A process and system for separating pentaerythritol and sodium formate from pentaerythritol mother liquor

Abstract

This invention relates to the field of pentaerythritol mother liquor recovery technology, specifically disclosing a process and system for separating pentaerythritol and sodium formate from pentaerythritol mother liquor, including step S1: adjusting the pH of the pentaerythritol synthesis mother liquor to 6.5-7.5, and decolorizing it by activated carbon adsorption; step S2: concentrating the pretreated mother liquor to a specific gravity of 1.25-1.35 g / cm³. 3 The process involves temperature-controlled crystallization followed by centrifugation to obtain crude pentaerythritol crystals and centrifugal mother liquor. Step S3: Using sulfonic acid-based cation exchange resin as the stationary phase and 10-30% ethanol aqueous solution as the mobile phase, the centrifugal mother liquor is continuously separated to obtain a high-purity sodium formate solution and a pentaerythritol enriched solution.

Description

Technical Field

[0001] This invention relates to the field of pentaerythritol mother liquor recovery technology, specifically a process and system for separating pentaerythritol and sodium formate from pentaerythritol mother liquor. Background Technology

[0002] The production of pentaerythritol (PE) generates a mother liquor containing 20-30% sodium formate. A Chinese patent (CN113603565A) discloses a novel membrane process for separating sodium formate, a byproduct of pentaerythritol production. This patent directly separates PE and sodium formate using an ion exchange membrane and electrodialysis, achieving a sodium formate removal rate of up to 99.5% and a PE yield exceeding 98%. Furthermore, it eliminates the need for a water washing step, saving 30% of water. However, it suffers from the drawback of the high cost of the high-performance ion exchange membrane and the need for further treatment of the resulting high-concentration sodium formate.

[0003] Chinese patent CN112745214A discloses a solid-phase extraction-dissolution crystallization method. This patent uses ethanol / isopropanol as the extractant to separate and purify sodium formate from pentaerythritol mother liquor. At a solid-liquid ratio of 1:1.5-4, the purity of sodium formate can reach over 95%, while simultaneously recovering residual PE (recovery rate >85%). However, the use of ethanol / isopropanol as both the extractant and solvent requires large quantities (solid-liquid ratio 1:1.5-4), and the solvent recovery (distillation) process is energy-intensive, increasing production costs and carbon emissions. Summary of the Invention

[0004] The purpose of this invention is to provide a process and system for separating pentaerythritol and sodium formate from pentaerythritol mother liquor, so as to solve the three major defects of the prior art: membrane fouling, high solvent consumption, and incomplete separation of by-products.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A process for separating pentaerythritol and sodium formate from pentaerythritol mother liquor, comprising:

[0007] Step S1: Adjust the pH of the pentaerythritol synthesis mother liquor to 6.5-7.5, and decolorize it by activated carbon adsorption;

[0008] Step S2: Concentrate the pretreated mother liquor to a specific gravity of 1.25-1.35 g / cm³. 3 The crystallization was carried out using a programmed cooling method with a temperature gradient of 30℃→10℃ and a cooling rate of 0.5-1℃ / min. The crude pentaerythritol crystals and the centrifugal mother liquor were obtained by centrifugation.

[0009] Step S3: Using sulfonic acid cation exchange resin as the stationary phase and 10-30% ethanol aqueous solution as the mobile phase, the centrifuged mother liquor is continuously separated to obtain high-purity sodium formate solution and tripentaerythritol enrichment solution.

[0010] Step S4: Evaporate the sodium formate solution to crystallize and obtain sodium formate product with a purity ≥ 99%.

[0011] A coupling system for separating pentaerythritol and sodium formate from pentaerythritol mother liquor includes: a horizontal screw centrifuge, a ceramic microfiltration membrane unit, a simulated moving bed chromatography system, and a sodium formate crystallizer connected in series, wherein the centrifuged mother liquor output from the horizontal screw centrifuge is processed by the ceramic microfiltration membrane unit and then enters the simulated moving bed chromatography system.

