CN1259310C - Process for extracting and separating caprolactam from amide oil - Google Patents

Abstract

The present invention relates to a method for extracting and purifying caprolactam from acid amide oil, which belongs to the technical field of chemical industry mass transfer and separation. In the method, cyclohexane or the mixed solvent of cyclohexane and benzene is used to pre-extract acid amide oil for removing parts of impurities; then, benzene or the mixed solvent of cyclohexane and benzene is used for extracting heavy phases obtained from the pre-extraction; and water is used for carrying back extraction to light phases for obtaining caprolactam water solution. Compared with the prior art, the technique has the advantages of low solvent consumption in the extraction and purification processes of acid amide oil, low energy consumption, large processing capability of single set of devices, fewer wastes, less impurity content and high purity of the obtained caprolactam water solution, and the present invention provides an effective method for extracting and purifying caprolactam. The method has important meaning for enhancing the quality of caprolactam products, reducing production cost and enhancing the market competitive power of the toluene method.

Description

A method for extracting and purifying caprolactam from amide oil

technical field

The invention relates to a method for extracting and purifying caprolactam from amide oil, which belongs to the technical field of chemical mass transfer and separation.

Background technique

Caprolactam is an important organic chemical raw material, mainly used in the production of nylon fiber and nylon resin. It is also an excellent solvent and has a wide range of applications.

There are many industrial preparation methods of caprolactam, such as cyclohexane-hydroxylamine method, toluene method and so on. Due to the long reaction route, the amide oil obtained by the reaction contains various impurities. To obtain the caprolactam product, a series of physical and chemical refining methods must be adopted, such as extraction, chemical treatment and multi-effect distillation. Solvent extraction is the most effective means for the preliminary purification of caprolactam from amide oil, and benzene and toluene are the most commonly used extraction agents.

As far as the synthesis reaction of caprolactam is concerned, the atom economy of the toluene method is higher than that of the traditional cyclohexanone-hydroxylamine method, but the types and contents of impurities in the amide oil are quite different from the latter, and the purification corresponding to the toluene method There are few studies on the method, and the only industrialized SNIA process so far uses toluene as the extraction agent. Compared with benzene, toluene has a lower extraction capacity for caprolactam and a higher boiling point, which limits the processing capacity of a single set of equipment, and the problem of energy and material consumption in the extraction process is more prominent. However, substituting benzene for toluene has proven to be inadvisable for selectivity reasons.

Obviously, the development of extraction solvents and extraction processes with higher selectivity and higher throughput is the key to improving the product quality of caprolactam, reducing production costs, and enhancing the market competitiveness of the toluene method.

Contents of the invention

The invention provides a method for extracting and purifying caprolactam from amide oil, the purpose of which is to further improve the product quality of caprolactam, reduce energy consumption, improve the processing capacity of a single set of equipment, thereby greatly reducing production costs and enhancing the market competitiveness of the toluene method.

The object of the present invention is achieved through the following technical solutions: a method for extracting and purifying caprolactam from amide oil, characterized in that the method comprises the steps:

1) The mixed solvent of amide oil and cyclohexane or cyclohexane and benzene is sent to the pre-extractor for pre-extraction; the volume ratio of cyclohexane and benzene in the mixed solvent of cyclohexane and benzene is 1～ 20:1; the volume ratio of the solvent used in the pre-extraction to the amide oil is 1:0.2～2;

2) Part or all of the light phase obtained by pre-extraction is sent to the pre-extraction solvent regeneration system for regeneration and recycling;

3) Send the heavy phase obtained by benzene or a mixed solvent of benzene and cyclohexane and the pre-extraction into the extractor for extraction; the volume ratio of the mixed solvent of benzene and cyclohexane used for extraction is 1～ 20:1.

4) The light phase obtained by the extraction is sent to the back extractor for back extraction with water;

5) Part or all of the light phase obtained by stripping is regenerated through the extraction solvent regeneration system;

6) Send the heavy-phase caprolactam aqueous solution obtained by back extraction for subsequent refining to obtain pure caprolactam.

The volume ratio of the solvent used in the pre-extraction described in the above step 1) to the amide oil is preferably 1: 0.5～1; the volume ratio of the mixed solvent of benzene and cyclohexane for extraction described in the step 3) Preferably it is 3-10:1.

Compared with the prior art, the present invention has the following advantages and outstanding effects: ① The present invention utilizes the significant impurity removal effect of pre-extraction to reduce the type and amount of impurities entering the extraction system, so that the extraction ability is strong but the impurity removal ability is poor Benzene can be used for the extraction of amide oil; ②Adding a small amount of cyclohexane to benzene can solve the entrainment problem caused by the difficulty of phase separation during stripping, avoiding the use of additives such as alkali and salt; ③Adding a small amount of cyclohexane to benzene Alkanes can further remove weakly polar impurities, reduce impurities entering the water phase after stripping, improve the purity of caprolactam, and reduce the burden of subsequent refining. In the process of extracting and purifying the amide oil, the method has less solvent consumption, low energy consumption, large processing capacity of a single set of equipment, less waste generated, and the obtained caprolactam aqueous solution has less impurity content and high purity.

