Purification method of high-purity trimethylaluminum

Abstract

The invention discloses a purification method of high-purity trimethylaluminum. The purification method comprises the following steps: dissolving a crude product TMA in dehydrated and deoxidized normal hexane or methylbenzene in an inert atmosphere; carrying out staged heat preservation at-30 DEG C,-50 DEG C and-80 DEG C in sequence by adopting a staged low-temperature crystallization method, so that impurities with different melting points are selectively separated out, filtered and removed; separating light and heavy components through molecular distillation under 0.1-10 Pa, and collecting a high-purity TMA fraction; removing trace metals by adopting a molecular sieve with the aperture of 0.3 nm or an MOFs adsorbent, and adding a 18-crown-6 or acetylacetone complexing agent with the molar ratio of 0.1-1% for further purification; and packaging after terminal filtering. According to the method, a multi-stage purification technology is innovatively combined, so that the TMA purity reaches 99.999% or above, the metal impurity content is smaller than or equal to 1 ppb, the moisture content is smaller than or equal to 3 ppm, and the waste is safely recycled through isopropyl alcohol quenching and acid pickling. The process has the characteristics of high efficiency, low energy consumption and good product consistency, and can meet the strict requirements of advanced semiconductor manufacturing.

Description

Technical Field

[0001] The present invention relates to the technical field of gas separation and purification, and in particular to a method for purifying high-purity trimethylaluminum. Background Art

[0002] High-purity trimethylaluminum (TMA) is a key precursor material in semiconductor manufacturing, organic light-emitting diodes (OLEDs), and advanced materials synthesis. Its purity directly impacts thin film deposition quality and device performance. For example, in the metal-organic chemical vapor deposition (MOCVD) process, if TMA contains trace metal impurities (such as Fe and Cu) or oxygen-containing compounds, it can lead to film defects and reduced carrier mobility. Therefore, the industrial demand for high-purity TMA typically requires a purity of ≥99.999% (5N grade) and a metal impurity content of ≤1 ppb.

[0003] Currently, the main industrial purification methods for TMA include distillation, crystallization, and adsorption, but all have significant limitations: Distillation: Conventional vacuum distillation can remove most low-boiling-point impurities, but it is difficult to separate components with similar boiling points (such as Al2(CH3)6 dimer), and high temperatures may cause thermal decomposition of TMA. Low-temperature crystallization: Some high-melting-point impurities can be separated through temperature-difference crystallization, but the efficiency of crystallization in a single temperature range is low, and the problem of solvent residue is prominent. Adsorption purification: Molecular sieves or activated carbon are commonly used to adsorb impurities, but traditional adsorbents (such as molecular sieves with a pore size of 0.4 nm) have insufficient selectivity for trace metals in TMA and are prone to adsorbing the target product, resulting in loss.

[0004] In addition, the existing technology is not capable of synergistically removing multiple types of impurities. For example: metal ions (such as 、 ) requires chelating agents, but subsequent separation is difficult; oxygen-containing organic matter (such as Al(CH3)2OCH3) has similar physical properties to TMA, and traditional distillation or crystallization is difficult to effectively separate; moisture control: even trace amounts of water (≥5ppm) will trigger violent hydrolysis of TMA, generating Al(OH)3 that blocks the pipeline.

[0005] Therefore, to address the above problems, the present invention provides a method for purifying high-purity trimethylaluminum, a low-temperature, high-efficiency, multi-stage purification process that achieves the simultaneous and deep removal of impurities such as metals, oxygen-containing substances, and moisture while avoiding TMA decomposition, meeting the semiconductor industry's stringent requirements for ultra-high-purity TMA. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for purifying high-purity trimethylaluminum to achieve the simultaneous deep removal of impurities such as metals, oxygenates and moisture, thereby meeting the stringent requirements of the semiconductor industry for ultra-high-purity TMA.

[0007] The purpose of the present invention is achieved through the following technical solutions: A method for purifying high-purity trimethylaluminum comprises the following steps: (1) Dissolution under inert gas protection: Under inert gas protection, dissolve the crude trimethylaluminum in a dehydrated and deoxygenated high-purity organic solvent to form a homogeneous solution; (2) Gradual low-temperature crystallization: Using the graded low-temperature crystallization method, keep the temperature at -30℃, -50℃, and -80℃ in stages for 0.5~2h, so that impurities with different melting points are gradually precipitated and filtered out; (3) Molecular distillation: Using molecular distillation technology, first remove the light components at 60~80℃, then collect the main fraction at 80~100℃, and the distance between the evaporation surface and the condensation surface is 5~20cm; (4) Adsorption-complexation refining: remove trace metals and oxygen-containing impurities through adsorbents; add complexing agents to chelate residual metal ions, and separate the complex by vacuum distillation; (5) Terminal treatment: Finally, it is filtered through a 0.22 μm filter membrane and packaged with high-purity argon gas to obtain trimethylaluminum with a purity of ≥99.999%.

