Techno-economic evaluation of squalene recovery from oil deodorizer distillates

https://doi.org/10.1016/j.cherd.2019.12.003Get rights and content

Highlights

  • First process simulation of a three step squalene recovery process

  • Comparison between olive, sunflower and soybean ODD for squalene recovery

  • Same process configuration for different feedstocks, ensuring flexibility

Abstract

The potential of squalene recovery from oil deodorizer distillates (ODD) via a combination of supercritical ethanol esterification, supercritical CO2-extraction and additional purification was assessed via detailed process simulations. The squalene yields and purity from olive, sunflower and soybean ODD were determined. The highest squalene yield and purity could be achieved starting from olive ODD (95 gsqualene kg−1ODD, 99 wt% pure), followed by soybean ODD (31 gsqualene kg−1ODD, 98 wt% pure) and sunflower ODD (24 gsqualene kg−1ODD, 98 wt% pure). Apart from squalene, two more value-added products can be produced, i.e., high purity ethyl esters (>88 wt%) and a mixture of tocopherols and sterols. On a scale of 1 kTonneODD per year, all feedstocks demonstrate economical potential in Europe. Even more, a flexible process configuration could be designed which is suitable for the treatment of the different feedstocks.

Introduction

Squalene, a terpenoid hydrocarbon, is an intermediate in the synthesis of phytosterols in plants, the biosynthesis of cholesterol and is used in cosmetics as a moisturizing or emollient agent (Bondioli et al., 1993). The highest squalene concentration is found in the liver of deep sharks from the family Squalidae (Popa et al., 2015). The recovery of squalene from these sharks endangers the subsistence of their kind due to their long reproductive cycle. Particularly in Europe, due to consumer and legislative pressures, there is an increased interest in vegetal squalene resources, especially in the cosmetic industry. The squalene concentration in vegetable oils varies between 9.9 mg/100 g for soybean oil and 564 mg/100 g for olive oil (Popa et al., 2015). However, the concentration is, in most cases, too small for direct separation to be economically viable. Therefore, the so-called oil deodorizer distillate (ODD), i.e., a side-product obtained during the refining of vegetable oils, represents a promising opportunity, as squalene accumulates in the ODD up to 150 times as compared to the original vegetable oil (Popa et al., 2015).

Deodorization of crude vegetable oils removes several undesirable components for the color, taste and stability by steam stripping (Dudrow, 1983). The obtained deodorizer distillate is a complex mixture of free fatty acids (FFA), fatty acid methyl esters (FAME), triglycerides (TG), diglycerides (DG), monoglycerides (MG), phytosterols and their esters, tocopherols, some aldehydes or ketones and hydrocarbons (e.g. squalene) (Laoretani and Iribarren, 2014). As high purity squalene is needed for the food industry, cosmetic industry and in medical applications, new processes were investigated to recover squalene from this sustainable source (Popa et al., 2015). Meanwhile, the upgradation of the other valuable substances present in ODD, such as sterols and tocopherols, was investigated as well (Popa et al., 2015).

The isolation of the ‘minor’ components, i.e. not only squalene but also sterols and tocopherols, by molecular distillation (Posada et al., 2007), countercurrent chromatography (Lu et al., 2003), crystallization (Moreira and Baltanás, 2004), saponification (Copeland and Belcher, 2001) has been earlier reported. The processes developed based on these methodologies have the drawback of being both economically and environmentally expensive, as they make use of organic solvents. Supercritical CO2 represents an interesting alternative. CO2 can be considered a “green solvent” as it is nontoxic, nonflammable, inert, renewable and relatively cheap (Naims, 2016; Sánchez-Camargo et al., 2014). Moreover, it is supercritical already at moderate pressures (7.4 MPa) and low temperatures (304 K), making it attractive for temperature sensitive components (Temelli, 2009).

