Numéro
OCL
Volume 28, 2021
Lipids and Cosmetics / Lipides et cosmétiques
Numéro d'article 16
Nombre de pages 10
Section Technology
DOI https://doi.org/10.1051/ocl/2021003
Publié en ligne 3 mars 2021

© P. Carré, Hosted by EDP Sciences, 2021

Licence Creative CommonsThis is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

1 Introduction

In the world of cosmetics, solvents have a public acceptability problem because they are associated with carcinogenic chlorinated solvents or with petroleum cuts of ill-defined composition which may also contain toxic molecules. Solvents are, at any rate, not anti-natural, and life could not be possible without the ubiquitous solvent known as water. The dogmatic rejection of solvents is not part of the COSMOS standard (COSMOS, 2020) which provides guiding rules for the preparation of cosmetics ingredients based on “organic” material. This allows their use with certain precautions when the physical methods are insufficient to achieve the desired quality. The only clearly stated prohibition concerns petroleum-based solvents. As part of the processing of vegetable oils, the conditions to be met for the use of solvents are as follows:

  • The solvent must come from renewable materials,

  • Its manufacture must comply with the green chemistry charter,

  • No product derived from GMOs must have been used to ensure its production

  • The solvent must not be toxic,

  • No residue should be found in the oil,

  • It must not harm the health of the workers who use it.

1.1 Regarding the limits of mechanical extraction

Mechanical extraction of vegetable oils is the preferred physical process for so-called “organic” oils because this process enables simple and relatively efficient extraction. More often, suppliers try to obtain oils by cold pressing to preserve the organoleptic quality of the oils, which in oils for cosmetic purposes means reducing odour uptake and preserving a relatively light colour (Matthäus and Spener, 2008). In general, this solution is satisfactory and provides access to a very wide range of good quality lipids as it is the case for argan oil (Matthäus, 2013).

However, this solution has several disadvantages which penalise certain specialty oils. The first of these limitations concerns the extraction yields of seeds with low oil content. Some important sources for cosmetics – such as Rosa mosqueta oil – are seeds with an oil content not exceeding 10%. In this case, it is difficult to obtain high extraction yields because screw presses rarely produce cakes with less than 5–6% oil (Savoire et al., 2013). Take the case of the rosehip, the seeds of which can be worth up to 2.5 €/kg and contain only 7% oil. Assuming that cold pressing yields 4 kg of oil per 100 kg of seeds – which is a rather optimistic yield (Topkafa (2016) reports a yield of 3.1% using an Ecotok press) – it takes 62.5 € of seeds to produce 1 kg of oil. When processing the same seeds using solvent extraction, we could obtain around 6.8 kg of oil for 100 kg of seeds at the OLEAD extraction plant with a continuous counterflow extractor. That yield reduces the cost of seeds per unit mass of oil to 36.8 €/kg. By adding to the cost of the seeds that of an extraction process evaluated at  500 €/t of crushed seeds, we can estimate that the cost of virgin oil would be 75 € per kilogram (if virgin oil cost = cost of the seeds + cost of the processing). As an assumption, we can therefore estimate that virgin oil cannot be worth less than 75 €/kg. Oil from solvent extraction will probably be discounted in comparison to virgin oil; if we apply a discount of 10%, the resulting estimated cost will be 67.5 €/kg.

As a result, by producing virgin oil with one ton of seed, we can produce 40 kg of oil with a total value of 3 000 € while with solvent extraction, we would produce 68 kg of oil with a total value of 4590 €: the purchasing cost of the seed is 2500 €/t, and the extraction and refining process 2090 €/t, with refining being made necessary for complete elimination of the solvent. According to our experience acquired within the CREOL then OLEAD1 unit, this amount may be realistic in the context of a unit working with a green solvent on a small scale (< 400 kg/h of seeds) provided that we are able to operate this unit for a sufficient period of time throughout the year.

1.2 Benefits of solvent extraction

The ability of solvent extraction to better extract lipids is a factor in reducing ecological impacts when the raw material comes from endemic wild species because it requires less consumption of raw material for the same amount of oil produced. It also has the benefit of an improved extraction of polar lipids like phospholipids, glycolipids, monoacylglycerol, which are of great interest in cosmetic products (Ghazani et al., 2014). Cold pressed oils are generally free of phospholipids due to the method of extraction. As a result, they are less rich in minor compounds like tocopherols and phytosterols which are partly linked to the cell membranes where the phospholipids are located (Prior et al., 1991).

