Method for recovering protein from chromium-containing sludge based on subcritical water

Abstract

The invention relates to a method for recovering protein from chromium-containing sludge based on subcritical water, which comprises the following steps: pretreatment: taking chromium-containing sludge, adding normal-temperature water, adding magnesium oxide, adjusting the pH value to 9-10, uniformly stirring, and standing for 3-6 hours; adding into a subcritical water reaction device, adding water, and sealing; raising the temperature to 150 to 200 DEG C within 2 to 3 hours, and then reacting for 60 to 120 minutes; cooling to normal temperature, and filtering by using a 100-150-mesh screen to obtain filtrate, namely protein liquid C hydrolyzed by the chromium-containing sludge, and filter residue, namely hydrolysis residue D; and drying the protein liquid C obtained by hydrolyzing the chromium-containing sludge by using an atomization dryer to obtain the protein powder. The chromium-containing sludge is treated by adopting the subcritical water, so that not only can protein in the chromium-containing sludge be recycled for resource utilization, but also the content of leached chromium in the chromium-containing waste can be reduced, and the environmental harmfulness of the chromium-containing waste is reduced.

Description

Technical Field

[0001] The invention relates to the field of leather wastewater treatment, in particular to a method for recovering protein from chromium-containing sludge based on subcritical water. Background Art

[0002] With increasingly stringent environmental regulations and the increasing awareness of global environmental protection, the leather industry is facing increasing environmental pressure. The national and local governments have issued a series of policies, regulations and development plans, requiring the leather industry to strengthen the treatment and disposal of chromium-containing sludge to prevent pollution to the environment.

[0003] As an inevitable product of the leather production process, chromium sludge contains a large amount of heavy metal chromium and organic matter (such as protein). If it is not properly treated, it will have a serious impact on the environment and ecosystem. At the same time, the protein resources in chromium-containing sludge have certain recycling value.

[0004] At present, the treatment methods of chromium-containing sludge in the leather industry mainly include solvent extraction, alkali precipitation, sludge transport, bioleaching, incineration and safe landfill. However, these methods have their own advantages and disadvantages in practical applications, and there are problems such as incomplete treatment, low resource utilization rate and high cost. For example, although the alkali precipitation method has simple process, mature technology and low investment, it is prone to problems such as incomplete precipitation and difficulty in separation; the incineration method will produce chromium-containing furnace ash, with low resource utilization rate and may cause secondary pollution to the environment. Summary of the invention

[0005] The invention provides a method for recovering protein from chromium-containing sludge based on subcritical water, so as to solve the problem that the existing treatment method for chromium-containing sludge in the leather industry has poor effect and secondary pollution.

[0006] The present invention adopts the following technical solution:

[0007] A method for recovering protein from chromium-containing sludge based on subcritical water comprises the following steps:

[0008] Pretreatment: Take 1000-1200g of chromium-containing sludge, add 80-84g of magnesium oxide to 8-10L of normal temperature water, adjust the pH to 9-10, stir evenly, and let stand for 3-6h to obtain pretreatment solution A;

[0009] Hydrolysis: Add the pretreatment liquid A to the subcritical water reaction device, then add 15-20L of water, and seal it; heat it to 150-200°C in 2-3h, and then react for 60-120min; cool it to room temperature to obtain the chromium-containing sludge hydrolyzate B;

[0010] Filtration: Filter the chromium-containing sludge hydrolyzate B with a 100-150 mesh screen, the filtrate is the protein liquid C of the chromium-containing sludge hydrolysis, and the filter residue is the hydrolysis residue D;

[0011] Drying: The protein liquid C obtained by hydrolyzing the chromium-containing sludge is dried using an atomizing dryer to obtain protein powder.

[0012] Furthermore, the above-mentioned subcritical water refers to water with a pressure below 22.1 MPa, which is heated to a high temperature above 100°C and below the critical temperature of 374°C, and the water body still remains in a liquid state.

[0013] It can be seen from the above description of the present invention that, compared with the prior art, the present invention has the following advantages:

[0014] 1. The treatment method of the present application adds the pretreatment liquid A to a subcritical water reaction device. Subcritical water refers to water heated to a high temperature of 100°C or above and below the critical temperature of 374°C at a pressure below 22.1MPa, and the water body remains in a liquid state. The concentration of H+ and OH- in the water in this state is high, and it has acid-base catalysis function, and the dielectric constant of the water in this state is reduced, which allows the water to dissolve many substances with weaker polarity. Using subcritical water to extract organic matter from substances can have a good effect.

[0015] 2. In the pretreatment of chromium-containing sludge, the present application uses magnesium oxide to adjust the pH value of chromium-containing sludge, which can increase the enrichment of chromium in waste residue and reduce the chromium content of recovered protein; in the process of treating chromium-containing sludge using a subcritical water device, only water, chromium-containing sludge and magnesium oxide need to be added. There are few reactants, the process is simple, and no secondary pollution will be generated.

[0016] 3. In the present application, all protein substances in the chromium-containing sludge can be recovered under the reaction conditions of subcritical water, and the recovery efficiency is high. Moreover, under this condition, all microorganisms in the system can be killed, and the odor in the chromium-containing sludge can be effectively removed.

