CN108584871B

CN108584871B - Process and system for recovering carbon nano-material and hydrogen from urban organic waste

Info

Publication number: CN108584871B
Application number: CN201810440084.9A
Authority: CN
Inventors: 黎晟; 周吕
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-05-08
Filing date: 2018-05-08
Publication date: 2022-03-25
Anticipated expiration: 2038-05-08
Also published as: CN108584871A

Abstract

The invention discloses a process for recovering carbon nano-materials and hydrogen from urban organic waste, which comprises anaerobic fermentation and catalytic cracking. The invention also discloses a system for recovering the carbon nano-material and the hydrogen from the urban organic waste. The process for recovering carbon nano-materials and hydrogen from urban organic waste effectively combines the anaerobic fermentation technology and the methane catalytic cracking technology for the first time, biological methane generated by anaerobic fermentation of urban waste is adopted, and because the urban waste treatment is a paid behavior, the cost of catalytic cracking can be greatly reduced by using an additional product (biological methane) of the waste treatment, and a low-price raw material is provided for methane catalytic cracking.

Description

Process and system for recovering carbon nano-material and hydrogen from urban organic waste

Technical Field

The invention relates to a process and a system for preparing carbon nano-materials and hydrogen, in particular to a process and a system for recovering the carbon nano-materials and the hydrogen from urban organic waste.

Background

The currently common methane hydrogen production process comprises the following steps: methane steam reforming and partial oxidation method for producing hydrogen.

The raw material for preparing hydrogen by reforming methane steam is natural gas. Catalytic reforming of methane to produce hydrogen is economically feasible, with greater than 90% of the hydrogen produced in the united states via steam reforming of methane. The hydrogen production by methane steam reforming comprises the following steps: methane steam reforming, water gas replacement reaction and hydrogen purification. The reaction for steam reforming of methane is:

CH₄+H₂O→3H₂+CO

the optimum reaction conditions are high temperature of 700 ℃ and 850 ℃ and pressure of 0.3-2.5 MPa. The reaction is endothermic and requires external input of heat, which is partly supplied by the feed gas (less than 25%) or the waste gas (purge gas in a hydrogen purification system). The synthesis gas after methane steam reforming is conveyed to 1 or more water-gas replacement reactors of the next stage, and the yield of hydrogen is greatly increased through water-gas replacement:

CO+H₂O→H₂+CO₂

the composition of the gas in the metathesis reactor was hydrogen (70-80%), carbon dioxide, methane and small amounts of water vapor and carbon monoxide. The final step is hydrogen purification, and the purity of the hydrogen depends on the application.

Partial oxidation hydrogen production is another method for producing hydrogen from hydrocarbons, where methane or other hydrocarbon feedstocks (e.g., waste oil) are partially oxidized to produce carbon monoxide and hydrogen.

2CH₄+O₂→4H₂+CO

As previously mentioned, the advantages of catalytic cracking of methane to produce hydrogen are: can avoid CO while obtaining renewable energy₂The generation of the carbon dioxide has great benefits for the natural environment. However, at present, the process is still in the research and development stage, and an industrialized methane catalytic cracking hydrogen production line cannot be formed.

The research on methane catalytic cracking mostly focuses on nickel-based and iron-based catalysts. As shown in table 1, nickel-based catalysts generally produce greater amounts of hydrogen gas than iron-based catalysts, while also requiring lower catalytic temperatures than iron-based catalysts.

TABLE 1 relationship between catalyst type, reaction conditions and Hydrogen gas yield

Kind of catalyst	Reaction temperature (. degree.C.)	Hydrogen yield (mol/g)_cat.)
			Fe/Al₂O₃	675	4.4
Fe/SiO ₂	800	2.3
			Fe/Al₂O₃	700	0.6
Ni	500	66
			Ni/SiO ₂	500	32
Ni-Fe-Al	650	92

While nickel-based catalysts crack more hydrogen than iron-based catalysts, the latter can greatly improve the economic viability and environmental friendliness of the process. The unit price of nickel is 10000 dollars per ton, so that the nickel-based catalyst causes high cost for catalytic cracking of the whole methane and is difficult to produce on a large scale. In the process of preparing hydrogen by catalytic cracking of methane, along with the generation of hydrogen, high-value carbon nano materials are also formed in the process and are attached to the surface of a catalyst. Thus, the solids produced in catalytic cracking are typically a mixture of carbon nanomaterials and solid metal catalysts. As has been described in the foregoing, the present invention,the nickel-based catalyst is expensive, so the carbon nano-material is usually required to be separated from the nickel-based catalyst, and the nickel-based catalyst can be recycled. The carbon nano material separation technology relates to a combustion process, on one hand, the operation cost of a system is further increased, and on the other hand, CO generated by combustion₂Also there is an adverse reduction of CO₂The initial purpose of emission.

