CN115806508A - Diphenylmethane diisocyanate with low 2,2' -MDI content and preparation method thereof - Google Patents
Diphenylmethane diisocyanate with low 2,2' -MDI content and preparation method thereof Download PDFInfo
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- UPMLOUAZCHDJJD-UHFFFAOYSA-N 4,4'-Diphenylmethane Diisocyanate Chemical compound C1=CC(N=C=O)=CC=C1CC1=CC=C(N=C=O)C=C1 UPMLOUAZCHDJJD-UHFFFAOYSA-N 0.000 title claims abstract description 106
- 238000002360 preparation method Methods 0.000 title claims abstract description 44
- 238000006243 chemical reaction Methods 0.000 claims abstract description 73
- 239000003054 catalyst Substances 0.000 claims abstract description 69
- PAYRUJLWNCNPSJ-UHFFFAOYSA-N Aniline Chemical compound NC1=CC=CC=C1 PAYRUJLWNCNPSJ-UHFFFAOYSA-N 0.000 claims abstract description 46
- 239000011964 heteropoly acid Substances 0.000 claims abstract description 46
- 238000000034 method Methods 0.000 claims abstract description 44
- 239000002608 ionic liquid Substances 0.000 claims abstract description 40
- 229920000768 polyamine Polymers 0.000 claims abstract description 33
- 239000000463 material Substances 0.000 claims abstract description 31
- 239000000203 mixture Substances 0.000 claims abstract description 28
- 150000003839 salts Chemical class 0.000 claims abstract description 24
- ZZTCPWRAHWXWCH-UHFFFAOYSA-N diphenylmethanediamine Chemical compound C=1C=CC=CC=1C(N)(N)C1=CC=CC=C1 ZZTCPWRAHWXWCH-UHFFFAOYSA-N 0.000 claims abstract description 23
- YGYAWVDWMABLBF-UHFFFAOYSA-N Phosgene Chemical compound ClC(Cl)=O YGYAWVDWMABLBF-UHFFFAOYSA-N 0.000 claims abstract description 12
- 238000006482 condensation reaction Methods 0.000 claims abstract description 10
- 230000017105 transposition Effects 0.000 claims abstract description 6
- -1 diphenylmethane diamines Chemical class 0.000 claims abstract description 5
- HIFVAOIJYDXIJG-UHFFFAOYSA-N benzylbenzene;isocyanic acid Chemical class N=C=O.N=C=O.C=1C=CC=CC=1CC1=CC=CC=C1 HIFVAOIJYDXIJG-UHFFFAOYSA-N 0.000 claims abstract 2
- WSFSSNUMVMOOMR-UHFFFAOYSA-N Formaldehyde Chemical compound O=C WSFSSNUMVMOOMR-UHFFFAOYSA-N 0.000 claims description 67
- 239000000047 product Substances 0.000 claims description 49
- XEKOWRVHYACXOJ-UHFFFAOYSA-N Ethyl acetate Chemical compound CCOC(C)=O XEKOWRVHYACXOJ-UHFFFAOYSA-N 0.000 claims description 36
- JUJWROOIHBZHMG-UHFFFAOYSA-N Pyridine Chemical compound C1=CC=NC=C1 JUJWROOIHBZHMG-UHFFFAOYSA-N 0.000 claims description 25
- 230000008569 process Effects 0.000 claims description 21
- 150000007854 aminals Chemical class 0.000 claims description 20
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 20
- 238000004519 manufacturing process Methods 0.000 claims description 17
- JUJWROOIHBZHMG-UHFFFAOYSA-O pyridinium Chemical compound C1=CC=[NH+]C=C1 JUJWROOIHBZHMG-UHFFFAOYSA-O 0.000 claims description 16
- 208000005156 Dehydration Diseases 0.000 claims description 14
- 230000018044 dehydration Effects 0.000 claims description 14
- 238000006297 dehydration reaction Methods 0.000 claims description 14
- 238000002156 mixing Methods 0.000 claims description 14
- IYDGMDWEHDFVQI-UHFFFAOYSA-N phosphoric acid;trioxotungsten Chemical compound O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.OP(O)(O)=O IYDGMDWEHDFVQI-UHFFFAOYSA-N 0.000 claims description 13
- UMJSCPRVCHMLSP-UHFFFAOYSA-N pyridine Natural products COC1=CC=CN=C1 UMJSCPRVCHMLSP-UHFFFAOYSA-N 0.000 claims description 13
- FSSPGSAQUIYDCN-UHFFFAOYSA-N 1,3-Propane sultone Chemical compound O=S1(=O)CCCO1 FSSPGSAQUIYDCN-UHFFFAOYSA-N 0.000 claims description 10
- 239000012071 phase Substances 0.000 claims description 10
- 238000001354 calcination Methods 0.000 claims description 9
- 238000000926 separation method Methods 0.000 claims description 9
- 238000005406 washing Methods 0.000 claims description 9
- 239000012074 organic phase Substances 0.000 claims description 8
- 238000003756 stirring Methods 0.000 claims description 8
- 238000000967 suction filtration Methods 0.000 claims description 6
- 238000010438 heat treatment Methods 0.000 claims description 5
- 238000002844 melting Methods 0.000 claims description 5
- 230000008018 melting Effects 0.000 claims description 5
- CGFYHILWFSGVJS-UHFFFAOYSA-N silicic acid;trioxotungsten Chemical compound O[Si](O)(O)O.O=[W]1(=O)O[W](=O)(=O)O[W](=O)(=O)O1.O=[W]1(=O)O[W](=O)(=O)O[W](=O)(=O)O1.O=[W]1(=O)O[W](=O)(=O)O[W](=O)(=O)O1.O=[W]1(=O)O[W](=O)(=O)O[W](=O)(=O)O1 CGFYHILWFSGVJS-UHFFFAOYSA-N 0.000 claims description 5
- 238000010521 absorption reaction Methods 0.000 claims description 4
- 239000002253 acid Substances 0.000 claims description 4
- 238000001291 vacuum drying Methods 0.000 claims description 4
- 239000007795 chemical reaction product Substances 0.000 claims description 3
- 239000012065 filter cake Substances 0.000 claims description 3
- 239000002808 molecular sieve Substances 0.000 claims description 3
- 238000007670 refining Methods 0.000 claims description 3
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 claims description 3
- DHRLEVQXOMLTIM-UHFFFAOYSA-N phosphoric acid;trioxomolybdenum Chemical compound O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.OP(O)(O)=O DHRLEVQXOMLTIM-UHFFFAOYSA-N 0.000 claims description 2
- 239000002952 polymeric resin Substances 0.000 claims description 2
- 230000035484 reaction time Effects 0.000 claims description 2
- 238000006462 rearrangement reaction Methods 0.000 claims description 2
- 238000010992 reflux Methods 0.000 claims description 2
- 229920003002 synthetic resin Polymers 0.000 claims description 2
- WSFSSNUMVMOOMR-NJFSPNSNSA-N methanone Chemical compound O=[14CH2] WSFSSNUMVMOOMR-NJFSPNSNSA-N 0.000 abstract description 2
- DZBUGLKDJFMEHC-UHFFFAOYSA-N acridine Chemical compound C1=CC=CC2=CC3=CC=CC=C3N=C21 DZBUGLKDJFMEHC-UHFFFAOYSA-N 0.000 description 24
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 12
