|Publication number||US2568925 A|
|Publication date||Sep 25, 1951|
|Filing date||Mar 1, 1948|
|Priority date||Mar 1, 1948|
|Publication number||US 2568925 A, US 2568925A, US-A-2568925, US2568925 A, US2568925A|
|Inventors||Gordon F Mills, John L Porter|
|Original Assignee||Chemical Process Company|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (7), Referenced by (9), Classifications (8)|
|External Links: USPTO, USPTO Assignment, Espacenet|
Patented Sept. 25, 1951 UNITED STATES P SUGAR SIRUP PREPARATION Gordon F. Mills, Palo Alto, Calif., and John L. Porter, Baton Rouge, La., assignors to Chemical Process Company, San Francisco, Calif., a corporation of Nevada No Drawing. Application March 1, 1948, Serial No. 12,474
ing application, Serial No. 324,624, filed March 18, 1940, now abandoned.
crystallized sugar may be obtained from numerous sources but because of the problems which are encountered commercially, in removing undesirable impurities to provide satisfactory sugar crystals as a final product, sugar cane and sugar beet are the source of materials most commonly used in commercial practice inasmuch as such materials have less refractory impurities than other raw sugar materials, such as sorghum. The impurities generally present are organic acids and bases, negatively and positively charged colloids, albumin and other proteins, salts, amino acids, betaine, etc. At present, the general commercial practice for eliminating such impurities from a sugar solution or juice obtained from the raw material, is to defecate the sugar solution with inorganic reacting agents, such as lime; remove the resultant precipitates; and then form a more or less concentrated sugar syrup from which sugar is crystallized in evaporator pans. I
The defecation only eliminates easily removable or non-refractory impurities leaving behind in the sugar solution which is subsequently concentrated, impurities that are more difiicultto remove, such as colloids, and inorganic and or ganic anions and cations. Thus, present commercial processes attempt to obtain pure sugar crystals by embodying the principle that crystals of a substance crystallized from a solution thereof will be substantially pure. However, such result is not generally obtained in present commercial sugar refinin processes because when the sugar is crystallized from the concentrated sugar solution, some of the impurities remaining in the solution become occluded in the sugar crystals or adsorbed thereon, rendering the initial crystals unsuitable for food use. As a result, such initial crystals frequently have to be redissolved in water or melted down, to enable recrystallization; and sometimes the sugar has to be crystallized as many as three times in order to obtain a satisfactory final product. Ihis obviously involves a vast amount of equipment and time, rendering the process costly. Also, the impurities in the solution impair the yield of sugar crystals because the solubil ty of sucrose is increased in the presence of such impurities. Furthermore, because of impurities remaining in the solution after crystallization of the sugar, the solution generally is not sulliciently pure to be used as a food syrup. In cases where it might be desired to produce an edible syrup fit for human consumption, directly from the sugar juice without crystallizing sugar therefrom, the'present commercial practices are unsatisfactory because of the diificulty of removal of the described refractory substances in the juice; particularly where the source of the juice produces a juice high in refractory materials.
Inasmuch as concentration of the juice is required to enable crystallization of the sugar and since such concentrated juice in present commercial processes has a relatively high percentage of refractory impurities therein, the problem of removing such refractory impurities from the solution is aggravated by the viscosity of the concentrated juice solution. From the preceding, it is seen that in present commercial processes, purification of the sugar crystals depends primarily upon exclusion of impurities from the sugar, by crystallization of sugar from solution; and this leaves impurities in the solution. The solution must necessarily be concentrated and hence viscons to facilitate crystallization of the sugar; and
such viscosity aggravates the impurity removal problem.
Our invention is designed to overcome the above described problems, and has as its objects, among others, the provision of improved sugar and sugar syrups and method for the production thereof, and an improved sugar refining process in which removal of impurities does not depend upon exclusion of impurities by crystallization of sugar; purifying agents used impart substantially no impurities to the sugar solution; the removal of impurities maybe effected from relatively thin sugar solutions; substantially all the impurities are actually removed from the solution, thus leaving the solution substantially pure, and enabling increased recovery of sugar compared to present commercial processes; and by which substantially pure sugar may be quickly and economically obtained by initial crystallization. Other objects of our invention will become apparent from the following description thereof.
