Method of producing powdery high HLB sugar fatty acid ester

Abstract: A new method of purifying a high HLB sugar fatty acid ester without using a solvent and yielding the product in powdery form, comprises neutralizing a crude sugar ester and mixing it with water, a neutral salt and sugar to give a sediment; this sediment is washed with acidic water; the washed water containing the high HLB sugar fatty acid ester at higher concentration is mixed with a fatty acid to separate a precipitate and the precipitate is neutralized and spray dried.

Description: The present invention relates to an industrial method of producing high HLB sugar fatty acid esters. At present, sugar fatty acid esters (hereinafter called also <<SE>> for short) useful for surfactants are industrially obtained by the reaction of sugar and higher fatty acid methyl esters of C₈ to C₂₂ in solvents (for example dimethyl formamide, dimethyl sulfoxide and the like) in the presence of suitable catalysts (the solvent method: Japanese Patent Publication No. Sho 35-13102) or by melting sugar together with fatty acid soaps without using solvents but using water and then acting the molten mixture upon higher fatty acid methyl esters in the presence of catalysts (the water medium method: Japanese Patent Publication No. Sho 51-14485). However, according to these two kinds of synthetic method, impurities, such as unreacted sugars, unreacted fatty acid methyl esters, remaining catalysts, soaps, free fatty acids and volatile matter (the remaining reaction solvent) used in the above mentioned "the solvent method" of SE synthesis are contained in the reaction mixture in addition to the desired SE and the impurities, of which contents exceed the regulation values, must be removed before the products are obtained. In particular, of the above described impurities, the removal of the remaining reaction solvents (volatile matter) in the former solvent method is particularly important in view of the recent increasingly severe regulation. According to the standard of the FDA in USA, the permissible concentration of remaining dimethyl sulfoxide in SE is 2 ppm or less [Fed. Regist., 51(214), 40160-1]. So, in order to remove the impurities from the crude SE, a large amount of organic solvent (for example butanol, toluene, methylethyl ketone and methyl acetate See, for example, Japanese Patent Publication No. Sho 42-11588 and Sho 48-1-448) has been used but the use of such a large amount of solvent has led to the following important disadvantages in the industrial production of SE. 1) The possibility of explosion and fire; 2) The provision of explosion proof electric apparatus having regard to 1) above; 3) The necessity of tight closure of the manufacturing apparatus having regard to 1) above; 4) The provision of fire resisting construction all over the building having regard to 1) above; 5) The increased fixed costs due to 2), 3), and 4) above. 6) The increased costs due to the loss of solvents; 7) The negative effect due to solvents remaining in the SE product; and 8) The bad influences on the health of workers and thus the increased fixed cost due to said bad influences. In view of such circumstances, it has been strongly desired in the industrial field in question to develop an art of making the use of organic solvents unnecessary in the purification of SE. It is true that the purification methods without utilizing organic solvents have been previously investigated experimentally and the following representative methods have been known. 1) The method of sedimenting SE with an acidic aqueous solution [British Patent 809,815 (1959)]; 2) The method of sedimenting SE with an aqueous solution of general neutral salts (Japanese Patent Publication No. Sho 42-8850); and the like. However, if, for example, an aqueous solution of hydrochloric acid is added to a reaction mixture, as in method 1), although SE is immediately sedimented, unreacted sugar is easily decomposed and transformed into glucose and fructose. Even though the main operation is conducted at low temperatures (0 to 5 °C), the decomposition cannot be avoided. Thus, the recovery and reuse of the unreacted sugar become particularly difficult. In addition, even though the aqueous solution of neutral salts, such as sodium chloride and sodium sulfate, is added to the reaction mixture, SE is immediately sedimented as in the method 2). In this case, the unreacted sugar is not decomposed but monoesters in SE, which are useful ingredients are more soluble in water than other diesters, triesters and so on in SE are dissolved in a water phase side, so that not only is loss increased but also the obtaining of sugar fatty acid esters (hereinafter referred to as <<high HLB-SE>>) having a high HLB value , which are in particular recently in great demand and the object of the present invention, is hindered. HLB value means hydrophile-lipophile balance which has a value within a range of about 1 to 20. The larger this value is, the stronger is the hydrophilicity. Furthermore, according to the more recent Japanese Patent Application Laid-Open No. Sho 51-29417, the property of separating the mixture of aqueous solution and the purification solvents (described as such to distinguish them from the reaction solvents) into a light liquid layer (a solvent phase side=upper layer) and a heavy liquid layer (a water phase side=lower layer) is used for purification. That is to say, since in general a large quantity of water is contained in the heavy liquid layer (a water phase side=lower layer), the hydrophilic unreacted sugar, salts resulting from the catalysts and the like are dissolved in the heavy liquid layer (a water phase side=lower layer) while since a large quantity of the purification solvents is contained in the light liquid layer (a solvent phase side=upper layers), substances such as SE, fatty acids and unreacted fatty acid methyl esters, having low polarity are dissolved in this light liquid layer (a solvent phase side=upper layer). Accordingly, unreacted sugar, salts and the like in the heavy liquid layer (a water phase side=lower layer) can be separated from SE, fatty acid and unreacted fatty acid methyl esters in the light liquid layer (a solvent phase side=upper layer) by phase separation. In this case, the reaction solvents, such as dimethyl sulfoxide which is used in SE synthesis are dissolved in the lower heavy liquid layer (the water phase side=lower layer) but, inconveniently, they are dissolved also in the upper light liquid layer (a solvent phase side=upper layer). In some cases, it is possible to remove the reaction solvents by this method from SE. With the aid of the difference between the solubilities of the reaction solvents in the lower layer and upper layer, many repetitions of this phase separation procedure make it possible to remove most of the reaction solvents, for example down to 2 ppm of Dimethyl sulfoxide. However this procedure necessitates a particularly large quantity of purification solvent for removing the reaction solvent completely and is expensive in the industrial manufacture of SE. Thus, the known SE purification method has several disadvantages as previously mentioned, i.e. the use of a purification solvent, possibility of fire, cost of the explosion electric apparatus, increase of fixed costs, negative effects due to the remaining solvents in the SE product and bad influences on the health of workers. In order to improve the known method of purifying crude SE industrially in a different