Method for resourceful treatment of furfural wastewater

Abstract

The invention discloses a method for resourceful treatment of furfural wastewater, and belongs to the field of industrial wastewater treatment. A method for resourceful treatment of furfural wastewater comprises the following steps: primary neutralization: adding an alkaline substance to neutralize the furfural wastewater until the furfural wastewater is neutral, converting acetic acid in the furfural wastewater into acetate through a neutralization reaction, and fixing acetate; primary evaporation: carrying out evaporation treatment on the furfural wastewater after the primary neutralization reaction by using a wastewater evaporator to obtain an evaporation concentrated solution; double decomposition: adding acid into the evaporation concentrated solution, and decomposing acetate into salt and acetic acid through double decomposition reaction; secondary evaporation: evaporating a product of the double decomposition reaction, and collecting condensate to obtain an acetic acid solution; secondary neutralization: adding an alkaline substance to neutralize the acetic acid solution obtained by secondary evaporation until the acetic acid solution is neutral, and adjusting COD (Chemical Oxygen Demand) to be more than 25000 to serve as a carbon source for biological sewage treatment; and evaporating to obtain an acetate solid as a raw material for preparing an acetic acid or acetone product.

Description

Technical Field

[0001] The present invention relates to the field of industrial wastewater treatment, and particularly to a method for resource treatment of furfural wastewater. Background Art

[0002] During the production process of furfural, a large amount of water is used. The wastewater at the bottom of the primary distillation tower of furfural contains various organic substances such as acetic acid, with a dark yellow or light yellow color, a pungent smell of acetic acid, a strong acidity (pH = 2 - 4), and a high COD value of 48000 - 56000 mg / mL. Currently, furfural plants generally use wastewater evaporators to evaporate the bottom wastewater for recycling. However, the disadvantage of this technology is that acetic acid contained in the furfural wastewater returns to the hydrolysis reactor during the evaporation process at high temperature and pressure, and the acetic acid in the furfural wastewater is not recovered and utilized, resulting in waste of resources. In addition, the original wastewater seriously cokes during evaporation at high temperature and pressure and needs to be cleaned once every more than a month, increasing the operating cost. Therefore, there is an urgent need for a furfural wastewater treatment technology with high treatment efficiency, simple treatment process, and low treatment cost to recover and utilize the acetic acid therein, turn waste into treasure, generate economic benefits, and solve the problem of serious coking of the wastewater evaporator. Summary of the Invention

[0003] In view of the deficiencies of the prior art, the present invention provides a method for resource treatment of furfural wastewater.

[0004] The purpose of the present invention can be achieved by the following technical solutions:

[0005] A method for resource treatment of furfural wastewater, comprising the following steps:

[0006] Primary neutralization: adding an alkaline substance to neutralize the furfural wastewater to neutral, and converting acetic acid in the furfural wastewater into acetate through a neutralization reaction to fix the acetate ion;

[0007] Primary evaporation: using a wastewater evaporator to evaporate the furfural wastewater after the primary neutralization reaction to obtain an evaporation concentrate;

[0008] Double decomposition: adding an acid to the evaporation concentrate, and decomposing the acetate into a salt and acetic acid through a double decomposition reaction;

[0009] Secondary evaporation: evaporating the product of the double decomposition reaction and collecting the condensate to obtain an acetic acid solution;

[0010] Secondary neutralization: adding an alkaline substance to neutralize the acetic acid solution obtained by secondary evaporation to neutral, adjusting the COD to more than 25000 as a carbon source for sewage biological treatment; evaporating to obtain a solid acetate as a raw material for the preparation of acetic acid or acetone products.

[0011] In summary, through a combination of five steps including one-time neutralization, one-time evaporation, decomposition, secondary evaporation, and secondary neutralization, the present invention achieves the effect of decolorizing and purifying furfural wastewater, and prepares a carbon source product or a high-purity acetate product whose appearance and other indicators meet the requirements of sewage biochemical treatment.

[0012] In the first step, the acetate ion is fixed by a one-time neutralization reaction. The furfural wastewater is neutralized to neutral with an alkaline substance, and the acetic acid in the furfural wastewater is converted into acetate through the neutralization reaction to fix the acetate ion. The alkaline substance includes but is not limited to sodium hydroxide, sodium carbonate, calcium hydroxide, calcium carbonate. The acetate ion fixation reaction is shown in formula (1):

[0013] M n+ +n AC - =M(AC) n (1)

[0014] Where n = 1 or 2. When M is a monovalent ion, n = 1; when M is a divalent ion, n = 2.

[0015] In the second step, a concentrated solution is obtained by one-time evaporation. The furfural wastewater after neutralization in the first step is evaporated under high temperature and high pressure using a wastewater evaporator for furfural production. The high temperature and high pressure are 160°C - 190°C, 6 atm - 12.27 atm. The high-temperature and high-pressure steam is input into the hydrolysis kettle to obtain a high-temperature and high-pressure concentrated solution.

