Gas separation: processes – Selective diffusion of gases – Selective diffusion of gases through substantially solid...
Reexamination Certificate
1999-09-30
2001-07-24
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Selective diffusion of gases
Selective diffusion of gases through substantially solid...
C095S050000
Reexamination Certificate
active
06264726
ABSTRACT:
FIELD OF THE INVENTION
The present invention is a method of separating a target compound from a first solvent that is above its critical density. More specifically, the present invention is a selective barrier separation of the target compound from the first solvent while the first solvent is above its critical density. The present invention specifically excludes perstraction; perstraction is a separation method based method upon permeation of a target compound through a selective barrier rather than blocking or retention of a target compound upon the selective barrier.
As used herein, the term selective barrier and/or grammatical variants thereof includes membrane and/or filter suitable for separations by microfiltration (blocked particle size range from about 2 &mgr;m to about 0.03 &mgr;m), ultrafiltration (blocked particle size range from about 0.11 &mgr;m to about 0.002 &mgr;m), nanofiltration (blocked particle size range from about 0.006 &mgr;m to about 0.0009 &mgr;m) and/or reverse osmosis (hyperfiltration) (blocked particle size range from about 0.0011 &mgr;m to about 0.0001 &mgr;m).
As used herein, the word membrane refers to a structure that may be thick or thin, homogeneous or heterogeneous, passive or active, biological or synthetic, symmetric or asymmetric, porous or non-porous. Passive refers to transport through the membrane based upon an energy potential for example pressure, concentration, temperature and combinations thereof.
BACKGROUND OF THE INVENTION
Separations of target compounds of microspecies (MW<1000 amu), macromolecules (MW>1000 amu) and/or macromolecular structures (including but not limited to micelles, reverse micelles, metal complexes) is generally accomplished with reverse osmosis, microfiltration, ultrafiltration, nanofiltration and combinations thereof. These methods suffer from high pressure drop and low flow rate.
Use of supercritical fluids as a solvent generally involves a depressurization so that the solvent quickly evaporates leaving behind the target compound. This method suffers from the inefficiency introduced by the depressurization.
U.S. Pat. No. 5,430,224 to Schucker discusses a supercritical perstraction process. Supercritical carbon dioxide is reported to increase toluene permeation through a polyesterimide membrane compared to n-heptane.
The paper Supercritical CO
2
Extraction Coupled With Nanofiltration Separation Applications to Natural Products, S J Sarrade, G M Rios, M Carles, Separation and Purification Technology 14 (1998) 19-25, states that the idea of coupling a supercritical CO
2
extration stage with nanofiltration separation to extract and purify low molecular weight compounds up to 1500 g/mol had been proposed as early as 1994. In this paper, Sarrade et al. discuss fractionation of fish oil to obtain essential fatty acids useful in treating heart disease, and purification of &bgr;-carotine from either carrot oil or carrot seeds.
The International Publication WO 96/18445, Jun. 20, 1996 by Sarrade et al. contains discussion of additional separations using supercritical fluids, for example triglycerides from butter, but again is limited to target compounds with molecular weights ranging from 50 to 1,000 Daltons.
Hence, there is a need for a method of separating a target compound having a macromolecular structure from a solvent with greater efficiency.
SUMMARY OF THE INVENTION
The present invention is a method of separating a first compound having a macromolecular structure from a mixture. The mixture is the first compound dissolved in a first solvent. The first solvent is a fluid that is a gas at standard temperature and pressure and is at a density greater than a critical density of the fluid. The mixture is contacted onto a membrane and the first solvent passed through the membrane, retaining the first compound, followed by recovering the first compound.
It is an object of the present invention to provide a method for filtering a target compound from a first solvent at greater efficiency.
By using a fluid that is a gas at standard temperature and pressure at a density greater than its critical density, membrane separation without depressurization is fast and efficient.
The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements.
REFERENCES:
patent: 4929357 (1990-05-01), Schucker
patent: 5158704 (1992-10-01), Fulton et al.
patent: 5430224 (1995-07-01), Schucker
patent: 5670051 (1997-09-01), Pinnau et al.
patent: 5843208 (1998-12-01), Anumakonda et al.
patent: 6039792 (2000-03-01), Calamur et al.
patent: 6039878 (2000-03-01), Sikdar et al.
patent: 6086768 (2000-07-01), Sims
patent: 96/18445 (1996-06-01), None
SJ Sarrade et al., “Supercritical CO2Extraction Coupled With Nanofiltration Separation Applications To Natural Products”, pp. 19-25, 1998.
Bowman Lawrence E.
Fulton John L.
Phelps Max R.
Yonker Clement R.
Battelle (Memorial Institute)
Spitzer Robert H.
Zimmerman Paul W.
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