Method for removing trace cyclopentadiene from m-pentadiene
By using a homogeneous reaction of organic bases with cyclic ketone compounds to form onium salts as intermediates, the problem of removing trace amounts of cyclopentadiene from isoprene has been solved, achieving efficient and low-cost deep removal of cyclopentadiene and avoiding the complexity of precipitation formation and wastewater treatment.
Patent Information
- Application Number
- CN202410564806.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-05-09
- Publication Date
- 2025-11-11
AI Technical Summary
Existing technologies are unable to efficiently remove trace amounts of cyclopentadiene from isoprene, which can poison the catalyst during polymerization. Furthermore, the process is complex and costly, and existing methods suffer from problems such as precipitation, excessive waste residue and liquid, and low removal rates.
An intermediate onium salt is formed by the synergistic formation of an organic base and a cyclic ketone compound. A high-boiling-point cyclopentadiene is generated through a homogeneous reaction and separated from isoprene. The cyclopentadiene is then removed by distillation. No precipitate is produced during the reaction process, and the treatment agent can be recycled.
It achieves efficient removal of cyclopentadiene, with the cyclopentadiene content in isoprene below 1.0 ppm, short reaction time, and recyclable treatment agent, thus reducing production costs.
Smart Images
Figure CN120923307A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for removing trace amounts of cyclopentadiene from isoprene, belonging to the field of isoprene refining. Background Technology
[0002] With the continuous expansion of ethylene production in my country, the output of cracked C5 fraction is becoming increasingly abundant. C5 fraction is rich in diolefins such as isoprene, isoprene, and cyclopentadiene. These diolefins are chemically reactive and are important resources for chemical applications.
[0003] Separating isoprene from the C5 fraction is extremely difficult due to the small boiling range and the presence of azeotropes. Industrial distillation is rarely sufficient to completely remove cyclopentadiene, and the isoprene obtained from the C5 separation process still contains 0.1–0.5% cyclopentadiene. The presence of cyclopentadiene impurities is poisonous to the polymerization catalyst and must be completely removed.
[0004] Because the boiling points of the components in crude isoprene feedstock are extremely similar, and the boiling point of cyclopentadiene lies between that of trans-isopentadiene and cis-isopentadiene, ordinary distillation methods cannot remove cyclopentadiene. Currently, methods for removing cyclopentadiene include extractive distillation, selective hydrogenation, dimerization distillation, adsorption, superdistillation, and chemical removal.
[0005] In extractive distillation, since cyclopentadiene is more soluble in solvents than isoprene, a single extractive distillation method can remove components with relatively high volatility such as isopentene and isopentane. However, cyclopentadiene cannot be completely removed from isoprene.
[0006] In the selective hydrogenation of isoprene to remove cyclopentadiene, the hydrogenation of cycloolefins is more difficult than that of chain olefins, resulting in a large loss of isoprene during the removal of cyclopentadiene, leading to very high production costs.
[0007] Dimerization can remove most of the cyclopentadiene, but to completely remove the cyclopentadiene, the dimerization reaction time is very long and there are many side reactions.
[0008] In the adsorption method, the surface acidity of the adsorbent has a catalytic effect on the polymerization of olefins and dienes, and the adsorbent is prone to deactivation.
[0009] Precision distillation requires very high distillation trays and a very high reflux ratio during operation, resulting in very high industrial costs.
[0010] CN104725182 discloses a method for removing cyclopentadiene from crude isoprene, wherein crude isoprene is mixed with a ketone as a remover, an alcohol as a solvent, and sodium hydroxide or potassium hydroxide as a catalyst, and reacted at room temperature for 3 to 4 days and nights, and then isoprene is obtained by distillation.
[0011] CN107840777 discloses a chemical method for removing trace amounts of cyclopentadiene from isoprene. The method involves first dissolving potassium hydroxide in n-butanol, then adding isoprene and cyclohexanone, reacting at room temperature for 3-4 days, and then obtaining isoprene by distillation.
[0012] The aforementioned patent has the following problems:
[0013] 1) Precipitation is generated during the process, and the solid-liquid separation process is complicated. Although the patent CN107840777 first dissolves potassium hydroxide in n-butanol during the process and there is no solid precipitate at first, the n-butanol and C5 azeotrope, and potassium hydroxide will still precipitate as the amount of n-butanol decreases during the distillation process.