- 239000000543 intermediate Substances 0.000 description 12
- 239000012535 impurity Substances 0.000 description 10
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 9
- 239000012467 final product Substances 0.000 description 9
- MVPPADPHJFYWMZ-UHFFFAOYSA-N chlorobenzene Chemical compound ClC1=CC=CC=C1 MVPPADPHJFYWMZ-UHFFFAOYSA-N 0.000 description 8
- 230000000052 comparative effect Effects 0.000 description 8
- 150000004985 diamines Chemical class 0.000 description 7
- 125000003636 chemical group Chemical group 0.000 description 5
- 239000011973 solid acid Substances 0.000 description 5
- ALYNCZNDIQEVRV-UHFFFAOYSA-N 4-aminobenzoic acid Chemical compound NC1=CC=C(C(O)=O)C=C1 ALYNCZNDIQEVRV-UHFFFAOYSA-N 0.000 description 4
- 238000010924 continuous production Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- IQPQWNKOIGAROB-UHFFFAOYSA-N isocyanate group Chemical group [N-]=C=O IQPQWNKOIGAROB-UHFFFAOYSA-N 0.000 description 4
- 239000011259 mixed solution Substances 0.000 description 4
- 229920000642 polymer Polymers 0.000 description 4
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- 229920000538 Poly[(phenyl isocyanate)-co-formaldehyde] Polymers 0.000 description 3
- 230000009471 action Effects 0.000 description 3
- 239000007864 aqueous solution Substances 0.000 description 3
- 230000003197 catalytic effect Effects 0.000 description 3
- 239000008098 formaldehyde solution Substances 0.000 description 3
- 238000011068 loading method Methods 0.000 description 3
- 239000003973 paint Substances 0.000 description 3
- 235000011121 sodium hydroxide Nutrition 0.000 description 3
- 239000002904 solvent Substances 0.000 description 3
- 238000005303 weighing Methods 0.000 description 3
- 125000002619 bicyclic group Chemical group 0.000 description 2
- 239000006227 byproduct Substances 0.000 description 2
- 238000006555 catalytic reaction Methods 0.000 description 2
- 239000003153 chemical reaction reagent Substances 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000001704 evaporation Methods 0.000 description 2
- 230000008020 evaporation Effects 0.000 description 2
- 239000006260 foam Substances 0.000 description 2
- 238000009472 formulation Methods 0.000 description 2
- 238000004811 liquid chromatography Methods 0.000 description 2
- 239000005022 packaging material Substances 0.000 description 2
- 239000004814 polyurethane Substances 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 238000003828 vacuum filtration Methods 0.000 description 2
- 230000004913 activation Effects 0.000 description 1
- 238000010923 batch production Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000007806 chemical reaction intermediate Substances 0.000 description 1
- 208000012839 conversion disease Diseases 0.000 description 1
- 238000001212 derivatisation Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- CZZYITDELCSZES-UHFFFAOYSA-N diphenylmethane Chemical class C=1C=CC=CC=1CC1=CC=CC=C1 CZZYITDELCSZES-UHFFFAOYSA-N 0.000 description 1
- 238000004821 distillation Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 239000005003 food packaging material Substances 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 238000013007 heat curing Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000003760 magnetic stirring Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 125000000325 methylidene group Chemical group [H]C([H])=* 0.000 description 1
- 230000005012 migration Effects 0.000 description 1
- 238000013508 migration Methods 0.000 description 1
- 150000007522 mineralic acids Chemical class 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 239000000178 monomer Substances 0.000 description 1
- 238000006386 neutralization reaction Methods 0.000 description 1
- 230000003472 neutralizing effect Effects 0.000 description 1
- 238000005839 oxidative dehydrogenation reaction Methods 0.000 description 1
- 239000008177 pharmaceutical agent Substances 0.000 description 1
- 229920001228 polyisocyanate Polymers 0.000 description 1
- 239000005056 polyisocyanate Substances 0.000 description 1
- 238000006116 polymerization reaction Methods 0.000 description 1
- 229920006389 polyphenyl polymer Polymers 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 150000003335 secondary amines Chemical class 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 230000003335 steric effect Effects 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- DVKJHBMWWAPEIU-UHFFFAOYSA-N toluene 2,4-diisocyanate Chemical compound CC1=CC=C(N=C=O)C=C1N=C=O DVKJHBMWWAPEIU-UHFFFAOYSA-N 0.000 description 1
- RUELTTOHQODFPA-UHFFFAOYSA-N toluene 2,6-diisocyanate Chemical compound CC1=C(N=C=O)C=CC=C1N=C=O RUELTTOHQODFPA-UHFFFAOYSA-N 0.000 description 1
- 230000005945 translocation Effects 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/54—Improvements relating to the production of bulk chemicals using solvents, e.g. supercritical solvents or ionic liquids
Abstract
The invention belongs to the technical field of preparation of diphenylmethane diisocyanate, and particularly relates to diphenylmethane diisocyanate with low 2,2' -MDI content and a preparation method thereof, wherein the method comprises the following steps: after condensation reaction of aniline and formaldehyde, carrying out transposition reaction in the presence of an ionic liquid heteropolyacid salt catalyst to obtain a material flow containing diphenylmethanediamine and polyamine, wherein the content of 2,2' -MDA isomer in the mixture of diphenylmethanediamine and polyamine is 10-1000ppm; the stream containing the diphenylmethane diamines and polyamines is then reacted with phosgene to produce a product stream containing diphenylmethane diisocyanates. The method of the invention can improve the product selectivity, further reduce the content of the undesired 2,2' -MDI isomer, and simultaneously keep the content of 4,4' -MDI and 2,4' -MDI stable.
