Mechanistic insight into sonochemical biodiesel synthesis using heterogeneous base catalyst

The beneficial effect of ultrasound on transesterification reaction is well known. Heterogeneous (or solid) catalysts for biodiesel synthesis have merit that they do not contaminate the byproduct of glycerol. In this paper, we have attempted to identify the mechanistic features of ultrasound–enhanced biodiesel synthesis with the base–catalyst of CaO. A statistical design of experiments (Box–Behnken) was used to identify the influence of temperature, alcohol to oil molar ratio and catalyst loading on transesterification yield. The optimum values of these parameters for the highest yield were identified through Response Surface Method (with a quadratic model) and ANOVA. These values are: temperature = 62 °C, molar ratio = 10:1 and catalyst loading = 6 wt.%. The activation energy was determined as 82.3 kJ/mol, which is higher than that for homogeneous catalyzed system (for both acidic and basic catalyst). The experimental results have been analyzed vis–à–vis simulations of cavitation bubble dynamics. Due to 3–phase heterogeneity of the system, the yield was dominated by intrinsic kinetics, and the optimum temperature for the highest yield was close to boiling point of methanol. At this temperature, the influence of cavitation bubbles (in terms of both sonochemical and sonophysical effect) is negligible, and ultrasonic micro–streaming provided necessary convection in the system. The influence of all parameters on the reaction system was found to be strongly inter–dependent.     

Synthesis of sub-micronic and nanometric PMMA particles via emulsion polymerization assisted by ultrasound: Process flow sheet and characterization

PMMA particle synthesis was performed from MMA (methyl methacrylate) and water mixtures, exposed to different ultrasonic systems and frequencies. The sonication sequence was 20 kHz → 580 kHz → 858 kHz → 1138 kHz, and the solution was sampled after each irradiation step for polymerization. Effects of sonication parameters (time, power), polymerization method (thermo-initiated or photo-initiated), use of small amounts of surfactant (Triton X-100™ or Tween® 20) and initial MMA quantity were investigated on particle size and synthesis yields. Particle size and size distribution were measured by DLS (Dynamic Light Scattering), and confirmed via SEM (Scanning Electron Microscopy) images. Synthesis yield was calculated using the dry weight method. Particle composition was estimated using FTIR (Fourier Transform Infra-Red) spectroscopy. PMMA (polymethylmethacrylate) monodispersed particles were successfully synthesized, with a possibility of control in the 78–310 nm size range. These sized-controlled particles were synthesized with a 7.5–85% synthesis yield (corresponding to 7.5–40 g/L particle solid content), depending on operational parameters. Furthermore, a trade-off between particle size and synthesis yield can be proposed: 20 kHz → 10 min waiting time → 580 kHz → 858 kHz leading to 90 nm particles diameter with 72% yield in less than 40 min for the whole sequence. Thus, the synthesis under ultrasound can be found easy to implement and time efficient, ensuring the success of the scale-up approach and opening up industrial applications for this type of polymeric particles.     

Ultrasound assisted co-precipitation of nanostructured CuO–ZnO–Al2O3 over HZSM-5: Effect of precursor and irradiation power on nanocatalyst properties and catalytic performance for direct syngas to DME

