Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
2001-03-13
2003-06-17
Kim, John (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S483000, C210S510100, C210S681000, C210S691000, C210S903000, C210S907000, C210S908000, C210S669000, C423S326000, C423S331000, C423S332000, C423S592100, C423S700000, C435S002000
Reexamination Certificate
active
06579460
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process and a composition for removing toxins from blood or dialysate solutions. The fluid is contacted with a combined cation and anion exchange composition to remove toxins such as ammonium cations and phosphate anions.
BACKGROUND OF THE INVENTION
In mammals, e.g., humans, when the kidneys and/or liver fail to remove metabolic waste products from the body, most of the other organs of the body also soon fail. Accordingly, extensive efforts have been made to discover safe and effective methods for removing toxins from patients' blood by extracorporeal treatment of the blood. Many methods have been proposed for removing small molecular toxins, protein-bound molecules or larger molecules thought to be responsible for the coma and illness of hepatic failure. Some of these toxic compounds have been identified as urea, creatinine, ammonia, phenols, mercaptans, short chain fatty acids, aromatic amino acids, false neural transmitters (octopamine), neural inhibitors (glutamate) and bile salts. Among these, phenols and mercaptans, along with bilirubin and bacterial endotoxins, also occur as strong protein-bound toxins and are thus more difficult to effectively remove from the blood. Middle molecular weight toxins having a molecular weight of about 300 to about 10,000 can also be present and are difficult to effectively remove.
The art shows a number of ways to treat blood containing such toxins. The classic method is of course dialysis. Dialysis is defined as the removal of substances from a liquid by diffusion across a semipermeable membrane into a second liquid. Dialysis of blood outside of the body (hemodialysis) is the basis of the “artificial kidney.” The artificial kidney treatment procedure generally used today evolved from that developed by Kolff in the early 1940s.
Since the 1940s there have been a number of disclosures which deal with improvements on artificial kidneys or artificial livers. Thus, U.S. Pat. No. 4,261,828 B1 discloses an apparatus for the detoxification of blood. The apparatus comprises a housing filled with an adsorbent such as charcoal or a resin and optionally an enzyme carrier. In order to prevent direct contact between the blood and the adsorbent, the adsorbent may be coated with a coating which is permeable for the substances to be adsorbed yet prevent the direct contact between the corpuscular blood components and the adsorbents. U.S. Pat. No. 4,581,141 B1 discloses a composition for use in dialysis which contains a surface adsorptive substance, water, a suspending agent, urease, a calcium-loaded cation exchanger, an aliphatic carboxylic acid resin and a metabolizable organic acid buffer. The calcium loaded cation exchanger can be a calcium-exchanged zeolite. EP 0 046 971 A1 discloses that zeolite W can be used in hemodialysis to remove ammonia. Finally, U.S. Pat. No. 5,536,412 B1 discloses hemofiltration and plasmafiltration devices in which blood flows through the interior of a hollow fiber membrane and during the flow of blood, a sorbent suspension is circulated against the exterior surfaces of the hollow fiber membrane. Another step involves having the plasma fraction of the blood alternately exit and re-enter the interior of the membrane thereby effectuating removal of toxins. The sorbent can be activated charcoal along with an ion-exchanger such as a zeolite or a cation-exchange resin.
There are problems associated with the adsorbents disclosed in the above patents. For example, charcoal does not remove any water, phosphate, sodium or other ions. Zeolites have the disadvantage that they can partially dissolve in the dialysis solution, allowing aluminum and/or silicon to enter the blood, directly or indirectly from the dialysate. Additionally, zeolites can adsorb sodium, calcium and potassium ions from the blood or dialysate thereby requiring that these ions be added back into the blood or dialysate. It is also known that zeolites only exchange cations and thus in order to remove phosphate anions a separate anion exchanger is required in order to keep the phosphorus concentration between desired levels. One system currently in use is the REDY™ Sorbent System which consists of a cartridge containing five layers or beds. The first layer is an activated carbon layer to remove heavy metals, the second layer is an urease layer which converts urea to ammonium carbonate, the third layer is a zirconium phosphate layer which removes cations such as ammonium ions, the fourth layer is a hydrous zirconium oxide layer which remove anions such as phosphates and finally the fourth layer is another activated carbon layer which removes organic metabolites such as creatinine.
Applicants have developed a process and composition which both simplifies the above described systems, e.g. REDY™ Sorbent System and has better performance without some of the disadvantages of the referenced art. The process involves using an ion exchange composite comprising a mixture of a microporous cation exchange composition and an anion exchange composition. Carbon beds can also be used in front of and in back of the ion exchange composite. A urease bed is also used in the case of dialysate solution. The microporous cation exchange compositions have an empirical formula on an anhydrous basis of:
A
p
M
x
Zr
1−x
Si
n
Ge
y
O
m
(I)
or
A
p
M
x
Ti
1−x
Si
n
Ge
y
O
m
(II)
where A is an exchangeable cation selected from the group consisting of potassium ion, sodium ion, rubidium ion, cesium ion, calcium ion, magnesium ion, hydronium ion or mixtures thereof, M is at least one framework metal selected from the group consisting of hafnium (4+), tin (4+), niobium (5+), titanium (4+), cerium (4+), germanium (4+), praseodymium (4+), and terbium (4+), except that M is not titanium in formula (II), “p” has a value from about 1 to about 20, “x” has a value from zero to less than 1, “n” has a value from 0 to about 12, “y” has a value from 0 to about 12, “m” has a value from about 3 to about 36 and 1≦n+y≦12. The germanium can substitute for the silicon, zirconium/titanium or combinations thereof. Examples of the anionic exchange compositions are hydrous zirconium oxide and zirconia.
SUMMARY OF THE INVENTION
This invention relates to a composition and a process for removing contaminants from a fluid. Accordingly, one embodiment of the invention is a process for removing toxins from a fluid selected from the group consisting of blood and a dialysate solution, the process comprising directly or indirectly contacting the fluid with a shaped ion exchange composite at ion exchange conditions thereby providing a purified fluid, the composite comprising a mixture of a microporous cation exchange composition and an anion exchange composition, where the cation exchange composition is selected from the group consisting of zirconium metallate, titanium metallate and mixtures thereof, the metallates respectively having an empirical formula on an anhydrous basis of:
A
p
M
x
Zr
1−x
Si
n
Ge
y
O
m
(I)
or
A
p
M
x
Ti
1−x
Si
n
Ge
y
O
m
(II)
where A is an exchangeable cation selected from the group consisting of potassium ion, sodium ion, calcium ion, magnesium and mixtures thereof, M is at least one framework metal selected from the group consisting of hafnium (4+), tin (4+), niobium (5+), titanium (4+), cerium (4+), germanium (4+), praseodymium (4+), and terbium (4+), except that M is not titanium in formula (II), “p” has a value from about 1 to about 20, “x” has a value from zero to less than 1, “n” has a value from 0 to about 12, “y” has a value from 0 to about 12, “m” has a value from about 3 to about 36 and 1≦n+y≦12, and the anion exchange composition is selected from the group consisting of hydrous zirconium oxide, zirconia, alumina, titania, hydrous titanium oxide, layered double hydroxides, single phase metal oxide solid solutions, magnesium hydroxide, calcium hydroxide, silica, amorphous mixed
Bem David S.
Ellig Daniel L.
Willis Richard R.
Kim John
Molinaro Frank S.
Tolomei John G.
UOP LLC
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