The existing hydrogen production process is realized by purchasing natural gas as a raw material, so the cost for purchasing the natural gas can be a large part of the production cost. The biological methane produced by anaerobic fermentation fails to reach the field of catalytic cracking researchers for the following reasons:

(1) the methane catalytic cracking is a new technology, and chemical engineering personnel specialized in catalytic cracking research are not very aware of the research on methane production by anaerobic fermentation process in the field of environmental engineering, and the availability of biological methane is not clear;

(2) the anaerobic fermentation process needs to be operated at 35-40 ℃, so that the anaerobic fermentation process has high energy consumption requirement, and the biological methane generated by the general anaerobic fermentation is combusted in situ to meet the energy requirement of the anaerobic fermentation process and cannot be used for catalytic cracking.

(3) Different anaerobic fermenters generate different methane contents, the anaerobic fermenters optimized for the growth environment of methanogens can generate biogas with the methane content of 90%, and the methane content of the unoptimized fermenters is only 30%. Therefore, in order to realize the application of the anaerobic fermentation and catalytic cracking composite process, a stable methanogen community needs to be cultured in an anaerobic fermentor, and researchers engaged in catalytic cracking may have insufficient knowledge storage in the aspects of anaerobic fermentation, flora culture and the like.

(4) The biogas generated by anaerobic fermentation not only contains methane, but also contains CO₂If the gas is directly sent into the catalytic cracker without purification, the production of the carbon nano material is not influenced, but high-purity hydrogen cannot be produced at the same time, and the aim of hydrogen production is difficult to realize.

Anaerobic fermentation refers to the stabilization of waste by the metabolic activity of microorganisms under anaerobic conditions,with simultaneous methane and CO₂The resulting change. Anaerobic fermentation comprises three stages: liquefying, producing acid and methane. The liquefaction stage mainly takes effect of zymocyte, including cellulose decomposition bacteria and protein hydrolysis bacteria, and is mainly responsible for degrading macromolecular organic matters in the waste to be treated into micromolecular substances. The acidogenic stage is mainly acted by acetic acid bacteria, and the methanogenic stage is mainly methane bacteria which degrade the products generated in the acidogenic stage into methane and CO₂Simultaneously utilizes hydrogen generated in the acid production stage to convert CO into CO₂Reducing to methane. Factors influencing anaerobic fermentation are: the raw material proportion is that the carbon-nitrogen ratio of anaerobic fermentation is preferably 20-30, and the gas production is obviously reduced when the carbon-nitrogen ratio is 35; the temperature is preferably 35-40 ℃; the pH value is absolutely necessary for methanogenic bacteria to maintain a weak alkali environment, the optimal pH value is 6.8-7.5, the pH value is low, and the pH value makes CO₂Greatly increased amount of water-soluble organic matter and H₂S generation, the increase of sulfide content inhibits the growth of methane bacteria, lime can be added to adjust the pH, but the best method for adjusting the pH is to adjust the carbon-nitrogen ratio of the raw material, because the alkalinity used for neutralizing acid in the substrate is mainly ammonia nitrogen, the higher the nitrogen content of the substrate, the higher the alkalinity, when VFA (volatile fatty acid)>At 3000 hours, the reaction was stopped.

Although both methane and hydrogen are renewable energy sources, the combustion of methane produces CO₂The greenhouse effect of the earth is intensified, and the moisture generated by the combustion of the hydrogen has no influence on the natural environment. The methane catalytic cracking technology is to promote methane to be cracked into pure hydrogen and high-value carbon nano-materials under the high-temperature condition by using a metal catalyst. In recent years, the preparation of hydrogen through a methane catalytic cracking technology is widely concerned and researched worldwide, but at present, the process is still in the research and development stage, and an industrialized production line for synchronously producing hydrogen and carbon nano-materials through methane catalytic cracking cannot be formed.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide a process and a system for recovering carbon nano-materials and hydrogen from urban organic waste.

In order to achieve the purpose, the invention adopts the technical scheme that: a process for recovering carbon nano-materials and hydrogen from urban organic waste comprises the following steps:

(1) and anaerobic fermentation: carrying out anaerobic fermentation on municipal sludge, organic solid garbage, sewage and organic waste liquid to obtain biological methane and fermented sludge;

(2) and catalytic cracking: and (2) carrying out catalytic cracking reaction on the biomethane obtained in the step (1) to obtain hydrogen and a carbon nano material.

The sewage and the organic wastewater are preferably concentrated high-concentration organic wastewater.