Nanostructured CuO–ZnO–Al₂O₃/HZSM-5 was synthesized from nitrate and acetate precursors using ultrasound assisted co-precipitation method under different irradiation powers. The CuO–ZnO–Al₂O₃/HZSM-5 nanocatalysts were characterized using XRD, FESEM, BET, FTIR and EDX Dot-mapping analyses. The results indicated precursor type and irradiation power have significant influences on phase structure, morphology, surface area and functional groups. It was observed that the acetate formulated CuO–ZnO–Al₂O₃/HZSM-5 nanocatalyst have smaller CuO crystals with better dispersion and stronger interaction between components in comparison to nitrate based nanocatalysts. Ultrasound assisted co-precipitation synthesis method resulted in nanocatalyst with more uniform morphology compared to conventional method and increasing irradiation power yields smaller particles with better dispersion and higher surface area. Additionally the crystallinity of CuO is lower at high irradiation powers leading to stronger interaction between metal oxides. The nanocatalysts performance were tested at 200–300 °C, 10–40 bar and space velocity of 18,000–36,000 cm³/g h with the inlet gas composition of H₂/CO = 2/1 in a stainless steel autoclave reactor. The acetate based nanocatalysts irradiated with higher levels of power exhibited better reactivity in terms of CO conversion and DME yield. While there is an optimal temperature for CO conversion and DME yield in direct synthesis of DME, CO conversion and DME yield both increase with the pressure increase. Furthermore ultrasound assisted co-precipitation method yields more stable CuO–ZnO–Al₂O₃/HZSM-5 nanocatalyst while conventional precipitated nanocatalyst lost their activity ca. 18% and 58% in terms of CO conversion and DME yield respectively in 24 h time on stream test.     

Green ultrasound-assisted extraction of carotenoids based on the bio-refinery concept using sunflower oil as an alternative solvent

A green, inexpensive and easy-to-use method for carotenoids extraction from fresh carrots assisted by ultrasound was designed in this work. Sunflower oil was applied as a substitute to organic solvents in this green ultrasound-assisted extraction (UAE): a process which is in line with green extraction and bio-refinery concepts. The processing procedure of this original UAE was first compared with conventional solvent extraction (CSE) using hexane as solvent. Moreover, the UAE optimal conditions for the subsequent comparison were optimized using response surface methodology (RSM) and ultra performance liquid chromatography – diode array detector – mass spectroscopy (UPLC–DAD–MS). The results showed that the UAE using sunflower as solvent has obtained its highest β-carotene yield (334.75 mg/l) in 20 min only, while CSE using hexane as solvent obtained a similar yield (321.35 mg/l) in 60 min. The green UAE performed under optimal extraction conditions (carrot to oil ratio of 2:10, ultrasonic intensity of 22.5 W cm^?2, temperature of 40 °C and sonication time of 20 min) gave the best yield of β-carotene.     

Carbon nanostructures synthesized by arc discharge between carbon and iron electrodes in liquid nitrogen

An idea of using pure iron and graphite electrodes was employed for synthesizing carbon nanoparticles by arc discharge in liquid nitrogen. The synthesized products consist of multiwalled carbon nanotubes (MW–CNT), carbon nanohorns (CNH), and carbon nanocapsules (CNC) with core–shell structure. Effect of metallic cathode and discharge current on product structure and yield had been experimentally investigated. Typical evidence of transmission electron microscopic images revealed that under some certain conditions of discharge in liquid nitrogen the synthesized products mainly consisted of CNCs with mean diameter of 50–400 nm. When conventional graphitic electrodes were employed, CNHs with some MW–CNTs were mainly synthesized. Meanwhile, MW–CNTs with diameter of 8–25 nm and length 150–250 nm became less selectively synthesized as cathode deposit under the condition of discharge in liquid nitrogen with higher arc current. The production yield of carbon nanoparticles synthesized by either carbon–carbon or carbon–iron electrodes became also lower with an increase in the arc current.     

Effect of oil extraction assisted by ultrasound on the physicochemical properties and fatty acid profile of pumpkin seed oil (Cucurbita pepo)

The effects of amplitude and time of ultrasound-assisted extraction on the physicochemical properties and the fatty acid profile of pumpkin seed oil (Cucurbita pepo) were evaluated. Ultrasound time (5–30 min) and the response variables amplitude (25–100%), extraction yield, efficiency, oxidative stability in terms of the free fatty acids (FFA) of the plant design comprising two independent experiments variables, peroxide (PV), p-anisidine (AV), totox value (TV) and the fatty acid profile were evaluated. The results were analyzed by multiple linear regression. The time and amplitude showed significant differences (P < 0.05) for all variables. The highest yield of extraction was achieved at 5 min and amplitude of 62.5% (62%). However, the optimal ultrasound-assisted extraction conditions were as follows: ultrasound time of 26.34 min and amplitude of 89.02%. All extracts showed low FFA (2.75–4.93% oleic acid), PV (1.67–4.68 meq/kg), AV (1.94–3.69) and TV (6.25–12.55) values. The main fatty acids in all the extracts were oleic and linoleic acid. Therefore, ultrasound-assisted oil extraction had increased performance and reduced extraction time without affecting the oil quality.     