[0008] Preferably, in step (1), the inert gas is argon or nitrogen, with an oxygen content of ≤1 ppm; and the high-purity organic solvent is n-hexane or toluene, with a purity of ≥99.99%.

[0009] Preferably, in step (2), the mass ratio of the solvent to trimethylaluminum used in the graded low-temperature crystallization method is 1:2-5, and the cooling gradient in each stage is 5-10°C / h.

[0010] Preferably, in step (3), the pressure in the light component removal stage of the molecular distillation is 5-10 Pa, the pressure in the main fraction collection stage is 0.1-1 Pa, and the distillation rate is controlled at 0.5-2 mL / min.

[0011] Preferably, in step (4), the adsorbent is loaded into a fixed bed adsorption column at a flow rate of 1 BV / h and a contact time of 1 to 4 hours; the adsorbent is a molecular sieve with a pore size of 0.3 nm or MIL-101MOFs, at 20 to 60°C.

[0012] Preferably, in step (4), the complexing agent is 18-crown-6 or acetylacetone, and the amount of the complexing agent added is 0.1% to 1% of the molar amount of trimethylaluminum; after the reaction, the complex is removed by reduced pressure distillation at 40°C and 1 kPa.

[0013] Preferably, the dew point of the inert gas protection is ≤-70°C, and all equipment is pre-treated with acid washing, high-temperature baking at 200-300°C, and inert gas replacement.

[0014] Preferably, the content of metal impurities (Fe, Cu, Zn) in the purified trimethylaluminum is ≤1 ppb, and the moisture content is ≤5 ppm.

[0015] Preferably, the method for purifying high-purity trimethylaluminum further comprises a waste treatment step: quenching the crystallization residue, the distillation heavy component and the adsorption waste with isopropanol to generate aluminum isopropoxide (Al(O-iPr)3), and washing the quenched product with 1M HCl to recover the metal ions.

[0016] Preferably, in step (5), the oxygen content of the high-purity argon gas is ≤0.1 ppm.

[0017] Due to the application of the above technical solution, the present invention has the following beneficial effects compared with the prior art: 1. This invention significantly improves product purity. Through the innovative process of multi-stage low-temperature crystallization coupled with molecular distillation, the purity of trimethylaluminum can be stably controlled at ≥99.999% (5N grade), and the key impurity contents are as follows: metal ions (Fe, Cu, Na, etc.) ≤1ppb, oxygen-containing compounds (such as Al(CH3)2OCH3) ≤5ppm, and moisture ≤3ppm, which is 1~2 orders of magnitude higher than the purity of traditional processes; 2. The present invention uses fractional crystallization technology to precisely control the temperature at three stages: -30°C / -50°C / -80°C, which increases the impurity removal rate by more than 80%. Compared with single-stage crystallization, the product yield is increased to 92%. Molecular distillation-adsorption synergistic system: short-path distillation (0.1~1Pa) ensures that heat-sensitive substances do not decompose; MOFs adsorbent is very effective for Fe 3+ The capture efficiency is 99.5%; 3. The present invention optimizes production costs, with a solvent recycling rate of ≥95% (n-hexane / toluene recovery system), reducing energy consumption by 40% compared to traditional high-temperature distillation; the raw material utilization rate is increased to 90%, and the recycling value of scrap aluminum is increased; 4. The present invention is safe and environmentally friendly, and waste materials are harmlessly treated: the isopropyl alcohol quenching process ensures a residual TMA conversion rate of ≥99.9%, and the aluminum salt recovered by pickling can be recycled; the green process design: inert gas protection is used throughout the entire process, VOCs emissions are reduced by 70%, and no strong acid or strong base waste liquid is generated; 5. The innovative process combination of the present invention, crystallization / distillation / adsorption / complexation quadruple purification, and waste recovery system build a closed-loop production system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific embodiments or the description of the prior art. Obviously, some of the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be made based on these drawings without paying any creative work.

