National Activities - UK Sustainable Surfactants: Renewable Feedstocks for the 21st Century - Fats and oils as oleochemical raw materials

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Detergents : Fine Chemicals : Integrated Crop Protection & Biological Control : National Activities - UK : Paints/Coatings/Plastics : Pharmaceuticals/Cosmetics : Vegetable Oil/Fat



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Ecological compatibility (5)
By using renewable resources it is possible to assume a more favourable ecological compatibility when compared with petrochemical-based substances - an important criterion in the development of a new product, just as price and performance are. For example, products based on renewable resources contribute less to the greenhouse effect because of their closed CO₂ cycle. During their growth the plants consume the same amount of carbon dioxide (CO₂) and water (H₂0) as they subsequently release into the atmosphere by biodegradation after use. Moreover, products based on renewable resources usually have a more favourable ecological balance when compared with petrochemical-based products. Ecological compatibility plays a decisive role in all research and development projects, no matter whether in the framework of developing a new raw material with better ecological properties, production processes which are more ecologically favourable, more ecologically acceptable packaging or protective work in order to meet current legal requirements or those to be expected in future. The term ecological compatibility covers two different aspects: remaining in the environment and the effects on the environment.

Various criteria are used to evaluate these two aspects. Exposure analysis is used to estimate the expected environmental concentration of a particular substance (in wastewater, in exhaust gases or in a sewage treatment plant) taking into consideration the amount of the substance produced and its biodegradation behaviour. The effect on the environment, e.g. toxicity to organisms such as fish, algae or micro-organisms, is determined by a series of standardised testing methods. The two results are brought into relationship with each other. If the expected environmental concentration of a particular substance is lower than the amount at which negative effects can no longer be determined then the product is ecologically compatible. An important role in this environmental evaluation is played by the biodegradation behaviour, as in rapid biodegradation the expected environmental concentration is naturally relatively low. A differentiation can be made into two main forms of biodegradation: primary degradation and ultimate degradation.

The primary degradation only describes the first stage in the degradation process of an organic compound, which is split into certain intermediate degradation products by bacteria and oxygen. Primary degradation provides no information about the further behaviour of this intermediate degradation stage. Whether a compound is totally degraded, in the final instance into carbon dioxide and water, is determined by methods such as the determination of the total oxygen demand or the amount of carbon dioxide. Apart from the ecological investigations, toxicological tests and microbiological and dermatological investigations are also carried out; this is particularly important when cosmetic ingredients are involved. In the framework of a successful marketing strategy all environmentally relevant parameters are evaluated at every product development stage (selection of raw materials, development of test formulations and technical application tests, process development, development of packaging, testing consumer satisfaction in test markets) in order to be able to guarantee optimal product safety right from the start.

Examples of products
Before oils and fats can be used as industrial and chemical raw materials these must be split into the so-called oleochemical base materials: fatty acid methyl esters, fatty acids, glycerol and, as secondary products of the fatty acid methyl esters, fatty alcohols (6). Innovative products, which are derived from fatty alcohols, fatty acids or glycerides and are used as surfactants in washing and cleansing agents as well as in cosmetic articles are as follows:

• alkyl polyglycoside
• fatty alcohol sulfate
• cocomonoglyceride sulfate
• protein-fatty acid condensate.

The basic way in which surfactants act is determined by their structure. With their hydrophilic head and hydrophobic tail, surfactant molecules interpose themselves between water and water-insoluble substances. By enriching themselves at the boundaries which water forms with air or oil they lower its surface tension; as ingredients in soaps and washing agents they make contact with soiled material in this way. When dissolved in water at higher concentrations these molecules group themselves together to form spherical structures (micelles); their inwards-pointing hydrophobic groups surround soil particles and keep these in solution. Surfactants are generally classified as being anionic, cationic, non-ionic or amphoteric surfactants depending on the type and charge of the hydrophilic groups (6)

