Process for recycling waste acid in graphene oxide production

Abstract

The invention relates to the field of C01B17 / 00, in particular to a recycling process of waste acid in graphene oxide production, which comprises the following steps: concentrating and desalting waste sulfuric acid generated in the graphene oxide production process through a first-stage evaporation concentration section, a second-stage concentration section, a crystallization separation section and a third-stage concentration section to realize resource recycling. According to the method, the problem that the oxidized graphene is not environmentally friendly in the production process is solved, meanwhile, process design is carried out based on mature engineering experience and detailed experimental data, and the problems that in the waste sulfuric acid concentration process, due to incomplete separation of inorganic salt crystals, a pipeline is blocked, and the concentration of concentrated sulfuric acid is not high are solved. The process is high in automation control level, safe, economical, continuous and reliable operation can be realized, the automation level of waste acid treatment is improved, the labor intensity is reduced, and the market application potential is huge.

Description

Technical Field

[0001] The present invention relates to the field of C01B17 / 00, and in particular to a process for recycling waste acid in graphene oxide production. Background Art

[0002] During the industrial redox production of graphene, large amounts of strong oxidizing acids such as concentrated sulfuric acid, concentrated nitric acid, dichromic acid, and potassium permanganate are required based on process requirements. Although graphene can absorb some oxygen and hydrogen during the reaction, most of these elements exist in the aqueous solution in the form of potassium sulfate and manganese sulfate, generating a large amount of waste acid.

[0003] With respect to the waste sulfuric acid generated in the graphene production process, the existing treatment technologies mainly include (1) utilizing the waste sulfuric acid generated in the graphene production process to produce calcium sulfate whiskers; (2) utilizing the waste sulfuric acid generated in the graphene production process to produce manganese sulfate; and (3) utilizing the waste sulfuric acid generated in the graphene production process to produce ammonium sulfate, potassium sulfate, and Mn3O4 products. CN103696015A discloses a method for treating waste sulfuric acid in the graphene production process. Although the waste sulfuric acid is utilized to obtain calcium sulfate whiskers, the potassium sulfate and manganese sulfate present in large quantities in the waste acid are not effectively removed, and secondary treatment is still required, consuming a large amount of manpower and material resources. Chinese patent CN106986389A discloses a method for preparing manganese sulfate using waste sulfuric acid in the graphite oxide production process. Manganese sulfate crystals are obtained by separating the waste sulfuric acid into solid and liquid, diluting, adding a manganese source material, filtering, etc. However, the potassium sulfate present in large quantities in the waste liquid cannot be effectively removed, which not only causes secondary pollution but also wastes resources.

[0004] Therefore, a process for recycling and reusing waste acid in graphene oxide production is provided. The waste sulfuric acid generated in the graphene oxide production process is concentrated and desalted before being recycled, thereby solving the environmental problem of the graphene oxide production process. At the same time, the process design is carried out based on mature engineering experience and detailed experimental data to solve the problems of pipeline blockage caused by incomplete crystallization and separation of inorganic salts during the waste sulfuric acid concentration process and the low concentration of concentrated sulfuric acid. This has high practical application value. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a process for recycling and reusing waste acid in graphene oxide production. The waste sulfuric acid generated in the graphene oxide production process is concentrated and desalted through a first evaporation and concentration section, a second concentration section, a crystallization separation section, and a third concentration section, thereby realizing resource recovery and reuse.

[0006] As a preferred technical solution, the process for recycling waste acid in graphene oxide production comprises at least the following steps:

[0007] S1. Preheating: The raw acid is pumped into a preheater after being measured by a feed pump, a regulating valve and a flow meter to preheat the raw acid;

[0008] S2, first stage evaporation and concentration: The preheated sulfuric acid enters the first stage concentrating condenser and is indirectly heated by a first stage heater under vacuum conditions to increase the sulfuric acid concentration from 45-50wt% to 60-65wt%. After the first stage evaporation and concentration is completed, the sulfuric acid directly flows into the glass cooler by gravity to exchange heat with the sulfuric acid at the outlet of the second stage concentrator, further utilizing the waste heat and saving energy.