The invention adopts an anaerobic fermentation mode to treat municipal sludge, organic solid garbage, sewage and organic waste liquid, and can realize the production of biological methane by utilizing floras such as hydrolytic bacteria, acetic acid bacteria, methanogen and the like cultured in a fermentation tank under the anaerobic condition. The biological methane is subjected to catalytic cracking under certain conditions to produce pure hydrogen and carbon nano materials. The hydrogen generated by the catalytic cracking system is collected for hydrogen energy enterprises, and the carbon nano material can be used as a water deep purification material and also can be used as a carbon raw material for manufacturing lithium batteries and super capacitors.

The invention converts municipal sewage, sludge and organic solid waste garbage into high-purity biological energy hydrogen and carbon nano-materials by adopting the anaerobic fermentation and methane catalytic cracking composite process, and converts the municipal organic waste into new energy and new materials with high added values at low price. The invention uses the biological methane of the anaerobic fermentation system to replace natural gas as the raw material for methane catalytic cracking, thereby reducing the cost of methane cracking.

As a preferred embodiment of the process for recovering the carbon nano-material and the hydrogen from the municipal organic waste, the process further comprises a step (1a) before the step (1): concentration of sewage and organic waste liquid: taking sewage and organic waste liquid as low-salt solution, and carrying out forward osmosis concentration treatment on the low-salt solution and high-salt solution.

The concentration method of the sewage and the organic wastewater of the invention is preferably a forward osmosis concentration treatment method. The forward osmosis membrane (FO) is a membrane that concentrates low-concentration sewage by utilizing the principle that water molecules in low-salt-concentration sewage at one end of the membrane naturally diffuse into a high-salt-concentration solution at the other end of the membrane. The forward osmosis membrane unit adopts a forward osmosis membrane to separate high salinity solution and low salinity municipal sewage. Because the forward osmosis membrane is a compact membrane, only water molecules are allowed to pass through, and salt molecules cannot pass through, the water molecules in the low-salinity sewage can be diffused into the high-salinity solution to dilute the high-salinity solution, and when the high-salinity solution is diluted to a certain degree, the salt difference of the solutions on the two sides of the membrane reaches balance, and the diffusion of the water molecules stops. In the invention, inorganic fertilizer is used as high-salt solution to concentrate low-salt urban sewage. After being treated by the forward osmosis membrane system, the urban sewage and the organic waste liquid with lower organic pollutant content can be concentrated, the sewage volume entering the anaerobic fermentation system is reduced, the organic matter concentration is improved, and the biological methane productivity of the anaerobic fermentation system is improved. The municipal sludge and the organic solid garbage can directly enter an anaerobic fermentation system for biological methane production.

As a preferred embodiment of the process for recovering carbon nanomaterials and hydrogen from municipal organic wastes according to the present invention, in the step (1a), the high-salt solution is an inorganic fertilizer, and the concentration of the inorganic fertilizer is 1mol/l or more.

As the low-concentration sewage water molecules enter the high-salt solution in the forward osmosis process, the high-concentration fertilizer solution of the forward osmosis membrane system is diluted, and the forward osmosis membrane system can be used for greenhouse soilless culture irrigation.

As a preferred embodiment of the process for recovering carbon nanomaterial and hydrogen from municipal organic waste according to the invention, in step (1a), when the volume of low-concentration wastewater is 25% of the volume of wastewater entering the forward osmosis membrane unit, the operation of the forward osmosis membrane unit is stopped, and high-concentration wastewater is delivered to an anaerobic fermentation system for biomethane production.

After the forward osmosis is repeated for three times, the high-salt solution (inorganic fertilizer) can be used for irrigating crops due to the corresponding dilution.

As a preferred embodiment of the process for recovering carbon nano-materials and hydrogen from municipal organic waste, the process further comprises a step (2a) after the step (1) and before the step (2): biological methane purification: purifying the biomethane produced in the step (1).

As a preferred embodiment of the process for recovering carbon nanomaterials and hydrogen from municipal organic wastes according to the present invention, in the step (2a), the method for purifying methane comprises: and (3) passing the methane gas generated in the step (2) through a sodium hydroxide solution to obtain purified methane. The purified methane is beneficial to the efficiency of subsequent catalytic cracking and the quality of the carbon material. The sodium hydroxide solution is mainly used for absorbing carbon dioxide in the biomethane.

As a preferable embodiment of the process for recovering the carbon nano-materials and the hydrogen from the urban organic waste, the concentration of the sodium hydroxide solution is 0.5-2 mol/L.

As a preferred embodiment of the process for recovering carbon nanomaterial and hydrogen from municipal organic waste according to the present invention, the fermented sludge is used for soil improvement.