[0014] 2) The large amount of descaling agent and catalyst added, the long reaction time, the large amount of waste residue and waste liquid, and the high production cost;
[0015] 3) The treated isoprene still contains about 10 ppm of cyclopentadiene, which still has a significant impact on the polymerization catalyst. Summary of the Invention
[0016] To address the problems existing in the prior art, the purpose of this invention is to provide a method for removing trace amounts of cyclopentadiene from isopentadiene. In this reaction process, an organic base is added to synergistically convert cyclopentadiene into an intermediate ononium salt. The ononium salt then rapidly reacts with trace amounts of cyclopentadiene to generate a high-boiling-point olefin, which is then separated from isopentadiene. This reaction process produces no precipitation, has a short reaction time, achieves a high degree of cyclopentadiene removal, and the treatment agents can be recycled.
[0017] To achieve the above-mentioned technical objectives, the present invention provides a method for removing trace amounts of cyclopentadiene from isoprene. The method involves mixing crude isoprene with a solution containing cyclic ketones, alcohols, and organic bases, followed by distillation to obtain isoprene containing alcohol and distillate liquid. The isoprene containing alcohol is then washed with water and separated to obtain high-purity isoprene and alcohol-containing wastewater.
[0018] The key to this invention lies in the use of a liquid organic base as a catalyst. Therefore, the entire reaction process is a homogeneous reaction with no precipitation, eliminating the need for solid-liquid separation. Simultaneously, the organic base readily forms an intermediate onium salt with cyclic ketones, which then rapidly reacts with trace amounts of cyclopentadiene to form high-boiling-point cyclopentadiene. After the reaction, due to the different boiling points of the components, the mixture can be separated using distillation principles, achieving deep removal of trace amounts of cyclopentadiene. Typically, the alcohol-containing isoprene evaporates and is collected before other substances, while unreacted raw materials or byproducts such as cyclic ketones and high-boiling-point cyclopentadiene remain in the distillation vessel as a still liquid. Further washing with water removes dissolved alcohols, while isoprene is separated due to its relatively low polarity or immiscibility. The preparation method of this invention features a short reaction time and a high degree of cyclopentadiene removal.
[0019] As a preferred embodiment, the cyclic ketone compound is cyclopentanone and / or cyclohexanone. The inventors have found that using short-chain ketones, such as acetone, increases the difficulty of subsequent distillation separation due to their low boiling point; while using long-chain ketones presents problems such as high steric hindrance, slow reaction rate, and low removal rate. Cyclic ketone compounds, however, readily form intermediate onium salts with organic bases.
[0020] As a preferred embodiment, the alcohol is at least one selected from methanol, ethanol, and isopropanol. All alcohols used in this invention exhibit good solubility for the reactants.
[0021] As a preferred embodiment, the organic base is tetrahydropyrrole and / or hexahydropyridine. The organic bases selected in this invention are all heterocyclic compounds containing nitrogen atoms. Their nitrogen atoms can provide lone pairs of electrons, thus exhibiting high basicity. Furthermore, both compounds have relatively stable structures and are not easily decomposed during the reaction, which is beneficial for improving the removal rate of trace amounts of cyclopentadiene.
[0022] As a preferred embodiment, the molar ratio of the cyclic ketone compound, alcohol, and organic base is 1:(0.5–2):(0.04–0.2). When the amount of cyclic ketone compound, alcohol, or organic base is too small, the purification rate of isoprene is low, the reaction time is long, and the removal rate of cyclic pentadiene is low; while when the amount of cyclic ketone compound, alcohol, or organic base is too large, the purification cost of isoprene increases, and there is no significant improvement in the removal rate.
[0023] As a preferred embodiment, the amount of the cyclic ketone compound added is 10-20 wt% of the crude isoprene.
[0024] As a preferred embodiment, the reaction conditions are: temperature 30–60°C and time 0.5–2 h. If the reaction temperature is too low, the reaction rate is low and the reaction time is long; if the reaction temperature is too high, side reactions will occur, generating high-boiling substances, which is detrimental to subsequent distillation and purification of isoprene.
[0025] As a preferred embodiment, the crude isoprene contains 0.05–0.5 wt% cyclopentadiene. The method of the present invention is effective in removing trace amounts of cyclopentadiene.
