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Review

Glycerol to Solketal for Fuel Additive: Recent Progress in Heterogeneous Catalysts

1
Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Islam Indonesia, Jl. Kaliurang Km 14, Sleman, Yogyakarta 55584, Indonesia
2
School of Information, Systems and Modelling, Faculty of Engineering and Information Technology, University of Technology Sydney, Sydney, NSW 2007, Australia
3
Center of Research Excellence in Nanotechnology and Chemical Engineering Department, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia
*
Authors to whom correspondence should be addressed.
Energies 2019, 12(15), 2872; https://doi.org/10.3390/en12152872
Submission received: 4 June 2019 / Revised: 6 July 2019 / Accepted: 10 July 2019 / Published: 25 July 2019
(This article belongs to the Special Issue Biofuels for Internal Combustion Engine)

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.

Graphical Abstract

1. Introduction

The exploration of renewable energy to supplement limited fossil fuels in the next few years is one the most concerned research topics. Among some renewable energy resources, biofuels are receiving intensive attention, especially for some countries with a large production of vegetable oils and bio-oils for biodiesel production [1,2,3,4]. Annual production and consumption of biodiesel is likely to increase significantly in the coming few years. Numerous sources of abundant edible and potential non-edible oils have been identified [5]. Regardless, this fact leads to increasing glycerol production as the byproduct of biodiesel conversion [2]. Due to the chemical process of the biodiesel production, the molar ratio of glycerol to the methyl ester is 3:1, or about 10% to 20% of the total volume of biodiesel produced is made up of glycerol. The rapid growth of biodiesel production has contributed much to the increasing glycerol production since it was reported that the worldwide production of glycerol increased from 7.8 billion liters in 2006 to 36 billion liters in 2018 [6,7]. This fact revealed that glycerol is an abundant renewable chemical feedstock in the world. The conversion of glycerol into more valuable chemicals is the best option to create a new market for glycerol and improve the sustainability of biodiesel production [7,8,9,10,11,12,13,14].
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].
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.
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.

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].
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.

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].
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.

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.
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. In general, at least three main challenges were identified:
  • The presence of water and impurities in the feed.
  • The shift from the batch reactor to the fixed bed reactor.
  • The presence of equilibrium offers other difficulties as higher acetone demand is expected. However, higher acetone to glycerol will lead to destructive instruments.
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.

Author Contributions

I.F. and O.M. contribute to design and conception, drafting the article, and final approval of the article. I.S., M.M.M., and G.F. contribute to collect the references, drafting the article, preparing all figures and all tables, and discussion. T.M.I.M. contributes to help data analysis and discussion.

Funding

This research was funded by Ministry of Research, Technology and Higher Education (KEMENRISTEKDIKTI) Republic of Indonesia through World Class Professor program in 2018, grant number: 123.6/D2.3/KP/2018. The APC was funded by the University of Technology Sydney seed fund (Org Unit 321740) with Account number (2232397).