manner from the above described method, inventors have researched for several years the use of only water as the purification solvent instead of organic solvent, and this has now been achieved commercially as is disclosed herein. The newly invented method is firstly characterised by the use of only water instead of organic solvents as the purification solvent i.e. nonorganic solvent purification of crude SE. Such a method has never been developed commercially. It is necessary to purify crude SE in a method capable of completely removing the reaction solvents without bringing about the loss of sugars and the SE product but using only water. Furthermore, a problem to be solved in order to make the purification of SE using only water industrially possible occurs in the drying of SE resulting from the use of water alone as the purification solvent. That is to say, usually the water-containing SE to be dried is an aqueous solution when the water-content is 80% or more and a slurry when the water-content is less than 80%. Such a water-containing SE exhibits remarkably peculiar viscosity behavior in that in general the viscosity rises rapidly from about 40°C with a maximum value at about 50°C and then rapidly reduces when the temperature exceeds 50°C (refer to pages 103, 107, 108, of <<The Story of Sugar Esters (1984)>> published by the applicant company). In addition, it is substantially practically impossible due to a significant degree of foaming to evaporate off the water by heating in a vacuum. And, if the heating temperature is high and the time of contact with the heating means is long, not only do the decomposition of SE and also strong coloring and carmellization occur but additionally the acid value rises due to free fatty acids produced by the decomposition of SE (refer to Japanese Patent Publication No. Sho 37-9966). In particular, at the final stage of evaporation of water, the SE itself has a tendency to foam with the remaining water due to its characteristic that its softening point or melting point is low (for example the softening point of sugar monostearate is about 52°C and the melting point of sugar distearate is about 110°C) and this leads to the more difficult dehydration and drying of SE. In addition, also the remarkably higher latent heat of vaporization (c.a. 500 Kcal/kg H₂O or more) has an effect. The higher vaporization temperature of water than that of solvents leads to more difficult dryability. Accordingly, also in cases where the so-called "flash type" drier is used, into which the SE slurry heated by steam is continuously supplied, flashed in the vacuum chamber, dehydrated and dried, the achievement of sufficient dehydration and drying is bedevilled by various kinds of difficulty as above mentioned and even though these difficulties can be overcome, the dehydrated and dried SE is kept in the molten condition by heating, and a larger number of steps, such as a step of taking the molten SE out of the drier, a step of cooling the molten SE so removed until a temperature of melting point or less is reached to solidify the product by blowing cool air and the like, and a final pulverization in the pulverizer, are required and there is not only the problem of degradation of SE due to the number of procedural steps, but also the possibility of a dust explosion in the final pulverization step. Accordingly, also a solution to the above described problems resulting from drying is important for achieving purification according to the present water only medium purification method for crude SE. Thus the newly invented method has secondly a characteristic of an improved SE drying method which is different from known SE manufacturing methods. Such an SE drying method has never been developed commercially before. It was, therefore, the problem to be solved by the inventors to develop an art of industrially obtaining purified powdery high HLB-SE capable of removing not only the unreacted sugar but also the remaining solvents, the by-product salts produced from the catalysts and other impurities without using purification solvents, thereby solving all problems resulting from the use of purification solvents. In order to achieve the above objects the present invention provides a method of producing powdery high HLB sugar fatty acid esters, which comprises adjusting to a neutral range the pH value of a reaction mixture comprising unreacted sugar, unreacted fatty acid methyl ester, catalysts, soaps, fatty acids and volatile matter in addition to the desired sugar fatty acid esters; adding water, at least one neutral salt and sugar to said reaction mixture to give sediments; washing the sediments with acidic water, and adding to the washing liquid a fatty acid which is identical with or similar to the constituent fatty acid of the sugar fatty acid esters to separate materials; neutralizing the materials; and then spray drying the resultant product. In the drawings: Fig. 1 is a ternary graph showing solubility of SE (Φ) in the solution which contains water, sugar and salt. The composition of the solution is shown as the sum quantity of the water, total sugar and total salts as 100 wt.% except SE quantity. Fig. 2 is a ternary graph showing the High HLB-SE ester-composition of the water phase side equilibrium to the low HLB-SE in the deposition ester-composition of the SE precipitation acidic water. Fig. 3 is a flow chart illustrating a process of obtaining a purified high HLB-SE from a crude SE. The present inventors have found from many experiments of sedimentation with salts aiming at meeting the following five requirements -(a) not only is the quantity of the SE dissolved in the aqueous phase suppressed to a minimum but also said quantity is reduced to zero in order to deposit the whole of the SE if possible; (b) the decomposition of unreacted sugar is avoided; (c) the remaining reaction solvents (volatile matter) are dissolved in the aqueous phase to be separated from the SE sedimentation; (d) the sedimented SE is turned into powder in a purified condition; and (e) the unreacted sugar in the filtrate (or the top), from which the above described sedimented SE has been separated, is effectively recovered - that when sugar and neutral salts are dissolved in the aqueous solution of the reaction mixture under the suitable combinations of pH, temperature and composition of the neutral salts, sugar and water, not only is the SE not dissolved in the aqueous phase but almost the whole of the SE is sedimented but also both the volatile matter and the salts resulting from the catalysts, which need to be removed from the SE, are dissolved in the aqueous phase in addition to the unreacted sugar. Also it has been found that even though the sedimented SE is dissolved in water again and then the reprecipitation process with the aqueous solution of neutral salts and sugar is repeated to remove impurities completely, the SE is not transferred into the aqueous phase but held in the sedimented condition and when acidic water having a suitable pH is added to this sediment to wash it, the high HLB SE fractions and soluble impurities in the remaining sediment are transferred to the acidic aqueous phase and the highly pure low HLB SE fractions remain on the bottom as precipitates. It has been found also that it is industrially possible to recover and turn the high HLB-SE, which has been transferred to the aqueous phase, into powders by the addition of fatty acids and the use of the spray drying method. Thus, (1) the