In general, the process of our invention comprises treating a relatively thin aqueous solution of sugar with material having the property of actually removing impurities from the solution. by exchange of ions which form water in the solution as a resultant product. For best results, we preferably employ an agent having the property of exchanging Water-forming hydrogen ions for positively charged ions of the impurities in the solution, and another agent having the property of exchanging water-forming hydroxyl ions for negatively charged ions of such impurities. By these exchanges, substantially all impurities are removed from the solution prior to crystallization of sugar and the solution merely gains hydrogen and hydroxyl ions which, because they merely form water, impart substantially no impurities to the solution. This is not the case with respect to inorganic defecating agents, such as lime and phosphate salts, which are in present commercial use. .Under some circumstances where the production of edible sugar syrup is desired, either of these ion exchanger agents may be used alone or in combination.
The hydroxyl ion exchanger, which may be called the anion exchanger may be employed first, but it is preferred to employ the hydrogen ion or cation exchanger first, and then neutralize with the anion exchanger. As the cation exchanger, we preferably employ any zeolitic or zeolite-like material having the property of exchanging hydrogen ions for other positively charged metallic or non-metallic ions; and as the anion exchanger, we preferably utilize any zeolitic or zeolite-like material having the property of exchanging hydroxy1 ions for other negative ions. These substances, it is to be noted, remove the impurities not by precipitation, as occurs with respect to ordinary defecating agents, but by actually extracting or removing the impurities from the solution, which results from the exchange of ions.
Although the method of our invention is applicable to a relatively thin solution and it is preferred to employ such method with a thin solution to overcome the physical problems which obtain with respect to eliminating impurities from a relatively thick or highly viscous solution or syrup, our method may be employed with a relatively thick solution with satisfactory results. Also, although the method of our invention may be employed directly on the sugar solution obtained from the sugar source, it is desirable to remove first easily removable impurities by any suitable or conventional defecation step or steps now commonly employed in the art.
In greater detail, the process of our invention is applicable to any sugar solution or juice obtained in any suitable way such as by pressing of the raw material or by water extraction, from any suitable raw material, such as sugar cane, sugar beet, or sorghum. Such solution or juice is first preferably defecated or otherwise clarified to relieve the load on the exchangers in any suitable or conventional way to precipitate readily removable impurities which are generally mechanically eliminated from the solution, by filtration or decantation. After removal of these impurities, and while the solution is relatively thin, preferably not more than twenty degrees (20) Brix, we treat the solution with any suitable cation exchanger of the described type, preferably by passing the solution through a suitable bed of the same. As previously related the solution may be more concentrated, but removal of impurities is facilitated in relatively thin solutions which are, consequently, preferred. Relatively thin solutions are also preferred because they present less danger of sugar inversion which is undesirable.
At elevated temperatures, inversion of the sugar is promoted; and to minimize such inversion, we preferably maintain the solution, preferably by cooling, below the temperature at which inversion becomes rapid; which is about thirty-five degrees centigrade (35 0.), and above the temperature below which a relatively viscous syrup forms. Another advantage of a relatively cool solution is that removal of impurities by the zeolitic material is more readil accomplished in a cool solution than in a hot solution.
The zeolitic cation exchangers which we may use are of comparatively recent origin, being organic in character inasmuch as they are usually resinous or carbonaceous and they are granular .4 in form. Substances of this type are synthetic, such as those disclosed in United States patents, 2,094,359; 2,104,501; and 2,136,167; and in British patents, 450,308; and 450,540; and they have the property of substituting substantially only hydrogen ions, although in some cases, they may have available relatively small quantities of other positive ions, such as sodium. which would also be substituted. A suitable product which may be employed is the carbonaceous composition manufactured by Permutit Company known as Zeo- Karb-I-I. In treating the sugar solution with the cation exchanger, positively charged impurities in the solution, such as the metal ions of salts. positively charged organic radicals, and positively charged colloids are directly eliminated from the solution by chemical substitution of hydrogen ions from the cation exchanger. It is to be noted that the exchange of ions imparts substantially only the hydrogen ion to the solution, which is an important factor is obtaining purity because of the water-forming characteristics of the hydrogen ion. In the subsequent treatment of the solution, as is explained more fully hereinafter, substantially only hydroxyl ions are substituted for negatively charged impurities, and these form water with the previously substituted hydrogen ions.
