SOLKETAL
Solketal is a protected form of glycerol with an isopropylidene acetal group joining two neighboring hydroxyl groups. Solketal contains a chiral center on the center carbon of the glycerol backbone, and so can be purchased as either the racemate or as one of the two enantiomers. Solketal has been used extensively in the synthesis of mono-, di- and triglycerides by ester bond formation. The free hydroxyl groups of solketal can be esterified with a carboxylic acid to form the protected monoglyceride, where the isopropylene group can then be removed using an acid catalyst in aqueous or alcoholic medium. The unprotected diol can then be esterified further to form either the di- or triglyceride.
Abstract
Commercial solketal is known as AugeoTM SL 191 s which stands out as a slow evaporation solvent derived from glycerin which is considered a renewable source. It has low toxicity to human health and the environment. It is a good solvent for resins and polymers, replacing solvents derived from petroleum, and can be used as an additive of (bio) fuels. This work aimed to study acidy zeolites (H-BEA, H-MOR, H-MFI, and H-FER) as new heterogeneous catalysts of solketal production, through the ketalization reaction of glycerol with acetone. The catalytic activity showed H-BEA > H-MOR = H-MFI > H-FER after 180 min, in kinetics study. The major conversion was 85% for H-BEA. It was also verified that all the catalysts can be reused four times without washing or pretreatment among reactions in batch reactor. The solketal produced in this work was characterized by comparing it with its commercial standard, obtaining very similar characteristics
transformation of glycerol into solketal (isopropylidene glycerol or 2,2-dimethyl-1,3-dioxolan-4-yl methanol) (green solvent) through the ketalization reaction of glycerol with acetone. The reaction for solketal production is facilitated by major homogeneous and heterogeneous acid catalysts (Figure 3). The ketalization of glycerol with ketones generates branched oxygenates, solketal (2,2-dimethyl-[1,3] dioxan-4-yl methanol), and 2,2-dimethyl-[1,3] dioxane-5-ol; however, when the reaction is carried out with acetone, the selectivity is higher for the solketal molecule, which has a five-membered ring [5].
Solketal is an excellent component for the formulation of gasoline, diesel, and biodiesel. it occurs that the output of the remaining acetone and water between 70 and 120°C plus a fraction containing solketal is distilled. Glycerol is only removed when the system reaches 200°C. The yield of the distillation was 60% by mass of solketal over the initial blend (solketal-water-glycerol-traces of acetone). The solketal fraction is colorless but with a lower viscosity than glycerol.
Figure 12 shows the appearance of the solketal GreenTec fraction after distillation of the initial blend.
FTIR analysis was used to confirm the presence of solketal in the distilled product and to compare it with its Sigma-Aldrich standard. The FTIR spectrum of the solketal GreenTec and solketal Sigma-Aldrich samples is shown in Figure 13.
When analyzing Table 4, it is observed that both solketal Sigma-Aldrich and solketal GreenTec present very close densities and viscosities.
Table 5 shows that only in the analysis of humidity a significant difference between the solketal samples was noticed.
Solketal GreenTec presents 56.41% more humidity than solketal Sigma-Aldrich. To remove this moisture, anhydrous sodium sulfate may be added among other drying agents, and/or the solketal GreenTec fraction is withdrawn from 75°C.
Glycerol to solketal transformation is possible to carry out using zeolite acidic catalysts, such as H-BEA, H-MOR, H-MFI, and H-FER, showing a very good activity (conversion 85%) and selectivity (98%). H-BEA presented a larger area, major SAR, and a bigger ratio of the strong:weak sites than the other zeolites. This characteristic contributes to a higher catalytic activity for H-BEA catalyst. All the catalysts can be reused for four times without washing or pretreatment among reactions in batch reactor, but the best catalyst is still the H-BEA zeolite for being more active and showing constant solketal selectivity. The solketal produced in this work was characterized by comparing it with its commercial standard, obtaining very similar characteristics.
