Process for preparing high-adsorption-performance biochar through cooperation of acid pretreatment and carbonization treatment of coked sludge

Abstract

The invention relates to the technical field of environmental protection and resource regeneration, and discloses a process for preparing biochar with high adsorption performance by acid pretreatment and carbonization treatment of coked sludge, the coked sludge is subjected to acid soaking pretreatment, and then hydrothermal carbon is prepared by a carbonization process; the pretreated liquid phase is recycled for three times to obtain iron-rich acid liquid, and diluted hydrochloric acid and ferric trichloride products are obtained at the same time through separation by an evaporation and concentration process. On one hand, inorganic mineral components in the coking sludge are effectively removed, and the internal pore structure of the sludge is dredged and improved, so that the hydrothermal carbon with excellent adsorption performance is prepared; on the other hand, most of heavy metals in the coking sludge are also removed through acid pretreatment, the environmental risk of biochar is also reduced synchronously, and the treatment process of the technical scheme provides a new thought for harmless treatment and resource utilization of hazardous waste; the method is of great significance to acceleration of construction of a waste recycling system and high-quality green development.

Description

Technical Field

[0001] The invention relates to the technical field of environmental protection and resource regeneration, and in particular to a process for preparing biochar with high adsorption performance by acid pretreatment and coordinated carbonization treatment of coking sludge. Background Art

[0002] Since my country's energy structure is characterized by "rich in coal and poor in oil", coal coking, as an important part of my country's energy, plays a vital role in the process of industrialization. With the acceleration of the industrialization process, the output of the coking industry has increased year by year, which has also led to the generation of more than 400 million cubic meters of coking wastewater each year. After biochemical treatment, these wastewaters further produce millions of tons of coking sludge. As one of the typical industrial solid wastes, coking sludge contains a variety of characteristic pollutants such as polycyclic aromatic hydrocarbons and heavy metals, and is included in my country's list of hazardous wastes. At the same time, the organic matter content of coking sludge can reach more than 65%, which is much higher than ordinary municipal sludge, and has a high potential for resource utilization. Therefore, how to achieve harmless treatment and resource utilization of coking sludge has become a difficult problem that needs to be solved urgently.

[0003] At present, the main treatment methods of coking sludge in actual production include blending with coal for coking and using it as a coal yard covering agent to suppress dust. However, both methods have their own limitations and problems. Coking with coal is to add dehydrated coking sludge to coal, and then blend with coal to produce coke; this method is simple to operate and does not generate additional energy consumption, but there are also some problems, such as uneven mixing of coking sludge and coal, and excessive fluctuations in the moisture content of the blended coal, which leads to a decrease in the quality of the prepared coke. On the other hand, the addition of coking sludge causes a sharp increase in the moisture content of the coal entering the furnace or a large fluctuation range, causing irreversible damage to the coke oven such as cracking and increased energy consumption. To suppress dust, the undehydrated coking residual sludge is directly transported to the coal yard by tank trucks and sprayed on the surface of the coal as a coal yard covering agent, which has achieved the purpose of reducing dust. However, direct spraying on the coal yard has led to increased pollution of the coal yard soil, which has a serious impact on the surrounding ecological environment.

[0004] In order to realize the resource utilization of coking sludge, preparing it into biochar material through pyrolysis is one of the more effective means. However, due to the presence of inorganic components such as metal oxides in coking sludge, the formation of pore structure will be hindered during the pyrolysis process, and even the existing pores will be blocked, resulting in the uneven pore structure of the obtained biochar, narrow pore size and low specific surface area, which ultimately affects its performance as an adsorption material. On the other hand, the heavy metals present in coking sludge will be enriched in biochar during the pyrolysis process, increasing its environmental risk in practical applications. Therefore, there is an urgent need for a new efficient and green technology based on pyrolysis to treat coking sludge, which can reduce the environmental risk of biochar while regulating the pore structure and improving its adsorption performance. Summary of the invention

[0005] The present invention aims to provide a process for preparing biochar with high adsorption performance by acid pretreatment and coordinated carbonization treatment of coking sludge, so as to realize resource utilization and harmless treatment of coking sludge.

[0006] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a process for preparing biochar with high adsorption performance by acid pretreatment and coordinated carbonization of coking sludge, wherein the coking sludge is pretreated by acid immersion and then hydrothermal carbonization is prepared by coordinated carbonization process; the pretreated liquid phase is recycled three times to obtain iron-rich acid liquid, and dilute hydrochloric acid and ferric chloride products are separated by evaporation and concentration process.