[0019] Figure 1 This is a flow chart of Example 1 of the present invention. DETAILED DESCRIPTION

[0020] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, a specific implementation scheme is now described in detail.

[0021] The present invention is further described below with reference to the following examples, but the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to the specific requirements of the application. The implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention may be combined with each other as long as they do not conflict with each other.

[0022] Example 1 See attached Figure 1 This embodiment provides a method for purifying high-purity trimethylaluminum, comprising the following steps: (1) Dissolution under inert gas protection: In an argon glove box (O2≤0.1ppm, H2O≤1ppm), 500g of crude trimethylaluminum (purity 98.5%) was mixed with 1.5kg of dehydrated and deoxygenated n-hexane (water content ≤1ppm) to form a homogeneous solution; (2) Gradual low-temperature crystallization: Transfer the solution to the crystallization kettle and program the temperature to decrease: The first stage: keep at -30℃ for 1 hour, filter and remove high melting point impurities such as Al(CH3)2Cl (filter residue A); The second stage: keep at -50℃ for 1.5h (cooling rate 8℃ / h), filter and remove Al(CH3)2OCH3 etc. (filter residue B); The third stage: keep at -80℃ for 2h, filter to remove eutectic impurities (filter residue C); (3) Molecular distillation: Transfer the filtrate to a short-range molecular distillation device (the distance between the evaporation surface and the condensation surface is 10 cm): First-stage distillation: 5Pa, 70℃ to remove light components (recover n-hexane); Secondary distillation: 0.5 Pa, 90 ° C to collect the main fraction (TMA); (4) Adsorption-complexation purification: The distilled product was passed through a molecular sieve adsorption column with a pore size of 0.3 nm (60°C, flow rate 1 BV / h); 0.3 mol% 18-crown-6 (based on the molar amount of TMA) was added, and the product was stirred for 2 h before vacuum distillation (50°C, 1 kPa) to remove the complex. (5) Terminal treatment: Filtered through 0.22 μm PTFE filter membrane and packaged with high-purity argon gas; (6) Waste treatment: Combine the filter residues A / B / C, slowly add isopropanol to quench, and generate Al(O-iPr)3; acid wash with 1M HCl and recover the AlCl3 solution.

[0023] Example 2 This embodiment provides a method for purifying high-purity trimethylaluminum, comprising the following steps: (1) Dissolution under inert gas protection: In an argon glove box (O2≤0.1ppm, H2O≤1ppm), 500g of crude TMA (purity 98.5%) was mixed with 1.0kg of dehydrated toluene (water content ≤1ppm, mass ratio 1:2) to form a homogeneous solution; (2) Gradual low-temperature crystallization: Transfer the solution to the crystallization kettle and program the temperature to decrease: The first stage: keep at -30℃ for 1.5h, filter and remove high melting point impurities such as Al(CH3)2Cl (filter residue A); The second stage: keep at -50℃ for 2h (cooling rate 5℃ / h), filter to remove Al(CH3)2OCH3, etc. (filter residue B); The third stage: keep at -80℃ for 1 hour, filter to remove eutectic impurities (filter residue C); (3) Molecular distillation: The filtrate was transferred to a short-range molecular distillation device (the distance between the evaporation surface and the condensation surface was 10 cm); First-stage distillation: 8Pa, 65℃ to remove light components (recover n-hexane); Secondary distillation: 0.3 Pa, 85 ° C to collect the main fraction (TMA); (4) Adsorption-complexation purification: A MIL-101MOFs adsorption column (40°C, flow rate 1.5 BV / h) was used; 0.5 mol% acetylacetone (based on TMA) was added, stirred for 3 h, and then vacuum distilled (45°C, 0.5 kPa) to remove the complex; (5) Terminal treatment: Filtered through 0.22μm PTFE filter membrane and packaged with high-purity argon gas; (6) Waste treatment: Combine the filter residues A / B / C, slowly add isopropanol to quench, and generate Al(O-iPr)3; acid wash with 1M HCl and recover the AlCl3 solution.