Description of drawings

Fig. 1 is the brief process flow of the method for extracting and purifying caprolactam from amide oil proposed by the present invention.

Detailed ways

The invention provides a method for extracting and purifying caprolactam from amide oil. The method is to pre-extract the amide oil with an organic solvent to remove some impurities, and then use another organic solvent to extract the raffinate phase obtained by the pre-extraction. The extract phase was back-extracted with water to obtain an aqueous solution of caprolactam. The method comprises the steps of:

1) Firstly, use a column or tank extractor to carry out countercurrent or single-stage pre-extraction between amide oil and cyclohexane or a mixed solvent of cyclohexane and benzene, so that impurities enter the light phase and most of the caprolactam remains in the heavy phase The volume ratio of cyclohexane and benzene in the mixed solvent of cyclohexane and benzene used for pre-extraction is 1～20:1; the volume ratio of the solvent used in the pre-extraction and amide oil is 1:0.2～2 , preferably 1:0.5~1;

2) Part or all of the light phase obtained by pre-extraction is sent to a distillation or rectification tower for solvent regeneration, and the regenerated solvent is mixed with the non-regenerated part as a pre-extraction solvent;

3) In a column or tank extractor, use benzene or a mixed solvent of benzene and cyclohexane to carry out multistage countercurrent extraction of the heavy phase obtained in step 1), so that most of the caprolactam enters the light phase; The volume ratio of the mixed solvent of benzene and cyclohexane is 1～20:1, preferably 3～10:1;

4) In a column or tank extractor, back-extract the light phase obtained in step 3) with water, and the obtained heavy phase is an aqueous solution of caprolactam, which is sent for subsequent refining;

5) Send part or all of the light phase obtained in the back extraction of step 4) to a distillation or rectification tower for solvent regeneration, and the regenerated solvent is mixed with the non-regenerated part as the extraction solvent in step 3);

The present invention will be further described below by only citing 3 embodiments (the rest are basically the same).

Example 1:

Get the amide oil obtained by the SNIA process, the first group uses cyclohexane to pre-extract the amide oil with a solvent-to-oil ratio of 1:1, after the heavy phase is extracted with benzene in a ratio of 3:1, then water is used in a ratio of 1:2 (heavy phase than light phase) back extraction to obtain caprolactam aqueous solution. The second group uses the mixed solvent (1:1) of hexanaphthene and benzene to pre-extract the amide oil with the solvent oil ratio of 1:2, and after the heavy phase is extracted with benzene in a ratio of 3:1, then water is used in a ratio of 1:2 ( Heavy phase (light phase) back extraction to obtain caprolactam aqueous solution. Gas chromatographic analysis of the caprolactam concentration in the aqueous solution, the caprolactam purity in the solute, and the 290nm absorbance value of the 20-fold dilution of the aqueous solution. : 2 back extraction of the caprolactam aqueous solution obtained. It can be seen that the concentration of caprolactam in the aqueous solution experimental samples obtained by using cyclohexane or a mixed solvent of cyclohexane and benzene (1:1) for pre-extraction and then benzene extraction and water back-extraction is higher than that of the reference sample, indicating that the concentration of caprolactam is higher than that of the reference sample. The yield is high. At the same time, the purity of caprolactam in the aqueous solution of the experimental samples was higher than that of the reference sample, and the 290nm absorbance value corresponding to the unit concentration of caprolactam was lower than that of the reference sample, indicating that the quality of the produced liquid was better. sample discription Reference sample Cyclohexane 1:1 pre-extraction Mixed solvent of cyclohexane and benzene (1:1) 1:2 pre-extraction Absorbance at 290nm 0.793 0.927 0.931 CPL concentration, g/g 0.121 0.150 0.149 purity 98.2% 99.0% 98.9% 290nm absorbance value/CPL concentration 6.55 6.20 6.26

Example 2:

Take the amide oil obtained by the SNIA process, use a mixed solvent of cyclohexane and benzene (20:1) to pre-extract the amide oil in a ratio of 1:1, and use a mixed solvent of benzene and cyclohexane (20:1) for the heavy phase After extracting with a mixed solvent (1:1) of cyclohexane and benzene at a ratio of 3:1, back-extract with water at a ratio of 2:1 (heavy phase to light phase) to obtain an aqueous solution of caprolactam. Use gas chromatography to analyze the concentration of caprolactam in the aqueous solution and the 290nm absorbance value of the 20-fold dilution of the aqueous solution. The experimental results are shown in the table below. The reference sample is extracted with toluene at a ratio of 3:1, and water is extracted at a ratio of 2:1. Caprolactam aqueous solution. It can be seen that for the experimental samples obtained by the two schemes of pre-extraction with the mixed solvent of cyclohexane and benzene (20:1), the absorbance value at 290 nm corresponding to the unit concentration of caprolactam is significantly lower than that of the reference sample, indicating that the quality of the produced liquid is better. excellent. Wherein the caprolactam concentration of the sample obtained using the mixed solvent (20:1) of benzene and cyclohexane as the extraction agent is significantly higher than that of the reference sample, indicating that the yield of caprolactam is high, and the use of this solvent can improve the processing capacity of the equipment. project reference sample Experimental sample one Experimental sample two Pre-extraction rings/benzene = 20/1 wash, compared to 1/1 x √ √ extraction 20/1 phenylcyclohexane solvent blend vs. 3/1 x √ x Toluene extract, compared to 3/1 √ x x 1/1 phenylcyclohexane solvent mixture vs. 3/1 x x √ Stripping Water stripping, compared to 1/2 √ √ √ index CPL concentration, g/g 0.096 0.158 0.056 yield 39.7% 65.1% 23.1% Absorbance at 290nm 0.385 0.494 0.154 290nm absorbance value/CPL concentration 4.00 3.13 2.76

Note: √, means there is this step; ×, means there is no such step; comparison refers to the volume ratio of solvent phase to water phase (or amide oil).

Example 3:

Get the amide oil obtained by the SNIA process, the first group is pre-extracted with cyclohexane in a ratio of 1: 0.2, and the heavy phase is extracted with benzene in a ratio of 3: 1, and water is used in a ratio of 1: 3 (heavy to light) phase) back extraction to obtain the caprolactam aqueous solution as experimental sample one. The second group was directly extracted with benzene at a ratio of 3:1, and back-extracted with water at a ratio of 1:3 (water to oil phase) to obtain a caprolactam aqueous solution as experimental sample 2. The third group was extracted with a mixed solvent of benzene and cyclohexane (3:1) in a ratio of 3:1, and water was back-extracted in a ratio of 3:1 to obtain an aqueous solution of caprolactam. Measure the 290nm absorbance of each sample diluted 20 times, and the experimental results are shown in the table below. It can be seen that the aqueous solution of caprolactam obtained directly with benzene as the extractant has a higher absorbance at 290 nm per unit concentration of CPL than when the mixed solvent (3:1) of benzene and cyclohexane is used as the extractant. Hexanaphthene is pre-extracted by 1: 0.2, then use benzene as extraction agent extraction, the caprolactam aqueous solution that water back-extraction obtains, the 290nm absorbance value of its unit concentration CPL is obviously lower than the mixed solvent of benzene and hexanaphthene (3 : 1) as the situation of the extractant, it shows that the sample quality has been significantly improved. project First group Second Group The third group Pre-extraction Cyclohexane extraction, compared to 1:0.2 none none extraction Benzene extraction, compared 3:1 Benzene extraction, compared 3:1 Benzene/ring = 3:1 extraction vs. 3:1 Stripping Water stripping, ratio 1:3 Water stripping, ratio 1:3 Water stripping, ratio 1:3 CPL concentration, g/g 0.180 0.185 0.161 Absorbance at 290nm 0.459 0.762 0.621 290nm absorbance value/CPL concentration 2.562 4.108 3.881

Claims (3)

1. A method for extracting and purifying caprolactam from amide oil, characterized in that the method may further comprise the steps: 1) The mixed solvent of amide oil and cyclohexane or cyclohexane and benzene is sent to the pre-extractor for pre-extraction; the volume ratio of cyclohexane and benzene in the mixed solvent of cyclohexane and benzene is 1～ 20:1; the volume ratio of the solvent used in the pre-extraction to the amide oil is 1:0.2～2; 2) Part or all of the light phase obtained by pre-extraction is sent to the pre-extraction solvent regeneration system for regeneration and recycling; 3) Send the heavy phase obtained by benzene or a mixed solvent of benzene and cyclohexane and the pre-extraction into the extractor for extraction; the volume ratio of the mixed solvent of benzene and cyclohexane used for extraction is 1～ 20:1; 4) The light phase obtained by the extraction is sent to the back extractor for back extraction with water; 5) Part or all of the light phase obtained by stripping is regenerated through the extraction solvent regeneration system; 6) Send the heavy-phase caprolactam aqueous solution obtained by back extraction for subsequent refining to obtain pure caprolactam. 2. The method according to claim 1, characterized in that: the volume ratio of the solvent used in the pre-extraction described in step 1) to the amide oil is 1: 0.5～1. 3. The method according to claim 1, characterized in that: the volume ratio of the mixed solvent of benzene and cyclohexane for extraction described in step 3) is 3-10:1.