Finally, in the case of matrices poor in oil and rich in lignified fibers (rosehip, passion fruit, grape, prickly pear seeds for example), it is impossible to obtain good yields of oil without a significant increase in the temperature during pressing. Venkitasamy et al. (2014), for example, obtained the best oil yields on grapeseed in a Komet press at temperatures between 130 and 140 °C. This increase in temperature can result in a loss of quality since high temperature promotes colour darkening, oxidation and degradation of antioxidant molecules (Choe and Min, 2006). In comparing the sensory quality of dehulled and undehulled sunflower cold pressed oils, Raß et al. (2008) found that dehulling improved the sensory quality, eliminating a bitter and woody taste that would otherwise be present. With oils that are very sensitive to oxidation such as flaxseed, pomegranate, chia, etc., high temperature can promote the oxidation of lipids. Thus, contrary to popular belief, a solvent extraction can often result in oils that are more interesting from the point of view of richness in micronutrients and oxidative stability.

2 Ethanol as an extraction solvent

Starting in 1927, ethanol was first employed as an extraction solvent in its first semi-industrial application in Manchuria, when the Central Laboratory of the South Manchuria Railway Company commissioned a project to extract soya oil with ethanol (Hron et al., 1982).

The disadvantages of using ethanol for lipid extraction are:

  • This solvent is completely miscible with water, unlike hexane, which is used for conventional oils. It is therefore likely to become mixed with water on contact with plant material.

  • The oil is poorly soluble in this solvent and its solubility depends on both the water content of the solvent and its temperature. For example, Rao et al. (1955) found that crude soybean oil maximum solubility at 40 °C in ethanol with 0%, 4.5% and 8.5% of water was 10.6, 4.2 and 2.4 g/100g and at 60 °C: 27.0, 7.5 and 4.2 g/100g respectively. Consequently, with a solvent close to the azeotropic concentration, more solvent is required to dissolve the oil to be extracted than in the case of hexane.

  • It forms an azeotrope with water which makes it difficult to obtain a 100% pure solvent during distillation. Moreover, the distillation in the presence of water is much more energy-intensive than the simple evaporation of hexane. This relates more particularly to the desolventization of the meal. In the case of hexane, it is possible to use direct steam to completely remove the solvent residues from the cake, but in the case of ethanol, this water vapor will mix with the solvent and require a distillation step with a large reflux of condensates to reach the azeotrope concentration. It is therefore necessary to employ rectification columns, which represent sizable capital costs and energy consumption. To avoid introducing water into the system, it is necessary to dry the oil-bearing material to less than 3% water, and this adds a significant energy cost (Hron et al., 1982).

However, these disadvantages are outweighed by many advantages:

  • Ethanol is a solvent produced by renewable biological processes,

  • The solvent has all the required authorizations and is available at low cost.

  • This solvent is often used in cosmetic products and the presence of residues in this case does not raise the same concerns as for residues of solvents such as hexane.

  • Its vapors are considered to be much less harmful to workers than hexane vapors.

  • The separation between oil and solvent does not require evaporating all of the miscella. The low oil/ethanol miscibility can be used to precipitate oil from miscella by reducing its temperature. This produces a heavy phase with more than 90% oil and a so-called “lean” miscella phase with less than 1–2% oil (Beckel et al., 1948). This lean miscella can undergo another extraction procedure involving a membrane separation step to recover the polar lipids it contains.

  • Ethanol extracts polar lipids and minor compounds that are of interest in cosmetics (glycolipids, phospholipids, phytosterols, tocopherols, phenolic, …) much better than hexane does (Moreau et al., 2003).

  • Ethanol makes it possible to extract non-lipidic compounds, especially phenolic compounds which may be of interest for cosmetic applications and also to reduce the colour and bad taste of delipidated flours (Johnson and Lusas, 1983; Kuk and Hron, 1998).