Esterification of sodium 4-hydroxybenzoate by ultrasound-assisted solid–liquid phase-transfer catalysis using dual-site phase-transfer catalyst

The catalytic esterification of sodium 4-hydroxybenzoate with benzyl bromide by ultrasound-assisted solid–liquid phase-transfer catalysis (U-SLPTC) was investigated using the novel dual-site phase-transfer catalyst 4,4′-bis(tributylammoniomethyl)-1,1′-biphenyl dichloride (BTBAMBC), which was synthesized from the reaction of 4,4′-bis(chloromethyl)-1,1′-biphenyl and tributylamine. Without catalyst and in the absence of water, the product yield at 60 °C was only 0.36% in 30 min of reaction even under ultrasound irradiation (28 kHz/300 W) and 250 rpm of stirring speed. When 1 cm³ of water and 0.5 mmol of BTBAMBC were added, the yield increased to 84.3%. The catalytic intermediate 4,4′-bis(tributylammoniomethyl)-1,1′-biphenyl di-4-hydroxybenzoate was also synthesized to verify the intrinsic reaction which was mainly conducted in the quasi-aqueous phase locating between solid and organic phases. Pseudo-first-order kinetic equation was used to correlate the overall reaction, and the apparent rate coefficient with ultrasound (28 kHz/300 W) was 0.1057 min⁻¹, with 88% higher than that (0.0563 min⁻¹) without ultrasound. The esterification under ultrasonic irradiation using BTBAMBC by solid–liquid phase-transfer catalysis was developed.     

Ultrasonic pretreatment of corn slurry for saccharification: A comparison of batch and continuous systems

The effects of ultrasound on corn slurry saccharification yield and particle size distribution was studied in both batch and continuous-flow ultrasonic systems operating at a frequency of 20 kHz. Ground corn slurry (28% w/v) was prepared and sonicated in batches at various amplitudes (192–320 μm_{peak-to-peak (p–p)}) for 20 or 40 s using a catenoidal horn. Continuous flow experiments were conducted by pumping corn slurry at various flow rates (10–28 l/min) through an ultrasonic reactor at constant amplitude of 12 μm_p–p. The reactor was equipped with a donut shaped horn. After ultrasonic treatment, commercial alpha- and gluco-amylases (STARGEN^TM 001) were added to the samples, and liquefaction and saccharification proceeded for 3 h. The sonicated samples were found to yield 2–3 times more reducing sugars than unsonicated controls. Although the continuous flow treatments released less reducing sugar compared to the batch systems, the continuous flow process was more energy efficient. The reduction of particle size due to sonication was approximately proportional to the dissipated ultrasonic energy regardless of the type of system used. Scanning electron microscopy (SEM) images were also used to observe the disruption of corn particles after sonication. Overall, the study suggests that both batch and continuous ultrasonication enhanced saccharification yields and reduced the particle size of corn slurry. However, due to the large volume involve in full scale processes, an ultrasonic continuous system is recommended.     

Ultrasound assisted extraction of pectin from waste Artocarpus heterophyllus fruit peel

Four factors three level face centered central composite response surface design was employed in this study to investigate and optimize the effect of process variables (liquid-solid (LS) ratio (10:1–20:1 ml/g), pH (1−2), sonication time (15–30 min) and extraction temperature (50–70 °C)) on the maximum extraction yield of pectin from waste Artocarpus heterophyllus (Jackfruit) peel by ultrasound assisted extraction method. Numerical optimization method was adapted in this study and the following optimal condition was obtained as follows: Liquid-solid ratio of 15:1 ml/g, pH of 1.6, sonication time of 24 min and temperature of 60 °C. The optimal condition was validated through experiments and the observed value was interrelated with predicted value.     

