Organic compounds -- part of the class 532-570 series – Organic compounds – Isocyanate esters
Reexamination Certificate
1999-12-28
2001-10-23
Ramsuet, Robert W. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Isocyanate esters
Reexamination Certificate
active
06307096
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the field of aliphatic diisocyanate production.
BACKGROUND OF THE INVENTION
Aliphatic diisocyanates are major building blocks for the value-added polyurethane products most commonly used in the coatings industry. There are important differences between aromatic and aliphatic diisocyanate monomers. Aromatic diisocyanates, for instance, are much more reactive than their aliphatic diisocyanate counterparts. Urethane products made from aromatic diisocyanate monomers oxidize more easily than those prepared from aliphatic diisocyanates, especially when exposed to UV-light. The higher resistance to UV light-induced degradation of products prepared from aliphatic diisocyanates make them more useful in high quality exterior coatings where gloss and color retention are most important.
Ongoing demand for aliphatic diisocyanates has increased a long felt need to develop a method for making aliphatic diisocyanates that meets the following criteria. First, the method should be highly selective to aliphatic diisocyanate monomers and dimers (uretdiones) such that only an insignificant amount of the aliphatic diisocyanate is wasted. This would result in a high yield of the aliphatic diisocyanate as well as provide a product stream of high purity. Second, the method should operate at a temperature that is lower than the operating temperatures of distillation processes, so that energy costs can be reduced. This would also help to avoid thermal degradation of the product and undesirable side reactions.
Applicants are not aware of any known method that meets this criteria. Hexamethylene diisocyanate, for instance, is ordinarily produced on an industrial scale by phosgenation of 1,6-hexamethylene diamine in the presence of an inert solvent such as chlorobenzene or ortho-dicloro benzene (see. Ullmans Encyklopädie der technischen Chemi, 4
th
edition (1977), Volume 14, page 350, et. seq.). After phosgenation, the resulting product is generally subjected to vacuum distillation from which two products are separated: (i) a purified hexamethylene diisocyanate (HDI) product and (ii) a “waste stream” (a stream of unpurified oligomeric products). The purified product is collected and the waste stream, (which often contains an appreciable amount of valuable materials, e.g., aliphatic diisocyanate monomers, uretdiones), is disposed of.
The disposal of valuable aliphatic diisocyanate monomers and uretdiones with the waste stream has long been regarded as a significant shortcoming of known aliphatic diisocyanate production methods. Efforts to recover aliphatic diisocyanate monomers and uretdiones from waste streams by subjecting a waste stream to multiple distillation steps have not been successful. This is because multiple distillation techniques increase the amount of high molecular weight oligomers. Purification efforts also require a considerable expenditure of energy and outlay in apparatus. Further, the distillation procedures produce an undistillable residue that is very expensive to dispose of because it contains aliphatic diisocyanate components, i.e., monomers, uretdiones, and isocyanurates.
U.S. Pat. No. 4,918,220 discloses a method for separating and recovering toluene diisocyanate, an aromatic diisocyanate, from residues formed during the production of toluene diisocyanate with supercritical extraction techniques. The patent is directed exclusively to the recovery and separation of toluene diisocyanate from residues. There is no discussion about how aliphatic diisocyanates can be extracted from residues formed during the production of aliphatic diisocyanates. There is no discussion about the intermolecular interactions of aliphatic diisocyanate waste streams in supercritical fluids.
U.S. Pat. No. 4,871,460 discloses the separation and purification of isocyanate condensates, reaction products of isocyanates that are used to make foams. The patent focuses in applying supercritical extraction techniques to crude reaction mixtures and does not discuss how supercritical extraction techniques can be applied to waste streams. The patent does not discuss how supercritical extraction techniques can be applied to selectively extract aliphatic monomers or uretdiones from waste streams. U.S. Pat. No. 4,871,828 is also directed to the separation and purification of isocyanate condensates.
U.S. Pat. No. 4,864,025 discloses substantially pure isocyanurate/polyisocyanates that are produced by extracting impure cyclotrimerized diisocyanates with an inert gas, either in the liquid or supercritical state. The method involves cyclotrimerizing at least one aliphatic, alicyclic or arylaliphatic diisocyanate (in which the isocyanate groups are not directly linked to an aromatic ring) and removing the excess diisocyanate monomer and dimer formed with an inert gas in the liquid state or supercritical state. The patent is directed primarily to applying supercritical extraction techniques for purifying isocyanurates from crude reaction mixtures. The patent, however, does not teach how supercritical extraction techniques can be applied to selectively extract an appreciable amount, e.g., 85% or more of aliphatic diisocyanate monomers or uretdiones from waste streams. The patent does not discuss the conditions that are necessary to selectively extract aliphatic diisocyanate monomers and uretdiones in a commercial-scale method.
It is an object of the invention to develop a method for making an aliphatic diisocyanate that overcomes the disadvantages of known methods.
SUMMARY OF THE INVENTION
The present invention relates to a method for making an aliphatic diisocyanate including the steps of (a) phosgenating an aliphatic diamine in the presence of an inert solvent or a gas to form a mixture containing an aliphatic diisocyanate component; (b) distilling the mixture to form a hexamethylene diisocyanate production stream and an aliphatic diisocyanate waste stream; (c) placing the waste stream under supercritical fluid conditions sufficient to dissolve an aliphatic diisocyanate component in the supercritical fluid; (d) separating the dissolved aliphatic diisocyanate component from the waste stream, wherein the remaining waste stream is a supercritically-purged aliphatic diisocyanate waste stream; (e) lowering the pressure sufficiently to precipitate the aliphatic diisocyanate component. The invention also relates to the supercritically-purged aliphatic diisocyanate waste stream formed by the method. These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is based on the discovery that an aliphatic diisocyanate component can be selectively extracted from waste streams with supercritical fluid extraction techniques under certain conditions. The phrase “aliphatic diisocyanate component” refers to an aliphatic diisocyanate monomer, an aliphatic diisocyanate uretdione, or mixtures thereof. Although there may be some aliphatic diisocyanate isocyanurates in the aliphatic diisocyanate component, the aliphatic diisocyanate component does not contain an appreciable amount of isocyanurates because modeling results have suggested that the process is not selective to isocyanurates because of its low solubility in supercritical fluids.
The discovery is remarkable because prior to this invention, supercritical fluid extraction techniques had not been applied to extract aliphatic diisocyanate monomers or uretdiones from waste streams. The level of understanding of intermolecular interactions of aliphatic diisocyanate waste streams in supercritical fluids precluded the possibility of reliably calculating solubility levels in many cases. Further, since it is extremely difficult to conduct experiments under supercritical conditions, namely high pressures and high temperatures, the phase behavior of fluids in this supercritical regime is highly non-ideal. Consequently, thermodynamic modeling techniques capable of predicting the behavi
Ciebien Jane F.
Hortelano Edwin Ray
Sommer Alexa B.
Wittig Mary Ann
Yeske Philip E.
Bayer Corporation
Gil Joseph C.
Murray Joseph
Ramsuet Robert W.
Roy Thomas W.
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