removal of the impurities from the SE reaction mixture and (2) the obtaining of the high HLB powdery SE and thus the classification of the SE depending upon its use from the SE reaction mixture have become industrially possible without using organic solvents. These have been thought to be impossible and have never been expected from the prior art. The present invention is based on the above described knowledge and the main point of the present invention lies in adjusting the pH of the reaction mixture comprising the unreacted sugar, the unreacted fatty acid methyl esters, the catalysts, the soaps, the fatty acids and the volatile matter in addition to the desired sugar fatty acid esters to a neutral range of pH, the sediments produced by adding water, the neutral salts and sugar to the reaction mixture separated sediment being washed with acidic water, the fatty acids being added to the washing acidic liquid to deposit High HLB-SE, the material being separated, and the resulting material being neutralized and then spray dried to produce the powdery high HLB sugar fatty acid esters. Accordingly, the method of the present invention comprises the following steps: (I) A step of removing the impurities from the crude SE reaction mixture (a step of sedimenting the crude SE with salts, sugar and water); (II) A step of washing the impure SE sediments (a step of classifying); (III) A step of recovering the high HLB-SE from washing liquid mentioned in above (II) by adding fatty acid (a step of depositing the high HLB-SE by the addition of the fatty acids); and (IV) A step of dehydrating and turning the recovered deposited high HLB-SE into powder (a step of spray drying). The process to purify the high HLB-SE from the crude SE is illustrated in Fig.3. The respective important aspects of the present invention are below described. Synthesis of SE by the Solvent Method In the synthesis of SE by the solvent method, usually a mixture of sugar and fatty acid methyl esters is dissolved in a reaction solvent, for example dimethyl sulfoxide, in an amount of several times the sum total quantity of said mixture in volume and the resulting solution is held at 80 to 90°C for several hours at about 20 to 30 Torr in the presence of alkaline catalysts, such as potassium carbonate (K₂CO₃), to easily produce the SE reaction mixture in reaction conversion % (based on the fatty acid methyl ester) of 90 or more. Subsequently, in order to eliminate the activity of the alkaline catalysts in the SE reaction mixture, an equivalent quantity of organic acids, such as lactic acid and acetic acid, or mineral acids, such as hydrochloric acid and sulfuric acid, is added to the SE reaction mixture. The catalysts are turned into the neutral salts corresponding to potassium lactate and the like by this neutralization. Finally, upon distilling away the reaction solvents, for example dimethyl formamide, in a vacuum, the crude mixture (the reaction mixture after neutralization and distillation) having a composition within the approximate following ranges is obtained. According to the above process the SE obtained usually contains monoesters in a quantity of 10 to 75 % (diesters or higher esters are obtained in a quantity of 90 to 25%). Also, the majority of the fatty acid radicals contained in the fatty acid methyl esters, the soaps and the fatty acids, respectively, are saturated ones and usually have a number of carbon atoms of 16 to 22. (1) The step of removing the impurities from the crude SE reaction mixture. Subsequently, water is added to the above described crude reaction mixture, so that a ratio of water to the crude reaction mixture may amount to 5:1 to 40:1, preferably about 20:1, by weight and at the same time the pH of the resulting mixture is regulated so as to be 6.2 to 8.2, preferably about 7.5. At this time, if the ratio of water to the reaction mixture is outside of the above described range, for example it is less than 5, the viscosity of the resulting aqueous solution is increased and thus the subsequent operations become substantially difficult to conduct. On the contrary, if it exceeds 40, the viscosity is reduced and thus the subsequent operations become easy to conduct and also the desired removal of reaction solvents can be readily conducted but a significantly increased amount of energy is required for the removal of water in the recovery of the unreacted sugar and the like and thus economy is lost. Furthermore, it is desirable for the prevention of the decomposition of the desired SE that the pH of the aqueous solution is adjusted at 6.2 to 8.2. If the pH is 8.2 or more, there is the possibility that the SE may be stoichiometrically decomposed with alkalies. Even if the pH is 6.2 or less, if for example the aqueous solution is exposed to high temperatures of 90 °C or more, there is a possibility of decomposition with acids. Additionally neutral salts and sugar are added to the aqueous solution of the SE reaction mixture, which has been adjusted in pH in the above described manner, while maintaining the temperature at 50 to 80 °C as far as possible. At this time, it is preferable that the neutral salts to be added meet the following equation (3) initially. [(weight of neutral salts to be added) + (weight of salts resulting from the catalysts)]/[(water content weight) + (total weight of salts) + (total weight of sugar)] = 0.015 to 0.12 (by weight) wherein the total weight of salts = (weight of neutral salts to be added) + (weight of salts resulting from the catalysts) and the total weight of sugar = (weight of sugar to be added) + (weight of the unreacted sugar from the beginning) Next, it is preferable that the weight of sugar to be added is determined by the equation (6). [(weight of sugar to be added) + (weight of unreacted sugar from the beginning)]/[(water content (weight)) + (total weight of salts) + (total weight of sugar)] = 0.025 to 0.20 (by weight) In addition, it is preferable also that the ratio of the total weight of salts to the total weight of sugar meets the following equation (7) in addition to both of the above described equations. (total weight of salts/ total weight of sugar) = 0.4 to 0.6, preferably 0.5 The inventors have found that when the aqueous solution containing the SE sediments obtained by adding the neutral salts and sugar so as to meet the above described three equations (3), (6) and (7) together is heated to 50 to 80°C, nearly the whole of the SE is sedimented even though any salt selected from lactates, acetates, sodium chloride and sodium sulfate is added as the neutral salt. This phenomenon is a peculiar one, which has not been previously known and it has an important value for achieving the objects of the present invention. Also, the skillful utilization of this fact leads to the transference of the following four kinds of ingredient into the aqueous phase and their separation from the cake of sedimented SE (that is the slurry):- 1) The whole sugar including the unreacted sugar (the sum total sugar); 2) The volatile matter; 3) The salts resulting from the catalysts; and 4) The neutral salts added. Incidentally, since the solution is not acidic at this time, sugar is not decomposed and thus sugar can be easily recovered and reused if required. The attached Fig. 1 is one of the ternary graphs showing this phenomenon in more detail. Referring to Fig. 1, provided that the weight of the SE dissolved in the aqueous phase = W Y [g] and the weight of the SE sedimented = W x [g], the ratio of the