Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-08-14
2004-11-30
Egwim, Kelechi C. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S369000, C525S387000
Reexamination Certificate
active
06825284
ABSTRACT:
The present invention relates to a method for preparing a poly-&agr;-hydroxyacrylate aqueous solution, particularly a method for preparing a high concentration aqueous solution having a concentration of at least 25 wt % of poly-&agr;-hydroxyacrylate.
A poly-&agr;-hydroxyacrylate (hereinafter referred to as “PHA salt”) represented by sodium poly-&agr;-hydroxyacrylate is an industrially important material as a hydrogen peroxide bleaching stabilizer for paper pulp or fibrous materials, a detergent builder, a chelating agent, a surfactant and the like.
It is known that a PHA salt is obtained by reacting a polylactone compound corresponding to poly-&agr;-hydroxyacrylic acid (hereinafter referred to as “PLAC”) with a corresponding alkaline material. Also, a method for preparing PLAC is proposed in an article by C. S. Marvel (J.A.C.S. 62, page 3495, 1940), JP-B-54-5839 and JP-B-54-20995 by Solvay Co., or German Patent Application No. 2,061,584 by Henkel Co.
PLAC is a material generally represented by the following structural formula.
A PHA salt in the present invention has an average molecular weight in a range of from 2,000 to 1,000,000, particularly an average molecular weight of from 5,000 to 200,000, more particularly an average molecular weight of from 10,000 to 100,000. If the average molecular weight is less than 2,000, particularly less than 1,000, a performance of stabilizing by hydrogen peroxide can not be expected. For a performance as a bleaching stabilizer for paper pulp, an average molecular weight of from 30,000 to 60,000 is most suitable.
In order to convert PLAC into an aqueous solution of a PHA salt, it is heretofore known to place PLAC in an aqueous solution of corresponding alkaline substance to make reaction.
However, according to this method, it takes a long time for the placed PLAC to be dissolved as a PHA salt, and in order to obtain a high concentration PLA salt aqueous solution, a side-reaction is caused, and a critical problem of generating a decomposed product having a molecular weight of at most 1,000 is caused.
JP-A-2-296803 proposes a method for dispersing PLAC in water and adding an alkaline substance thereto, and according to this method, it requires a large amount of water to make a slurry of PLAC, and it is therefore difficult to obtain a PHA salt aqueous solution having a concentration of at least 25 wt %.
Accordingly, in order to obtain a high concentration product of at least 25 wt % by the above method, it was necessary to employ an unfavorable method in view of energy which requires concentration of a low concentration product.
JP-A-7-224111 proposes a method for reacting PLAC with an alkaline aqueous solution containing hydrogen peroxide in the synthesis of a poly-&agr;-hydroxyacrylate aqueous solution by the reaction of PLAC with an alkali aqueous solution.
However, this method produces a very sticky material in the initial stage of adding PLAC, and the sticky material sticks to a stirring vane (hereinafter referred to as “sticking”), and provides a problem of causing a weight eccentricity of a stirring vane axis. If this method is carried out on an industrial scale, there is caused a serious problem of damaging a stirring vane axis, a bearing, a stirring motor or the like. Also, this method of using a total alkali amount in the initial stage has a defect of producing a PHAS having a relatively small molecular weight.
A problem to be solved by the present invention resides in a discovery of a stably operable method for obtaining a PHA salt aqueous solution having a high concentration of at least 25 wt % without a concentration step, without producing a by-product and without damaging a stirring machine.
Present inventors have intensively studied a preparation step of a poly-&agr;-hydroxyacrylate aqueous solution and have discovered that a reaction can be stably carried out without causing “sticking” by initiating addition of PLAC with an addition of a part of a total addition amount of alkali in the initial stage and adding the remaining alkali on the halfway of the reaction, and the present invention was accomplished on the basis of this discovery.
Thus, the present invention relates to a method for preparing a poly-&agr;-hydroxyacrylate aqueous solution which comprises a step of obtaining the poly-&agr;-hydroxyacrylate aqueous solution by reacting a polylactone compound corresponding to poly-&agr;-hydroxyacrylic acid (PLAC) with an alkali, characterized in that an alkali is dividedly added.
PLAC is a material represented by the above-mentioned structural formula, and its basic unit is expressed by the following formula (I), and a theoretical unit formula amount of PLAC is C
3
H
2
O
2
=70. However, actually, a part having free —COOH and —OH groups as illustrated in the formula (II) (C
3
H
4
O
3
=88) is about 1/3 of the total, and the remaining part having a lactone structure is about 2/3 of the total. Accordingly, the actual unit formula amount is calculated to be 76 (calculation formula: 70×(2/3)+88×(1/3)=76), and in the method of the present invention, a unit formula amount of PLAC is calculated to be 76. Hereinafter, this unit formula amount of 76 is determined to be PLAC 1 mol for convenience when expressing a quantitative relationship with other materials added.
A total amount of an alkali material to be added is from 0 .5 to 1.7 times mol to the unit formula amount of PLAC, and an amount of an alkali material to be added in the initiation of reaction is adjusted in such a manner as to provide an alkali concentration in a range of from 1 to 12 wt % in the reaction system at the initial stage of reaction. The remaining alkali material is added dividedly or continuously during the dissolving reaction.
A reaction temperature is in a range of from 20 to 70° C.
Generally, PLAC is obtained as a water-insoluble wet cake by polymerizing &agr;-halogenoacrylic acid in water. If necessary, it is possible to dry the cake to obtain a dry PLAC.
However, when a final product is obtained in a state of a PHA salt aqueous solution, it is generally not necessary to dry PLAC, and it is usual to use the wet cake in a succeeding step.
In the method of the present invention, PLAC may be either a dry product or a wet cake, but the wet cake is particularly advantageously usable in the present invention.
An alkali material used in the present invention is not specially limited, examples of which include inorganic alkalis such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium hydrogencarbonate or ammonia, organic alkali materials such as dimethylamine, diethylamine or diethanolamine, and the like. Particularly, sodium hydroxide is a typical example.
In the present invention, a method of conducting a reaction of PLAC and an alkali in the presence of hydrogen peroxide or a peroxide generating hydrogen peroxide is the most preferable embodiment which does not provide “sticking”, produces substantially a colorless PHA salt aqueous solution, and produces a less by-product.
Hydrogen peroxide or a peroxide generating hydrogen peroxide in an aqueous solution is added in an amount of from 0.005 to 2.0 times mol (hydrogen peroxide conversion value in case of a peroxide) to a unit formula amount of PLAC, preferably from 0.01 to 0.1 time mol, more preferably from 0.015 to 0.07 time mol, to a unit formula amount of PLAC. If an amount of hydrogen peroxide is less than 0.005 time mol to a unit formula amount of PLAC, a product is colored (yellow) and a side-reaction is caused. Also, if an amount of hydrogen peroxide exceeds 2.0 times mol, it is uneconomical
Hydrogen peroxide used in the present invention may be a usual industrial product, and its concentration is not limited but is preferably in a range of from 20 to 65%.
A peroxide generating hydrogen peroxide in an aqueous solution may be used as hydrogen peroxide. Examples of a peroxide generating hydrogen peroxide in an aqueous solution include sodium carbonate-hydrogen peroxide adduct (generally called as “sodium percarbonate”), urea-hydrogen peroxide adduct, sodium
Kayama Ryuichi
Suzuki Toshio
Egwim Kelechi C.
Nippon Peroxide Co., Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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