Description
Technical Field
The invention belongs to the technical field of preparation of diphenylmethane diisocyanate, and particularly relates to diphenylmethane diisocyanate with low 2,2' -MDI content and a preparation method thereof.
Background
At present, the production process of diphenylmethane diisocyanate (MDI) mainly adopts a phosgenation reaction; firstly, aniline and formaldehyde are subjected to condensation reaction under the action of a catalyst to generate diamine and polyamine polymer (DAM); then, diamine and polyamine polymer (DAM) react with phosgene in a solvent to generate crude MDI; meanwhile, the crude MDI is purified in a rectification mode to obtain pure MDI and polymeric MDI; finally, pure MDI is adopted according to a certain extraction proportion to obtain different MDI isomers, including 4,4' -MDI, 2,4' -MDI and 2,2' -MDI and the mixture thereof. In an industrial process, the reaction mechanism for the preparation of MDI can be expressed as follows:
the first step is as follows: condensation reaction
Aniline + formaldehyde → diamine and polyamine polymers (DAM)
The second step is that: phosgenation reaction
DAM + phosgene → crude MDI
The third step: separation of
And (3) rectifying and purifying the crude MDI product, and separating into a pure MDI product containing various MDI isomers and PM.
The first condensation reaction, namely the reaction of aniline and formaldehyde to generate corresponding diamine and polyamine polymers, mainly comprises two steps:
(1) Aniline and formaldehyde are subjected to polymerization reaction to generate aminal, and the aminal is converted into non-translocated secondary amines PABA and OABA, namely non-translocated diamine and polyamine;
(2) Continuously reacting un-translocated PABA and OABA under the catalysis of a catalyst to gradually convert into a mixture of diamine and polyamine, namely DAM; in the process of PABA and OABA transposition, three isomers, namely 4,4' -MDA, 2,4' -MDA and 2,2' -MDA, exist in the produced bicyclic product due to different steric hindrance, and are respectively an ortho isomer, a meta isomer and a para isomer. The reaction process is shown as follows:
three spatial isomers of 4,4' -MDA, 2,4' -MDA and 2,2' -MDA are obtained in the translocation process of PABA and OABA, wherein 4,4' -MDA belongs to para-isomer, the steric hindrance is minimum, the specific gravity is highest in a bicyclic product, and the content of 2,2' -MDA is minimum. The contents of the three isomers are determined by the type of the selected catalyst and the activation energy of the reaction.
MDI prepared by the reaction (especially 4,4'-MDI, 2,4' -MDI) is more suitable for obtaining a determined structure than PMDI due to the dual functionality of MDI. 4,4'-MDI contains two isocyanate groups with the same activity, and people often expect to obtain an MDI mixture with a higher 4,4' -MDI ratio in previous researches, but 4,4'-MDI is difficult to realize the subsequent treatment of only one isocyanate group, and 2,4' -MDI has two isocyanate groups with different activities, so that the requirement can be well realized; at the same time, the reaction in the para position is better than the reaction in the ortho position because of steric effects, and products with specifically functionalized para isocyanate groups can be obtained.
The use of MDI mixtures with high contents of 2,4' -MDI has been widely demonstrated, for example:
the patent document EP0676434B states that the use of monomeric 2,4' -MDI in PU flexible foam systems can replace the previously additionally added mixture of 2,4-TDI and 2,6-TDI.
The patent document EP0431331B discloses the use of 2,4' -MDI in heat-curing one-component PU systems.
However, according to the conventional production process, if a high content of 2,4'-MDI is desired, a large increase in the content of 2,2' -MDI is inevitable, which has hitherto been regarded as useless. For example, it is indicated in patent document WO 2007/087987 that: "for monomeric MDI, 4,4'MDI and 2,4' MDI isomers are predominant for reasons of synthesis. A minor amount of the 2,2' MDI isomer, which is present and essentially of no commercial value, is also formed to a lesser extent ".
This can be partly attributed to the fact that pure 2,2'-MDI cannot be used industrially and formulations containing 2,2' MDI isomers often have the following disadvantages: the monomer reacts significantly more slowly, thus causing the reaction to be less complete. This can lead to undesired migration or to the ejection of foam, for example during the bonding of food packaging materials.
2,2' -MDI or formulations containing it are therefore also considered to be waste and must be disposed of in a cost-intensive manner. Meanwhile, the 2,2' -MDI can gradually react in a system to generate acridine, and the acridine can enter a final product, particularly MDI-50, so that the problems existing in downstream application are caused, particularly in the field of paint, the smoothness of the paint surface cannot reach the standard, and the paint color is influenced.
Therefore, how to prepare an MDI mixture of 4,4' -MDI, 2,4' -MDI and 2,2' -MDI with a higher proportion and a lower content in the production process of MDI becomes a problem worthy of study.
Disclosure of Invention
The invention aims to provide a preparation method of diphenylmethane diisocyanate with low 2,2'-MDI content aiming at the defects of 2,2' -MDI isomer content reduction in the existing MDI production process, wherein the content of 2,2'-MDA isomer in a mixture of reaction intermediate diphenylmethane diamine and polyamine is effectively controlled, so that the content of undesired 2,2' -MDI isomer is further reduced, the content of 4,4'-MDI and 2,4' -MDI is kept stable, and the content of other components in target products MDI and PMDI is not changed.
