Inhibition process of dioxane and unsulfonated substances in AES production and preparation of high-purity product

Abstract

The invention provides a process for inhibiting dioxane and unsulfonated substances in AES production, which comprises the following steps: (1) adding a composite inhibitor into a fatty alcohol-polyoxyethylene ether raw material for pretreatment, the composite inhibitor being composed of citric acid and EDTA (Ethylene Diamine Tetraacetic Acid); (2) carrying out sulfonation reaction on the pretreated raw materials by adopting sulfur trioxide; (3) neutralizing a sulfonated product; (4) sequentially carrying out water washing-azeotropic distillation and nanofiltration membrane separation on the neutralized product; and (5) drying to obtain a high-purity AES product. Synchronous removal of unsulfonated substances is realized, and an unexpected synergistic effect is generated through a composite inhibitor in a specific proportion.

Description

Technical Field

[0001] This invention relates to the field of chemical process technology, specifically to the inhibition process of dioxane and unsulfonated compounds in AES production and the preparation of high-purity products. Background Technology

[0002] AES, an important anionic surfactant, is typically produced industrially from fatty alcohol polyoxyethylene ether (AEO) via a sulfur trioxide sulfonation reaction. This process generally suffers from two significant problems: firstly, the sulfonation process easily generates the potentially carcinogenic 1,4-dioxane (typically with a residual amount reaching 80 × 10⁻⁶). -6 The above are the first two issues: firstly, the presence of unsulfonated substances (such as unreacted AEO) (usually >2%), which affects product purity and application performance.

[0003] Chinese invention application publication number CN117105823A, published on November 24, 2023, discloses a process for removing dioxane from fatty alcohol ether sulfates. The process includes: fatty alcohol polyoxyethylene ether sulfate material after dioxane removal in a vacuum tubular separator; the material is then pumped, with part being discharged as product and part as recycled material; the recycled material passes through a Venturi jet injector and simultaneously enters a neutralizer with fatty alcohol polyoxyethylene ether sulfate, alkali, and water for neutralization; a certain flow rate of mixed gas is simultaneously supplied to the suction end of the Venturi jet injector; the material exiting the neutralizer enters the vacuum tubular separator via pipeline, where dioxane is removed under vacuum. This invention further innovates upon the existing continuous tubular vacuum neutralization system by introducing a combination of steam and non-condensable gas before the neutralizer, effectively improving the system's dioxane removal efficiency; the dioxane residue in the product after removal by this system can be reduced from 10 mg / kg to 5 mg / kg. One approach fails to address the issue of unsulfonated compounds; another approach improves the reaction process by adding alkylbenzenes (such as dodecylbenzene) during sulfonation, which can reduce dioxane to some extent, but it does not address source inhibition and simultaneous removal of unsulfonated compounds, and the residual rate remains as high as 2.5% or more. Therefore, there is an urgent need for an integrated process that can simultaneously inhibit dioxane formation and efficiently remove unsulfonated compounds. Summary of the Invention

[0004] To address the above problems, this invention provides a process for inhibiting dioxane and unsulfonated compounds in AES production, achieving simultaneous removal of unsulfonated compounds and generating an unexpected synergistic effect through a specific ratio of compound inhibitors.

[0005] This invention is achieved through the following steps:

[0006] Raw material pretreatment (source inhibition): Add a complex inhibitor to the AEO raw material. The complex inhibitor is composed of citric acid and EDTA in a mass ratio of 3:1. The amount added is 0.5% of the mass of AEO. Stir at 60°C for 30 minutes. By complexing metal ions and stabilizing reaction intermediates, the cyclization formation of dioxane is inhibited at the molecular level.

[0007] Sulfonation reaction: A multi-stage jet sulfonation reactor is used, which includes a three-stage jetting unit and an interstage static mixer. The SO3 concentration is controlled at 4%, the temperature at 50±2℃, the pressure at 0.3MPa, and the residence time at 25 minutes to ensure uniform reaction and reduce side reactions caused by local overheating.

[0008] Specifically, the first-stage injection unit includes:

[0009] Feeding system: includes AEO raw material inlet, SO3 gas inlet and venturi tube;

[0010] Reaction chamber: cylindrical structure with internal swirl guide plates;

[0011] Outlet connection device: connected to the first-stage static mixer via a flange. The first-stage static mixer can be selected as model SX-0.3, which contains 24 mixing elements.

