Method for promoting efficient cracking of sludge to produce aliphatic hydrocarbon by eliminating negative effect of ferric iron through melanin-like compound

Abstract

The invention discloses a method for promoting efficient cracking of sludge to produce aliphatic hydrocarbon by eliminating the negative effect of ferric iron through melanin-like substances, and belongs to the field of organic solid waste energy recovery. In order to solve the problems of low iron-rich sludge cracking efficiency and insufficient aliphatic hydrocarbon resource recovery, the negative effect of ferric iron is eliminated through melanin-like substances, the catalytic performance of derived carbon is promoted, cracking of macromolecular organic matters such as sludge protein, carbohydrate and fat is accelerated, C-C bond breakage and recombination are caused, C-H bond breakage is inhibited, and the purpose of recycling aliphatic hydrocarbon resources is achieved. And finally, the aliphatic hydrocarbon yield is improved. And the highest aliphatic hydrocarbon yield is obtained under the DS dosage of 2.5 mg / g, and is increased by 44.1%. The method effectively solves the problem of iron negative effects caused by direct pyrolysis of traditional iron-rich sludge, obtains the optimal addition proportion, realizes efficient preparation of aliphatic hydrocarbon resources of the sludge pyrolysis system, overcomes the engineering bottleneck problems of low sludge pyrolysis efficiency and insufficient aliphatic hydrocarbon resource recovery, and has the advantages of high efficiency, high efficiency and low energy consumption. And a new strategy is provided for organic solid waste efficient treatment and value-added resource recovery.

Description

Technical Field

[0001] The present invention relates to the technical field of organic solid waste energy recovery, and particularly relates to a method for eliminating the negative effect of ferric iron by using melanoidin to promote the efficient pyrolysis of sludge to produce aliphatic hydrocarbons. Background Technique

[0002] As an emerging technology for the efficient conversion of the organic components of sludge into energy-intensive gases, pyrolysis technology heats organic matter to a high temperature under anoxic conditions to achieve the pyrolytic conversion of organic components, generating gas (methane, hydrogen, ethylene, etc.), liquid (pyrolysis oil) and solid (biochar) products with high energy density, and can achieve the efficient conversion of organic matter within a few hours. However, pyrolysis is a complex thermochemical interaction reaction involving multiple components, and the generated gas components are complex, mainly including C1–C4 gas components, such as CH 4 , H 2 , CO 2 , CO, C 2 H 4 etc. Among these gas components, aliphatic hydrocarbon fuels have the advantages of extensive industrial and energy applications, convenient storage and transportation, reduction of greenhouse gas emissions, and mature application technologies and equipment. As a fuel, its chemical structure is similar to that of traditional petroleum products, and it can be compatible with existing infrastructure (such as internal combustion engines, gas turbines, etc.), and can be used for large-scale substitution in a short time; aliphatic hydrocarbon fuels are liquid at normal temperature and pressure, and can be stored, transported and distributed as conveniently as traditional petroleum products; the combustion of aliphatic hydrocarbons produces lower carbon dioxide emissions than traditional fossil fuels. If biomass or waste is converted into aliphatic hydrocarbon fuels through pyrolysis technology, it can even achieve the goal of carbon neutrality or even negative carbon. Therefore, optimizing and improving the yield of aliphatic hydrocarbons through pyrolysis technology has great practical significance for solving the global energy crisis and environmental problems, and is more conducive to realizing the recycling of resources and promoting the construction of a circular economy system.

[0003] Although pyrolysis technology has high energy recovery efficiency, in actual operation, changes in reaction conditions during pyrolysis, the occurrence of redox reactions, and different catalysts often restrict the efficient production of aliphatic hydrocarbons. Some studies have shown that adding melanoidin substances during sludge pyrolysis can significantly promote the cleavage and recombination reactions of C-C bonds and the cleavage of C-H bonds in macromolecular organic substances such as sludge proteins, carbohydrates, and fats, while inhibiting the aromatization reaction of hydrocarbon substances (especially olefins and some small-molecule hydrocarbons) to transform into aromatic hydrocarbons, thereby inducing the conversion of pyrolysis gas to hydrogen and reducing the production of aliphatic hydrocarbons. However, some studies have also shown that melanoidin has extremely similar structures and properties to humus and can bind to metal ions (such as ferric ions) to produce a synergistic effect. This synergistic effect will lead to the generation of more free radicals, and the generation of these free radicals will promote the cleavage of C-C bonds and inhibit the cleavage of C-H bonds, which also means that more pyrolysis gas will be converted into aliphatic hydrocarbons. Therefore, using ferric ions to combine with melanoidin and co-pyrolyze with sludge is a feasible strategy to achieve the conversion of pyrolysis gas to aliphatic hydrocarbons, providing a new research direction for the resource utilization of sludge. Summary of the Invention

[0004] The present invention aims to solve the engineering bottleneck problems of low sludge cracking efficiency and insufficient recovery of aliphatic hydrocarbon resources, and further proposes a method for using melanoidin to eliminate the negative effects of ferric ions and promote the efficient cracking of sludge to produce aliphatic hydrocarbons, providing a new strategy for the efficient treatment of organic solid waste and the recovery of value-added resources.

