Toluene, method for recovering toluene from organic solution containing toluene and application of toluene

Abstract

The invention relates to the field of substance purification, in particular to methylbenzene, a method for recovering methylbenzene from an organic solution containing methylbenzene and application. The method comprises the following steps: carrying out first-stage refining and second-stage refining on an organic solution subjected to water washing, dehydration and distillation; the first-stage refining is carried out in the presence of a 4A molecular sieve, and the second-stage refining is carried out in the presence of a 5A molecular sieve. According to the method, the toluene-containing organic solution subjected to pretreatment under different conditions is treated, so that the content of impurities such as alkane in toluene can be remarkably reduced, and the recycling frequency of the obtained toluene is remarkably increased.

Description

Technical Field

[0001] This invention relates to the field of substance purification, and more specifically to toluene and a method and application for recovering toluene from toluene-containing organic solutions. Background Technology

[0002] Since the advent of Ziegler-Natta catalysts in the 1950s, their overall performance, appearance, and preparation methods have been continuously improved, driving the vigorous development of the polyolefin industry. Although subsequent developments of metallocene and post-transition metal catalysts have attracted much attention, Ziegler-Natta catalysts currently and in the future still dominate the polyolefin field. Particulate polyolefin catalysts, as a typical ZN catalyst, generally require the dissolution of magnesium chloride in toluene, followed by esterification, toluene-titanium tetrachloride treatment, hexane washing, and catalyst drying. However, the amount of toluene input during preparation far exceeds the amount consumed, leading to a continuous increase in organic solvent content, affecting the long-term operation of the plant. Toluene is an important organic solvent, and its purity significantly impacts the quality of the synthesized catalyst. Therefore, toluene requires a certain purity level, necessitating purification and recycling of the organic solvent. CN111111248A proposes a method to remove titanium-containing substances and impurities such as hexane from organic solvents through water washing, distillation, and rectification to obtain toluene with a purity of 99.5%, which can then be reused in the catalyst preparation process. However, as the plant operates, it is found that the organic solvents still contain small amounts of straight-chain and branched alkanes such as hexane, ethylpentane, and 3-methylheptane, and their concentrations gradually increase with the increase of operating time, which affects the quality of the catalyst product. Summary of the Invention

[0003] The purpose of this invention is to overcome the problems of incomplete purification and difficulty in recycling toluene solutions in existing technologies, and to provide a method and application for recovering toluene from toluene-containing organic solutions. This method ensures that the obtained toluene contains no more than 0.2 wt% impurities, such as alkanes, significantly increasing the number of toluene recycling cycles.

[0004] To achieve the above objectives, a first aspect of the present invention provides a method for recovering toluene from a toluene-containing organic solution, the method comprising performing a first-stage purification and a second-stage purification on the organic solution after washing, dehydration, and distillation; the first-stage purification is performed in the presence of a 4A molecular sieve, and the second-stage purification is performed in the presence of a 5A molecular sieve.

[0005] The second aspect of the present invention provides toluene recovered by the method of the first aspect, wherein the toluene contains ≥99.80% by weight of toluene and ≤0.20% by weight of total alkane content.

[0006] The third aspect of this invention provides the application of toluene as described in the second aspect in the preparation of polyolefin catalysts.

[0007] Through the above technical solution, the present invention has the following advantages:

[0008] This invention significantly reduces the content of impurities such as alkanes in toluene by treating the pretreated toluene-containing organic solution under different conditions, thereby increasing the number of times the obtained toluene can be recycled. Attached Figure Description

[0009] Figure 1 This is an apparatus and flowchart for recovering toluene from a toluene-containing organic solution according to a preferred embodiment of the present invention.

[0010] Explanation of reference numerals in the attached figures

[0011] 1. Storage tank; 2. First washing tank; 3. Layered tank; 4. Wastewater collection tank; 5. Second washing tank; 6. Distillation tower; 7. Toluene recovery tank; 8. Distillate recovery tank; 9. Toluene primary purification tower; 10. Toluene secondary purification tower; 11. Refined toluene recovery tank. Detailed Implementation

[0012] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0013] A method for recovering toluene from a toluene-containing organic solution, the method comprising a first-stage purification and a second-stage purification of the organic solution after washing with water, dehydration, and distillation; the first-stage purification is carried out in the presence of a 4A molecular sieve, and the second-stage purification is carried out in the presence of a 5A molecular sieve.