Solketal: Green and catalytic synthesis and its classification as a solvent - 2,2-dimethyl-4-hidroxymethyl-1,3-dioxolane, an interesting green solvent produced through heterogeneous catalysis
Most solvents have been labelled as toxic or hazardous substances, but the use of glycerol derivatives could help solve these and other problems. An alternative, green synthesis of 2,2dimethyl-4-hidroxymethyl-1,3-dioxolane (solketal), using solid acid catalysts, has been developed. It is shown that using auxiliary solvents is not essential to get good results, and that the solid catalyst can be recovered and reused, improving the productivity. Moreover solketal has been characterized by determining its polarity and hydrophobicity parameters, which allow identifying possible solvent substitution applications more easily. Abstract
Solvent-free reactions are the systems of choice in green chemistry. In addition to contributing to lowering the environmental impact of chemical processes, solvent-free systems can reduce production costs, reaction times, and the dimensions of reactors, thereby decreasing investment costs. An improved procedure to prepare 2,2-dimethyl-4-hydroxymethyl-1,3-dioxolane (solketal) fatty esters from soybean seeds has been developed. Yields higher than 90% were achieved by combining 15 h of hydrolysis with 6 h of esterification with a stepwise addition of solketal. The synthesis was performed in a solvent-free medium, and the final extraction was accomplished using supercritical CO2 . Hence, we have successfully prepared these esters from soybean beans without using organic solvents. In addition, given the non-toxicity of Rhizopus oryzae and the composition of the remaining solid, it might be used as a raw material for feedstock production.
Applications
Solketal is useful for synthesis of mono-, di- and triglycerides. It is used as the starting reagent for synthesis of tulipaline derivatives. It acts as a fuel additive in gasoline. It is an inhibitor of Methyl ethyl ketone . Notes
Store in cool place. Keep container tightly closed in a dry and well-ventilated place. Incompatible materials are acids, Strong oxidizing agents.
Ketalization of glycerol with acetone to synthesize solketal-a potential fuel additive is one of the most promising routes for valorization of glycerol. In this article, state-of-the-art of glycerol ketalization is reviewed, focusing on innovative and potential technologies towards sustainable production of solketal. The glycerol ketalization processes developed in both batch and continuous reactors and performance of some typical catalysts are compared. The mechanisms for the acid-catalyzed conversion of glycerol into solketal are presented. The main operation issues related to catalytic conversion of crude glycerol in a continuous-flow process and the direct use of crude glycerol are discussed.
Glycerol to Solketal for Fuel Additive: Recent Progress in Heterogeneous Catalysts
Abstract: Biodiesel has been successfully commercialized in numerous countries. Glycerol, as a byproduct in biodiesel production plant, has been explored recently for fuel additive production. One of the most prospective fuel additives is solketal, which is produced from glycerol and acetone via an acetalization reaction. This manuscript reviewed recent progress on heterogeneous catalysts used in the exploratory stage of glycerol conversion to solketal. The effects of acidity strength, hydrophobicity, confinement effect, and others are discussed to find the most critical parameters to design better catalysts for solketal production. Among the heterogeneous catalysts, resins, hierarchical zeolites, mesoporous silica materials, and clays have been explored as effective catalysts for acetalization of glycerol. Challenges with each popular catalytic material are elaborated. Future works on glycerol to solketal will be improved by considering the stability of the catalysts in the presence of water as a byproduct. The presence of water and salt in the feed is certainly destructive to the activity and the stability of the catalysts.
Keywords: fuel additives; biodiesel; glycerol; solketal; solid acid catalysts.
This mini review paper aims to emphasize the potential exploration of catalytic materials for the conversion of glycerol to solketal by analyzing recent papers, especially open literature from after 2010. Rahmat et al. (2010) [15] wrote an overview of glycerol conversion to fuel additives, with an emphasis on reaction parameters (catalyst, reactant, temperature, and reaction time). In the range of 2009 to 2018, Cornejo et al. [16] wrote a review in 2017 on glycerol valorization to fuel additives over different co-reactants. These included second feeds, such as formaldehyde, acetaldehyde, butanal, and acetone, and many others. Nanda et al. [17] published a review on solketal as a fuel additive, with an emphasis on the historical and future context. This paper also summarized the effect of acidity, reactor models, kinetics and reactor kinetics, and the daily procedure to use glycerol to solketal.