Surfactants are used in a wide range of fields. By far the most important field of application is the washing and cleansing sector as well as textile treatment and cosmetics; these use more than 50% of the total amount of surfactants. Surfactants are also used in the food sector, in crop protection, in mining, in the production of paints and dyes and paper. The total worldwide market amounts to approx. 9.3m. tonnes (1996, without soap). It is true that the most important surfactant from the amount produced apart from soap is still the petrochemical-based alkyl benzene sulfonate; however, in recent years a continuous trend towards surfactants based on renewable resources has become apparent. In western Europe a total of 2.1 8m. tonnes of surfactant was produced in 1996. The amounts involved, broken down into the individual surfactant classes, are summarised in Table 2. Surfactants which are successful on the market fulfil a number of criteria. Apart from price and performance the product safety (consumer and ecological compatibility) has an equally high importance in the sense of an effective economic management (Table 3).

Carbohydrate surfactants - alkyl polyglycosides (7, 8)
The development of surfactants based on carbohydrates and oils is the result of a product concept which is based on the exclusive use of renewable resources. Previously industrially developed products were based on the carbohydrates saccharose, glucose and sorbitol which were available in large amounts and at attractive prices: saccharose esters, sorbitan esters, N-methylglucamides and alkyl glucosides. The selective functionalization of saccharose and sorbitol for the construction of a perfect amphiphilic structure cannot be realised in simple technical processes because of the polyfunctionality of the molecule and the relatively slight differences in the reactivity of the individual hydroxyl groups. This is why the products offered on the market contain different amounts of mono-, di- and tri-esters and are therefore only suitable for particular applications, e.g. as emulsifiers for foodstuffs and cosmetics or, in the case of the sorbitan esters, also in technical branches such as explosives and in emulsion polymerisation.

The ideal raw material for selective derivatization is glucose. Reaction with alcohol produces alkyl glucosides; N-methylglucamides are prepared by reductive amination with methylamine and subsequent acylation. Both products have proved to be highly effective surfactants in washing and cleansing agents. For these applications N-methylglucamides are currently used only by a single manufacturer. The alkyl glucosides have also additionally established themselves in the cosmetic products sector, as auxiliaries in crop protection formulations and as surfactants in industrial cleansing agents and today can already be said to be the most important sugar surfactants based on the yearly production amounts.

Alkyl polyglycosides have been known for a long time but only now, following several years' research work, has it been possible to develop reaction conditions which allow manufacture on a commercial scale. The structure on which these compounds are based corresponds exactly to the surfactant model described above. The hydrophobic (or lipophilic) hydrocarbon chain is formed by a fatty alcohol (dodecanol/tetradecanol) obtained from palm kernel oil or coconut oil. The hydrophilic part of the molecule is based on glucose (dextrose) obtained from starch.

The chemical challenge to process technology was to find reaction conditions which allowed fatty alcohol to react directly with glucose on a commercial scale and at an acceptable cost. In order to realise as environmentally-friendly method as possible the use of solvents was rejected right from the start. Method development was successfully completed: Henkel currently has a capacity of approx. 50 000 tonnes/year available for the manufacture of this class of compounds (further manufacturers are Kao, SEPPIC, Akzo Nobel and ICI). By combining vegetable oil and sugar as raw materials it has for the first time become possible to offer commercially important amounts of non-ionic surfactants which are completely based on renewable resources.

As an example of the manufacturing process glucose is suspended in excess fatty alcohol (2-6 molar) and allowed to react in the presence of an acidic catalyst (sulfonic acid) at 100-120 °C. By splitting off 1 mol water (referred to glucose) a complex product mixture is formed consisting of alkyl mono-, alkyl oligo- and alkyl polyglycosides. The average degree of polymerisation (DP) of this product mixture i.e. the average number of glucose units per alkyl chain - depends principally on the molar excess of the fatty alcohol used in the reaction. Technical products have DP values between 1.2 and 1.7.