[0026] As a preferred embodiment, crude isoprene and alcohol are added to the distillation kettle liquid to further remove cyclopentadiene from isoprene; the alcohol-containing wastewater is stripped to recover alcohol, and the recovered alcohol is reused.
[0027] As a preferred embodiment, the distillation vessel liquid is recycled 2 to 5 times; the mass of the added crude isoprene is the same as the mass of the crude isoprene added in the first reaction; and the mass of the added alcohol is 2 to 4 wt% of the crude isoprene added in the first reaction.
[0028] As a preferred embodiment, after the distillation vessel liquid is recycled, a saturated ammonium chloride solution is added to the distillation vessel liquid, and the mixture is stirred and hydrolyzed at room temperature for 20–24 hours. Distillation is then performed to recover the alcohol, organic base, and ketone. The recovered alcohol, organic base, and ketone are then reused. The reason for adding saturated ammonium chloride in this invention is to utilize the weak acidity of the ammonium chloride solution to promote the hydrolysis of the intermediate onium salt into ketones and bases, thereby facilitating their recovery.
[0029] As a preferred embodiment, the cyclopentadiene content in the high-purity isoprene is less than 1.0 ppm. The method of this invention can further reduce or completely remove trace amounts of cyclopentadiene, avoiding side reactions during the polymerization process.
[0030] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:
[0031] 1) All raw materials used in this invention are liquids, the reaction process is homogeneous without precipitation, the reaction process is simple, the reaction time is short, the degree of cyclopentadiene removal is high, and the cyclopentadiene content in isoprene is less than 1.0 ppm; all treatment agents can be recycled, and the production cost is low.
[0032] 2) This invention uses an organic base instead of an inorganic base as a catalyst, which not only avoids the precipitation during the reaction process, but also easily forms an intermediate onium salt with cyclic ketone compounds, and then rapidly reacts with trace amounts of cyclopentadiene to form a high-boiling-point cyclopentadiene, further achieving deep removal of cyclopentadiene. Attached Figure Description
[0033] Figure 1The images show gas chromatograms of isoprene before and after cyclopentadiene removal (the distillation vessel liquid was recycled 4 times), where 1 represents isoprene before cyclopentadiene removal and 2 represents isoprene after cyclopentadiene removal. The comparison in the images shows that the method of this invention can significantly remove trace amounts of cyclopentadiene from isoprene. Detailed Implementation
[0034] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by those skilled in the art without creative effort are still within the scope of protection of the present invention.
[0035] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.
[0036] Example 1
[0037] 1700g of crude isoprene, 340g of cyclohexanone, and 135g of methanol were added to a 5L pressure vessel. The crude isoprene contained 0.12wt% cyclopentadiene. The mixture was stirred, and 25g of tetrahydropyrrole was added dropwise. The mixture was heated to 42℃ and reacted for 30min. The reaction solution was then distilled at atmospheric pressure at 45–70℃, and the fraction collected at 34–37℃ was used to obtain 1695g of isoprene fraction. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1631g of isoprene. According to standard SH / T 1790-2015, the cyclopentadiene content in the isoprene was 0ppm by gas chromatography. After washing and steam stripping, 58g of methanol was obtained.
[0038] First reuse of the distillation vessel liquid: 1700g crude isoprene and 60g methanol were added to the distillation vessel liquid, and the reaction was carried out at 42℃ for 30min. The reaction solution was distilled at atmospheric pressure at 45-70℃, and the fraction at 34-37℃ was collected to obtain 1715g isoprene fraction. The isoprene fraction was washed three times with 300ml deionized water to obtain 1651g isoprene. According to the standard SH / T 1790-2015, the cyclopentadiene content in isoprene was 0ppm by gas chromatography. After washing and steam stripping, 59g methanol was obtained.
[0039] The reaction mixture was recycled a second time: 1700g of crude isoprene and 60g of methanol were added to the distillation vessel liquid again, and the reaction was carried out at 42℃ for 45min. The reaction solution was distilled at atmospheric pressure at 45-70℃, and the fraction at 34-37℃ was collected to obtain 1714g of isoprene fraction. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1650g of isoprene. According to the standard SH / T 1790-2015, the cyclopentadiene content in isoprene was 0ppm by gas chromatography. After washing and steam stripping, 59g of methanol was obtained.