[0016] In the third step, acetic acid is released by a double decomposition reaction. Concentrated sulfuric acid is added to the high-temperature and high-pressure concentrated solution obtained in the second step to decompose the acetate in it into sulfate and acetic acid. The general reaction formula is as follows:

[0017] a M X (AC) Y +b H 2 SO 4 = c M Z SO 4 + d HAC (2)

[0018] When M is a monovalent ion, a = d = z = 2, X = Y = b = c = 1; when M is a divalent ion, a = X = b = c = Z = 1, Y = d = 1;

[0019] In the fourth step, a condensate is obtained by secondary evaporation. The concentrated solution after the double decomposition reaction in the third step is input into the evaporator for further evaporation. The evaporation temperature range can be 70 - 190°C and the pressure can be 0.3 atm - 12.27 atm. The evaporated steam is condensed to obtain a colorless and transparent concentrated acetic acid condensate.

[0020] Step 5: Neutralize the concentrated acetic acid condensate obtained in Step 5 by secondary neutralization. The neutralizing reagent and neutralization reaction are the same as in Step 1. Adjust the COD of the condensate after secondary neutralization to be above 25,000, which serves as the carbon source for sewage biochemical treatment. Or evaporate the water in it and then dry it to obtain pure acetate solid products such as calcium acetate, sodium acetate, and potassium acetate. Or heat and decompose the acetate to prepare pure acetone or acetic acid products.

[0021] Advantages of the present invention:

[0022] Compared with the existing method of directly recycling furfural wastewater by high-temperature and high-pressure evaporation in a wastewater evaporator, the present invention uses neutralization, primary evaporation, double decomposition reaction, secondary evaporation, and secondary neutralization to obtain a pure, colorless, and transparent concentrated acetic acid solution, and then prepares various chemical products by modulation. The process has low energy consumption and low investment cost. While solving the serious problem of coking in systems such as wastewater evaporators during furfural production, it by-produces various chemical products, turning waste into treasure, and improving the economic efficiency and environmental protection of the furfural production process. Specific embodiments

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0024] In some embodiments of the present invention, a method for resource treatment of furfural wastewater is disclosed, which specifically may include the following steps:

[0025] Step 1: Fix acetate ions through a primary neutralization reaction

[0026] Neutralize furfural wastewater to neutral with an alkaline substance. Through the neutralization reaction, acetic acid in the furfural wastewater is converted into acetate, fixing the acetate ions, so that in the next evaporation process, the acetate ions exist in the concentrated solution in the form of acetate. The alkaline substance includes but is not limited to sodium hydroxide, sodium carbonate, calcium hydroxide, calcium carbonate. The acetate ion fixation reaction is shown in formula (1):

[0027] M n+ +n AC - =M(AC) n (1)

[0028] Where n = 1 or 2. When M is a monovalent ion, n = 1; when M is a divalent ion, n = 2.

[0029] Step 2: Obtain a concentrated solution through primary evaporation

[0030] The wastewater evaporator used in furfural production evaporates the furfural wastewater after the first - step neutralization under high temperature and high pressure, where the high temperature and high pressure are 160°C - 190°C and 6 atm - 12.27 atm. The high - temperature and high - pressure steam is input into the hydrolysis kettle to obtain a high - temperature and high - pressure concentrated liquid. In this step, the wastewater evaporator of the current furfural production process is coupled with this new process of the invention to avoid additional energy consumption and other cost inputs;

[0031] Step 3: Release acetic acid through double - decomposition reaction

[0032] Concentrated sulfuric acid is added to the high - temperature and high - pressure concentrated liquid obtained in the second step to decompose the acetate therein into sulfate and acetic acid. The reaction general formula is as follows:

[0033] aM X (AC) Y + bH 2 SO 4 = cM Z SO 4 + dHAC (2)

[0034] When M is a monovalent ion, a = d = z = 2, X = Y = b = c = 1;

[0035] When M is a divalent ion, a = X = b = c = Z = 1, Y = d = 1;

[0036] Step 4: Secondary evaporation to obtain condensate

[0037] The concentrated liquid after the double - decomposition reaction in the third step is input into the evaporator for further evaporation. The evaporation temperature range can be 70 - 190°C and the pressure can be 0.3 atm - 12.27 atm. The evaporated steam is condensed to obtain condensate, which is a concentrated acetic acid solution and appears as a colorless and transparent liquid;

[0038] Step 5: Secondary neutralization to prepare chemical products

[0039] The basic substance mentioned above is added to neutralize the concentrated acetic acid in the fourth step to neutrality, adjust the COD to be above 25000, which can be used as a carbon source for sewage biological treatment, or the water in it is evaporated and then dried to obtain pure acetate solid products such as calcium acetate, sodium acetate and potassium acetate, etc., or the acetate is heated and decomposed to prepare pure acetone or acetic acid products.

