CoCuAl-LDOs catalyst, preparation method, application and application method thereof

Abstract

The invention discloses a CoCuAl-LDOs catalyst, a preparation method, application and an application method thereof, the molar ratio of Co element to Cu element to Al element in the CoCuAl-LDOs catalyst is 3: (1-3): 2, and the CoCuAl-LDOs catalyst is obtained by adopting a coprecipitation method and a sintering method. According to the method, the CoCuAl-LDOs catalyst is prepared and used for catalyzing and activating the free radical initiator to generate free radicals to participate in the sludge thermal hydrolysis reaction, the reaction conditions are mild and easy to control, the product is clean and not prone to causing secondary pollution, part of toxic and harmful substances existing in the sludge can be effectively removed, the sludge thermal hydrolysis efficiency is enhanced, and the sludge thermal hydrolysis efficiency is improved. The dehydration performance of the treated sludge is obviously improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a CoCuAl-LDOs catalyst, a preparation method, an application in strengthening municipal sludge thermal hydrolysis and a method of application, belonging to the technical field of sludge treatment and disposal. BACKGROUND

[0002] Due to the progress of industrialization and the explosive growth of urban population, more and more sewage treatment facilities have been built, and the amount of sludge produced by municipal sewage treatment plants has increased to a non-negligible level. The current mainstream sludge treatment technology is facing significant challenges: traditional aerobic fermentation is prone to produce odorous gas and leachate; landfill treatment is prone to produce landfill gas such as methane and leachate leakage risk; incineration disposal is accompanied by ash residue and tail gas pollution. Under this background, developing environmentally friendly sludge resource technology has become an important direction. Thermal hydrolysis treatment as a new pretreatment technology can significantly improve the dewatering performance and promote the subsequent resource utilization by destroying the colloidal structure of sludge under high temperature and pressure. The popularization and application of this technology system have important practical significance for realizing the goals of sludge reduction, harmlessness and resource utilization.

[0003] Studies have shown that after treatment by thermal hydrolysis coupled with aerobic fermentation or anaerobic digestion process, the easily degradable organic matter in the sludge can be efficiently converted, and the dewatering performance of the sludge can be improved, thereby realizing the reduction and resource utilization of sludge treatment. For example, CN115259597A discloses an acid-base thermal hydrolysis method and system for municipal sludge, which can improve the breaking speed of the sludge, improve the solid-liquid separation efficiency, and thus improve the nutritional properties of the end resource product. CN119898934A discloses a sludge treatment process based on ultrasonic hydrothermal carbonization technology, which can effectively reduce the treatment difficulty of the sludge, has a short treatment period, low treatment cost, and strong usability of the sludge treatment product. Although the sludge thermal hydrolysis technology has been widely used in sludge treatment of municipal sewage treatment plants, some existing treatment processes still face the problems of insufficient hydrolysis efficiency and poor dewatering performance of the treated sludge in the industrialized scale promotion in many cities. SUMMARY

[0004] The present application relates to a CoCuAl-LDOs catalyst, a preparation method, an application in strengthening municipal sludge thermal hydrolysis and a method of application, belonging to the technical field of sludge treatment and disposal.

[0005] Technical solution: The present invention provides a CoCuAl-LDOs catalyst in which the molar ratio of Co, Cu and Al elements is 3:(1-3):2, preferably 3:(2-3):2, and most preferably 3:3:2.

[0006] The preparation method of the CoCuAl-LDOs catalyst of the present invention includes the following steps:

[0007] Dissolve Co(NO3)2·6H2O, Cu(NO3)2·3H2O, and Al(NO3)3·9H2O in water, adjust the pH of the solution, heat and age, centrifuge, wash, dry, and calcine to obtain the final product.

[0008] Further, the molar ratio of Co(NO3)2·6H2O, Cu(NO3)2·3H2O, and Al(NO3)3·9H2O is 3:(1-3):2, preferably 3:(2-3):2, and optimally 3:3:2. The pH is adjusted to 10-12 using a mixed solution of NaOH and Na2CO3. The aging temperature is 60-70℃, and the aging time is 20-24 hours. The calcination temperature is 600-800℃, and the calcination time is 3-5 hours.