[0040] The reaction mixture was recycled for the third time: 1700g of crude isoprene and 60g of methanol were added to the distillation vessel liquid again, and the reaction was carried out at 42℃ for 60min. The reaction solution was distilled at atmospheric pressure at 45-70℃, and the fraction at 34-37℃ was collected to obtain 1715g of isoprene fraction. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1650g of isoprene. According to the standard SH / T 1790-2015, the cyclopentadiene content in isoprene was 0ppm by gas chromatography. After washing and steam stripping, 59g of methanol was obtained.
[0041] The reaction mixture was recycled for the fourth time: 1700g of crude isoprene and 61g of methanol were added to the distillation mixture again, and the reaction was carried out at 42℃ for 90min. The reaction mixture was distilled at atmospheric pressure at 45-70℃, and the fraction collected at 34-37℃ was obtained, yielding 1714g of isoprene fraction. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1660g of isoprene. According to the standard SH / T 1790-2015, the cyclopentadiene content in isoprene was analyzed by gas chromatography and found to be 0.6ppm. After washing and steam stripping, 58g of methanol was obtained.
[0042] Add 50g of saturated ammonium chloride solution to the distillation vessel liquid, stir and hydrolyze at room temperature for 24h, then distill to recover 72g of methanol, 20g of tetrahydropyrrole, and 321g of cyclohexanone.
[0043] Example 2
[0044] 1700g of crude isoprene, 255g of cyclohexanone, and 60g of ethanol were added to a 5L pressure vessel. The crude isoprene contained 0.12wt% cyclopentadiene. The mixture was stirred, and 8g of tetrahydropyrrole was added dropwise. The mixture was heated to 60℃ and reacted for 40min. The reaction solution was then distilled at atmospheric pressure at 45-75℃, and the fraction collected at 36-42℃ was used to obtain 1690g of isoprene fraction. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1659g of isoprene. According to standard SH / T1790-2015, the cyclopentadiene content in the isoprene was 0ppm by gas chromatography. After washing and steam stripping, 30g of ethanol was obtained.
[0045] First reuse of the distillation vessel liquid: Add 1700g of crude isoprene and 34g of ethanol to the distillation vessel liquid, and react at 60℃ for 30min. Distill the reaction solution at atmospheric pressure at 45-75℃, and collect the fraction at 36-42℃ to obtain 1705g of isoprene fraction. Wash the isoprene fraction three times with 300ml of deionized water to obtain 1673g of isoprene. According to standard SH / T 1790-2015, the cyclopentadiene content in isoprene is 0ppm by gas chromatography. After washing and steam stripping, 31g of ethanol is obtained.
[0046] The reaction mixture was recycled a second time: 1700g of crude isoprene and 34g of ethanol were added to the distillation vessel liquid again, and the mixture was reacted at 60℃ for 45min. The reaction solution was distilled at atmospheric pressure at 45-75℃, and the fraction at 36-42℃ was collected to obtain 1710g of isoprene fraction. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1671g of isoprene. According to the standard SH / T 1790-2015, the cyclopentadiene content in isoprene was 0ppm by gas chromatography. After washing with water and vapor stripping, 30g of ethanol was obtained.
[0047] The reaction mixture was recycled for the third time: 1700g of crude isoprene and 34g of ethanol were added to the distillation vessel liquid again, and the reaction was carried out at 60℃ for 70min. The reaction solution was distilled at atmospheric pressure at 45-75℃, and the fraction at 36-42℃ was collected to obtain 1712g of isoprene fraction. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1676g of isoprene. According to the standard SH / T 1790-2015, the cyclopentadiene content in isoprene was 0ppm by gas chromatography. After washing with water and vapor stripping, 32g of ethanol was obtained.
[0048] The reaction mixture was recycled for the fourth time: 1700g of crude isoprene and 34g of ethanol were added to the distillation vessel liquid again, and the reaction was carried out at 60℃ for 100min. The reaction solution was distilled at atmospheric pressure at 45-75℃, and the fraction at 36-42℃ was collected to obtain 1710g of isoprene fraction. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1675g of isoprene. According to the standard SH / T 1790-2015, the cyclopentadiene content in isoprene was analyzed by gas chromatography and found to be 0.8ppm. After washing and steam stripping, 33g of ethanol was obtained.
[0049] Add 50g of saturated ammonium chloride solution to the distillation vessel liquid, stir and hydrolyze at room temperature for 24h, then distill to recover 25g of ethanol, 6g of tetrahydropyrrole, and 241g of cyclohexanone.