Many scenarios were conducted for the conversion of glycerol to different value-added chemicals, such as propane-acrolein, 1, 3-diol, propane-1,2-diol, acetal or ketal, polyols and polyurethane foams, glycerol carbonate, etc. [10,11,18]. Table 1 shows that among these glycerol conversions, the conversion of glycerol to solketal by acetalization is an interesting route. Solketal is one of the glycerol acetalization products together with glycerol acetal and glycerol formal (GlyF). Similar to other acetalization products, solketal can be used directly as a fuel additive for the reduction of soot and gum formation [19]. Solketal addition to a gasoline blend showed better fuel properties with a higher octane number [19]. Other applications of solketal are in solvents, inks, pharmaceuticals, and paints [20].
Table 1. Different conversion routes from glycerol to value-added products.
As shown in Table 2 and Figure 1, different types of catalyst materials were reported for the solketal production consisting of zeolites, clays, resins, heteropolyacids, and others. Each catalyst has both advantages and drawbacks. A homogeneous catalyst, such as H2SO4, offers high activity, however, these homogenous catalysts are corrosive, not recyclable, difficult to separate, and considerably more expensive. Similarly, chloride, such as tin chloride (SnCl2), is also unwanted due to its corrosion tendency [30]. Reusability is also an important part of studies. Reusability is a factor which is studied as a typical sustainable principle. The basic mechanism of the metal salt catalysis is a nucleophilic attack by the hydroxyl group of glycerol to the carbocation obtained from the protonation step, resulting in the formation of the intermediate, followed by a water elimination step. The carbocation is produced from the Lewis or Brønsted acid sites, which activates the ketone carbonyl group through a protonation step (i.e., Brønsted acids) or polarization.
Energies 12 02872 g001 550Figure 1. Popularity of different types of catalytic materials for solketal production from 2014 to 2018. (Source: Web of Knowledge, https://www.webofknowledge.com, November 2018).
Table 2. Classification of heterogeneous catalysts for solketal production.
However, homogeneous catalysts are not considered as environmental-friendly for the reaction system. Another challenge in the utilization of heterogeneous catalysts in solketal production is the byproduct (water) formed during the reaction, which induces a reversible reaction. Heterogeneous catalysts are regenerated easily and are more easily handled. Many resin catalysts exhibited excellent conversion of glycerol to solketal and selectivity, where the best catalytic performance was obtained by amberlyst. However, it is not feasible for a higher scale of production due to the limitation of thermal stability, so it is not easy to regenerate. The higher thermal stability can be found in hierarchical zeolite. The highest conversion of glycerol to solketal of 72% and the selectivity of 72% are reached by using H-Beta (BEA framework) under the condition of 60 °C, stirring at 700 rpm, 5% of catalyst, and molar ratio of glycerol:acetone of 1:4 for H-BEA. Within the zeolite materials, MFI zeolite showed 80%, which is a lower catalytic activity in comparison with amberlyst, but with almost 100% selectivity. The lower conversion is due to the relatively narrow channel size that affects the transport of the reactant carried out and the shape selectivity.
2. Glycerol-to-Solketal Over Resin Catalysts
Overall, the most important properties of solid acid catalysts for the conversion glycerol to solketal production was the Brønsted acidity of solid acids [31]. The conversion of glycerol to solketal with resin catalysts has been carried out [32,33,34,35,36]. Table 3 summarizes the conversion of glycerol to solketal over resin catalysts. A typical resin catalyst (i.e., amberlyst) catalyzed the reaction of glycerol with acetone to produce above 80% of the glycerol conversion. Guidi et al. [36] reported that a resin, amberlyst-36, which was applied at different reaction temperatures from 25 to 70 °C, was an excellent catalyst to convert glycerol with a conversion of 85% to 97% to solketal with a selectivity of 99%. The catalyst is also active at lower pressures with similar reaction parameters either in pure glycerol or in an equimolar reactant. According to some references, the high conversion was influenced not only by the surface acidity but also by the resin structure. Moreover, the surface acidity was an important parameter that played a crucial role in improving the selectivity and the conversion in the production of solketal. Although amberlyst-46 and amberlyst-36 is a similar material, both types of resins have a different acid capacity and structure morphology. Furthermore, all resins showed good selectivity to solketal (>80%), and the important catalytic parameter of the resin to conversion glycerol is the acid capacity (oversulfonated resin). With the highest acid capacity (sulfonic acid), these catalyst materials can improve not only the selectivity to solketal production but also the conversion of raw glycerol to above 90%. Another important thing to be highlighted as a limitation of the catalyst activity is the presence of NaCl as a poison for the surface acidity, which is possibly due to the impurities in glycerol.