After anaerobic fermentation, the municipal organic waste is converted into biological methane, and simultaneously, a small amount of excess sludge is generated. The excess sludge is stabilized after anaerobic treatment, does not contain harmful substances such as pathogenic bacteria and the like, but contains considerable elements such as nitrogen, phosphorus and the like, so the excess sludge can be used for soil improvement after being subjected to plate filtration, compression and dehydration, and the waste recycling is realized.

As a preferred embodiment of the process for recovering carbon nanomaterials and hydrogen from municipal organic wastes according to the present invention, in the step (2), the catalyst for catalytic cracking is an iron-based catalyst having a particle size of 50 μm or less.

The iron-based catalyst is iron oxide loaded by a porous material, wherein the porous material can be inorganic porous materials such as alumina, silicon dioxide, molecular sieves, activated carbon and the like. The invention uses biological methane of an anaerobic fermentation system to replace natural gas as a raw material for catalytic cracking of methane; meanwhile, the invention uses cheap iron-based catalyst (the price of the iron-based catalyst is about $ 80/ton, and the price of the nickel-based catalyst is up to $ 10000/ton), and the cost of methane catalytic cracking is reduced simultaneously. Because the iron-based catalyst is low in price, the mixture of the carbon nano material and the catalyst after the cracking reaction can be integrally taken out, and the carbon nano material and the catalyst are directly recycled without separation treatment. The nickel-based catalyst adopted in the research is expensive, so that the methane catalytic cracking cannot enter the industrialization stage, the iron-based catalyst adopted by the invention is low in price, the problem of catalyst recovery is not considered, and the cost of methane catalytic cracking is greatly reduced. The iron-based catalyst with the particle size of less than or equal to 50 microns is beneficial to the contact of the catalyst and methane, the catalytic efficiency is high, the carbon nano tube can be prepared, and the carbon nano tube is difficult to prepare by the iron-based catalyst with larger particle size. As a preferable embodiment of the process for recovering carbon nano-materials and hydrogen from urban organic waste, the iron oxide accounts for 10-80% of the weight of the iron-based catalyst.

As a preferred embodiment of the process for recovering carbon nanomaterials and hydrogen from municipal organic wastes according to the present invention, in the step (2), the catalytic cracking reaction conditions are as follows: the pressure is 1-10 atm, the temperature is 500-1000 ℃, and the time is 8-12 h.

As a more preferable embodiment of the process for recovering the carbon nano-material and the hydrogen from the urban organic waste, the temperature of the catalytic cracking reaction is 700-800 ℃. And (2) carrying out catalytic cracking reaction for 8-12 hours at the temperature in combination with 1-10 atmospheric pressure, so as to selectively prepare the multi-walled carbon nanotube, wherein the diameter of the inner wall of the multi-walled carbon nanotube ranges from 20 nm to 100 nm.

As a preferred embodiment of the process for recovering carbon nanomaterial and hydrogen from municipal organic waste according to the present invention, the temperature of the catalytic cracking reaction is 750 ℃.

As a preferable embodiment of the process for recovering the carbon nano-materials and the hydrogen from the urban organic waste, in the step (2), the flow rate of the biomethane is 1.8-1.9L/h/gCat. L/h/gCat is the liter/hr/g of iron-based catalyst (i.e., gas space velocity of methane through the catalyst layer: GHSV).

As a preferred embodiment of the process for recovering the carbon nano-material and the hydrogen from the urban organic waste, the waste heat in the catalytic cracking reaction process in the step (2) is used for maintaining the anaerobic fermentation condition in the step (1) at 35-40 ℃ by water.

The common anaerobic fermentation system adopts in-situ combustion of methane to heat the fermentation reactor, consumes methane with great potential value and causes a great deal of CO₂And the invention transmits the extra heat generated by the preheater and the reaction furnace in the catalytic cracking device to the continuous stirring reactor for anaerobic fermentation by a water bath heat transmission mode, thereby fully utilizing the waste heat generated by catalytic cracking and reducing the energy requirement of anaerobic fermentation.

The invention also aims to provide a system for recovering carbon nano-materials and hydrogen from urban organic waste, which comprises an anaerobic fermentation system and a catalytic cracking device; and the gas outlet of the anaerobic fermentation system is connected with the gas inlet of the catalytic cracking device. As a preferred embodiment of the system for recovering carbon nanomaterial and hydrogen from municipal organic waste according to the invention, the system further comprises a forward osmosis unit; and a liquid outlet of the forward osmosis unit is connected with an anaerobic fermentation system.

As a preferred embodiment of the system for recovering carbon nanomaterial and hydrogen from municipal organic waste according to the invention, the system further comprises a biomethane purification apparatus; and a gas outlet of the anaerobic fermentation system is connected with a gas inlet of the biological methane purification device, and a gas outlet of the biological methane purification device is connected with a gas inlet of the catalytic cracking device.