weight of the SE dissolved in the aqueous phase to the sum total weight (W X +W Y ) [g] of the SE Φ [%] is defined by the following equation (8). Φ = {W Y /(W X +W Y )} x 100 (%) It is shown by the triangular coordinates in Fig. 1 how Φ is changed under the following conditions: Temperature = 80 °C, pH = 7.5; Water : reaction mixture = 7.4 : 1 (by weight); Fatty acid radical = stearic acid radical; Composition of the reaction mixture Water content (weight) + the total weight of salts + the total weight of sugars = 100 % (weight) In Fig.1, the total weight of salts and the total weight of sugars are the quantities defined by the equations (4) and (5), respectively. Also, the shaded portion of Fig. 1 is a range meeting the requirements of equations (3), (6) and (7) discovered by the present inventors at the same time. Φ = 0 can be substantially held good, that is approximately the whole quantity of SE can be sedimented, by determining the quantities of the neutral salts and sugar dissolved so that Φ may be put in this shaded portion and sugar, the volatile matter, the neutral salts and the like dissolved in the aqueous phase can be removed by filtrating or centrifugally separating the sedimented SE. (II) The step of washing the impure SE sediments: The SE, which has been almost completely sedimented from the aqueous solution of the crude reaction mixture by adding the neutral salts and sugar in said step of sedimentation with salts, is in a hydrated condition, that is a slurry condition. This SE still includes impurities, such as the volatile matter, the salts, sugar and the like, although in comparatively small quantities The present inventors have found from their investigations of the method of purifying the impure slurry that an excellent result can be obtained by washing it with acidic water. That is to say, the impurities are dissolved away by washing the above described impure SE slurry with acidic water, of which the pH has been adjusted at 3.0 to 5.5. Here, for example the mineral acids, such as hydrochloric acid and sulfuric acid and the organic acids, such as acetic acid and lactic acid, can be suitably used but every edible acid can be used. In addition, the temperature of acidic water is preferably 10 to 40 °C. The impurities (that is the volatile matter, the whole sugar, the added neutral salts, the salts resulting from the catalysts and the like) to be removed from the cake side can be transferred into the aqueous phase by washing under such the conditions. In the above described washing step, if the temperature of the acidic water is 40°C or more, not only is there the possibility of decomposition of the SE with the acids but also the viscosity is increased so as to make the operation difficult when the operation is continued for a long time, for example several months. On the other hand, it is necessary for the maintenance of the low temperature of 10 °C or less to install a refrigerator which has an adverse effect on the economy of the process. Accordingly, it is usually desirable that the operation is conducted at 10 to 40°C, in particular at temperatures close to room temperature. In addition, since it is necessary to remove four kinds of ingredient, that is the volatile matter (reaction solvents), the unreacted sugar, the added neutral salts and the salt by-products of the neutralization of the catalysts, contained in the cake so far as possible in this step of washing the SE cake with acidic water, it is desirable that the SE cake to be treated is finely divided in said acidic water until the particle size is as small as possible in order to make the particles of impurity entrained in said cake easily isolatable from the cake. This object can be efficiently achieved by means of fractionalization apparatus, such as dispersion mixer (for example <<Homomixer>> made by Tokushu Kiki Kogyo KK) and a homogenizer or a colloid mill (for example <<Micolloider>>), and the four kinds of ingredient, that is the volatile matter (reaction solvents), the unreacted sugars, the salts resulting from the catalysts and the neutral salts, are completely transferred into the acidic aqueous phase from the cake of the sedimented SE. At this time, the significant phenomenon that the high HLB SE begins to be dissolved in the aqueous side from the sediments occurs. The solubility of this high HLB-SE in water depends upon factors such as temperature and pH of the system. For example, it is shown in the attached Fig. 2 at normal temperature and a pH of about 3.5. Here, since the high HLB-SE has the high solubility in water, it is temporarily called the <<water-soluble SE>> and marked "Y". Y has high HLB and thus exhibits the high water-solubility. Accordingly, Y is not precipitated even in the acidic aqueous solution but is dissolved in it in the usual manner. On the contrary, since the low HLB-SE has low water-solubility, it has a tendency to be precipitated at certain acidic concentrations of hydrogen ion. So, it is temporarily called the <<precipitated SE>> and marked "X". X has low HLB and thus it is apt to be precipitated from the acidic aqueous solution. The above described Fig. 2 is a graph of triangular coordinates in which the sum total of three ingredients - monoesters, diesters and triesters - is expressed by 100 %. Referring to Fig. 2, the point M shows the composition of the original sample SE. The point X shows the composition of the low HLB precipitated SE. The point Y shows the composition of the high HLB water-soluble SE. The suffixes 1, 2, 3 show SEs having different distributions of esters. It is shown that provided that the aqueous solution having the pH of 3.5 is added to the sample SE having the distribution of esters of M₂ (monoesters = 73 %, diesters = 22 %, triesters = 5 %) in Fig. 2 so that the concentration of SE may be 3 %, said SE is divided into said precipitated SE having the distribution of esters of X₂ (monoesters = 68 %, diesters = 25 %, triesters = 7 %) and the water-soluble SE having the distribution of esters of Y₂ (monoesters = 84 %, diesters = 13 %, triesters = 3 %). The weights WX₂ and WY₂ of X₂ and Y₂ divided are calculated by working out the following equations (a), (b) in view of the properties of the triangular coordinates. WM₂ = WX₂ + WY₂ WY₂· Y₂M₂ = WX₂· X₂M₂ wherein Y₂M₂ is a distance between point M₂ and the point Y₂; X₂M₂ is a distance between the point X₂ and the point M₂: WM₂ is the weight of M₂; WX₂ is the weight of X₂; WY₂ is the weight of Y₂ converted into a dry weight, respectively. As above described, by skillfully utilizing the properties that SE having relatively high monoester-content (that is high HLB-SE) is apt to be dissolved in the acidic water while SE having the relatively low monoester-content (that is low HLB-SE) is apt to remain in the precipitate the SE can be quantitatively divided into high HLB-SE and low HLB-SE. It has been found also that in general the higher the monoester-content in the SE is, the more the quantity of the SE (Y) dissolved in water is, and vice versa. And, the quantity of the SE having an optional composition dissolved in the acidic water can be quantitatively determined by substituting the value of Φ given by the data shown in Fig. 2 in the equations (a) and (b) to work out the values of WX and WY. Thus, the acidic aqueous solution obtained in this washing step contains high HLB-SE in a relatively large quantity, so that the high HLB-SE is separated from the precipitated SE mainly comprising the low HLB-SE by the filtration