CN109734626B - Depolymerization method for forming polymer in isocyanate preparation process by thermal cracking - Google Patents
Depolymerization method for forming polymer in isocyanate preparation process by thermal cracking Download PDFInfo
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Abstract
The invention relates to a depolymerization method for forming a polymer in the process of preparing isocyanate by thermal cracking, which comprises the following steps: sequentially adding a polymer formed in the isocyanate preparation process by thermal cracking, a nitrogen-containing micromolecule serving as a sacrificial agent or a carbonylation agent, micromolecule alcohol, water and a catalyst into a stainless steel autoclave, heating to 170-220 ℃, and reacting for 4-20 hours; after the reaction is finished, the catalyst is separated and recovered through centrifugation or filtration, and the N-substituted carbamic acid alkyl ester is obtained. The yield of the polymerization substrate converted into the corresponding N-substituted alkyl carbamate is higher than 80%, and the yield of the isocyanate is improved by recycling the polymerization byproducts, so that the key problem of the route for preparing the isocyanate by thermal cracking in the promotion of practical application is hopefully solved.
Description
Technical Field
The invention relates to the technical field of isocyanate synthesis, in particular to a depolymerization method for forming a polymer in the process of preparing isocyanate by thermal cracking.
Background
Isocyanate is an important organic synthesis intermediate, is a main raw material for polyurethane synthesis, and can be widely applied to high polymer materials such as polyurethane, paint, dye, pesticide and the like. Common aromatic isocyanates are 4, 4-diphenylmethane diisocyanate (MDI) and 2, 4-Toluene Diisocyanate (TDI), which are important raw materials for preparing polyurethane, and are widely used for producing polyurethane foam, polyurethane elastomer, mixed elastomer, polyurethane coating, polyurethane adhesive, polyurethane waterproof material, detergent, thickener, antioxidant and the like, besides being widely used for manufacturing microcellular elastomers, thermoplastic elastomers, casting elastomers, artificial leather, synthetic leather, adhesives, coatings, sealants and the like. At present, the isocyanate is prepared by mainly using virulent phosgene as a raw material in industry, and a byproduct in the process is hydrogen chloride, so that the defects of serious environmental hazard, complex process, more byproducts, high separation and purification difficulty and the like exist.
Therefore, research and development of a clean production technology for preparing isocyanate chemicals without phosgene become a focus of attention of chemical research institutions and chemical enterprises of various countries in the world. With the development of thermal cracking process research, the process of conducting carbonylation on nitrogen-containing compounds to obtain N-substituted alkyl carbamates and then conducting thermal cracking is recognized as the most promising route for preparing isocyanate from phosgene. In order to increase the cracking rate, thermal cracking of the alkyl N-substituted carbamates is often carried out above 210 ℃. The high reactivity and instability of the isocyanate aggravate the occurrence of polymerization side reaction under high temperature condition, which leads to the great reduction of the yield of the isocyanate (less than 80 percent), thereby leading the non-phosgene route for preparing the isocyanate by clean thermal cracking of the N-substituted alkyl carbamate to have no competitive power and practical industrial application value compared with the existing route for preparing the isocyanate by phosgene. Although the addition of some polymerization inhibitors inhibits the occurrence of polymerization to some extent, polymerization during thermal cracking is almost inevitable.
According to the previous literature reports and preliminary studies, the polymers produced during the thermal cracking of N-substituted alkyl carbamates mainly contain some polyureas, polyimines, trimers of isocyanates, and the like, and the composition and structure of the polymers change due to the change of thermal cracking conditions (see FIGS. 1 to 3). Polyimines are formed by removing one molecule of carbon dioxide from two isocyanate molecules (equation 1) and trimers of isocyanates are formed by cyclization between isocyanate molecules (equation 2). Polyureas are derived primarily from the interaction between isocyanates and N-substituted carbamates or amines (equations 3 and 4).
