Method for separating and refining biphenyl from medium washing oil

Abstract

The invention relates to a method for separating and refining biphenyl from medium wash oil, which comprises the following steps: by taking the medium wash oil obtained by deep processing of coal tar wash oil as a raw material, removing indole through a phase transfer pickling method, neutralizing, carrying out intermittent normal-pressure rectification to obtain crude biphenyl with the mass fraction of more than 80%, carrying out solution crystallization on the crude biphenyl by using a solvent petroleum ether, and separating the refined biphenyl from the crude biphenyl. A biphenyl product with the purity of more than 99% is obtained. The phase transfer pickling method is thorough in indole removal, the normal pressure rectification operation is simple, production parameters are easy to control, petroleum ether is used as a solvent for solution crystallization, and the product is good in quality and high in yield.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry, and in particular relates to a method for separating and refining biphenyl from medium-quality washed oil obtained by deep processing of coal tar washed oil. Background Art

[0002] Biphenyl is a polycyclic aromatic hydrocarbon composed of two independent benzene rings, which is white or slightly yellow flaky crystals with a boiling point of 254.9°C and a melting point of 68.84°C. It can be used as a raw material in industries such as chemicals, medicines, plastics and dyes. Due to its good thermal stability, it is also widely used as a heat carrier.

[0003] The mass fraction of biphenyl in coal tar is 0.2% to 0.4%, mainly concentrated in the wash oil fraction after the initial separation of coal tar, with a mass fraction of 3% to 4%. After further processing of the wash oil, biphenyl is concentrated in the medium wash oil, with a mass fraction of more than 10% (Coal Tar Chemical Engineering, 2nd Edition, edited by Xiao Ruihua, P164-P167, Table 7-2 and Table 7-5).

[0004] The main methods for separating and refining biphenyl from wash oil include potassium melting method, distillation method and azeotropic distillation method (Coal Tar Chemical Engineering, 2nd Edition, edited by Xiao Ruihua, P203-P204). The potassium melting method is to use potassium hydroxide and indole to react to generate potassium indole to remove indole. Because the boiling point of indole is 253°C, which is less than 2°C different from biphenyl, it is concentrated in the wash oil fraction, which makes it very difficult to separate and purify biphenyl. After removing indole, the wash oil is further distilled, cooled and crystallized, and recrystallized with solvent ethanol to obtain industrial biphenyl with a purity greater than 90% (mass fraction, the same below). The distillation method uses medium wash oil as raw material, first distills and cuts the biphenyl fraction with a mass fraction greater than 60%, then cools and crystallizes to obtain crude biphenyl, and the crude product is recrystallized with ethanol to obtain industrial biphenyl with a purity greater than 95%. The azeotropic distillation method uses ethylene glycol as an azeotrope. The boiling point of the azeotrope formed by biphenyl and ethylene glycol is 230.4°C, and the boiling point of the azeotrope formed by indole and ethylene glycol is 242.6°C, with a difference of 12.2°C, so biphenyl is separated. The reaction of indole and potassium hydroxide is not easy, the indole extraction rate is low, and there is still a lot of indole left in the wash oil, so the industrial biphenyl product has low purity and high cost, so the potassium melting method has been eliminated. The distillation method is simple, but because the influence of indole in the wash oil is not considered, the product purity is not high. The azeotropic distillation method introduces an azeotrope, and the separation effect is better than the ordinary distillation method, but the separation effect is still limited, and the azeotrope evaporates from the top of the tower, resulting in a large amount of heat energy consumption.

