MATERIAL FOR EXPERIMENT NO. 09 Continuous process of detergents production on the basis of alkylarylsulfonic acids based on: Podręcznik do ćwiczeń z technologii chemicznej (Ed. T. Kasprzycka-Guttman), Wydawnictwa UW, Warszawa 1996. translated by Tomasz Pawłowski General information. Detergents are surfactants that reduce surface tension at the interface. Activity at the interface is associated with amphiphile of detergents, that means detergents possess dual affinity, which in the case of the aquatic environment indicates that the detergent contains in its structure both hydrophilic and hydrophobic parts. Amphiphile gives to detergents ability for their adsorption at the interface and possibility of micelles formation, that are spherical or oval groups of emulsifier molecules which hydrophilic parts are directed toward the water. The result is that aqueous solutions of detergents have many useful properties such as: wetting and washing of solid surfaces, foaming ability, solubilization, emulsifying and dispersing properties, the ability to act as a protective colloid, and the ability to disperse magnesium and calcium soaps. All these properties are related to capacity to adsorb at the interface with the appropriate orientation of the hydrophilic and hydrophobic parts, and the aggregation of detergent molecules and ions. Wetting of solid surfaces is related to the adsorption of detergent molecules on these surfaces in such a way that the hydrophilic parts are directed toward the aqueous phase. The ability to wash the surface of solids and solubilization, emulsifying and dispersing properties are similar in nature. Washing the surface, that is removing insoluble liquid drops in water (e. g. oil) or solid particles consists in a liquid emulsifying or dispersing crumble solids. Both of these phenomena are the result of the concentration of detergent particles at the interface, thus preventing the microdroplets integration (micelle formation) and the aggregation of solid particles. Solubilization is giving the apparent solubility in water for insoluble or poorly soluble substances by the implementation of these substances in micelles; this is essentially a variation of emulsification. A very interesting phenomenon is the foaming of aqueous solutions of detergents. During mixing, the solutions are introduced by air bubbles which are gathered by the detergent molecules directed, of course, the hydrophilic portions towards the aqueous phase. Cutting through the surface the bubbles entailing film particles collected there, forming a lamellar system composed of two layers of detergent, between which there is water. This triple layer forms very flexible film which enables creating the formation of bubbles on the surface, and even the pulling of the solution. The action of a protective colloid and dispersing calcium and magnesium soaps are also similar to emulsification and dispersion phenomena. In the first case, the highmolecular emulsifiers, often polymers are applied and this type of interaction of detergents is used to stabilize hydrophobic colloids, as well as in suspension polymerization. Dispersing calcium and magnesium soaps prevent the formation of deposits in the washing process. 1
Due to chemical structure detergents can be divided into four types: anionic, cationic, nonionic and amphoteric. Anionic detergents are anion-active compounds in which the hydrophilic part is the anionic group and the counterions are generally the cations of sodium, potassium and ammonium. Cationic detergents also known as invert soaps, are surface-active compounds in which the hydrophilic groups are cationic and counterions are chloride, sulfate or acetate anions. Nonionic detergents contain hydrophilic and hydrophobic parts, whose mechanism of action is not related to the phenomenon of dissociation. Amphoteric detergents combine features of cationic and anionic detergents, and their mode of action is dependent on the ph of the solution. The hydrophilicity of these detergents is the result of formation of zwitterions, for example in aminoacids. One of the parameters characterizing the detergents is the critical micelle concentration (known in English-speaking countries as CMC). This parameter is related to the mechanism of dissolution of detergent in water. Detergent in cold water is generally not very well dissolved and creates gels. The mechanism of transformation of a gel in a clear solution can be of two types: for low concentrations of detergent molecules are dissolving in a monodisperse way, but above a certain critical concentration is only a micellar solution, that means there are formed characteristic aggregates (micelles) in oval or ball shape. This phenomenon is very advantageous for the performance properties of the detergent, since the formation of the micelles is a prerequisite for emulsification, and thus holding cleaning properties. The critical concentration of micelle formation is a parameter associated with the specified temperature. The smaller CMC, the better properties of a detergent. The differences in the properties of ionic and non-ionic detergents are significant. The former are characterized by an increase of solubility with temperature, and the temperature has little effect on the mechanism of the solubility, and after a certain concentration the solution is purely micellar (see on the figure below): Triple point on the graph is also characteristic parameter of the detergent and is called the power point. It can therefore be concluded that with increasing temperature ionic detergent 2