Ultrasound-assisted extraction and purification of schisandrin B from Schisandra chinensis (Turcz.) Baill seeds: Optimization by response surface methodology

The objective of this study is to develop a process consisting of ultrasonic-assisted extraction, silica-gel column chromatography and crystallization to optimize pilot scale recovery of schisandrin B (SAB) from Schisandra chinensis seeds. The effects of five independent variables including liquid–solid ratio, ethanol concentration, ultrasonic power, extraction time, and temperature on the SAB yield were evaluated with fractional factorial design (FFD). The FFD results showed that the ethanol concentration was the only significant factor for the yield of SAB. Then, with the liquid–solid ratio 5 (mL/g) and ultrasonic power 600 W, the other three parameters were further optimized by means of response surface methodology (RSM). The RSM results revealed that the optimal conditions consisted of 95% ethanol, 60 °C and 70 min. The average experimental SAB yield under the optimum conditions was found to be 5.80 mg/g, which was consistent with the predicted value of 5.83 mg/g. Subsequently, a silica gel chromatographic process was used to prepare the SAB-enriched extract with petroleum ether/acetone (95:5, v/v) as eluents. After final crystallization, 1.46 g of SAB with the purity of 99.4% and the overall recovery of 57.1% was obtained from 400 g seeds powder. This method provides an efficient and low-cost way for SAB purification for pharmaceutical industrial applications.     

Improved synthesis of sucrose fatty acid monoesters under ultrasonic irradiation

Sucrose fatty acid esters were synthesized by the transesterification of sucrose with aliphatic esters under ultrasound irradiation in good yield (?73%). The optimum reaction conditions for the transesterification reaction include a molar ratio of sucrose to fatty acid ethyl ester of 2:1 and the use of a 13% mol anhydrous K₂CO₃ catalyst. The optimum reaction temperature was set at 70 °C, the optimum reaction time was 2 h, and the optimum reaction pressure was 11 kPa. The reaction had excellent monoester selectivity. The proportion of monoester (6-monoester + 6′-monoester) in the purified products was up to 92–95% via flash column chromatography over silica gel, the ratios of 6-monoester/6′-monoester are 2.1–2.7, and the sucrose monoesters were identified by HPLC–MS, NMR and IR.     

High yield synthesis of Ni-BTC metal–organic framework with ultrasonic irradiation: Role of polar aprotic DMF solvent

Nickel based porous solid was synthesized with 20 kHz ultrasonic irradiation. The reaction of Ni(II) nitrate hexahydrate with 1,3,5-benzene tricarboxylic acid in N,N-Dimethylformamide (DMF) as the sole solvent under ultrasonic radiation produced porous Ni-BTC MOF. Choice of correct solvent for the ultrasonic treatment was proven important. The effect of varying ultrasonic powers (40%, 60% and 80% of 750 W) along with different temperature conditions (50 °C, 60 °C, 70 °C and 80 °C) influenced the respective yield. A very high yield of 88% Ni-BTC MOF was obtained from 80% ultrasonic power at 60 °C. BET surface areas of the MOF crystals measured by N₂ gas adsorption isotherms were in the range of 960–1000 m²/g.     