[0014] This invention significantly reduces the content of impurities such as alkanes in toluene by treating the pretreated toluene organic solution under different conditions, thereby significantly increasing the number of times the obtained toluene can be recycled.

[0015] According to a preferred embodiment of the present invention, the first-stage purification is carried out in the presence of a mixture consisting of at least one of modified ZSM-5 molecular sieve, CHA molecular sieve, ZSM-11 molecular sieve, and ZSM-35 molecular sieve, and 4A and 5A molecular sieves. Preferably, the content of 4A molecular sieve in the mixture is 20-30% by weight, and the content of 5A molecular sieve is 30-50% by weight. By adopting the aforementioned preferred embodiment, the content of impurities such as alkanes and water in the organic solution can be further reduced.

[0016] According to a preferred embodiment of the present invention, the second-stage purification is carried out in the presence of a mixture consisting of at least one of modified ZSM-5 molecular sieve, CHA molecular sieve, ZSM-11 molecular sieve, and ZSM-35 molecular sieve, and 5A molecular sieve, preferably with the content of 5A molecular sieve in the mixture being 15-25% by weight. By adopting the aforementioned preferred embodiment, the content of impurity alkane in the organic solution can be further reduced.

[0017] According to a preferred embodiment of the present invention, the conditions for the first-stage purification include: a purification temperature of 15-40°C and a purification time of 15-25 hours. By adopting the aforementioned preferred embodiment, the content of impurities such as alkanes in the organic solution can be further reduced.

[0018] According to a preferred embodiment of the present invention, the conditions for the second-stage purification include: a purification temperature of 25-50°C and a purification time of 10-20 hours. By adopting the aforementioned preferred embodiment, the content of impurities such as alkanes in the organic solution can be further reduced.

[0019] According to a preferred embodiment of the present invention, the temperature of the second-stage purification is 10-25°C higher than the temperature of the first-stage purification. By adopting the aforementioned preferred embodiment, the content of impurities such as alkanes in the organic solution can be further reduced.

[0020] According to a preferred embodiment of the present invention, the toluene-containing organic solution is an organic solution produced during the preparation of a polyolefin catalyst.

[0021] According to a preferred embodiment of the present invention, the organic solution contains 1-5% by weight of hexane, 94-98% by weight of toluene, 0.5-1% by weight of titanium-containing substances, 0.5-1% by weight of other alkanes and 0.01-0.5% by weight of water.

[0022] In this invention, the washing, dehydration, and distillation methods can be conventional techniques in the field.

[0023] According to the present invention, the washing method is agitated washing, and the organic solution and washing water are mixed in a countercurrent contact manner. The washing conditions include: washing temperature of 10-40°C and washing time of 15-30 minutes. This method can remove titanium-containing substances from the organic solution.

[0024] According to the present invention, the dehydration method is static stratification, with a static temperature of 10-40°C and a static time of 60-120 minutes, resulting in an aqueous phase and an organic phase.

[0025] According to the present invention, the distillation method is segmented distillation, with a pressure of 0-10 kPa and a temperature of 85-110°C at the top, a temperature of 100-115°C in the distillation section, and a temperature of 105-120°C at the bottom; thus obtaining preliminarily separated impurities and crude toluene.

[0026] According to a preferred embodiment of the present invention, before distillation, the organic layer obtained by standing and separating is stirred and washed with water to further remove titanium-containing substances from the organic solution.

[0027] The present invention provides a method for recovering toluene by means of a method, wherein the toluene content is ≥99.8% by weight and the total alkane content is ≤0.2% by weight;

[0028] According to a preferred embodiment of the present invention, the water content in the toluene is ≤15μg / g.

[0029] This invention provides an application of the toluene described above in the preparation of polyolefin catalysts.

[0030] like Figure 1 As shown, the present invention provides a preferred apparatus and flowchart for recovering toluene from a toluene-containing organic solution:

[0031] The device includes:

[0032] The storage tank 1, the first washing tank 2, the layered tank 3, the second washing tank 5, the distillation tower 6, the toluene recovery tank 7, the primary toluene refining tower 9, the secondary toluene refining tower 10, and the refined toluene recovery tank are connected in series. Among them, the bottom of the layered tank 5 is also connected to the wastewater collection tank 4, the upper part of the distillation tower 6 is also equipped with the distillate recovery tank, the primary toluene refining tower 9 is two packed towers arranged in parallel, and the secondary toluene refining tower 10 is two packed towers arranged in parallel. Optionally, a switch or pumping device can be installed at the inlet and outlet of each unit.

