis product and hydrogen-rich gas product which are liquid at room temperature, and the separated hydrogen-rich gas product passes through the CaO packed tower (i.e. Figure 1 The drying tower) reduces the H2O and CO2 therein, and finally collects the hydrogen-rich gas product and analyzes its purity online (or in a short period of time).

[0033] In specific applications, if used in conjunction with a solid-state fuel cell, the collected hydrogen-rich gas product can be reintroduced into the gas heating pipe in reactor a for isolated heating, and after the gas is heated, it is immediately connected to the solid-state fuel cell reaction zone.

[0034] 6) When the H2 content in the collected gas is monitored to be lower than 70%, steps 3) and 4) need to be stopped, and the molten salt in reactor a is then pumped into reactor b for electrolysis. The electrolysis is performed at a constant cell pressure of 2.1-2.8V and for a time of 0.1-8h. The anode is a metal molybdenum rod or sheet, serving as a sacrificial anode; the cathode is a rotating disk or rotating cylindrical electrode (such as Figure 2 As shown), the cathode material is molybdenum or stainless steel; the rotation speed is 100-2000rpm.

[0035] 7) The molten salt obtained after the electrolysis in reactor b in step 6) can be transported back to reactor a to repeat steps 3) and 4).

[0036] 8) The molybdenum carbide / carbon composite solid product deposited on the cathode in reactor b (formed by co-deposition of molybdate and carbonate, and the lost molybdate ions are replenished by the sacrificial anode) is regularly recovered and the cathode surface can be reused after grinding and polishing.

[0037] Example 1 A corn straw biofermentation hydrogen production system uses pre-enzymatic saccharification followed by fermentation of the saccharified liquid for hydrogen production. The solid residue primarily comes from the residue from the corn straw enzymatic hydrolysis. Using the aforementioned method, a salt mixture was prepared in a molar ratio of Li2O: Li2CO3: Na2CO3: K2CO3: Na2MoO4 = 4:40:32:22:2, with a mass of 111g Li2O, 2739g Li2CO3, 3171g Na2CO3, 2837g K2CO3, and 381g Na2MoO4, for a total weight of approximately 9.24kg. The salt mixture was thoroughly mixed in a mechanical mixer under inert gas, then transferred to a reactor (a) of suitable capacity. The mixture was heated until the molten salt melted and then cooled to 530°C.

[0038] After the temperature stabilized, the gaseous products generated by the biofermentation hydrogen production system were introduced into the molten salt chamber of reactor a at a gas flow rate of approximately 0.3 L / min·kg salt x 9.24 kg = 2.77 L / min. After 30 minutes of complete absorption, the gas flow was stopped and the gas exiting reactor a was collected. 200 g of the washed and dried solid residue from the enzymatic hydrolysis of the straw was then wrapped in nickel foam and immersed in the molten salt chamber of reactor a for 20 minutes. The generated gas was condensed to remove the volatile liquid products and then collected using the same collection system as previously described, ultimately yielding hydrogen product with a purity exceeding 70%. After the molten salt immersion was completed, the nickel foam bag was removed to obtain the pyrolysis biomass carbon product.

[0039] The proportion of H₂ in the collected gas was dynamically analyzed. When the proportion fell below 70%, the reaction in reactor a was stopped, and the molten salt was pumped heat-insulated to reactor b. Constant-cell-pressure electrolysis was performed using a molybdenum sheet anode and a rotating disk molybdenum cathode. The minimum electrode spacing was 5 cm, the cathode speed was 800 rpm, the cell voltage was 2.6 V, and the electrolysis time was 200 minutes. At the end of the electrolysis, the molten salt in reactor b was returned to reactor a for further use, and the solid product on the molybdenum cathode was collected to obtain a molybdenum carbide / carbon composite product.

[0040] Example 2 A peanut straw biofermentation hydrogen production system uses direct crushing and alkaline treatment followed by microbial fermentation to produce hydrogen. The solid residue primarily consists of the residual residue from dark fermentation of the straw. A salt mixture is prepared in a molar ratio of Li2O: Li2CO3: Na2CO3: K2CO3: Na2MoO4 = 3:35:40:20:2, with a mass of 58g Li2O, 1671g Li2CO3, 2720g Na2CO3, 1777g K2CO3, and 264g Na2MoO4, for a total weight of approximately 6.51kg. The salt mixture is thoroughly mixed in a mechanical mixer under inert gas. The mixture is then transferred to a reactor of suitable capacity, heated until the molten salt melts, and then cooled to 640°C.