[0050] Example 3
[0051] 1700g of crude isoprene, 170g of cyclohexanone, and 208g of isopropanol were added to a 5L pressure vessel. The crude isoprene contained 0.12wt% cyclopentadiene. The mixture was stirred, and 30g of hexahydropyridine was added dropwise. The mixture was heated to 45℃ and reacted for 45min. The reaction solution was then distilled at atmospheric pressure at 45-80℃, and the fraction distilled at 36-42℃ was collected to obtain 1705g of isoprene fraction. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1651g of isoprene. According to standard SH / T 1790-2015, the cyclopentadiene content in the isoprene was 0ppm by gas chromatography. After washing and steam stripping, 52g of isopropanol was obtained.
[0052] First reuse of the distillation vessel liquid: Add 1700g crude isoprene and 51g isopropanol to the distillation vessel liquid and react at 45℃ for 45min. Distill the reaction solution at atmospheric pressure (45-80℃), collecting the fraction at 34-38℃ to obtain 1712g isoprene fraction. Wash the isoprene fraction three times with 300ml deionized water to obtain 1658g isoprene. According to standard SH / T 1790-2015, the cyclopentadiene content in isoprene is 0ppm by gas chromatography. After washing and steam stripping, 51g isopropanol is obtained.
[0053] The reaction mixture was recycled a second time: 1700g of crude isoprene and 51g of isopropanol were added to the distillation vessel liquid again, and the reaction was carried out at 45℃ for 60min. The reaction solution was distilled at atmospheric pressure at 45-80℃, and the fraction at 36-42℃ was collected to obtain 1713g of isoprene fraction. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1661g of isoprene. According to the standard SH / T 1790-2015, the cyclopentadiene content in isoprene was 0ppm by gas chromatography. After washing and steam stripping, 51g of isopropanol was obtained.
[0054] The reaction mixture was recycled for the third time: 1700g of crude isoprene and 51g of isopropanol were added to the distillation vessel liquid again, and the reaction was carried out at 45℃ for 90min. The reaction solution was distilled at atmospheric pressure at 45-80℃, and the fraction at 36-42℃ was collected to obtain 1713g of isoprene fraction. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1661g of isoprene. According to the standard SH / T 1790-2015, the cyclopentadiene content in isoprene was 0ppm by gas chromatography. After washing and steam stripping, 50g of isopropanol was obtained.
[0055] The reaction mixture was recycled for the fourth time: 1700g of crude isoprene and 51g of isopropanol were added again to the distillation mixture, and the reaction was carried out at 45℃ for 120min. The reaction mixture was distilled at atmospheric pressure at 45-70℃, and the fraction at 36-42℃ was collected to obtain 1712g of isoprene fraction. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1662g of isoprene. According to the standard SH / T 1790-2015, the cyclopentadiene content in isoprene was analyzed by gas chromatography and found to be 0.6ppm. After washing and steam stripping, 50g of isopropanol was obtained.
[0056] Add 40g of saturated ammonium chloride solution to the distillation vessel liquid, stir and hydrolyze at room temperature for 24h, then distill to recover 155g of isopropanol, 22g of hexahydropyridine, and 153g of cyclohexanone.
[0057] Example 4
[0058] 1700g of crude isoprene, 340g of cyclopentanone, and 258g of methanol were added to a 5L pressure vessel. The crude isoprene contained 0.46wt% cyclopentanone. The mixture was stirred, and 52g of hexahydropyridine was added dropwise. The mixture was heated to 30℃ and reacted for 60min. The reaction solution was then distilled at atmospheric pressure at 45–70℃, and the fraction collected at 34–37℃ was used to obtain 1723g of isoprene fraction. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1658g of isoprene. According to standard SH / T 1790-2015, the cyclopentanone content in the isoprene was 0ppm by gas chromatography. After washing and steam stripping, 63g of methanol was obtained.
[0059] First reuse of the distillation vessel liquid: 1700g of crude isoprene and 68g of methanol were added to the distillation vessel liquid, and the reaction was carried out at 30℃ for 60min. The reaction solution was distilled at atmospheric pressure at 45-70℃, and the fraction at 34-37℃ was collected to obtain 1721g of isoprene fraction. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1655g of isoprene. According to the standard SH / T 1790-2015, the cyclopentadiene content in isoprene was 0ppm by gas chromatography. After washing with water and vapor stripping, 64g of methanol was obtained.