The first large-scale study2 that we carried out on the use of ethanol as an extraction solvent is a study which aimed to test a process proposed by the company Alfa-Laval based on a solid-liquid separation by means of hydrocyclones. The original idea was to compensate for the low solubility of the oil in the solvent by working at temperatures above the boiling point of the solvent. This is not possible in conventional extractors which all operate by percolating liquid under atmospheric pressure. For this, Alfa-Laval proposes to reduce the matrix (that will undergo extraction) to the form of a fine powder (50–200 μm) so as to form a suspension, the separation of which would be achieved in small cyclonettes arranged in large numbers in devices such as the one in Figure 1. The advantage of this device, besides requiring less solvent, is to accelerate the diffusion of oil. Indeed, the diffusion is linked by an exponential relation to the size of the particles according to the equation (1). (1)

  • E: extraction rate (oil extracted/extractable oil) (%);

  • Deff: Diffusivity coefficient (m2s−1);

  • r: Particles radius (m);

  • t: time (s).

In consequence, it becomes possible to run the unit at high capacity with equipment of limited scale, and to restrict the time that proteins and ethanol are in contact, thereby lessening the impact on their solubility. The Deff values depend on the matrix and on the extraction conditions, including temperature. In the best scenario, contact times of less than 2 minutes are sufficient to extract 95% of the oil contained the solid particles of less than 100 µm in comparison to nearly 20 minutes for conventional flakes of material.

A cascade of cyclonettes, would facilitate a countercurrent extraction according to the diagram in Figure 2. The figure shows the presence of two clarification stages and the presence of a horizontal centrifuge decanter. These devices are made necessary by an imperfect quality of separation of the hydrocyclones which decompose the suspension between an overflow still containing 2 to 10% of particles and an underflow which must remain sufficiently rich in liquid to make it possible not to clog the cyclonettes with too much solid. The clarification cyclonettes thus serve to eliminate the residual particles to a level close to zero in the miscella, which itself must then be cooled and decanted for oil recovery. At the other end of the line, the centrifuge decanter has to dry the spent solid which then proceeds to the desolventizer, holding the least possible amount of liquid to limit the energy required to remove it.

Upstream of this installation, there must be a drying unit to remove unwanted water in the system as indicated above and a grinding unit in the solvent whose function is to reduce the material to the desired particle size. Heat exchanger systems are required at the inlet and outlet of the flows to limit the heat flow: the heat from the outgoing flows serving to warm up the incoming flow. The liquid phase after cooling is fractionated into a oily rich phase which goes on to a stripping step to recover the contained ethanol residue and an ethanolic phase returned to the extractor. The meal has to be desolventized under vacuum without using steam, which would cause protein heat damage (Salazar-Villanea et al., 2016) and reintroduce water into the solvent.

The totality of these steps is presented in the diagram of Figure 3. The performance of this process was simulated on a laboratory scale by working at approximately 90 °C with 95% ethanol in a Nutsche filter on a partially mechanically defatted dehulled rapeseed cake. The device was used to follow the extraction kinetic (evolution of oil concentration in the miscella with the time) and to simulate a multistage extraction. A typical experiment required a Silverson L5M-A high-shear laboratory mixer; an agitated Nutsche filter (POPE Scientific Inc., Saukville, WI) of total capacity 2.78 L, equipped with a stainless steel 20 µm mesh; a 5L boiler on a scale for the solvent pre-heating equipped with a chamber for the introduction of oil in the solvent prior to extraction and a heating circulator (Huber Kiss 212B) ensuring the temperature regulation of the Nutsche filter. The prepressed rapeseed was dispersed thanks to the high shear disperser (room temperature, 175 g of press cake in 3.5 kg of solvent added with 75 g of oil, 10 000 rpm, 5 min). The liquid was then poured in the preheated filter and 525 g of new solvent preheated at 110 °C was added with 75 g of oil. When the temperature of the mixture was reaching 90 °C, 750 g of miscella was subtracted letting 350 g of liquid in the filter to simulate the solid ratio found in the heavy phase of cyclonettes (underflow). After removal of this miscella, a new quantity of solvent and oil were directed into the filter for further extractions. The added masses of oil were 75, 12, 4, 2 and 0 g for the washes 1, 2, 3, 4 and 5 respectively to simulate the decreasing oil concentration of the miscella used in each counterflow steps. The results obtained demonstrated a more efficient extraction of polar lipids and therefore a more thorough extraction of the fats than with the hexane in the same conditions. A whitening of the delipidated flour and a reduction in its bitterness were also observed concomitantly with a significant reduction in protein solubility linked to the dehydration effect caused by ethanol (Kalaydzhiev et al., 2020). In the lipid fraction, a partitioning effect was observed during decantation leading to the concentration of triglycerides in the heavy phase while most of the lipids bearing OH groups were present in the solvent phase as illustrated in Figure 4 (Citeau et al., 2018).

