Method for resourceful treatment of cold-rolled oil sludge

Abstract

The invention relates to the technical field of harmlessness and resource utilization of hazardous wastes, and provides a cold-rolled oil sludge resource treatment method which utilizes the characteristics of low hydrogen bond degree, low dielectric constant and strong reactivity of methanol in a supercritical state. The method comprises the following steps: carrying out esterification reaction on oil-water, oil-solid, oil-water-solid and other interface fatty acids in the cold-rolled oil sludge and methanol to generate fatty acid methyl ester, and dissolving the fatty acid methyl ester in the methanol by utilizing the strong solubility of the supercritical methanol; the method comprises the following steps: firstly, separating iron filings in the cold-rolled oil sludge, so that the interface acting forces of oil-water, oil-solid, oil-water-solid and the like in the cold-rolled oil sludge are reduced, the interface structure is damaged and liquid drops are gathered, a liquid phase consisting of high-grade iron filings and oil-water can be obtained through simple solid-liquid separation, and then oil-water separation is realized through extraction, so that the oil-water-solid three-phase separation in the cold-rolled oil sludge is realized.

Description

Technical Field

[0001] The invention relates to the technical field of harmless treatment and resource utilization of hazardous wastes, and in particular to a method for resource treatment of cold rolling sludge. Background Art

[0002] Cold rolling sludge is a complex water-in-oil (W / O) emulsion structure mixture formed by the friction between the rollers and the workpiece during the cold rolling of crude steel, the waste rolling oil in the emulsion, and water. It is severely emulsified, has an unpleasant odor, is black and viscous, and is difficult to biodegrade. Because cold rolling sludge is highly toxic and emits a foul odor, it is listed in the category of waste mineral oil and mineral oil-containing waste (HW08) in the "National List of Hazardous Wastes" (2021 edition). It is estimated that my country produces about 1.8 million tons of cold rolling sludge each year, which has attracted much attention from the government and the public. In addition, since cold rolling sludge contains 5-60wt% of oil, its main components are palm oil, oleic acid, stearic acid and other C14-C18 higher fatty acids and 20-90wt% of iron chips, its main components are Fe, Fe 3 O 4 Direct emissions will not only pollute the air, groundwater and soil, cause serious ecological problems and endanger people's health, but also lead to serious waste of oil and iron resources.

[0003] At present, the main methods for treating cold rolling sludge include high-temperature incineration and pyrolysis, medium-temperature distillation, room-temperature organic solvent extraction, acid-base cleaning and microwave radiation physics. However, the above methods all have certain limitations in industrial applications: incineration is prone to secondary pollution, pyrolysis has high energy consumption, distillation requires pre-dehydration, organic solvent extraction has high operating costs, acid-base cleaning requires strong corrosion resistance, and microwave radiation equipment has high investment costs. These problems seriously restrict the resource utilization of cold rolling sludge. In addition, some researchers directly add cold rolling sludge to the iron ore sintering process or mix it with coal powder and inject it into the blast furnace, but due to process limitations, the proportion of addition is relatively low.

[0004] CN109679676A discloses a method of using an alkaline conditioning agent to separate water from rolling sludge, reacting the obtained water-free sludge with an alkaline methanol solution to synthesize biodiesel. This method requires the use of an alkaline conditioning agent to pre-treat the cold-rolled sludge by dehydration, and requires the addition of a large amount of alkaline reagents. Zhou et al. disclose a method of first extracting and recovering grease from the cold-rolled sludge using a mixed solvent of 1,2-dichloroethane and isopropanol, and then using H 2 SO 4A method for preparing biodiesel by promoting esterification and transesterification reaction as a homogeneous catalyst. The method needs to separate the grease in the cold rolling sludge first, and needs to use a large amount of organic solvent. CN109797002A discloses that in the presence of a catalyst and a solvent, the scrap steel rolling oil is first subjected to a hydrogenation reaction in a hydrogen atmosphere, the mixture after the reaction is subjected to solid-liquid separation, and the separated liquid phase is distilled to obtain gasoline and diesel fractions. In this method, the reaction atmosphere is hydrogen, which has the problems of high energy consumption and high risk, and it is difficult to ensure the complete reaction of hydrogen during the hydrogenation process, resulting in a waste of resources. Therefore, it is of great significance to provide a method for resource-based cold rolling sludge with a small amount of chemical reagents, safe and efficient. Summary of the invention