[0009] S3, Secondary Concentration: The 60-65wt% sulfuric acid after heat exchange is sprayed from the middle of the purification tower into the second-stage concentrator for mass and heat transfer with the secondary steam on the tower plate. The overflowed secondary steam is purified by the spray scrubber and then enters the tail gas condenser to condense into secondary condensate with an acid content of less than 1wt%;

[0010] S4, crystallization: The concentrated sulfuric acid containing crystals with a concentration of about 80-85 wt% is pumped into a glass cooler through a high-temperature delivery pump for preliminary cooling, and then into a cooling crystallization kettle for crystallization;

[0011] S5, separation: After the crystallization is completed, the concentrated liquid is sent to the vacuum belt filter by screw conveyor, and the two phases are separated by filtration;

[0012] S6, three-stage concentration: The sulfuric acid separated in step S5 enters the sulfuric acid buffer tank and is pumped into the sulfuric acid heat exchanger through a delivery pump. The sulfuric acid is concentrated to 93-95 wt% through heat exchange and heating.

[0013] As a preferred technical solution, the raw acid in step S1 includes at least 45-50 wt% sulfuric acid, 1.5-2.5 wt% potassium sulfate, and 2.8-3.5 wt% manganese sulfate;

[0014] As a preferred technical solution, the flow rate of the feed pump in step S1 is 20-25m 3 / hr, with a lift of 15-20m; the temperature setting of the first-stage preheater in step S1 includes: controlling the shell side temperature at 95-60°C using hot water, and controlling the tube side temperature at 25°C-55°C using 45wt% H2SO4; the shell material of the first-stage preheater in step S1 is carbon steel, and the tube side material is graphite.

[0015] As a preferred technical solution, the specific settings of the first-stage concentrating condenser in step S2 include: shell-side pressure of -0.05 to -0.08 MPa, tube-side pressure of 0.3 to 0.5 MPa; shell-side temperature is controlled at 80 to 100°C using secondary steam, and tube-side temperature is controlled at 32 to 40°C using circulating cooling water.

[0016] As a preferred technical solution, the specific settings of the first-stage heater in step S2 include: the shell-side pressure is 0.4-0.6 MPa, and the tube-side pressure is -0.06 to -0.075 MPa; the shell-side temperature is controlled at 120-140°C using low-pressure steam, and the tube-side temperature is controlled at 100°C to 110°C using 45-65wt% H2SO4.

[0017] As a preferred technical solution, in step S2, a non-powered circulating evaporation system is used in the first stage heater for evaporation, the system has a low negative pressure, and the evaporation temperature is ≥120°C, which reduces both energy consumption and equipment investment; preferably, the heating equipment in the first stage heater in step S2 adopts a graphite round block hole reboiler, the evaporation chamber is enameled, a purification demister is provided on the top, and a DN200mm circulation port and a drain port are provided on the bottom; preferably, the acid content of the secondary steam condensate during the first stage evaporation and concentration process does not exceed 0.5%;

[0018] Through an evaporation and concentration section, the sulfuric acid concentration is concentrated to 60-65wt%. At this stage, the inorganic salts in the sulfuric acid have not reached saturation, crystallized salts have not precipitated, the sulfuric acid has good fluidity in the equipment, and convection circulation is used for concentration.

[0019] As a preferred technical solution, the specific steps of the second-stage concentration in step S3 are as follows: the 60-65wt% sulfuric acid after heat exchange is sprayed from the middle of the purification tower into the second-stage concentrator and performs mass and heat transfer with the secondary steam on the tower plate; the superheated steam forms a high-temperature, low-pressure steam mist in the injection pipe and is fully mixed with the acid in the evaporator below the sulfuric acid liquid level in the second-stage concentrator to perform mass and heat transfer; a large amount of water vapor forms low-speed bubbles through the porous structure injection pipe and is sprayed into the sulfuric acid solution, and overflows from the sulfuric acid vapor-liquid interface and carries out water in the sulfuric acid to achieve the purpose of concentration; a large number of low-speed bubbles stir the solution, avoid the risk of sulfate crystallization and scaling, and greatly improve the stability of the concentration and desalination process; the injection pipe is made of forged tantalum material with good high-temperature corrosion resistance.