To exploit this effect, it is envisaged to recover the polar lipids after concentration of a fraction of the lean miscella. This concentration would use the heat of the vapors produced by desolventization of the cake. The resulting concentrated miscella would then be fractionated by ultra-filtration on membranes and by using the solubility differentials. The potentially obtainable purified fractions are expected to be rich in phospholipids, tocopherols and sterols, free fatty acids, mono and diglycerides, polyphenolic compounds and finally carbohydrates and other non-lipid compounds.

Using the results of the laboratory study, a computer model was developed (1) to predict the flow of material in a 160 kt/year rapeseed processing unit, and (2) to estimate the process costs. The simulation was performed using an Excel spreadsheet. The solution used to avoid iterative calculation problems was to open the circular calculation loops and use Excel’s solver function to find the values allowing to balance the flows taking into account the constraints of the system such as mass balance, saturation concentration of oil/solvent. To estimate the process costs, an approach was used which consisted in evaluating the capital costs based on the cost of the main equipment, using Lang factors to estimate their cost when installed and surrounded by the various utilities. The variable costs could be estimated on the basis of the energy costs calculated via simulation. The estimated costs are nearly € 50/t of processed seed (Tab. 1) (Carré et al., 2018).

thumbnail Fig. 1

Cyclonette (right) and plate device grouping many cyclonettes for industrial solid/liquid separation (courtesy of Alfa-Laval).

thumbnail Fig. 2

Flowchart for a counterflow extraction system using 5 steps of solid/liquid separation and using two clarifying stages for the miscella and a centrifuge decanter for dewatering the spent solid (courtesy of Alfa-Laval).

thumbnail Fig. 3

Flow-chart of the hydrocyclone counterflow extraction system using pressurised ethanol as solvent.

thumbnail Fig. 4

Proportion of lipid fractions in the “lean miscella” or supernatant fractions resulting from the cooling of the miscella (ethanolic extract of cold pressed rapeseed obtained at 90°C) at 3decantation temperatures.

Table 1

Estimate of processing costs for a 160 kt/year rapeseed processing unit using the pressurised ethanol extraction process (Carré et al., 2018).

3 Project to deacidify fragile oils by fractionation in ethanol

This project3 was initiated by OLEAD, faced with a problem regarding the fruit oils sector and more particularly walnut oils. The walnut oils sold on the French market are mainly oils obtained from a mixture of refined oils and virgin oils. Refined oils are usually obtained from second-grade nuts which have gone through various separation processes during which the kernels can be contaminated with phthalates and can sometimes reach significant acidity. To deal with this problem, refining is usually done by the process of physical deacidification during deodorisation (information communicated by the Union Producers of Oils with Taste of France, FRUITOL). The problem is that in order to properly remove phthalates, it is necessary to heat the oils to fairly high temperatures (240 °C), which can cause the formation of unwanted compounds such as the 3MCPD esters (mono-chloro-propane-diol) and glycidyl esters and induce cis/trans isomerization of polyunsaturated fatty acids (Hénon et al., 1999; Hrncirik and van Duijn, 2011). For this reason, OLEAD has proposed using liquid/liquid extraction in ethanol to lower the acidity of oils and reduce their phthalate concentration.

The process consists in bringing food grade ethanol into contact with the crude oil in a stirred tank and then allowing the mixture to settle to recover an ethanolic supernatant enriched in polar lipids and contaminants (phthalates) and an oily phase containing around 10% ethanol. With a given walnut oil containing 5.8% free fatty acids, different concentrations of ethanol and water were tested at a temperature of 27 °C (room temperature) and several washes with a solvent oil ratio of 1:2 (m/m) were carried out, thereafter allowing the mixture to settle at 7 °C (cold-room) overnight. An example of the free fatty acid extraction yields is shown in Figure 5. This graph presents the progressive reduction of the free fatty acids content of a walnut oil when mixed with 2 kg of solvent (for 1 kg of oil) for a total of 3–4 repetitions of this mixing. It can be seen from this figure that the lower the water content of ethanol, the better the acid extraction. However, as shown in Figure 6, the lower concentration of water in the solvent results in a greater retention of neutral lipids in the solvent fraction. It turns out that the best trade-off is obtained using solvents with between 82.8 and 88.6% ethanol (Bou Orm et al., 2020).