As a preferred embodiment of the system for recovering carbon nanomaterials and hydrogen from municipal organic wastes according to the present invention, a methane storage tank and a pressure raising device are disposed between the gas outlet of the methane purification apparatus and the gas inlet of the catalytic cracking apparatus.

The methane gas storage tank is made of 304 stainless steel, the seal of the methane gas storage tank is sealed by a DN219 metal chuck, and the operating pressure is 0.2 Mpa. And the methane gas storage tank is provided with a pressure gauge, a pressure release valve, an emptying valve and an air compressor, so that the pressure boosting operation of methane gas can be realized.

As a preferred embodiment of the system for recovering carbon nanomaterial and hydrogen from municipal organic waste according to the present invention, the catalytic cracking unit comprises a preheater, a reactor, a hydrogen collecting unit, and a reactor; the catalytic cracking device is characterized in that an air inlet of the catalytic cracking device is connected with a preheater, the preheater is connected with a reactor, the reaction furnace is used for maintaining the temperature in the reactor, the reactor is connected with a hydrogen collecting device, and a catalyst is arranged in the reactor.

The invention has the beneficial effects that: the invention provides a process for recovering carbon nano-materials and hydrogen from urban organic waste, which effectively combines an anaerobic fermentation technology and a methane catalytic cracking technology for the first time, adopts biological methane generated by anaerobic fermentation of urban waste, and uses an additional product (biological methane) of the waste treatment to greatly reduce the cost of catalytic cracking because the urban waste treatment is a paid behavior, thereby providing a low-price raw material for methane catalytic cracking.

The invention also provides a system for recovering the carbon nano-materials and the hydrogen from the urban organic waste.

Drawings

FIG. 1 is a schematic diagram of the process flow for recovering carbon nanomaterials and hydrogen from municipal organic waste according to example 1;

FIG. 2a is a graph of the effect of temperature on methane conversion efficiency at a gas space velocity per hour (GHSV) of 0.8 liters/hr/g iron-based catalyst, a methane gas supply of 100 ml/min, and 5 atmospheres pressure;

figure 2b is a graph of the effect of gas space velocity (GHSV) on methane conversion efficiency at 100 ml/min methane gas supply at 750 ℃ at 5 atmospheres during the initial phase of methane conversion (first 30 minutes).

Fig. 3 is a TEM image of carbon nanomaterials produced by the process for recovering carbon nanomaterials and hydrogen from municipal organic waste described in example 1, wherein: the magnification of fig. 3a is 3 ten thousand times; the magnification of fig. 3b is 80 ten thousand times; the magnification of fig. 3c is 3 ten thousand times; FIG. 3d is a magnification of 3 ten thousand; the magnification of fig. 3e is 3 ten thousand times.

FIG. 4 is a comparison of the effects of the carbon nanomaterial, high-quality powdered activated carbon, and wastewater to be treated in (a) total organic carbon, (b) chromophoric humic acid removal, produced by the process for recovering carbon nanomaterial and hydrogen from municipal organic waste described in example 1;

FIG. 5 is a comparison of the removal rates of caffeine, atenolol (drug residue), pamidone and atrazine (herbicide) by Carbon Nanomaterials (CNOs) prepared by the process for recovering carbon nanomaterials and hydrogen from urban organic waste described in example 1 and high-quality Powdered Activated Carbon (PACs);

FIG. 6 is a schematic representation of the forward osmosis membrane unit of example 2;

FIG. 7 is a schematic diagram showing the structures of an anaerobic fermentation system, a biological methane-extracting apparatus and a methane-storing tank according to example 2;

FIG. 8 is a schematic view of a methane storage tank pressurization system;

FIG. 9 is a schematic view showing the construction of a catalytic cracking unit according to example 2;

FIG. 10 is a heat recovery device;

wherein, 1, an anaerobic fermentation system; 2. a biological methane purification device; 3. a methane storage tank; 4. an excess methane combustion system; 5. a catalytic cracking unit; 501. a preheater; 502. a reactor; 503. a reaction furnace; 504. an iron-based catalyst.

Detailed Description

To better illustrate the objects, aspects and advantages of the present invention, the present invention will be further described with reference to specific examples.