[0024] Example 3 This embodiment provides a method for purifying high-purity trimethylaluminum, comprising the following steps: (1) Inert gas protection dissolution: Use crude TMA (Fe 50 ppb, Na 80 ppb) with high metal impurities and mix it with 2.0 kg of n-hexane (mass ratio 1:4) to form a homogeneous solution; (2) Gradual low-temperature crystallization: Transfer the solution to the crystallization kettle and program the temperature to decrease: The first stage: keep at -30℃ for 2h, filter and remove high melting point impurities such as Al(CH3)2Cl (filter residue A); The second stage: keep at -50℃ for 2.5h (cooling rate 10℃ / h), filter and remove Al(CH3)2OCH3 etc. (filter residue B); The third stage: keep at -80℃ for 1.5h, filter to remove eutectic impurities (filter residue C); (3) Molecular distillation: Transfer the filtrate to a short-range molecular distillation device (the distance between the evaporation surface and the condensation surface is 10 cm): First-stage distillation: 3Pa, 75℃ to remove light components (recover n-hexane); Secondary distillation: 0.1 Pa, 95 ° C to collect the main fraction (TMA); (4) Adsorption-complexation refining: Combined treatment with molecular sieves with a pore size of 0.3 nm and 18-crown-6 (1 mol%); secondary molecular sieve adsorption (60 ° C); (5) Terminal treatment: Filtered through 0.22μm PTFE filter membrane and packaged with high-purity argon gas; (6) Waste treatment: Combine the filter residues A / B / C, slowly add isopropanol to quench, and generate Al(O-iPr)3; acid wash with 1M HCl and recover the AlCl3 solution.

[0025] Comparative Example 1 This comparative example is a traditional distillation method, in which crude TMA is directly subjected to conventional vacuum distillation (100 Pa, 120°C) without a crystallization / adsorption step.

[0026] Comparative Example 2 This comparative example is a single-stage crystallization method. Crude TMA is dissolved in n-hexane (1:3) and only a single crystallization is performed at -80°C without molecular distillation.

[0027] Comparative Example 3 This comparative example is carried out on the basis of the above-mentioned Example 1, and the similarities with the above-mentioned Example 1 are not repeated here.

[0028] There is no complexing agent adsorption in this comparative example.

[0029] The products obtained in the above examples and comparative examples were tested, and the test results are shown in Table 1.

[0030] Table 1

[0031] As can be seen from Table 1, Example 1 improves the purity of TMA to 5N grade (99.999%) through triple purification by fractional crystallization-molecular distillation-adsorption complexation, far exceeding the level of less than 99.9% in Comparative Examples 1-3; key metal impurities (Fe, Na) are all less than 1ppb, meeting the requirements of semiconductor process. In terms of impurity control: Metal ions: In Example 1, due to the introduction of 18-crown-6, Na + The removal rate increased by 200% compared to Comparative Example 3. Regarding oxygenates, fractional crystallization (at -50°C) specifically removed Al(CH₃)₂OCH₃, reducing its content to 3 ppm (compared to 120 ppm in Comparative Example 1). In terms of yield advantage, Example 1's 90% yield significantly surpassed Comparative Example 1's 65%, primarily due to low-temperature crystallization, which avoided thermal decomposition losses. The test data from Comparative Examples 2 (single-stage crystallization) and 3 (no complexation) demonstrate that multiple purification steps are essential; missing any one step leads to a decline in key performance indicators. Compared to Example 1, Example 2 shows that toluene (1:2) is superior to n-hexane (1:3) in oxygenate removal (2 ppm vs. 3 ppm), but the yield is slightly lower (88% vs. 90%). Compatibility with high-impurity feedstocks (Example 3): Even with initial Fe / Na impurities as high as 50-80 ppb, they can ultimately be reduced to 1-2 ppb. The residual Na in Comparative Example 3 (no complexation) (3 ppb) was significantly higher than that in Examples 1 to 3 (≤ 2 ppb), demonstrating the key role of adsorption-complexation synergy.