Picosecond molecular switch based on the influence of photogenerated electric fields on optical charge transfer transitions

A concept for a picosecond molecular switch is demonstrated using a photoinduced electron transfer reaction in a covalently linked, fixed distance donor–acceptor molecule D–A linked to a perylene-3,4-dicarboximide chromophore, C. The chromophore C possesses a strong charge transfer transition in its optical spectrum. Selective excitation of C within D–A–C using 530 nm, 130 fs laser pulses produces^1 * C, which undergoes singlet–singlet energy transfer to produce^1 * D, which in turn transfers an electron to A. If the D–A–C system is selectively excited with 416 nm, 130 fs laser pulses to produce D ⁺ – A ⁻ –C prior to excitation of C with 530 nm, 130 fs laser pulses, a 25% lower yield of^1 * C is generated. The intense local electric field produced by D ⁺ – A ⁻ causes a 15 nm electrochromic red shift of the charge transfer absorption of C. Thus, the absorption of C at 530 nm is significantly diminished by the presence of D ⁺ – A ⁻ . The need to use two laser pulses with different wavelengths to observe these effects, and the resulting picosecond time response makes it possible to consider applications of this concept in the design of molecular switches.     

Activation of methyl acetate on Pd(111)

The adsorption and activation of methyl acetate (CH₃COOCH₃), one of the simplest carboxylic esters, on Pd(111) have been studied using self-consistent periodic density functional theory calculations. Methyl acetate adsorbs weakly through the carbonyl oxygen. Its activation occurs via dehydrogenation, instead of direct C–O bond dissociation, on clean Pd(111): It is much more difficult to dissociate the C–O bonds (E_a ≈ 2.0 eV for the carbonyl and acetate–methyl bonds; E_a = 1.0 eV for the acetyl–methoxy bond) than to dissociate the C–H bonds to produce enolate (CH₂COOCH₃; E_a = 0.74 eV) or methylene acetate (CH₃COOCH₂; E_a = 0.82 eV). The barriers for C–H and C–O bond dissociation are directly calculated for enolate and methylene acetate, and estimated for further dehydrogenated derivatives (CH₃COOCH, CH₂COOCH₂, and CHCOOCH₃) based on the Brønsted–Evans–Polanyi linear energy relations formed by the calculated steps. The enolate pathway leads to successive dehydrogenation to CCOOCH₃, whereas methylene acetate readily dissociates to yield acetyl. The selectivity for dissociating the acyl–alkoxy C–O bond, which is desired for alcohol formation, is therefore fundamentally limited by the facility of dehydrogenation under vacuum/low-pressure conditions on Pd(111).     

Baeyer–Villiger oxidation of cyclohexanone to ε-caprolactone in airlift sonochemical reactor

Baeyer–Villiger oxidation of cyclohexanone to ε-caprolactone was studied in a new type reactor – the airlift loop sonochemical reactor. The reactor plays a synergistic effect of sonochemsity and higher oxygen transfer rate. The influences of ultrasound intensity, reaction temperature, the molar ratio of benzaldehyde to cyclohexanone and oxygen gas flow rate on the conversion and selectivity of cyclohexanone were investigated and discussed. Under ultrasound, the amount of benzaldehyde can be reduced from 75% to 67%. Ultrasound not only intensified the rates of reactions but also increased the yield of product. The optimized operation conditions are listed as follows: the reaction temperature is 30 °C, the molar ratio of cyclohexanone to benzaldehyde is 1:2, the oxygen gas flow rate is 1.15 cm s⁻¹, and ultrasonic irradiations 2 h at 40 kHz, 2.25 W cm⁻². Under the optimum operation conditions, the average molar yield of ε-caprolactone comes up to 87.7%.     

Intensification of biodiesel production from soybean oil and waste cooking oil in the presence of heterogeneous catalyst using high speed homogenizer