[0005] The technical solution adopted by the present invention to solve the above problems is as follows:

[0006] The method for using melanoidin to eliminate the negative effects of ferric ions and promote the efficient cracking of sludge to produce aliphatic hydrocarbons according to the present invention includes the following steps:

[0007] Step 1, sludge pretreatment:

[0008] Collect the sludge, sieve the sludge and let it stand for 24 hours. After the mud-water separation interface appears, discard the supernatant to obtain concentrated sludge;

[0009] The concentration process is as follows: Pass the original sludge through a 20-mesh sieve to remove large-particle inorganic substances and impurities, and let it stand in a refrigerator at 4°C for 24 hours to obtain concentrated sludge.

[0010] Step 2, preparation of demineralized sludge sample:

[0011] Centrifuge the concentrated sludge to obtain a solid-phase product, dry and grind the solid-phase product to obtain sludge powder;

[0012] The centrifugation process is as follows: Centrifuge at 10000 rpm for 5-10 minutes; the drying temperature of the solid-phase product is 105°C, and the drying time is 24 hours.

[0013] Remove the minerals in the sludge powder by pickling method to obtain demineralized sludge powder;

[0014] The pickling treatment specifically includes the following steps:

[0015] Step 2.1: Immerse the sludge sample in 10% hydrochloric acid solution and stir for 30 min to remove the metal oxide components;

[0016] Step 2.2: Place the sludge sample treated with hydrochloric acid and rinsed clean in 10% hydrofluoric acid solution, soak and stir for 30 min to further remove silicate and other insoluble minerals in the sludge;

[0017] Step 2.3: Rinse the sludge sample with deionized water multiple times to remove the acid solution, and centrifuge the pickled sludge sample at 10000 rpm for 1 min;

[0018] Step 2.4: Dry the solid-phase product in a vacuum drying oven at 50 °C for 48 hours and grind it to obtain a demineralized sludge powder sample as a pyrolysis test sample.

[0019] Step 3: Preparation of melanoidin-like substances:

[0020] Dissolve glucose and tryptophan in phosphate buffer solution, react under high temperature and high pressure conditions, filter the liquid-phase product through a filter membrane, and after dialysis and freeze-drying, obtain a melanoidin-like sample, which specifically includes the following steps:

[0021] Step 3.1: Dissolve glucose and tryptophan in a phosphate buffer solution with a concentration of 50 mM and pH = 7.0 to form a mixed solution, and the concentrations of glucose and tryptophan are both 50 mM;

[0022] Step 3.2: Place the mixed solution (60 mL) obtained in Step 3.1 in a polytetrafluoroethylene-lined autoclave at 170 °C. The working volume of the autoclave is 100 mL, and the reaction time is 8 hours.

[0023] Step 3.3: After the reaction, filter the liquid-phase product with a 0.22 μm microporous filter membrane to remove impurities;

[0024] Step 3.4: Perform dialysis treatment on the filtered product to remove small organic molecules with a molecular weight below 500 Da;

[0025] Step 3.5: Freeze-dry the dialyzed solution in a freeze dryer for 48 hours to obtain melanoidin-like powder.

[0026] Step 4: Co-pyrolysis of demineralized sludge, melanoidin-like substances and ferric iron:

[0027] Mix the ferric oxide powder and the melanoid obtained in step 3 with the demineralized sludge powder obtained in step 2 in a mass ratio of 20:1:200 to 40:1:400 and mix them evenly, and carry out pyrolysis treatment through a pyrolysis reactor. Purge the pyrolysis chamber with nitrogen at a flow rate of 100 mL / min for 10 min. Then, take a certain amount of sludge powder samples and pyrolyze them at 500 °C and 700 °C respectively at a nitrogen flow rate of 20 mL / min and a heating rate of 20 °C / min for 20 min. Finally, the solid residue is biochar, and the tar is collected with CH 2 Cl 2 solution, and the gas is collected through a gas collection bag.