[0033] The process includes: feeding the toluene-containing organic solution from storage tank 1 into the first washing tank 2 for washing with countercurrent water; feeding the washing stream into the separation tank 3 for settling to obtain an aqueous phase which is then fed into the wastewater collection tank 4; feeding the obtained organic phase into the second washing tank 5 for washing with countercurrent water; feeding the washed stream into the distillation column 6 for distillation to remove some impurities, which is then collected in the distillate recovery tank 8; feeding the crude toluene into the toluene recovery tank 7; feeding the crude toluene from the toluene recovery tank 7 into one of the packed columns in the primary toluene refining column 9 for refining (the other column is used for packing regeneration or replacement); feeding the refined stream into one of the packed columns in the secondary toluene refining column 10 for refining (the other column is used for packing regeneration or replacement); and feeding the distillate product into the refined toluene recovery tank 11 for collection and reuse.

[0034] The present invention will be described in detail below through embodiments.

[0035] In the following examples, organic compounds such as toluene and alkanes were tested by gas chromatography, and the water content in the solution was determined by Karl Fischer method. The raw material was an organic solution produced during the preparation of polyolefin catalyst, in which toluene accounted for 99.12% by weight, impurities accounted for 0.88% by weight, and water content was approximately 500 μg / g.

[0036] Example 1

[0037] use Figure 1The apparatus shown involves batch-pressing the recovered organic solvent from the bottom of the first washing tank 2 (specifically, an enamel-lined kettle) into the first washing tank 2 containing a certain amount of fresh water. The washing temperature in the first washing tank 2 is 25°C. The organic solvent is stirred and held in the first washing tank for 30 minutes (water is injected from the top of the first washing tank, creating a countercurrent with the organic solvent being pressed in from the bottom). The titanium-containing components in the organic solvent are removed through washing, and the titanium-containing wastewater is pressed into the wastewater collection tank 4. The washed organic solvent is then transferred to the layering tank 3, where it is allowed to stand at 25°C for 90 minutes. The wastewater at the bottom of the layering tank is also pressed into the wastewater collection tank 4. The organic solvent in the layering tank 3 is then pressed into the second washing tank 5, where the washing temperature is 30°C. The organic solvent is stirred and held in the second washing tank for 25 minutes before being pressed into the distillation column 6. The distillation column 6 is configured with the following settings: a pressure of 7 kPa and a temperature of 99°C at the top, a temperature of 108°C in the distillation section, and a temperature of 1... At 14℃, fractional distillation is performed, and the collected hexane and crude toluene are sent to distillate recovery tank 8 and toluene recovery tank 7, respectively. The crude toluene in toluene recovery tank 7 is sent to toluene primary purification column 9. In toluene primary purification column 9, after rectification and dehydration, hexane removal, and preliminary debranching of alkanes by molecular sieves (30 wt% 4A molecular sieve, 50 wt% 5A molecular sieve, and 20 wt% modified ZSM-5 molecular sieve) built into toluene purification column 9, the primary purified toluene solution is then sent to... The toluene is then transferred to the secondary toluene refining tower 10. After further debranching of alkanes by distillation and the presence of molecular sieves (20 wt% 5A molecular sieve and 60 wt% modified ZSM-5 and 20 wt% ZSM-35 molecular sieves) inside the toluene refining tower 10, the final refined toluene is transferred to the refined toluene recovery tank 11 for later use. The primary distillation temperature of the toluene is 30°C and the time is 20 h, while the secondary distillation temperature of the toluene is 40°C and the time is 15 h.

[0038] The toluene in the refined toluene recovery tank 11 was analyzed: the toluene content was 99.80% by weight, the water content was 15 μg / g, and the alkane content was 0.20% by weight.

[0039] Example 2

[0040] use Figure 1The apparatus shown is the same as in Example 1, except that in this example, after dehydration, hexane removal, and preliminary debranching of toluene in the primary toluene refining tower 9 via distillation and the presence of molecular sieves (35 wt% 4A molecular sieve, 40 wt% 5A molecular sieve, and 25 wt% modified ZSM-5 molecular sieve) within the toluene refining tower 9, the primary refined toluene solution is sent to the secondary toluene refining tower 10. In the secondary toluene refining tower 10, after further debranching of toluene via distillation and the presence of molecular sieves (15 wt% 5A molecular sieve, 65 wt% modified ZSM-5, and 20 wt% ZSM-35 molecular sieve) within the toluene refining tower 10, the finally obtained refined toluene is transferred to the refined toluene recovery tank 11 for later use. The primary distillation temperature is 25°C and the time is 20 hours, while the secondary distillation temperature is 50°C and the time is 15 hours.