[0009] Hydrotalcite and hydrotalcite-like materials are commonly referred to as layered metal hydroxides (LDHs), which have the chemical formula: [A... (1-m) 2+ A 3+ m (OH)2] m+ (B n- ) m / n ·xH2O (where A is a metal ion, B) n- It is an inner-shell anion, m is A 3+ / (A 2+ +A 3+ Two-dimensional inorganic functional materials with a molar ratio of 1:1. These materials often possess high specific surface area and excellent anion exchange properties. Their interlayer structure can accommodate various anions and polar molecules, exhibiting good adsorption effects on different types of substances such as halides, oxygen-containing anions, and organic pollutants. Layered metal oxides (LDOs) are obtained by high-temperature calcination of LDH precursors, and their chemical formula is: A (1-m) 2+ A 3+ m O(OH) x LDO possesses both the adsorption and structural restoration properties of LDH, as well as a higher specific surface area and a large number of active sites, among which the catalytically active metals are well dispersed.

[0010] By containing divalent (A)2+ ) and trivalent (A 3+ ) metal ions with aqueous solutions of target interlayer anions through a precipitation aging process. The key of this method is to maintain supersaturation reaction conditions to ensure that the multivalent cations can achieve synchronous precipitation. According to the difference of supersaturation, the coprecipitation method can be divided into two types of low supersaturation and high supersaturation: the low supersaturation process adopts a stepwise feeding method, and the metal salt mixed solution is gradually added to the anion solution according to a certain ratio; the high supersaturation process is to inject the metal salt solution and the anion solution into the reactor at the same time through a synchronous feeding system, and the pH value of the system is accurately controlled to maintain the coprecipitation conditions. Compared with the low supersaturation process, the high supersaturation condition is more likely to cause the rapid formation of a large number of crystal nuclei, but the size of the finally generated crystal is smaller. The precipitates obtained by the two types of processes need to be subjected to subsequent heat treatment to improve the crystallinity and yield of the LDH product.

[0011] The application of the CoCuAl-LDOs catalyst in the thermal hydrolysis of municipal sludge.

[0012] A method for strengthening the thermal hydrolysis of municipal sludge by using the CoCuAl-LDOs catalyst, comprising the following steps:

[0013] (1) Sludge preparation: adding a free radical initiator and a CoCuAl-LDOs catalyst to municipal sludge, stirring with water and dilute sulfuric acid solution to obtain a slurry;

[0014] (2) Sludge hydrolysis and flash evaporation: performing a hydrolysis reaction on the slurry, and then performing flash evaporation;

[0015] (3) Dewatering of the remaining material: dewatering the remaining material after flash evaporation.

[0016] Further, in step (1), the water content of the municipal sludge is 65-75%, the free radical initiator is at least one of persulfate and Fenton reagent, the addition amount of the free radical initiator is 2-5wt% of the mass of the municipal sludge, the addition amount of the catalyst is 1-5wt% of the addition amount of the free radical initiator, the water content of the slurry is 90-95%, and the pH value is 4-5. In step (2), the temperature of the hydrolysis reaction is 160-180℃, the time of the hydrolysis reaction is more than 2h, the pressure in the reaction container during the hydrolysis reaction is 2.5-3.0Mpa, and the pressure in the flash evaporation container after flash evaporation is released to normal pressure within 1-30s. In step (3), a filter press is used for dewatering, the pressure during dewatering is more than 2Mpa, and the pressing time is more than 30min.

[0017] Beneficial effects: Compared with the prior art, the present application has the following remarkable advantages: (1) The CoCuAl-LDOs catalysts prepared by the present application have the advantages of simple preparation, high purity, stable physical and chemical properties, good adsorption performance, large specific surface area and a large number of active sites, and good catalytic activity of the metal dispersion. The Co, Cu and Al oxide materials have the characteristics of long service life, excellent catalytic performance, easy separation and convenient recovery. (2) The free radical initiator used in the present application is persulfate or Fenton reagent, which has a high oxidation potential and a mild reaction condition. The various free radicals generated after activation can effectively participate in the thermal hydrolysis reaction of the municipal sludge. (3) The present application prepares CoCuAl-LDOs catalysts and uses them to catalyze and activate free radical initiators to generate free radicals to participate in the thermal hydrolysis reaction of the sludge. The reaction conditions are mild and easy to control, the product is clean and not easy to cause secondary pollution, and the method can effectively remove part of the toxic and harmful substances in the sludge, strengthen the thermal hydrolysis efficiency of the sludge, and significantly improve the dewatering performance of the treated sludge. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The preparation process flow chart of the CoCuAl-LDOs catalysts of the present application.