Table 3. Glycerol-to-solketal over resin catalysts.
Table
3. Glycerol-to-Solketal over Mesoporous Silica
Koranyi et al. [37] reported the superiority of hafnium and zirconium modified TUD-1 as superior catalysts for the conversion of glycerol to solketal. These two catalysts (Hf-TUD-1 and Zr-TUD-1) were more active than Sn-MCM-41 and Al-TUD-1. The Zr and Hf-TUD-1 are examples of active metal-modified mesoporous silica in which Hf and Zr are in the framework. Their activity was higher than FAU(USY) and Al(TUD-1). The highest conversion of glycerol to solketal was more than 50%. The catalytic activity was a function of (i) the number of acid sites, (ii) the presence of mesopores, (iii) the existence of a large surface area, and (iv) the hydrophobicity of the catalyst [38]. The later, the hydrophobicity of the catalyst, was crucial to prevent the hydrolysis of solketal [37,38,39,40,41]. According to Table 4, Cs 2.5/KIT-6 catalyst was one of the best catalysts for the conversion of glycero-to-solketal [42]. KIT-6 was selected because of its large surface area (600-1000 m2/g), active sites, and accessible pores [42].
Table 4. Glycerol-to-solketal over mesoporous silica.
Numerous references reported that mesoporous silica catalysts have the advantage of high stability in the conversion of glycerol to solketal, resulting in products with a relatively large percentage of conversion (95%) and selectivity to solketal (98%) [37,42,43,44,45,46]. The mesoporous structure with an activated surface by sulfonic acid might be applied efficiently for the conversion of glycerol to fuel additive [37,43,47]. A sulfonic acid-functionalized mesoporous polymer (MP-SO3H) contains a high acidity surface (1.88 mmol/g). The surface acidity of catalytic materials can accelerate the formation products of solketal via ketalization reactions as shown in Figure 2.
Energies 12 02872 g002 550Figure 2. Scheme of mechanism for the ketalization reaction of glycerol and acetone.
4. Ketalization of Glycerol over Clay Minerals
Malaya et al. [17,48] studied different clay-based catalysts with different acid strengths ranging from 0.12 to 5.7 meq/g [17]. The results show that a stronger acidity improved the conversion of glycerol up to ca. 80%. As shown in Table 5, solketal production from glycerol used two different sources, namely acetone or formaldehyde over solid acid catalysts [49,50,51,52]. Based on the conversion of glycerol and selectivity to solketal, the clay catalyst which showed the optimum results was reported by Timofeeva et al. in a batch reactor with activated catalyst by nitric acid of 0.5 M [53]. In the activated K10 montmorillonite by acid solution, this impact causes an increasing rate of reaction with the acid site of the material. It is well-known that the acid activation of natural montmorillonite with nitric acid can change the structure of montmorillonite (leaching of Al3+ cations from the octahedral to increase the surface area and microporosity of catalyst materials) [54,55,56]. The reaction of solketal production is shown in Figure 3. The use of formaldehyde as the major source of solketal production has a lower conversion value (only 83% glycerol conversion), with the K10 montmorillonite used as a catalyst. It may be due to the formation of the hemiacetal or hemicetal via two different pathways. The reaction between glycerol and acetone is preferred as it produces a more stable intermediate, hemicetal compound, with a tertiary carbenium ion [37]. While, in the reaction between glycerol with formaldehyde, the produced hemiacetal formation is not a stable carbenium ion. Thus, the conversion value for the glycerol-formaldehyde system is relatively small as compared to the reaction where acetone is used as a co-reactant [57,58,59].
Energies 12 02872 g003 550Figure 3. Synthesis scheme of glycerol to solketal.