Therefore, how to realize the recycling of the polymerization byproducts and further improve the yield of thermal cracking is a key problem for solving the practical application of the route for preparing isocyanate by thermal cracking.
Disclosure of Invention
The invention aims to solve the technical problem of providing a depolymerization method for forming a polymer in the process of preparing isocyanate by thermal cracking, which has low cost and high yield.
In order to solve the above problems, the present invention provides a depolymerization method for forming a polymer during thermal cracking to produce isocyanate, comprising: sequentially adding a polymer formed in the isocyanate preparation process by thermal cracking, a nitrogen-containing micromolecule serving as a sacrificial agent or a carbonylation agent, micromolecule alcohol, water and a catalyst into a stainless steel autoclave, heating to 170-220 ℃, and reacting for 4-20 hours; after the reaction is finished, the catalyst is separated and recovered through centrifugation or filtration, and the N-substituted carbamic acid alkyl ester is obtained; the molar ratio of the polymer to the nitrogen-containing small molecule and the small molecule alcohol is 1: 1-3: 5-50; the using amount of the water is 0-5% of that of the polymer; the amount of the catalyst is 1-10 wt% of the amount of the polymer.
The polymer is formed in any one thermal cracking process of toluene dicarbamate, hexamethylene dicarbamate, 4-diphenylmethane dicarbamate, 4-dicyclohexylmethane dicarbamate, isophorone dicarbamate and [3- (triethoxysilyl) propyl ] carbamate.
The nitrogen-containing small molecule refers to urea or ethyl carbamate.
The small molecular alcohol is methanol or absolute ethyl alcohol.
The catalyst refers to a supported metal catalyst or an organic metal framework catalyst.
The supported metal catalyst is characterized in that active components are Fe and Ni, a carrier is aluminum oxide, and the supported amount is 1-20 wt%.
The organometallic framework catalyst is characterized in that metal ions are zinc, and an organic ligand is aminotetrazole.
Compared with the prior art, the invention has the following advantages:
1. under the action of a catalyst, a nitrogen-containing micromolecule is used as a sacrificial agent or a carbonylation agent, a carbonyl source, alkoxy, water and the like are supplemented into a polymer, wherein imine in the polymer is firstly changed into polyurea in the presence of water so that the polymer can be further subjected to alcoholysis), and the polymer formed in the process of preparing isocyanate through thermal cracking is reacted with micromolecule alcohol to obtain the corresponding N-substituted alkyl carbamate.
2. The invention carries out alcoholysis on the thermal cracking polymerization substrate to obtain the corresponding N-substituted carbamic acid alkyl ester again, thereby avoiding the waste of resources and effectively improving the yield of isocyanate prepared by thermal cracking.
3. The invention adopts the supported metal catalyst or the organic metal framework catalyst (MOF), has high catalyst activity, good stability, easy regeneration and repeated use, reduces the reaction temperature, shortens the reaction time and reduces the operation cost.
4. The yield of the polymerization substrate converted into the corresponding N-substituted alkyl carbamate is higher than 80%, and the yield of the isocyanate is improved by recycling the polymerization byproducts, so that the key problem of the route for preparing the isocyanate by thermal cracking in the promotion of practical application is hopefully solved.
Drawings
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
FIG. 1 is an infrared spectrum of a [3- (triethoxysilyl) propyl ] urethane thermal cracking polymerization substrate.
FIG. 2 is a time-of-flight mass spectrum of [3- (triethoxysilyl) propyl ] urethane thermal cracking polymerization substrate at 150 ℃.
FIG. 3 is a time-of-flight mass spectrum of a 220 ℃ thermal cleavage polymerization substrate of hexamethylene diamine urethane.
