An overview of recent research in the conversion of glycerol into biofuels, fuel additives and other bio-based chemicals

The depletion of fossil fuels has heightened research and utilization of renewable energy such as biodiesel. However, this has thrown up another challenge of significant increase in its byproduct, glycerol. In view of the characteristics and potentials of glycerol, efforts are on the increase to convert it to higher-value products, which will in turn improve the overall economics of biodiesel production. These high-value products include biofuels, oxygenated fuel additives, polymer precursors and other industrial bio-based chemicals. This review gives up-to-date research findings in the conversion of glycerol to the above high-value products, with a special focus on the performance of the catalysts used and their challenges. The specific products reviewed in this paper include hydrogen, ethanol, methanol, acetin, glycerol ethers, solketal, acetal, acrolein, glycerol carbonate, 1,3-propanediol, polyglycerol and olefins

Promotional effect of transition metals (Cu, Ni, Co, Fe, Zn)–supported on dolomite for hydrogenolysis of glycerol into 1,2-propanediol

Hydrogenolysis of biomass-derived glycerol is an alternative route to produce 1,2- propanediol. A series of transition metals supported on dolomite catalysts (Cu/Dol, Ni/Dol, Co/ Dol, Fe/Dol, Zn/Dol) were prepared via impregnation, calcined at 500 C and reduced at 600 C. The synthesized catalysts were then characterized by BET, BJH, XRD, H2-TPR, NH3– TPD, and SEM, and subsequently evaluated in glycerol hydrogenolysis reaction to produce 1,2- propanediol (1,2-PDO). The nature of transition metals was found to influence the activation of the catalysts. Among the tested catalysts, copper supported on dolomite (Cu/Dol) exhibited appre ciable hydrogenolysis performance due to the mutual interaction between the copper species and the dolomite. The findings from the various characterization results showed the addition of copper to dolomite ameliorates the chemical and reduction of the catalyst. It appears that the copper species were essentially enriched on the grain surfaces of the dolomite, the reduction properties, and the acidity of the catalyst enhanced. All the features of Cu/Dol catalyst contributed to the high glycerol conversion (78.5%) and high 1,2-PDO selectivity (79%) with low methanol production as the by

Optimization and characterization of mesoporous sulfonated carbon catalyst and its application in modelling and optimization of acetin production

In this study, an optimized mesoporous sulfonated carbon (OMSC) catalyst derived from palm kernel shell biomass was developed using template carbonization and subsequent sulfonation under different temperatures and time conditions. The OMSC catalyst was characterized using acid-base titration, elemental analysis, XRD, Raman, FTIR, XPS, TPD-NH3, TGA-DTA, SEM, and N2 adsorption–desorption analysis to reveal its properties. Results proved that the OMSC catalyst is mesoporous and amorphous in structure with improved textural, acidic, and thermal properties. Both FTIR and XPS confirmed the presence of -SO3H, -OH, and -COOH functional groups on the surface of the catalyst. The OMSC catalyst was found to be efficient in catalyzing glycerol conversion to acetin via an acetylation reaction with acetic acid within a short period of 3 h. Response surface methodology (RSM), based on a two-level, three-factor, face-centered central composite design, was used to optimize the reaction conditions. The results showed that the optimized temperature, glycerol-to-acetic acid mole ratio, and catalyst load were 126 °C, 1:10.4, and 0.45 g, respectively. Under these optimum conditions, 97% glycerol conversion (GC) and selectivities of 4.9, 27.8, and 66.5% monoacetin (MA), diacetin (DA), and triacetin (TA), respectively, were achieved and found to be close to the predicted values. Statistical analysis showed that the regression model, as well as the model terms, were significant with the predicted R2 in reasonable agreement with the adjusted R2 (<0.2). The OMSC catalyst maintained excellent performance in GC for the five reaction cycles. The selectivity to TA, the most valuable product, was not stable until the fourth cycle, attributable to the leaching of the acid sites

Effect of different supports for copper as catalysts on glycerol hydrogenolysis to 1,2-propanediol

In this work, several copper supported catalysts, Cu/Dol, Cu/Al2O3, Cu/Bent, Cu/Mont, and Cu/Talc were prepared using wet impregnation route and characterized using BET, BJH, XRD, H2-TPR, NH3–TPD, and SEM analytical techniques and subsequently tested in hydrogenolysis of glycerol to 1,2-propanediol (1,2-PDO). The nature of support was found to determine the activation of the catalysts. Among the tested catalysts, dolomite supported copper catalyst (Cu/Dol) exhibited superior performance due to the copper and dolomite species mutual interaction. The findings from the various characterization tests showed that the presence of copper species were essentially enriched on the dolomite grain surfaces, the redox properties, and acidic property of the catalyst enhanced, as well as the formation of the small size of the catalyst (Cu/Dol) contributed to the high conversion of glycerol (78.5%) and high 1,2-PDO selectivity (79%) with low methanol production as the by-product at 200 °C, 4 MPa H2 and 10 h reaction conditions