Unique properties had previously been determined for alkyl polyglycosides, particularly in combination with other surfactants. For example, the use of alkyl polyglycosides in a light-duty detergent formulation means that the total amount of surfactants can be reduced without sacrificing any performance. In other combinations a particularly stable and fine foam can be produced which protects sensitive textiles during the washing process. Toxicological and ecological laboratory investigations have also produced favourable results. Alkyl polyglycosides have a good compatibility with the eyes, skin and mucous membranes and even reduce the irritant effects of surfactant combinations. On top of this they are completely biodegradable, both aerobically and anaerobically. The relatively favourable classification (for surfactants) into class I under the German water hazard classification (WGK I) results from this.

Fatty alcohol sulfates (6)
The second example from the surfactant sector concerns the fatty alcohol sulfates (FAS), which are manufactured in a continuous reaction process with sulfur trioxide (S0₃). This class of products has been known and used for a long time; in recent years has gained in importance because of its good technical application performances and environmental compatibility. Fatty alcohol sulfates are, like the alkyl polyglycosides, completely biodegradable, both under aerobic and anaerobic conditions. In an ecological balance fatty alcohol sulfates based on renewable resources turn out more favourably than corresponding products derived from crude oil. The ecological balance starts with harvesting the fruits, in this case palm kernels or coconuts, from the palm trees and then subjecting them to various processes before the vegetable oil is separated off in the oil mill. This is then processed industrially: transesterification produces fatty acid methyl esters, which are converted into the corresponding fatty alcohol by hydrogenation. The final process step, sulfation, supplies the fatty alcohol sulfates. In the ecological balance all process steps as well as the associated substance, residue and wastewater circulation flows are taken into account. Fatty alcohol sulfate based on vegetable oil, when compared with a petrochemical-based product, has a 70% lower consumption of fossil resources, a 50% lower air pollution during production and the amount of waste produced is also reduced by 15%. On the other hand, the wastewater load is increased by 50%; this is caused by small, decentralised plants and the relatively high amount of water required for oil recovery in the palm oil mill. (9) The fact that with the oleochemical raw material the higher wastewater load is of a less toxic quality is not taken into account in the ecological balance. (10)

Fatty alcohol sulfates are particularly interesting for use in powder-form washing agents. It is true that for this application alkyl benzene sulfonate (LAS) is still the most important surfactant when amounts are considered; however, in this case fatty alcohol sulfates (FAS) not only have ecological advantages but also technical application advantages. In particular, differences in performance are evident in combination with various builder systems. In contrast to phosphate-containing washing agents, FAS in zeolite-containing forrnulations can attain at least the washing performance of LAS or can even exceed it. As well as the washing effects, the performance characteristics of a washing agent are continually increasing in importance. A powder-form washing agent should not produce dust, should always have good pourability and be easy to dose in. Even under these aspects FAS has clear advantages over LAS because of its crystalline properties. (11)

Cocomonoglyceride sulfate (CMGS) (12)
Cocomonoglyceride sulfate has been known for a long time and has already been used in isolated products. However, the normal manufacturing methods have various disadvantages such as high production costs, the use of solvents or large amounts of secondary products and, as a result, a product quality which is not optimal. In a newly developed manufacturing process CMGS is obtained directly from coconut oil in a solvent-free two-stage process. In the first stage technical-quality cocomonoglyceride is obtained by simple transesterification of coconut oil with glycerol in a molar ratio of 1:2. A product mixture is obtained which apart from mono- (46%), di- (32%) and triglyceride (7%) still contains 10% free glycerol. This pure vegetable raw material is continually converted to CMGS with S03 gas (1-8% v/v in air or nitrogen) in a falling-film reactor without additional purification. The raw product is then neutralised with aqueous sodium hydroxide using a buffer if necessary; a certain amount of sodium sulfate (Na₂SO₄) is formed. If required, the salt present in the product can be reduced by membrane filtration. The membranes which are used are offered as tube modules and have small pores which allow dissolved substances with a low molecular weight (such as sodium sulfate) to pass (permeate) but retain substances with a high molecular weight and undissolved substances (retentate). It has proved to be particularly advantageous that anionic surfactants such as CMGS form larger surfactant aggregates (micelles) in aqueous solutions. These CMGS micelles are retained by the membrane and therefore remain in the retentate. The use of this solvent-free method allows any sodium sulfate content including a completely salt-free product to be achieved.