[0020] As a preferred technical solution, the specific settings of the purification tower in step S3 include: a pressure of -0.06 to -0.09 MPa, and a temperature controlled by secondary steam at 100°C to 50°C.

[0021] The creative design of the two-stage concentration process in the present application effectively prevents crystallization blockage. First, the heating method in the two-stage concentration process is adopted. The two-stage concentration is carried out by superheated steam jet heating. A large amount of water vapor forms low-speed bubbles through the porous structure of the injection pipe and is sprayed into the sulfuric acid solution. It flashes and overflows from the sulfuric acid vapor-liquid interface and carries out the water in the sulfuric acid to achieve the purpose of concentration. A large number of low-speed bubbles stir the solution in all directions without dead angles. The sulfate crystals precipitated in the sulfuric acid form a suspension with the sulfuric acid, which is not easy to settle and form accumulation and blockage, thereby avoiding the risk of sulfate crystallization and scaling, and greatly improving the stability of the concentration and desalination process. Secondly, the equipment structure: the secondary steam generated by the evaporation of sulfuric acid enters the azeotropic distillation tower and further transfers mass and heat with the 60-65wt% sulfuric acid delivered from the first concentrator on the tower plates, reducing the temperature and sulfuric acid content of the secondary steam and maximizing heat utilization. A high-temperature circulating pump is used to continuously transport the concentrated liquid to the glass cooler at the bottom of the evaporation chamber to promptly transfer the crystals in the concentrator. The azeotropic distillation tower is designed with structured packing in the upper half and specially designed PTFE sieve plates in the lower half, ensuring effective mass and heat transfer while avoiding the risk of crystallization clogging the packing.

[0022] As a preferred technical solution, the crystallization process in the crystallization kettle is an intermittent operation, the pressure during the intermittent operation is normal pressure, the stirring speed is 10-20rpm, and the cooling time is 1-2h. In the present application, the glass cooler tube diameter is large, there is no dead angle, and the crystallized material will not produce a blockage phenomenon under the action of the pump. The particle size of the sulfate crystallization is controlled by controlling the stirring speed and the cooling time under normal pressure, avoiding rapid cooling or excessively high temperature to cause incomplete sulfate crystallization, and the particles are too small to be difficult to filter, so that the generated sulfate crystal form is reasonable and of appropriate size, which is convenient for subsequent filtration operation.

[0023] As a preferred technical solution, the three-stage concentration in step S6 is specifically as follows: the separated sulfuric acid enters the sulfuric acid buffer tank and is pumped into the sulfuric acid heat exchanger through a delivery pump. The finished acid is then heated to 95-105° C. by a high-temperature heat exchanger, and then enters the sulfuric acid heater to 140-160° C., and then enters the sulfuric acid scrubber, where the sulfuric acid is heated to 93-95wt% by a tantalum tube heater. The vacuum system uses a steam jet pump to increase the negative pressure, and the tail gas is subjected to three-stage condensation treatment. The condensed water enters the condensate tank for collection, enters the subsequent process, and is treated in a water treatment station before being discharged.

[0024] As a preferred technical solution, in step S6, two sulfuric acid buffer tanks are configured for switching. The volume of the sulfuric acid buffer tanks is designed based on the temporary storage time exceeding 24 hours, in which case a large amount of potassium sulfate crystals will be deposited at the bottom of the finished acid tank. In step S6, two delivery pumps are configured: one for transporting the bottom sediment layer to the raw material feeding and mixing process, and one for transporting the material from the top to the recycling process.

[0025] As a preferred technical solution, each device in the process for recycling and reusing waste acid in graphene oxide production is provided with a quick cleaning port, which is convenient for steam or compressed air blowing and cleaning during shutdown maintenance, and the cleaning can be achieved conveniently and quickly within 1-2 hours.

[0026] Beneficial effects:

[0027] 1. The present invention provides a process for recycling and reusing waste acid in graphene oxide production. By concentrating and desalting the waste sulfuric acid generated in the graphene oxide production process and then recycling it, the environmental problem of the graphene oxide production process is solved. At the same time, based on mature engineering experience and detailed experimental data, the process design is carried out to solve the problems of pipeline blockage caused by incomplete crystallization and separation of inorganic salts during the concentration process of waste sulfuric acid, and the low concentration of concentrated sulfuric acid.