[0005] The purpose of the present invention is to provide a method for resource treatment of cold rolling sludge. The method provided by the present invention uses methanol as raw material, uses a small amount of chemical reagents, and has a simple treatment method, thereby achieving harmless and resourceful utilization of cold rolling sludge.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for resource processing of cold rolling sludge, comprising the following steps:

[0008] (1) mixing methanol and cold rolling sludge, and then performing an esterification reaction under supercritical conditions to obtain a solid-liquid mixture;

[0009] (2) subjecting the solid-liquid mixture obtained in step (1) to solid-liquid separation to obtain iron filings and a liquid phase;

[0010] (3) removing methanol from the liquid phase obtained in step (2) and then extracting to obtain an oil phase product and an aqueous phase product.

[0011] Preferably, in step (1), the mass ratio of methanol to cold-rolled sludge is (4-19):1.

[0012] Preferably, the supercritical condition in step (1) is to heat the mixture of methanol and cold rolling sludge in a closed reactor and then keep it warm.

[0013] Preferably, the insulation temperature is 250-325° C., and the insulation time is 15-60 min.

[0014] Preferably, the heating rate of the heating is 2-4°C / min.

[0015] Preferably, the esterification reaction in step (1) is carried out under an inert atmosphere.

[0016] Preferably, the solid-liquid separation in step (2) is vacuum filtration separation.

[0017] Preferably, after the solid-liquid separation in step (2), the solid phase obtained by the solid-liquid separation is washed and dried to obtain iron filings.

[0018] Preferably, the method for removing methanol in step (3) is rotary evaporation.

[0019] Preferably, the extraction agent in step (3) is dichloromethane.

[0020] The present invention provides a method for resource processing of cold rolling sludge, comprising the following steps: (1) mixing methanol and cold rolling sludge, and then performing an esterification reaction under supercritical conditions to obtain a solid-liquid mixture; (2) performing solid-liquid separation on the solid-liquid mixture obtained in step (1) to obtain iron filings and a liquid phase; (3) removing methanol from the liquid phase obtained in step (2) and then extracting to obtain an oil phase product and a water phase product. The present invention utilizes the characteristics of low hydrogen bonding degree, low dielectric constant, and strong reactivity of methanol in a supercritical state, so that the fatty acids at the interfaces of oil-water, oil-solid, oil-water-solid, etc. in the cold rolling sludge are all esterified with methanol to generate fatty acid methyl esters, and at the same time, the strong solubility of methanol in a supercritical state is utilized to dissolve the fatty acid methyl esters in methanol, and due to the hydrophobicity and FeO2 repellency of the fatty acid methyl esters, the fatty acid methyl esters are soluble in the methanol. x The properties of the cold-rolled sludge are reduced, resulting in the reduction of the interfacial forces of oil-water, oil-solid, oil-water-solid, etc. in the cold-rolled sludge, the destruction of the interfacial structure, and the aggregation of droplets. After a simple solid-liquid separation, a high-grade iron scrap and a liquid phase composed of oil-water can be obtained, and then the oil-water separation is achieved by extraction, so that the oil, water, and solid phases in the cold-rolled sludge are separated. The results of the embodiment show that the resource treatment method of the cold-rolled sludge provided by the present invention can separate the water, oil, and solid phases of the cold-rolled sludge, wherein the oil phase yield can reach 47.23%, the calorific value is 38.14MJ / kg, and can be used as fuel; the solid phase is iron scraps with a grade of 59.89%, which are reused as iron ore; the water phase does not need to be further treated and can be directly discharged as industrial wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the process of resource recovery of cold rolling sludge in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] All raw materials of the present invention have no particular limitation on their sources and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0023] There is no particular restriction on the purity of all raw materials in the present invention, and industrial pure raw materials are preferably used in the present invention.