In order to achieve the above purpose, the invention provides the following technical scheme:
a preparation method of diphenylmethane diisocyanate (MDI) with low 2,2'-MDI content comprises condensation reaction of aniline and formaldehyde, and transposition reaction in the presence of ionic liquid heteropolyacid salt catalyst to obtain a stream containing diphenylmethane diamine and polyamine, wherein the content of 2,2' -MDA isomer in the mixture of diphenylmethane diamine and polyamine is 10-1000ppm (for example, 15ppm, 30ppm, 50ppm, 80ppm, 100ppm, 200ppm, 400ppm, 500ppm, 650ppm, 800 ppm); the stream containing the diphenylmethane diamines and polyamines is then reacted with phosgene to produce a product stream containing diphenylmethane diisocyanate (MDI).
According to the preparation method provided by the present invention, in some embodiments, the preparation method comprises the steps of:
s1: mixing aniline and formaldehyde for condensation reaction to obtain a material flow containing aminal;
s2: after dehydration treatment, the stream containing aminal continues to react in the presence of an ionic liquid heteropolyacid salt catalyst, a material stream containing diphenylmethane diamine and polyamine is obtained through transposition rearrangement reaction, and then the material stream is washed, layered and optionally refined, and then refined (intermediate) diphenylmethane diamine and polyamine (DAM) material streams are obtained through separation;
s3: the diphenylmethane diamine and polyamine (DAM) material flow contacts phosgene to generate a phosgenation reaction, and a crude MDI product is generated; optionally, after the crude MDI is purified by distillation, a mixture containing MDI and polymeric MDI (polyphenyl polymethylene polyisocyanate, i.e. PM) is obtained;
s4: after the polymeric MDI in the mixture is separated, the MDI product containing 4,4'-MDI, 2,4' -MDI and 2,2'-MDI isomers (comprising 4,4' -MDI, 2,4'-MDI and 2,2' -MDI and the mixture thereof) is obtained.
In accordance with the preparation process provided herein, in some embodiments, the ionic liquid heteropolyacid salt catalyst (i.e., heteropolyacid-supported ionic liquid catalyst) comprises a heteropolyacid (as the active component) and an ionic liquid (as the support);
the heteropolyacid is selected from one or more of silicotungstic acid, silicomolybdic acid, phosphotungstic acid and phosphomolybdic acid;
the ionic liquid is pyridinium type ionic liquid.
In some embodiments, the ionic liquid heteropolyacid salt catalyst, the heteropolyacid content is in the range of 10-20wt% (e.g., 12wt%, 14wt%, 15wt%, 16wt%, 18 wt%) of the mass of ionic liquid.
In some embodiments, a method of making the ionic liquid heteropolyacid salt catalyst comprises the steps of:
and (4) SS1: mixing 1,3-propane sultone with pyridine, adding ethyl acetate to dissolve, heating and stirring for reaction, and performing post-treatment (reduced pressure suction filtration, washing and drying) to obtain an intermediate A (such as sulfonic pyridinium);
and (4) SS2: melting and mixing the intermediate A and heteropoly acid, and then transferring the mixture into a supercritical reaction kettle for supercritical treatment; and calcining the material obtained by supercritical treatment to obtain the ionic liquid heteropolyacid salt catalyst.
In some embodiments, in step SS1, the mass ratio of 1,3-propane sultone to pyridine is 1: (0.5 to 0.7), for example, 1; 1,3-propane sultone and ethyl acetate in a mass ratio of 1: (4-10), for example, 1:5, 1:6, 1:7, 1:8, 1:9.
In some embodiments, the process conditions for the reaction described in step SS1 include:
the heating temperature is 50-100 deg.C (e.g., 60 deg.C, 80 deg.C, 90 deg.C); the stirring speed is 200-600 rpm/min (such as 250rpm/min, 300rpm/min, 400rpm/min, 500 rpm/min); the reaction time is 4-8 h (such as 5h, 6h and 7 h); optionally, the fractions are refluxed during the reaction.
In some embodiments, the process conditions of the post-treatment of step SS1 include: filtering the reaction product under reduced pressure at 10-20 kPa (such as 12kPa, 14kPa, 16kPa, 18 kPa); washing the mixture by using ethyl acetate during reduced pressure suction filtration; vacuum drying the filter cake obtained by suction filtration at 100-200 deg.C (e.g., 120 deg.C, 140 deg.C, 180 deg.C) under 10-20 kPa (e.g., 15kPa, 18 kPa).
In some embodiments, in step SS2, the mass ratio of the heteropolyacid to intermediate a is (0.1 to 0.2): 1 (e.g., 0.12.
In some embodiments, the melting temperature is 50 to 100 ℃ (e.g., 60 ℃, 80 ℃, 95 ℃), preferably 70 to 90 ℃.
In some embodiments, the process conditions of the supercritical treatment include: the treatment temperature is 80-140 deg.C (e.g. 90 deg.C, 100 deg.C, 120 deg.C), the treatment pressure is 4-6 MPa (e.g. 4.5MPa, 5MPa, 5.5 MPa), and the treatment time is 6-10 h (e.g. 7h, 8h, 9 h).
In some embodiments, the process conditions of the calcining include: the calcining temperature is 350-600 ℃ (such as 400 ℃, 500 ℃ and 550 ℃) and the calcining time is 2-5 h (such as 3h and 4 h).
According to the preparation method provided by the invention, the selected methylene donor can be formaldehyde prepared by oxidative dehydrogenation of methanol, can be formaldehyde solution (with mass concentration of 30-50%), gas-phase formaldehyde and the like, for example, gaseous formaldehyde with HCHO content of more than or equal to 70% or formaldehyde solution with mass concentration of 35-45% is used; a formaldehyde solution having a mass concentration of 37% is preferred.
In some embodiments, the molar ratio of formaldehyde to aniline in step S1 is from 0.1 to 1 (e.g., 0.15, 0.25, 0.4, 0.5, 0.8, 0.9), preferably from 0.3 to 0.6.
In some embodiments, the reaction temperature in step S1 is from 30 to 80 deg.C (e.g., 40 deg.C, 50 deg.C, 65 deg.C), preferably from 60 to 70 deg.C.