activity augments. Non-ionic detergents have quite the opposite characteristics. After exceeding a certain temperature, they precipitate from the solution, and the activity of their micellar solution decreases with temperature. Monodisperse solution area is generally small. These abnormalities are the result of detergent hydration and dehydration phenomena. As far as the solubility of ionic detergents is corresponding to the dissociation in the case of nonionic detergents decisive role plays the hydration of molecules. The increase in temperature causes dehydration of the hydrophilic part of the detergent by breaking hydrogen bonds. This makes the whole molecule more hydrophobic and eventually followed by precipitation of the detergent from the solution. These phenomena are characterized by a graph in the second figure below: Characteristic value of the non-ionic detergent is a so-called cloud point, which is the temperature at which the solution with a predetermined concentration becomes cloudy. The critical concentrations of micelle formation for these detergents are generally several times smaller than for ionic detergents, but their activity with temperature strongly decrease. Their advantage is low sensitivity to electrolytes and ph change. Anionic detergents. Undoubtedly, the largest group of detergents form anionic surfactants. Among them, the largest tonnage production is for salts of carboxylic and sulfonic acids. Majority of carboxylates are soaps. Their production is based mostly on the reaction of saponification of natural animal and vegetable fats, which are in many cases the waste material, which reduces production costs. The most important group of compounds of the anionic detergents are undoubtedly sulfonates. Among them, alkylbenzenesulfonates occupy a special position. This is due to their very broad application. For this reason, the method of production of these detergents are described below in more detail. They are produced in the form of sodium, potassium and ammonium salts. Depending on the length of the chain R alkylbenzenesulfonates can be used as wetting agents (C 8 - C 10 ), detergents, cleaning and 3
cosmetic agents (C 10 - C 14 ), oil cooling during machining, emulsifiers biphasic systems of water in oil, detergents of motor oil (greater than C 15 ). The most versatile in the use are alkylbenzenesulfonates with chains C 10 - C 14, which are mixtures of homologues of the average chain length of C 12, and are known as dodecylbenzenesulfonates. In addition, two types of these compounds should be distinguished. The first of these are sulfonates derived from products of benzene alkylation by means of highly branched propylene tetramer (the TPS - tetrapropylenebenzenesulfonates) and the second one comprises dodecylbenzenesulfonates with linear alkyl substituents (the LAS - linear alkylbenzene sulfonates). TPS sulfonates have worse properties and are worse biodegradable than their linear counterparts and, therefore, their importance is slowly decreasing. Alkylbenzenesulfonates are produced in the technological sequence comprising: alkylation of benzene in the Friedel - Crafts reaction, alkylbenzenes sulfonation and neutralization of sulphonic acids obtained. The alkylation may be carried out using alkyl chlorides, olefins or alcohols. In the case of alkyl chlorides the installations to their receiving are often part of the technological production of alkylbenzene. These chlorides are obtained in the process of radical chlorination of paraffin s fractions by chlorine gas at a temperature of 100-150 C. Benzene Alkylation occurs at a temperature of 60-80 C in the presence of AlCl 3 as catalyst: Alkylbenzene sulfonation reaction may be carried out by using various sulfonic mediums: 70-100% H 2 SO 4, oleum, SO 3, chlorosulfonic acid HSO 3 Cl and complexes of SO 3 with Lewis bases. In the technology producing of alkylbenzenesulfonates only the first three reagents are mostly used. Appropriate sulfonating agent is cation HSO 3 + and SO 3 : 4
Unlike most electrophilic substitutions sulfonation of aromatic compounds is a reversible reaction. The presence of the water, or even dilute sulfuric acid gives hydrolysis of sulfonic acids to the starting aromatic compounds: Ar-H + H 2 SO 4 ArSO 3 H + H 2 O This is the reason for which the sulfonation with SO 3 is a process that gives a guarantee of equilibrium shift to the right. The mechanism of sulfonation with SO 3 is more complex than indicated by the previous considerations. In aprotic solvents (and also in the alkylbenzenes environment) giving the minimum of the side reactions shown the existence of the primary and secondary sulfonation. This is illustrated in the following diagram: Dashed lines in the diagram indicate secondary reactions, and the solid lines show original reactions. These reactions are mostly reversible, so that even the final product at high temperatures can be broken. In industrial conditions sulfonation with SO 3 alkylbenzenes can be performed in several ways. The high heat of reaction (about 170 kj/mol), and its high rate, make necessary to dilute SO 3 either by appropriate solvents, or - in the gaseous state - by nitrogen or air. It is known sulfonation method in liquid sulfur dioxide at temperature -10 C (boiling point of 5