Effect of different supports for copper as catalysts on glycerol hydrogenolysis to 1,2-propanediol

In this work, several copper supported catalysts, Cu/Dol, Cu/Al2O3, Cu/Bent, Cu/Mont, and Cu/Talc were prepared using wet impregnation route and characterized using BET, BJH, XRD, H2-TPR, NH3–TPD, and SEM analytical techniques and subsequently tested in hydrogenolysis of glycerol to 1,2-propanediol (1,2-PDO). The nature of support was found to determine the activation of the catalysts. Among the tested catalysts, dolomite supported copper catalyst (Cu/Dol) exhibited superior performance due to the copper and dolomite species mutual interaction. The findings from the various characterization tests showed that the presence of copper species were essentially enriched on the dolomite grain surfaces, the redox properties, and acidic property of the catalyst enhanced, as well as the formation of the small size of the catalyst (Cu/Dol) contributed to the high conversion of glycerol (78.5%) and high 1,2-PDO selectivity (79%) with low methanol production as the by-product at 200 °C, 4 MPa H2 and 10 h reaction conditions

K2O doped dolomite as heterogeneous catalyst for fatty acid methyl ester production from palm oil

Biodiesel obtained from palm oil over an environmentally friendly catalyst is highlydesirable. For that matter, dolomite, a natural material was used as a catalyst in this work, and this included potassium oxide (K2O)-doped dolomite, 5 wt% K/D, 10 wt% K/D, 15 wt% K/D, and 20 wt% K/D. X-ray diffraction analysis of dolomite revealed the CaO and MgO phases with high crystallinity, in which intensity reduced after doped with varying concentrations of K2O. When the catalysts were evaluated, the K2O-doped dolomite exhibited a better catalytic activity for palm oil transesterification. In the presence of K2O, the methyl ester reached 98.7%, with the highest being displayed by 15 wt% K/D as compared to 87% over dolomite at reaction temperature of 60 °C, 12:1 methanol to palm oil ratio, 1 wt% catalyst amount and 1 h reaction time. SEM revealed that as more K2O was doped on dolomite, the particles became more agglomerated, with a reduced BET surface area of 1.3 m2/g in 20 wt% K/D as opposed to homogeneously small-sized MgO and CaO particles in dolomite with a high BET surface area of 19.0 m2/g. However, the high activity of the doped catalyst was dictated by the high amount of basic site, as evidenced in TPD-CO2 which showed an increase in the capacity of the basic site with an increased amount of K2O. The catalyst was also reusable up to six times with a negligible decrease in activity due to K+ leaching

Copper-dolomite as effective catalyst for glycerol hydrogenolysis to 1,2-propanediol

A series of Cu/dolomite catalysts were synthesized using the impregnation technique, characterized using NH3–TPD, FTIR-Pyridine, XRD, H2-TPR, BET, BJH, FESEM-EDX, and XPS techniques and evaluated in glycerol hydrogenolysis into 1,2-propanediol (1,2-PDO). Remarkably, dolomite support exhibited high acidity, which is, to our knowledge the first acid characteristic revealed among the reported literatures. By doping copper on dolomite support, the acid amount and strength of the catalyst increased. N2O chemisorption analysis suggests that the metallic copper species were well dispersed on dolomite support while the copper surface area increased with copper loading. The formation of metallic copper on dolomite support agreed well with findings derived from XRD and XPS analysis. According to the results of XPS and H2-TPR, metallic copper species were enriched on the grain surfaces of dolomite and not in the bulk. The addition of copper to dolomite ameliorates the redox properties of the catalysts, owing to the reduction at a lower temperature than that of pure CuO and dolomite support. From the catalytic results, 20 wt% Cu/dolomite was the most active catalyst by giving 100% glycerol conversion and 92% selectivity toward 1,2-PDO at 180 ºC, 2 MPa H2 in 6 h reaction time

Development of sulfonated carbon-based catalysts derived from palm kernel shell for acetylation of glycerol

