Method for promoting sludge catalytic cracking and reforming to efficiently produce hydrogen by using sludge pyrohydrolysis byproduct melanin

Abstract

The invention discloses a method for promoting sludge catalytic cracking and reforming to efficiently produce hydrogen by using sludge pyrohydrolysis byproduct melanin, and belongs to the field of organic solid waste energy recovery. Aiming at the problems that melanin in a high-temperature pyrohydrolysis-pyrolysis process inhibits sludge decomposition, pyrolysis gas components are complex and H2 directional regeneration is difficult, the byproduct melanin in the high-temperature pyrohydrolysis process is extracted and is used for enhancing the pyrolysis gas production efficiency of the pyrohydrolysis sludge. The sludge is subjected to low-temperature pyrohydrolysis treatment, the surface is loose, and the organic matter devolatilization degree is enhanced, so that solid-phase pyrolysis gas production of the pyrohydrolysis sludge is promoted. Furthermore, the melanin-like compound shows excellent reaction catalytic activity due to carboxyl and a nitrogen-containing structure, the optimal effect is achieved when the concentration is 2.5 mg / g DW, the total gas production rate is increased by 6.54%, the melanin-like compound induces pyrohydrolysis sludge cracking mixed gas to generate methane catalytic cracking CH4-> C + 2H2 and catalytic reforming CH4 + CO2-> 2CO + 2H2 reactions, and the hydrogen yield is increased by 35.92% at most. The method effectively solves the engineering bottleneck problems of melanin-like negative effects in the thermal hydrolysis-pyrolysis field and low green energy recovery rate.

Description

Technical Field

[0001] The present invention relates to the technical field of organic solid waste energy recovery, and particularly to a method for promoting high-efficient hydrogen production from catalytic cracking and reforming of sludge by using melanoidins, a by-product of sludge hydrothermal hydrolysis. Background Art

[0002] Pyrolysis is recognized as an emerging technology for the efficient conversion of organic components in sludge into energy-intensive gases (methane, hydrogen). Through the gradient heating mechanism, the efficient conversion of organic matter can be achieved within a few hours. Compared with the traditional anaerobic digestion technology, it has significant advantages of low carbon and rapidity. At the same time, as a pretreatment technology, hydrothermal hydrolysis induces the lysis of the cell wall of sludge through high temperature and high pressure (50–260 °C, 0.6–6 Mpa), promoting the collapse of the internal structure of sludge and the loosening of the surface. The sludge solid-phase resource disposal technology based on the coupling of hydrothermal hydrolysis and pyrolysis will further promote the volatilization of sludge solid-phase volatiles and accelerate the pyrolysis reaction of volatiles, thereby significantly improving the potential of pyrolysis gas production. However, pyrolysis is a complex thermochemical interaction reaction involving multiple components, and the gas components produced are complex, mainly including C1–C4 gas components such as CH 4 、H 2 、CO 2 、CO、C 2 H 4 etc. Among many gas components, H 2 is a zero-carbon, clean and renewable energy source with a high energy yield (142.35 kJ / g), and its energy yield can reach 2.75 times that of other hydrocarbons. Therefore, how to direct the conversion and regeneration of pyrolysis gas into H 2 is of great significance for solving the large-scale production of global green hydrogen.

[0003] Although hydrothermal hydrolysis is considered a promising technology for the efficient conversion of sludge resources by stimulating the release of organic matter inside and outside the cells. However, under high-temperature hydrothermal hydrolysis conditions, the Maillard reaction occurs in hydrothermal hydrolysis. First, the amino group of protein and the carbonyl group of sugar undergo a heterocyclic reaction to form a colorless intermediate, and the intermediate undergoes a series of reactions such as cyclization and condensation to generate refractory by-products melanoidins. Melanoidins have been proven to significantly reduce the degree of devolatilization of sludge organic matter and hinder the degradation of flocs and the conversion of organic matter. Based on the hydrothermal hydrolysis treatment technology coupled with the addition of alkali and photocatalysis, the negative effect of melanoidins has been effectively reduced. Summary of the Invention

[0004] In order to solve the problems of drug residues in the hydrothermal hydrolysis treatment technology coupled with the addition of alkali and photocatalysis for sludge hydrothermal hydrolysis, as well as the complex composition of pyrolysis gas and the difficult directional regeneration of H 2 , in order to achieve the efficient conversion of sludge organic matter and the recovery of green energy, the present invention further provides a method for promoting high-efficient hydrogen production from catalytic cracking and reforming of sludge by using melanoidins, a by-product of sludge hydrothermal hydrolysis.

