Organic compounds -- part of the class 532-570 series – Organic compounds – Fatty compounds having an acid moiety which contains the...
Reexamination Certificate
2001-06-01
2002-12-31
Carr, Deborah D. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Fatty compounds having an acid moiety which contains the...
C554S068000, C554S047000
Reexamination Certificate
active
06500973
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to extractive solution crystallization techniques for a broad class of chemical compounds, including salts of chemical compounds. More particularly, the invention relates to a process for the isolation and purification of inorganic salts or organic salts by extractive solution crystallization. In a highly preferred embodiment, the invention relates to phenyl ester salts.
BACKGROUND OF THE INVENTION
Phenyl ester salts, as are known in the art, have been used in detergents and as bleach activators for fabric laundering and cleaning applications. The synthesis and purification of phenyl ester salts is described in U.S. Pat. No. 5,717,188, U.S. Pat. No. 5,650,527, and U.S. Pat. No. 5,523,434. In most cases, the phenyl ester salt to be purified is first isolated in a crude form, for example, through either evaporation of the reaction solvent, or by solid-liquid separation through filtration or centrifugation. This crude product is then purified using techniques known in the art, such as distillation or crystallization.
For the isolation and purification of solid chemical compounds, crystallization is often more appropriate than distillation. Crystallization comprises precipitating a chemical compound from a solution, followed by crystal growth. As a purification technique, crystallization has been used extensively to separate inorganic and organic chemical compounds from impurities, and thereby purifying the inorganic or organic chemical compound.
Many industrial chemical processes isolate and purify chemical compounds using crystallization techniques. Comprehensive accounts of various crystallization techniques have been discussed in several publications. (See Mullins, J. W., “Ullmann's Encyclopedia of Industrial Chemistry,” Volume B2, 3-1, 1988, for example). In many situations, crystallization can yield compounds of high purity in one theoretical stage with minimal energy costs. In other cases, however, crystallization may be inefficient for a variety of reasons.
One problem commonly encountered when using crystallization techniques is the co-crystallization of undesired impurities. These impurities may include, for example, unreacted starting materials or undesired byproducts produced during synthesis. In the case of phenyl ester salts, co-crystallization can lead to purity or separability problems which preclude isolation of the phenyl ester salt or which preclude its intended use in a subsequent chemical process or product. The impurities can sometimes be removed through multiple purification or recrystallization steps. However, the use of numerous purification or recrystallization steps has many disadvantages including: high capital costs, low overall yield, loss of product, poor product quality, lack of process robustness, additional steps for solvent recovery, and slower throughput. For large scale production, these problems can be particularly unacceptable.
Generally, simple fractional crystallization is used to separate and/or purify chemical compounds from crude mixtures containing the desired compound and one or more undesired impurities. Simple fractional crystallization is the sequential and separate crystallization of more than one compound from the same solution. Where simple fractional crystallization cannot be used to completely separate pure chemical compounds from mixtures, crystallization techniques such as adductive crystallization and extractive crystallization have been employed. Adductive crystallization processes have been described, for example, in U.S. Pat. Nos. 2,768,222; 2,778,864; and 2,520,716. Extractive crystallization processes have been described, for example, in U.S. Pat. Nos. 3,767,724 and 2,398,526.
Both adductive crystallization and extractive crystallization have been effectively used to (i) separate mixtures which form eutectics upon crystallization, (ii) separate pure isomers where distillation, extraction, and adsorption fail, (iii) separate compounds by shape and size rather than by chemical type, and (iv) eliminate deep refrigeration (e.g., Dale, G. H., “Crystallization, Extractive and Adductive,” in Encyclopedia of Chemical Processing and Design, J. J. McKetta and W. A. Cunningham, Eds., Vol. 13, p. 456, 1981).
Adductive crystallization involves adding an adductive agent to a solution containing a mixture of chemical compounds to selectively form an adduct with a desired chemical compound, which then selectively crystallizes or crystallizes out of the solution. The resulting adduct may then be separated as a solid from the mixture. The desired product is subsequently recovered by “breaking” the adduct and removing the adductive agent. Disadvantages of adductive crystallization include the extra steps which are required to isolate the desired chemical compound, as well as the mechanical problems and large expense involved if this process is to be adapted for large scale production. Further, some chemical compounds, such as the detergent or bleach activators described below, may not be stable under the conditions required to remove the adductive agent from the resulting adduct of the compound.
Extractive crystallization, in contrast, involves adding an additional component, such as a solvent, to a solution containing a mixture of chemical compounds (e.g., isomers, binary pairs, or similar compounds) to lower the eutectic point of the mixture. Extractive crystallization affords enhanced recovery of the purified desired component as a solid, and may also allow the recovery of the other isomer as a purified co-product. Extractive crystallization is normally limited to separations of fairly high molecular weight compounds with relatively high freezing points (Dale, G. H., “Crystallization, Extractive and Adductive,”
Encyclopedia of Chemical Processing and Design,
J. J. McKetta and W. A. Cunningham, Eds., Vol. 13, p. 456, 1981; Dye, S. R. et al,
Process Systems Engineering,
41, 1456-1470, 1995). Methods for selecting the extractive solvent for extractive crystallization have been studied (e.g., Dikshit, et al., Chem. Eng.,
Science,
26, 719-727, 1971). However, extractive crystallization is not readily adaptable to a wide variety of substrates or solvent systems.
Extractive crystallization has also been adapted to crystallize salts from concentrated aqueous solutions. Here, the added solvent extracts the water away from the inorganic salt phase (e.g., Weingaertner, D. L., et al.,
Ind. Eng. Chem. Res.,
30, 490-501, 1991; Zerres, H., et al., A. I. Ch. E., 40, 676-691, 1994; Lynn Scott, A. L., et al.,
Ind. Eng. Chem. Res.,
35, 4236-4245, 1996). This results in the crystallization and crystal growth of the salt solute, as the original aqueous phase becomes more concentrated and its saturation limit is exceeded. This mechanism is different from conventional extractive crystallizations since two liquid phases are actually present. However, both of these phases are considered to be aqueous, and not biphasic.
Another recent offshoot of extractive and adductive crystallization techniques is dissociation extractive crystallization (Lashanizadegan, A. et al.,
Chem. Eng. Res. and Design, Trans. Inst. Chem. Eng.,
74, Part A, 1996). Here, the extractant contains a reactive agent that reacts with the desired compound in either the same phase or a separate phase. The resulting product or complex is insoluble and crystallizes out. Since the reaction is equilibrium-based, an excess of the extractant that contains the reactive agent may be used to recover the desired compound in high yields. As with adductive crystallization, however, further processing steps are required to ultimately isolate the desired product from the complex. Often, the desired product must be recovered from the complex through additional steps, such as heating or other chemical means. Similar problems as described above for adductive crystallization are encountered, which limits the utility of this technique.
Extractive crystallization using biphasic systems is described in U.S. Pat. No. 5,298,611 and U.S. Pat. No. 4,980,463.
Blake Michael J.
Carr Deborah D.
Eastman Chemical Company
Graves Bernard J.
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