[0060] The reaction mixture was recycled a second time: 1700g of crude isoprene and 68g of methanol were added to the distillation vessel liquid again, and the reaction was carried out at 30℃ for 75min. The reaction solution was distilled at atmospheric pressure at 45-70℃, and the fraction at 34-37℃ was collected to obtain 1722g of isoprene fraction. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1656g of isoprene. According to the standard SH / T 1790-2015, the cyclopentadiene content in isoprene was 0ppm by gas chromatography. After washing with water and vapor stripping, 64g of methanol was obtained.
[0061] The reaction mixture was recycled for the third time: 1700g of crude isoprene and 68g of methanol were added to the distillation vessel liquid again, and the reaction was carried out at 30℃ for 90min. The reaction solution was distilled at atmospheric pressure at 45-70℃, and the fraction at 34-37℃ was collected to obtain 1723g of isoprene fraction. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1659g of isoprene. According to the standard SH / T 1790-2015, the cyclopentadiene content in isoprene was 0ppm by gas chromatography. After washing and steam stripping, 63g of methanol was obtained.
[0062] The reaction mixture was recycled for the fourth time: 1700g of crude isoprene and 68g of methanol were added to the distillation vessel liquid again, and the reaction was carried out at 30℃ for 120min. The reaction solution was distilled at atmospheric pressure at 45-70℃, and the fraction at 34-37℃ was collected to obtain 1723g of isoprene fraction. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1657g of isoprene. Gas chromatography analysis showed that the cyclopentadiene content in the isoprene was 0.9ppm. After washing and steam stripping, 64g of methanol was obtained.
[0063] Add 50g of saturated ammonium chloride solution to the distillation vessel liquid, stir and hydrolyze at room temperature for 24h, then distill to recover 191g of methanol, 43g of hexahydropyridine, and 320g of cyclohexanone.
[0064] Comparative Example 1
[0065] At room temperature, 135g of methanol was added to 25g of potassium hydroxide for 30 minutes to obtain solution A.
[0066] 1700g of crude isoprene and 340g of cyclohexanone were added to solution A. The crude isoprene contained 0.12wt% cyclopentadiene. The mixture was stirred for 72h to obtain a mixed solution B1. Solution B1 was distilled at atmospheric pressure at 75℃ to obtain 1705g of isoprene fraction and distillate D1. According to standard SH / T 1790-2015, the cyclopentadiene content in the isoprene fraction was 12ppm and the methanol content was 4.2%. A precipitate formed after the distillate was cooled to room temperature.
[0067] 1700 g of isoprene was added to distillate D1 and stirred for 98 h to obtain mixed solution B2. Solution B2 was then distilled at atmospheric pressure at 75 °C to obtain 1710 g of isoprene fraction and distillate D2. Gas chromatography analysis of the isoprene fraction according to standard SH / T1790-2015 showed that the cyclopentadiene content was 36 ppm and the methanol content was 3.9%.
[0068] 1700 g of isoprene was added to distillate D2 and stirred for 72 h to obtain mixed solution B3. Solution B3 was then distilled at atmospheric pressure at 75 °C to obtain 1707 g of isoprene fraction and distillate D3. Gas chromatography analysis of the isoprene fraction according to standard SH / T1790-2015 showed that the cyclopentadiene content was 75 ppm and the methanol content was 3.2%.
[0069] Compared with Example 1, since an equal amount of inorganic base was used instead of organic base in Comparative Example 1, not only did precipitation occur in the distillation kettle liquid, leading to process complexity and a reduced removal rate, but the distillation kettle liquid also could not be recycled.
[0070] Comparative Example 2
[0071] 1700g of crude isoprene, 340g of cyclohexanone, and 135g of n-butanol were added to a 5L pressure vessel. The crude isoprene contained 0.12wt% cyclopentadiene. The mixture was stirred, and 25g of tetrahydropyrrole was added dropwise. The mixture was heated to 42℃ and reacted for 30min. The reaction solution was then distilled at atmospheric pressure at 45–70℃, and the fraction collected at 35–39℃ was used to obtain 1698g of isoprene fraction. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1646g of isoprene. According to standard SH / T 1790-2015, the cyclopentadiene content in the isoprene was 62ppm by gas chromatography.