[0028] 2. The processing capacity of the waste acid recovery and reuse process in graphene oxide production provided by the present invention is 1 T / h, the sulfuric acid output is 0.45-0.55 T / h, the concentration of the concentrated sulfuric acid is 93-95wt%, and the sulfate output is 0.016-0.02 T / h.

[0029] 3. The recycling and reuse process of waste acid in graphene oxide production provided by the present invention uses mature and efficient equipment to improve energy utilization, so as to minimize the operating energy consumption of the system. The equipment is resistant to acid corrosion and has low equipment loss. At the same time, the cleaning water in each process uses the system outlet water, which greatly reduces the consumption of new industrial water and is highly efficient and energy-saving.

[0030] 4. The recycling and reuse process of waste acid in graphene oxide production provided by the present invention has a high level of automation control, can achieve safe, economical, continuous and reliable operation, improve the automation level of waste acid treatment, reduce labor intensity, and has huge market application potential. DETAILED DESCRIPTION

[0031] Example 1

[0032] Example 1 of the present invention provides a process for recycling and reusing waste acid in graphene oxide production. The waste sulfuric acid generated in the graphene oxide production process is concentrated and desalted through a first evaporation and concentration section, a second concentration section, a crystallization separation section, and a third concentration section, thereby achieving resource recovery and reuse.

[0033] The process for recycling waste acid in graphene oxide production comprises the following steps:

[0034] S1. Preheating: The raw acid is pumped into a preheater after being measured by a feed pump, a regulating valve and a flow meter to preheat the raw acid;

[0035] S2, first-stage evaporation and concentration: The preheated sulfuric acid enters the first-stage concentrator and is indirectly heated by a first-stage heater under vacuum conditions to increase the sulfuric acid concentration from 48wt% to 60wt%. After the first-stage evaporation and concentration, the sulfuric acid directly flows into a glass cooler by gravity to exchange heat with the sulfuric acid at the outlet of the second-stage concentrator, further utilizing the waste heat and saving energy.

[0036] S3, Secondary Concentration: The 60wt% sulfuric acid after heat exchange is sprayed from the middle of the purification tower into the second-stage concentrator for mass and heat transfer with the secondary steam on the tower plate. The overflowed secondary steam is purified by the spray scrubber and then enters the tail gas condenser to condense into secondary condensate with an acid content of less than 1wt%;

[0037] S4, crystallization: The concentrated sulfuric acid containing crystals with a concentration of about 80 wt% is pumped into a glass cooler through a high-temperature delivery pump for preliminary cooling, and then into a cooling crystallization kettle for crystallization;

[0038] S5, separation: After the crystallization is completed, the concentrated liquid is sent to the vacuum belt filter by screw conveyor, and the two phases are separated by filtration;

[0039] S6, three-stage concentration: The sulfuric acid separated in step S5 enters the sulfuric acid buffer tank and is pumped into the sulfuric acid heat exchanger through a delivery pump. The sulfuric acid is concentrated to 95 wt% through heat exchange and heating.

[0040] In step S1, the raw acid comprises 48 wt% sulfuric acid, 1.9 wt% potassium sulfate, and 3.2 wt% manganese sulfate;

[0041] The flow rate of the feed pump in step S1 is 25m 3 / hr, with a lift of 20m; the temperature setting of the first-stage preheater in step S1 includes: the shell side temperature is controlled at 95°C using hot water, and the tube side temperature is controlled at 40°C using 45wt% H2SO4; the shell material of the first-stage preheater in step S1 is carbon steel, and the tube side material is graphite.

[0042] The specific settings of the first-stage concentrating condenser in step S2 include: shell side pressure of -0.06 MPa, tube side pressure of 0.4 MPa; shell side temperature is controlled at 100° C. using secondary steam, and tube side temperature is controlled at 40° C. using circulating cooling water.