[0041] After the temperature stabilized, the gaseous products generated by the biofermentation hydrogen production system were introduced into the molten salt chamber of reactor a at a gas flow rate of approximately 0.2 L / min / kg salt x 6.51 kg ≈ 1.30 L / min. After 40 minutes of complete absorption, the gas flow was stopped and the gas exiting reactor a was collected. 150 g of the washed and dried solid residue from the straw fermentation hydrogen production process was then wrapped in nickel foam and immersed in the molten salt chamber of reactor a for 60 minutes. The generated gas was condensed to remove the volatile liquid products and then collected using the same collection system as previously described, ultimately yielding hydrogen product with a purity exceeding 70%. After the molten salt immersion was complete, the nickel foam bag was removed to obtain the pyrolyzed biomass carbon product.

[0042] The proportion of H₂ in the collected gas was dynamically analyzed. When the proportion fell below 70%, the reaction in reactor a was stopped, and the molten salt was pumped into reactor b while maintaining its heat. Constant-cell-pressure electrolysis was performed using a molybdenum rod anode and a rotating cylindrical stainless steel cathode. The minimum electrode spacing was 5 cm, the cathode speed was 600 rpm, the cell voltage was 2.4 V, and the electrolysis time was 300 minutes. At the end of the electrolysis, the molten salt in reactor b was returned to reactor a for further use, and the solid product on the stainless steel cathode was collected to obtain a molybdenum carbide / carbon composite product.

[0043] Example 3 A rice straw bio-fermentation hydrogen production system uses direct crushing and steam explosion treatment followed by microbial dark fermentation to produce hydrogen. The solid residue is mainly the remaining residue after the dark fermentation of straw. The proportion of the substance is Li2O:Li2CO 3: Prepare a salt mixture using a ratio of Na2CO3: K2CO3: Na2MoO4 (4:45:27:21:3) consisting of 97g Li2O, 2712g Li2CO3, 2308g Na2CO3, 2409g K2CO3, and 505g Na2MoO4, for a total weight of approximately 8.03kg. Thoroughly mix the salt mixture in a mechanical mixer under inert gas. Transfer the mixture to a reactor of suitable capacity, heat until the molten salt melts, and then cool to 700°C.

[0044] After the temperature stabilized, the gaseous products generated by the biofermentation hydrogen production system were introduced into the molten salt chamber of reactor a at a gas flow rate of approximately 0.1 L / min / kg salt x 8.03 kg ≈ 0.8 L / min. After 15 minutes of complete absorption, the gas flow was stopped and the gas exiting reactor a was collected. 300 g of the washed and dried solid residue from the straw fermentation hydrogen production process was then wrapped in copper foam and immersed in the molten salt chamber of reactor a for 90 minutes. The generated gas was condensed to remove the volatile liquid products and then collected using the same collection system as previously described, ultimately yielding hydrogen product with a purity exceeding 70%. After the molten salt immersion was complete, the copper foam was removed to obtain the pyrolyzed biomass carbon product.

[0045] The proportion of H₂ in the collected gas was dynamically analyzed. When the proportion fell below 70%, the reaction in reactor a was stopped, and the molten salt was pumped heat-insulated to reactor b. Constant-cell-pressure electrolysis was performed using a molybdenum rod anode and a rotating cylindrical molybdenum cathode. The minimum electrode spacing was 5 cm, the cathode speed was 900 rpm, the cell voltage was 2.8 V, and the electrolysis time was 120 minutes. At the end of the electrolysis, the molten salt in reactor b was returned to reactor a for further use, and the solid product on the molybdenum cathode was collected to obtain a molybdenum carbide / carbon composite product.

[0046] The corn straw enzymatic hydrolysis residue was pyrolyzed in the molten salt system described in Example 1. The H2 yield in the pyrolysis gas at different temperatures was as follows: Figure 3 As shown, the volume percentage of H2 is significantly higher than that of the other gas products. Within the temperature range described in this invention, the H2 product in the pyrolysis gas accounts for at least 65%, and when mixed with the purified fermentation gas, the H2 proportion exceeds 70%.

[0047] like Figure 4 As shown, the mixed salt system described in Example 1 was prepared in the ratio of Li2O: Li2CO3: Na2CO3: K2CO3: Na2MoO4 = 4:40:32:22:2, with no sodium molybdate added in system (A) and a sufficient amount added in system (B). Pyrolysis of corn straw residues was performed at 550°C. The addition of molybdate significantly increased the relative H2 yield compared to the absence of molybdate, demonstrating that the molten salt system described in this invention significantly enhances secondary hydrogen production from the pyrolysis of solid residues from bio-fermentation hydrogen production.

[0048] In summary, the method provided by the present invention utilizes the properties of molten salt, such as good thermal stability, high thermal conductivity and low vapor pressure, to introduce molten salt into the treatment process of solid residue from straw fermentation to produce hydrogen. This method can not only accelerate the depolymerization of lignin and hemicellulose in the residue under relatively mild conditions and convert unused organic matter into synthesis gas, but also increase the relative content of hydrogen in the gas product with the help of the catalytic effect of certain active ions in the molten salt (such as alkali metal ions, OH-, molybdate ions, etc.).