[0024] The present invention provides a method for resource processing of cold rolling sludge, comprising the following steps:

[0025] (1) mixing methanol and cold rolling sludge, and then performing an esterification reaction under supercritical conditions to obtain a solid-liquid mixture;

[0026] (2) subjecting the solid-liquid mixture obtained in step (1) to solid-liquid separation to obtain iron filings and a liquid phase;

[0027] (3) removing methanol from the liquid phase obtained in step (2) and then extracting to obtain an oil phase product and an aqueous phase product.

[0028] The invention mixes methanol with cold rolling sludge, performs esterification reaction under supercritical conditions, and obtains a solid-liquid mixture.

[0029] The present invention has no special requirements for the source of the cold rolling sludge, and any sludge produced by the cold rolling process of steel can be used. In an embodiment of the present invention, the cold rolling sludge comes from the cold rolling process of a large domestic steel enterprise. The appearance of the cold rolling sludge is dark black and viscous. Microscopic observation shows that the interior as a whole presents an oil-in-water (W / O) structure. The continuous oil phase wraps the solid iron filings particles and emulsified water droplets. The three phases of oil, water and solid are intertwined and highly emulsified, and the emulsified water droplets are almost spherical. The mass fractions of the three phases of oil, water and solid in the cold rolling sludge are 47.28%, 27.15% and 25.57%, respectively. The oil phase in the cold rolling sludge is mainly long-chain fatty acids such as palmitic acid, oleic acid, and stearic acid, accounting for as high as 82.772%, and the sum of the mass fractions of C, H, and O elements in the oil phase is 99.82%, which has a very high calorific value; the solid phase in the cold rolling sludge is mainly Fe 3 O 4 and metallic Fe, accounting for 95.782%, which can be reused as fine iron ore.

[0030] The present invention adds methanol to the cold rolling sludge, utilizes the characteristics of methanol in a supercritical state to react with the oil in the cold rolling sludge to produce fatty acid methyl ester, and dissolves the fatty acid methyl ester in the supercritical methanol. x It can reduce the interfacial forces of oil-water, oil-solid, oil-water-solid, etc. in cold rolling sludge, and the droplets can aggregate. After simple solid-liquid separation, high-grade iron chips and a liquid phase composed of oil and water can be obtained, and the methanol in the liquid phase can be recovered and reused.

[0031] In the present invention, the mass ratio of methanol to cold rolling sludge is preferably (4-19):1, more preferably (8-19):1, and further preferably (12-19):1. In the present invention, the greater the mass ratio of methanol to cold rolling sludge, the more conducive it is for the oil phase in the cold rolling sludge to undergo esterification reaction with methanol, and for the oil phase to be dissolved in methanol, thereby promoting solid-liquid separation; however, too much methanol will cause excessive energy consumption in subsequent methanol recovery. In the present invention, the mass ratio of methanol to cold rolling sludge is limited to the above range, which can not only realize the resource utilization of the oil phase in the cold rolling sludge, but also take into account the energy consumption of methanol recovery.

[0032] In the present invention, the supercritical condition is preferably to heat the mixture of methanol and cold rolling sludge in a closed reactor and then keep it warm. The present invention has no special requirements for the closed reactor, as long as it meets the requirements of the supercritical condition. The present invention is preferably a high-pressure reactor.

[0033] In the present invention, the insulation temperature is preferably 250-325° C., more preferably 275-300° C. The present invention heats methanol in a closed reactor to achieve a supercritical state. Within the above temperature range, methanol is conducive to reaching a supercritical state without causing excessive energy consumption.

[0034] In the present invention, the insulation time is preferably 15 to 60 minutes, more preferably 30 to 45 minutes. During the above time, the oil phase in the cold-rolled sludge fully undergoes esterification reaction with methanol, which is beneficial to improving the yield of the oil phase.

