Production of Biofuel Additives from Esterification and Acetalization of Bioglycerol over SnO2-Based Solid Acids

Nanostructured Solid/Liquid Acid Catalysts for Glycerol Esterification: The Key to Convert Liability into Assets

Owing to the growing concerns about the dwindling fossil fuel reserves, increasing energy demand, and climate emergency, it is imperative to develop and deploy sustainable energy technologies to ensure future energy supply and to transition to the net-zero world. In this context, there is great potential in the biorefinery concept for supplying drop in biofuels in the form of biodiesel. Biodiesel as a fuel can certainly bridge the gap where electrification or the use of hydrogen is not feasible, for instance, in heavy vehicles and in the farm and marine transportation sectors. However, the biodiesel industry also generates a large amount of crude glycerol as the by-product. Due to the presence of several impurities, crude glycerol may not be a suitable feedstock for all high-value products derived from glycerol, but it fits well with glycerol esterification for producing glycerol acetins, which have numerous applications. This review critically looks at the processes using nanostructured solid/liquid acid catalysts for glycerol esterification, including the economic viability of the scale-up. The homogeneous catalysts reviewed herein include mineral acids and Brønsted acidic ionic liquids, such as SO3H-functionalized and heteropoly acid based ionic liquids. The heterogeneous catalysts reviewed herein include solid acid catalysts such as metal oxides, ion-exchange resins, zeolites, and supported heteropoly acid-based catalysts. Furthermore, the techno-economic analysis studies have shown the process to be highly profitable, confirming the viability of glycerol esterification as a potential tool for economic value addition to the biorefinery industry.

Kinetic Analysis of Glycerol Esterification Using Tin Exchanged Tungstophosphoric Acid on K-10

Glycerol acetins (mono-, di-, and tri) are produced via esterification with acetic acid. The acetins are commercially important industrial chemicals including their application as fuel additives, thus significant to environmental sustainability and economic viability of the biorefinery industry. Glycerol esterification with acetic acid was studied using partial tin exchanged tungstophosphoric acid supported on montmorillonite K-10 as catalysts. Partially exchanging the H+ ion of DTP with Sn (x = 1) increased the acidity of the catalyst and showed an increase in the catalytic activity as compared to the DTP/K-10 catalyst. A series of tin exchanged tungstophosphoric acid (20% w/w) supported on montmorillonite K-10 clay (Snx-DTP/K-10, where x = 0.5-1.5) were synthesized and thoroughly characterized by using BET, XRD, FT-IR, UV-vis, and titration techniques. Among various catalysts, Sn1-DTP/K-10 was found to be the most active catalyst for glycerol esterification. Effects of different reaction parameters were studied and optimized to get high yields of glycerol triacetin. A suitable kinetic model of the reaction was fitted, and the Langmuir-Hinshelwood (L-H) dual-site model was able to describe the experimental data with high agreement between the experimental and calculated results. The prepared catalyst could be recycled at least four times without significant loss of activity. The overall process is green and environment friendly.

Current Trends in Acetins Production: Green versus Non-Green Synthesis

To utilize excess glycerol produced from the biodiesel industry, researchers are developing innovative methods of transforming glycerol into value-added chemicals. One strategy adopted is the conversion of glycerol into acetins, which are esters of glycerol that have wide applications in cosmetics, pharmaceuticals, food and fuel additives, and plasticizers and serve as precursors for other chemical compounds. Acetins are synthesized either by traditional chemical methods or by biological processes. Although the chemical methods are efficient, productive, and commercialized, they are "non-green", meaning that they are unsafe for the environment and consumers. On the other hand, the biological process is "green" in the sense that it protects both the environment and consumers. It is, however, less productive and requires further effort to achieve commercialization. Thus, both methodologies have benefits and drawbacks, and this study aims to present and discuss these. In addition, we briefly discuss general strategies for optimizing biological processes that could apply to acetins production on an industrial scale.

