Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2002-11-25
2003-11-18
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S791000, C568S619000, C568S680000, C568S698000
Reexamination Certificate
active
06649690
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of polymerizing glycerol using a synthetic or extremely pure clay catalyst of magnesium saponite in the H form to obtain advantages in catalyst life and to synthesize predominantly linear and branched polyglycerol.
BACKGROUND OF THE INVENTION
Polyglycerol has many uses, for example, for foaming, as a food emulsifier, as a humectant for cosmetics, as a dispersing agent, as an antistatic agent for plastics, as a surface controller for fibers, as a sizing agent, etc. Linear polyglycerol is preferred because it is more biodegradable and more soluble in water than is cyclic polyglycerol. Basic catalysts can be used to obtain linear polyglycerols, while acid catalysts yield mostly the cyclic forms. It is generally difficult to polymerize glycerol using clay catalysts, since the glycerol is usually strongly absorbed by the catalyst so it does not react.
When basic catalysts, such as caustic, potassium hydroxide or sodium hydroxide, or basic clay catalysts, such as hydrotalcite, are used to polymerize glycerol, the yield is predominantly linear at both lower and higher conversions of glycerol. The primary drawback of the basic catalysts is that they are primarily homogenous, which means that they are in the same phase as the reactants and products. If they are not homogenous, for example, like hydrotalcite, they are in powder form and very difficult to separate from the product mix. As a result, it is difficult to separate the catalyst from the reaction products and the catalyst cannot be easily re-used.
WO 94/21582 to Henkel exemplifies the problems with basic catalysts. It uses sodium hydroxide in a homogenous continuous process of polymerizing glycerol. To separate the catalyst out a distillation procedure is required. It also discloses a zeolite heterogeneous catalyst using a fixed bed at 240° C., but provides no details on catalyst life or polyglycerol yield.
Basic clay catalysts are not homogenous. They are heterogeneous because they are in a different phase from the reactants/products. However, the powdery consistency of these catalysts also makes it difficult to recover them following the reaction. This is especially true when the catalyst is used to polymerize glycerol. Adding a basic clay catalyst to glycerol is the same as adding powder (clay) to honey (glycerol), which results in the formation of a slurry. It is an understatement to say that it is difficult to separate the powdery clay catalyst from the honey-like glycerol. It can be separated, albeit expensively, by distilling under vacuum.
Eshuis WO 95/16723 is an example of an anionic basic clay catalyst. It discloses using hydrotalcite as a slurry catalyst for the polymerization of glycerol.
Acid catalysts are primarily heterogeneous catalysts, meaning that the catalyst is in a different phase from the reactants/products. The advantage of using an acid catalyst is that it can be supported for use in a continuous fixed bed reactor, which permits easy separation and re-use of the catalyst. Unfortunately, when acid catalysts, such as zeolite are used to polymerize glycerol, the reaction yields predominantly cyclic compounds at lower conversions. Zeolite catalysts, for example, are known to yield mostly cyclic polyglycerol. See, for example, WO 94/18259. Additionally, polymerization of glycerol with acid catalysts usually yields a brownish product with a burnt smell.
Purely natural acid clay catalysts, such as that disclosed in JP 95321207, have additional problems. The catalyst in JP 95321207 is a layered silicate, such as saponite, with three different acidity zones which is made by subjecting saponite to acid treatment. It is used for manufacturing polyglycerine.
The acid treatment results in leaching the catalyst, so that it is unknown how much catalyst is left or what it comprises. Acid treatment leaches out anions, magnesium, etc. The catalyst structure resulting from the treatment varies and cannot be predicted. Further, because the clay is a purely natural material, it includes different types of clays, including different types of smectite family clay. As a result, the composition of the catalyst is variable and unknown. Still further, because the purely natural clay starts out as a solid, it cannot be precipitated on to a support for use in a fixed bed reactor. The solid or powder form of the clay can, nevertheless, be used in a fixed bed reactor, but then it is difficult to handle.
SUMMARY OF THE INVENTION
The present invention relates to the use of a synthetic or extremely pure clay catalyst of magnesium saponite in the H form to polymerize glycerol. It has a surprisingly long catalyst life and yields more linear oligomers than expected with typical clay catalysts in the acid form, such as bentonite.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention, a special catalyst is used to polymerize glycerol or derivatives thereof. Glycerol derivatives, such as glycidol, glycerol carbonate, etc. form glycerol on the addition of water and can be polymerized using the catalyst in accordance with the invention. The catalyst has a long catalytic life and when the catalyst is used to polymerize glycerol, the product yield is predominantly linear and branched at lower conversions. This is entirely unexpected, since acid catalysts normally yield mostly cyclic oligomers when polymerizing glycerol.
The catalyst is synthetic so that its structure and properties are uniform from batch to batch and it functions in a predictable manner. The synthetic portion of the catalyst has a specific acidity and a specific structure. The catalyst is referred to herein as a synthetic clay of magnesium saponite in the H form. Generally, Na
+
is replaced by H
+
by NH
4
+
ion exchange in the preparation of the catalyst employed in the present invention. When saponite is exchanged with ammonium ions, zero sodium is targeted and “H-form” is a measure of the amount of sodium exchanged. Advantageously, when the catalyst is used to polymerize glycerol, the product is clearer and has less of a burnt smell, as compared with the polyglycerol produced by other acidic catalysts.
Magnesium saponite in the H form is a layered alumina silicate wherein substitution of silicon atoms by aluminum generates a negative charge in the tetrahedral sheet, which is compensated by the cations, normally sodium ions. The catalyst has a special double layer sheet structure comprised of clay platelets arranged like a house of cards. This arrangement facilitates the transport of large molecules into the clay structure. As a result of the open structure of the catalyst, liquid reactants and products readily diffuse through the catalyst.
Saponite clay is a smectite, with a 2:1 trioctahedral interlayer structure. Without wishing to be bound by a particular theory or general formula, it is believed that the composition of saponites can be exemplified by the following theoretical formula:
{Na
x
(M
2+
)
6
{Si
8-x
,Al
x
}O
20
(OH)
4
}
wherein Mg is the M
2+
species and x is an integer of from greater than zero up to about 1.25. In another embodiment, x is from about 0.75 to about 1.25.
The magnesium saponite clay catalyst of the invention is made acidic by ion exchange with ammonium ions and is not acid treated like other natural clays since this procedure leads to undefined losses of framework magnesium. A discussion of this ion exchange method can be found in WO 96/07477 which is incorporated herein by reference.
In the catalyst, it is preferred that the ratio of silica to alumina be between about 4 and about 40. In another embodiment, the silica/alumina ratio is between about 10 and 30. In still another embodiment, the silica/alumina ratio is between about 11 and 20.
The catalyst used in the inventive method can be in the form of a solid/powder or it can be supported. When the catalyst is in the solid/powder form, the reaction preferably takes place in a batch reactor so that water is periodically removed to increase the yield of polyglycerol. The catalyst is us
Acquah Samuel A.
Akzo Nobel N.V.
Mancini Ralph J.
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