Example 1

In an embodiment of the process for recovering carbon nanomaterials and hydrogen from municipal organic wastes, the process for recovering carbon nanomaterials and hydrogen from municipal organic wastes comprises the following steps:

(1) and concentrating sewage and organic waste liquid: taking sewage and organic waste liquid as low-salt solution, taking chemical fertilizer as high-salt solution, and performing forward osmosis concentration treatment to obtain high-concentration organic waste liquid;

(2) and anaerobic fermentation: carrying out anaerobic fermentation on the sludge, the organic solid garbage and the high-concentration organic waste liquid obtained in the step (1) to obtain biological methane and fermented sludge;

(3) and biological methane purification: purifying the biomethane produced in the step (2) to obtain purified biomethane;

(4) and catalytic cracking: and (4) carrying out catalytic cracking reaction on the purified biomethane in the step (3) under the catalytic action of an iron-based catalyst to obtain hydrogen and a carbon nano material.

In the step (1), the diluted fertilizer solution is used for agricultural fertilization. In the step (2), the fermented sludge is stabilized after anaerobic treatment, does not contain harmful substances such as pathogenic bacteria and the like, but contains considerable elements such as nitrogen, phosphorus and the like, and the sludge is subjected to plate filtration, compression and dehydration and is used for soil improvement. In the step (3), the method for purifying the biological methane comprises the following steps: and (3) passing the biomethane gas generated in the step (2) through 0.5-2mol/L sodium hydroxide solution to obtain purified biomethane. In the step (4), the carbon nano material is used for efficient advanced treatment of drinking water and prevention and control of membrane filtration pollution (as shown in figures 4 and 5). In the step (4), the residual heat in the catalytic cracking reaction process is subjected to heat exchange through a water medium, so that the anaerobic fermentation condition in the step (2) is maintained at 35-40 ℃.

In the step (1), because no external pressure requirement exists, the energy consumption for treating each ton of sewage is about 0.8 yuan/ton in terms of the area of a forward osmosis membrane of 1 square meter; in the step (2), the process can treat 0.72 ton of sewage per square meter of forward osmosis membrane per day, and 1 cubic anaerobic fermentation tank can treat 0.17 ton of sludge per day (or 0.034 ton of organic garbage per day +0.136 cubic concentrated sewage) in terms of 6 days of residence time, and the methane yield of the anaerobic fermentation tank reaches 11.56 cubic/day. In the step (4), the process can produce 1.6 cubic hydrogen and 0.5 kilogram carbon nano material per 1 cubic methane gas under the conditions of methane gas supply of 100 ml/min, 5 atmospheric pressures and 850 ℃.

Figure 2a is a graph of the effect of temperature on methane conversion efficiency at a gas space velocity per hour (GHSV) of 0.8 liters/hour/gram iron-based catalyst, a methane gas supply of 100 ml/minute, and 5 atmospheres pressure. The determination of the preferred temperature must be evaluated under conditions where the methane gas is in sufficient contact with the catalyst, otherwise, because a large amount of methane which is not in sufficient contact with the catalyst for reaction leaves the reaction furnace in advance, the influence of different temperatures on the methane conversion rate cannot be reflected, and the influence of the temperature on the methane conversion rate is underestimated. The use of the iron-based catalyst of 0.8 l/hr/g was employed in the search for the preferable reaction temperature in the present example, because it was found from the past experimental experience that the gas space velocity (GHSV) for achieving sufficient contact between methane and the catalyst could be ensured. In addition, because the pressure in the cracking process can compress the reaction gas, the yield of the carbon nano-material and hydrogen generated by single batch methane conversion can be improved, the pressure in the cracking process is preferably 10 atmospheres (the reaction requires 1-10 atmospheres) from the yield point of view, but the energy consumption of the reaction is increased due to the excessively high pressure requirement, so the reaction yield and the energy consumption are considered comprehensively, and the working pressure of 5 atmospheres is selected as the pressure when the preferable temperature is researched. It can be seen from fig. 2a that as the temperature increases, the theoretical conversion efficiency of methane at equilibrium increases; in addition, when the temperature reaches 750 ℃ or more, methane can be converted under the action of the iron-based catalyst under the ideal equilibrium state of the reaction. Thus, at a GHSV of 0.8L/hr/g iron-based catalyst, a methane gas supply of 100 ml/min, 5 atmospheres, the desired reaction temperature is 750 ℃.

Figure 2b is a graph of the effect of gas space velocity (GHSV) on methane conversion efficiency at 750 ℃ at 5 atmospheres, 100 ml/min methane gas supply, at the initial stage of methane conversion (first 30 minutes). As can be seen from fig. 2b, the methane conversion efficiency decreases when the gas space velocity exceeds 2 l/h/g iron based catalyst. Therefore, in consideration of both the methane conversion efficiency and the conversion rate, an iron-based catalyst of 1.8 to 1.9 l/hr/g is a preferred GHSV.