[0043] The specific settings of the first stage heater in step S2 include: the shell side pressure is 0.4 MPa, the tube side pressure is -0.07 MPa; the shell side temperature is controlled at 140°C using low-pressure steam, and the tube side temperature is controlled at 100°C using 60wt% H2SO4.

[0044] In step S2, a non-powered circulating evaporation system is used in the first stage heater for evaporation, the system is low negative pressure, and the evaporation temperature is 120° C.; the heating equipment in the first stage heater in step S2 is a graphite round block hole reboiler, the evaporation chamber is enameled, a purification demister is provided on the top, and a DN200mm circulation port and a drain port are provided on the bottom; the acid content of the secondary steam condensate during the first stage evaporation and concentration process is 0.2%;

[0045] The specific steps of the second-stage concentration in step S3 are as follows: the 60wt% sulfuric acid after heat exchange is sprayed from the middle of the purification tower into the second-stage concentrator and undergoes mass and heat transfer with the secondary steam on the tower plate; the superheated steam forms a high-temperature, low-pressure steam mist in the injection pipe and is fully mixed with the acid in the evaporator below the sulfuric acid liquid level in the second-stage concentrator to undergo mass and heat transfer; a large amount of water vapor forms low-speed bubbles through the porous structure injection pipe and is sprayed into the sulfuric acid solution, and overflows from the sulfuric acid vapor-liquid interface to remove water in the sulfuric acid, thereby achieving the purpose of concentration; a large number of low-speed bubbles stir the solution, avoiding the risk of sulfate crystallization and scaling, and greatly improving the stability of the concentration and desalination process; the injection pipe is made of forged tantalum material, which has good high-temperature corrosion resistance.

[0046] The specific settings of the purification tower in step S3 include: a pressure of -0.09 MPa, and a temperature controlled at 100° C. using secondary steam.

[0047] The crystallization process in the crystallization kettle is an intermittent operation. The pressure during the intermittent operation is normal pressure, 15 rpm, and the cooling time is 1.5 h.

[0048] The three-stage concentration in step S6 is specifically as follows: the separated sulfuric acid enters the sulfuric acid buffer tank and is pumped into the sulfuric acid heat exchanger through a delivery pump. The finished acid is then heated to 100° C. by a high-temperature heat exchanger. The sulfuric acid then enters the sulfuric acid heater to 150° C. and enters the sulfuric acid scrubber. The sulfuric acid is heated to 95% by weight by a tantalum tube heater. The vacuum system uses a steam jet pump to increase the negative pressure. The tail gas undergoes three-stage condensation treatment. The condensed water enters the condensate tank for collection, enters the subsequent process, and is treated in a water treatment station before being discharged.

[0049] In step S6, two sulfuric acid buffer tanks are configured for switching. The volume of the sulfuric acid buffer tanks is designed based on the temporary storage time exceeding 24 hours. In this case, a large amount of potassium sulfate crystals will be deposited at the bottom of the finished acid tank. In step S6, two delivery pumps are configured: one for transporting the bottom sediment layer to the raw material feeding and mixing process, and one for transporting the material from the top to the recycling process.

[0050] In the process for recycling and reusing waste acid in graphene oxide production, each device is provided with a quick cleaning port, which is convenient for steam or compressed air blowing and cleaning during shutdown maintenance, and the cleaning can be achieved conveniently and quickly within 1 hour.

[0051] After 1T of waste acid generated in graphene production was treated for 1 hour by the above-mentioned waste acid recovery and reuse process in graphene oxide production, 473 kg of 95% sulfuric acid, 511 kg of water (acidic), and 16 kg of sulfate were produced.

Claims

1. A process for recycling waste acid in graphene oxide production, characterized in that: The waste sulfuric acid generated in the graphene oxide production process is concentrated and desalted through a first evaporation concentration section, a second concentration section, a crystallization separation section, and a third concentration section.