[0005] The patent "Method for extracting biphenyl from medium wash oil" (CN101182277B) uses medium wash oil containing 15% (mass fraction, the same below) biphenyl as raw material, and obtains biphenyl products with a purity greater than 95% through three intermittent distillations in a distillation kettle and a distillation tower with 50 to 80 theoretical plates. Although biphenyl is enriched in medium wash oil, the content is generally above 10%, and it is not easy to have a content greater than 15%. This technology has strict requirements on raw materials; the energy consumption of three distillations is too large and uneconomical; the influence of indole is not considered, and the product purity is not high. The patent "Method for extracting biphenyl and indole from coal tar recycled wash oil" (CN101245044B) uses recycled wash oil for producing β-methylnaphthalene as raw material, firstly obtains indole biphenyl fraction by vacuum distillation, and then separates indole and biphenyl by double solvent extraction, and obtains biphenyl product by distillation and crystallization of the raffinate. The invention requires two vacuum distillations, which consumes slightly more energy. The selectivity of the extractants currently used in dual solvent extraction is not ideal, resulting in loss of the target product and difficulty in solvent recovery, leading to high production costs, especially when the indole content is low. The patent "An environmentally friendly method for extracting biphenyl from coal tar washing oil" (CN102731238B) uses supercritical extraction to purify biphenyl. Supercritical extraction needs to be carried out under high pressure, and the investment and maintenance costs of the equipment are high, and it is more dangerous. The patent "A method for extracting biphenyl from coal tar washing oil" (CN103772132A) uses vacuum distillation and solution crystallization to obtain biphenyl products. The operation is simple, but the description of the patent is too rough. The number of plates of the distillation tower, the content of crude biphenyl, and the purity of the biphenyl product are not described, and indole is not removed first. The patent "Biphenyl Purification Method" (CN100473631C) also uses the recovered washing oil from the production of β-methylnaphthalene as raw material, and obtains the biphenyl product through one vacuum distillation and two solution crystallizations. Since indole is not removed in advance, two solution crystallizations with a large amount of solvent are required, and the yield is too low. The patent "Equipment and method for separating indole and biphenyl from washing oil fractions" (CN101912693A) separates indole and biphenyl through azeotropic distillation, and the addition of azeotropes increases energy consumption. The paper "Discussion on the process of extracting biphenyl from coal tar washing oil" (Si Leiting et al., Shanxi Chemical Industry, February 2010) uses a combination of azeotropic distillation and mixed solvent precipitation to separate and purify biphenyl from the fraction, but it also has the problems of high energy consumption and general separation effect, and the product purity and yield are low.

[0006] The present invention is a method for separating and refining biphenyl from medium wash oil, which is developed on the basis of summarizing the advantages and disadvantages of the above technologies. The medium wash oil obtained by deep processing of wash oil to obtain methylnaphthalene fraction and acenaphthene fraction is used as raw material, and the biphenyl content is more than 10%. Indole is removed by phase transfer acid washing method, and indole is removed completely; crude biphenyl is obtained by atmospheric distillation, which is simple to operate and easy to control production parameters; and the product quality is good and the yield is high by crystallization of petroleum ether solution. Summary of the invention

[0007] The purpose of the present invention is to provide a method for separating and refining biphenyl from medium wash oil. The method uses the medium wash oil obtained during deep processing of the wash oil as a raw material, first removes the impurity indole by a phase transfer acid washing method, then obtains a crude biphenyl with a content greater than 80% by atmospheric distillation, and then obtains a biphenyl product with a purity greater than 99% by crystallization using a petroleum ether solution.

[0008] The technical solution of the present invention consists of the following steps: Step 1: adding the medium wash oil, sulfuric acid solution with a mass fraction of 30% to 35% and phase transfer catalyst polyethylene glycol-400 in a mass ratio of 100:10:0.1 to 0.2 into a scrubber with stirring, heating to 70°C to 80°C, stirring for 2h to 3h, standing to separate into layers, obtaining the medium wash oil with indole removed in the upper layer and the indole sulfate solution in the lower layer, and releasing the indole sulfate solution in the lower layer for producing indole; Step 2: Continue to add 20% sodium carbonate solution by mass into the scrubber, the mass ratio of the medium wash oil to the sodium carbonate solution is 100:1, stir for 1 hour, let stand to separate, then release the sodium carbonate solution in the lower layer, and the upper layer is the medium wash oil after acid washing to remove indole and neutralization; Step 3: adding the acid-washed, indole-free and neutralized medium wash oil obtained in step 2 to an intermittent atmospheric distillation device for distillation, wherein the theoretical number of plates of the distillation tower is 80 to 100, the operating reflux ratio is 10 to 15, and the fraction between 252° C. and 256° C. is collected to obtain a crude biphenyl having a mass fraction greater than 80%; Step 4: The crude biphenyl obtained in step 3 is heated to 80°C to melt, and then added to a crystallizer with solvent petroleum ether heated to 40°C in a mass ratio of 1:2, kept warm for 1 hour, the stirring speed is controlled to be 20r~30r / min, and then cooled to 0°C~10°C by passing refrigerated brine at a cooling rate of 5°C~6°C / h, centrifugally filtered and dried to obtain a biphenyl product with a purity greater than 99%, and the filtrate is subjected to reduced pressure distillation to recover the solvent petroleum ether for recycling.