Table 5. Glycerol-to-solketal over clay minerals.
Koranyi et al. (2012) [37] reported the effect of water as an impurity in the acetalization of glycerol. The presence of water reduced the activity ca. 50% lower than the one with the model compound (pure glycerol). A high number of Brønsted and Lewis sites does not correspond directly to a high activity. Dealumination FAU and Al-TUD-1 with a high Brønsted and Lewis acidity were poor in the acetalization of glycerol [37]. Hydrophobic catalysts, such as hafnium and TUD-1 zirconium on TUD-1, are very prospective for glycerol to solketal. Ammaji et al. (2017) [62] also reported a similar observation, as the Zr-SBA-15 was the most active and selective catalyst.
5. Perspective on Ketalization of Glycerol over Hierarchical Zeolites
Dmitriev et al. (2016) [63] reported that zeolite beta was the most active solid acid catalyst as compared to amberlist-35 and cation-exchange resin (KU-2-8) [62]. The zeolite beta applied was a commercial one from zeolyst with SiO2/Al2O3 of 25 and a zeolite beta made by Angarsk. Kowalska et al. [64,65] studied the effect of (i) different zeolite topologies (MFI, BEA, and MOR), (ii) Si/Al ratio from 9.2 to 25.8, and (iii) mesoporosity. Two parent MFI zeolites with different Si/Al were applied (Si/Al = 12 and Si/Al = 27) [64]. The hierarchical zeolites were obtained by desilication using 0.2 M NaOH and dealumination using citric acid (0.5 M) and nitric acid (0.5 M). The diffusion limitation of the parent zeolites was considered as the highest activity of the parent MFI was significantly lower than the one from the hierarchical MFI. A high selectivity (up to 100%) to solketal was obtained with an acetone:glycerol ratio of 1. A higher acetone to glycerol ratio was obtained over a higher acetone to glycerol ratio. Both desilication and dealumination are very effective in improving the catalyst stability of zeolite based catalyst [66,67,68].
Rossa et al. [69] conducted the kinetics study of acetalization of glycerol with acetone to produce solketal with optimization of the kinetics parameters. Zeolite beta with an Si/Al of 19 was applied to find the best parameters: (i) External mass transfer (stirring rate), (ii) temperature, (iii) catalyst amount, and (iv) glycerol to acetone ratio. The targeted goals were glycerol conversion and solketal selectivity. The experimental design for beta zeolite showed that the suggested reaction parameters are: Temperature at 60 °C, stirring rate of 700 rpm, catalyst loading of 5%, and glycerol to acetone ratio of 1:3. A higher acetone content will increase the conversion of glycerol [24,70]. However, an increase of the acetone to glycerol ratio will increase the exergy destruction rate due to a reduction in the rate of formation toward the product and a higher consumption of electrical exergy to the acetalization reactor [20,71,72,73,74,75,76,77,78,79,80].
Hierarchical zeolite shows excellent glycerol conversion and selectivity to solketal through acetalization reactions. The catalytic materials show a higher glycerol conversion (until more than an 80% glycerol conversion) as compared to other porous and non-porous catalysts due to a large pore size and easy molecular diffusivity. The enhancement of the catalytic activity of zeolites in glycerol acetalization, through the generation of a hierarchical porosity, has been applied by different authors as shown in Table 6. Based on the literature, the crystallite size was one of the most determining factors in the activity of hierarchical zeolite as a catalyst [64,81,82,83,84,85]. The smaller the crystal size of zeolite, the easier the diffusion of the reactant and products though the zeolite pores [73,86,87]. The pore structure of the zeolite can be changed through the dealumination and desilication processes. The process not only can change the mesopore materials but also can increase the catalytic activity (improving the accessibility and mass transfer on the surface) [88]. Hierarchical zeolites with different topologies, such as ZSM-5 (MFI) [67,89,90], beta (BEA) [81,91,92], and Y (FAU) [64], have also been used in the acetalization of glycerol, and the results show that smaller pores can produce high glycerol conversion and selectivity to selectivity (almost 100% selective for solketal formation). However, overall, all materials displayed very good catalytic performance when reacting equimolar mixtures of glycerol and acetone [37,39]. From the experiments on H-beta zeolite, it was found that dealumination resulted in a decrease of strong acid sites, thus decreasing the catalytic activity.