[0012] As a further embodiment of the present invention: the inlet end of the horizontal screw centrifuge is provided with a series pretreatment component for performing steps S1-S2. The series pretreatment component includes, from front to back, a pH adjustment tank, an activated carbon adsorption tower, a four-effect falling film evaporator, and a four-pot series crystallizer. The end of the four-pot series crystallizer is connected to the horizontal screw centrifuge, and the crude pentaerythritol crystals separated by the horizontal screw centrifuge are transported to the pentaerythritol refining section.

[0013] As a further embodiment of the present invention: the programmed cooling crystallization in step S2 is carried out in the four-reactor series crystallizer, and the temperature of each reactor is controlled at 30±2℃, 20±2℃, 15±2℃ and 10±2℃ respectively.

[0014] As a further embodiment of the present invention: the centrifugation factor of the horizontal screw centrifuge is ≥3000g, the average particle size of the pentaerythritol crystals after separation is ≥120μm, and the yield is ≥97%.

[0015] As a further embodiment of the present invention, the operating parameters of the simulated moving bed chromatography system include: switching time 8-15 min, mobile phase flow rate 0.8-1.5 BV / h, and zone flow rate ratio (I:II:III:IV) = (1.2-1.5):(0.8-1.2):(1.0-1.3):(0.5-0.8).

[0016] As a further embodiment of the present invention: the tripentaerythritol enriched solution output by the simulated moving bed chromatography system is returned to the reaction vessel after passing through a nanofiltration concentration unit. The nanofiltration concentration unit has a membrane molecular weight cutoff of 200-300 Da and an operating pressure of 1.5-2.5 MPa.

[0017] As a further embodiment of the present invention: the activated carbon addition amount of the activated carbon adsorption tower is 0.5-1.5% of the mother liquor mass, the adsorption temperature is 60-80℃, and the contact time is 30-60min.

[0018] As a further aspect of the present invention: the simulated moving bed chromatography system is equipped with an online conductivity detector and a 254nm ultraviolet detector, and the detection signal is fed back to the DCS system to dynamically adjust the flow rate ratio of the zones.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] This technical solution improves separation efficiency: PE yield ≥97%, sodium formate purity ≥99%, and tripentaerythritol recovery rate >90%; it also reduces costs: solvent consumption is reduced by 70%, energy consumption is reduced by 45% compared to solvent extraction, flammable solvents are avoided, wastewater COD is reduced by 60%, and the pretreatment + SMB combination solves the membrane fouling problem, thus addressing the three core defects of existing technologies: membrane fouling, high solvent consumption, and incomplete separation of by-products. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of a coupling system for separating pentaerythritol and sodium formate from pentaerythritol mother liquor;

[0023] Figure 2 This is a schematic diagram of a four-reactor crystallizer connected in series in a coupled system for separating pentaerythritol and sodium formate from pentaerythritol mother liquor;

[0024] In the diagram: 101, pH adjustment tank; 102, activated carbon adsorption tower; 201, quadruple-effect falling film evaporator; 202, four-stage crystallizer in series; 203, horizontal screw centrifuge; 204, ceramic microfiltration membrane unit; 301, simulated moving bed chromatography system; 401, sodium formate crystallizer; 501, nanofiltration concentration unit; 601, reaction vessel. Detailed Implementation

[0025] Please see Figures 1-2 In this embodiment, a process for separating pentaerythritol and sodium formate from pentaerythritol mother liquor includes:

[0026] Step S1 Pretreatment: Adjust the pH of the pentaerythritol synthesis mother liquor to 6.5-7.5, and decolorize it by adsorption with activated carbon (addition amount 0.5-1.5%);

[0027] Step S2: Fractional crystallization: Concentrate the pretreated mother liquor to a specific gravity of 1.25-1.35 g / cm³. 3 The crystallization was carried out using a programmed cooling method with a temperature gradient of 30℃→10℃ and a cooling rate of 0.5-1℃ / min. The crude pentaerythritol crystals (particle size ≥120μm) and the centrifugal mother liquor were obtained by centrifugation.

[0028] Step S3 Chromatographic separation: The centrifuged mother liquor is introduced into a simulated moving bed chromatograph (SMB). The centrifuged mother liquor is continuously separated using a sulfonic acid cation exchange resin as the stationary phase and a 10-30% ethanol aqueous solution as the mobile phase to obtain a high-purity sodium formate solution and a tripentaerythritol enrichment solution.