In some embodiments, the step of dehydrating in step S2 comprises:
1) Sending the mixture flow containing the aminal in the step S1 into a delayer, carrying out preliminary dehydration separation on oil-water two phases, and separating out a lower-layer organic phase (the main component is the aminal);
2) And (3) carrying out secondary dehydration on the lower organic phase separated by the primary dehydration, wherein the secondary dehydration is carried out by adopting one or more of molecular sieve water absorption, polymer resin water absorption and rectification, and preferably adopting rectification (for example, adopting rectification at 180-200 ℃).
The reaction device used for the salt-forming reaction of formaldehyde and aniline in step S1 is conventional equipment in the art. Step S2 the equipment used for dehydrating the produced aminal-containing stream prior to the reaction, and the reaction apparatus (e.g. fixed bed reactor) used in the reaction stage of step S2 are also conventional in the art and will not be described herein.
In some embodiments, the reaction temperature in step S2 is 80 to 120 deg.C (e.g., 90 deg.C, 110 deg.C), preferably 100 to 120 deg.C.
For a continuous production process, the ionic liquid heteropolyacid salt catalyst can be used in an amount based on the residence time of the aminal. In some embodiments, in step S2, the ionic liquid heteropolyacid salt catalyst is used in an amount such that the reaction residence time of the aminal in the system in which the ionic liquid heteropolyacid catalyst is present is 1 to 5 hours (e.g., 2 hours, 2.5 hours, 4 hours, 4.5 hours), preferably 1.5 to 3 hours, based on the residence time of the aminal.
In some embodiments, in step S3, the mass ratio of diphenylmethanediamine and polyamine (DAM) to phosgene is in the range of 1:1-1:5 (e.g., 1.5, 1:2, 1:3, 1:4, 1; the technological conditions of the phosgenation reaction comprise: the reaction pressure is 0.1-3.0MPa (e.g., 0.3MPa, 0.5MPa, 1.0MPa, 2.0 MPa), and the reaction temperature is 80-150 deg.C (e.g., 90 deg.C, 100 deg.C, 120 deg.C, 140 deg.C).
The washing of the crude DAM prior to the phosgenation may be accomplished by conventional means in the art, for example, by washing with a water wash column followed by separation of the oil and water phases by passage through a delayer. The reaction device used for the phosgenation reaction can be a device commonly used in the field, and the process conditions for rectifying and purifying the crude MDI product and the used device thereof are also conventional in the field and are not described herein again.
In the present invention, the preparation method of diphenylmethane diisocyanate (MDI) can be realized by a batch production process or a continuous production process, which is commonly used in the art.
The invention also provides diphenylmethane diisocyanate (MDI) prepared by the above preparation method, wherein the diphenylmethane diisocyanate (MDI) has a 2,2' -MDI isomer content of 10-800ppm (e.g., 20ppm, 40ppm, 50ppm, 80ppm, 100ppm, 150ppm, 200ppm, 300ppm, 400ppm, 500ppm, 600 ppm), and the MDI-50 product produced contains substantially no acridine.
Solid acid as a catalyst for condensation reaction of aniline and formaldehyde is known in the art, but in the existing process, the main concern is to increase the proportion of 4,4 '-isomer and the reaction conversion rate in the preparation process of (intermediate) diphenylmethane diamine and polyamine (DAM), and some studies have focused on the content of 2,4' -isomer, but no study has been made on how to further reduce the content of undesired 2,2 '-isomer so as to avoid the occurrence of acridine and other impurities in the product in the rear-end reaction stage, and particularly, in the case of high 2,4' -isomer content in the intermediate, how to avoid the increase of 2,2 '-isomer content and the increase of acridine impurity content in the rear-end reaction due to the increase of 2,2' -isomer content.
Although the traditional solid acid catalyst can greatly improve the proportion of 4,4'-MDA in (intermediate) diphenylmethane diamine and polyamine (DAM), the content of 2,2' -MDA isomer is also greatly improved, and the 2,2'-MDA with the increased content enters a rear-end reaction stage, high-content 2,2' -MDI is generated in a phosgenation reaction and is further converted into acridine and other impurities, so that the quality of a final product is influenced.
The inventor of the invention discovers, through research, that a specific ionic liquid heteropoly acid salt catalyst (such as a pyridine ionic liquid heteropoly acid salt catalyst obtained through supercritical treatment) is selected, on one hand, the B acid strength of the ionic liquid is provided through heteropoly acid, the defect of the traditional inorganic acid in use is avoided, and meanwhile, the reaction selectivity can be improved; on the other hand, the ionic liquid heteropolyacid salt catalyst prepared by the supercritical method can enable the heteropolyacid load in the ionic liquid heteropolyacid salt catalyst to be more uniform, avoids the problem that the catalysis effect is influenced due to the fact that the local distribution of the heteropolyacid salt catalyst is uneven, the catalyst load is low, the local impurity content is high and the like, and further improves the improvement effect of the catalyst on the reaction selectivity when the catalyst is used.
Compared with the prior art, the technical scheme of the invention has the beneficial effects that:
(1) The specific solid acid catalyst can effectively avoid the generation of 2,2' -isomer in (intermediate) diphenylmethane diamine and polyamine (DAM) obtained in the MDI production process, has influence on the selectivity of three MDI isomers, and can reduce the selectivity of 2,2' -MDI under the condition of high 2,4' -isomer content, thereby avoiding a series of problems in the subsequent use of MDI products;
the pyridine ionic liquid heteropoly acid catalyst is selected, the B acid strength of the ionic liquid is improved by adding the heteropoly acid, compared with the traditional heteropoly acid catalyst, the loading capacity of the ionic liquid heteropoly acid catalyst is greatly improved under the condition of the same heteropoly acid dosage, the catalytic activity is effectively improved, and meanwhile, the catalyst containing the ionic liquid and the heteropoly acid is added into a reaction system, so that the generation of 2,2 '-isomer can be avoided under the condition of high 2,4' -isomer content; in addition, the processing technology of the supercritical method enables the loading of the heteropoly acid to be more uniform, and the generation of local impurities is avoided;
the inventor finds that the high-content 2,2'-MDI isomer generated in the MDI production process can be converted into acridine, and the pyridine ionic liquid heteropolyacid catalyst is selected to greatly reduce the content of 2,2' -MDI isomer so as to effectively inhibit the generation of acridine impurities;
(2) The method also adopts a phosgenation method, obviously reduces the content of 2,2' -MDI in the target product or converts the target product into acridine impurities, does not cause subsequent cost increase, and does not change the content of each component in MDI and PMDI. The inventive concept of the preparation method can be realized by using the existing phosgenation device and separation device, and meanwhile, the risk in the production process and the reduction of the product quality can not be increased.