All carbon materials were prepared under the same conditions (5 atm, 100 ml/min methane gas supply, 850 ℃, reaction time 9 hours) in FIG. 3, in which FIGS. 3a and 3b are different magnification graphs of the same batch of carbon materials, and FIGS. 3c, 3d, and 3e are carbon materials prepared from different batches, respectively. As can be seen from FIG. 3, the carbon material produced by the reaction is in the nanometer level, the size is between 20 and 100nm, and the part is in the shape of a tube.

FIG. 4 is a comparison of the effect of the carbon nanomaterial and high quality powdered activated carbon produced by the process for recovering carbon nanomaterial and hydrogen from municipal organic waste described in example 1 on the removal of (a) total organic carbon and (b) chromophoric humic acid from the wastewater to be treated. As can be seen from fig. 4a, the carbon nanomaterial produced by the process described in example 1 can remove 25% more total organic carbon than the fine powder activated carbon; as can be seen from FIG. 4b, the carbon nanomaterial produced by the process described in example 1 is better than high-quality powdered activated carbon in removing chromogenic humic acid (the effluent after treatment is nearly transparent) (the chromaticity of the effluent after treatment is improved compared with that of the raw water, but the effluent is still brownish yellow).

Fig. 5 is a comparison of the removal rate effects of Carbon Nanomaterials (CNOs) prepared by the process for recovering carbon nanomaterials and hydrogen from urban organic waste and high-quality Powdered Activated Carbon (PACs) on micropollutants such as caffeine, atenolol (drug residue), pamicone and atrazine (herbicide). As can be seen from the results of fig. 5, the carbon nanomaterial prepared by the present example has a slightly different and even better micro-contaminant removal rate than that of the high-quality powdered activated carbon.

As can be seen from fig. 3 to 5, the carbon nanomaterial obtained in the process for recovering carbon nanomaterial and hydrogen from urban organic waste in the embodiment is a high-quality carbon nanomaterial.

From the process for recovering carbon nano-materials and hydrogen from the whole urban organic waste in the embodiment 1, the process flow is to perform forward osmosis membrane sewage concentration process, generate methane through anaerobic fermentation, and catalytically crack the methane by using an iron-based catalyst to obtain carbon materials and hydrogen, so that the urban organic waste is treated at low cost, high-quality carbon nano-materials and hydrogen are also recovered, and a new direction is provided for the treatment of organic waste in future cities.

Example 2

One embodiment of the system for recovering carbon nanomaterials and hydrogen from municipal organic wastes comprises a forward osmosis membrane unit, an anaerobic fermentation system, a biological methane purification device and a catalytic cracking device; the liquid outlet of the forward osmosis membrane unit is connected with an anaerobic fermentation system, the gas outlet of the anaerobic fermentation system is connected with the gas inlet of the biological methane purification device, and the gas outlet of the biological methane purification device is connected with the gas inlet of the catalytic cracking device.

The schematic structural diagram of the forward osmosis membrane unit in this embodiment is shown in fig. 6, and the forward osmosis membrane unit uses a forward osmosis membrane to separate a high-salt fertilizer solution from low-salt low-concentration sewage. The driving force for a forward osmosis membrane is the difference in salt concentration between the solutions on either side of the membrane, and in the presence of a salt concentration difference, the solutions on either side will diffuse freely to achieve a concentration equilibrium with each other. The forward osmosis membrane is a compact membrane, only water molecules are allowed to pass through, and salt molecules cannot pass through, so that when the forward osmosis membrane is used for treatment, the water molecules in the low-salinity sewage can be diffused into the high-salt solution and dilute the high-salt solution, and when the high-salt solution is diluted to a certain degree, the salt difference of the solutions on the two sides of the membrane reaches balance, and then the diffusion of the water molecules is stopped. The forward osmosis membrane unit adopts a sequencing batch treatment mode: circulating low-salt low-concentration sewage and high-salt fertilizer solution with fixed volumes at the speed of 8.5cm/S at two sides of a forward osmosis membrane respectively, stopping the operation of the forward osmosis membrane unit when the volume of the low-salt sewage is reduced to 25% of the original volume after water molecules in the low-salt sewage enter high-salt solution through the forward osmosis membrane, and transferring the concentrated high-concentration sewage to an anaerobic fermentation system for anaerobic fermentation; then injecting low-concentration sewage with the same initial volume and low salt into the forward osmosis membrane unit, and restarting a new round of concentration treatment. After 3 batches of low-salt sewage are concentrated, the high-salt solution is diluted and transferred to a soilless culture greenhouse for crop irrigation.