Acknowledgments

Authors would like to express appreciation for the support from Ministry of Research, Technology and Higher Education (KEMENRISTEKDIKTI) Republic of Indonesia through World Class Professor program in 2018, grant number: 123.6/D2.3/KP/2018. The authors are thankful to Professor Paolo Pescarmona from University of Groningen for his rich suggestions on prospective catalytic materials in glycerol to solketal.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 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).
Figure 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).
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Figure 2. Scheme of mechanism for the ketalization reaction of glycerol and acetone.
Figure 2. Scheme of mechanism for the ketalization reaction of glycerol and acetone.
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Figure 3. Synthesis scheme of glycerol to solketal.
Figure 3. Synthesis scheme of glycerol to solketal.
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Table 1. Different conversion routes from glycerol to value-added products.
Table 1. Different conversion routes from glycerol to value-added products.
ConversionCatalystResultsRef
EtherificationLi/clayDiglycerol isomer was also increased from 35% to 55% while the selectivity to aa isomer was decreased from 65% to 35%[21]
Conversion glycerol to allyl AlcoholK/Al2O3-ZrO2-FeOX
Alkali metals supported to ZrO2-FeOx
Improvement in conversion
With the increase of the K content in the catalyst, allyl alcohol yield increased up to 27%-C
[22]
Allyl alcoholZSM-5-supported iron catalystsThe prepared catalyst performed better for allyl alcohol production as compared to catalysts synthesized by other methods[23]
Conversion alcohol to glycerol carbonateMg3−xAl1Cux Transesterification of glycerol to glycerol carbonate (GC) increased to 96% of yields[24]
Acetalization glycerol with acetoneMoPO supported to SBA-15A 40% MoPO/SBA-15 showed a conversion of 100% and selectivity of 98%[25]
Acetalization of glycerol with butanalBEA zeolite with the ratio Si/Al of 40Showed conversion of 88% and selectivity 80% of five member rings acetal (2-propyl-1,3-dioxolan-4-yl)methanol[26]
Glycerol etherification with benzaldehydeCationic acidic resinAchieving conversion of 93% and selectivity above 80% of 2-phenyl-1,3-di-oxan-5-ol[27]
Acetalization of glycerol with mono-substitude benzaldehydeMoOx/TiO2-ZrO2Glycerol conversion to 1,3-dioxolane (74%) within 30 min[28]
Acetalization of glycerol with acetoneMoO3 and WO3 supported to SnO2A 71% glycerol conversion and a 96% solketal selectivity were achieved.[29]
Table 2. Classification of heterogeneous catalysts for solketal production.
Table 2. Classification of heterogeneous catalysts for solketal production.
OthersHeteropolyacidResinMeso-SiO2Double Layer Hydroxide and ClayZeolites
Co/CNTSi-W (tungstosilisic) Amberlyst KIT-6ZrO2 dolomiteZeolite X
Na-lignosulfonateHMQ-SJWCat. Ex.Me-SBA-5JNb, AlOxVnOx/FER MOR
SnF2H3PW12040Amberlyst-46Hf-SBA-15Nb oxy OHBEA
Ionic liquid Amberlyst-46Mo-SBA-15COK-SHierarchical
Carbon KU-2-8Sn TUD-1MgLDHBEA, MOR
Lewatit GF101Al-MCM-41MontmorilloniteZSM-5 (MFI)
SulfonicGa-MCM-4 DeAl BEA
Amberlyst-35 Acidity BEA
Table 3. Glycerol-to-solketal over resin catalysts.
Table 3. Glycerol-to-solketal over resin catalysts.
SourceCatalystConditionConversionSelectivity to SolketalRemarkRef
Glycerol and AcetoneAmberlyst-1550 °C92% 96%Glycerol:acetone = 1:2, 7.0 g of amberlyst-15 in 96 min[32]
Glycerol and AcetoneAmberlyst-4660 °C84% 97%%1 (w/w) catalyst, 30 min[33]
Glycerol and AcetoneAmberlyst DPT-170 °C97%98%Glycerol:acetone = 1:2
at ambient pressure
[34]
Glycerol and AcetoneDT-851 sulfonic acid resin58 °C95% 99%Glycerol:acetone = 1:20, catalyst DT-851 sulfonic acid resin dosage is 5% (wt., calculated by glycerol), reaction time is 2 h. [35]
Glycerol and acetoneAmberlyst-3625 °C85%–97%99%At 10 barr and 25 °C, A36 was a highly active catalyst allowing good-to-excellent conversion (85%–97%) and selectivity (99%) when either pure or wet glycerol was used as a reagent.[36]
Note: glycerol to the second reactant ratio was presented as molar ratio.
Table 4. Glycerol-to-solketal over mesoporous silica.
Table 4. Glycerol-to-solketal over mesoporous silica.
SourceCatalystConditionConversionSelectivity to SolketalRemarkRef
Glycerol and AcetoneCs 2.5/KIT-625 °C95% in 15 min98%Glycerol:acetone = 1:6, catalyst loading was 5 wt.%.[42]
Glycerol and formaldehydePropylsulfonic Acid Functionalized SBA-15 Mesoporous Silica90 °C91.5 in 8 h98%Glycerol:formaldehyde = 1:1.5 with 4 wt.% catalyst loading[43]
Glycerol and Acetonearenesulfonic acid-functionalized silica70 °C84% in 30 min81%Glycerol:acetone = 1:6[44]
methyl acetate to glycerolSulfonic acid-functionalized mesostructured SBA-15 silicas170 °C99.5% in 4 h74.2%Glycerol:methyl acetate = 1:50 and catalyst loading (7.5 wt.% based on glycerol)[45]
Glycerol and acetoneA sulfonic acid-functionalized mesoporous polymer (MP-SO3H)30 °C94%98.5%The MP-SO3H catalyst performed better than other conventional solid acid catalysts[46]
Glycerol and acetoneZr-TUD-180 °C64% Glycerol:acetone = 1:2, 25 mg of catalyst, at room temperature, for 6 h. [37]
Glycerol and acetoneHf-TUD-180 °C65% Glycerol:acetone = 1:2, 25 mg of catalyst, at room temperature, for 6 h.[37]
Note: glycerol to the second reactant ratio was presented as molar ratio.
Table 5. Glycerol-to-solketal over clay minerals.
Table 5. Glycerol-to-solketal over clay minerals.
SourceCatalystConditionConversionSelectivity to SolketalRemarkRef
Glycerol and acetoneMontmorilonite modified by HNO3T = 25 °C94%95.4%Glycerol:acetone = 1:4, 10 mg of catalyst, time at 10 min[53]
Glycerol and benzaldehydeK10 MontmorilloniteT = 40 °C83%99%Glycerol:benzaldehyde dimethyl acetal = 1:1.1 at 6 h.[17]
Glycerol and acetoneK10 claysT = 30 °C87%85%Glycerol:acetone = 1:6, catalyst loading was 3 wt.% of total reactant weight, time at 120 min[60]
Glycerol and formaldehydeK10 MontmorilloniteT = 70 °C80%-Glycerol: formaldehyde = 1:1.2[61]
Glycerol and acetoneK10 MontmorilloniteT = 40 °C69%68%Glycerol:acetone = 2:6, P=600 psi, The amount of catalyst in each run was determined by the selected weight hourly space velocity (WHSV) at 4 h−1[48]
Note: glycerol to the second reactant ratio was presented as a molar ratio.
Table 6. Glycerol-to-solketal over hierarchical zeolite catalysts.
Table 6. Glycerol-to-solketal over hierarchical zeolite catalysts.
SourceCatalystConditionConversionSelectivity to SolketalRemarkRef
Glycerol and acetonehierarchical (micro-mesoporous) MFI zeolites (pore diameter 0.51–0.55 nm)T = 70 °C80%100%Glycerol:acetone = 1:1, catalyst in the amount of 1% related to glycerol. [64]
Glycerol and acetoneH-B-1 zeolitesT = 28 °C (room temperature)86%98.5%Glycerol:acetone = 1:2, catalyst amount = 5 wt.% referred to glycerol in 1 h.[73]
Glycerol and acetoneDealumination of BEA ZeolitesT = 30 °C80%100%Glycerol:acetone = 1:1, t = 30 min, catalyst loading was 0.5 g[72]
Glycerol and acetoneH-Zeolite (pore size 4.10 nm)T = 70 °C75%92%Glycerol:acetone = 1:3 were used with 0.05 g of catalyst for 2 h[65]
Glycerol and acetoneH-BEA ZeoliteT = 60 °C70%97.9%Glycerol:acetone = 1:4, catalyst amount was loading at 5 wt.% for 1 h.[69]
Table 7. Glycerol-to-solketal over carbon/activated carbon-based catalyst.
Table 7. Glycerol-to-solketal over carbon/activated carbon-based catalyst.
SourceCatalystConditionConversionSelectivity to SolketalRemarkRef
acetone and glycerolacid functionalized activated carbonRoom temperature, glycerol to acetone molar ratio of 1:497%96%The highest number and strength of acid sites generated by the acid treatments onto activated carbon gave better yield and selectivity[39]
glycerol with benzaldehyde atGraphene100 °C and 120 °C97% Graphene catalyst produced 76% yield at 100 °C and 85% yield at 120 °C, selectivity 100%[98]
acetone and glycerolsulfonated carbon-silica-meso composite materialsacetone and glycerol molar ratio of 1:6, re- fluxed at 70 °C 82%99% [99]
acetone and glycerolacidic carbon-based catalysts 80%95% [93]
acetone and glycerolNi-Zr supported on mesoporous activated carbonRoom Temperature glycerol/acetone ratio of 1:1075%100%Conversion and selectivity are affected by glycerol/acetone ratio and temperature[100]