[0072] Compared with Example 1, the results show that when an equal amount of n-butanol is used instead of the alcohols selected in this invention, the removal effect of cyclopentadiene from isoprene decreases.
[0073] Comparative Example 3
[0074] 1700g of crude isoprene, 340g of butanone, and 135g of methanol were added to a 5L pressure vessel. The crude isoprene contained 0.12wt% cyclopentadiene. The mixture was stirred, and 25g of tetrahydropyrrole was added dropwise. The mixture was heated to 42℃ and reacted for 30min. The reaction solution was then distilled at atmospheric pressure at 45–70℃, and the fraction collected at 34–37℃ was used to obtain 1693g of isoprene. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1646g of isoprene. According to standard SH / T1790-2015, the cyclopentadiene content in the isoprene was 47ppm by gas chromatography.
[0075] Compared with Example 1, when an equal amount of chain-like short carbon ketones are used to replace cyclic ketones, the low boiling point increases the difficulty of separation by distillation and makes it impossible to form high-boiling-point intermediate onium salts, thus reducing the removal effect.
[0076] Comparative Example 4
[0077] 1700g of crude isoprene, 340g of cyclohexanone, and 30g of methanol were added to a 5L pressure vessel. The crude isoprene contained 0.12wt% cyclopentadiene. The mixture was stirred, and 25g of tetrahydropyrrole was added dropwise. The mixture was heated to 42℃ and reacted for 30min. The reaction solution was then distilled at atmospheric pressure at 45–70℃, and the fraction collected at 35–39℃ was used to obtain 1682g of isoprene fraction. The isoprene fraction was washed three times with 300ml of deionized water to obtain 1658g of isoprene. According to standard SH / T1790-2015, the cyclopentadiene content in the isoprene was 52ppm by gas chromatography.
[0078] Compared with Example 1, when the amount of alcohol is too small, the purification rate of isoprene is low and the removal rate of cyclopentadiene is reduced.
Claims
1. A method for removing trace amounts of cyclopentadiene from isoprene, characterized in that: After reacting crude isoprene with a solution containing cyclic ketones, alcohols, and organic bases, the mixture is distilled to obtain isoprene containing alcohol and distillate. The isoprene containing alcohol is then washed with water and separated to obtain high-purity isoprene and alcohol-containing wastewater.
2. The method for removing trace amounts of cyclopentadiene from isoprene according to claim 1, characterized in that: The cyclic ketone compounds are cyclopentanone and / or cyclohexanone.
3. The method for removing trace amounts of cyclopentadiene from isoprene according to claim 2, characterized in that: The alcohol is at least one of methanol, ethanol, and isopropanol.
4. A method for removing trace amounts of cyclopentadiene from isoprene according to any one of claims 1 to 3, characterized in that: The organic base is tetrahydropyrrole and / or hexahydropyridine.
5. The method for removing trace amounts of cyclopentadiene from isoprene according to claim 4, characterized in that: The molar ratio of the cyclic ketone compound, alcohol, and organic base is 1:(0.5-2):(0.04-0.2).
6. The method for removing trace amounts of cyclopentadiene from isoprene according to claim 2, characterized in that: The amount of the cyclic ketone compound added is 10-20 wt% of the crude isoprene.
7. The method for removing trace amounts of cyclopentadiene from isoprene according to claim 1, characterized in that: The reaction conditions are: temperature 30–60°C, time 0.5–2 h.
8. A method for removing trace amounts of cyclopentadiene from isoprene according to claim 1, 2, 3, 5, 6 or 7, characterized in that: The crude isoprene contains 0.05 to 0.5 wt% cyclopentadiene.
9. The method for removing trace amounts of cyclopentadiene from isoprene according to claim 1, characterized in that: The crude isoprene and alcohol are added to the distillation kettle liquid to further remove cyclopentadiene from isoprene; the alcohol-containing wastewater is stripped to recover alcohol, and the recovered alcohol is reused.
10. A method for removing trace amounts of cyclopentadiene from isoprene according to claim 9, characterized in that: The distillation vessel liquid is recycled 2 to 5 times; The mass of the added crude isoprene is the same as the mass of the crude isoprene added in the first reaction; the mass of the added alcohol is 2-4 wt% of the crude isoprene added in the first reaction.
11. The method for removing trace amounts of cyclopentadiene from isoprene according to claim 1, characterized in that: The high-purity isoprene contains less than 1.0 ppm of cyclopentadiene.