[0017] 4. The present application adopts subcritical water to treat chromium-containing sludge, which can not only recover the protein in the chromium-containing sludge for its resource utilization, but also reduce the leached chromium content of chromium-containing waste and reduce the environmental hazards of chromium-containing waste. DETAILED DESCRIPTION

[0018] Embodiment 1:

[0019] A method for recovering protein from chromium-containing sludge based on subcritical water comprises the following steps:

[0020] Pretreatment: Take 1200g of chromium-containing sludge, add 10L of normal temperature water, add 84g of magnesium oxide, adjust the pH to 9-10, stir evenly, and let stand for 3h to obtain pretreatment solution A;

[0021] Hydrolysis: Add the pretreatment liquid A into a subcritical water reaction device, then add 20 L of water and seal it; heat it to 150° C. in 2 h, then react for 60 min; cool it to room temperature to obtain the chromium-containing sludge hydrolyzate B.

[0022] Filtration: Filter the chromium-containing sludge hydrolyzate B with a 150-mesh screen. The filtrate is the protein liquid C of the chromium-containing sludge hydrolysis, and the filter residue is the hydrolyzate residue D.

[0023] Drying: The protein liquid C obtained by hydrolyzing the chromium-containing sludge is dried using an atomizing dryer to obtain protein powder.

[0024] The above-mentioned subcritical water refers to water with a pressure below 22.1MPa, which is heated to a high temperature above 100°C and below the critical temperature of 374°C, and the water body still remains in a liquid state.

[0025] Embodiment 2:

[0026] A method for recovering protein from chromium-containing sludge based on subcritical water comprises the following steps:

[0027] Pretreatment: Take 1000g of chromium-containing sludge, add 8L of normal temperature water, add 80g of magnesium oxide, adjust the pH to 9-10, stir evenly, and let stand for 6h to obtain pretreatment solution A;

[0028] Hydrolysis: Add the pretreatment liquid A to a subcritical water reaction device, add 15 L of water, and seal it; heat it to 200°C in 2 hours, and then react for 120 minutes; cool it to room temperature to obtain the chromium-containing sludge hydrolyzate B;

[0029] Filtration: Filter the chromium-containing sludge hydrolyzate B with a 100-mesh screen, the filtrate is the protein liquid C of the chromium-containing sludge hydrolysis, and the filter residue is the hydrolysis residue D;

[0030] Drying: The protein liquid C obtained by hydrolyzing the chromium-containing sludge is dried using an atomizing dryer to obtain protein powder.

[0031] In the above Example 1, after testing, the hydrolysis rate of the chromium-containing sludge, the solid content of the protein solution, the molecular weight of the protein powder and the chromium content are respectively:

[0032] Table 1 Detection data of protein recovered from chromium-containing sludge

[0033]

[0034] In the above Example 1, after testing, the leaching chromium contents of chromium-containing sludge and hydrolysis residue before and after subcritical water treatment are respectively:

[0035] Table 2 Comparison of leached chromium content in chromium-containing sludge and hydrolysis residue

[0036]

[0037] Subcritical water reactor: It is a 50L cylindrical pressure vessel that can heat water to room temperature -200℃ and maintain a maximum pressure of 2MPa.

[0038] Testing indicators and methods:

[0039] Hydrolysis rate of chromium-containing sludge:

[0040] Where: W——Hydrolysis rate of chromium-containing sludge (%) m1——Dry mass of chromium-containing sludge (g) m2——Dry mass of hydrolysis residue (g)

[0041] Solid content of protein solution: Take 1L of chromium-containing sludge recovered hydrolyzate and put it into an oven at 105 degrees Celsius for 48 hours. The mass of protein powder obtained is the solid content of the protein solution.

[0042] Molecular weight of protein powder: Gel chromatography (GPC) was used to detect the molecular weight of protein powder.

[0043] Chromium content of protein powder: Take 0.1 g of protein powder, add 20 mL of deionized water, 3 mL of nitric acid and 2 mL of 30% H2O2 for digestion, and determine the chromium content of the sample by ICP method.

[0044] Determination of leachable chromium content of hydrolyzed slag: The leaching toxicity of chromium slag was determined using the standard method, acetate buffer solution method.

[0045] The above is only a specific implementation of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial changes to the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. A method for recovering protein from chromium-containing sludge based on subcritical water, characterized in that: The steps include: Pretreatment: Take 1000-1200g of chromium-containing sludge, add 80-84g of magnesium oxide to 8-10L of normal temperature water, adjust the pH to 9-10, stir evenly, and let stand for 3-6h to obtain pretreatment solution A; Hydrolysis: Add the pretreatment liquid A to the subcritical water reaction device, then add 15-20L of water, and seal it; heat it to 150-200°C in 2-3h, and then react for 60-120min; cool it to room temperature to obtain the chromium-containing sludge hydrolyzate B; Filtration: Filter the chromium-containing sludge hydrolyzate B with a 100-150 mesh screen, the filtrate is the protein liquid C of the chromium-containing sludge hydrolysis, and the filter residue is the hydrolysis residue D; Drying: The protein liquid C obtained by hydrolyzing the chromium-containing sludge is dried using an atomizing dryer to obtain protein powder.

2. A method for recovering protein from chromium-containing sludge based on subcritical water as claimed in claim 1, characterized in that: Subcritical water refers to water with a pressure below 22.1 MPa, which is heated to a high temperature above 100°C and below the critical temperature of 374°C, and the water body remains in a liquid state.

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