Colloid systems and wetting agents; subcombinations thereof; pro – Continuous or semicontinuous solid phase – The solid phase contains organic material
Reexamination Certificate
1997-04-09
2001-01-09
Griffin, Steven P. (Department: 1754)
Colloid systems and wetting agents; subcombinations thereof; pro
Continuous or semicontinuous solid phase
The solid phase contains organic material
C516S111000
Reexamination Certificate
active
06172120
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for producing low density gel compositions, including aerogels, xerogels and the like, without the need for a supercritical drying step or thermal treatment.
BACKGROUND
The term “gel” encompasses wet gels, including hydrogels and alcogels; and gels dried from the wet gels including aerogels and xerogels. The term “aerogel” was coined by S. S. Kistler in U.S. Pat. No. 2,188,007 and is generally utilized to refer to a gel which has been dried under supercritical temperature/pressure conditions. The term “xerogel” is generally utilized to refer to a gel which has been dried by evaporation of the solvent. Gel composition refers to a composition comprising a gel which may further include other components, for example an opacifying agent or coloring agent.
Gel compositions are utilized in a wide variety of applications, including thermal and acoustic insulation; catalyst supports and carriers; filters and molecular sieves; rheology control agents; reinforcing agents; thickeners and electronics; adsorbents; flatting agents; particulate additives; membranes; filters; radiation detectors; coatings; and dielectrics and other applications set forth herein and/or known to those of ordinary skill in the art. Gel compositions having lower rod densities, and/or higher surface areas, and/or higher structure are more advantageous for use in many applications. A gel composition's rod density is related to the gel composition's porosity wherein gel composition's with lower rod densities will generally have higher porosities.
Gel compositions are generally produced by combining a gel precursor and suitable solvent to form a sol and then initiating gelation in the sol to form a “wet” gel comprising the solid gel structure and the liquid solvent. The liquid solvent is then removed to form a dry gel composition.
Aerogels produced utilizing a supercritical drying step generally have lower rod densities than heretofore known gel compositions produced without the use of supercritical drying and have therefore become the gel of choice for many applications. However, the supercritical drying step necessary for the production of an aerogel may require the use of relatively expensive and/or complex processing equipment and conditions and therefore be disadvantageous.
In addition to approaches utilizing supercritical drying, at least several other approaches to producing gels have been proposed.
Alexander et al. U.S. Pat. No. 2,765,242 disclose a process for producing gels utilizing aging in water at high temperature followed by heat treatment in alcohols at temperatures significantly above the boiling point in order to esterify the surface. The gel granules may then be milled until a fine powder is obtained. Disadvantages of the approach disclosed in Alexander et al. include the cost of the high pressure esterification step.
WO 94/25149 discloses a process for the preparation of xerogels by chemical surface modification. The disclosed chemical surface modification agents have the formula R
x
MX
y
where R is an organic group such as CH
3
, C
2
H
5
etc.; X is a halogen and M is Si or Al. Potential disadvantages of the approach disclosed in WO 94/25149 include the high cost of the reagents and potential problems relating to disposal of the by-products of the reaction.
U.S. Pat. No. 5,270,027 discloses a process for preparing silica xerogels using alkanolamines. The disclosed process produces xerogels having a total pore volume variable from 2 to 3 cc/g. The equivalent density of individual granules is 0.29 to 0.37 g/cc. Potential disadvantages of the approach disclosed in U.S. Pat. No. 5,270,027 include the complicated steps disclosed as part of the process, in particular the thermal treatment step, and that the process is not disclosed as producing aerogels with densities low enough for certain applications.
It would be advantageous to have a process for producing a low rod density gel composition which does not require a supercritical drying step or thermal treatment step and which utilizes economical reagents.
SUMMARY OF THE INVENTION
The present invention provides processes for producing gel compositions comprising esterifying a portion of the surface of the gel composition sufficient to produce a gel composition having a rod density of less than or equal to 0.27 g/cc, and/or a tap density of less than or equal to 0.2 g/cc, through contact with at least one esterification agent and at least one catalyst. Preferably at least 20% of the surface of the gel composition is esterified through contact with the esterification agent and the catalyst.
In a first aspect, the present invention provides a process comprising:
esterifying a portion of the surface of a gel composition sufficient to produce a gel composition having a rod density of less than or equal to 0.27 g/cc through contact with at least one esterification agent in the presence of at least one catalyst at a pressure of less than or equal to 300 psia.
In a second aspect, the present invention provides a process comprising:
esterifying a portion of the surface of a gel composition sufficient to produce a gel composition having a rod density of less than or equal to 0.27 g/cc through contact with at least one esterification agent in the presence of at least one catalyst at a temperature of less than or equal to the atmospheric boiling point of the esterification agent.
In a third aspect, the present invention provides a process comprising: esterifying a portion of the surface of a gel composition sufficient to produce a gel composition having a rod density of less than or equal to 0.27 g/cc through sequential contact with at least one esterification agent and at least one catalyst at a pressure of less than or equal to 300 psia.
In a fourth aspect, the present invention provides a process comprising:
esterifying a portion of the surface of a gel composition sufficient to produce a gel composition having a rod density of less than or equal to 0.27 g/cc through sequential contact with at least one esterification agent and at least one catalyst at a temperature of less than or equal to the atmospheric boiling point of the esterification agent.
In a fifth aspect, the present invention provides a process comprising:
esterifying a portion of the surface of a gel composition sufficient to produce a gel composition having a tap density of less than or equal to 0.2 g/cc through contact with at least one esterification agent in the presence of at least one catalyst at a pressure of less than or equal to 300 psia.
In a sixth aspect, the present invention provides a process comprising:
esterifying a portion of the surface of a gel composition sufficient to produce a gel composition having a tap density of less than or equal to 0.2 g/cc through contact with at least one esterification agent in the presence of at least one catalyst at a temperature of less than or equal to the atmospheric boiling point of the esterification agent.
In a seventh aspect, the present invention provides a process comprising: esterifying a portion of the surface of a gel composition sufficient to produce a gel composition having a tap density of less than or equal to 0.2 g/cc through sequential contact with at least one esterification agent and at least one catalyst at a pressure of less than or equal to 300 psia.
In an eighth aspect, the present invention provides a process comprising:
esterifying a portion of the surface of a gel composition sufficient to produce a gel composition having a tap density of less than or equal to 0.2 g/cc through sequential contact with at least one esterification agent and at least one catalyst at a temperature of less than or equal to the atmospheric boiling point of the esterification agent.
An advantage of aspects of the present invention is that the processes may be performed at ambient temperatures and/or ambient pressures.
The features and advantages of the processes of the present invention are described in more detail in the following sections.
REFERENCES:
patent:
Ackerman William C.
Lokey Elsbeth R.
Smith Douglas M.
Wallace Stephen
Cabot Corporation
Griffin Steven P.
Hendrickson Stuart L.
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