[0041] The toluene in the refined toluene recovery tank 11 was analyzed: the toluene content was 99.82% by weight, the water content was 12 μg / g, and the alkane content was 0.18% by weight.

[0042] Example 3

[0043] use Figure 1 The apparatus shown is the same as in Example 1, except that in this example, after dehydration, hexane removal, and preliminary debranching of toluene by distillation and molecular sieves (30 wt% 4A molecular sieve, 50 wt% 5A molecular sieve, and 20 wt% modified ZSM-5 molecular sieve) in the primary toluene refining tower 9, the primary refined toluene solution is sent to the secondary toluene refining tower 10. In the secondary toluene refining tower 10, after further debranching of toluene by distillation and molecular sieves (20 wt% 5A molecular sieve, 60 wt% modified ZSM-5, and 20 wt% ZSM-35 molecular sieve) in the secondary toluene refining tower 10, the finally obtained refined toluene is transferred to the refined toluene recovery tank 11 for later use. The primary distillation temperature is 35°C and the time is 25 hours, while the secondary distillation temperature is 45°C and the time is 20 hours.

[0044] The toluene in the refined toluene recovery tank 11 was analyzed: the toluene content was 99.85% by weight, the water content was 14 μg / g, and the alkane content was 0.15% by weight.

[0045] Example 4

[0046] use Figure 1The apparatus shown is the same as in Example 1, except that in this example, after dehydration, hexane removal, and preliminary debranching of toluene by distillation and molecular sieves (50 wt% 4A molecular sieve and 50 wt% 5A molecular sieve) in the primary toluene refining tower 9, the primary refined toluene solution is sent to the secondary toluene refining tower 10. After further debranching of toluene by distillation and molecular sieves (100 wt% 5A molecular sieve) in the secondary toluene refining tower 10, the finally obtained refined toluene is transferred to the refined toluene recovery tank 11 for later use. The primary distillation temperature of the toluene is 30°C and the time is 20 hours, and the secondary distillation temperature of the toluene is 40°C and the time is 15 hours.

[0047] The toluene in the refined toluene recovery tank 11 was analyzed: the toluene content was 99.65% by weight, the water content was 12 μg / g, and the alkane content was 0.35% by weight.

[0048] Example 5

[0049] use Figure 1 The apparatus shown is the same as in Example 1, except that in this example, after dehydration, hexane removal, and preliminary debranching of toluene by distillation and molecular sieves (30 wt% 4A molecular sieve, 50 wt% 5A molecular sieve, and 20 wt% modified ZSM-5 molecular sieve) in the primary toluene refining tower 9, the primary refined toluene solution is sent to the secondary toluene refining tower 10. In the secondary toluene refining tower 10, after further debranching of toluene by distillation and molecular sieves (20 wt% 5A molecular sieve, 60 wt% modified ZSM-5, and 20 wt% ZSM-35 molecular sieve) in the secondary toluene refining tower 10, the finally obtained refined toluene is transferred to the refined toluene recovery tank 11 for later use. The primary distillation temperature is 50°C and the time is 5 hours, and the secondary distillation temperature is 15°C and the time is 5 hours.

[0050] The toluene in the refined toluene recovery tank 11 was analyzed: the toluene content was 99.50% by weight, the water content was 25 μg / g, and the alkane content was 0.50% by weight.

[0051] Example 6

[0052] use Figure 1 The device shown is the same as in Embodiment 1, except that: in this embodiment,

[0053] The molecular sieves built into the toluene primary refining tower 9 are 80% by weight 4A molecular sieve and 20% by weight modified ZSM-5 molecular sieve.

[0054] The toluene in the refined toluene recovery tank 11 was analyzed: the toluene content was 99.55% by weight, the water content was 11 μg / g, and the alkane content was 0.45% by weight.

