Organic compounds -- part of the class 532-570 series – Organic compounds – Isocyanate esters
Reexamination Certificate
2000-10-13
2003-06-10
Rotman, Alan L. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Isocyanate esters
C560S331000, C560S334000, C560S347000, C560S352000, C560S358000, C560S359000
Reexamination Certificate
active
06576788
ABSTRACT:
The present invention relates to a process for preparing mixtures of diphenylmethane diisocyanates and polyphenylpolymethylene polyisocyanates, known as PMDI, having a reduced content of chlorinated by-products and a reduced iodine color number by two-stage reaction of the corresponding mixtures of diphenylmethanediamines and polyphenylpolymethylenepolyamines, known as PMDA, with phosgene in the presence of at least one inert organic solvent, where the corresponding carbamoyl chlorides formed in the first stage of the phosgenation and the amine hydrochlorides in the second stage of the phosgenation run through a residence time apparatus in which the amine hydrochlorides are phosgenated to the corresponding carbamoyl chlorides and the carbamoyl chlorides are dissociated into the corresponding isocyanates and hydrogen chloride and the mass ratios of phosgene to hydrogen chloride are at the same time 10-30:1 in the liquid phase and 1-10:1 in the gas phase.
PMDI is the industrially most important isocyanate for producing rigid polyurethane foams which are preferably used as insulation material in the building industry, as insulating foam in the refrigeration appliance industry and as sandwich construction material. Usually, part of the diphenylmethane 4,4′-diisocyanate, known as MMDI, present in the PMDI is recovered by means of a suitable technological operation such as distillation or crystallization. MMDI is in turn an important constituent of polyurethane formulations for compact, microcellular and cellular polyurethanes such as adhesives, coatings, fibers, elastomers and integral foams. Accordingly, the term “PMDI” used in the present text also encompasses PMDI mixtures in which monomeric MDI, for example 4,4′-, 2,2′- and/or 2,4′-MDI, is present.
PMDI is, as is known, prepared by phosgenation of the corresponding PMDA in the presence of an inert organic solvent. PMDA is in turn obtained by means of an acid aniline-formaldehyde condensation which can be carried out industrially either continuously or batchwise. The proportions of diphenylmethanediamines and the homologous polyphenylpolymethylenepolyamines and their positional isomerism in the PMDA are controlled by selection of the ratios of aniline, formaldehyde and acid catalyst and also by means of a suitable temperature and residence time profile. High contents of 4,4′-diphenylmethanediamine together with a simultaneously low proportion of the 2,4′ isomer of diphenylmethanediamine are obtained on an industrial scale by the use of strong mineral acids such as hydrochloric acid as catalyst in the aniline-formaldehyde condensation.
All the acid aniline-formaldehyde condensation processes described in the specialist and patent literature have in common the formation of undesired by-products, for example the formation of N-methylated and N-formylated compounds and also the formation of dihydroquinazolines. In addition, industrial PMDAs can contain residual amounts of unrearranged aminobenzylanilines which can in turn be a further starting point for further reactions. Another disadvantage is that the acid aniline-formaldehyde condensation forms chromophores which discolor the PMDA. These discolorations are reduced only insufficiently, if at all, in the subsequent neutralization of the acid condensation catalyst and the removal of the aniline used in excess in the condensation; the same applies to the subsequent process steps of the PMDI preparation.
In the phosgenation step, the PMDA is reacted with phosgene in an inert organic solvent to form PMDI. The undesired by-products and chromophores in the PMDA can react with phosgene to form further compounds such as secondary carbamoyl chlorides and products of chlorination of the aromatic ring and/or at the methylene bridge. In addition, the phosgenation step forms further chlorine-containing by-products such as allophanoyl chlorides and isonitrile dichlorides. The chlorine-containing compounds and chromophores are incorporated both into the low molecular weight fraction whose central constituent is the diphenylmethane diisocyanate and also into the oligomeric fractions of polyphenylpolymethylene polyisocyanate.