Regarding the removal of phthalates: when walnut oil was spiked with 116 ppm of butyl-benzyl-phthalate, the extraction yield was 90% after 3 washes with the oil/solvent in a 2:1 ratio.

Complementary work has been carried out to reduce the volumes of solvent to be used by working at countercurrent in a multistage device. This work was carried out with a batch of oil that is less acidic than in the previous case (3.2%). The device used presented in Figure 7 comprised 4 stages which allowed the static settling of the mixtures and contacting via static mixers after passing through peristaltic pumps. The residence time in the settlers was of the order of 10 minutes.

This process proves to be effective, making it possible to achieve residual acidities of the order of 0.2% from a 3.2% initial oleic acity, but as a result of a relatively short settling time, the losses of neutral oil were not below the desired level: approximately 6% of oil was lost while according to our previous experiences, losses of a little more than 4% should have occurred. The reason for these losses is probably the short settling time, which failed to achieve the separation quality of static systems with long duration. This problem could be reduced by using centrifuges, but because this equipment is expensive, it is more realistic for a small-scale unit to opt for larger settling volumes compared to experimental ones (results to be published in an article in preparation).

thumbnail Fig. 5

Effect of ethanol content of the ethanol-water solvent and the number of extraction steps in the free fatty acids extraction at room temperature with 2:1 ration solvent/walnut oil (masses) in liquid/liquid extraction of acid walnut oil.

thumbnail Fig. 6

Evolution of the oil losses as a function of the solvent concentration in ethanol and the number of extraction steps (Solvent/oil 2:1 ratio, room temperature) in the liquid/liquid extraction of acid walnut oil.

thumbnail Fig. 7

Diagram of a 4-stage countercurrent extraction device including static decanters and blenders.

4 Use of 2-methyloxolane (EcoXtract®) as an extraction solvent

2-methyloxolane is a solvent derived from the recovery of non-food plant biomass (sugar cane bagasse or corn cobs). It is produced by the chemistry of pentoses which undergo initial reducing treatments resulting in the production of furfuraldehyde which then undergoes hydrogenation to 2-methyloxolane (MeOx) (Fig. 8) (Alcantara and de Maria, 2018).

According to the company Pennakem LLC. (Memphis, USA), which produces this solvent, it has a carbon footprint that is significantly lower than that of fossil-carbon-sourced solvents. The main characteristics are a boiling point of 80 °C, a flash point of −11 °C, a specific gravity at 20 °C of 0.855. Compared to hexane, it has a certain miscibility with water. Up to 14% of the solvent can be dissolved in water and the solvent can contain up to 4.4% water (20 °C). This partial miscibility with water introduces certain constraints to which we will return later. MeOx is a very good solvent which can, as a result, act on many polymers. It is therefore necessary to take precautions in its implementation by checking its compatibility with the elastomers with which the seals are made. It also presents a risk of formation of hydroperoxides during storage, which means that it must be stored with antioxidants. Finally, it should be noted that it is very fragrant (ether odour) which in a way improves its detection and avoids the occurrence of handling errors; any insufficiently desolventized product can be detected by its scent.

The affinity of the MeOx solvent was evaluated by Anne-Gaëlle Sicaire (Sicaire et al., 2015a) using Hansen’s solubility parameters. This approach characterises molecules according to 3 parameters:

  • δd: Force of dispersion between molecules (London);

  • δp: Dipolar intermolecular force;

  • δh: Hydrogen bond between molecules.

The compatibility of a solvent and a solute can be evaluated by determination of the relative energy difference (RED) between these compounds and this is estimated by calculating their distance in the parameter space defined by the axes δd, δp and δh. Table 2 shows the values of the Hansen parameters and average RED of some lipids vis-à-vis hexane and MeOx. The lower the value of RED, the stronger the proximity between the solvent and the solute.

The data in Table 2 show that according to the Hansen parameters, which characterise a method based on the rule “like dissolves like”, 2-Methyloxolane is a solvent closer to most lipids than hexane, except for waxes. That means that in theory, n-hexane is not the best solvent for the dissolution of oils and that MeOX molecules interact better with most of lipids molecules.