[0055] Comparative Example 1

[0056] Similar to Example 1, but with the following difference: After dehydration, hexane removal, and preliminary debranching of toluene in the primary toluene refining tower 9 via distillation and the presence of molecular sieves (30 wt% 4A molecular sieve, 50 wt% 5A molecular sieve, and 20 wt% modified ZSM-5 molecular sieve) within the toluene refining tower 9, the primary refined toluene solution is sent to the secondary toluene refining tower 10. In the secondary toluene refining tower 10, after further debranching of toluene via distillation and the presence of molecular sieves (20 wt% 4A molecular sieve, 60 wt% modified ZSM-5, and 20 wt% ZSM-35 molecular sieve) within the toluene refining tower 10, the finally obtained refined toluene is transferred to the refined toluene recovery tank 11 for later use. The primary distillation temperature is 30°C and the time is 20 hours, while the secondary distillation temperature is 40°C and the time is 15 hours.

[0057] The toluene in the refined toluene recovery tank 11 was analyzed: the toluene content was 99.22% by weight, the water content was 12 μg / g, and the alkane content was 0.78% by weight.

[0058] Comparative Example 2

[0059] Similar to Example 1, but with the following difference: After dehydration, hexane removal, and preliminary debranching of toluene in the primary toluene refining tower 9 via distillation and the presence of molecular sieves (30 wt% 5A molecular sieve, 50 wt% 5A molecular sieve, and 20 wt% modified ZSM-5 molecular sieve) within the toluene refining tower 9, the primary refined toluene solution is sent to the secondary toluene refining tower 10. In the secondary toluene refining tower 10, after further debranching of toluene via distillation and the presence of molecular sieves (20 wt% 5A molecular sieve, 60 wt% modified ZSM-5, and 20 wt% ZSM-35 molecular sieve) within the toluene refining tower 10, the finally obtained refined toluene is transferred to the refined toluene recovery tank 11 for later use. The primary distillation temperature is 30°C and the time is 20 hours, while the secondary distillation temperature is 40°C and the time is 15 hours.

[0060] The toluene in the refined toluene recovery tank 11 was analyzed: the toluene content was 99.25% by weight, the water content was 300 μg / g, and the alkane content was 0.75% by weight.

[0061] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for recovering toluene from a toluene-containing organic solution, characterized in that, The method includes a first-stage purification and a second-stage purification of the organic solution that has been washed, dehydrated, and distilled; The first stage of purification is carried out in the presence of 4A molecular sieve, and the second stage of purification is carried out in the presence of 5A molecular sieve.

2. The method according to claim 1, wherein, The first stage of purification is carried out in the presence of a mixture consisting of at least one of modified ZSM-5 molecular sieve, CHA molecular sieve, ZSM-11 molecular sieve, and ZSM-35 molecular sieve, and 4A and 5A molecular sieves. Preferably, the content of 4A molecular sieve in the mixture is 10-35% by weight, and the content of 5A molecular sieve in the mixture is 20-55% by weight.

3. The method according to claim 1 or 2, wherein, The second-stage purification is carried out in the presence of a mixture consisting of at least one of modified ZSM-5 molecular sieve, CHA molecular sieve, ZSM-11 molecular sieve, and ZSM-35 molecular sieve, and 5A molecular sieve. Preferably, the content of 5A molecular sieve in the mixture is 10-25% by weight.

4. The method according to any one of claims 1-3, wherein, The conditions for the first stage of refining include: a refining temperature of 15-40℃ and a refining time of 15-25 hours.

5. The method according to any one of claims 1-4, wherein, The conditions for the second stage of refining include: a refining temperature of 25-50℃ and a refining time of 10-20 hours.

6. The method according to any one of claims 1-5, wherein, The temperature of the second-stage refining is 10-25°C higher than that of the first-stage refining.

7. The method according to any one of claims 1-6, wherein, The toluene-containing organic solution is an organic solution produced during the preparation of polyolefin catalysts.

8. The method according to any one of claims 1-7, wherein, The organic solution contains 1-5% by weight hexane, 94-98% by weight toluene, 0.5-1% by weight titanium-containing substances, 0.5-1% by weight other alkanes and 0.01-0.5% by weight water.

9. The toluene recovered by the method according to any one of claims 1-8, characterized in that, The toluene content in this toluene is ≥99.80% by weight, and the total alkane content is ≤0.20% by weight; Preferably, the water content in the toluene is ≤15μg / g.

10. The use of toluene as described in claim 9 in the preparation of polyolefin catalysts.

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