[0012] The second and third stage injection units adopt the same structural specifications, and the temperature between each stage is controlled at 50±2℃ through a jacket cooling system. The outlet of the third stage injection unit is equipped with a pressure sensor (accuracy class 0.5) and a temperature sensor (Pt100, accuracy ±0.5℃), which provide real-time feedback to the central control system.

[0013] The innovation of this reactor lies in the specific combination of the three-stage injection unit and the static mixer, which enables the materials to be fully mixed and reacted step by step, effectively avoiding local overheating and thus inhibiting the formation of dioxane.

[0014] Neutralization and purification:

[0015] Neutralization: Adjust the pH to 7.5-8.0 using a 30% NaOH solution;

[0016] Water washing-azeotropic distillation: Dioxane is removed by stripping at 80℃, taking advantage of its azeotropic properties with water (azeotropic point 87.8℃);

[0017] Membrane separation: A spiral-wound nanofiltration membrane module with a molecular weight cutoff of 200 Da is used, operating at a pressure of 1.5 MPa and a membrane surface flow rate of 0.5 m / s, selectively removing unsulfonated substances. The nanofiltration membrane is a spiral-wound membrane module (model NF-200-4040), and its operating pressure is controlled at 1.5 MPa ± 0.1 MPa by a variable frequency centrifugal pump. The feed channel width is 2.0 mm ± 0.1 mm, and the feed velocity at the membrane surface is monitored and controlled at 0.5 m / s ± 0.05 m / s by a flow meter (accuracy class 0.5). The permeate is collected through a central collection pipe, and the concentrate is returned to the neutralization vessel for recycling through a reflux pipe.

[0018] The specific structure of the membrane module includes:

[0019] Membrane element: Polyamide composite membrane with a molecular weight cutoff of 200 Da;

[0020] Pressure vessel: made of fiberglass, designed pressure 2.5MPa;

[0021] Sealing system: Double O-rings are used for end face sealing;

[0022] Guide net: It adopts a diamond mesh structure and is made of polypropylene.

[0023] During membrane separation, the permeate quality is monitored in real time using an online conductivity meter (accuracy ±1%). When the conductivity value exceeds 50 μS / cm, the cleaning procedure is automatically triggered.

[0024] The innovation of this device lies in the synergistic combination of specific operating parameters (pressure 1.5MPa, flow rate 0.5m / s) and membrane module structure (channel width 2.0mm), which enables efficient separation of unsulfonated substances without affecting product yield.

[0025] Drying and shaping: Spray drying yields a powdered high-purity AES product.

[0026] The beneficial effects of this invention are:

[0027] 1. The compound inhibitor precisely blocks the dioxane formation pathway through chemical complexation, unlike the physical blending (alkylbenzene) or end removal of existing technologies, thus reducing the generation of byproducts at the source.

[0028] 2. Nanofiltration membranes are specifically designed for the removal of unsulfonated substances, solving the purity problem that has long been unresolved in existing technologies, and achieving simultaneous deep removal of dioxane and unsulfonated substances.

[0029] 3. The organic combination of inhibitor pretreatment and multi-stage purification process produces a synergistic effect of "1+1>2", significantly improving the overall quality of the product.

[0030] The integrated process of this invention simplifies the process, reduces energy consumption by more than 20%, and does not require the addition of expensive special equipment, making it easy to implement in industrial applications. Attached Figure Description

[0031] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0032] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments, but the implementation of the present invention is not limited thereto.

[0033] Example 1: Implementation of Optimal Parameters

[0034] Raw materials: C12-14 AEO, EO addition number 3, inhibitor addition amount 0.5%, citric acid:EDTA = 3:1;

[0035] Sulfonation: SO3 concentration 4%, temperature 50℃, pressure 0.3MPa, residence time 25 minutes;

[0036] Purification: water washing-azeotropic distillation at 80℃ for 1 hour; nanofiltration, operating pressure 1.5MPa, molecular weight cutoff 200Da;

[0037] Result: Dioxane content 8×10 -6 The unsulfonated residue rate was 0.9%, and the product yield was 95%.