[0019] Figure 2 The process flow chart of the method for strengthening the thermal hydrolysis efficiency of the municipal sludge of the present application. DETAILED DESCRIPTION

[0020] The municipal sludge in the examples was taken from a certain municipal sewage treatment plant in Nanjing, Jiangsu Province, and had a moisture content of 67%, a pH value of 7.2, a TCOD of 95.28 g / L, a C / N of 10.71, and a VS / TS of 60.30%. The above values are the average values during the experiment.

[0021] The LDO material can be prepared by synthesizing the LDH precursor by the coprecipitation method, and then removing the interlayer water, interlayer anions and hydroxyl groups by calcination. The preparation process is as shown in Figure 1

[0022] Preparation of LDO catalysts in Example 1

[0023] ​(1) Preparation of precursor CoCuAl-LDHs material: a certain amount of Co(NO3)2.6H2O, Cu(NO3)2.3H2O and Al(NO3)3.9H2O (molar ratio of Co:Cu:Al is controlled as 1:1:2, 2:1:2, 3:1:2, 4:1:2, 3:2:2, 3:3:2 respectively) was weighed according to the set molar ratio and added into a conical flask, and an appropriate amount of pure water was added. After shaking to completely dissolve the medicine, a mixed alkali solution of NaOH and Na2CO3 (molar ratio of NaOH and Na2CO3 is 2:1) was added dropwise into the conical flask, and the pH value of the solution was adjusted to 11. During the adjustment process, the solution was mixed uniformly by stirring with a glass rod. Then the conical flask was placed in a water bath constant temperature oscillator, and aged at 60°C for 24h. Then the suspension after aging was placed in a centrifuge (4000r / min, 15min), and after centrifugation, the separated liquid was poured out, and pure water was added again for centrifugation. Repeat the centrifugation process until the pH of the separated liquid is neutral. The black-brown solid obtained by separation was placed in an oven at 105°C and dried for 12h. After drying, the black-brown powder CoCuAl-LDHs material was obtained by grinding and sieving.

[0024] (2) Preparation of CoCuAl-LDOs material: the black-brown powder CoCuAl-LDHs material prepared in step (1) was placed in a ceramic container and then placed in a muffle furnace. After calcination at 600°C for 5h, black powder CoCuAl-LDOs material was obtained. Six LDO catalysts were recorded as Co1Cu1Al2-LDOs, Co2Cu1Al2-LDOs, Co3Cu1Al2-LDOs, Co4Cu1Al2-LDOs, Co3Cu2Al2-LDOs, Co3Cu3Al2-LDOs respectively. The preparation process is shown in Figure 1 .

[0025] Example 2 Enhanced thermal hydrolysis of municipal sludge

[0026] The six CoCuAl-LDOs catalysts prepared in Example 1 were used to enhance the thermal hydrolysis efficiency of municipal sludge, and the specific process was as follows:

[0027] (1) Sludge preparation: a certain amount of municipal sludge with water content of 67% and 5wt% of PMS (peroxymonosulfate) were put into a slurry tank, and then divided into seven groups. One group was added with PMS only without LDO catalyst, and the remaining six groups were added with PMS and 5wt% of the six LDO catalysts prepared in Example 1. Finally, water and dilute sulfuric acid solution were added, and stirred for 15min at a stirring speed of 500rpm to prepare a slurry with water content of 90% and pH value of 4.5.

[0028] (2) Sludge hydrolysis flash evaporation: the slurry is first introduced into the hydrolysis reactor to heat to 180°C, and then hydrolysis is carried out for 2h, the stirring paddle in the hydrolysis reactor rotates at 500rpm throughout the process. After the timer ends, the hydrolysis reactor pressure indicates 2.0Mpa, and then the remaining material in the flash tank is introduced into the flash tank to exhaust and release pressure, and the pressure in the flash tank is reduced to normal pressure within 10s;

[0029] (3) Residual material dewatering: the residual material in the flash tank is transported to the filter press dewatering equipment (filter press) for dewatering, the pressing pressure is 2.0Mpa, and the pressing time is 30min, to obtain dewatered sludge cake and hydrolysis liquid. The process is shown in Figure 2 .