Detailed Description
In order that the technical features and contents of the present invention can be understood in detail, preferred embodiments of the present invention will be described in more detail below. While the preferred embodiments of the present invention have been described in the examples, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein.
< sources of raw materials >
Aniline materials: ningbo Wanhua industrial garden Ningbo aniline production device, industrial product;
formaldehyde material: ningbo Wanhua industrial garden Ningbo formaldehyde device production, industrial product, concentration is 37wt%;
hydrochloric acid aqueous solution: a byproduct of Ningbo MDI device in Ningbo Wanhua industrial park, industrial products, with the concentration of 33%;
aqueous caustic soda solution: a byproduct of Ningbo MDI device in Ningbo Wanhua industrial park, namely industrial products, with the concentration of 48 percent;
1,3-propane sultone, national chemical group of pharmaceutical reagents, analytical pure;
pyridine, analytically pure from national chemical group, ltd;
ethyl acetate, analytically pure from national chemical group of pharmaceutical chemicals, ltd;
phosphotungstic acid (H3O 40PW 12) analytically pure from the national pharmaceutical Agents chemical group, inc.;
silicotungstic acid (H6O 41SiW 12) was analytically pure from the national reagent chemical group, inc.
< detection method >
The determination method of each component in DAM is carried out by adopting liquid chromatography, and an analytical instrument is Agilent 1200;
the determination method of each component in MDI is carried out by adopting a liquid chromatography derivatization method, and an analytical instrument is Agilent 1260.
Preparation of ionic liquid heteropolyacid salt catalyst
Preparation example 1:
the preparation method of the phosphotungstate pyridinium catalyst PW-1 comprises the following steps:
and (4) SS1: weighing 61.07g of 1,3-propane sultone and 39.55g of pyridine, weighing 350mL of solvent ethyl acetate, adding the solvent ethyl acetate into a round-bottom flask with a mixed magnetic stirring function, and mixing, wherein the stirring speed is controlled at 400rpm/min; reacting for 6 hours at the temperature of 80 ℃ under reflux, carrying out vacuum filtration on a product material flow under the pressure of 10kPa after the reaction is finished, washing a filter cake by using ethyl acetate during the vacuum filtration, and drying in a vacuum drying oven at the temperature of 130 ℃ under the pressure of 10kPa to obtain an intermediate A1 (sulfonic pyridine salt);
and (4) SS2: weighing 10g of the intermediate A1, mixing with 2g of phosphotungstic acid (H3O 40PW 12), completely melting at 90 ℃, adding into a supercritical reaction kettle, performing supercritical reaction at 130 ℃ and 5MPa for 8H, taking out the obtained material, and calcining at 600 ℃ for 5H to obtain a final product, namely a phosphotungstic acid pyridinium catalyst (PW-1).
Preparation example 2:
a preparation method of a silicotungstic acid pyridinium catalyst SW-1 is as shown in preparation example 1, except that: the phosphotungstic acid used is replaced by silicotungstic acid (H6O 41SiW 12), and the final product is a silicotungstic pyridinium catalyst (SW-1).
Preparation example 3:
a preparation method of a phosphotungstate pyridinium catalyst PW-2 refers to preparation example 1, and is characterized in that: the adding amount of phosphotungstic acid is replaced by 1g, and the final product is a phosphotungstic acid pyridinium catalyst (PW-2).
Preparation example 4:
a preparation method of a phosphotungstate pyridinium catalyst PW-3 is as shown in preparation example 1, except that: the addition of phosphotungstic acid was replaced with 1.5g to obtain the final product, a pyridinium phosphotungstate catalyst (PW-3).
Preparation example 5:
a preparation method of a phosphotungstate pyridinium catalyst PW-4 is as shown in preparation example 1, except that: 1,3-propane sultone, pyridine and ethyl acetate in a mass ratio of 1:0.5:4, obtaining a final product, namely a phosphotungstic acid pyridinium catalyst (PW-4).
Catalyst 6:
a preparation method of a phosphotungstate pyridinium catalyst PW-5 is as shown in preparation example 1, except that: 1,3-propane sultone, pyridine and ethyl acetate in a mass ratio of 1:0.7:5, obtaining a final product, namely a phosphotungstic acid pyridinium catalyst (PW-5).
Comparative preparation example 1:
process for the preparation of catalyst PW-1', reference being made to preparation 1, with the exception that: in the step SS2, the intermediate A1 prepared in the step SS1 and phosphotungstic acid are added into a common reaction kettle without being treated by a supercritical method, and are stirred and reacted for 8 hours at the temperature of 130 ℃, so that a final product, namely the catalyst (PW-1'), is obtained.