After treatment with the described type of cation exchanger, which as previously explained, is preferably effected by passage of an appropriate volume of the sugar solution at an appropriate rate, through a bed of the granular exchanger, the solution will become extremely acid because of the imparted hydrogen ion. In many instances, the acidity may become as great as that corresponding to a pH of one and one-half (1.5); and to preclude substantial inversion of the acid sugar solution, we promptly treat the solution with a neutralizing agent so as to reduce the hydrogen ion concentration (raise the pH) to the point at which danger of inversion is minimized. A hydrogen ion concentration corresponding to a (pH) of about seven ('7) or more is satisfactory for this purpose. In this connection, colored bodies which might be in the solution prior to neutralization can be very readily removed in acid solution by treatment with any suitable color adsorbent such as active carbon or fullers earth. Hence, as an optional step, to enhance removal of such colored bodies if still present, we preferably treat the acid solution resulting from the hydrogen ion exchanger treatment of the originally non-acid juice, prior to neutralization, with Such color adsorbent. This may be done in the usual manner, by passing the solution through a bed of the adsorbent, or by mixing the adsorbent in the solution and then filtering.
This treatment of the juice with color adsorbent after the hydrogen ion exchanger treatment, becomes particularly desirable and is consequently preferred where the ultimate object in view is the production of sugar syrup from the sugar juice rather than the production of sucrose crystals. This is so because discoloration is more apparent in the syrup than in the crystals obtained therefrom because crystallization results in the rejection of color to some extent. When the ultimate product is to be sugar syrup, it is desirable that inversion of the sugar occur in the syrup so as to avoid any possibility of crystallization of sucrose when the syrup is concentrated.
In this connection, to prevent such crystallization, the degree of inversion of the sugar need not be more than about ten percent (10%). Hence,
gas-eases when juice syrup is to be produced, we treat the juice with the hydrogen ion exchanger at a temperature which will be sufiicient to bring about the desired extent of inversion. To insure such inversion to the desired extent, which we previously pointed out need not be more than about ten percent the temperature of the sugar juice should be above thirty-five .degrees centigrade (35 C.) and-preferably at least as high as forty degrees centigrade (40 C.)
Any suitable alkali, such as calcium or sodium hydroxide, may be employed to neutralize the solution after treatment with the cation exchanger. Such type of alkali, because of the metallic ions present, wilI impart impurities to the solution. We, therefore, preferably employ as the neutralizer especially in cases where it is desired to produce crystallized sugar, a zeolitic material having the property of also directly eliminating additional impurities by exchanging substantially only hydroxyl (OI-I) ions for negatively charged impurities in the solution, to thus serve as an anion exchanger. However, where the. production of sugar syrup is the ultimate obheat, it is not so important to obtain further purification by employment of an anion exchanger as a neutralizing agent because the materials thus removed are for the most part only important from the standpoint of their interference with crystallization. Hence, where the cation exchanger is employed followed by treatment with the color adsorbent, if it is desired to neutralize the juice, this can be done by means of any suitable alkali such as sufiicient amount of sodium hydroxide or calcium hydroxide.
Anion exchangers of the type related are also usually synthetic, and carbonaceous or resinous, being comparatively new and usually granular in form; examples of which are disclosed in United States Patents 2,106,486; and 2,151,883; and in French Patent 826,408. In some instances, the anion exchanger may have available relatively small quantities of other negative ions, such as the sulphate ion, which would also be substituted.
if it does not have substantially all hydrogen ions 1 available, will not materially affect the purity of the resultant solution. For best results, it is desirable to employ as pure a cation or anion exchanger (with reference to their properties of substituting only hydrogen and hydroxyl ions, respectively) as is practically possible.
Types of anions directly eliminated by the anion exchanger are negatively charged. organic ions such as acetates an dtartrates; negatively charged inorganic ions such as sulphates, phosphates, chlorides and nitrates; and negatively charged colloids and gums. Such substitution imparts substantially only water-forming hydroxyl (OH) ions to the solution; and since the cation exchanger imparts substantially only hydrogen ions to the solution, the resultant product formed in the solution by the double exchange of ions, is substantially only water which does not impart any impurity to the solution. As previously related, the process may be reversed by employing the anion exchanger prior to the cation exchanger.