As shown in fig. 7, the sludge, organic solid waste and high concentration sewage are fed into an anaerobic fermentation system 1, wherein the anaerobic fermentation system 1 is a continuous stirred reactor (CSTR) in this embodiment, and the device is equipped with an on-line monitoring device for dissolved oxygen, ph value, redox degree, etc., so as to realize the overall process control of the device and maintain the optimal anaerobic fermentation environment under the condition of full automatic control. Biogas generated from the continuous stirred reactor is collected from the top of the reactor and transferred to a biomethane purification apparatus 2 filled with a sodium hydroxide solution having a concentration of 1mol/L, and carbon dioxide generated during anaerobic fermentation is removed, thereby purifying biomethane. The biomethane purified by the sodium hydroxide solution is stored in a methane storage tank 3. When the methane stored in the methane storage tank 3 is excessive, the redundant methane can jack the air pressure valve at the upper part of the tank body and enter the excess methane combustion system 4, so that the condition of excess methane gas storage cannot occur.

As shown in fig. 8, the biomethane stored in the methane storage tank is pressurized by a pneumatic pump and then sent to a catalytic cracking device for catalytic cracking, as shown in fig. 9, the catalytic cracking device 5 of the embodiment includes a preheater 501, a reactor 502, a hydrogen collecting device (not shown in the figure) and a reactor 503; the air inlet of the catalytic cracking unit is connected with a preheater 501, the preheater 501 is connected with a reactor 502, the reactor 503 is used for maintaining the temperature in the reactor 502, the reactor 502 is connected with a hydrogen collecting device, and an iron-based catalyst 504 is arranged in the reactor 502. In the catalytic cracking process of the biomethane, the purified biomethane enters a reactor 502 filled with an iron-based catalyst 504 through a preheater 501 at a constant flow rate and is cracked for 8-12 hours under the conditions of 1-10 atmospheric pressure and 500-1000 ℃ of temperature. Hydrogen generated in the reaction is collected in a hydrogen collecting device 503 at the top of the reactor 502 and is conveyed to a storage device, and the collected hydrogen is sampled to be detected by gas chromatography; and the cracked carbon nanomaterial is taken out from the bottom of the reactor 502.

The progress of catalytic cracking reaction is known by detecting the hydrogen content of the gas produced by the reactor 502, if the hydrogen component is reduced, the iron-based catalyst in the reactor gradually loses activity, the catalyst needs to be replaced, and at the moment, the iron-based catalyst and the carbon nano material mixture in the reactor are taken out and can be used as the carbon nano material for efficient advanced treatment of drinking water, prevention and control of membrane filtration pollution and the like.

In this embodiment, heat is transferred through the heat recovery device shown in fig. 10, specifically: the extra heat generated by the preheater 502 and the reaction furnace 503 in the catalytic cracking device is transmitted to the fermentation tank, so that the waste heat generated by catalytic cracking is fully utilized, and the energy requirement of anaerobic fermentation is reduced.

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the protection scope of the present invention, and although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A process for recovering carbon nano-materials and hydrogen from urban organic waste is characterized by comprising the following steps:

(2) and catalytic cracking: carrying out catalytic cracking reaction on the biomethane obtained in the step (1) to obtain hydrogen and a carbon nano material;

the method also comprises a step (2a) after the step (1) and before the step (2): biological methane purification: purifying the biomethane produced in the step (1);

the step (1) is also preceded by a step (1 a): concentration of sewage and organic waste liquid: taking sewage and organic waste liquid as low-salt solution, and carrying out forward osmosis concentration treatment on the sewage and the organic waste liquid and high-salt solution; the high salt solution is an inorganic fertilizer with the concentration of more than or equal to 1 mol/L;

in the step (2), the catalyst for catalytic cracking is an iron-based catalyst with the particle size of less than or equal to 50 microns; the reaction conditions of catalytic cracking are as follows: 1-10 atm, 750 deg.C, 8-12 h.

2. A system for recovering carbon nano-materials and hydrogen from urban organic waste is characterized by comprising an anaerobic fermentation system and a catalytic cracking device; the gas outlet of the anaerobic fermentation system is connected with the gas inlet of the catalytic cracking device;

the catalytic cracking device comprises a preheater, a reactor, a hydrogen collecting device and a reaction furnace; the catalytic cracking device is characterized in that an air inlet of the catalytic cracking device is connected with a preheater, the preheater is connected with a reactor, the reaction furnace is used for maintaining the temperature in the reactor, the reactor is connected with a hydrogen collecting device, and a catalyst is arranged in the reactor;

the system further comprises a forward osmosis unit; a liquid outlet of the forward osmosis unit is connected with an anaerobic fermentation system;

the system further comprises a biomethane purification unit; and a gas outlet of the anaerobic fermentation system is connected with a gas inlet of the biological methane purification device, and a gas outlet of the biological methane purification device is connected with a gas inlet of the catalytic cracking device.