SO 2 ). Evaporating SO 2 takes away the heat of reaction and its removing from the reaction mixture is not a problem. After condensation the solvent is recycled to the reaction. Diluted, gaseous SO 3 at its concentration about 4-8% can be obtained by passing dry air or nitrogen through the heated liquid SO 3 or oleum. Such concentration of SO 3 in inert gas, however, is achieved in a much more convenient way by contact oxidation of SO 2 with air. As the catalyst is mainly used vanadium pentoxide supported on aluminosilicate and activated by potassium, aluminum, barium, and others oxides. This catalyst operates at a temperature of about 500 C converting SO 2 to SO 3 at yield of 93-95%. Acids obtained after degassing and maturation are neutralized in conventional reactors with a stirrer and a cooling jacket (the heat of reaction of about 180 kj/kg). The amount of water introduced with the neutralizing solution is generally low, so that the crude product is 50 percent tan-colored paste where this colour is reduced by the addition of bleaching agents containing active chlorine. Non-ionic detergent. Non-ionic detergents do not dissociate and do not have ionic structure; they are surface active agents which hydrophobic part is alkyl or arylalkyl chain, and hydrophilic part is polyether chain or hydroxyl groups. This is a group of detergents with versatile applications. They possess weaker foaming properties than anionic detergents, low sensitivity to hard water, low toxicity, very good biological tolerance and high biodegradability. These properties make them suitable in particular for use in the cosmetic, pharmaceutical and food industries. The most important non-ionic detergents are the ethoxylated derivatives of hydrophobic alcohols, alkylphenols, mercaptans, amines, carboxylic acids and their amides, and partially esterified derivatives of glycerol, di-glycerol, sugars, pentaerythritol and sorbitol. Ethoxylated derivatives of OH-, SH- or NH- acidic compounds are prepared by the reaction with ethylene oxide, catalyzed by bases or acids (Lewis). The mechanism of the reaction catalyzed by the bases represent patterns: Where: BH is a OH-, SH- or NH- acidic compound. The catalysts used are hydroxides, alkoxides and carbonates of alkali metals or these metals. 6
The mechanism of acid catalysis with the participation of Lewis acids (e.g. BF 3 ) can be summarized as follows: Cationic detergents. The group of cationic detergents include quaternary ammonium, pyridinium, phosphonic and tertiary sulfonic salts. In the industry are used only ammonium salts having at least one strongly hydrophobic alkyl or aryl substituent, as well as pyridinium salts and imidazoline alkyl derivatives. Quaternary ammonium salts are prepared by alkylation of the tertiary fatty amines with one or two long substituents by chloride, bromide and alkylsulfate (methyl or ethyl). These reactions take several hours and occurs preferably in a polar solvent (alcohol) at 50-100 C. Under similar conditions pyridine is alkylated, but in this case the alkylating agents are alkyl chlorides and bromides with long chain hydrocarbons. There is also the possibility of obtaining the quaternary fatty amine derivatives by reaction with ethylene oxide and water, for example: Formed in this reaction quaternary ammonium hydroxide can then be readily converted to the corresponding salt. Alkyl imidazoline derivatives are obtained by condensation of fatty acids with substituted ethylenhdiamines: 7
and then ethylation using methyl chloride: Cationic detergents are in many cases strong bactericidal and therefore found - among others - the use in human and veterinary medicine as a disinfectant cleansing ingredients. Moreover, they are also used as herbicides, corrosion inhibitors, apertures, dispersing and hydrophobic agents and as fabric softeners and others. Special type of detergents. Detergents with unusual properties, rarely used and generally expensive were classified as special type. These include amphoteric detergents, for example, the ampholytes and betaines. Ampholytes representatives are, for example amino acids, which occur at the isoelectric point as internal salts, which at lower ph values are in the form of cations, and at higher ph in the form of anions: They are obtained by substitution of primary fatty amines by methylcarboxylic groups or by addition of these amines to the double bond of acrylic acid: Betaines are true zwitterionic passing at low ph values in the form of a cation: 8
One of the methods for their synthesis is the reaction between tertiary fatty amines and chloroacetic acid: The greatest use have so-called amide betaines and imidazoline derivatives: Good tolerance of betaines makes them valuable detergent in cosmetics. Finally, it should also be mentioned silicone and fluoric detergents. Their ability to reduce the surface tension of water is much greater than the detergent with a hydrophobic alkyl and alkylaryl chains. Barrier to their widespread use is the high price. 9