[0029] Step S4: Evaporate the sodium formate solution to crystallize and obtain sodium formate product with a purity ≥ 99%.

[0030] To achieve the above process, the following system is prepared:

[0031] A coupling system for separating pentaerythritol and sodium formate from pentaerythritol mother liquor includes a horizontal screw centrifuge 203, a ceramic microfiltration membrane unit 204, a simulated moving bed chromatography system 301, and a sodium formate crystallizer 401 connected in series. The centrifuged mother liquor output from the horizontal screw centrifuge 203 is processed by the ceramic microfiltration membrane unit 204 and then enters the simulated moving bed chromatography system 301. The inlet end of the horizontal screw centrifuge 203 is equipped with a series pretreatment component for performing steps S1-S2. The series pretreatment component includes, from front to back, a pH adjustment tank 101, an activated carbon adsorption tower 102, a four-effect falling film evaporator 201, and a four-pot series crystallizer 202. The end of the four-pot series crystallizer 202 is connected to the horizontal screw centrifuge 203, and the crude pentaerythritol crystals separated by the horizontal screw centrifuge 203 are transported to the pentaerythritol refining section.

[0032] The operating parameters of the simulated moving bed chromatography system 301 include: switching time 8-15 min, mobile phase flow rate 0.8-1.5 BV / h, and zone flow rate ratio (I:II:III:IV) = (1.2-1.5):(0.8-1.2):(1.0-1.3):(0.5-0.8); the activated carbon addition amount of the activated carbon adsorption tower 102 is 0.5-1.5% of the mother liquor mass, the adsorption temperature is 60-80℃, and the contact time is 30-60 min; the simulated moving bed chromatography system 301 is equipped with an online conductivity detector and a 254nm ultraviolet detector, and the detection signal is fed back to the DCS system to dynamically adjust the zone flow rate ratio.

[0033] Specific applications are as follows:

[0034] (1) Take sodium PE mother liquor (containing 18.7wt% PE and 24.3wt% sodium formate), adjust the pH of the mother liquor to 7.0 through pH adjustment tank 101, and then enter the activated carbon adsorption tower 102. Add 1.0wt% activated carbon to the activated carbon adsorption tower 102 and adsorb at 60℃ for 45min.

[0035] (2) The mother liquor after adsorption was concentrated to a specific gravity of 1.30 g / cm³ using a four-effect falling film evaporator 201. 3Then, the mixture was pumped into a four-reactor series crystallizer 202, and finally passed through a horizontal decanter centrifuge 203 to obtain pentaerythritol crystals (average particle size 125 μm, yield 97.5%). The centrifugation factor of the horizontal decanter centrifuge 203 was ≥3000g. The parameters of the four-reactor series crystallizer 202 are shown in Table 1.

[0036] Table 1. Parameters of the Four-Bottle Series Crystallizer 202

[0037]

[0038] (3) The centrifuged mother liquor is filtered through ceramic microfiltration membrane unit 204. Ceramic microfiltration membrane unit 204 uses ceramic microfiltration membrane (pore size 0.1-0.2μm) to remove suspended solids with a particle size >1μm. After filtration, the centrifuged mother liquor enters the simulated moving bed chromatography system 301. The parameters of the simulated moving bed chromatography system 301 are as follows:

[0039] Stationary phase: Sulfonate-based polystyrene resin

[0040] Mobile phase: 20% aqueous ethanol solution

[0041] Parameters: Switching time 12 min, flow rate ratio I:II:III:IV = 1.3:1.0:1.2:0.6

[0042] (4) A high-purity sodium formate solution was obtained by continuous separation using a simulated moving bed chromatography system 301 and then entered into a sodium formate crystallizer 401. The sodium formate solution was evaporated and crystallized: purity 99.2% and yield 95.6%.

[0043] Based on the above, keeping other conditions constant, the concentration of ethanol in the mobile phase 301 of the simulated moving bed chromatography system was changed. The specific solvent recovery energy consumption is shown in Table 2.

[0044] Table 2. Solvent Recovery Energy Consumption Table

[0045]

[0046] (5) The tripentaerythritol enriched solution output by the simulated moving bed chromatography system 301 is returned to the reaction vessel 601 after passing through the nanofiltration concentration unit 501. The membrane molecular weight cutoff of the nanofiltration concentration unit 501 is 200-300 Da, and the operating pressure is 1.5-2.5 MPa.

