Chemistry of inorganic compounds – Zeolite – With change of synthesized zeolite morphology
Reexamination Certificate
2000-03-23
2002-09-17
Sample, David (Department: 1755)
Chemistry of inorganic compounds
Zeolite
With change of synthesized zeolite morphology
C423S712000, C423SDIG002, C423SDIG002
Reexamination Certificate
active
06451283
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to zeolitic molecular sieve compositions characterized by outstanding capability to complex multivalent cations, especially calcium. In particular, the invention relates to zeolitic molecular sieve compositions, especially those based on molecular sieves having a high aluminum content, in which the zeolites are characterized by novel particulate morphology. The invention also relates to novel methods of forming zeolites to increase rates of zeolite crystallization, provide the novel morphology and provide a direct effect on sequestration performance.
With environmental concerns over phosphates rising during the last generation, zeolite molecular sieves have taken a dominant role as the water softening builder component of most detergents. Environmentally “friendly”, zeolites have been a poor substitute for phosphates from a performance standpoint, having both lower calcium and magnesium sequestration capacities as well as much lower rates of sequestration. The sequestration properties of zeolites arise from their ability to ion exchange. This ion-exchange ability derives from tetrahedral Al(III) inherent in classical zeolite frameworks. Each aluminum induces one negative charge on the framework which is counterbalanced by an exchangeable cationic charge. Thus, exchange capacity is limited by the aluminum content and “detergent” zeolites have been restricted to the relatively short list of “high aluminum” zeolites. By Lowenstein's Rule, the Si/Al ratio of a zeolite may not be lower than 1.0 and concomitantly, the aluminum content may not exceed 7.0 meq per gram for an anhydrous material in the sodium form. This capacity may alternatively be expressed as 197 mg CaO per gram zeolite (anhydrous) when water softening is the desired exchange reaction. Zeolites demonstrating this maximum aluminum content include Zeolite A, high aluminum analogs of Zeolite X and high aluminum analogs of gismondine (often referred to as Zeolite B, P or MAP).
While Zeolite A has been the “detergent zeolite” of choice for years, the possibility of employing a high aluminum version of gismondine-type materials in calcium sequestration has been known for more than a generation (U.S. Pat. No. 3,112,176 Haden et al.) and has recently found renewed interest (for example, U.S. Pat. No. 5,512,266 Brown, et al.). In addition to zeolites, the ability of silicates to complex ions such as calcium and especially magnesium has long been known and sodium silicate has long been employed as a cheap, low performance detergent builder. More recently, complex silicates such as Hoechst SKS-6 have been developed which are claimed to be competitive with higher performance zeolites.
The capacity for silicates to complex ions such as calcium and magnesium is inversely proportional to silicate chain length and directly proportional to the electronic charge on that chain fragment. Silicates depolymerize with increasing alkalinity. At moderate pH (where wash cycles are conducted) silicates are polymeric. However, at much higher pH's silica not only becomes predominantly monomeric, but that monomer may possess multiple charges. If such small, highly charged silicate fragments could be exposed to solutions bearing multivalent cations, very powerful high capacity sequestration agents would result. In commonly assigned U.S. Pat. No. 5,948,383 (Kuznicki, et. al.) such a situation was created by isolating and stabilizing substantial concentrations of such charged silicate species within zeolite cages where ions such as calcium are free to enter from an aqueous environment (such as wash water) and react with these powerful sequestration agents. The zeolites of this patent have been characterized as hybrid zeolite-silica compositions (HZSC) which demonstrate unusual and beneficial properties in complexing multivalent cations. Such hybrid materials are prepared by crystallizing high aluminum zeolites in highly alkaline/high silica environments. Chemical analysis indicates an excess of silicate in these species beyond that inherent to their crystalline frameworks. Such materials demonstrate sequestration capacities for cations such as calcium which not only exceed the amount of zeolitic aluminum available for ion-exchange, but in fact, may exceed the theoretical limit possible for a zeolite. These materials and their properties must be considered something distinctly different than zeolitic. Such compositions show extreme promise as water softening agents and detergent builders and may find other applications in complexing multivalent cations such as in the removal of calcium from sugars and fatty oils or in removing heavy metal such as lead from various streams.
It is believed that the key mechanism in the effectiveness of these patented materials is derived from the ability of zeolite cages to isolate and stabilize much smaller, more highly charged silicate units than exist in normal aqueous solutions such as wash water. These silicate units are introduced during synthesis of said hybrid zeolite-silica compositions by providing an environment wherein silica in the reaction mixture is depolymerized to highly charged predominantly monomeric units before crystallization begins.
These occluded silicate units are readily visible in
29
Si NMR spectra. Such units are much more powerful in complexing multivalent cations than existing silicate compositions used for that purpose. The zeolite framework and occluded silicate units act in concert, as a new type of hybrid composition, showing properties neither zeolites, silicates nor physical blends of the two demonstrate. In addition to high capacity, these new hybrid compositions demonstrate unusually rapid rates of sequestration, a critical parameter in applications such as detergent building.
It has now been discovered that the condition used to form the hybrid zeolite-silica compositions as described in U.S. Pat. No. 5,948,383, can yield novel zeolite particle morphologies. The zeolite particles which are formed are extremely rapid cationic sequestrants rendering the zeolite compositions useful, particularly as detergent builders. In the field of detergent building, rapid calcium sequestration is key to effective employment of surfactants. Commercial zeolite A suffers from slow exchange kinetics. This is especially true in the growing area of cold water detergents where the rate problem renders it essentially ineffective. While zeolite A, by definition, contains equimolar aluminum and silicon in its framework structure and thus the maximum possible zeolite ion-exchange capacity, useful ion-exchange capacity in most processes, however, is a dynamic function based on inherent capacity, ion selectively and kinetics of exchange. While zeolite A is a fixed composition with a fixed exchange capacity and fixed ion selectivities, the kinetics of exchange vary widely with the physical and morphological properties of zeolite A crystals and the aggregates into which they are formed. Microcrystalline zeolite A has long been known to improve exchange kinetics, but these submicron particles tend to stick to fabric in a wash cycle rendering such kinetically enhanced builders essentially unusable in real world detergent applications. Submicron microcrystals grown into macroscopic aggregates would solve this problem, yielding the kinetic advantages of microcrystalline exchangers and the handling
on-sticking properties of macroscopic ensembles.
SUMMARY OF THE INVENTION
It has now been found that uniform aggregates of submicron zeolite microcrystals can be formed by in situ processes where essentially all of the aggregrate material is between 1 and 5 microns. Surprisingly, even though such materials exist as macroscopic aggregates, the exchange kinetics are extraordinarily rapid, reflecting the inherent rate of the substituent submicron crystals. The advantages of maintaining the substituent crystals as coherent macroscopic aggregates is both in the ease of handling when used as a substituent in manufacturing compounds such as detergent mixtures, as we
Bell Valerie A.
Curran Jacqueline S.
Kuznicki Steven M.
Langner Tadeusz W.
Engelhard Corporation
Frenkel Stuart D.
Sample David
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