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

[0006] The method for promoting the efficient hydrogen production of sludge catalytic cracking and reforming by using melanoidins in the by-products of sludge hydrothermal hydrolysis of the present invention includes the following steps:

[0007] Step 1: Collect the sludge. Pass the original sludge through a 20-mesh sieve to remove large particle impurities, and let it stand at 4°C for 24 hours. After obvious stratification appears at the mud-water interface, slowly pour off the supernatant to obtain concentrated sludge.

[0008] Step 2: Perform low-temperature hydrothermal hydrolysis treatment on the concentrated sludge, and then centrifuge to obtain a solid-phase product. Freeze-dry and grind the solid-phase product to obtain sludge powder; perform high-temperature hydrothermal hydrolysis treatment on the concentrated sludge, and then centrifuge to obtain the hydrothermal hydrolysis sludge supernatant;

[0009] The process of the low-temperature hydrothermal hydrolysis treatment is as follows: the low-temperature hydrothermal hydrolysis temperature is 90°C - 100°C, the pressure is 70×10 3 Pa - 150×10 3 Pa, and the reaction time is 1 hour;

[0010] The process of the high-temperature hydrothermal hydrolysis treatment is as follows: the high-temperature hydrothermal hydrolysis temperature is 160°C - 180°C, the pressure is 550×10 3 Pa - 885×10 3 Pa, and the reaction time is 1 hour;

[0011] The process of the centrifugation is to centrifuge at 10000 rpm for 10 minutes;

[0012] The temperature of freeze-drying the solid-phase product is -55°C, and the time is 24 hours;

[0013] Step 3: Extract melanoidins:

[0014] 3.1. Filter the sludge supernatant obtained by the high-temperature hydrothermal hydrolysis treatment in Step 2, and then mix the hydrothermal hydrolysis sludge supernatant with macroporous adsorption resin in a 500 mL flask for adsorption; the macroporous adsorption resin is Amberlite XAD761 ion-exchange macroporous adsorption resin;

[0015] The mass ratio of the macroporous adsorption resin to the volume of the hydrothermal hydrolysis sludge supernatant is 20 g:100 mL; filter through a 0.45 μm filter;

[0016] 3.2. After the adsorption is completed, separate the macroporous adsorption resin and the hydrothermal hydrolysis sludge supernatant, and then replace the new macroporous adsorption resin to adsorb the hydrothermal hydrolysis sludge supernatant twice;

[0017] The adsorption process described in Steps 3.1 and 3.2 is as follows: oscillate at 150 rpm and 25 °C for 12 hours;

[0018] 3.3. Collect the macroporous adsorption resin after adsorption and perform desorption to obtain a melanoid solution;

[0019] The desorption process is as follows: First, wash the adsorbed macroporous adsorption resin with deionized water; then, take hydrochloric acid as the solvent and accurately prepare 75% acidified ethanol; the hydrochloric acid content is 36.0 - 38.0% w / %, the ethanol content ≥ 99.7 w / %, measure 25 mL of hydrochloric acid and 75 mL of ethanol and mix them evenly;

[0020] Finally, add the macroporous adsorption resin to 75% acidified ethanol and oscillate at 150 rpm and 25 °C for 24 hours;

[0021] 3.4. Concentrate the obtained melanoid solution and freeze-dry it in a freeze dryer for 48 hours to obtain melanoid powder; the concentration uses a rotary evaporation process, and the concentration temperature is 80 °C;

[0022] Step 4. Co-pyrolysis of hot water-hydrolyzed sludge and melanoid for hydrogen production:

[0023] Mix the sludge powder obtained by low-temperature hot water hydrolysis in Step 2 and the melanoid obtained in Step 3 evenly, and then perform pyrolysis in a pyrolysis reactor; the solid residue obtained after pyrolysis is biochar, and the tar obtained after pyrolysis is collected with CH 2 Cl 2 solution, and the gas obtained after pyrolysis is collected with a gas collection bag;

[0024] Furthermore, purge the pyrolysis chamber with nitrogen at a flow rate of 150 mL / min for 10 min. Then, take a certain amount of sludge powder sample and pyrolyze it at 500 °C and 700 °C 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, the tar is collected with CH 2 Cl 2 solution in an ice-water bath, and the gas is collected with a gas collection bag.