or the centrifugal separation. The filtrate obtained (or the top) contains, in addition to the high HLB-SE, a reduced quantity of remaining volatile matter (dimethyl sulfoxide and the like), salts, sugar and the like. (III) The step of recovering the high HLB-SE from the washing liquid by adding fatty acid So, the present inventors have found from their investigations aimed at obtaining high HLB-SE (in short the water-soluble SE) from the impure high HLB-SE-containing filtrate obtained by the above described washing step that this object can be effectively achieved by adding fatty acids to said filtrate. It has been known that SE can be associated in an aqueous solution under the relevant conditions to produce a high molecular congregate body having a micell structure (refer to page 102 in the above described publication). By way of explanation, as to the possible kinds of SE, the SE in which 1 to 3 fatty acid radicals are connected with oxygen atoms of three primary hydroxylic groups of a molecule of sugar, respectively, are called the monoester, diester and triester. And, as is well known, the monoester is superior to the diester and triester in hydrophilicity but inferior to the latter in the formation of micells in water, so that the relatively low molecular SE micell congregate body (having a small molecular diameter) is formed. On the contrary, the diester and triester have relatively low hydrophilicity but remarkably high micell-formation capacity, so that they form a remarkably high molecular SE micell congregate body (having a large molecular diameter). The present inventors have induced from the above described fact that upon contacting the high HLB highly hydrophilic SE (in short the water-soluble SE containing monoesters in a quantity exceeding about 80 %) with hydrophobic substances, such as fatty acids, in water, an SE micell congregate body having a micell structure different from the usual one is formed and the resulting congregate body is macro-sized and already unable to exist in the form of an aqueous solution so that the SE is combined with the fatty acids to be deposited. Supposing that this presumption is right, it ought to be expected that the water-soluble SE, which has hitherto been difficult to separate by the usual methods, can be deposited on an industrial scale by skillfully utilizing this deposition phenomenon. So, various kinds of investigation conducted on the basis of the above described idea led to the discovery that the high HLB-SE is selectively deposited by the use of fatty acids. This discovery is below in detail described item by item. (a) Deposition Phenomenon of High HLB-SE by the Addition of the Fatty Acids The present inventors have found an astonishing fact that the fatty acids are floating in the aqueous solution in the beginning but soon grow into the depositing condition or the molten condition and are at last deposited in the bottom of the vessel when the fatty acids are added to the aqueous solution containing the water-soluble SE (monoesters in a quantity of 80 % or more and thus diesters and triesters in a quantity of 20 % or less in all) at temperatures of ambient temperature up to 90°C and a pH of 3.0 to 5.5 in compliance with the above described assumption. These depositions collected in the bottom of the vessel were formed of a mixture comprising a large quantity of high HLB-SE and the fatty acids in a quantity nearly close to the quantity added. In addition, it has been successively found also that in general 1) the higher (within a range of ambient temperature up to 90°C) the temperature of the aqueous solution; 2) the lower (within a range of 3.0 to 5.5) the pH ; 3) the more (within a certain range) the quantity of the fatty acids added; 4) the larger (within a range of 1 to 4 %) the concentration of the water-soluble SE dissolved: and; 5) the lower (at the monoester-content of 80 % or more) the ratio of monoesters in the water-soluble SE; the more the quantity of these depositions formed. As to the above described phenomena, the reason why the higher the temperature, the more the quantity of the depositions (1) is assumed to be the promotion of the combination of the SE with the fatty acids by the melting of the fatty acids. In fact, the quantity of the depositions is reduced to a fraction at temperatures of melting point or less. It is, however, desired that the temperature is low as possible in view of the stability of SE relative to temperature, so that it is not desirable that the temperature is increased without any restriction. Accordingly, experimentally judging, temperatures within the range of about 50 to 80 °C give a desirable result meeting both aspects of the quantity of the depositions and the stabilized maintenance of the SE. Incidentally, even alakynic acid of C₂₀ has a melting point of 77 °C, so that this upper limit of temperature is not less than the melting points of the usual fatty acids comprising the SE. The lower the pH, the more the quantity of the sediments is 2). As is well known, SE is remarkably stable in the acidic pH range as compared to alkaline pH range. But, also in the case where acidity is too strong, the stability of SE is damaged, so that it is preferable to set the pH within the weakly acidic range, that is about 3.0 to about 5.5. Within such a pH range, the lower pH the more the quantity of depositions formed. In order to obtain a large quantity of deposition it is suitable taking other conditions into consideration that the pH is set within the weakly acidic range, that is from about 3.5 to about 4.0. The quantity of the required fatty acids added is dependent upon the quantity and concentration of the water-soluble SE dissolved. Accordingly, strictly speaking, the quantity of the fatty acids added is not always correlated with the quantity of the depositions but there is a tendency that the quantity of the depositions is increased with an increase of the quantity of the fatty acids added in many cases. However, the addition of an excessively large quantity of fatty acid generally leads to an increased quantity of the depositions formed and contrarily an increased quantity of fatty acid as the impurities, so that the undesirable effect occurs in that the purity of the high HLB-SE obtained is reduced. In the case where the water-soluble SE (high HLB-SE) is dissolved in an excessively large quantity (4), both the viscosity and the specific gravity of the aqueous solution are increased too much to separate the depositions. So, for example, in the case where stearic acid is a constituent fatty acid of the SE, it is preferable in respect of separation efficiency that the concentration of the water-soluble SE is set at about 2.0 %. In the case where the monoester-content of the SE is generally 80 % or less(5), the water-solubility cannot be maintained within the acidic pH range, and monoesters are partially deposited. According to the present inventors' experiences, if the monoester-content is 80 % or more (accordingly, diesters and triesters are contained in a quantity of 20 % or less in total), the SE is water-soluble at a pH of about 3.5 to 4.0 in many cases. In the case where the monoesters are contained in a quantity of 90 % or more, the SE maintains the water-solubility more surely and does not settle even within the acidic range of the above described extent. Next, as to the quantity of the depositions, the SE containing monoesters in a lower quantity (wherein the monoester-content > 80%) form depositions