[0007] Preferably, as an improvement, in the acid soaking pretreatment step, the acid reagent is hydrochloric acid with a concentration of 2.3-2.7 M, the acid soaking pretreatment is carried out under oscillating conditions, and the mass ratio of coking sludge to hydrochloric acid is 1:20-25.

[0008] Preferably, as an improvement, the oscillation rate is 150 r / min and the treatment time is 7-9 h.

[0009] Preferably, as an improvement, the carbonization treatment method is pyrolysis carbonization, and the pyrolysis process is carried out under oxygen-free conditions.

[0010] Preferably, as an improvement, the pyrolysis temperature is 700-900°C and the pyrolysis time is 2-3h.

[0011] Preferably, as an improvement, the iron-rich acid solution is evaporated and concentrated by means of electric heating.

[0012] Preferably, as an improvement, the treatment time of evaporation concentration is 8 hours, and the gas after evaporation concentration is recovered by condensation reflux to obtain dilute hydrochloric acid, and the bottom liquid is concentrated to precipitate ferric chloride crystals.

[0013] Preferably, as an improvement, a process for preparing biochar with high adsorption performance by acid pretreatment and coordinated carbonization of coking sludge comprises the following steps:

[0014] Step 1: Acid pretreatment: fully mix the coking sludge with the hydrochloric acid solution and shake it to fully extract it;

[0015] Step 2, solid-liquid separation: solid-liquid separation is performed by centrifugation, the solid phase coking sludge is dried, and the liquid phase acid solution is recycled and used in step 1;

[0016] Step 3, pyrolysis reaction: placing the acid pretreated coking sludge in a reactor, pyrolyzing the sludge in an oxygen-free environment to prepare biochar;

[0017] Step 4: The liquid acid solution obtained by circulating three times in step 2 is treated by evaporation and concentration, and dilute hydrochloric acid is obtained by condensation and reflux collection, and the bottom solution is concentrated to precipitate the ferric chloride product.

[0018] The principle and advantages of this scheme are: in actual application, in this technical scheme, the inventor comprehensively optimizes and upgrades the treatment process of coking sludge in view of the problems existing in the treatment process of coking sludge in the prior art. First, the causes of the above technical problems in the treatment process of coking sludge are reversely analyzed: in addition to organic matter, the inorganic mineral components of coking sludge also account for 35-40%, and are rich in heavy metals. These inorganic components not only have a negative impact on the formation of the pore structure of biochar, but also the heavy metal components contained therein will increase the environmental risks of subsequent use. In response to the above two problems: the inventor creatively coordinated the acid pretreatment and pyrolysis carbonization process. First, the inorganic mineral components therein are removed by leaching through acid pretreatment, and the internal structure of the coking sludge is improved in advance to promote the formation of a developed pore structure in the subsequent pyrolysis process. Secondly, after the acid pretreatment, the iron-rich acid solution is obtained synchronously, and the product is recovered and reused through the evaporation and concentration process. The residual hydrochloric acid is recovered by volatilization and condensation of the upper layer, and the iron at the bottom is precipitated in the form of ferric chloride crystals. During the technical research and development stage, ensuring the appropriate pore structure of biochar is one of the difficulties of this technical solution. Based on this, the inventors found that the pore structure of biochar is closely related to the temperature conditions of the pretreatment process and the pyrolysis process, and these two process conditions do not act independently, but influence each other and complement each other; the focus is on targeted optimization of the above-mentioned process conditions, and through repeated research and verification, this solution was obtained.

[0019] In summary, the beneficial effects of this technical solution are: this technical solution treats coking sludge, and not only does the hydrothermal carbon obtained have a developed pore structure, but also exhibits excellent adsorption performance for organic pollutants. Moreover, the heavy metal components in the sludge are removed in advance through acid pretreatment, which, on the one hand, reduces the environmental risk of biochar, and on the other hand, enriches the heavy metal iron in the sludge for product recovery, and finally realizes the efficient resource utilization of coking sludge. According to the experimental verification results, the biochar obtained by this technical solution exhibits excellent adsorption performance for a variety of organic pollutants, and the equilibrium adsorption capacity for methylene blue and Congo red reaches 251.03 and 226.44 mg / g respectively, and the equilibrium adsorption capacity for the typical antibiotic tetracycline reaches 154.61 mg / g; at the same time, the recovery rate of iron through evaporation concentration reaches more than 90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the overall process flow chart of Example 1.