[0025] The beneficial effects of the present invention are as follows:

[0026] 1. The present invention first proposes to extract the melanoid, a by-product of sludge hot water hydrolysis, and use the melanoid to catalyze the pyrolysis of hot water-hydrolyzed sludge for hydrogen production. Compared with the existing technologies of adding alkali and photocatalysis to eliminate the negative effects of melanoid, it not only has significant advantages in terms of process cost, but importantly, it is an innovation to reuse the by-product of hot water hydrolysis to promote hydrogen production.

[0027] 2. The present invention makes full use of the carboxyl group and nitrogen-containing structure of melanoidin to exhibit excellent catalytic performance, which can enhance the pyrolysis efficiency of hydrolyzed sludge and combine with the endogenous metals in the hydrolyzed sludge to promote the catalytic performance of the derived carbon. The redox ability of melanoidin catalyzes the cracking and reforming of the pyrolysis mixed gas, thereby inducing the conversion of the pyrolysis gas to hydrogen. Finally, the hydrogen production is increased.

[0028] 3. The present invention proposes a strategy for producing hydrogen by inducing the catalytic cracking and reforming of the pyrolysis mixed gas by melanoidin and finally enhancing the pyrolysis efficiency of hydrolyzed sludge: After the sludge powder treated by low-temperature hydrothermal hydrolysis has a loose surface and a collapsed internal structure, the degree of organic matter devolatilization is enhanced; further, due to the carboxyl group and nitrogen-containing structure, melanoidin exhibits excellent reaction catalytic activity, promoting the volatilization and cracking of the volatiles to produce gas; finally, melanoidin induces the pyrolysis mixed gas to undergo catalytic cracking (CH 4 catalytic cracking (CH 4 →C + 2H 2 )) and catalytic reforming (CH 4 + CO 2 →2CO + 2H 2 )) reactions, resulting in a decrease in the yields of CH 4 and CO 2 , thereby achieving an increase in the H 2 yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a diagram of the types and yields of gas produced by the co-pyrolysis of melanoidin and hydrolyzed sludge in Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] Example 1 Melanoidin and the sludge powder obtained under the hydrothermal hydrolysis intensity of 90°C for 60 min were mixed evenly at different mass ratios as the experimental groups. Among them, the melanoidin concentrations were 2.5 mg / g DW (DW refers to the dry basis of the sludge) and 5 mg / g DW, and they were respectively named the 90-2.5 group and the 90-5 group. The unhydrolyzed sludge (group 0) and the hydrolyzed sludge at 90°C for 60 min (group 90) were used as the control groups respectively. Pyrolysis treatment was carried out through a fixed-bed 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 700°C for 20 min at 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 in an ice-water bath, and the gas was collected through a gas collection bag.

[0031] From Figure 1It can be found that the total gas production of the hydrothermally hydrolyzed sludge and the experimental group with 2.5 mg / g DW increased significantly, and the total gas production increased by up to 6.54%. Further analysis of the gas component distribution showed that the production rate of CH 4 and CO 2 decreased, while the production rate of H 2 increased by up to 35.92%. This result is attributed to the catalytic cracking of CH 4 (CH 4 →C + 2H 2 ) and the catalytic reforming of CH 4 + CO 2 →2CO + 2H 2 ) reactions. The increase in the production rates of C 2 H 4 , C 2 H 6 , and C 3 H 8 is related to the bond cleavage and cyclization of aliphatic compounds. The decrease in the CO production rate may be attributed to the catalytic reaction of minerals and melanoidins. Most importantly, the optimal dosage of melanoidin obtained in this experiment is 2.5 mg / g DW, which has important practical significance for the selection of melanoidin dosage in the actual operation of future sludge pyrolysis projects.