[0035] In the present invention, the heating rate is preferably 2-4°C / min. Within the above heating rate range, both the reaction rate and the reaction stability of the esterification reaction are taken into consideration.

[0036] In the present invention, the esterification reaction is preferably carried out under an inert atmosphere. The inert atmosphere is preferably a nitrogen atmosphere. In the present invention, after adding the mixture of methanol and cold-rolled sludge into the autoclave, nitrogen is introduced into the autoclave to purge and discharge the air in the autoclave, so that the autoclave forms a nitrogen atmosphere. In the present invention, the nitrogen atmosphere is preferably at normal pressure.

[0037] In the present invention, the esterification reaction is preferably carried out under stirring, the stirring rate is preferably 60-300 r / min, and the stirring device is preferably a stirring paddle. Stirring can make the cold rolling sludge fully contact and react with methanol, which is beneficial to improve the oil phase yield.

[0038] Supercritical methanol has special physical and chemical properties such as low dielectric constant, weak hydrogen bonding, high reactivity, and strong solubility. It can quickly react with higher fatty acids in the oil phase of cold rolling sludge to produce high-value biodiesel - fatty acid methyl esters. It can also act as a hydrogen donor, which helps stabilize free radicals to reduce the repolymerization of intermediate products. Its strong solubility can be used to dissolve the product fatty acid methyl esters into liquid products to prevent coke formation. In addition, supercritical methanol has a low dielectric constant and strong solubility, which can promote the dissolution of organic matter and reaction products in steel rolling sludge into methanol, avoiding the product from forming a new emulsified structure with water and solids, thereby destroying the stable emulsified structure of steel rolling sludge. In addition, iron oxide (FeO x )'s Fe3d orbital Lewis acid iron sites and water are easily ionized under subcritical conditions, and the hydronium ions (H 3 O + ) can be used as catalysts for the esterification reaction of supercritical methanol and higher fatty acids, further improving the reaction rate of supercritical methanol and higher fatty acids in the oil phase of steel rolling sludge.

[0039] After the esterification reaction is completed, the present invention preferably uses methanol to clean the high-pressure reactor and the stirring blade, and the obtained cleaning liquid is combined with the product of the esterification reaction as a solid-liquid mixture.

[0040] After obtaining the solid-liquid mixture, the present invention performs solid-liquid separation on the solid-liquid mixture to obtain iron filings and a liquid phase.

[0041] In the present invention, the solid-liquid separation is preferably vacuum filtration separation. The present invention has no special requirements for the specific conditions of the vacuum filtration, as long as the solid phase and the liquid phase can be separated well. Vacuum filtration separation has simple equipment requirements, is easy to operate, and is suitable for industrial-scale use.

[0042] The present invention preferably washes and dries the solid phase obtained by the solid-liquid separation to obtain iron filings. The present invention has no particular requirements for the specific drying method, as long as the methanol on the surface of the iron filings can be removed. The present invention preferably dries, and the drying temperature is preferably 100-110°C.

[0043] After obtaining the liquid phase, the present invention removes methanol from the liquid phase and then performs extraction to obtain an oil phase product and a water phase product.

[0044] In the present invention, the method for removing methanol is preferably rotary evaporation. The present invention has no special requirements on the specific conditions of the rotary evaporation, as long as the methanol in the liquid phase can be separated and recovered.

[0045] In the present invention, the extractant of the extraction is preferably dichloromethane. The present invention uses dichloromethane to extract the liquid phase obtained by the solid-liquid separation, so that the oil phase substances such as fatty acid methyl esters are dissolved in dichloromethane, and the water-soluble substances such as inorganic salts are dissolved in water, so as to achieve the separation of the oil phase and the water phase.

[0046] In the present invention, the volume ratio of the extractant to the liquid phase obtained after the methanol removal is preferably (1-3): 1. The more the amount of the extractant is used, the better the separation effect of the oil phase and the water phase, but the subsequent recovery cost of the extractant will increase or decrease. The present invention limits the amount of the extractant to the above range, which has both a good extraction effect and a consideration of the recovery cost of the extractant.