Versatile Coordination Polymer Catalyst for Acid Reactions Involving Biobased Heterocyclic Chemicals

The chemical valorization/repurposing of biomass-derived chemicals contributes to a biobased economy. Furfural (Fur) is a recognized platform chemical produced from renewable lignocellulosic biomass, and furfuryl alcohol (FA) is its most important application. The aromatic aldehydes Fur and benzaldehyde (Bza) are commonly found in the slate of compounds produced via biomass pyrolysis. On the other hand, glycerol (Gly) is a by-product of the industrial production of biodiesel, derived from fatty acid components of biomass. This work focuses on acid catalyzed routes of Fur, Bza, Gly and FA, using a versatile crystalline lamellar coordination polymer catalyst, namely [Gd(H4nmp)(H2O)2]Cl·2H2O (1) [H6nmp=nitrilotris(methylenephosphonic acid)] synthesized via an ecofriendly, relatively fast, mild microwave-assisted approach (in water, 70 °C/40 min). This is the first among crystalline coordination polymers or metal-organic framework type materials studied for the Fur/Gly and Bza/Gly reactions, giving heterobicyclic products of the type dioxolane and dioxane, and was also effective for the FA/ethanol reaction. 1 was stable and promoted the target catalytic reactions, selectively leading to heterobicyclic dioxane and dioxolane type products in the Fur/Gly and Bza/Gly reactions (up to 91% and 95% total yields respectively, at 90 °C/4 h), and, on the other hand, 2-(ethoxymethyl)furan and ethyl levulinate from heterocyclic FA.

Esterification of glycerol with acetic acid using a sulfonated polyphenylene sulfide non-woven fabric as a catalyst

In this work, the esterification of glycerol with acetic acid (HOAc) was investigated under sulfonated polyphenylene sulfide non-woven fabric (SPSF) as a solid catalyst. The effects of the amount of catalyst, reaction temperature, molar ratio of glycerol to HOAc and the reaction time on the esterification were studied in detail. It was found that SPSF has good catalytic activity and stability. Under the reaction conditions of the molar ratio of glycerol/HOAc of 1:6 (glycerol 0.1 mol), the reaction temperature of 110 °C, the amount of catalyst of 3 g, and the reaction time of 2 h, the glycerol conversion and the selectivity to diacetin (DAG) reached upto 96 and 56.1%, respectively. Reusability test of SPSF showed that no significant declination in the glycerol conversion and the selectivity was observed after five reaction cycles. The experimental results proved the esterification of glycerol with HOAc by SPSF a promising and green process.

Widely used catalysts in biodiesel production: a review

An ever-increasing energy demand and environmental problems associated with exhaustible fossil fuels have led to the search for an alternative renewable source of energy. In this context, biodiesel has attracted attention worldwide as an eco-friendly alternative to fossil fuel for being renewable, non-toxic, biodegradable, and carbon-neutral. Although the homogeneous catalyst has its own merits, much attention is currently paid toward the chemical synthesis of heterogeneous catalysts for biodiesel production as it can be tuned as per specific requirement and easily recovered, thus enhancing reusability. Recently, biomass-derived heterogeneous catalysts have risen to the forefront of biodiesel productions because of their sustainable, economical and eco-friendly nature. Furthermore, nano and bifunctional catalysts have emerged as a powerful catalyst largely due to their high surface area, and potential to convert free fatty acids and triglycerides to biodiesel, respectively. This review highlights the latest synthesis routes of various types of catalysts (including acidic, basic, bifunctional and nanocatalysts) derived from different chemicals, as well as biomass. In addition, the impacts of different methods of preparation of catalysts on the yield of biodiesel are also discussed in details.

Catalytic performance of cerium-modified ZSM-5 zeolite as a catalyst for the esterification of glycerol with acetic acid

Esterification of glycerol with acetic acid was carried out over cerium-modified ZSM-5 zeolites to synthesize monoacetin (MA) and diacetin (DA). The modified zeolite catalyst was characterized. The effect of reaction process parameters such as acetic acid to glycerol mole ratio (1–11), reaction temperature (30–120 °C), and catalyst weight (2–8 wt %) on the selectivity of the product was investigated. At 120 °C reaction temperature, 8 wt % catalyst, and 9:1 acetic acid to glycerol mole ratio, about 98.32% conversion of glycerol were obtained. This reaction follows pseudo-first-order reaction kinetics and the activation energy was found to be 63.72 kJ mol−1.

Advances in Nanocatalysts Mediated Biodiesel Production: A Critical Appraisal

The excessive consumption of petroleum resources leads to global warming, fast depletion of petroleum reserves, as well as price instability of gasoline. Thus, there is a strong need for alternative renewable fuels to replace petroleum-derived fuels. The striking features of an alternative fuel include the low carbon footprints, renewability and affordability at manageable prices. Biodiesel, made from waste oils, animal fats, vegetal oils, is a totally renewable and non-toxic liquid fuel which has gained significant attraction in the world. Due to technological advancements in catalytic chemistry, biodiesel can be produced from a variety of feedstock employing a variety of catalysts and recovery technologies. Recently, several ground-breaking advancements have been made in nano-catalyst technology which showed the symmetrical correlation with cost competitive biodiesel production. Nanocatalysts have unique properties such as their selective reactivity, high activation energy and controlled rate of reaction, easy recovery and recyclability. Here, we present an overview of various feedstock used for biodiesel production, their composition and characteristics. The major focus of this review is to appraise the characterization of nanocatalysts, their effect on biodiesel production and methodologies of biodiesel production.