[0038] Example 2: Parameter Range Verification

[0039] At the sulfonation temperatures of 45℃ and 55℃, the dioxane content of the product was 10×10⁻⁶. -6 and 14×10 -6 The unsulfonated residue rates were 1.0% and 1.1%, respectively, both significantly better than the control group.

[0040] Comparison Example 1: Closest to Existing Technology

[0041] Using the alkylbenzene method (adding 0.5% dodecylbenzene):

[0042] Dioxane content: 15×10 -6 ;

[0043] Unsulfonated residue rate: 2.5%;

[0044] Product yield: 92%;

[0045] Comparative Example 2: Effect of a Single Inhibitor

[0046] Citric acid only (0.5% added):

[0047] Dioxane content: 25 × 10 -6;

[0048] Unsulfonated residue rate: 2.0%;

[0049] Experimental data summary table;

[0050] Table 1 Comparison of the effects of different technical solutions

[0051] Technical solution <![CDATA[Dioxane (×10 -6 )]]> Unsulfonated matter (%) Yield (%) Remark This invention 5 0.9 95 Best results Alkylbenzene process 15 2.5 92 Closest to existing technology No processing 80 2.5 90 conventional process Citric acid only 25 2.0 93 Comparative proof of synergistic effect

[0052] Test methods

[0053] Dioxane content: GC-MS method (SH-Rxi-5 SiMS column, SIM mode, ion detection m / z = 88)

[0054] Unsulfonated products: Ethanol extraction method (GB / T 13530)

[0055] Yield calculation: Actual yield / Theoretical yield × 100%.

[0056] This invention's composite inhibitor precisely blocks the dioxane formation pathway through chemical complexation, unlike existing technologies that rely on physical blending (alkylbenzenes) or end-of-pipe removal, thus reducing byproduct generation at its source. The nanofiltration membrane is specifically designed for the removal of unsulfonated compounds, solving the long-standing purity problem of existing technologies and achieving simultaneous deep removal of both dioxane and unsulfonated compounds. The organic combination of inhibitor pretreatment and multi-stage purification processes produces a synergistic effect of "1+1>2," significantly improving the overall product quality. This invention's integrated process simplifies the workflow, reduces energy consumption by more than 20%, and eliminates the need for expensive specialized equipment, making it easy to implement in industrial applications.

[0057] The above embodiments illustrate only three implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A process for the inhibition of dioxane and unsulfonated material in AES production, characterized by, The method comprises the following steps: (1) adding a composite inhibitor consisting of citric acid and EDTA to the raw material of fatty alcohol polyoxyethylene ether for pretreatment; (2) performing sulfonation reaction on the pretreated raw material by using sulfur trioxide; (3) neutralizing the sulfonation product; (4) sequentially performing water washing-azeotropic distillation and nanofiltration membrane separation on the neutralized product; (5) drying to obtain the high-purity AES product.

2. The process for inhibition of dioxane and unsulfonated substances in AES production according to claim 1, characterized in that, The composite inhibitor consists of citric acid and EDTA at a mass ratio of 3:1, and the addition amount is 0.5% of the mass of AEO.

3. The process of claim 1, wherein the process is characterized by, The step (2) uses a multi-stage jet sulfonation reactor, which comprises three-stage jet units and inter-stage static mixers, and the control parameters are as follows: SO3 concentration 4%, temperature 45-55 ℃, pressure 0.3 MPa, and residence time 25 minutes.

4. The process of claim 1, wherein the process is characterized by, In the step (3), 30% NaOH solution is used to adjust the pH to 7.5-8.

0.

5. The process of claim 1, wherein the process is carried out at a temperature of about 50°C to about 70°C. In the water washing-azeotropic distillation of the step (4), 80 ℃ stripping is used to remove dioxane by using the azeotropic characteristics of dioxane and water.

6. The process of claim 5, wherein the process is carried out at a temperature of from 50°C to 70°C. In the nanofiltration membrane separation of the step (4), a roll-type nanofiltration membrane module with a molecular weight cut-off of 200 Da is used, the operating pressure is 1.5 MPa, the membrane surface flow rate is 0.5 m / s, and the un-sulfonated substances are selectively removed.

7. The process of claim 1, wherein the process is carried out at a temperature of about 50°C to about 70°C. In the step (5), the drying uses spray drying.

8. A high purity AES product characterized by, The product has a dioxane content of <10 x 10 -6 and a non-sulfonated residue content of <1%.

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