[0028] The beneficial effects of the present invention are as follows:

[0029] 1. The present invention proposes a method and application for using melanoid to eliminate the negative effects of trivalent iron and promote the efficient pyrolysis of sludge to produce aliphatic hydrocarbons, effectively solving the problems of low volatile cracking activity and insufficient recovery efficiency of aliphatic hydrocarbon products in the direct pyrolysis of traditional iron-rich sludge, and proposing a method for using melanoid to eliminate the negative effects of iron components and further strengthen the efficient recovery of aliphatic hydrocarbons by sludge pyrolysis.

[0030] 2. The present invention realizes the efficient preparation of aliphatic hydrocarbon resources in the sludge pyrolysis system. Through the combination of melanoid and trivalent iron, the catalytic performance of the derived carbon is promoted, the cracking of macromolecular organic substances such as sludge proteins, carbohydrates, and fats is accelerated, the cleavage and recombination of C-C bonds are caused, and the cleavage of C-H bonds is inhibited, ultimately increasing the yield of aliphatic hydrocarbons.

[0031] 3. In the experimental groups of 2.5 mg / g DS and 5 mg / g DS (DS is dry solid) of the melanoid of the present invention, the gas production of aliphatic hydrocarbons increased significantly, with a maximum increase of 44.1%, obtaining the optimal dosing ratio, realizing the efficient preparation of aliphatic hydrocarbon resources in the sludge pyrolysis system, overcoming the engineering bottleneck problems of low sludge pyrolysis efficiency and insufficient recovery of aliphatic hydrocarbon resources, and providing a new strategy for the efficient treatment of organic solid waste and the recovery of value-added resources. Description of the Drawings

[0032] Figure 1 It is a schematic diagram of the synergistic pyrolysis gas production of the melanoid, trivalent iron and demineralized sludge of the present invention. Examples

[0033] Melanin-like substances, iron(III) oxide powder, and demineralized sludge powder were mixed evenly in different mass ratios as the experimental groups. Among them, the melanin-like concentration was 2.5 mg / g DS and 5 mg / g DS, the iron(III) oxide powder concentration was 0.1 g / g DS, and the demineralized sludge and the mixture of iron(III) oxide powder and demineralized sludge were used as the control groups respectively. Pyrolysis treatment was carried out in a pyrolysis reactor. The pyrolysis chamber was purged with nitrogen at a flow rate of 100 mL / min for 10 min. Then, 1 g of the experimental sample was pyrolyzed at 500 °C for 20 min with a nitrogen flow rate of 20 mL / min and a heating rate of 20 °C / min. Finally, the solid residue was biochar, the tar was collected with CH 2 Cl 2 solution, and the gas was collected through a gas collection bag.

[0034] From Figure 1 the results shown, it was found that the yield of aliphatic hydrocarbon gas accounted for the highest proportion in the pyrolysis mixed gas. The yield of aliphatic hydrocarbons increased by up to 44.1% at the dosages of 2.5 mg / g DS and 5 mg / g DS of melanin-like substances. Further analysis of the gas component distribution showed that the yields of CH 4 , C 2 H 4 , and C 2 H 6 increased by 40.8%, 79.8%, and 28.3% respectively. This result was attributed to the bond cleavage and cyclization of aliphatic compounds. It was shown that melanin-like substances and trivalent iron synergistically promoted the cracking of macromolecular organic substances such as sludge proteins, carbohydrates, and fats, resulting in the cleavage and recombination of C-C bonds and the inhibition of C-H bond cleavage, ultimately promoting the production of aliphatic hydrocarbons.

[0035] The present invention effectively solves the problems of low volatile cracking activity and insufficient recovery efficiency of aliphatic hydrocarbon products in the direct pyrolysis of traditional iron-rich sludge, and proposes a method for using melanin-like substances to eliminate the negative impact of iron components and further strengthen the efficient recovery of aliphatic hydrocarbons from sludge pyrolysis, overcoming the engineering bottleneck problems of low sludge pyrolysis efficiency and insufficient recovery of aliphatic hydrocarbon resources, and providing a new strategy for the efficient treatment of organic solid waste and the recovery of value-added resources.

[0036] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or equivalent changes and modifications within the scope of the technical solution of the present invention. However, as long as it does not depart from the technical solution content of the present invention and is based on the technical essence of the present invention, any simple modification, equivalent replacement, and improvement of the above embodiments are still within the protection scope of the technical solution of the present invention.