Advances in porous and nanoscale catalysts for viable biomass conversion

Solid catalysts with unique porosity and nanoscale properties play a promising role for efficient valorization of biomass into sustainable advanced fuels and chemicals.

Rate enhancement by Cu in NixCu1−x/ZrO2 bimetallic catalysts for hydrodeoxygenation of stearic acid

The combination of Cu and Ni in bimetallic catalysts on ZrO₂, leads to a more efficient HDO of stearic acid.

Nanostructured Nickel/Silica Catalysts for Continuous Flow Conversion of Levulinic Acid to γ-Valerolactone

Selective transformation of levulinic acid (LA) to γ-valerolactone (GVL) using novel heterogeneous catalysts is one of the promising strategies for viable biomass processing. In this framework, we developed a continuous flow process for the selective hydrogenation of LA to GVL using several nanostructured Ni/SiO₂ catalysts. The structural, textural, acidic, and redox properties of Ni/SiO₂ catalysts, tuned by selectively varying the Ni amount from 5 to 40 wt %, were critically investigated using numerous materials characterization techniques. Electron microscopy images showed the formation of uniformly dispersed Ni nanoparticles on the SiO₂ support, up to 30% Ni loading (average particle size is 9.2 nm), followed by a drastic increase in the particles size (21.3 nm) for 40% Ni-loaded catalyst. The fine dispersion of Ni particles has elicited a synergistic metal-support interaction, especially in 30% Ni/SiO₂ catalyst, resulting in enhanced acidic and redox properties. Among the various catalysts tested, the 30% Ni/SiO₂ catalyst showed the best performance with a remarkable 98% selectivity of GVL at complete conversion of LA for 2 h reaction time. Interestingly, this catalyst showed a steady selectivity to GVL (>97%), with a 54.5% conversion of LA during 20 h time-on-stream. The best performance of 30% Ni/SiO₂ catalyst was attributed to well-balanced catalytic properties, such as ample amounts of strong acidic sites and abundant active metal sites. The obtained results show a great potential of applying earth-abundant nickel/silica catalysts for upgrading biomass platform molecules into value-added chemicals and high-energy-density fuels.

Functionalised heterogeneous catalysts for sustainable biomass valorisation

Functionalised heterogeneous catalysts show great potentials for efficient valorisation of renewable biomass to value-added chemicals and high-energy density fuels.

Catalytic hydrodeoxygenation of palmitic acid over a bifunctional Co-doped MoO2/CNTs catalyst: an insight into the promoting effect of cobalt

HDO of palmitic acid into C₁₆ hydrocarbons was successfully achieved over Co doped MoO₂/CNTs catalysts at a much lower temperature. Co could promote the formation of Lewis acidic sites, oxygen vacancies and Mo₂C particles, which are all decisive factors for better catalytic activity.

POSS-derived solid acid catalysts with excellent hydrophobicity for highly efficient transformations of glycerol

New POSS-derived acid catalysts were synthesized, which proved to be highly efficient, and steadily reused for glycerol transformations.

Highly efficient continuous-flow oxidative coupling of amines using promising nanoscale CeO2–M/SiO2 (M = MoO3 and WO3) solid acid catalysts

Nanoscale CeO₂–MoO₃/SiO₂ solid acid shows an outstanding catalytic performance in the oxidative coupling of amines under industrially-favourable conditions.

β-Cyclodextrin supported MoO3–CeO2 nanocomposite material as an efficient heterogeneous catalyst for degradation of phenol

The β-cyclodextrin supported MoO₃–CeO₂ nanocomposite material is an efficient heterogeneous catalyst for the degradation of phenol to non-toxic pollutants at room temperature with continuous stirring and without light irradiation.

Glycerol acetins: fuel additive synthesis by acetylation and esterification of glycerol using cesium phosphotungstate catalyst

Glycerol acetylation and esterification reactions with acetic anhydride and acetic acid respectively give acetins, in which di and tri acetins are commercially important products used as fuel additives.