Detailed Description
Example 1 a depolymerization process for forming a polymer during thermal cracking to isocyanate, refers to: 20g of the polymer formed in the preparation of isocyanate by thermal cracking, 3g of urea, 46g of methanol, 1g of Zn (ATZ) were placed in a 0.5L stainless steel autoclave in this order2Heating the catalyst to 190 ℃ and reacting for 20 hours; after the reaction is finished, the catalyst is separated and recovered through centrifugation or filtration, and 21g of toluene dicarbamate product is obtained, wherein the yield is 83%.
Wherein: the polymer refers to a toluene dicarbamate polymerization substrate thermally cracked at 220 ℃.
Amino tetrazole zinc salt { Zn (ATZ)2Preparation of the catalyst: firstly, 1g of zinc hydroxide is dissolved in ammonia water to prepare a solution A, 2.2g of 5-aminotetrazole is dissolved in isopropanol to obtain a solution B, and the solution A and the solution B are mixed and stirred at room temperature until a transparent solution is obtained. The clear solution was left at room temperature for 5 days, and the resulting white crystals were washed with water and absolute ethanol, and then dried at 60 ℃ under reduced pressure for use.
Example 2 a depolymerization process for forming a polymer during thermal cracking to isocyanate, refers to: 20g of a polymer formed in the preparation of isocyanate by thermal cracking, 5.6g of urea, 107g of absolute ethyl alcohol and 2g of Fe-Ni/Al were sequentially added to a 0.5L stainless steel autoclave2O3The catalyst is heated to 200 ℃ and reacts for 12 hours; after the reaction is finished, the catalyst is separated and recovered through centrifugation or filtration, and 20g of hexamethylene diamine ethyl formate is obtained, wherein the yield is 82%.
Wherein: the polymer refers to the polymerization substrate obtained by thermal cracking of hexamethylene diamine urethane at 220 ℃ (see FIG. 3).
Fe-Ni/Al2O3Preparation of the catalyst: al (Al)2O3Used after pretreatment at 500 ℃ for 4 h. Al (Al)2O3Has a water absorption capacity of 1 mL/gAl2O3Thus diluting the aqueous solution containing iron and nickel to the water absorption of the added carrier, with Al2O3Soaking in the same volume, drying at 120 deg.C, calcining at 400-800 deg.C for 4 hr to obtain reddish brownBefore the solid catalyst is used, the solid catalyst is refluxed and cleaned in an absolute ethyl alcohol solvent to remove the physical attachments on the surface.
Example 3 a depolymerization process for forming a polymer during thermal cracking to isocyanate, refers to: 20g of a polymer formed in the preparation of isocyanate by thermal cracking, 5.6g of urea, 86g of absolute ethyl alcohol, 0.2g of water and 2g of Fe-Ni/Al were sequentially added to a 0.5L stainless steel autoclave2O3The catalyst is heated to 200 ℃ and reacts for 12 hours; after the reaction is finished, the catalyst is separated and recovered through centrifugation or filtration, and 22g of hexamethylene diamine ethyl formate is obtained, wherein the yield is 94%.
Wherein: the polymer refers to a hexamethylene diamine ethyl formate thermal cracking polymerization substrate at 220 ℃.
Fe-Ni/Al2O3The catalyst was prepared as in example 2.
Example 4 a depolymerization process for forming a polymer during thermal cracking to isocyanate, refers to: 20g of a polymer formed in the preparation of isocyanate by thermal cracking, 6g of urea, 77g of absolute ethyl alcohol and 2g of Fe-Ni/Al were sequentially added to a 0.5L stainless steel autoclave2O3The catalyst is heated to 220 ℃ and reacts for 12 hours; after the reaction is finished, the catalyst is separated and recovered through centrifugation or filtration, and 18g of 4, 4-diphenylmethane ethyl diamino formate is obtained, and the yield is 80%.
Wherein: the polymer refers to a polymerization substrate of 4, 4-diphenylmethane-diamino-ethyl formate thermally cracked at 230 ℃.
Fe-Ni/Al2O3The catalyst was prepared as in example 2.