[0021] Figure 2 SEM images of coking sludge and the corresponding biochar. DETAILED DESCRIPTION

[0022] The following is further described in detail through specific implementations, but the implementation of the present invention is not limited thereto. Unless otherwise specified, the technical means used in the following implementations are conventional means well known to those skilled in the art; the experimental methods used are all conventional methods; the materials, reagents, etc. used can all be obtained from commercial channels.

[0023] Program Overview:

[0024] A process for preparing biochar with high adsorption performance by acid pretreatment and coordinated carbonization of coking sludge, wherein the coking sludge is pretreated by acid immersion, and then hydrothermal carbon is prepared by coordinated carbonization process; the pretreated liquid phase is recycled three times to obtain iron-rich acid solution, and dilute hydrochloric acid and ferric chloride products are separated and simultaneously obtained by evaporation and concentration process, specifically comprising the following steps:

[0025] Step 1: Acid pretreatment: fully mix the coking sludge with 2.5M hydrochloric acid solution and shake it at 150r / min for 8h to fully extract it;

[0026] Step 2, solid-liquid separation: solid-liquid separation is performed by centrifugation at 3000r / min for 5min, the solid phase coking sludge is dried at 105°C, and the liquid phase acid solution is recycled and used in step 1;

[0027] Step 3, pyrolysis reaction: the coking sludge after acid pretreatment is placed in a reactor, the pyrolysis temperature is set to 800°C, the pyrolysis time is set to 2h, the sludge is pyrolyzed in an oxygen-free environment, and the product is repeatedly rinsed with 0.1M sodium hydroxide solution until it is neutral;

[0028] Step 4: The liquid acid solution obtained by circulating three times in step 2 is treated by evaporation and concentration. The evaporation method is electric heating for 8 hours. The upper layer is collected by condensation reflux to obtain dilute hydrochloric acid, and the bottom solution is concentrated to precipitate the ferric chloride product.

[0029] Example 1

[0030] A process for preparing biochar with high adsorption performance by acid pretreatment and coordinated carbonization of coking sludge, comprising the following steps:

[0031] Step 1: Acid pretreatment: 5 g of coking sludge was fully mixed with 100 mL of 2.5 mol / L hydrochloric acid solution and shaken at 150 r / min for 8 h to fully extract it;

[0032] Step 2, solid-liquid separation: solid-liquid separation is performed by centrifugation at 3000r / min for 5min, the solid phase coking sludge is dried at 105°C, and the liquid phase acid solution is recycled and used in step 1;

[0033] Step 3: Pyrolysis reaction: the acid-pretreated coking sludge is placed in a reactor, the pyrolysis temperature is set to 800°C, the pyrolysis time is set to 2 hours, the sludge is pyrolyzed in an oxygen-free environment, and the product is repeatedly rinsed with 0.1M sodium hydroxide solution until it is neutral;

[0034] Step 4: The liquid acid solution obtained by circulating three times in step 2 is treated by evaporation and concentration. The evaporation method is electric heating for 8 hours. The upper layer is collected by condensation reflux to obtain dilute hydrochloric acid, and the bottom solution is concentrated to precipitate the ferric chloride product.

[0035] Comparative Example 1

[0036] The difference between this comparative example and Example 1 is that in this comparative example, in step 1, the leaching solution is NaOH.

[0037] Comparative Example 2

[0038] The difference between this comparative example and Example 1 is that in this comparative example, in step 1, the acid concentration is 1.5M.

[0039] Comparative Example 3

[0040] The difference between this comparative example and Example 1 is that in this comparative example, in step 1, the oscillation time is 4 hours.

[0041] Comparative Example 4

[0042] The difference between this comparative example and Example 1 is that in this comparative example, in step 3, the pyrolysis temperature is 500°C.

[0043] Comparative Example 5

[0044] The difference between this comparative example and Example 1 is that in this comparative example, in step 3, the pyrolysis time is 1 h.

[0045] Experimental Example 1

[0046] The coking sludge, coking sludge biochar and acid-pretreated coking sludge biochar of the present invention were observed by scanning electron microscope. The results are as follows: Figure 2 As shown, A is the original coking sludge, B is the coking sludge biochar, and C is the coking sludge biochar after acid pretreatment.

[0047] Experimental Example 2 Performance Test

[0048] Experimental methods:

[0049] The equilibrium adsorption capacity of organic pollutants by coking sludge biochar was determined by batch adsorption experiment. The main operation steps are as follows:

[0050] (1) Weigh 50 mg of biochar sample and mix it with 150 ml of 200 mg / L organic pollutant solution (Congo red, methylene blue and tetracycline).