[0047] After the extraction is completed, the present invention preferably separates the product obtained by the extraction to obtain an extraction solution and an aqueous phase product, and then removes the extractant from the extraction solution to obtain an oil phase product.

[0048] In the present invention, when the extractant is dichloromethane, the obtained extraction solution is a dichloromethane solution; the dichloromethane solution is subjected to rotary evaporation to remove dichloromethane to obtain an oil phase product. The present invention has no special requirements for the specific conditions of the rotary evaporation, as long as the dichloromethane can be separated and recovered.

[0049] The present invention utilizes the characteristics of low hydrogen bonding degree, low dielectric constant and strong reactivity of methanol in a supercritical state, so that the fatty acids at the interfaces of oil-water, oil-solid, oil-water-solid, etc. in the cold rolling sludge undergo esterification reaction with methanol to generate fatty acid methyl esters, and at the same time utilizes the strong solubility of supercritical methanol to dissolve the fatty acid methyl esters in methanol. x The properties of the cold-rolled sludge result in the reduction of the interfacial forces between oil and water, oil and solid, and oil and water and solid in the cold-rolled sludge, the destruction of the interfacial structure, and the aggregation of droplets. After a simple solid-liquid separation, high-grade iron filings and a liquid phase composed of oil and water can be obtained, and then the oil-water separation is achieved through extraction, so that the oil, water and solid three phases in the cold-rolled sludge are separated, realizing the resource treatment of the cold-rolled sludge.

[0050] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] Example 1

[0052] A method for resource processing of cold rolling sludge, the flow diagram is as follows Figure 1 , the specific steps are as follows:

[0053] (1) Weigh 6.97 g of cold-rolled oil sludge into a beaker, and then add methanol into the beaker at a mass ratio of 5.66:1 to obtain a mixture;

[0054] (2) Add the mixture into the autoclave, start stirring at a speed of 300 rpm, use nitrogen to exhaust the air in the autoclave, raise the temperature to 275°C at a rate of 3°C / min, and maintain the temperature for 30 minutes to carry out the esterification reaction. After the reaction is completed, the autoclave is cooled to room temperature with the furnace, and the cooled mixed solution is poured into a beaker. At the same time, 15 mL of methanol is used to clean the inside of the autoclave and the stirring paddle, and the cleaning solution is also poured into the beaker;

[0055] (3) The mixed solution in the beaker is filtered with vacuum filter paper, and the filter residue is washed with 5 mL of methanol to obtain a filtrate and a filter residue; the filter residue is dried at 105° C. for 5 h to obtain 2.40 g of residue, which is iron filings;

[0056] (4) removing methanol from the filtrate by rotary evaporation at 50°C for 30 min to obtain an aqueous oil phase;

[0057] (5) Add 100 mL of dichloromethane to the aqueous oil phase and separate the phases in a separatory funnel. The upper layer is the aqueous phase product and the lower layer is the dichloromethane solution.

[0058] (6) The lower layer of dichloromethane solution was rotary evaporated at 50°C for 30 min to remove dichloromethane to obtain 3.29 g of oil phase product.

[0059] Example 2

[0060] Same as Example 1, except that the esterification reaction temperature is 250°C.

[0061] Example 3

[0062] Same as Example 1, except that the esterification reaction temperature is 300°C.

[0063] Example 4

[0064] Same as Example 1, except that the esterification reaction temperature is 325°C.

[0065] Comparative Example 1

[0066] Same as Example 1, except that the esterification reaction temperature is 200°C.

[0067] Example 5

[0068] Same as Example 1, except that the mass ratio of methanol to cold rolling sludge is 19:1.

[0069] Example 6

[0070] Same as Example 1, except that the mass ratio of methanol to cold rolling sludge is 9:1.

[0071] Example 7

[0072] Same as Example 1, except that the mass ratio of methanol to cold rolling sludge is 4:1.

[0073] Example 8

[0074] Same as Example 1, except that the mass ratio of methanol to cold rolling sludge is 3:1.

[0075] Example 9

[0076] Same as Example 1, except that the esterification reaction time is 15 min.