Various authors have reported the extraction of squalene with supercritical CO2 (sc-CO2) from an ODD without prior ODD treatment. Akgün (2011) attempted such a squalene recovery from olive ODDs. This was, however, nor practical nor economically viable as a result of the long extraction time and low squalene purity (66 wt%). Squalene recoveries up to 95% via sc-CO2 extraction have been achieved by other authors, but at relatively low extraction yields (Chang et al., 2000; Güçlü‐Üstündağ and Temelli, 2007; Hurtado Benavides et al., 2014; Gunawan et al., 2008) or commercially complex process conditions (Al-Darmaki et al., 2012; Sugihara et al., 2010; Mendes et al., 2005; Vázquez et al., 2007). This is the result of the comparable solubility of the FFAs and the squalene in sc-CO2 (Fornari et al., 2008; Torres et al., 2011). To separate squalene more efficiently, a difference in solubility between these components needs to be induced, e.g., by removing or modifying the FFAs. By modifying the latter via esterification, the isolation of squalene can be achieved (Nilsson et al., 1991; de Castro et al., 2012). Simultaneously, the glycerides present in the oil will also react with the alcohol. The transesterification of the triglycerides in rapeseed oil (Kusdiana and Saka, 2001; Demirbaş, 2002), soybean oil (Bertoldi et al., 2009; Diasakou et al., 1998; He et al., 2007), sunflower oil (Demirbaş, 2002; Madras et al., 2004) and linseed oil (Varma and Madras, 2007) at supercritical conditions was already investigated. At such conditions, the thermophysical properties of all components, such as viscosity, density and polarity, are reducing the impact of mass-transfer limitations of the solute in the supercritical solvent, resulting in higher reaction rates even in the absence of a catalyst (Kusdiana and Saka, 2001; Demirbaş, 2002).

Esterified ODDs have mainly been investigated for tocopherol and phytosterol isolation through CO2-extraction (Fornari et al., 2008; Nagesha et al., 2003; Fang et al., 2007; Ito et al., 2005). Fornari et al. (2008) extended the scope towards squalene as a product of extraction of esterified olive ODD (90 wt% purity, 64% yield). Akgün (2011) recurred to an esterification with supercritical methanol of an olive ODD prior to squalene extraction with sc-CO2, resulting in a 75 wt% squalene product. Nevertheless, this purity was still not sufficient for pharmaceutical applications.

Process simulations constitute an alternative to investigate squalene yield optimization and explore technical and economic viability. However, there are still some challenges in simulating complex mixtures, such as ODD, and supercritical conditions. Firstly, significantly different values can be sometimes obtained for the supercritical properties, i.e. the critical temperature, the critical pressure, the critical volume and acentric factor, when using different methods, as incorporated into process modelling software (Lee et al., 2011). Secondly, there is a shortage of well estimated phase equilibria for supercritical extraction or fractionation for the components in this mixture. This renders it difficult to obtain meaningful predictions for multicomponent mixtures, such as ODD.

In this work, detailed process simulations for squalene recovery from three different ODDs via supercritical ethanol esterification followed by a supercritical CO2-extraction are performed via a process simulator. A comparison between olive, sunflower and soybean ODD as a vegetal source for squalene, as an alternative for deep shark liver oil, is established both on technical and economic aspects. Supercritical ethanol esterification is performed first to reduce the FFA content in the ODD, enhancing the squalene extraction potential by sc-CO2. To purify the squalene and other valuable by-products from this two-step process, a separation via flashing and distillation is included and tailored for each of the considered ODDs. After the process design, a simplified economic study is performed and technical solutions to improve the process flexibility are explored.

Section snippets

Simulation methodology and procedures

The simulations were performed using the Aspen Plus® V10 software. The procedure consists of defining representative components (Section 2.1.1), selecting the appropriate thermodynamic model (Section 2.1.2) and selecting the required equipment and operating conditions (Section 3.1.1). For obtaining the mass and energy balances for each unit, the default convergence methods were used. The compressors were assumed to have an isentropic efficiency of 72%, while the pumps were simulated at 80%

Process simulations

The considered process scheme for squalene recovery from ODDs with high purity, is shown in Fig. 1. It comprises three sections for which the relevant unit operations are indicated. In the first section, also denoted as the reaction section, the FFA content was reduced by esterification with supercritical ethanol (EtOH) of the FFAs and glycerides present in the ODDs. Subsequently, squalene was recovered from the obtained mixture in the extraction section. Finally, a more concentrated squalene

Conclusions

Recovering squalene from sunflower, soybean and olive ODD using supercritical ethanol and CO2 was assessed as a sustainable alternative for its recovery from deep shark liver oil. A three-step process was simulated to obtain squalene with purities exceeding 98 wt%. First, a reactive pre-treatment of the ODD with supercritical ethanol was performed. In this step, the concentration of FFA, which exhibits a similar solubility in CO2 as squalene, is reduced. Next, a supercritical CO2-extraction is

Acknowledgements

The authors would like to thank M. Willekens for the contribution on the kinetic modelling work. Financial support was provided by CATALISTI, in the scope of the SUperCritiCal Solutions for Side-stream valorization (SUCCeSS) project (n° 150399).

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