Process for preparing diphenylmethane diisocyanate (MDI)
Example 1:
the preparation method of the diphenylmethane diisocyanate (MDI) by adopting a continuous production process comprises the following steps:
s1: introducing an aniline material (the mass concentration of aniline is 94%) and a formaldehyde material (the mass concentration of formaldehyde is 37%) into a reactor, mixing and carrying out condensation reaction, wherein the molar ratio of formaldehyde to aniline is 0.4;
s2: feeding the obtained material flow containing the aminal into a first oil-water demixer, preliminarily dehydrating an oil-water phase, and separating to obtain a lower-layer organic phase, wherein the main component of the lower-layer organic phase is the aminal; then rectifying the oil phase at 200 ℃, and further removing water in the oil phase by secondary dehydration;
feeding the aminal stream obtained after secondary dehydration into a fixed bed reactor, heating the reactor to 120 ℃, and reacting in the presence of a phosphotungstic acid pyridinium catalyst (PW-1) for 90min to obtain a stream containing diphenylmethane diamine and polyamine;
the material flow containing the diphenylmethane diamine and the polyamine is fully contacted with water and fully mixed for washing under the stirring action; the material after water washing enters a second oil-water demixer for demixing, after an oil phase (crude DAM) is separated, light components such as aniline and water in the material are removed by a refining means of evaporation at 210 ℃ and steam stripping at 190 ℃, and finally a refined DAM material flow is obtained, wherein the content of 2,2' -MDA is 60ppm;
s3: mixing the refined DAM and chlorobenzene in a dynamic mixer according to a mass ratio of 1:4 to obtain a mixed solution, mixing the mixed solution and phosgene according to a mass ratio of 5:4 (namely, mixing the DAM and the phosgene according to a mass ratio of 1:4), and carrying out two-stage phosgenation reaction on the mixed material: the first-stage reaction temperature is controlled to be 90 ℃, the pressure is 270KPaG, the second-stage reaction temperature is controlled to be 145 ℃, and the pressure is 270KPaG; generating crude MDI;
rectifying the crude MDI mixture obtained by the reaction at 240 ℃, stripping at 210 ℃, and removing chlorobenzene in a separation unit to obtain a product, namely diphenylmethane diisocyanate (MDI), wherein the 2,2' -MDI content is 40ppm, and acridine is not detected in the MDI-50 product. The product data for each reaction stage are shown in the table below.
Example 2:
the procedure was as in example 1, except that the catalyst used in step S2 was replaced with SW-1. The product diphenylmethane diisocyanate (MDI) was obtained and the product data for each reaction stage are shown in the following table.
Example 3:
the procedure was as in example 1, except that the catalyst used in step S2 was replaced with PW-2. The product diphenylmethane diisocyanate (MDI) was obtained and the product data for each reaction stage are shown in the following table.
Example 4:
the preparation was carried out as described in example 1, except that the catalyst used in step S2 was replaced with PW-3. The product diphenylmethane diisocyanate (MDI) was obtained and the product data for each reaction stage are shown in the following table.
Example 5:
the procedure was as in example 1, except that the catalyst used in step S2 was replaced with PW-4. The product diphenylmethane diisocyanate (MDI) was obtained and the product data for each reaction stage are shown in the following table.
Example 6:
the procedure was as in example 1, except that the catalyst used in step S2 was replaced with PW-5. The product diphenylmethane diisocyanate (MDI) was obtained and the product data for each reaction stage are shown in the following table.
Example 7:
the preparation is as described in example 1, with the exception that the aminal-containing stream formed in step S1 is not subjected to a dehydration treatment in step S2. The product diphenylmethane diisocyanate (MDI) was obtained and the product data for each reaction stage are shown in the following table.
Example 8:
the preparation is as described in example 1, except that the stream comprising aminal in step S2 has a reaction residence time of 3h in the fixed-bed reactor. The product diphenylmethane diisocyanate (MDI) was obtained and the product data for each reaction stage are shown in the following table.
Comparative example 1:
the procedure is as described in example 1, except that the catalyst used in step S2 is replaced with ITQ-2 solid molecular sieve catalyst (prepared in example 1 of patent document CN 1642901A). The product diphenylmethane diisocyanate (MDI) was obtained and the product data for each reaction stage are shown in the following table.
Comparative example 2:
in the process of preparing MDI by adopting the continuous production procedure, the traditional hydrochloric acid is selected as a catalyst.
The method comprises the following specific steps:
introducing a hydrochloric acid aqueous solution and an aniline material (the mass concentration of aniline is 94%) and a formaldehyde material (the mass concentration of formaldehyde is 37%) into a reactor to react, wherein the molar ratio of hydrochloric acid to aniline is 0.11; then the mixture enters a fixed bed reactor, the temperature is raised to 120 ℃, and the reaction is continued for 90min, so that a material flow containing diphenylmethane diamine and polyamine is obtained; then the mixture enters a mixer, and the stream containing the diphenylmethane diamine and polyamine is neutralized by NaOH aqueous solution (with the mass concentration of 50 percent), wherein the addition amount of the NaOH is 120 percent of the amount required for neutralizing hydrochloric acid in the stream;
the mixture obtained after neutralization enters an oil-water demixer i, and is separated into an organic phase and a water phase containing diamine and polyamine of diphenylmethane series, the organic phase is fully contacted with water in a stirring tank and is fully mixed and washed under the stirring action;
the washed material enters an oil-water demixer ii for demixing, and light components such as aniline, water and the like in the separated oil phase (crude DAM) are removed by a refining means of evaporation at 210 ℃ and steam stripping at 190 ℃ to finally obtain refined DAM;
mixing the refined DAM and chlorobenzene in a dynamic mixer according to a mass ratio of 1:4 to obtain a mixed solution, mixing the mixed solution and phosgene according to a mass ratio of 5:4, and carrying out two-stage phosgenation reaction on the mixed material: the first-stage reaction temperature is controlled to be 90 ℃, the pressure is 270KPaG, the second-stage reaction temperature is controlled to be 145 ℃, and the pressure is 270KPaG;
rectifying the mixture obtained by the reaction at 240 ℃, stripping at 210 ℃, and removing chlorobenzene in a separation unit to obtain the product diphenylmethane diisocyanate (MDI). The product data for each reaction stage are shown in the table below.
Comparative example 3
The preparation was carried out as described in example 1, except that the catalyst used in step S2 was replaced with PW-1'. The product diphenylmethane diisocyanate (MDI) was obtained and the product data for each reaction stage are shown in the following table.
TABLE 1 data of reaction products obtained in the respective examples and comparative examples
The experimental results in table 1 show that the pyridine ionic liquid heteropolyacid salt catalyst obtained by the supercritical process is selected for producing MDI in each embodiment, the specific solid acid catalyst has higher catalytic activity and catalytic selectivity, the generation of 2,2 '-isomer of (intermediate) diphenylmethane diamine and polyamine (DAM) obtained in the MDI production process can be effectively avoided, the selectivity of three isomers of MDI can be influenced, the selectivity of 2,2' -MDI can be reduced under the condition of high 2,4 '-isomer content, and the 2,2' -MDI isomer content can be greatly reduced, so that the generation of acridine impurities can be effectively inhibited.