[0032] The above is only a preferred embodiment of the present invention, and it does not impose any form of limitation on the present invention. Although the present invention has been disclosed above with a preferred embodiment, 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 content of the present invention, according to the technical essence of the present invention, any simple modification, equivalent replacement, and improvement of the above embodiments within the spirit and principle of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for utilizing melanin-like byproducts of sludge thermal hydrolysis to promote catalytic cracking and reforming of sludge to produce hydrogen efficiently, characterized in that: The method comprises the following steps: Step 1, collecting sludge, sieving the sludge and placing it in a refrigerator for concentration to obtain concentrated sludge; Step 2: performing low-temperature thermal hydrolysis on the concentrated sludge, and then centrifuging to obtain a solid phase product, freeze-drying and grinding the solid phase product to obtain sludge powder; performing high-temperature thermal hydrolysis on the concentrated sludge, and then centrifuging to obtain a thermal hydrolysis sludge supernatant; Step 3, extracting melanin, specifically comprising: 3.1 Filter the supernatant of the high-temperature thermal hydrolysis sludge obtained in step 2, and then mix the supernatant of the thermal hydrolysis sludge with a macroporous adsorption resin for adsorption; 3.2 After the adsorption is completed, the macroporous adsorption resin and the thermal hydrolysis sludge supernatant are separated, and then a new macroporous adsorption resin is replaced to adsorb the thermal hydrolysis sludge supernatant twice; 3.3 Collect the adsorbed macroporous adsorption resin and desorb it to obtain a melanin-like solution; 3.4 The obtained melanin solution is concentrated and freeze-dried in a freeze dryer for 48 hours to obtain melanin powder; Step 4: Thermal hydrolysis of sludge and melanin to produce hydrogen: The sludge powder obtained in step 2 and the melanin-like powder obtained in step 3 are mixed evenly, and then pyrolyzed in a pyrolysis reactor; the solid residue obtained after pyrolysis is biochar, the tar obtained after pyrolysis is collected with a CH2Cl2 solution in an ice water bath, and the gas obtained after pyrolysis is collected through a gas collecting bag.

2. The method of using melanin-like byproducts of sludge thermal hydrolysis to promote catalytic cracking and reforming of sludge to produce hydrogen efficiently according to claim 1, characterized in that: In step 1, the concentration process is as follows: the original sludge is sieved through a 20-mesh screen to remove large particle impurities, and is allowed to stand at 4° C. for 24 hours. After obvious stratification occurs at the mud-water interface, the supernatant is slowly poured off to obtain concentrated sludge.

3. The method of claim 1, wherein the method comprises: In step 2, The process of low-temperature hot water hydrolysis is as follows: the low-temperature hot water hydrolysis temperature is 90°C to 100°C, the pressure is 70×10 3 Pa-150×10 3 Pa, reaction time is 1h; The process of high temperature thermal hydrolysis treatment is as follows: the high temperature thermal hydrolysis temperature is 160°C to 180°C, the pressure is 550×10 3 Pa~885×10 3 Pa, reaction time is 1h; The centrifugation process is centrifugation at 10000 rpm for 10 minutes; the solid phase product is freeze-dried at a temperature of -55°C for 24 hours.

4. The method of claim 1, wherein the method comprises: In step 3.1, the volume ratio of the mass of the macroporous adsorption resin to the supernatant of the thermal hydrolysis sludge is 20 g:100 mL; filtered through a 0.45 μm filter.

5. The method of using melanin-like byproducts of sludge thermal hydrolysis to promote catalytic cracking and reforming of sludge to produce hydrogen efficiently according to claim 4, characterized in that: The macroporous adsorption resin is Amberlite XAD761 ion exchange macroporous adsorption resin.

6. The method of claim 1, wherein the method comprises: The adsorption process of step 3.1 and step 3.2 is: shaking at 150 rpm and 25°C for 12 hours.

7. The method of claim 1, wherein the method comprises: In step 3.3, the desorption process is: first, wash the adsorbed macroporous adsorption resin with deionized water; then, take hydrochloric acid as the solvent and accurately prepare acidified ethanol with a mass fraction of 75%; the hydrochloric acid content is 36.0-38.0% w / %, and the ethanol content is ≥99.7 w / %. 25 mL of hydrochloric acid and 75 mL of ethanol are measured and mixed evenly; finally, the macroporous adsorption resin is added to 75% acidified ethanol and shaken at 150 rpm and 25°C for 24 hours.

8. The method of claim 1, wherein the method comprises: In step 4, the pyrolysis process is as follows: nitrogen flow rate is 150 mL / min, purge time is 10 min, pyrolysis temperature is 500-700° C., heating rate is 20° C. / min, and pyrolysis time is 20 min.

9. The method of claim 1, wherein the method comprises: In step 4, the optimal dosage of melanin powder in the thermal hydrolyzed sludge powder is 0-2.5 mg / g DW.

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