Liquid purification or separation – Processes – Chromatography
Reexamination Certificate
1999-11-18
2002-04-30
Therkorn, Ernest G. (Department: 1723)
Liquid purification or separation
Processes
Chromatography
C210S198200, C127S046200, C127S070000
Reexamination Certificate
active
06379554
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention pertains to a process of simulated moving bed chromatography. It is particularly directed to operation of a simulated moving bed in coupled relation to a second chromatographic separation process. It provides for the recovery of a betaine and/or invert fraction from sugar solutions and the coupled production of a high purity sucrose product.
2. Background Art
U.S. Pat. No. 4,412,866 describes the operation of an SMB to separate the components of a feed stock. A resin bed is divided into a series of discrete vessels, each of which functions as a zone within a circulation loop. A manifold system connects the vessels and directs in appropriate sequence to (or from) each vessel each of the four media accommodated by the process. Those media are generally referred to as feed stock, eluent, extract and raffinate, respectively. As applied to a sugar factory, a typical feed stock is sucrose solution, the eluent is water, the extract is an aqueous solution of sucrose and the raffinate is an aqueous solution containing nonsucrose, such as salts and high molecular weight compounds. The SMB disclosed by the '866 patent is of the type sometimes referred to as a “continuous SMB,” to distinguish it from another type, sometime referred to as a “sequential SMB.” Unless otherwise indicated, the term “SMB” is used in this disclosure to denote a continuous SMB.
The largest single loss of sugar values from a typical sugar factory is attributable to molasses formation. Molasses comprises the byproduct (or waste) stream remaining after repeated crystallization procedures are applied to recover purified sugar. This molasses is typically of such low purity that further crystallization procedures for the recovery of additional sugar are economically impractical. SMB arrangements similar to those disclosed by the '866 patent are used in sugar factories to process molasses; typically producing a product fraction of relatively high (e.g., 90%) purity and low ash content and a byproduct fraction, comprising, typically, 40-50% of the feed, of relatively low purity and low ash content. (As used in the sugar industry, “purity” specifies percent by weight sucrose of the solids contained in a sample, on a dry weight basis.)
In the sugar beet industry, the byproduct fraction contains most of the betaine values of the molasses feed. Betaine, being the most abundant nitrogenous compound found in molasses, has been recognized as a commercially useful byproduct; notably for use in animal feeds. In the sugar cane industry, the byproduct fraction contains most of the invert sugar (i.e., glucose and fructose) values of the molasses feed. The invert is a valuable digestible carbohydrate. As used herein, the term “invert” refers to “invert sugar” (a mixture of glucose and fructose formed in equal quantities by the hydrolysis of sucrose).
In the typical operation of SMB chromatography, the product sucrose fraction (extract) is contaminated to some extent by betaine and/or invert. Such contamination reduces the recovery of these valuable byproducts and reduces the purity of the sucrose product. This disadvantage is attributable to the steps inherent in typical SMB operation. The SMB is initially inventoried with solids to an equilibrium state, and thereafter, feed and eluent are fed into the continuously recycling inventory while extract and raffinate are withdrawn from the recycling inventory. In the context of this disclosure, the term “inventory” refers to the distribution and identity of chemical species constituting the recycle stream. This recycling of inventory is generally a very favorable aspect of the SMB, because material is subjected to a very long chromatographic path for separation; dependent upon chosen recycle rates and inventory levels. As a result, difficult-to-remove materials, such as certain color compounds, are efficiently removed. In comparison, inventory build-up and long separation path length (due to circulation) are inconsistent with batch chromatography. Eluent use is also much lower in SMB chromatography because the eluent is continuously recycled (eluent phase) as part of the internal inventory.
Unfortunately, providing a continuous, quickly recycling, internal configuration results in only two well separated components, one on each end of the separation profile. Some nonsucroses, such as ash and high molecular weight compounds, move much more quickly than sucrose through the monovalent form ion exchange separation resins typically employed, and therefore move to the front of the recirculating separation profile. Some other nonsucroses, such as betaine, invert and certain amino acids, move much more slowly than sucrose through these resins. As a consequence, either the faster moving nonsucroses or the slower moving nonsucroses must always be crossing through the separated sucrose, thereby contaminating the sucrose.
The extract obtained from the chromatography of sucrose solutions is conventionally subjected to crystallization procedures, resulting in an acceptably pure saleable sugar product. The highest present day commercial standards for overall recovery of crystallized sucrose from beet molasses suggest a chromatography efficiency of 92 purity sucrose at 90% recovery. At this purity level, subsequent recovery by crystallization procedures is typically about 87%, with a loss of some sucrose to a second molasses (60 purity). Overall, a “superior” combined result of conventional chromatography and crystallization procedures has been the recovery of up to about 78% of the sucrose content of the initial molasses as crystalized sucrose.
U.S. Pat. Nos. 4,359,430 and 5,127,957 describe methods for the recovery of a betaine fraction from various sources, such as the molasses produced by a sugar factory. The '957 patent discloses a discontinuous circulation, batch-wise operation. The method involves shutting off all input and output streams to the SMB while maintaining circulation through the resin bed. Thereafter, circulation is halted, and water and/or molasses feed are introduced at specified locations to displace betaine, sucrose and rest molasses from separate columns in the loop. The “circulation” taught by the '957 patent is not a true recycle conventional to continuous SMB systems; it merely functions to displace the separation profile to an assigned location in the resin bed. By contrast, the continuous recycle stream, which is essential to a continuous SMB operation, circulates the separation profile continuously through the resin bed.
International Application WO 96/10650 describes a proposed betaine-recovery process which accepts the conventional 92 purity standard as the applicable goal for the sucrose fraction of the process. The WO 96/10650 process contains no suggestion that a sucrose fraction free from significant quantities of betaine or other small organic molecules be collected.
Ordinarily, the chromatography of sucrose containing mixtures, such as sugar beet molasses, involves variations of elution chromatography. The feed mixture enters a chromatographic configuration of some type, and due to a preferential adsorption, the sucrose product is collected somewhere roughly from the middle to the trailing edge of the developed elution profile. As an elution system is loaded higher and higher with feed mixture, or as eluent is progressively reduced, the bands of separated material broaden and increasingly overlap. As a consequence, separation deteriorates. Inevitably, the efficiency of elution chromatography is limited by mixture loading and elution volume.
It is understood by those skilled in batch chromatography (as opposed to simulated moving bed chromatography) that very high column loading under appropriate conditions provides potentially advantageous specific effects. At large sample load, the components of the mixture to be separated can interfere, and the elution peaks can be modified. A favorable case occurs when the most retained component has the highest saturation capacity. In that case, th
Kearney Michael M.
Kochergin Vadim N.
Amalgamated Research Inc.
Therkorn Ernest G.
TraskBritt
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