[0051] (2) The mixed solution was oscillated at 150 r / min until adsorption equilibrium was reached. The concentration of organic pollutants before and after adsorption was determined by spectrophotometry, and the equilibrium adsorption amount Q was calculated by Equation 1 e ;

[0052]

[0053] Where C0 (mg / L) is the initial concentration, C e (mg / L) is the concentration after adsorption equilibrium, V (mL) is the volume of the adsorption liquid, and m (mg) is the mass of the adsorbent.

[0054] After the iron-rich acid solution is evaporated and concentrated, the ferric chloride crystals are collected at the bottom, dried and weighed, and the iron recovery rate R (%) is determined by formula 2;

[0055]

[0056] Where C0 (g / g) is the mass concentration of iron in coking sludge, M (g) is the mass of coking sludge, and m (g) is the mass of ferric chloride crystals obtained after evaporation and concentration.

[0057] The experimental results of Example 1 and Comparative Examples 1-5 are shown in Table 1. It can be found that when other chemical reagents such as acetic acid and phosphoric acid are used for leaching, the adsorption performance of the obtained biochar for the three organic pollutants is not as good as that of the biochar after hydrochloric acid leaching, and the subsequent recovery rate of iron is less than 40%; in addition, when the hydrochloric acid leaching concentration and time conditions are changed, the adsorption performance and iron recovery rate of the biochar obtained simultaneously decrease due to insufficient leaching of inorganic mineral components such as iron in the coking sludge. Only 2.5M hydrochloric acid is used to leach the coking sludge for 8h and the pyrolysis temperature is 800℃ for synergistic carbonization for 2h, the obtained biochar has the best adsorption performance for tetracycline, Congo red and methylene blue, and the subsequent recovery rate of iron is 91.21%.

[0058] Table 1

[0059]

[0060] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A process for preparing biochar with high adsorption performance by acid pretreatment and coordinated carbonization of coking sludge, characterized in that: Coking sludge was pretreated by acid soaking and then prepared into hydrothermal charcoal by synergistic carbonization process; The pretreated liquid phase is recycled three times to obtain an iron-rich acid solution, which is separated by an evaporation concentration process to obtain dilute hydrochloric acid and ferric chloride products at the same time.

2. The process for preparing biochar with high adsorption performance by acid pretreatment and coordinated carbonization of coking sludge according to claim 1 is characterized by: In the acid soaking pretreatment step, the acid reagent is hydrochloric acid with a concentration of 2.3-2.7 M. The acid soaking pretreatment is carried out under oscillation conditions, and the mass ratio of the coking sludge to the hydrochloric acid is 1:20-25.

3. The process for preparing biochar with high adsorption performance by acid pretreatment and coordinated carbonization of coking sludge according to claim 2 is characterized by: The oscillation rate is 150 r / min and the processing time is 7-9 h.

4. The process for preparing biochar with high adsorption performance by acid pretreatment and coordinated carbonization of coking sludge according to claim 3 is characterized by: The carbonization treatment method is pyrolysis carbonization, and the pyrolysis process is carried out under oxygen-free conditions.

5. The process for preparing biochar with high adsorption performance by acid pretreatment and coordinated carbonization of coking sludge according to claim 4, characterized in that: The pyrolysis temperature is 700-900°C and the pyrolysis time is 2-3h.

6. The process for preparing biochar with high adsorption performance by acid pretreatment and coordinated carbonization of coking sludge according to claim 5, characterized in that: The iron-rich acid solution is evaporated and concentrated by means of electric heating.

7. The process for preparing biochar with high adsorption performance by acid pretreatment and coordinated carbonization of coking sludge according to claim 6, characterized in that: The treatment time of evaporation and concentration is 8 hours. After evaporation and concentration, the gas is recovered by condensation reflux to obtain dilute hydrochloric acid, and the bottom liquid is concentrated to precipitate ferric chloride crystals.

8. The process for preparing biochar with high adsorption performance by acid pretreatment and coordinated carbonization of coking sludge according to claim 7, characterized in that: The steps include: Step 1: Acid pretreatment: fully mix the coking sludge with the hydrochloric acid solution and shake it to fully extract it; Step 2, solid-liquid separation: solid-liquid separation is performed by centrifugation, the solid phase coking sludge is dried, and the liquid phase acid solution is recycled and used in step 1; Step 3, pyrolysis reaction: placing the acid pretreated coking sludge in a reactor, pyrolyzing the sludge in an oxygen-free environment to prepare biochar; Step 4: The liquid acid solution obtained by circulating three times in step 2 is treated by evaporation and concentration, and dilute hydrochloric acid is obtained by condensation and reflux collection, and the bottom solution is concentrated to precipitate the ferric chloride product.

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