The technological operations which follow the phosgenation, namely removal of the phosgene used in excess, the removal of the inert solvent, the thermal treatment, the so-called dechlorination and the removal of part of the MMDI present in the crude PMDI by distillation and/or crystallization, do not lastingly reduce the content of chlorine-containing compounds and the discoloration of the crude PMDI increases with continuing, especially thermal, stressing of the product.
Chlorine-containing and/or discolored PMDI is undesirable in further processing to form polyisocyanate-polyalcohol polyaddition plastics. In particular, chlorine-containing compounds which can readily form ionic chloride, as determined by the ASTM D 1638-74 method, can cause considerable interference in the blowing reaction of foam production by forming salts with the blowing catalyst. Undesirable discolorations of the PMDI also show up in the plastics prepared therefrom. Although the color of the polyisocyanate-polyalcohol polyaddition plastics does not have an adverse effect on their mechanical properties, light-colored products are preferred because of their good versatility in the production process of the processor, e.g. the ability of light to pass through thin covering layers and the ability to produce a variety of colors.
There have therefore been many attempts to reduce the content of chlorinated by-products and the discoloration of PMDI in mixtures with MMDI.
According to GB 1 549 294, addition of isoureas in an amount of 25-250 mol % can reduce the ASTM D 1638-74 acidity of the PMDI. A disadvantage of this method is that an additional agent has to be used and the lowering of the acidity is only partially successful.
DD 285 593 proposes treating PMDI with acid amides in an amount of 0.01-0.2% at 100-140° C. for 0.2-6 hours. After the treatment, the hydrogen chloride formed is driven off by stripping with nitrogen or solvent vapors. Disadvantages of this process are the insufficient effect of the acid amides, the formation of additional constituents in the PMDI as a result of the unavoidable secondary reaction of the isocyanates with the acid amides to form acylated ureas and the outlay in terms of apparatus for treating the PMDI with the acid amides and for stripping out the hydrogen chloride, both that added as catalyst and that which is formed.
DE 2 847 243 proposes removal of phosgene by stripping with gaseous hydrogen chloride or nitrogen at 170° C. for 2 hours. A disadvantage is the considerable amounts of gases laden with phosgene or with phosgene/hydrogen chloride which make an additional outlay for the subsequent materials separation or an additional outlay for the neutralization of the acidic gas constituents absolutely necessary. The additional disadvantage of the process described in DE 2 847 243, namely the long residence time for stripping, is partially alleviated in JP 07 233 136 A by two-stage stripping with hydrogen chloride after phosgene removal at 115° C./30 minutes and 160° C./3 minutes. However, this results in the disadvantage of an additional technological operation and an again significant gas stream which requires treatment.
According to JP 07 082 230 A, organic phosphites are added to the aniline before the aniline-formaldehyde condensation.
To lower the iodine color number, the addition of numerous compounds after the phosgenation has been proposed: water (U.S. Pat. No. 4,465,639), phenol derivatives (DE 4 300 774), amines and/or ureas (DE 4 232 769), acid chlorides/chloroformates (DE 4 118 914), polyoxyalkylene polyalcohols (DE 4 021 712), dialkyl or trialkyl phosphites (DE 4 006 978), low molecular weight monohydric or polyhydric alcohols (EP 445 602), acid chlorides/antioxidant (DE 4 318 018).
All processes which propose the addition of compounds to raw materials or products of a preparation stage for PMDI have the disadvantage of t
Abeel Peter van den
Boesel Hilmar
Dosch Jürgen
Jacobs Jan
Näumann Fritz
Borrego Fernando A.
Oh Taylor V.
Rotman Alan L.
LandOfFree
METHOD FOR PRODUCING MIXTURES CONSISTING OF DIPHENYLMETHANE... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with METHOD FOR PRODUCING MIXTURES CONSISTING OF DIPHENYLMETHANE..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and METHOD FOR PRODUCING MIXTURES CONSISTING OF DIPHENYLMETHANE... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3157037