[0047] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A process for separating pentaerythritol and sodium formate from pentaerythritol mother liquor, characterized in that: include: Step S1: Adjust the pH of the pentaerythritol synthesis mother liquor to 6.5-7.5, and decolorize it by activated carbon adsorption. The amount of activated carbon added is 0.5-1.5% of the mass of the mother liquor, the adsorption temperature is 60-80℃, and the contact time is 30-60min. Step S2: Concentrate the pretreated mother liquor to a specific gravity of 1.25-1.35 g / cm³. 3 The crystallization was carried out using a programmed cooling method in a four-reactor crystallizer (202). The temperatures of each reactor were controlled at 30±2℃, 20±2℃, 15±2℃, and 10±2℃, respectively, with a cooling rate of 0.5-1℃ / min. Crude pentaerythritol crystals and centrifugal mother liquor were obtained by centrifugation. The centrifugal mother liquor was filtered through a ceramic microfiltration membrane to remove suspended solids with a particle size >1μm. The pore size of the ceramic microfiltration membrane was 0.1-0.2μm. Step S3: The filtered centrifuged mother liquor is continuously separated using sulfonic acid cation exchange resin as the stationary phase and 10-30% ethanol aqueous solution as the mobile phase to obtain high-purity sodium formate solution and tripentaerythritol enrichment solution. Step S4: Evaporate the sodium formate solution to crystallize and obtain sodium formate product with a purity ≥ 99%.

2. A coupling system for separating pentaerythritol and sodium formate from pentaerythritol mother liquor, characterized in that: For performing the process of claim 1, the system comprises: a horizontal screw centrifuge (203), a ceramic microfiltration membrane unit (204), a simulated moving bed chromatography system (301), and a sodium formate crystallizer (401) connected in series, wherein the centrifuged mother liquor output from the horizontal screw centrifuge (203) is processed by the ceramic microfiltration membrane unit (204) and then enters the simulated moving bed chromatography system (301).

3. The coupling system for separating pentaerythritol and sodium formate from pentaerythritol mother liquor according to claim 2, characterized in that: The inlet of the horizontal screw centrifuge (203) is equipped with a series pretreatment assembly for performing steps S1-S2. The series pretreatment assembly includes, from front to back, a pH adjustment tank (101), an activated carbon adsorption tower (102), a four-effect falling film evaporator (201), and a four-pot series crystallizer (202). The end of the four-pot series crystallizer (202) is connected to the horizontal screw centrifuge (203), and the crude pentaerythritol crystals separated by the horizontal screw centrifuge (203) are transported to the pentaerythritol refining section.

4. The coupling system for separating pentaerythritol and sodium formate from pentaerythritol mother liquor according to claim 2, characterized in that: The centrifugation factor of the horizontal screw centrifuge (203) is ≥3000g, the average particle size of the pentaerythritol crystals after separation is ≥120μm, and the yield is ≥97%.

5. The coupling system for separating pentaerythritol and sodium formate from pentaerythritol mother liquor according to claim 2, characterized in that: The operating parameters of the simulated moving bed chromatography system (301) include: switching time 8-15 min, mobile phase flow rate 0.8-1.5 BV / h; The velocity ratio of the regions (I:II:III:IV) = (1.2-1.5):(0.8-1.2):(1.0-1.3):(0.5-0.8).

6. The coupling system for separating pentaerythritol and sodium formate from pentaerythritol mother liquor according to claim 2, characterized in that: The tripentaerythritol enriched solution output by the simulated moving bed chromatography system (301) is returned to the reaction vessel (601) after passing through the nanofiltration concentration unit (501). The nanofiltration concentration unit (501) has a membrane molecular weight cutoff of 200-300 Da and an operating pressure of 1.5-2.5 MPa.

7. The coupling system for separating pentaerythritol and sodium formate from pentaerythritol mother liquor according to claim 2, characterized in that: The simulated moving bed chromatography system (301) is equipped with an online conductivity detector and a 254nm ultraviolet detector, and the detection signal is fed back to the DCS system to dynamically adjust the flow rate ratio of the zones.

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