in a greater quantity. That is to say, there is the tendency that the larger the content of diesters and triesters (wherein the content of diesters and triesters < 20%), the more is the quantity of the depositions. The above described discoveries lead to the following art of recovering the water-soluble SE. (b) The Art of Recovering the Water-Soluble SE by the Addition of Fatty Acids It has been not easy industrially to obtain the water-soluble SE (containing a large quantity of monoester and having a high HLB value) without using solvents. However, skillful utilization of the above described phenomena found by the inventors of the present Patent Application leads to the prospect of the development of a novel industrial art of recovering the water-soluble high HLB-SE as depositions without using solvents by merely adding harmless substances (in short, fatty acids), The art of recovering the water-soluble high HLB-SE mainly comprising stearic acid as the constituent fatty acids is described hereinafter but it goes without saying that this art is not limited to the use of stearic acid. This art can be put into practice industrially also by adding other kinds of fatty acid. However, in order not to make the problem complicated, it is desirable that fatty acids of the same kind as the constituent fatty acids of the SE are added. i) The acidic aqueous solution obtained in the pickling step on the crude SE product containing the high HLB-SE (water-soluble SE) contains a minor quantity of remaining volatile matter, salts, sugar and the like in addition to a major quantity of high HLB-SE. This acidic aqueous solution is maintained at the pH of 3.0 to 5.5 and preferably heated to 50 to 80 °C to set the concentration of the SE contained at 1.0 to 4.0 %, preferably 2 %. ii) The Quantity of Fatty Acids Added Upon adding stearic acid (or fatty acids similar to stearic acid) to the above described acidic aqueous solution, the water-soluble SE having the high HLB value begins to cohere around the fatty acids and at last it is combined with each other to form depositions. It is desirable that the quantity of fatty acids to be added is set within the following range: [the weight of fatty acids added]/[the solid weight of the high HLB-SE (water-soluble SE)] = 1/4 to 1/30 However, taking two points - the purity of the high HLB-SE obtained and the recovery rate of the high HLB-SE-into consideration, the preferred quantity of the fatty acids added is set within the following range: [the weight of fatty acids added]/[the solid weight of the high HLB-SE (water-soluble SE)] = 1/12 to 1/20 iii) The pH of the Aqueous Solution It has been described above that suitable acids must be added to the aqueous solution containing the desired high HLB-SE to adjust the pH at 3.0 to 5.5 prior to the addition of the fatty acids but it is desirable in view of some aspects that the pH is adjusted to 3.5 to 4.0. In view of the stability of the SE, a pH within the high alkaline range should be avoided most. The SE is stable for a short time at a pH within the weakly acidic range (3.5 to 4.0). In addition, this pH range is preferable also in view of the increase of the quantity of the high HLB-SE (water-soluble SE) settled. In addition, if the pH is 3.5 to 4.0, there is little possibility that the apparatus for separating the formed depositions will be corroded. However, the use of hydrochloric acid and high-temperature sulfuric acid as the pH-adjuster should be avoided.) Next, the aqueous solution having a weakly acidic pH is stirred to complete the deposition. Strong stirring is preferable and a time of about 10 minutes is sufficient. The thus separated depositions comprise about 80°C water and about 20°% solid fractions. The dried solid fractions, from which water has been removed, have a compositional ratio expressed by the following equation in many cases. [the weight of the fatty acids]/[the weight of the high HLB-SE] = 1/10 to 1/20 iv) Washing of the depositions The depositions obtained by combining the high HLB-SE deposited by the above described addition of the fatty acids with the fatty acids contain a smaller quantity of impurity, such as remaining volatile matter (for example DMSO as the reaction solvent), salts and sugar, in addition to water but these impurities are separated from the aqueous solution phase (the top) by successively washing with the acidic water and the content of impurities (the volatile matter, salts, sugar and the like) is reduced, thereby improving the purity. In addition, the washing operation can be repeated additionally two or more times if desired, whereby the purity of the high HLB-SE is still more improved. v) Recovery Rate 85 to 95 % of the high HLB-SE, which has existed under water-soluble condition in the beginning, can be recovered in the form of depositions by the above described operation. Also, the resulting high HLB-SE-containing depositions containing solid fractions in a quantity of 5 to 20 % are filtered to be recovered and then neutralized and dissolved in water again followed by the following step. (IV) A step of dehydrating and turning the recovered deposited high HLB-SE into powders step of spray drying) (a) Outline It has been described in detail in the Prior Art that industrial difficulties occur in the drying of aqueous solutions of sugar fatty acid esters. That is to say, the deterioration of the quality, such as the rise of the acid value of the SE, the coloring and the caramellization, cannot be avoided on account of the properties, such as the viscosity characteristics and the low melting point, incidental to the SE both where a usual vacuum drier represented by the so-called "mixing type stirring drier" is used but also where the so-called "flash type drier", in which the SE slurry heated by steam is continuously supplied, flashed in the vacuum chamber, dehydrated and dried, is used. In addition, in both cases, also the possibility of a dust explosion cannot be overlooked when cooled SE solid is pulverized. However, the inventors of the present Patent Application have found from the results of their many experiments that spray drying is optimum for the dehydration and drying of the above described high HLB-SE depositions and the disadvantages of conventional drying means can be solved. In the drying step, the water-containing high HLB-SE existing in the form of an aqueous solution is continuously supplied to the spray dring tower through a pump to be divided into mist-like particles in a spray by means of a nozzle or the centrifugal force of a rotary disk, thereby being brought into contact with the dry air current. Thereupon, the evaporation area of water is significantly increased and thus the dehydration and drying can be completed in a remarkably short time (within several seconds from spraying). Generally speaking, the rotary disk is more desirably used for the spray-drying of the water-containing SE. (b) Spray Drying Conditions The temperature of the aqueous solution of the high HLB-SE can be optionally varied between 40°C and 80°C but it is desirable from the point of view of quality that it is selected within a range of 40 to 60°C. In order to spray the above described solution or aqueous solution by means of a rotary disk, it is desirable that the rotation frequency is set at 15,000 to 24,000 rpm for a disk having a diameter of 5 to 10 cm. Air to be supplied to the inside of the drying tower should contain sufficient heat to evaporate the water contained in the solution, or