Although for best results we preferably employ the types of organic zeolite-like: cation and anion exchangers which substitute substantially only hydrogen and hydroxyl ions, respectively,
6 mixed zeolitic material having the property of substituting material quantities of metal ions, as well as. hydrogen ions, may be substituted for a whole or a part of such preferred organic zeolitic exchangers. In this connection, should a mixed zeolitic material be used as the cation exchanger, which for example will substitute both hydrogen and a material quantity of metal ions such as sodiumv for positive ions in the solution, the resultant solution after treatment may not be acid. This would eliminate the necessity of using the anion exchanger for the purposes of neutralization; and such non-acid solution in some instances may be sufficiently pure for crystallization of sugar or for direct sugar syrup use without further purification. However, if acid, the anion exchanger capable of substituting hydroxyl ions or any other suitable neutralizer, as previously explained, maybe employed. The zeolitic materials capable of substituting a material quantity of metal ions are not nearly as effective because they impart additional impurities to the solution inasmuch as they act at least in part by replacing specific metal ions for other less de- 'sirabl'e positive ions.
In some cases, particularly where the sugar solution obtained from the source of material is normally acid, namely inherently acid because of the original character of the juice such as obtains with respect to juice from citrus and pineapple waste, or which under conventional methods or preparation becomes acid, for example, in the preparation or a dextrose sugar bearing solu tion by the acid hydrolysis of starch, it may be desirable to employ only the anion exchanger prior to any employment of the cation exchanger. When the anion exchanger is used alone without any subsequent treatment with the cation exchanger, such treatment will accomplish both neutralization and a substantial improvement of the purity by virtue of the substitution of the water forming hydroxyl ions for other refractory anions in the solution. In this connection, the refractory anions which can be removed are not only inorganic acid radicals but also the complex negatively charged organic acids, organic gums, colloids and other organic materials of an anionic nature which heretofore have made it impossible to employ such juice. as a syrup. Thus, the anion exchanger treatment of the normally acid juice is particularly advantageous in preparing such juice for use as an edible syrup in contradistinction to its preparation for crystallization of sugar therefrom.
Depending on the extent of impurities in the normally acid juice, a single step of anion exchanger treatment may not be sufificient to remove all the undesired impurities from the normally acid juice for preparation of the edible syrup therefrom. In such event, the anion exchanger treatment may be continued by subjecting the juice to repeated treatments with the anion exchanger, with an. intervening step of acidification each time, so as to render the anion exchanger operable because it is not efiective in solutions. above about pH 7 in removing the above described refractory organic ions to render the juice suitable for use as a syrup.
For imparting the acidity to the juice in case repeated.- anion exchanger treatments are required, any acid such as hydrochloric or phosphoric acids may be employed between'the successive anion exchanger treatments. However, to: enhance further the purity, the intervening acidification may be accomplished by subjecting 'duce better results than others.
the juice to the cation exchanger which thus performs the double function of acidifying thejuice after each anion exchanger treatment, to condition the juice for effective treatment by the subsequent anion exchanger, and at the same time removing any refractory cationic impurities in the juice. However, the single step treatment with the anion exchanger alone may suffice depending upon how pure it is desired the syrup shall be and how impure the normally acid juice may be.
From the preceding it is seen that our method enables the production of inexpensive sweetening syrup bearing substantially all of its natural nutrient substances, and which need not be entirely demineralized. Where the juice is normally non-acid, edible syrup may be produced therefrom by treatment with the organic or resinous cation exchanger which removes impurities and produces sufficient inversion to insure against crystallization of sugar therefrom when the purified juice is converted to a high density syrup by evaporation of water therefrom. .When the juice is normally acid, the organic or resinous anion exchanger may be employed to remove impurities and prepare an edible syrup. Such organic anion exchanger treatment of the normally acid juice is particularly advantageous because, since it can remove whole molecules of negatively charged complex organic acids, and organic gums and colloids, it effects removal of these undesirable non-sugar constituents in the juice which are responsible for unfavorable taste, odor and color of the untreated juice, without demineralization of the juice, thus leaving in the juice the natural mineral ions which are desirable constituents in sugar syrup as a food product.
If the initial normally acid juice has not undergone sufficient inversion to preventcrystallization of sugar therefrom when the juice is concentrated to syrup, it should be heated sufficiently before the anion exchanger treatment, to convert at least about ten percent (10%) of the sucrose to invert sugars so as to prevent such crystallization. Such heating should also be employed during intervening acidification treatments, if repeated anion exchanger steps are utilized. As previously related, the heating should be above thirty-five degrees centigrade (35 C.) and preferably at least about forty degrees centigrade (40 C.)