Claims

1. A method for utilizing melanin to eliminate the negative effects of ferric iron and promote efficient cracking of sludge to produce aliphatic hydrocarbons, characterized in that: The method comprises the following steps: Step 1: Sludge pretreatment: Collect the sludge, sieve the sludge and let it stand for 24 hours. After the mud-water separation interface appears, discard the supernatant to obtain concentrated sludge; Step 2: Demineralized sludge sample preparation: The concentrated sludge is centrifuged to obtain a solid phase product, and the solid phase product is dried and ground to obtain sludge powder; minerals in the sludge powder are removed by an acid washing method to obtain demineralized sludge powder; Step 3, preparation of melanin-like substance: Glucose and tryptophan are dissolved in a phosphate buffer, reacted under high temperature and high pressure conditions, and the liquid product is filtered through a filter membrane, dialyzed, and freeze-dried to obtain a melanin sample; Step 4: Co-pyrolysis of demineralized sludge, melanin-like substances and trivalent iron: The ferric oxide powder, the melanin obtained in step 3, and the demineralized sludge powder obtained in step 2 are uniformly mixed according to a mass ratio, and pyrolysis is carried out in a pyrolysis reactor. The solid residue obtained after pyrolysis is biochar, and the tar obtained after pyrolysis is collected with a CH2Cl2 solution in an ice water bath. The gas obtained after pyrolysis is collected through a gas collecting bag.

2. The method of using melanin to eliminate the negative effects of ferric iron and promote efficient sludge cracking to produce aliphatic hydrocarbons according to claim 1, characterized in that: In step 1, the concentration process is as follows: the original sludge is sieved with a 20-mesh screen to remove large particles of inorganic matter and impurities, and is allowed to stand at 4° C. for 24 hours to obtain concentrated sludge.

3. The method of using melanin to eliminate the negative effects of ferric iron and promote efficient sludge cracking to produce aliphatic hydrocarbons according to claim 1, characterized in that: In step 2, the centrifugation process is: centrifugation at 10000 rpm for 5-10 min; the solid phase product drying temperature is 105° C., and the drying time is 24 hours.

4. The method of using melanin to eliminate the negative effects of ferric iron and promote efficient sludge cracking to produce aliphatic hydrocarbons according to claim 1, characterized in that: In step 2, the pickling treatment specifically includes the following steps: Step 2.1, soak the sludge sample in 10% hydrochloric acid solution and stir for 30 minutes to remove the metal oxide components; Step 2.2, soaking the sludge sample treated with hydrochloric acid and rinsed clean in a 10% hydrofluoric acid solution and stirring for 30 minutes to further remove silicates and other insoluble minerals in the sludge; Step 2.3, rinse the sludge sample with deionized water several times to remove the acid solution, and centrifuge the acid-washed sludge at 10,000 rpm for 1 min; Step 2.4: Dry the solid product in a vacuum drying oven at 50° C. for 48 hours, and grind it to obtain a demineralized sludge powder sample as a pyrolysis test sample.

5. The method of using melanin to eliminate the negative effects of ferric iron and promote efficient sludge cracking to produce aliphatic hydrocarbons according to claim 1, characterized in that: Step 3 specifically includes the following steps: Step 3.1, dissolving glucose and tryptophan in a phosphate buffer with a concentration of 50 mM and a pH of 7.0 to form a mixed solution, wherein the concentrations of glucose and tryptophan are both 50 mM; Step 3.2, placing the mixed solution obtained in step 3.1 in a polytetrafluoroethylene-lined autoclave, the reaction conditions are 170° C., and the reaction time is 8 hours; Step 3.3: After the reaction is completed, the liquid product is filtered using a 0.22 μm microporous filter membrane to remove impurities; Step 3.4, dialyzing the filtered product to remove small organic molecules below 500 Da; Step 3.5: freeze-dry the dialyzed solution in a freeze dryer for 48 hours to obtain melanin powder.

6. The method of claim 1 for utilizing melanin to eliminate the negative effects of ferric iron and promote efficient sludge cracking to produce aliphatic hydrocarbons, characterized in that: In step 4, the pyrolysis process is as follows: nitrogen is purged in the pyrolysis chamber at a flow rate of 100 mL / min for 10 min; a certain amount of sludge powder sample is taken and pyrolyzed at 500°C and 700°C for 20 min at a nitrogen flow rate of 20 mL / min and a heating rate of 20°C / min.

7. The method of claim 1 for utilizing melanin to eliminate the negative effects of ferric iron and promote efficient sludge cracking to produce aliphatic hydrocarbons, characterized in that: In step 4, the mass ratio of ferric oxide powder, melanin and demineralized sludge powder is 20:1:200 to 40:1:

400.

8. The method of using melanin to eliminate the negative effects of ferric iron and promote efficient sludge cracking to produce aliphatic hydrocarbons according to claim 1 or 7, characterized in that: In step 4, the optimal dose of melanoidin is 2.5 mg / g DS-5 mg / g DS.

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