2. The process for recycling waste acid in graphene oxide production according to claim 1, wherein: The process for recycling waste acid in graphene oxide production comprises at least the following steps: S1. Preheating: The raw acid is pumped into a preheater after being measured by a feed pump, a regulating valve and a flow meter to preheat the raw acid; S2, first stage evaporation and concentration: The preheated sulfuric acid enters the first stage concentrating condenser and is indirectly heated by a first stage heater under vacuum conditions to increase the sulfuric acid concentration from 45-50wt% to 60-65wt%. After the first stage evaporation and concentration is completed, the sulfuric acid directly flows into the glass cooler by gravity to exchange heat with the sulfuric acid at the outlet of the second stage concentrator, further utilizing the waste heat and saving energy. S3, Secondary Concentration: The 60-65wt% sulfuric acid after heat exchange is sprayed from the middle of the purification tower into the second-stage concentrator for mass and heat transfer with the secondary steam on the tower plate. The overflowed secondary steam is purified by the spray scrubber and then enters the tail gas condenser to condense into secondary condensate with an acid content of less than 1wt%; S4, crystallization: The concentrated sulfuric acid containing crystals with a concentration of about 80-85 wt% is pumped into a glass cooler through a high-temperature delivery pump for preliminary cooling, and then into a cooling crystallization kettle for crystallization; S5, separation: After the crystallization is completed, the concentrated liquid is sent to the vacuum belt filter by screw conveyor, and the two phases are separated by filtration; S6, three-stage concentration: The sulfuric acid separated in step S5 enters the sulfuric acid buffer tank and is pumped into the sulfuric acid heat exchanger through a delivery pump. The sulfuric acid is concentrated to 93-95 wt% through heat exchange and heating.

3. The process for recycling waste acid in graphene oxide production according to claim 2, wherein: The raw acid in step S1 at least includes 45-50 wt% of sulfuric acid, 1.5-2.5 wt% of potassium sulfate, and 2.8-3.5 wt% of manganese sulfate.

4. The process for recycling waste acid in graphene oxide production according to claim 2, wherein: The temperature setting of the first stage preheater in step S1 includes: controlling the shell side temperature at 95-60°C using hot water, and controlling the tube side temperature at 25-55°C using 45wt% H2SO4.

5. The process for recycling waste acid in graphene oxide production according to claim 2, wherein: The specific settings of the first-stage concentrating condenser in step S2 include: shell side pressure of -0.05 to -0.08 MPa, tube side pressure of 0.3 to 0.5 MPa; shell side temperature controlled at 80 to 100° C. by secondary steam, and tube side temperature controlled at 32 to 40° C. by circulating cooling water.

6. The process for recycling waste acid in graphene oxide production according to claim 2, wherein: The specific settings of the first stage heater in step S2 include: the shell side pressure is 0.4-0.6MPa, the tube side pressure is -0.06~-0.075MPa; the shell side temperature is controlled at 120-140℃ using low-pressure steam, and the tube side temperature is controlled at 100℃~110℃ using 45-65wt% H2SO4.

7. The process for recycling waste acid in graphene oxide production according to claim 2, wherein: The specific settings of the purification tower in step S3 include: a pressure of -0.06 to -0.09 MPa, and a temperature controlled by secondary steam at 100° C. to 50° C.

8. The process for recycling waste acid in graphene oxide production according to claim 2, wherein: The crystallization process in the crystallization kettle is an intermittent operation. During the intermittent operation, the pressure is normal pressure, the stirring speed is 10-20 rpm, and the cooling time is 1-2 hours.

9. The process for recycling waste acid in graphene oxide production according to claim 2, wherein: The three-stage concentration in step S6 is specifically as follows: the separated sulfuric acid enters the sulfuric acid buffer tank and is pumped into the sulfuric acid heat exchanger through a delivery pump. The finished acid is then heated to 95-105° C. by using a high-temperature heat exchanger. The sulfuric acid then enters the sulfuric acid heater to 140-160° C. and enters the sulfuric acid scrubber. The sulfuric acid is heated to 93-95% by weight by using a tantalum tube heater. The vacuum system uses a steam jet pump to increase the negative pressure. The tail gas undergoes three-stage condensation treatment. The condensed water enters the condensate tank for collection, enters the subsequent process, and is treated in a water treatment station before being discharged.

10. The process for recycling waste acid in graphene oxide production according to claim 9, characterized in that: In step S6, two sulfuric acid buffer tanks are set to switch, and two delivery pumps are set to switch.