As part of her thesis work, Anne-Gaëlle Sicaire also compared the degree of affinity of MeOx for lipids with the one of various solvents such as cyclopentyl-methyl-ether (CPME), dimethyl-carbonate (DMC), isopropanol, ethanol, ethyl-acetate, p-cymene and d-limonene using Cosmos-RS, a powerful software program that simulates the electronic states on the surface of molecules in order to predict their interactions (Sicaire et al., 2015b). The result of these simulations also led to classifying MeOx as the solvent having the best characteristics for solubilizing common fatty substances. These data have been confirmed by experience, the solvents being compared in a Soxhlet apparatus for measuring the extraction kinetics, yields and oil quality. With the kinetics data obtained by extracting rapeseed prepress cakes and the characterization of the material particle size, Sicaire determined the diffusivity coefficients (Deff) of MeOx and hexane, obtaining the respective values of 12.2 × 10−12 and 3.3 × 10−12 m2s−1 – which means that MeOx diffuses almost 4 times faster in the matrix than hexane does. This difference would be explained by a lower hydrophobicity allowing it to more easily cross cell walls rich in cellulose.

In terms of the composition of the oils, Sicaire found a great similarity in composition between the oils obtained from hexane and the oils obtained with MeOx both in terms of fatty acid profile and in terms of minor compounds (tocopherols, phytosterols). Regarding the colour of the oils it was observed that MeOx produced darker oils than hexane but this colour difference tended to disappear during refining. Figure 9 shows soybean and rapeseed oils as crude oil, after bleaching and after deodorisation. For soybeans, the oil was obtained by direct extraction, whereas for rapeseed, the crude oil was a mixture of press and extraction oils. Thanks to a method developed in the ITERG analytical lab, the MeOx residues in oils, meal, and co-products can be measured. Table 3 presents the results of a comparison test carried out in our pilot plant where a commercial batch of rapeseed press-cake was divided into two sub-batches of 70 kg to be extracted with technical hexane or with MeOx. The press cakes were prepared by cold-pressing (MBU20 press, Olexa) and contained 22.8 g of oil for 100 g of dry matter. The extractions were carried out in a 480L Nutsche filter (Guedu-de Dietrich ML500) using 2.5 kg of solvent for 1 kg of initial cake at 50 °C during 15 min. These extractions were made with 3 successive washes in the same conditions. The resulting oils were refined by phosphoric acid conditioning, followed by alkali neutralization, washing to remove the residuals soaps and the caustic soda excess, drying, bleaching with Tonsil 210 FF and deodorisation at 180 °C, 2–3 mbar, and steam sparging. The refined oils show similar composition in phytosterols concentration, free fatty acids content (FFA), peroxide value (PV), anisidine value (AV) and solvent residues. For the EcoXtract® (MeOx) sample, a larger concentration of tocopherols was found but in the context of this study, it was not possible to rule out a possible contamination of the sample via the solvent which may have been protected against oxidation with tocopherols.

thumbnail Fig. 8

Production of 2-methyloxolane from hemicellulose-rich biomass (summarized).

Table 2

Comparison of the Hansen parameters and RED values between n-hexane and MeO and a selection of important lipid classes (Sicaire et al., 2015a).

thumbnail Fig. 9

Oil appearance. a) crude oils, b) alkali neutralised and bleached oils, c) neutralised, bleached deodorised oils. SH: soybean hexane extracted; SM, soy MeOx extracted; RH: rapeseed hexane extracted; RM Rapeseed MeOx extracted.

Table 3

Main characteristics of two refined rapeseed oils obtained from hexane or 2-Methyloxolane extraction (EcoXtract®).

5 Conclusion

Ethanol has three main advantages: of the three solvents, the lowest toxicity for humans4; ease of production from renewable products; good acceptance by consumers who consume it in their diet and use it in certain body care products. On the other hand, it is quite disadvantageous as regards miscibility with water and affinity for lipids. This can be turned to advantage if used in a clever way, either via a temperature variation to precipitate lipids after extraction, or by using it to split lipids between neutral lipids and polar lipids. This possibility could be adapted to the production of lipid concentrates of interest, starting from oils intended for uses for which they are not normally valorised as in the case of biofuels. What most certainly penalises ethanol is the energy cost of its implementation, especially when rectification is necessary.

The strong point of hexane, which makes it currently the solvent of choice for crushers, is its low cost of implementation which results, on the one hand from its almost total lack of miscibility with water and, on the other hand, its low latent heat of vaporization; this low latent heat promotes easy recycling and consumes little energy. Its hydrophobicity greatly reduces the presence of undesirable compounds in the oil and makes efficient refining possible. However, it has a serious lack of acceptability linked to its bad reputation as a petroleum product, its toxicity, and the fact that it originates from a non-renewable resource.