[0009] The main impurities of biphenyl are indole with similar boiling points and dimethylnaphthalene mixed with various isomers. Due to the high melting point of indole, it will precipitate along with the crystallization of biphenyl during cooling and crystallization, which has the greatest impact on the purity of biphenyl. Therefore, indole must be removed first to obtain high-purity biphenyl products. The mass fraction of indole in the medium wash oil is 3% to 4%, which is a low content; the more thoroughly indole needs to be removed, the better. Considering these two characteristics, the phase transfer acid washing method is selected to remove indole. This method is suitable for removing indole from raw materials with low indole content. The medium wash oil after indole removal is tested by gas chromatography. Indole is basically undetectable, indicating that indole is removed very thoroughly, which is conducive to improving the purity of biphenyl products. The removed indole can be recycled to produce indole products.

[0010] When choosing a distillation operation, atmospheric pressure distillation is generally the first choice. Although vacuum distillation can reduce some heat loss by lowering the boiling point, it is not easy to maintain a stable vacuum degree. At the same time, it increases power consumption and requires higher equipment airtightness and pressure resistance. The volume expansion of low-pressure gas will reduce the material processing capacity, so vacuum distillation is more suitable for the distillation of heat-sensitive or easily oxidized materials. The technical solution has basically removed the easily oxidized indole in advance, and the remaining biphenyl and dimethylnaphthalene have very good thermal stability. Therefore, atmospheric pressure distillation with simple equipment and easy operation can be selected, which is more conducive to the control of operating parameters such as tower top temperature and reflux ratio, thereby ensuring product quality.

[0011] At present, the solvents used for the crystallization and refining of crude biphenyl solution are generally alcohols or benzene solvents, and the product purity is high, but the yield of the product is low due to the strong solubility of these solvents for biphenyl. Mixed dimethylnaphthalene is composed of 10 isomers, which is liquid at room temperature and is miscible with almost all organic solvents. This technical solution selects petroleum ether as the crude biphenyl crystallization solvent. The solubility of petroleum ether for biphenyl is relatively weak, but the ability to dissolve mixed dimethylnaphthalene is comparable to that of alcohols or benzene solvents. Selecting petroleum ether as the crystallization solvent can effectively improve the yield of biphenyl.

[0012] The invention adopts a phase transfer acid washing method to remove indole, performs atmospheric distillation to obtain crude biphenyl, and crystallizes a petroleum ether solution to obtain a biphenyl product with a purity greater than 99%. The production operation is simple, the cost is low, and the product yield is high. DETAILED DESCRIPTION

[0013] The present invention is further described below by examples: Example 1

[0014] At 5m 3 Add 2000kg of medium wash oil, 200kg of 35% sulfuric acid solution and 3kg of phase transfer catalyst polyethylene glycol-400 to the scrubber, heat to 75℃, stir for 2h, let stand for 1h, and then release the lower layer of indole sulfate solution. Add 20kg of 20% sodium carbonate solution to the scrubber, stir for 1h, let stand for 1h, and release the lower layer of sodium carbonate solution. Gas chromatography detection shows that indole is basically undetectable in the upper layer of medium wash oil. The amount of medium wash oil after indole removal and neutralization obtained in each washing will vary slightly depending on the indole content, generally between 1900kg and 1950kg. Multiple washings accumulate the amount of medium wash oil for subsequent distillation. Indole sulfate solution can be used to produce indole products.

[0015] 13m 3The intermittent distillation kettle was loaded with 10 tons of neutralized medium wash oil after indole removal. After testing, it was found that the oil contained 11.2% biphenyl. The distillation tower was equipped with stainless steel wire mesh packing, with 90 theoretical plates. The distillation tower was distilled at normal pressure, and the reflux ratio was controlled to be 10. The fraction with the top temperature between 252℃ and 256℃ was collected, i.e., a total of 1180kg of crude biphenyl. The gas chromatography detected that the oil contained 80.74% biphenyl, with a yield of 85.07%. At 6m 3 2360kg of petroleum ether was added to the crystallizer in advance, and a condenser was installed on the top of the crystallizer to prevent the petroleum ether from volatilizing. Stirring was started at a stirring speed of 25r / min, and the petroleum ether was heated to 40℃, and then 1180kg of crude biphenyl heated to 80℃ was added to the crystallizer. After keeping the temperature for 1h, the temperature was cooled by passing refrigerated brine, and the cooling rate was controlled to be 5℃ / h. After cooling to 10℃, the temperature was stopped, and then centrifuged and dried to obtain 769kg of biphenyl with a purity of 99.13% and a yield of 80.01%. The total yield was 68.06%.