The production and utilization of biodiesel have led to a significant increase in its by-product, glycerol, leading to a glut and value depreciation. Catalytic conversion of glycerol to acetin, a versatile industrial chemical, is one of the routes to improve its utilization. Currently, the homogeneous catalysts deployed are associated with many negative effects, while some of the existing heterogeneous catalysts exhibits low selectivity to triacetin, which is the most valued product. Carbon-based material, palm kernel shell (PKS), was processed and carbonized using direct, chemical, and template methods under CO2 environment and subsequently functionalized using inorganic, organic, and hybrid of organic-inorganic sulfonating agents. The catalysts were characterized using proximate analysis, acid-base titration, CHNS analyzer, X-ray diffraction (XRD), Fourier transform infra-red (FTIR) spectroscopy, temperature programmed desorption of ammonia (TPD-NH3), N2 physiosorption analysis (BET), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX), thermogravimetric-differential thermogravimetric analysis (TGA-DTG), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and solid state Nuclear Magnetic Resonance (NMR) spectroscopy, respectively. The carbon-based catalysts were deployed in glycerol acetylation and the product was analyzed using gas chromatography coupled with mass spectrometer (GC-MS), gas chromatograph equipped with flame ionization detector (GC-FID), FTIR and NMR. The catalyst obtained via template carbonization method at 800℃ exhibited excellent glycerol conversion (GC) with the highest triacetin selectivity. On optimization using RSM based on two-level, three-factor, face-centred central composite design (23 CCD), 97% GC and selectivity of 4.9, 27.8, and 66.5% monoacetin (MA), diacetin (DA), and triacetin (TA) were achieved under the optimum conditions of temperature 126±2℃, glycerol-to-acetic acid mole ratio (G/AA) 1:10.4, and catalyst load (CL) 0.45 g in 3 h reaction time. Amongst the organosulfonic acid functionalized catalysts, the ethanesulfonic acid (ESA) catalyst exhibited the highest TA selectivity and on optimization using RSM, 99.03% GC and selectivity of 6.91, 54.86, and 37.71% MA, DA, and TA were achieved at the optimum conditions of temperature 120±2℃, G/AA mole ratio 1:8, CL of 0.69 g and 3 h reaction time. Furthermore, the carbon-based catalyst obtained from the functionalization using the hybrid mixture of concentrated ethanesulfonic acid and sulfuric acid (1:9) exhibited excellent results after optimization. 99.8% GC and selectivity of 1.48, 24.64, and 73.81% MA, DA, and TA, respectively, were obtained under optimum conditions of temperature 110±2℃, G/AA mole ratio 1:10, and catalyst load 0.6 g in 3 h reaction time. On validation, all the model results exhibited good fit with good agreement between the predicted and the experimental data with the determination coefficient (R2) > 0.9500 and adequate signal-to-noise ratio >4. The high performance of the synthesized carbon catalysts was attributed to the synergistic effect of good physicochemical characteristics, including good textural properties and high acidic site density and very importantly, the configuration of the surface acid moieties on the catalyst allowing unhindered access to the active sites during the reaction. On evaluating the reusability and stability of the selected catalysts in five reaction cycles each, they maintained excellent performance in glycerol conversion but inferior in TA selectivity after the first use. The DA selectivity became higher in the subsequent reaction cycles. The instability of TA was due to the leaching of active sites (-SO3H)

Synthesis and characterization of sulfonated carbon catalysts derived from biomass waste and its evaluation in glycerol acetylation

Sulfonated carbon catalysts were synthesized from palm kernel shell biomass using direct, chemical and template methods of carbonization under CO2 environment at 400 and 800 °C respectively and subsequently functionalized with concentrated sulfuric acid. The precursor material and the synthesized catalysts were characterized by proximate analysis, CHNS, XRD, FTIR, TPD, TGA, SEM, N2 adsorption isotherm, BET surface area, and acid-base titration. The synthesized acid catalysts were evaluated in glycerol acetylation with acetic acid (molar ratio 1:6) in a batch liquid phase reaction under atmospheric pressure at 120 °C, 450 rpm for 1 h, 3 h, and 5 h respectively. The performance was compared with commercial Amberlyst-15 catalysts and homogeneous concentrated sulfuric acid. Of all the synthesized catalysts, the catalyst obtained from the template method carbonized at 800 °C showed the highest selectivity to triacetin (58.9%) with over 97% glycerol conversion within a 3-h reaction time. The selectivity to monoacetin and diacetin was 5.8 and 32.2% respectively. The catalytic activity of the catalyst was attributed to the synergistic effect of good physicochemical characteristics including textural properties and high acidic site density

Glycerol acetylation over yttrium oxide (Y2O3) catalyst supported on palm kernel shell-derived carbon and parameters optimization studies using response surface methodology (RSM)

A biomass derived carbon supported yttrium oxide catalyst (Y2O3/PKS-T700) was synthesized and evaluated in glycerol acetylation reaction using four-factor, two-level face-centred central composite design (24 CCD) of the response surface methodology (RSM). The catalyst exhibited high glycerol conversion (GC) (99.8%) and product selectivity of 11.1%, 60.2%, and 29.6% monoacetin (MA), diacetin (DA) and triacetin (TA) under optimized conditions of temperature 130 ℃, glycerol-to-acetic acid molar ratio 1:12 and catalyst loading 0.5 g in 5 h reaction time. The catalyst was synthesized via carbonization of palm kernel shell (PKS), impregnated with 15 wt% yttrium oxide (Y2O3) and calcined appropriately. The synthesized catalyst was further characterized by N2 physisorption analysis (BET surface area), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX), Fourier transform infra-red (FTIR), and temperature programmed desorption-ammonia (TPD-NH3). Results revealed that the catalyst is more of mesoporous material with large surface area, good pore volume and average size distributions. It is thermally stable with good acidity and various functional groups. On subjecting the catalyst to a reusability test in three (3) reaction cycles under the optimal conditions, it was found to maintain good acetylation reaction with little degradation