[0032] In summary, the present invention significantly improves the purity of the product. Through the innovative process of multi-stage low-temperature crystallization coupled with molecular distillation, the purity of trimethylaluminum can be stably controlled at ≥99.999% (5N grade), and the key impurity content reaches: metal ions (Fe, Cu, Na, etc.) ≤1ppb, oxygen-containing compounds (such as Al(CH3)2OCH3) ≤5ppm, moisture ≤3ppm, which is 1~2 orders of magnitude higher than the traditional process. The present invention uses fractional crystallization technology -30℃ / -50℃ / -80℃ three-stage precise temperature control to increase the impurity removal rate by more than 80%. Compared with single-stage crystallization, the product yield is increased to 92%; Molecular distillation-adsorption synergistic system: short-path distillation (0.1~1Pa) ensures that heat-sensitive substances do not decompose; MOFs adsorbent has good adsorption performance on Fe 3+The capture efficiency reaches 99.5%; the production cost of the present invention is optimized, and the solvent recycling rate is ≥95% (n-hexane / toluene recovery system), which is 40% lower than the energy consumption of traditional high-temperature distillation; the raw material utilization rate is increased to 90%, and the recovery value of scrap aluminum is increased; the present invention is safe and environmentally friendly, and waste is harmlessly treated: the isopropyl alcohol quenching process makes the residual TMA conversion rate ≥99.9%, and the aluminum salt recovered by pickling can be resourced; green process design: inert gas protection throughout the entire process, VOCs emissions are reduced by 70%, and no strong acid / strong alkali waste liquid is generated; the present invention has an innovative process combination, crystallization / distillation / adsorption / complexation quadruple purification, and the waste recovery system builds a closed-loop production system.

[0033] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for purifying high-purity trimethylaluminum, characterized in that: The steps include: (1) Dissolution under inert gas protection: Under inert gas protection, dissolve the crude trimethylaluminum in a dehydrated and deoxygenated high-purity organic solvent to form a homogeneous solution; (2) Gradual low-temperature crystallization: Using the graded low-temperature crystallization method, keep the temperature at -30℃, -50℃, and -80℃ in stages for 0.5~2h, so that impurities with different melting points are gradually precipitated and filtered out; (3) Molecular distillation: Using molecular distillation technology, first remove the light components at 60~80℃, then collect the main fraction at 80~100℃, and the distance between the evaporation surface and the condensation surface is 5~20cm; (4) Adsorption-complexation refining: remove trace metals and oxygen-containing impurities through adsorbents; add complexing agents to chelate residual metal ions, and separate the complex by vacuum distillation; (5) Terminal treatment: Finally, it is filtered through a 0.22 μm filter membrane and packaged with high-purity argon gas to obtain trimethylaluminum with a purity of ≥99.999%.

2. The method for purifying high-purity trimethylaluminum as claimed in claim 1, wherein: In step (1), the inert gas is argon or nitrogen, and the oxygen content is ≤1ppm; the high-purity organic solvent is n-hexane or toluene, and the purity is ≥99.99%.

3. The method for purifying high-purity trimethylaluminum as claimed in claim 1, wherein: In step (2), the mass ratio of the solvent to trimethylaluminum used in the graded low-temperature crystallization method is 1:2~5, and the cooling gradient in each stage is 5~10°C / h.

4. The method for purifying high-purity trimethylaluminum as claimed in claim 1, wherein: In step (3), the pressure in the light component removal stage of the molecular distillation is 5~10Pa, the pressure in the main fraction collection stage is 0.1~1Pa, and the distillation rate is controlled at 0.5~2mL / min.

5. The method for purifying high-purity trimethylaluminum as claimed in claim 1, wherein: In step (4), the adsorbent is loaded into a fixed bed adsorption column at a flow rate of 1 BV / h and a contact time of 1 to 4 hours; the adsorbent is a molecular sieve with a pore size of 0.3 nm or MIL-101MOFs, at 20 to 60°C.

6. The method for purifying high-purity trimethylaluminum according to claim 1, wherein: In step (4), the complexing agent is 18-crown-6 or acetylacetone, and the amount of the complexing agent added is 0.1% to 1% of the molar amount of trimethylaluminum; after the reaction, the complex is removed by reduced pressure distillation at 40°C and 1 kPa.

7. The method for purifying high-purity trimethylaluminum according to claim 1, wherein: The dew point of the inert gas protection is ≤-70°C, and all equipment is pre-treated with acid cleaning, high-temperature baking at 200~300°C and inert gas replacement.

8. The method for purifying high-purity trimethylaluminum according to claim 1, wherein: The metal impurity content of the purified trimethylaluminum is ≤1ppb, and the moisture content is ≤5ppm.

9. The method for purifying high-purity trimethylaluminum according to claim 1, wherein: The method also includes a waste treatment step: quenching the crystallization residue, the distillation heavy component and the adsorption waste with isopropyl alcohol to generate aluminum isopropylate, and using 1M HCl to acid-wash the quenched product to recover metal ions.

10. The method for purifying high-purity trimethylaluminum according to claim 1, wherein: In step (5), the oxygen content of the high-purity argon gas is ≤0.1 ppm.

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