[0016] The solvent petroleum ether is recovered and reused, and the residual oil after recovering the petroleum ether can be added to the medium wash oil to increase the yield of biphenyl. Example 2

[0017] The same method as in Example 1 is used to obtain a sufficient amount of acid washing to remove indole and neutralize the medium wash oil for distillation.

[0018] 13m 3 The intermittent distillation kettle was loaded with 10 tons of treated medium-quality wash oil, containing 11.2% biphenyl. The distillation tower was equipped with stainless steel wire mesh packing, with 90 theoretical plates, and atmospheric distillation. The reflux ratio was controlled to be 12. The fraction with a top temperature between 252°C and 256°C was collected, i.e., a total of 1,179 kg of crude biphenyl. The gas chromatography detected that the biphenyl content was 81.46%, and the yield was 85.75%. At 6m 3 2358kg of petroleum ether was added to the crystallizer in advance, stirring was started at a speed of 25r / min, 1179kg of crude biphenyl heated to 80℃ was added to the crystallizer, and after keeping warm for 1h, the temperature was cooled by passing refrigerated brine at a controlled cooling rate of 5℃ / h. After cooling to 5℃, the temperature was stopped, and then centrifuged and dried to obtain 781kg of biphenyl with a purity of 99.19% and a yield of 80.66%. The total yield was 69.17%.

[0019] The solvent petroleum ether is recovered and reused, and the residual oil is added to the medium wash oil to increase the yield. Example 3

[0020] The same method as in Example 1 is used to obtain a sufficient amount of acid washing to remove indole and neutralize the medium wash oil for distillation.

[0021] 13m 3The intermittent distillation kettle was loaded with 10 tons of treated medium-quality wash oil, containing 11.2% biphenyl. The distillation tower was equipped with stainless steel wire mesh packing, with 90 theoretical plates, and atmospheric distillation. The reflux ratio was controlled to be 15. The fraction with a top temperature between 252℃ and 256℃ was collected, i.e., a total of 1176kg of crude biphenyl. The gas chromatography detected that the biphenyl content was 82.84%, and the yield was 86.98%. At 6m 3 2352kg of petroleum ether was added to the crystallizer in advance, stirring was started at a speed of 25r / min, 1176kg of crude biphenyl heated to 80℃ was added to the crystallizer, and after keeping warm for 1h, the temperature was cooled by passing refrigerated brine at a controlled cooling rate of 5℃ / h. After cooling to 0℃, the temperature was stopped, and then centrifuged and dried to obtain 796kg of biphenyl with a purity of 99.21% and a yield of 81.06%. The total yield was 70.51%.

[0022] The solvent petroleum ether is recovered and reused, and the residual oil is added to the medium wash oil to increase the yield.

Claims

1. A method for separating and refining biphenyl from medium wash oil, characterized in that The following steps are involved: Step 1: adding the medium wash oil, sulfuric acid solution with a mass fraction of 30% to 35% and phase transfer catalyst polyethylene glycol-400 in a mass ratio of 100:10:0.1 to 0.2 into a scrubber with stirring, heating to 70°C to 80°C, stirring for 2h to 3h, standing to separate into layers, obtaining the medium wash oil with indole removed in the upper layer and the indole sulfate solution in the lower layer, and releasing the indole sulfate solution in the lower layer for producing indole; Step 2: Continue to add 20% sodium carbonate solution by mass into the scrubber, the mass ratio of the medium wash oil to the sodium carbonate solution is 100:1, stir for 1 hour, let stand to separate, then release the sodium carbonate solution in the lower layer, and the upper layer is the medium wash oil after acid washing to remove indole and neutralization; Step 3: adding the acid-washed, indole-free and neutralized medium wash oil obtained in step 2 to an intermittent atmospheric distillation device for distillation, wherein the theoretical number of plates of the distillation tower is 80 to 100, the operating reflux ratio is 10 to 15, and the fraction between 252° C. and 256° C. is collected to obtain a crude biphenyl having a mass fraction greater than 80%; Step 4: The crude biphenyl obtained in step 3 is heated to 80°C to melt, and then added to a crystallizer with solvent petroleum ether heated to 40°C in a mass ratio of 1:2, kept warm for 1 hour, the stirring speed is controlled to be 20r~30r / min, and then cooled to 0°C~10°C by passing refrigerated brine at a cooling rate of 5°C~6°C / h, centrifugally filtered and dried to obtain a biphenyl product with a purity greater than 99%, and the filtrate is subjected to reduced pressure distillation to recover the solvent petroleum ether for recycling.