EcoXtract®, the trade name for 2-methyloxolane, is a solvent that could be substituted for hexane (with which it shares a high affinity for oils) while being renewable, less toxic, and easier to recycle than ethanol, in particular regarding the proteins fraction. Its main weakness is its cost of implementation because it is more expensive to purchase and because it requires slightly more complex installations to deal with its partial miscibility with water – thus making its recycling more difficult than hexane. Another delicate point regarding this solvent is its acceptability to the general public, who view any novelty with suspicion, and this will require a great deal of caution in the early stages of its development.

Regarding the oils used in cosmetics, ethanol offers interesting possibility for their fractionation, especially for the concentration of active molecules (polar lipids, micronutrients) or the removal of undesirable ones (phthalates). EcoXtract® as extraction solvent has the potential to enable better use of materials sourced from wild species by improving the extraction efficiency and decreasing the volumes taken from the nature.

Conflict of interest

Studies carried out on 2-methyloxolane by OLEAD (pilot plant studies) were funded by the Pennakem Company when the author was R&D manager of OLEAD.

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1

CREOL was a small commercial company running a pilot plant dedicated to the processing of oilseeds. It became OLEAD in 2016 when ITERG brought its refining plant to it. The solvent extraction plant is currently at a standstill but will resume service next year as part of a new venture.

2

PROVEGAL project funded by the French Agency for the Research ANR13-ALID-0003-01.

3

DEACOL project funded by a grant from the French Ministry of agriculture (CAS-DAR 2015).

4

NOAEL: 1730, 23, 250 mg/kg for ethanol, n-hexane, 2-Methyloxolane respectively. Sources: for ethanol: ECHA (registration Reach); for n-hexane: European Commission (1996); for MeOx: Rapinel et al. (2020).

Cite this article as: Carré P. 2021. About solvents used in the preparation of oils for cosmetic products complying with the Cosmos standard. OCL 28: 16.

All Tables

Table 1

Estimate of processing costs for a 160 kt/year rapeseed processing unit using the pressurised ethanol extraction process (Carré et al., 2018).

Table 2

Comparison of the Hansen parameters and RED values between n-hexane and MeO and a selection of important lipid classes (Sicaire et al., 2015a).

Table 3

Main characteristics of two refined rapeseed oils obtained from hexane or 2-Methyloxolane extraction (EcoXtract®).

All Figures

thumbnail Fig. 1

Cyclonette (right) and plate device grouping many cyclonettes for industrial solid/liquid separation (courtesy of Alfa-Laval).

In the text
thumbnail Fig. 2

Flowchart for a counterflow extraction system using 5 steps of solid/liquid separation and using two clarifying stages for the miscella and a centrifuge decanter for dewatering the spent solid (courtesy of Alfa-Laval).

In the text
thumbnail Fig. 3

Flow-chart of the hydrocyclone counterflow extraction system using pressurised ethanol as solvent.

In the text
thumbnail Fig. 4

Proportion of lipid fractions in the “lean miscella” or supernatant fractions resulting from the cooling of the miscella (ethanolic extract of cold pressed rapeseed obtained at 90°C) at 3decantation temperatures.

In the text
thumbnail Fig. 5

Effect of ethanol content of the ethanol-water solvent and the number of extraction steps in the free fatty acids extraction at room temperature with 2:1 ration solvent/walnut oil (masses) in liquid/liquid extraction of acid walnut oil.

In the text
thumbnail Fig. 6

Evolution of the oil losses as a function of the solvent concentration in ethanol and the number of extraction steps (Solvent/oil 2:1 ratio, room temperature) in the liquid/liquid extraction of acid walnut oil.

In the text
thumbnail Fig. 7

Diagram of a 4-stage countercurrent extraction device including static decanters and blenders.

In the text
thumbnail Fig. 8

Production of 2-methyloxolane from hemicellulose-rich biomass (summarized).

In the text
thumbnail Fig. 9

Oil appearance. a) crude oils, b) alkali neutralised and bleached oils, c) neutralised, bleached deodorised oils. SH: soybean hexane extracted; SM, soy MeOx extracted; RH: rapeseed hexane extracted; RM Rapeseed MeOx extracted.

In the text

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