Comparative example 1 used a solid acid catalyst that was not supported by an ionic liquid, and not only was the 2,2 '-isomer very high in content, but also the production of the higher 2,4' -isomer could not be guaranteed; comparative example 2 the production of MDI using ordinary hydrochloric acid as a catalyst also suffers from the problem of very high content of 2,2' -isomer, which is easily converted to acridine impurity at this high content, resulting in a reduced product quality. The catalyst used in comparative example 3 is not treated by the supercritical process, so that uneven loading of heteropoly acid is easy to occur, local impurity generation is caused, and product quality and subsequent application are influenced.
While certain embodiments of the present invention have been described above, the above description is illustrative, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.
Claims (10)
1. A preparation method of diphenylmethane diisocyanate with low 2,2'-MDI content is characterized in that aniline and formaldehyde are subjected to condensation reaction and then subjected to transposition reaction in the presence of an ionic liquid heteropolyacid salt catalyst to obtain a material flow containing diphenylmethane diamine and polyamine, wherein the content of 2,2' -MDA isomer in a mixture of the diphenylmethane diamine and the polyamine is 10-1000ppm; the stream containing the diphenylmethane diamines and polyamines is then reacted with phosgene to produce a product stream containing diphenylmethane diisocyanates.
2. The method of claim 1, comprising the steps of:
s1: mixing aniline and formaldehyde for condensation reaction to obtain a material flow containing aminal;
s2: after dehydration treatment, the stream containing aminal continues to react in the presence of an ionic liquid heteropolyacid salt catalyst, a material stream containing diphenylmethane diamine and polyamine is obtained through transposition rearrangement reaction, and then the material stream is separated to obtain the diphenylmethane diamine and polyamine material stream after washing, layering and optional refining treatment;
s3: the diphenylmethane diamine and polyamine material flow contacts phosgene to generate a phosgenation reaction, and a crude MDI product is generated; optionally, after the crude MDI is purified by rectification, a mixture containing MDI and polymeric MDI is obtained;
s4: after separation of the polymeric MDI in the mixture, an MDI product containing 4,4' -MDI, 2,4' -MDI and 2,2' -MDI isomers is obtained.
3. The method of claim 1, wherein the ionic liquid heteropolyacid salt catalyst comprises a heteropolyacid and an ionic liquid;
the heteropolyacid is selected from one or more of silicotungstic acid, silicomolybdic acid, phosphotungstic acid and phosphomolybdic acid;
the ionic liquid is pyridinium ionic liquid;
preferably, in the ionic liquid heteropolyacid salt catalyst, the content of the heteropolyacid is 10-20wt% of the mass of the ionic liquid.
4. The method of claim 1, wherein the ionic liquid heteropolyacid salt catalyst is prepared by a method comprising the steps of:
and (4) SS1: mixing 1,3-propane sultone with pyridine, adding ethyl acetate to dissolve, reacting under heating and stirring, and performing aftertreatment to obtain an intermediate A;
and SS2: melting and mixing the intermediate A and heteropoly acid, and then transferring the mixture into a supercritical reaction kettle for supercritical treatment; and calcining the material obtained by supercritical treatment to obtain the ionic liquid heteropolyacid salt catalyst.
5. The method according to claim 4, wherein in step SS1, the mass ratio of 1,3-propane sultone to pyridine is 1: (0.5-0.7), wherein the mass ratio of 1,3-propane sultone to ethyl acetate is 1: (4-10); and/or
The process conditions of the reaction include:
the heating temperature is 50-100 ℃; the stirring speed is 200-600 rpm/min; the reaction time is 4-8 h; optionally refluxing the fractions during the reaction; and/or
The process conditions of the post-treatment comprise: carrying out reduced pressure suction filtration on the reaction product under 10-20 kPa; washing the mixture by using ethyl acetate during reduced pressure suction filtration; and vacuum drying the filter cake obtained by suction filtration at 100-200 ℃, wherein the pressure is controlled at 10-20 kPa.
6. The preparation method according to claim 4, wherein in step SS2, the mass ratio of the heteropoly acid to the intermediate A is (0.1-0.2): 1; and/or
The melting temperature is 50-100 ℃, and preferably 70-90 ℃; and/or
The process conditions of the supercritical treatment comprise: the treatment temperature is 80-140 ℃, the treatment pressure is 4-6 MPa, and the treatment time is 6-10 h; and/or
The calcining process conditions comprise: the calcining temperature is 350-600 ℃, and the calcining time is 2-5 h.
7. The production method according to claim 1, wherein, in step S1,
the molar ratio of formaldehyde to aniline is 0.1 to 1, preferably 0.3 to 0.6; and/or
The reaction temperature is 30 to 80 ℃, preferably 60 to 70 ℃.
8. The production method according to claim 1, wherein the step of dehydration treatment in step S2 includes:
1) Sending the mixture flow containing the aminal in the step S1 into a delayer, carrying out preliminary dehydration separation on oil-water two phases, and separating out a lower-layer organic phase;
2) And (3) carrying out secondary dehydration on the lower-layer organic phase separated by the primary dehydration, wherein the secondary dehydration is preferably carried out by adopting one or more of molecular sieve water absorption, polymer resin water absorption and rectification, and is more preferably carried out by adopting rectification.
9. The method according to claim 1, wherein in step S2, the reaction temperature is 80-120 ℃, preferably 100-120 ℃; and/or
In the step S2, the amount of the ionic liquid heteropolyacid salt catalyst is calculated by the residence time of the aminal, and the reaction residence time of the aminal in the system in which the ionic liquid heteropolyacid salt catalyst exists is 1 to 5 hours, preferably 1.5 to 3 hours; and/or
In the step S3, the mass ratio range of the diphenylmethane diamine, the polyamine and the phosgene is 1:1-1:5; the technological conditions of the phosgenation reaction comprise: the reaction pressure is 0.1-3.0MPa, and the reaction temperature is 80-150 ℃.
10. The diphenylmethane diisocyanate obtained by the process of any one of claims 1 to 9, wherein the diphenylmethane diisocyanate has a content of 2,2' -MDI isomer of 10 to 800ppm.
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