Because of its technical application properties CMGS is predestined for use in cosmetic products such as shower gels and foam baths or shampoos. Here it can be seen that CMGS in comparison to ether sulfate, the standard surfactant for this application, has a similar good foaming power. Combinations of alkyl polyglycosides (APG) and CMGS, in which CMGS acts as foam intensifier, are particularly interesting. The CMGS/APG mixtures additionally show an adequate thickening ability. An acceptable viscosity is already achieved with 10% solutions without the addition of co-surfactants by using small amounts of sodium chloride. In dermatological tests for skin compatibility (epidermis swelling test) CMGS proved to be considerably less of a skin irritant than ether sulfate or other anionic surfactants such as sulfosuccinates. It is comparable to a - very mild to the skin oleylmethyltauride. In the test for investigating mucus membrane irritation (HETCAM) CMGS proved to be more compatible than ether sulfate, with even better results being achieved than with the combination of ether sulfate with a betaine (cocoamidopropylbetaine) which is known to be compatible with mucus membranes. By mixing with alkyl polyglycoside the skin compatibility of CMGS, which is already good for an anionic surfactant, can be improved still further.

Protein-fatty acid condensates (13)
In the development of the protein-fatty acid condensates it was possible to combine the renewable resources fatty acids (from vegetable oil) and protein, which can be obtained from both animal waste (leather) as well as from many plants, to construct a surfactant structure with a hydrophobic (fatty acid) and a hydrophilic (protein) part. This was carried out by reacting protein hydrolyzate with fatty acid chloride under Schotten-Baumann conditions. Products were obtained which had an excellent skin compatibility and additionally had a good cleaning effect - particularly on the skin - and in combination with other surfactants led to an increase in performance. The fact that even small additions of the acylated protein hydrolyzate improve the skin compatibility of other surfactants out of all proportion is important from a technical formulation point of view. An explanation for this protective effect could lie in the amphoteric behaviour of the product. There is an interaction between the protein-fatty acid condensate and skin collagen. This leads to the formation of a protective layer, which reduces the excessive attack of surfactants on the upper layers of the skin, their strong degreasing effect and the direct interaction of anionic surfactants with the skin. In the cosmetic branch protein-fatty acid condensates are chiefly used in mild shower and bath products, mild shampoos, surfactant-based face cleansers, cold-wave preparations and fixatives or surfactant preparations for babies.

Perspectives
With the examples of recent product innovations from the oleochemical sector the successful development of environmentally compatible and powerful products in the sense of an sustainable development has been demonstrated. Where do we go from here?

It can be assumed that in future further possibilities for using renewable resources will continue to be sought for in an ever-increasing manner. As far as the development of new raw materials is concerned, Henkel is involved with plant breeders and government agencies within the framework of government sponsored projects in the realisation of new oils which, because of their optimised fatty acid composition, will satisfy the requirements for industrial use in a better manner. An example worthy of being mentioned is sunflower oil with a high content of oleic acid (> 85%) and a low stark acid content. How the breeders' successes, the yields in individual regions and therefore the economic efficiency of industrial use will turn out to be remains to be seen.

The combination of various vegetable raw materials to form new products will also be a challenge for research and development in future. Two examples of such combination products have been described: alkyl polyglycosides and protein-fatty acid condensate. We ourselves believe that a great potential for further development work exists here. We are also still confronted by the question as to how more use can be made in future of domestic raw materials - particularly domestic oils and fats - for industrial applications. From our point of view basic investigations into the use of new long-chain fat derivatives as surfactant raw materials are necessary in this respect and, in order to provide the necessary stimulus, also worthy of being sponsored. Without sponsorship it will be difficult to move the focal point of surfactant development away from the lauric oils towards long-chain oleochemical raw materials.