[0040] Example 1 was operated according to the steps of the present invention. 100 mL of furfural wastewater with a COD of 48,000 was taken, neutralized to neutral with calcium hydroxide, and evaporated at 160 °C and 6 atm. In the laboratory example, the steam was discarded (in actual industrial applications, the steam was returned to the hydrolysis kettle), and 31 mL of concentrated solution was obtained. An appropriate amount of concentrated sulfuric acid was added to the concentrated solution until no more white precipitate was formed. Then, the addition of sulfuric acid was stopped. All the liquid in the concentrated solution was evaporated at 70 °C and 0.3 atm, and the steam was condensed to obtain 29 mL of concentrated acetic acid solution. Calcium hydroxide was added to neutralize it, and the COD content was adjusted to 294,876 to be used as a carbon source product for sewage biochemical treatment.

[0041] Example 2 was operated according to the steps of the present invention. 100 mL of furfural wastewater with a COD of 48,000 was taken, neutralized to neutral with calcium hydroxide, and evaporated at 190 °C and 12.27 atm. In the laboratory example, the steam was discarded (in actual industrial applications, the steam was returned to the hydrolysis kettle), and 32.6 mL of concentrated solution was obtained. An appropriate amount of concentrated sulfuric acid was added to the concentrated solution until no more white precipitate was formed. Then, the addition of sulfuric acid was stopped. All the liquid in the concentrated solution was evaporated at 190 °C and 12.27 atm, and the steam was condensed to obtain 28.5 mL of concentrated acetic acid solution. Calcium hydroxide was added to neutralize it, and the COD content was adjusted to 304,855 to be used as a carbon source product for sewage biochemical treatment.

[0042] Example 3 was operated according to the steps of the present invention. 100 mL of furfural wastewater with a COD of 48,000 was taken, neutralized to neutral with calcium hydroxide, and evaporated at 100.2 °C and 1 atm. In the laboratory example, the steam was discarded (in actual industrial applications, the steam was returned to the hydrolysis kettle), and 30.6 mL of concentrated solution was obtained. An appropriate amount of concentrated sulfuric acid was added to the concentrated solution until no more white precipitate was formed. Then, the addition of sulfuric acid was stopped. All the liquid in the concentrated solution was evaporated at 100.2 °C and 1 atm, and the steam was condensed to obtain 28.8 mL of concentrated acetic acid solution. Calcium hydroxide was added to neutralize it, and the COD content was adjusted to 284,871 to be used as a carbon source product for sewage biochemical treatment.

[0043] In the description of this specification, the descriptions referring to terms such as "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0044] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and what is described in the above embodiments and the specification is only to illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements fall within the scope of the present invention claimed.

Claims

1. A method for recycling furfural wastewater, characterized in that: The following steps are involved: Primary neutralization: adding alkaline substances to neutralize the furfural wastewater to neutrality. Through the neutralization reaction, the acetic acid in the furfural wastewater is converted into acetate, and the acetate ion is fixed; Primary evaporation: using a wastewater evaporator to evaporate the furfural wastewater after the primary neutralization reaction to obtain an evaporation concentrate; Double decomposition: Add acid to the evaporated concentrate to decompose the acetate into salt and acetic acid through double decomposition reaction; Secondary evaporation: evaporate the product of the double decomposition reaction, collect the condensate, and obtain acetic acid solution; Secondary neutralization: add alkaline substances to neutralize the acetic acid solution obtained by secondary evaporation to neutrality, adjust the COD to above 25,000, and use it as a carbon source for sewage biological treatment; evaporate to obtain acetate solid, which is used as a raw material for the preparation of acetic acid or acetone products.

2. The method for recycling furfural wastewater according to claim 1, characterized in that: In the primary evaporation, the evaporation temperature is set to 160-190° C., and the evaporation pressure is set to 6 atm-12.27 atm.

3. The method for recycling furfural wastewater according to claim 1, characterized in that: The alkaline substance in the primary neutralization and / or secondary neutralization is one or more of sodium hydroxide, sodium carbonate, calcium hydroxide and calcium carbonate.

4. The method for recycling furfural wastewater according to claim 1, characterized in that: The acid in the double decomposition is concentrated sulfuric acid.

5. The method for recycling furfural wastewater according to claim 1, characterized in that: The acetate in the double decomposition includes one or more of sodium acetate, calcium acetate and potassium acetate.

6. The method for recycling furfural wastewater according to claim 1, characterized in that: In the secondary evaporation, the evaporation temperature is set to 70-190 degrees Celsius, and the evaporation pressure is set to 0.3atm-12.27atm.