Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
2001-04-30
2002-11-19
Therkorn, Ernest G. (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S659000, C210S198200, C127S046200
Reexamination Certificate
active
06482323
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process of chromatographic separation and, more particularly, to a process for chromatographically separating a fluid mixture comprising two or more components into two or more fractions enriched in the respective components.
2. Description of the Related Art
Chromatographic separation techniques using solid adsorbents are extensively conducted in industries. Various techniques of chromatographic separation have been proposed for separating a mixture of two or more components into fractions enriched in each component.
Among chromatographic separation systems is a simulated moving-bed system, which is widely used in industries for its excellent separation performance and high productivity. In this system a feedstock fluid or a desorbent is supplied to a packed bed at a constant flow rate, and the fluid flows through the packed bed also at a constant flow rate. The simulated moving-bed system, however, requires complicated apparatus and high skill of control on the supply of a feedstock fluid or a desorbent to the packed bed and on the movement of the fluid circulating through the packed bed. While the simulated moving-bed system shows excellent performance in separating a mixture into two fractions, great difficulty has been encountered with this system in achieving separation into three or more fractions.
Chromatographic separation processes, which can achieve satisfactory separation results with simpler apparatus, have been proposed as disclosed in JP-A-63-158105 (corresponding to U.S. Pat. No. 4,970,002 and Canadian Patent No. 1305434) and JP-A-2-49159. The process disclosed in JP-A-63-158105, for example, comprises repetition of cycles each including at least three steps; a step of supplying a feedstock fluid, a step of supplying a desorbent fluid, and a step of circulating the fluid in the packed bed.
In the simulated moving-bed system, the concentration distribution curves made in the packed bed macroscopically have almost the same form and circulatively move through the packed bed with time while keeping the form. Accordingly, the pressure required for moving the fluid through the packed bed, namely, the pressure drop (pressure loss) produced while the liquid moves from the upstream end to the downstream end of the packed bed may be seen substantially equal in any time zone. In this situation, the above-described process control relying on a constant flow rate is an effective system for controlling the apparatus with good reproducibility to obtain desired separation performance.
According to the method of JP-A-63-158105, the flow rate of the feedstock liquid and the desorbent fluid while being supplied and the flow rate of the liquid moving through the packed bed are controlled at a prescribed rate, and switches among the steps are made for a certain amount of the liquid or for a certain lapse of time. In this case, however, the concentrations of the individual components in the packed bed and the concentration distributions formed in the bed gradually vary with time in every step. More specifically, in the step wherein the feed stock fluid is supplied while a fraction enriched in a certain component is withdrawn, the concentration of the components present in the packed bed gradually increases from start to stop of the supply, and the feedstock is distributed in its maximum concentration in the packed bed to which it is supplied. In the step where the desorbent is supplied while a fraction enriched in another certain component is withdrawn, the concentration of the components present in the packed bed gradually decreases from start to stop of the supply. In other words, the feedstock supplied to the packed bed gradually decreases its concentration as it flows downstream. Even in the step where the fluid is moved circulatively with no liquid supplied nor withdrawn thereby to allow a zone in which a plurality of components are present in admixture to move to the upstream end of the packed bed, the concentration distribution in the packed bed gradually changes from start to stop of the step.
A mixture of saccharides (i.e., a carbohydrate solution including various kinds of sugars and/or sugar alcohols) is one of the most common feedstock fluid to be treated by chromatographic separation. In the present invention, the mixture of saccharides means a mixture solution of at least two selected from the group consisting of sugars and sugar alcohols. A mixture of saccharides greatly varies its viscosity depending on the concentration, and a higher concentration mixture has a higher viscosity. In treating such a fluid like a saccharides mixture as would greatly vary its viscosity according to the concentration, variations in concentrations of, or concentration distributions of, the components present in the packed bed necessitate variations of the pressure for moving the fluid through the bed at a constant rate. In other words, the pressure drop generated in moving the fluid in an upstream packed bed to which the feedstock fluid is supplied, being expressed in terms of pressure drop per unit height of the packed bed (hereinafter “unit pressure drop”), is different from that in a packed bed positioned downstream. That is, the packed bed to which the feedstock fluid is supplied shows a greater unit pressure drop than any other packed bed.
The changes in pressure drop are analyzed as follows. In the supply step in which a feedstock fluid containing a plurality of components is fed, a fluid having a lower concentration than the feedstock fluid and enriched in a certain component is withdrawn. Accordingly, the average concentration of the components in the bed gradually increases during this step. In the step of supplying the desorbent and withdrawing another fraction enriched in another certain component, the fluid withdrawn is obviously higher in concentration than the desorbent. This means that the average concentration of the components present in the packed bed is gradually decreasing in this desorption step. The feedstock fluid supplied moves through the packed bed with a descending unit pressure drop. In general, a maximum unit pressure drop is reached in the packed bed where the feedstock is supplied at about the end of the step of feeding the feedstock fluid.
Apparatus used in the above-described chromatographic separation processes including the simulated moving-bed system comprise a plurality of unit beds packed with an adsorbent selected according to the components to be separated. Cation-exchange resins have been in frequent use as an adsorbent. Because the purity or recovery of a component separated or recovered is greatly influenced by the properties of a chosen cation-exchange resin, various attempts have been made in making a choice of an adsorbent. For example, it has been proposed to use ion-exchangers having different ionic forms fit for the individual components or to use a combination of two or more kinds of adsorbents in separating a feedstock comprising three or more components into the individual fractions (see JP-A-11-183459 and JP-A-11-267404).
In order to improve separation efficiency of a chromatographic separation apparatus having a plurality of unit packed beds, it is generally preferred that every bed is packed with an ion-exchange resin having a small average particle size and/or a low degree of crosslinking. However, an adsorbent having a smaller particle size makes the unit pressure drop greater, and a resin having a lower degree of crosslinking has lower strength.
The method of JP-A-63-158105 supra employs an apparatus comprising a packed bed to which a feedstock fluid is supplied and other packed bed(s). As previously noted, where a feedstock fluid largely varies its viscosity with concentration as with the case of a saccharides mixture, the unit pressure drop reaches the maximum in the packed bed to which the feedstock fluid is supplied. The pressure applied to the fluid imposes a mechanical force on the adsorbent, i.e., an ion-exchange resin, as a friction pressure
Ikemoto Manabu
Tanimura Masakate
Nippon Rensui Co.
Sughrue & Mion, PLLC
Therkorn Ernest G.
LandOfFree
Chromatographic separation process does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Chromatographic separation process, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Chromatographic separation process will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2983074