[0030] The moisture content of the sludge cake obtained in step (3), the COD, ammonia nitrogen and total nitrogen content in the hydrolysis liquid, and the removal rate of sulfamethoxazole (SMX, sulfonamide antibiotic) and chloramphenicol (CPL, amphenicol antibiotic) in the hydrolysis liquid are determined, and the determination results are shown in Table 1 as follows:

[0031] Table 1 Effect of LDO materials with different Co / Cu ratios on municipal sludge thermal hydrolysis

[0032]

[0033]

[0034] As can be seen from Table 1, the introduction of the catalyst can effectively catalyze the release of free radicals from PMS to participate in the sludge thermal hydrolysis reaction, thereby improving the sludge hydrolysis efficiency, reducing the moisture content of the dewatered sludge cake, and removing the organic pollutants present in the sludge. In addition, under the condition that the Cu / Al ratio in the LDO material is constant and the Co ratio is 1-4, the sludge hydrolysis efficiency and antibiotic removal rate increase first and then decrease with the increase of the Co ratio, which is due to the fact that when Co 2+ is introduced into the hydrotalcite layer, Co 2+ replaces Al 3+ into the layer, making the active metal uniformly dispersed and the active point increased, thereby enhancing the catalytic performance; but when the Co ratio continues to increase to 4, it is not conducive to the hydrolysis reaction of the sludge, which may be affected by the Jiang-Taylor effect, which may be related to the Jiang-Taylor effect: excessive Co 2+The hydrogen bond and electrostatic force between the hydrotalcite-like layers are weakened, leading to the distortion of the layers. When the Co:Al ratio is constant and the Cu ratio is 1-3, the sludge hydrolysis efficiency and antibiotic removal rate increase with the increase of the Cu ratio. This is due to the good dispersion of CoAl spinel phase and CuO phase in the LDO interlayer, and the synergistic effect of Co-Cu intermetallic. The introduction of appropriate Cu on the LDO layer can enhance the reducibility of Co species and CuO itself. In addition, the increase of Cu content promotes the reduction of Co 2+ , the increase of more active Co 3+ , and the increase of more active Co 2+ . In addition, the electron transfer from Cu to Co increases the electron cloud density of Co, making it more prone to attack S2O8 2- in PMS, and the loss of electrons by Cu makes it more prone to adsorb the remote oxygen in the PMS molecule. These phenomena are beneficial to improve the catalytic activity of the LDO material. From the above experiments, it is found that when the molar ratio of Co:Cu:Al is 3:(1-3):2, the water content of the mud cake is below 32%, the COD in the hydrolysate is above 70000mg / L, the ammonia nitrogen is above 6500mg / L, the SMX removal rate is above 96%, and the CPL removal rate is above 80%, the comprehensive effect is very good, especially when the molar ratio of Co:Cu:Al is 3:3:2.

[0035] Example 3

[0036] In the experimental process, the same as in Example 2, except that the experiment is divided into six groups, and the dosing of persulfate (PMS) and catalyst in step (1) of each group is different, respectively: ① no PMS and LDO catalyst is added; ② only 5wt% PMS of sludge is added; ③ only 5wt% Co3Cu3Al2-LDHs of sludge is added; ④ only 5wt% Co3Cu3Al2-LDOs of sludge is added; ⑤ 5wt% PMS of sludge + 5wt% Co3Cu3Al2-LDHs of PMS is added; ⑥ 5wt% PMS of sludge + 5wt% Co3Cu3Al2-LDOs of PMS is added. The dosing amount of the above six groups of persulfate is 5% of the sludge mass.

[0037] The water content of the mud cake obtained in step (3), the COD, ammonia nitrogen and total nitrogen content in the hydrolysate, and the removal rate of sulfamethoxazole (SMX, sulfonamide antibiotic) and chloramphenicol (CPL, amide alcohol antibiotic) in the hydrolysate are determined, and the determination results are shown in Table 2.

[0038] Table 2 Influence of different reaction systems on municipal sludge thermal hydrolysis

[0039]

[0040] As can be seen from Table 2, the promotion effect of PMS or catalyst alone on sludge thermal hydrolysis is not obvious. The LDHs / PMS system and the LDOs / PMS system both have a strong promotion effect on the thermal hydrolysis efficiency of municipal sludge. This is because Co 2+ , Cu 2+ and Cu + on the surface of the catalyst activate HSO5 - to generate sulfate radicals and hydroxyl radicals, and Co 3+ , Cu 3+ on the surface of the catalyst are also reduced by HSO5 - to Co 2+ , Cu 2+ with higher catalytic activity, thereby improving the sludge hydrolysis efficiency. Compared with the LDHs / PMS system, the LDOs / PMS system has a more obvious effect on the thermal hydrolysis efficiency of municipal sludge. This is because the LDO material has a higher specific surface area and pore structure. The mesoporous structure of LDO can significantly increase the number of active sites, promote the adsorption and activation of persulfate, and the surface of LDO is rich in hydroxyl groups, which can directly activate PMS to generate SO4 ·- or 1 O2. Secondly, the redox cycle and electron transfer efficiency of the LDO material are more excellent. The transition metal in LDO exists in multiple valence states, which can form an efficient redox cycle and accelerate electron transfer, avoiding single metal deactivation. Finally, the high selectivity of LDO to anions significantly reduces the competition of Cl - , HCO3 - and other substances in water for active sites, while LDH is easily disturbed.

