Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment
Reexamination Certificate
2000-09-22
2002-05-21
Phasge, Arun S. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
C205S768000
Reexamination Certificate
active
06391185
ABSTRACT:
The present invention is related to the electrochemical regeneration of composite activated carbon materials and the separation of adsorbed organic compounds and heavy metals there from. The overall process can be used for purification of liquid and gaseous media.
BACKGROUND OF THE INVENTION
Activated carbon adsorbent is widely used for purification of liquid and gaseous media from organic matter. Typically, activated carbon adsorbent is used in the so-called percolation method, where liquid or gas containing organic compounds is pumped through the column containing the adsorbent.
After the activated carbon is saturated with the organic compounds, the saturated activated carbon adsorbent is either replaced with the new one (and the old adsorbent is discarded or burned) or regenerated for reuse by heating it with or without steam to high temperature (typically from 300 to 600 degrees C), whereby the adsorbed organic compounds are vaporized/destroyed. Thermal regeneration of the activated carbon adsorbents requires large energy expenditures, degradation (to 5-10%) of the activated surface during each regeneration and expensive high temperature equipment. Either chemical or electrochemical regeneration can also be used. Chemical regeneration of the activated carbon adsorbents causes degradation and blockage of the activated carbon to 10-15%.
There are known methods of electrochemical regeneration (desorption) of the activated carbon adsorbents, mainly activated carbons in granular or powdered form. U.S. Pat. No. 3,730,885 (issued May 1, 1973) describes a method of electrochemical regeneration of the activated carbon by creating a potential differential between the surface of the activated carbon adsorbent saturated with organic compounds and the desorbing solution. It describes the desorption of the described compounds from the surface of the activated carbon material by the way of polarizing activated carbon to −1 volt (in reference to a saturated calomel electrode). Solutions for desorption were 10
−2
M Na
2
SO
4
and 0.7·10
−2
NaCl. Powdered activated carbon (an average particle size was 0.044 mm) in a mixture with Teflon dispersion (fluoroplastics) (17:3 ratio) was used as activated carbon material. U.S. Pat. No. 3,730,885 describes using currents up to 1 milliampere per gram of the activated carbon at the potential of up to 1 volt. This patent shows that changing polarity of the activated carbon material causes the desorption of strongly polarized organics—acetic acid (initial adsorption capacity of the activated carbon material) during an hour at a current of less than 1 milliampere per gram of adsorbent. The attempts to desorb the adsorbed weakly polarized organic compound (amyl alcohol) resulted in that only half of the adsorbed amyl alcohol was desorbed into solution. The degree of desorption of the organic compounds adsorbed from municipal wastewater by changing polarity within the limits of 1 volt was equal to 30% (19 mg per gram of the activated carbon adsorbent was desorbed from 60 mg per gram adsorbed initially) (prototype). Thus the system of U.S. Pat. No. 3,730,885 is relatively ineffective is desorbing weekly adsorbed organic compounds.
U.S. Pat. No. 5,904,832 (issued May 18, 1999) and publications by I. V. Sheveleva et al. (“Relationship between electrochemical and adsorption properties of the hydrate cellulose and polyacrylonitrile based carbon fibers” Chemistry and Technology of Water, V. 12, 7, 613-616, 1990; “Adsorption of phenol from water solutions by carbon fibrous electrodes”, Journal of Physical Chemistry, V.64, 1, 166-169, 1990) also describe regeneration of activated carbon material that has adsorbed thereon polar/ionic organic compounds. The regeneration is done by contacting this activated carbon material with electrolyte solution, creating an electrical polarization potential on the carbon at the boundary of the carbon material and the electrolyte solution, followed by regeneration of this activated carbon material. The adsorbed organic compounds are thus transferred from the carbon adsorbent into the electrolyte solution due to their charge, and movement in the electric field. In the above publications I. V. Sheveleva describes the regeneration of the activated carbon fibers with phenol adsorbed thereon by contacting activated carbon fibers with 1 N potassium sulfate solution (pH 12) and by creating a potential from −0.7 to −1.3 volt.
U.S. Pat. No. 5,904,832 describes the regeneration of activated carbon adsorbent with the simultaneous destruction of the desorbed organic compounds. It was possible to regenerate activated carbon adsorbent while desorbing the adsorbed phenol removed from a waste stream. A negative potential is applied to the activated carbon adsorbent. Any type of activated carbon may be employed. The electrolyte concentration for desorption is chosen so as to avoid excessively high voltage (too much heat generation). The carbon column in U.S. Pat. No. 5,904,832 comprises metal screens inside carbon electrodes for distributing electric current inside the column. In experiments (1-16) of U.S. Pat. No. 5,904,832 by Clifford there was achieved regeneration from 30% to 80% of the phenol adsorption capacity by using currents of up to 5-10 milliamperes per gram of activated carbon adsorbent. The time of regeneration was from two hours for regeneration of less than 50% to 45 hours for 80% regeneration.
The aforesaid prior art systems displace the adsorption equilibrium by polarizing the boundary between carbon adsorbent—solution. In this case the drop of the potential at the cell is several volts (mostly, less than a volt), the currents—from 1 to 10 milliamperes per gram of adsorbent. It is only possible to shift the equilibrium significantly by means of polarization for compounds that are ionic form in one or another range of pH: phenols, sulfosalicilic acid, organic bases. This is the reason why all examples in these reference descriptions are based on these compounds.
The above described methods of regenerating carbon adsorbents with the organic matter adsorbed thereon by polarization have not been commercialized due to a number of drawbacks:
relatively efficient regeneration (over 50%) of the adsorbed organic matter was achieved only for ionic (strongly polarized) organic pollutants (acetic acid, phenol). Regeneration took place due to electrostatic (ionic) repulsion of the charged organic molecules from the same charged surface of the activated carbon adsorbent (electrode).
at these conditions only 50-90% regeneration for phenol was achieved.
regeneration required a long time (from several to 45 hours).
THE PRESENT INVENTION
The present invention teaches a new improved electrochemical process for desorbing adsorbed materials (nonpolar and polar organic compounds and heavy metal ions) from carbon adsorbents. The time for regeneration is decreased, and the degree of regeneration increased. Multiple regenerations may be employed.
For achieving a high degree regeneration and adsorption it is necessary that:
The composite adsorption regenerable carbon material (CRAC) has sufficiently high electric conductivity for uniform potential distribution—a volumetric electric conductivity of 1-100 (Ohm.m)
−1
The adsorbent (CRAC) specific volumetric electric must differ from the specific electric conductivity of electrolyte which fills up the pores of the adsorbent by not more than an order of magnitude (if the specific electric conductivity of the adsorbent (CRAC) is much higher, the current will flow preferably through the adsorbent, and if the specific electric conductivity of the electrolyte is much higher, the current will flow through the electrolyte),
The specific current density has to be at least 0.01 ampere per gram of CRAC (so as to provide a uniform current flow through the surface of the adsorbent-electrolyte solution interface). When there is such high current flow, the surface of the adsorbent becomes highly hydrophilic due to the discharges of the ionic particles taking place at the adsorbent&ap
Mitilineos Alexander G.
Pimenov Alexander V.
Shmidt Joseph L.
Shvarev Alexey E.
Cornell Ronald S.
Electrophor, Inc.
Phasge Arun S,.
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