Example 5 a depolymerization process for forming a polymer during thermal cracking to isocyanate, refers to: 20g of a polymer formed in the preparation of isocyanate by thermal cracking, 3.9g of urea, 75g of absolute ethyl alcohol and 2g of Fe-Ni/Al were sequentially added into a 0.5L stainless steel autoclave2O3The catalyst is heated to 200 ℃ and reacts for 12 hours; after the reaction is finished, the catalyst is separated and recovered through centrifugation or filtration, and 20g of 4, 4-dicyclohexyl methane ethyl diamino formate product is obtained, wherein the yield is 90%.
Wherein: the polymer refers to a polymerization substrate obtained by thermal cracking of 4, 4-dicyclohexylmethane ethyl dithiocarbamate at 220 ℃.
Fe-Ni/Al2O3The catalyst was prepared as in example 2.
Example 6 a depolymerization process for forming a polymer during thermal cracking to isocyanate, refers to: 20g of polymer formed in the process of preparing isocyanate by thermal cracking, 6g of urea, 52g of absolute ethyl alcohol and 2g of Fe-Ni/Al are sequentially added into a 0.5L stainless steel autoclave2O3The catalyst is heated to 200 ℃ and reacts for 12 hours; after the reaction is finished, the catalyst is separated and recovered through centrifugation or filtration, and 21g of isophorone diamine ethyl formate product is obtained, wherein the yield is 92%.
Wherein: the polymer refers to a polymerization substrate obtained by thermally cracking isophorone diisocyanate ethyl formate at 210 ℃.
Fe-Ni/Al2O3The catalyst was prepared as in example 2.
Example 7 a depolymerization process for forming a polymer during thermal cracking to isocyanate, refers to: 20g of the polymer formed in the preparation of isocyanate by thermal cracking, 3.4g of urethane, 34g of absolute ethanol, 0.2g of Zn (ATZ) were placed in a 0.5L stainless steel autoclave in this order2The catalyst is heated to 170 ℃ and reacts for 8 hours; after the reaction is finished, the catalyst is separated and recovered by centrifugation or filtration to obtain the [3- (triethoxysilyl) propyl group]The yield of the urethane product is 20g and 92 percent.
Wherein: the polymer refers to a polymerization substrate thermally cracked at 150 ℃ by [3- (triethoxysilyl) propyl ] ethyl carbamate (see figure 1 and figure 2).
Zn(ATZ)2The catalyst was prepared as in example 1.
Example 8 a depolymerization process for forming a polymer during thermal cracking to isocyanate, refers to: 20g of the polymer formed in the preparation of isocyanate by thermal cracking, 2.7g of urea, 56g of absolute ethanol, 1g of Zn (ATZ) were placed in a 0.5L stainless steel autoclave in this order2Heating the catalyst to 180 ℃ and reacting for 4 hours; after the reaction is finished, the catalyst is separated and recovered by centrifugation or filtration to obtain the [3- (triethoxysilyl) propyl group]Urethane products21g, yield 96%.
Wherein: the polymer is a polymerization substrate thermally cracked at 150 ℃ by [3- (triethoxysilyl) propyl ] ethyl carbamate.
Zn(ATZ)2The catalyst was prepared as in example 1.
Example 9 a depolymerization process for forming a polymer during thermal cracking to isocyanate, refers to: 20g of polymer formed in the process of preparing isocyanate by thermal cracking, 2.8g of urea, 86g of absolute ethyl alcohol, 1g of water and 1g of Fe-Ni/Al are sequentially added into a 0.5L stainless steel autoclave2O3The catalyst is heated to 200 ℃ and reacts for 12 hours; after the reaction is finished, the catalyst is separated and recovered through centrifugation or filtration, and 19g of hexamethylene diamine ethyl formate is obtained, wherein the yield is 80%.
Wherein: the polymer refers to a hexamethylene diamine ethyl formate thermal cracking polymerization substrate at 220 ℃.
