Distillation: apparatus – Apparatus – Systems
Reexamination Certificate
1995-12-05
2003-10-28
Caldarola, Glenn (Department: 1764)
Distillation: apparatus
Apparatus
Systems
C202S185100, C422S198000, C422S234000
Reexamination Certificate
active
06638397
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a distillation system and, more particularly, to a simplified and automated distillation system which is capable of recovering a purified solvent from a solvent mixture.
2. Description of the Related Art
Distillation is widely used, both in the laboratory and on a large industrial scale, to separate boilable liquids (solvents) present in a liquid mixture. During distillation, the liquid mixture is at least partially vaporized and collected separately from the residue. For the most part, the effectiveness of separation by distillation is determined by differences in the boiling points of the solvents which make up the liquid mixture. In other words, it is more difficult to separate by distillation, liquid mixtures having solvents with close boiling points.
Most distillation systems have several common features. The common features are illustrated schematically in embodiments of a laboratory-type distillation system,
FIG. 5
, and a batch-type distillation system, FIG.
6
. The common features are:
1. A heated area
510
,
610
where volatile components are evaporated to form vapors.
2. A reflux section
520
,
620
where vapors are “washed” by cooler liquid returning to the evaporation area.
3. A condenser section
530
,
630
where the “washed” vapors are condensed to form a condensate.
4. Single or multiple discharge ports
540
,
640
for the collection and/or recirculation of the condensate.
Distillation is a very old technology, and was developed for the distillation of alcohol spirits, perfumes, and oils. Today, the distillation equipment is relatively more sophisticated, and even a small laboratory-type unit has the capability to provide high-purity separations of closely-boiling solvents. The modern equipment achieves such high-purity separations by a variety of techniques including spinning band techniques, the use of many theoretical plates (stages), high ref lux ratios, multiple collection ports, and water-cooled spirally-arranged condenser tubes.
For simple distillation tasks, however, such high-performance equipment has many disadvantages. For example:
1. It can be very expensive.
2. It requires careful attention during operation.
3. An experienced operator is generally required.
4. It often contains glass and other breakable parts that can cause hazardous conditions should they break or leak.
5. It requires frequent maintenance and parts replacement.
6. Special work areas and facilities (water and 220 volt outlets, hoods, etc.) normally are required.
7. Operating cycles can be quite long.
Moreover, in many small clinical and research laboratories, cleaning facilities, and machine shops, only relatively small amounts of one or two solvents are used on a regular basis, and there thus has been little incentive to recycle solvents. The relatively high costs of the modern distillation equipment, its operation, and the required manpower and working space have discouraged widespread use.
At the same time, however, there have been mounting pressures for solvent recycling both for cost and environmental reasons. Substantial costs are associated with the purchase and disposal of the solvents. Therefore, recycling the solvents would generate considerable cost savings, and would have beneficial environmental effects.
SUMMARY OF THE INVENTION
An object of the invention is to provide a distillation system which is simple in structure and operation.
Another object of the invention is to provide a simplified and an automated distillation system which is capable of recovering a purified distillable component from a starting mixture having relatively close boiling points.
Still another object of the invention is to provide a simplified and an automated distillation system which is small, operator-independent, inexpensive, safe, durable, virtually maintenance-free, requires no special facilities, and is usable in virtually any location.
Still another object of the invention is to provide a simplified method for automatically recovering a purified distillable component from a starting mixture having relatively close boiling points.
The above and other objects of the invention are accomplished with a distillation system whose design resulted, in part, from the following simplifying specifications for its operation:
1. In a preferred embodiment, one volatile component can be purified in a single distillation cycle.
2. A minimum acceptable purity of the recovered distillable component is specified rather than just trying to obtain as high purity as possible. The specified purity is that which is needed for the particular application.
3. Distillable component yields are dependent upon the purity specification. The total collected fraction will contain some portions which have less than the specified purity and some portions which have more than the specified purity, but, on the average, meets the purity specification.
The distillation system according to the invention includes a transition tank. When a starting mixture including at least distillable component is distilled batch-wise, there exists a separation problem at the point when one fraction is ending and the next fraction is beginning. To minimize the mixing of one distillable component with another distillable component or with waste component(s) from the starting mixture during this transition, rather sophisticated techniques are used conventionally, including the use of spinning band, vacuum, large number of theoretical plates, high reflux ratios, and multiple collection ports.
The transition tank eliminates the need to separate these transition mixtures into their separate components. Instead, these mixtures are simply put aside and stored in the transition tank until the current distillation cycle is completed. The transition tank is then drained into the evaporation tank at or prior to the beginning of the next distillation cycle. Volume-wise, these transition mixtures are usually not particularly large. At two to three theoretical plates and a specified purity level of greater than 99.5%, they tend to be about 10-25% of the starting volume. At five to ten theoretical plates and a specified purity level greater than 99.5%, the transition mixtures tend to be about 1-5% of the starting volume.
A first advantage of the distillation system according to the invention is that high purities can be obtained with relatively small numbers of theoretical plates. During the distillation of a distillable component, the purity of the collected product is highest at around the midpoint of the collection cycle, and it decreases toward both ends of the cycle (i.e., beginning and end). If a minimum acceptable purity is established for this middle cut, it then is possible to determine the minimum number of theoretical plates that are needed to produce the minimum specified purity. For example, in a laboratory environment in which a purity of 99.0% can be more than adequate, only two to three theoretical plates are required with the distillation system according to the invention.
With the distillation system according to the invention, simply by increasing the number of theoretical plates from two or three, the yields (amounts) of the purified distillable component at a specified purity are increased. As a corollary, if a desired yield is specified, then the minimum number of theoretical plates which are required for a particular distillation run can be determined. By reducing the number of plates, equipment size, run times, cooling and the like are minimized. For the distillation system according to the invention, preferred results are obtained most often with theoretical plates numbering from one to about twenty. By definition, “one plate” consists of simply boiling and condensing a solution with no refluxing.
As noted earlier, the end portions (end cuts) of each fraction that do not meet the minimum purity specifications are simply put aside in the transition tank and reprocessed in the next run. The point at which each cut is made is controlled by the te
Camiener Alan M.
Camiener Gerald W.
Caldarola Glenn
CBG Biotech, Ltd.
Doroshenk Alexa A.
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