Gas separation: processes – Chromatography – Plural separate columns
Patent
1995-03-17
1996-11-26
Spitzer, Robert
Gas separation: processes
Chromatography
Plural separate columns
95107, 95113, 96104, 96123, 96124, 96125, B01D 1508, B01D 5304, B01D 5306
Patent
active
055781110
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
This invention concerns a process and a device for continuous chromatography (CC).
The term chromatography indicates a separation process, in which the substances to be separated can generally be separated from each other by phase distribution based on physical and chemical differences and principles, detected by suitable sensing procedures and isolated by elution. One of the phases used in chromatography is immobile (stationary) and usually has a large surface area, while the other is mobile and moves over or through the stationary phase. The stationary phase can be a solid (absorbent) or a liquid, in which latter case the immobilization of the phase and its large surface area is achieved by coating the liquid as a thin film onto a porous, small-particle carrier material. The mobile phase is generally a liquid that is not miscible with the stationary phase or a gas. Based on these differences, a distinction is usually made between liquid-solid chromatography, gas-solid chromatography and gas-liquid chromatography. Another distinction, made based on the operating separation principle, is that of adsorption and distribution chromatography; the resolution of mixtures of substances is based on the differing retention times of the individual substances on the stationary phase, and the degree of resolution depends on several factors, especially the differences in retention of the component substances on the stationary phase. The separation efficiency of a chromatography column is, to a large measure, also determined by the particle size of the stationary phase (e.g. the extent of the surface area, the band widening due to differing path lengths), and hence the so-called high-efficiency (or high pressure) liquid chromatography (HPLC) employs substantially finer grained materials (5 to 30 .mu.m) than the gel chromatography (35 to 75 .mu.m) or the column chromatography (120 to 200 .mu.m). The small particle size of the adsorbents dictates, however, the use of high pressures (up to 400 bar).
Performance of the chromatography itself involves applying the mixture of substances to a confined "dot" area at the starting zone (on the column, thin layer etc.) and transporting it forward by means of the mobile phase (gas in GC, solvent in HPLC). Depending on the adsorption/desorption equilibrium of a given substance, it is migrating at a different speed through or over the stationary phase, and the maximum possible speed is that of the mobile phase.
The chromatographic processes known heretofore do, however, exhibit certain disadvantages. For instance, a continuous operation of such chromatography installations is not possible, and electronically regulated, automatic optimization during the progress of a separation is hardly meaningful, nor even feasible. When the retention times for different substances are similar, the separation achieved is often incomplete. The state of loading (capacity utilization) of the absorptive phase during preparative separation (which is equivalent to the migration zone of the as yet un-separated mixture of substances) usually represents a local overloading of the stationary phase, e.g. of a column. Full efficiency of separation is then achieved only toward the end, when the substances to be separated are already distributed over a major volume of the column, i.e. are separated already to a significant extent, while the greater portion of the adsorptive phase (that outside the migrating zone) is not even participating in the instantaneous separation process.
The distribution (equilibration) always occurs only between an adsorptive medium (stationary phase) and the eluent (mobile phase), and not between two adsorption media which can be chosen essentially without restrictions, such as e.g. between adsorption media which are suitably selected by their physical, chemical and/or chiral properties and specifically chosen for effective separation of certain substances (for example, two enantiomers, sorption media with different polarity, acidity/basicity or opposite (and adjustable) ele
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Reuter Chemischer Apparatebau GmbH
Spitzer Robert
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