Table 6. Glycerol-to-solketal over hierarchical zeolite catalysts.
6. Solketal Synthesis over Carbon/Activated Carbon-Based Catalyst
Considering the abundant source of biomass as carbon and activated-carbon precursor, activated carbons were functionalized with acid groups for solketal synthesis [93,94]. Some papers showed the excellent performance of activated carbon for catalyzing the conversion of glycerol to solketal (Table 7) and some of these exhibited a high activity and selectivity under green conditions (solvent-free conditions at a mild temperature). The high surface area of activated carbon preserves the higher surface acid sites by some modification, including acid, metal, and composite modifications [24,95,96,97]. Therefore, they are promising candidates as heterogeneous catalysts for the acetalization of acetone with glycerol. From the utilization of acid functionalized activated carbon, the superior catalytic activity of the four acid-treated carbons was underlined as compared to the untreated activated carbon, confirming the importance of the higher number and strength of acid sites generated by the acid treatments. The catalysts were prepared by HNO3 and H2SO4 treatment to activated carbon. The catalytic activity of the catalyst showed excellent performance due to the high conversion and selectivity at room temperature.
Table 7. Glycerol-to-solketal over carbon/activated carbon-based catalyst.
From the acid-modified carbon catalyst, it was found that the presence of acid groups, mainly sulfonic groups, was the key factor for the improved catalytic performance. A similar pattern also appeared from the Ni-Zr support on the activated carbon [100], in which the active metal contributes by enhancing the catalyst acidity. Another factor affecting the catalytic activity was the higher total acid density, the large mesopore of the carbon structure, and the activity of the metals.
7. Perspective and Conclusions
This mini review highlighted the recent development on solid catalysts for the conversion of glycerol-to-solketal. The product is an additive for fuels, which are very useful to reduce GHGs and to improve the economic viability of biodiesel business [6,8,16,20,34,101,102,103,104,105]. Tailor-made heterogeneous catalyst for an optimal conversion of glycerol is developed and required. Five major heterogeneous catalysts were emphasized in this study: Resins, mesoporous silica, zeolites, clays, and activated carbons. The stability of catalysts is one of the main hurdles for the commercialization of glycerol to solketal. Even though the reaction temperature was considered as mild, the stability of most of the solid catalysts decayed in the presence of water as a byproduct and other impurities (NaCl, methanol) from the glycerol source. The deactivation rate is even higher when the raw glycerol (contaminated with water) was fed to the reactor [106,107,108,109]. Therefore, the viability of the commercial plant depends on (i) the source of feeds [110], (ii) availability of glycerol and other feeds, and (iii) cost of glycerol as the feed. Acidity is agreed as an important properties of zeolite catalysts for glycerol to solketal. Strong acidity and medium hydrophobicity were expected in the design of the reactor. Based on some limitations of the catalyst performance, the utilization of raw glycerol directly will reduce the stability of the catalyst. This review described how a better material should be designed for the optimum conversion of glycerol (and generally polyol) to solketal. Hydrophobic catalysts, such as hafnium/TUD-1 and zirconium/TUD-1, are very prospective for glycerol to solketal. Extended works on low aluminum mesoporous silica materials are expected in the coming years.
Conflicts of Interest
The authors declare no conflict of interest.
Solketal is a protected form of glycerol with an isopropylidene acetal group joining two neighboring hydroxyl groups. Solketal contains a chiral center on the center carbon of the glycerol backbone, and so can be purchased as either the racemate or as one of the two enantiomers. Solketal has been used extensively in the synthesis of mono-, di- and triglycerides by ester bond formation. The free hydroxyl groups of solketal can be esterified with a carboxylic acid to form the protected monoglyceride, where the isopropylene group can then be removed using an acid catalyst in aqueous or alcoholic medium. The unprotected diol can then be esterified further to form either the di- or triglyceride.