[0049] The invention develops a molten salt-enhanced straw fermentation hydrogen production solid residue treatment and secondary hydrogen production technology, which is not only a key path to break through the bottleneck of traditional hydrogen production technology, but also an important support for promoting the high-value utilization of agricultural waste and achieving the "dual carbon" goals. It has strategic significance for building a green energy system.

[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for enhancing hydrogen production using solid residues from dark fermentation of straw, characterized in that: The following steps are involved: Step 1) collecting the solid residue remaining after hydrogen production by the straw fermentation hydrogen production system, washing the solid residue with water to remove the water-soluble components in the solid residue, and drying it for later use; Step 2) Molten salts of the same composition are placed in reactors a and b. At a specified reaction temperature and under an inert gas atmosphere, the gaseous products produced by the straw fermentation hydrogen production system are passed into the molten salt in reactor a to purify the H2; Step 3) After the H2 purification in step 2) is completed, the solid residue obtained in step 1) is wrapped in nickel foam or copper foam and then added to the molten salt in reactor a for reaction. The reaction gas products are mainly H2, CO and methane. After the reaction is completed, the solid residue is removed and washed with dilute acid to obtain a biomass pyrolysis carbon product; In step 4), the gaseous product produced in step 2) and the hydrogen-rich combustible gas produced in step 3) are introduced into a low-temperature condensation collection device to separate the liquid pyrolysis product and the hydrogen-rich gas product, and the hydrogen-rich gas product is dehydrated and carbon dioxide is captured, and finally the hydrogen-rich gas product is collected.

2. The method for enhancing hydrogen production by utilizing solid residues from dark fermentation of straw for hydrogen production according to claim 1, characterized in that: The molten salt is obtained by adding a mixture containing Li2O, Li2CO3, Na2CO3, K2CO3 and Na2MoO4 into reactor a and reactor b respectively, and heating to 930°C to melt the mixture into a liquid state.

3. The method for enhancing hydrogen production by using solid residues from dark fermentation of straw for hydrogen production according to claim 2, characterized in that: The molar proportion of Li2CO3 in the mixture is 20%-50%; the total molar proportion of Na2CO3 and K2CO3 is 30%-60%, the molar proportion of Na2MoO4 is 2%-6%; the molar proportion of Li2O is 1%-5%; and the molar ratio of Na2CO3 to K2CO3 is 1:1-2:

1.

4. The method for enhancing hydrogen production by utilizing solid residues from dark fermentation of straw for hydrogen production according to claim 1, characterized in that: The gas product gas produced by the straw fermentation hydrogen production system in step 2) is introduced into the reactor a at a depth of not less than 2 cm below the molten salt liquid level, and the gas flow rate is about 0.1-1 L / min·kg salt; the ventilation time is 0.5-2.5 h; the inert gas is Ar.

5. The method for enhancing hydrogen production by utilizing solid residues from dark fermentation of straw for hydrogen production according to claim 1, characterized in that: The reaction time of the solid residue in step 3) in the molten salt in reactor a is 5-180 min.

6. The method for enhancing hydrogen production by utilizing solid residues from dark fermentation of straw for hydrogen production according to claim 1, characterized in that: The specified reaction temperature is 500-700°C.

7. The method for enhancing hydrogen production by utilizing solid residues from dark fermentation of straw for hydrogen production according to claim 1, characterized in that: The method further includes step 5) online monitoring of the H2 content in the collected hydrogen-rich gas product. When the H2 content in the gas product is detected to be lower than 70%, steps 2) and 3) are stopped, the molten salt in reactor a is extracted into reactor b for electrolysis, and the molten salt obtained after the electrolysis in reactor b is refluxed into reactor a for reuse.

8. The method for enhancing hydrogen production by utilizing solid residues from dark fermentation of straw for hydrogen production according to claim 7, characterized in that: The electrolysis treatment adopts constant cell pressure electrolysis, the cell pressure is 2.1-2.8V, and the electrolysis time is 0.1-8h; the anode of the electrolysis treatment is a metal molybdenum rod or molybdenum sheet; the cathode is a rotating disk or rotating cylindrical electrode, and the cathode material is molybdenum or stainless steel; the rotation speed is 100-2000rpm.

9. The method for enhancing hydrogen production by utilizing solid residues from dark fermentation of straw for hydrogen production according to claim 8, characterized in that: The molybdenum carbide and carbon composite solid product deposited on the cathode of the electrolytic treatment are regularly recovered, and the cathode surface is polished and reused.

10. The method for enhancing hydrogen production by utilizing solid residues from dark fermentation of straw for hydrogen production according to claim 1, characterized in that: The hydrogen-rich gas product collected in step 4) is introduced into reactor a again for heating, and then the heated gas product is connected to the solid-state fuel cell reaction zone for use.

Images