the aqueous solution. Accordingly, a larger quantity of air is required with a reduction in the temperature of the air. For this step, the temperature of the air may be set within a wide range of 10 to 100°C but it is advantageous taking into consideration the drying efficiency and the prevention of thermal decomposition of the desired high HLB-SE that the temperature is selected in a range of 60 to 80°C. Also the humidity of air to be supplied to the inside of the tower has an effect on the drying efficiency as well as the temperature of the air. It is economical that the operationally suitable absolute humidity is set within the following range: Absolute humidity = 0.01 to 0.04 (Kg.water/Kg.dry air) Various parameters, such as the capacity, the diameter and the height, of the spray drying tower are designed on the basis of the above described spraying conditions. If the design and operational conditions of the tower are suitable, the powdery dry high HLB-SE containing water in a quantity of 5 % or less can be continuously discharged from the lower portion of the spray drying tower. The resulting products are remarkably superior in quality due to the short thermal hysteresis thereof and personnel for the drying operation are hardly required. If acids are added to the high HLB-SE forming reaction mixture containing the unreacted sugar, the unreacted fatty acid methyl esters, the catalysts, the soaps, fatty acids and the volatile matter (remaining reaction solvents) to regulate the pH within the neutral range followed by adding water, neutral salts and sugar to settle said impurities with salts at suitable temperatures, the high HLB sugar fatty acid esters, the unreacted fatty acid methyl esters, the soaps and the fatty acids are settled and at the same time the volatile matter (remaining reaction solvents) are transferred to the aqueous phase side, so that the remaining volatile matter can be removed without using organic solvents at all. In particular, the remaining solvents can be removed under conditions that the sugar fatty acid esters are not substantially lost at all by conducting the operation so that the conditions expressed by the equations (3), (6) and (7) may be satisfied. Then, the resulting sediments are washed with acidic water to separate the depositions brought about by adding fatty acids to the filtrate, thereby obtaining the high HLB sugar fatty acid esters containing solid fractions in a quantity of 5 to 20 % from which impurities, such as volatile matter, sugar, the neutralization of the catalysts, have been removed. The resulting depositions are neutralized and spray dried to continuously produce the high HLB sugar fatty acid esters in the form of powders superior in color, odor, and fluidity and thus the powdery sugar fatty acid esters having high HLB values can be industrially produced without using solvents in the purification at all. In addition, in the above described pickling step, the sugar fatty acid esters remaining in the precipitation are highly pure low HLB sugar fatty acid esters, so that additionally the object of separating the high HLB sugar fatty acid esters from the low HLB sugar fatty acid esters together with the purification of the crude sugar fatty acid esters can be achieved. The practice and effects of the present invention are below described with reference to the preferred embodiment but it goes without saying that the preferred embodiment is illustrative. Example The residue obtained by distilling away the reaction solvents from the sugar fatty acid ester reaction mixture by the solvent method having the composition shown in the following Table-l was neutralized with lactic acid and then dried. The resulting dry matter of 100 Kg was dissolved in water of 1,000 Kg. Sugar of 62.5 Kg and a 50 %-aqueous solution of potassium lactate of 97.6 Kg were added to the resulting aqueous solution and the resulting mixture was heated to 75 °C to filtrate the settled cake which was dried at 80 °C in a vacuum and then investigated in respect of composition with the results shown in the following Table-2. At this time, the water-content of the above described cake was 45%. In addition, the quantity of the sugar fatty acid esters contained in the filtrate filtered from the cake was measured by the gel percolation chromatographic (GPC) method (refer to page 63 in the above publication) with the result that the existence of sugar fatty acid esters was not found at all and 95 % of dimethyl sulfoxide as the reaction solvent was removed. Subsequently, the cake (of 80 Kg) shown in the above Table-2 was suspended in an aqueous solution of acetic acid (400 kg) at ambient temperature and a pH of 3.5 and then stirred for 10 minutes in a homomixer to filtrate fractionalized precipitates followed repeating the operation of washing the filtrate precipitates with the aqueous solution of acetic acid again four times in all. The composition of the obtained filtrate (pH = 3.5) is shown in the following Table-3. The pH of the aqueous solution (390 kg) shown in Table-3 was regulated at 3.5 and then the aqueous solution was heated to 80 °C followed by adding stearic acid of 0.78 kg and stirring well for 10 minutes. Upon stopping the stirring, water-containing depositions of 54.1 kg were separated from the top. Powders obtained by drying a part of the deposition had the composition shown in the following Table-4. Sodium hydroxide was added to the water-containing deposition having the composition shown in Table-4 of 54.0 kg drop by drop with stirring to regulate the pH at 7.8, thereby obtaining a neutral aqueous solution of high HLB sugar fatty acid esters. Upon drying a part of this aqueous solution in a vacuum, high HLB sugar fatty acid esters containing monoesters in a quantity of about 89.0 % and having the composition shown in the following Table-5 were obtained. In addition, the precipitates remaining after washing the sugar fatty acid esters having the composition shown in Table-2 with acetic acid to purify were low HLB sugar fatty acid esters containing monoesters in a quantity of 67 %. Finally, the neutral aqueous solution of high HLB sugar fatty acid esters, of which the pH had been regulated at 7.8, was subjected to spray drying under the following conditions: Diameter of the spray drying tower: 2.0 m Length of the straight cylindrical portion: 1.5 m Blast quantity: 320 Nm³/hour Diameter of the rotary disk: 10 cm Rotation frequency of the rotary disk: 24,000 rpm Temperature of air at the inlet: 55.0 °C Absolute humidity of air at the inlet: 0.015 (kg.water/kg.dry air) Supply rate of the slurry: 1.3 kg/hour Powdery high HLB sugar fatty acid esters obtained from the lower portion of the spray drying tower had the composition shown in the following Table-6, water-content of 1.9 % and a bulk specific gravity of 0.40 and exhibited no coloring, good odor and the superior fluidity. That is to say, high HLB sugar fatty acid esters containing monoesters in a quantity of 89.2 % were obtained form the sugar fatty acid esters having a distribution of esters of monoesters = 70.0 % and diesters or higher esters = 30 % in the reaction mixture in the beginning. In addition, the sugar fatty acid esters obtained form the pickled precipitates are the low HLB products containing monoesters in a quantity of 67 %, as above described, so that the sugar fatty acid esters contained in the reaction mixture in the beginning were separated into high HLB products and low HLB products in the present Example.