Fe-Ni/Al2O3The catalyst was prepared as in example 2.
The catalysts obtained in the above examples 1 to 9 can be reused after being washed and dried with acetone or ethanol.
In the above examples 1 to 9, when the catalyst is a supported metal catalyst, the active component can be Co, Cu, Ti instead of Fe, Ni, and the carrier can be ferric oxide, silicon dioxide, titanium dioxide instead of aluminum oxide.
When the catalyst is an organic metal framework catalyst, the metal ions can replace zinc by lithium, sodium, potassium, zirconium and chromium, and the organic ligand can replace amino tetrazole by amino triazole.
In examples 1 to 8, methyl carbamate and butyl carbamate can be used as the nitrogen-containing small molecule instead of urea and ethyl carbamate.
In the above examples 1 to 9, butanol may be used as the small molecule alcohol instead of methanol or absolute ethanol.
The reaction products obtained in the above examples 1 to 9 were first qualitatively analyzed by gas chromatography and then quantitatively analyzed by gas chromatography (biphenyl as an internal standard).
The products after the reaction were quantitatively analyzed using an Agilent Technologies 6820 gas chromatography system. The chromatographic conditions are as follows: chromatography column 30 m × 0.25 mm × 0.33 μm capillary, hydrogen Flame Ionization (FID) detector. Qualitative analysis was done using HP 6890/5973 GC-MS, HP 6890/5973 GC-MS with a 30 m 0.25 mm 0.33 μm capillary and a chemical workstation with NIST spectroscopy database.
Claims (3)
1. A depolymerization process for forming a polymer during thermal cracking to isocyanate, characterized by: sequentially adding a polymer formed in the isocyanate preparation process by thermal cracking, a nitrogen-containing micromolecule serving as a sacrificial agent or a carbonylation agent, micromolecule alcohol, water and a catalyst into a stainless steel autoclave, heating to 170-220 ℃, and reacting for 4-20 hours; after the reaction is finished, the catalyst is separated and recovered through centrifugation or filtration, and the N-substituted carbamic acid alkyl ester is obtained; the molar ratio of the polymer to the nitrogen-containing small molecule and the small molecule alcohol is 1: 1-3: 5-50; the using amount of the water is 0-5% of that of the polymer; the amount of the catalyst is 1-10 wt% of the amount of the polymer; the polymer is formed in any one thermal cracking process of toluene dicarbamate, hexamethylene dicarbamate, 4-diphenylmethane dicarbamate, 4-dicyclohexylmethane dicarbamate, isophorone dicarbamate and [3- (triethoxysilyl) propyl ] carbamate; the catalyst refers to a supported metal catalyst or an organic metal framework catalyst; the supported metal catalyst is characterized in that active components are Fe and Ni, a carrier is aluminum oxide, and the supported amount is 1-20 wt%; the organometallic framework catalyst is characterized in that metal ions are zinc, and an organic ligand is aminotetrazole.
2. The depolymerization process for forming a polymer during thermal cracking of isocyanate, according to claim 1, wherein: the nitrogen-containing small molecule refers to urea or ethyl carbamate.
3. The depolymerization process for forming a polymer during thermal cracking of isocyanate, according to claim 1, wherein: the small molecular alcohol is methanol or absolute ethyl alcohol.
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| CN115569670A (en) * | 2022-09-29 | 2023-01-06 | 四川元理材料科技有限公司 | Catalyst in industrial thermal cracking process of isophorone diamino formic acid n-butyl ester |
| CN116459822A (en) * | 2023-03-31 | 2023-07-21 | 南京工业大学 | Oxide catalyst for preparing aliphatic isocyanate by catalytic pyrolysis |
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| CN1500776A (en) * | 2002-11-18 | 2004-06-02 | 1 | Method for synthesis of aliphatic isocyanates from aromatic isocyanates |
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