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Fatimah, I.; Sahroni, I.; Fadillah, G.; Musawwa, M.M.; Mahlia, T.M.I.; Muraza, O. Glycerol to Solketal for Fuel Additive: Recent Progress in Heterogeneous Catalysts. Energies 2019, 12, 2872. https://doi.org/10.3390/en12152872

AMA Style

Fatimah I, Sahroni I, Fadillah G, Musawwa MM, Mahlia TMI, Muraza O. Glycerol to Solketal for Fuel Additive: Recent Progress in Heterogeneous Catalysts. Energies. 2019; 12(15):2872. https://doi.org/10.3390/en12152872

Chicago/Turabian Style

Fatimah, Is, Imam Sahroni, Ganjar Fadillah, Muhammad Miqdam Musawwa, Teuku Meurah Indra Mahlia, and Oki Muraza. 2019. "Glycerol to Solketal for Fuel Additive: Recent Progress in Heterogeneous Catalysts" Energies 12, no. 15: 2872. https://doi.org/10.3390/en12152872

APA Style

Fatimah, I., Sahroni, I., Fadillah, G., Musawwa, M. M., Mahlia, T. M. I., & Muraza, O. (2019). Glycerol to Solketal for Fuel Additive: Recent Progress in Heterogeneous Catalysts. Energies, 12(15), 2872. https://doi.org/10.3390/en12152872

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