Claims: A method of producing powdery high HLB sugar fatty acid esters, which comprises adjusting to a neutral range the pH value of a reaction mixture comprising unreacted sugar, unreacted fatty acid methyl ester, catalysts, soaps, fatty acids and volatile matter in addition to the desired sugar fatty acid esters; adding water, at least one neutral salt and sugar to said reaction mixture to give sediments; washing the sediments with acidic water, and adding to the washing liquid a fatty acid which is identical with or similar to the constituent fatty acid of the sugar fatty acid esters to separate materials; neutralizing the materials; and then spray drying the resultant product. A method as claimed in claim 1, wherein said reaction mixture has the following composition: A method as claimed in claim 1 or claim 2, wherein the pH of the reaction mixture is adjusted to 6.2 to 8.2. A method as claimed in any one of the preceding claims wherein the reaction mixture is heated to 50 to 80°C after adjustment of the pH. A method as claimed in any one of the preceding claims wherein the ratio of water added to the reaction mixture is 5 : 1 to 40 : 1 by weight. A method as claimed in any one of the preceding claims wherein the neutral salts and sugar are added to said reaction mixture, of which the pH has been adjusted, so that the following relative expressions hold good:- (total weight of (salts)/(water content by weight + total weight of salts + total weight of sugars) = 0.015 to 0.12; (total weight of sugars)/(water content by weight + total weight of salts + total weight of sugars) = 0.025 to 0.20; and (total weight of salts)/(total weight of sugars) = 0.4 to 0.6 wherein the total weight of salts = weight of neutral salts to be added + weight of salts formed by neutralizing the catalysts and the total weight of sugars = weight of sugars to be added + weight of unreacted sugars from the beginning. A method as claimed in any one of the preceding claims wherein the acid used for the pH adjustment of the reaction mixture is selected from lactic acid, acetic acid, hydrochloric acid and sulfuric acid. A method as claimed in any one of the preceding claims wherein the majority of the fatty acid radicals contained in the fatty acid methyl esters, soaps and fatty acids, respectively, in said reaction mixture are saturated fatty acid radicals of C₁₆ to C₂₂. A method as claimed in any one of the preceding claims wherein the volatile matter (remaining reaction solvents) contained in the reaction mixture is dimethyl sulfoxide or dimethyl formamide. A method as claimed in any one of the preceding claims wherein the neutral salt added to the reaction mixture is any salt selected from sodium chloride, sodium sulfate, potassium lactate and potassium acetate. A method as claimed in any one of the preceding claims wherein the content of monoesters in the sugar fatty acid esters is 10 to 75% and 90 to 25% as for diesters and higher esters. A method as claimed in any one of the preceding claims wherein the pH of the acidic water is 3.0 to 5.5. A method as claimed in any one of the preceding claims wherein the pH of the washing liquid, to which the fatty acids have been added, is 3.0 to 5.5. A method as claimed in any one of the preceding claims wherein the temperature of the washing liquid, to which the fatty acids have been added, is 50 to 80°C. A method as claimed in any one of the preceding claims wherein said high HLB sugar fatty acid esters contain monoesters in a quantity of 80% or more, the sum total quantity of diesters and triesters being 20% or less. A method as claimed in any one of the preceding claims wherein the concentration of said high HLB sugar fatty acid esters contained in said washing liquid, to which the fatty acids have been added, is 1 to 4%. A method as claimed in any one of the preceding claims wherein fatty acids are added in a quantity of 1/4 to 1/30 times that of said high HLB sugar fatty acid esters dissolved in said washing liquid to which the fatty acids are added. A method as claimed in any one of the preceding claims wherein the solid content of the slurry to be spray dried is 4 to 40%. A method as claimed in any one of the preceding-claims wherein the humidity and the temperature of air to be used during the spray drying are set so that the following expression may hold good: Absolute humidity = 0.008 to 0.05 [water (kg)/dry air (kg)] wherein the temperature is 10.0 to 100.0°C. A method as claimed in any one of the preceding claims wherein the powdery high HLB sugar fatty acid esters produced have the following composition:

Inventors: HATAKAWA YOSHIO, MATSUMOTO SHUSAKU ROSE MANSION, NAKAJIMA AKIHIKO, HATAKAWA, YOSHIO, MATSUMOTO, SHUSAKU, ROSE MANSION FUJIMORI A-308, NAKAJIMA, AKIHIKO
Applicants: DAI ICHI KOGYO SEIYAKU CO LTD, DAI-ICHI KOGYO SEIYAKU CO., LTD.
Application year: 1990
Main classification: C07H13
IPC codes: C07H1, C07H13