Treatment of the solution with the anion exchanger may be effected in any suitable way, but we preferably utilize the same method employed with respect to the cation exchanger, namely, by passing an appropriate volume of the solution through a bed of the anion exchanger at an appropriate rate. The particle sizes of both the cation exchanger and the anion exchanger may be relatively fine or large, but should be so chosen as to give the maximum purifying action with minimum time of flow through the adsorbing mass. However, with respect to the cation exchanger, finer particles act more effectively as a decolorizer because of the greater surface area presented for adsorbing the color matter, and may hence be preferred for this reason.
Our process is not dependent on any particular kind of described organic or resinous cation, and anion exchangers, although some may pro- It is only necessary that these materials possess the properties of substituting hydrogen or hydroxyl ions, for
the reasons previously explained. In this connection, the organic or resinous character of the exchangers obviates contamination of the sugar juice, inasmuch as such exchangers contain no mineral matter that would be releasable in the juice and consequently contaminate it.
After the described preferred treatment of the solution, the resultant product is substantially pure, colorless sugar syrup free of molasses odor or taste, and from which substantially pure sugar crystals may be obtained upon initial crystalent commercial processes, because, as was previously related, the impurities present increase the solubility of sucrose. The solution might, however, contain mechanically entrapped foreign particles such as collected dust and fine particles of zeolitic material which might be collected by the solution in its passage through the beds of the zeolitic material, but these are not impurities inherently occurring in the solution; and they may be readily removed by simple filtration or decantation any time after the zeolitic treatment and prior to crystallization of the sugar.
The residual syrup or molasses, after crystallization of the sugar is also substantially free of undesirable impurities, and can be used as a food directly without further purification, which is not generally the case with respect to present commercial processes wherein much of the impurity in the solution cannot be removed, and the molasses, being concentrated, results in increase of the quantity of impurity therein. In some instances the molasses is absolutely useless as a food because of its impurity, which is particularly true with respect to the present commercial molasses obtained from sugar beet as the source.
Because of the purity of the solution obtained by our preferred process, it may be used directly as a sugar syrup, in places such as canneries, without crystallizing the sugar therefrom which is not possible with present commercial sugar syrups, because of impurities still remaining prior to crystallization of the sugar. Also, the acid solution resulting from the treatment with our preferred zeolitic cation exchanger, is sufficiently pure to be employed directly as a sweetening agent in soft drinks wherein acid sugar syrup is generally employed to impart the desired tang to the drink.
The acid solution resulting from the preferred treatment with the cation exchanger of our invention, provides another important advantage. For some industrial uses, such as candy manufacture, it is desirable, as is well known, that the sugar syrup contain suflicient invert sugar (glucose and fructose) to prevent crystallization of sucrose contained therein. For this purpose, it is the present commercial practice to dissolve pure sugar crystals in the requisite amount of water and then add the necessary amount of acid, such as hydrochloric acid, to the solution which is then heated for a sufficient period to produce the desired amount of invert sugar by hydrolysis of part of the sucrose in the solution.
To stop such inversion, the acid is then neutralized with an alkali, such as sodium hydroxide. Such procedure, since it requires the employment of pure crystallized sugar and the additional reacting agents to bring about the desired inversion, is costly.
In the preferred procedure of our invention, the solution resulting from treatment with our preferred cation exchanger, becomes acid by virtue of the substituted hydrogen ion. Such acid solution may be allowed to remain acid for a sufiicient period to permit the desired degree of inversion, for the above described uses of the solution. After the desired inversion, the solution may then be neutralized as previously ex plained. Thus, our process eliminates the added expense now required in present commercial processes for preparing invert sugar solution.
Also, should all the solution treated by our preferred cation exchanger be intended for production of invert sugar containing solution, then care need not be taken to maintain the temperature of the solution while being treated with the cation exchanger, below the point at which inversion becomes rapid.