[0041] From the results of the above examples, it can be seen that:

[0042] The introduction of free radicals into the municipal sludge thermal hydrolysis reaction system is beneficial to the improvement of hydrolysis efficiency, sludge dewatering performance and antibiotic removal. The addition of PMS+CoCuAl-LDOs in the municipal sludge thermal hydrolysis reaction can significantly improve the hydrolysis efficiency of sludge, basically remove the antibiotics in the sludge, and greatly reduce the moisture content of the subsequent dewatering sludge cake. In addition, among the six LDO catalysts prepared in Example 1, the optimal ratio of Co:Cu:Al is 3:3:2, and the CoCuAl-LDOs / PMS system has the best strengthening effect on the thermal hydrolysis of municipal sludge.

[0043] In summary, the application provides a method for strengthening the thermal hydrolysis efficiency of municipal sludge, which comprises the following steps: preparing a CoCuAl-LDOs catalyst, and using the catalyst to catalyze and activate a free radical initiator to generate free radicals to participate in a sludge thermal hydrolysis reaction. The method has the advantages of mild reaction conditions, easy control, clean product, and no secondary pollution, and can effectively remove part of the toxic and harmful substances in the sludge, strengthen the thermal hydrolysis efficiency of the sludge, and significantly improve the dewatering performance of the treated sludge.

Claims

1. A CoCuAl-LDOs catalyst, characterized in that, The molar ratio of Co, Cu and Al in the CoCuAl-LDOs catalyst is 3:(1-3):

2.

2. The method for preparing the CoCuAl-LDOs catalyst according to claim 2, characterized in that, Includes the following steps: Co(NO3)2·6H2O, Cu(NO3)2·3H2O and Al(NO3)3·9H2O are dissolved in water, the pH of the solution is adjusted, heated and aged, centrifuged, washed, dried and calcined to obtain the final product.

3. The preparation method according to claim 2, characterized in that, The molar ratio of Co(NO3)2·6H2O, Cu(NO3)2·3H2O and Al(NO3)3·9H2O is 3:(2-3):

2.

4. The preparation method according to claim 2, characterized in that, The pH value was adjusted to 10-12 using a mixed solution of NaOH and Na2CO3, and the aging temperature was 60-70℃ for 20-24 hours.

5. The preparation method according to claim 2, characterized in that, The calcination temperature is 600-800℃, and the calcination time is 3-5 hours.

6. The application of the CoCuAl-LDOs catalyst according to claim 1 in the thermal hydrolysis of municipal sludge.

7. A method for enhancing the thermal hydrolysis of municipal sludge using the CoCuAl-LDOs catalyst as described in claim 1, characterized in that, Includes the following steps: (1) Sludge preparation: Add free radical initiator and CoCuAl-LDOs catalyst to municipal sludge, add water and dilute sulfuric acid solution and stir to obtain slurry; (2) Sludge hydrolysis flash evaporation: The sludge is hydrolyzed and then flash evaporated; (3) Dehydration of remaining materials: Dehydrate the remaining materials after flash evaporation.

8. The method according to claim 7, characterized in that, In step (1), the free radical initiator is at least one of persulfate and Fenton reagent, the amount of free radical initiator added is 2-5 wt% of the municipal sludge mass, the amount of catalyst added is 1-5 wt% of the amount of free radical initiator added, the sludge moisture content is 90-95%, and the pH value is 4-5.

9. The method according to claim 7, characterized in that, In step (2), the hydrolysis reaction temperature is 160-180℃, the hydrolysis reaction time is more than 2 hours, the pressure inside the reaction vessel during the hydrolysis reaction is 2.5-3.0 MPa, and after flash evaporation, the pressure inside the flash evaporation vessel is released to atmospheric pressure within 1-30 seconds.

10. The method according to claim 7, characterized in that, In step (3), a filter press is used for dewatering. The pressure during dewatering is above 2 MPa and the pressing time is above 30 minutes.

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