(APG is a registered trademark of the Henkel group)

References

1. a) Baumann, H., Buhler, M., Fochem, H., lIirsinger, F., Zoebelein, H., Falbe, J.: Natural Fats and Oils - Renewable Raw Materials for the Chemical Industry, Angew. Chem. Int. Ed. Engl. 27 (1988), 41; Angew. Chemie 100 (1988), 41.
   b) Hovelmann, P., Brackmann, B., INFORM 9 (1998), 800.
2. Eierdanz, H. (Ed.): Perspektiven nachwachsender Rohstoffe in der Chemie, VCH, Weinheim, 1996.
3. Kreienfeld, G., Stoll, G.: Surfactants in Consumer Products and Raw Material Situation - A Brief Survey. In: Hill, K., von Rybinski, W., Stoll, G. (Eds.): Alkyl Polyglycosides Technology, Properties and Applications, VCH, Weinheim, 1997, p. 225.
4. Robbelen, G.: Pflanzliche Ole als Rohstoffbasis - Potential und Veranderungen in der Verfugbarkeit. In: Tagungsband 3. Symposium Nachwachsende Rohstoffe - Perspektiven fur die Chemie, Schriftenreihe des Bundesministeriums fur Ernahrung, Landwitschaft und Forsten, Landwitschaftsverlag, Munster, 1994, p. 115.
5. Steber, J.: Wie vollstandig sind Tenside abbaubar?, Textilveredlung 26 (1991), 348.
6. a) Falbe, J. (Ed.): Surfactants in Consumer Products: Theory, Technology, Applications, Springer, Heidelberg, 1987.
   b) B. Davis, Chemical Week 1/98, 27.
7. Knaut, J., G. Kreienfeld: Alkyl Polyglycosides. A New Surfactant Class based on Renewable Raw Materials, Chimica Oggi 1993, 41.
8. a) Hill, K., von Rybinski, W., Stoll, G. (Eds.): Alkyl Polyglycosides -Technology, Properties and Applications, VCH, Weinheim, 1997.
   b) von Rybinski, W., K. Hill: Alkyl Polyglycosides - Properties andApplications of a new Class of Surfactants, Angew. Chem. Int. Ed. 37 (1998), 1328; Angew. Chem. 110 (1998), 1394.
   c) K. Hill, O. Rhode: Carbohydrate-based surfactants, Fett/Lipid, submitted for publication.
9. Stalmans, M. et al.: European Life-Cycle Inventory for Detergent Surfactants Production, Tenside Surf. Det. 32 (1995), 84.
10. Hirsinger F.,13unzel, F.: Okobilanz von Fettalkoholsulfat - Petrochemische versus oleochemische Rohstoffe. In Ref. [2], 228.
11. Schmid, K.: Tenside aus nachwachsenden Rohstoffen fur Wasch- und Reinig,ungsmittel. In Ref. (2), p. 41.
12. a) Behler, A., Hensen, H., Vier, J.: Kokosmonoglyceridsulfat - ein Aniontensid fur kosmetische Formulierungen, FettlLipid 98 (1996), 309.
    b) Behler, A., Hensen, H., Vier, J.: Cocomonoglyceride Sulfate - An Anionic Surfactant for Cosmetic Formulations, Henkel Referate 33 (1997), 7.
13. a) Sander, A., Eilers, E., Heilemann, A., von Kries, E.: Herstellung und Anwendungs- moglichkeiten von EiweiRFettsaurekondensaten, Fett/Lipid 99 (1997), 115.
    b) Sander, A., Eilers, E., Heilemann, A., von Kries, E.: Production and Application of Protein/Fatty Acid Condensates, Henkel-Referate 34 (1998), 14.