[0077] Example 10

[0078] Same as Example 1, except that the esterification reaction time is 45 min.

[0079] Embodiment 11

[0080] Same as Example 1, except that the esterification reaction time is 5 min.

[0081] The iron filings obtained in the embodiment and the comparative example were subjected to a grade test (Determination of total iron content of iron ore by titanium trichloride reduction method GB / T 6730.5-2007), and the oil phase product was subjected to a calorific value test (Separated two-stage hydrothermal liquefaction of livestock manure for high-quality bio-oil with low-nitrogen content: Insights on nitrogen migration and evolution, Chemical Engineering Journal 477 (2023) 146999), and the test data are recorded in Table 1.

[0082] Table 1 Performance test record of cold rolling sludge resource products

[0083]

[0084]

[0085] It can be seen from Examples 1 to 4 and Comparative Example 1 that when the system temperature is not enough to make methanol reach a supercritical state, the oil phase yield and the oil phase calorific value are both low; when the system temperature makes methanol reach a supercritical state, the higher the temperature, the higher the oil phase yield and the higher the calorific value of the oil phase, but after the temperature reaches 275°C, the oil phase yield and the oil phase calorific value are slightly reduced if the temperature is continued to increase.

[0086] It can be seen from Examples 5 to 8 that the higher the mass ratio of methanol to cold-rolled sludge, the higher the oil phase yield and the oil phase calorific value. However, when the mass ratio of methanol to cold-rolled sludge reaches 5.66:1, the oil phase yield and the oil phase calorific value both increase if the ratio of methanol is further increased. However, too low cold-rolled sludge will lead to a decrease in treatment efficiency.

[0087] It can be seen from Examples 1 and 9 to 11 that when the esterification reaction time is too short and the esterification reaction is incomplete, the oil phase yield and the oil phase calorific value are both low. When the esterification reaction reaches 30 min, the reaction time is further extended, and the oil phase yield and the oil phase calorific value change very little.

[0088] It can be seen from the above embodiments and comparative examples that the present invention utilizes the characteristics of low hydrogen bonding degree, low dielectric constant and strong reactivity of methanol in a supercritical state to separate the oil, water and solid phases in the cold rolling sludge, thereby obtaining an oil phase with higher yield and calorific value, which can be used as fuel; the solid phase is high-grade iron filings, which can be reused as iron ore; the water phase does not need to be further treated and can be directly discharged as industrial wastewater, thereby realizing the resource utilization of cold rolling sludge.

[0089] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for resource processing of cold rolling sludge, comprising the following steps: (1) mixing methanol and cold rolling sludge, and then performing an esterification reaction under supercritical conditions to obtain a solid-liquid mixture; (2) subjecting the solid-liquid mixture obtained in step (1) to solid-liquid separation to obtain iron filings and a liquid phase; (3) removing methanol from the liquid phase obtained in step (2) and then extracting to obtain an oil phase product and an aqueous phase product.

2. The method according to claim 1, characterized in that: In the step (1), the mass ratio of methanol to cold rolling sludge is (4-19):

1.

3. The method according to claim 1, characterized in that The supercritical condition in step (1) is to heat the mixture of methanol and cold rolling sludge in a closed reactor and then keep it warm.

4. The method according to claim 3, characterized in that: The insulation temperature is 250-325° C., and the insulation time is 15-60 minutes.

5. The method according to claim 3, characterized in that: The heating rate is 2-4°C / min.

6. The method according to claim 1, characterized in that The esterification reaction in step (1) is carried out under an inert atmosphere.

7. The method according to claim 1, characterized in that The solid-liquid separation in step (2) is vacuum filtration separation.

8. The method according to claim 1 or 7, characterized in that: After the solid-liquid separation in step (2), the solid phase obtained by the solid-liquid separation is washed and dried to obtain iron filings.

9. The method according to claim 1, characterized in that: The method for removing methanol in step (3) is rotary evaporation.

10. The method according to claim 1, characterized in that The extraction agent used in step (3) is dichloromethane.

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