Certain sugar sources, such as sorghum, provide sugar solutions so refractory, as to render commercial recovery of sugar crystals extremely difiicult, Which has consequently rendered these sources impractical for commercial use. The process of our invention can treat these materials, as well as the more common sources, such as sugar beet and cane sugar, because of the facility with which impurities are removed. This is another important advantage, particularly with respect to sorghum which is comparatively inexpensive; and because of its high sugar content, it provides a desirable source. Also, our treatment is suficiently effective to make available as a sugar source, waste materials from canneries, such as fruit peelings and waste fruits and fruit juices, which have heretofore been a complete economic loss inasmuch as present commercial processes cannot use these materials as a sugar source in view of the refractory impurities therein.
The described cation and anion exchangers in the course of time become exhausted or fouled by impurities removed from the sugar solution, but their characteristics are such that they may be readily and repeatedly regenerated for further use, thus making for economy. Such regeneration may be accomplished, in the usual manner, by first washing or flushing the exchangers with water at room temperature to leach out any of the sugar solution remaining therein. Such wash water may be used as maceration or diffusion water for extraction of the sugar from the raw material; or it may be returned to any other prior part of the process and run through the exchangers again. The exchangers are then treated with hot Water at any suitable temperature, preferably about eighty to one hundred degrees centigrade (80 to 100 C.) for the purpose of washing out adsorbed or occluded impurities, other than chemically bound ions.
The cation exchanger is regenerated by treatment with an appropriate amount of acid solution, such as sulphuric (H2804) or hydrochloric (HCl) acid solution, which results in the positive ions previously removed from the sugar solution being replaced by hydrogen (H) ions; and the anion exchanger is regenerated in a similar manner by treatment with a suitable quantity of an alkali solution, such as sodium or ammonium hydroxide solution, which results in the negative ions previously removed from the sugar solution being replaced by hydroxyl (OI-I) 'ions. Finally, the regenerated exchangers are washed with Water to free them from excessregenerating solution. Under some circumstances where the sugar solution is particularly high in colloidal impurities, the cation exchanger, which is preferably employed prior to the anion exchanger, may become badly gummed up or clogged by adsorbed colloids or other organic materials. Should this occur, regeneration may be obtained by treatment with ammonia (NHs) and potassium chlorate (K0103) under heat and pressure.
The described zeolitic-like anion exchangers may not act entirely by direct substitution of hydroxyl ions for negatively charged ions in the sugar solution but may act instead by sorbing complete acid molecules which include such negatively charged ions, or by both partially substituting hydroxyl ions for negatively charged ions or sorbing entire acid molecules. In any event the result is the same because irrespective of whether hydroxyl ions are substituted for negatively charged ions or entire acid molecules are sorbed, no additional refractory impurities are imparted to the solution by the treatment; and because the cation exchanger substitutes only hydrogen ions for positively charged ions, refractory impurities will be removed, leaving water as the only resultant product. The term anion exchanger employed herein is, therefore, employed to designate generically the described type of zeolitic material whether it only substitutes hydroxyl ions for negatively charged ions or sorbs entire acid molecules, or both. In this connection, such anion exchanger acts as a deacidifying agent while the cation exchanger acts as an acidifying agent.
The method of producing edible sugar syrup from a normally acid sugar juice without effecting substantial crystallization of sugar therefrom which comprises heating the juice above approximately 35 C. to convert at least 10% of the sucrose to invert sugars so as to prevent crystallization of sugar from the juice, treating such acid juice with an organic anion exchanger prior to any cation exchanger treatment of the juice to remove refractory impurities therefrom, and further purifying said juice by then acidifying the juice below approximately pH 7 and again treating such acidified juice with such anion exchanger, and utilizing such treated juice as the syrup without crystallization of sugar therefrom.
GORDON F. MILLS. JOHN L. PORTER.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 2,155,318 Liebknecht Apr. 18, 1939 2,191,365 Boyd Feb. 20, 1940 2,198,393 Smit Apr. 23, 1940 2,221,683 Smit Nov. 12, 1940 2,388,194 Vallez Oct. 30, 1945 2,388,222 Behrman Oct. 30, 1945 2,389,119 Cantor Nov. 20, 1945 OTHER REFERENCES "Apple Sirup by Ion Exchange Process Buck et al., Ind. 8; Eng. Chem., July 1945, pp. 635-638.
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|U.S. Classification||127/41, 127/46.2|
|International Classification||C13B20/14, C13K3/00|
|Cooperative Classification||C13K3/00, C13B20/14|
|European Classification||C13B20/14, C13K3/00|