Due to the high growth of biodiesel production, glycerol, a major by-product from transesterification, is also produced at the same growing rate, resulting in its oversupply. This situation brings the price of glycerol to drop dramatically. Solketal, a derivative from glycerol, can be utilized by blending with gasoline or biodiesel as an additive. This work studies the synthesis of solketal from glycerol and acetone using homogeneous acid catalyst. The reaction progresses successfully when using the acetone in excess. Subsequently, the prepared solketal is used for synthesizing benzyl solketal ether by performing reaction with benzyl alcohol. However, several other products such as benzyl glycerol ether, dibenzyl ether and glycerol are formed. It was found that the high ratio of solketal to benzyl alcohol is required to increase selectivity toward benzyl solketal ether.
In the first generation biodiesel production, triglyceride from vegetable oil and methanol are reacted by transesterification reaction to produce fatty acid methyl ester or biodiesel and also obtain glycerol as an unavoidable by-product. Since the production of biodiesel has been increasing rapidly, this causes the glycerol obtained as a by-product to be oversupplied, leading to the price drop of glycerol. Therefore, finding the way to utilize glycerol is suggested to help the overall economic of biodiesel production. Solketal is a derivative which the two adjacent hydroxyl groups of glycerol are reacted via condensation acetone [1]. Solketal can be blended for fuel additives in gasoline [2] or biodiesel [3]. Nowadays solketal can be produced by condensation reaction of glycerol and acetone with acid catalyst [2]. The interesting derivative from solketal is benzyl solketal ether. Benzyl solketal ether is the oxygenated compound and also can be use for fuel additives. Currently, benzyl solketal ether was produced by organic synthesis. In this organic synthesis, solketal is reacted with benzyl chloride with solvents [4]. The problem is using a lot of solvents in the synthesis of benzyl solketal ether. The purpose of this work is divided into two parts. First is the solketal production from glycerol and acetone. Subsequently, the synthesis of benzyl solketal ether from solketal and benzyl alcohol is investigated in the system without solvent. The effect of molar ratio is studied in this part and the optimum condition to produce benzyl solketal ether is investigated. Glycerol and acetone are the raw materials used for producing solketal by condensation reaction. Solketal or isopropylidene glycerol contains the center of glycerol backbone which an isopropylidene group bound to two neighboring hydroxyl group as shown in Fig. 1. Benzyl solketal ether is derived from etherification between solketal and benzyl alcohol (Fig. 3). Benzyl solketal ether can be used as fuel additive. Moreover benzyl solketal ether can be deprotected to obtained benzyl glycerol ether with the ether group at D position of glycerol. In general, benzyl solketal ether is synthesized by reacting benzyl chrolide or benzyl bromide and solketal with solvent [5]. But there are many disadvantages from this organics synthesis for example: a lot of waste from used solvent. In this work, the etherification reaction between solketal and benzyl alcohol without solvent is investigated. However, there were several by-products, which are glycerol, acetone, benzyl solketal ether, benzyl glycerol ether and dibenzyl ether. Fig. 3 is shown the possible reactions and products from reaction of solketal and benzyl alcohol. The main reaction is the reaction between solketal and benzyl alcohol to produce benzyl solketal ether and water (Fig. 3 (1)). From the acid catalyst, solketal could be able to be decomposed to produce acetone and glycerol (Fig. 3 (2)). Benzyl alcohol is also reacted with each other to produce dibenzyl ether and water (Fig. 3 (3)). Glycerol from the deprotection is able to react with benzyl alcohol to produce benzyl glycerol ether (Fig. 3 (4)). Fortunately, the di- and tri- benzyl glycerol ether are not observed from the GC×GC time of flight mass spectroscopy. In this case, glycerol reacted with acetone back to produce solketal to protected glycerol before reacted with other benzyl alcohol. The last suggested reaction is benzyl solketal ether is depotected by the water in the system to produce benzyl glycerol ether (Fig. 3 (5)). The solketal to benzyl alcohol molar ratio is first set at 1:1 solketal to benzyl alcohol molar ratio. Fig. 4 shows the relationships between benzyl alcohol conversion, selectivity and time. As observed, after 2 hours, the benzyl alcohol quickly converts to 57.5% conversion and then continuously converts to 92.9% after 12 hours. The selectivity of dibenzyl ether is very high at 2 hour (59.