In the present work, high speed homogenizer has been used for the intensification of biodiesel synthesis from soybean oil and waste cooking oil (WCO) used as a sustainable feedstock. High acid value waste cooking oil (27 mg of KOH/g of oil) was first esterified with methanol using sulphuric acid as catalyst in two stages to bring the acid value to desired value of 1.5 mg of KOH/g of oil. Transesterification of soybean oil (directly due to lower acid value) and esterified waste cooking oil was performed in the presence of heterogeneous catalyst (CaO) for the production of biodiesel. Various experiments were performed for understanding the effect of operating parameters viz. molar ratio, catalyst loading, reaction temperature and speed of rotation of the homogenizer. For soybean oil, the maximum biodiesel yield as 84% was obtained with catalyst loading of 3 wt% and molar ratio of oil to methanol of 1:10 at 50 °C with 12,000 rpm as the speed of rotation in 30 min. Similarly biodiesel yield of 88% was obtained from waste cooking oil under identical operating conditions except for the catalyst loading which was 1 wt%. Significant increase in the rate of biodiesel production with yields from soybean oil as 84% (in 30 min) and from WCO as 88% (30 min) was established due to the use of high speed homogenizer as compared to the conventional stirring method (requiring 2–3 h for obtaining similar biodiesel yield). The observed intensification was attributed to the turbulence caused at microscale and generation of fine emulsions due to the cavitational effects. Overall it can be concluded from this study that high speed homogenizer can be used as an alternate cavitating device to efficiently produce biodiesel in the presence of heterogeneous catalysts.     

Sub-ps pump and probe photoemission from polycrystalline molybdenum

Pump and probe electron photoemission, induced by 150 fs–790 nm laser pulses on polycrystalline molybdenum, is used to investigate the non-linear photoemissive regime. The analysis of these experimental data evidences third and fourth order thermally assisted currents that contribute to the electron yield. In addition, partial yield measurements at very low pulse intensities confirm the above analysis, evidencing a change in the logarithmic slope as predicted by the theory.     

Ultrasonic biodiesel synthesis from crude Jatropha curcas oil with heterogeneous base catalyst: Mechanistic insight and statistical optimization

This paper reports studies in ultrasound-assisted heterogeneous solid catalyzed (CaO) synthesis of biodiesel from crude Jatropha curcas oil. The synthesis has been carried out in two stages, viz. esterification and trans-esterification. The esterification process is not influenced by ultrasound. The transesterification process, however, shows marked enhancement with ultrasound. A statistical experimental design has been used to optimize the process conditions for the synthesis. XRD analysis confirms formation of Ca(OMe)₂, which is the active catalyst for transesterification reaction. The optimum values of parameters for the highest yield of transesterification have been determined as follows: alcohol to oil molar ratio ≈ 11, catalyst concentration ≈ 5.5 wt.%, and temperature ≈ 64 °C. The activation energy of the reaction is calculated as 133.5 kJ/mol. The heterogeneity of the system increases mass transfer constraints resulting in approx. 4× increase in activation energy as compared to homogeneous alkali catalyzed system. It is also revealed that intense micro-convection induced by ultrasound enhances the mass transfer characteristics of the system with ∼20% reduction in activation energy, as compared to mechanically agitated systems. Influence of catalyst concentration and alcohol to oil molar ratio on the transesterification yield is inter-linked through formation of methoxy ions and their diffusion to the oil–alcohol interface, which in turn is determined by the volume fractions of the two phases in the reaction mixture. As a result, the highest transesterification yield is obtained at the moderate values of catalyst concentration and alcohol to oil molar ratio.     

Methylamine decomposition on nickel surfaces: A density functional theory study

The adsorption and decomposition of methylamine on Ni(1 1 1), Ni(1 0 0), stepped Ni(1 1 1), and nitrogen atom modified Ni(1 0 0) (denoted N–Ni(1 0 0)) have been studied with the DFT–GGA method using the periodic slab models. The initial scissions of C–H, N–H and C–N bond are considered. The adsorption energies under the most stable configurations for the possible species and the activation energies for the possible initial elementary reactions involved are obtained in the present work. Through systematic exploring of the kinetics mechanism of methylamine decomposition on these four surfaces, it is found that the reactivity of these surfaces decreased with the order of stepped Ni(1 1 1) > Ni(1 0 0) > Ni(1 1 1) > N–Ni(1 0 0). This indicates that the reactivity is related to the openness of the surface, and the presence of nitrogen atom reduces the reactivity of the Ni(1 0 0). For the three reactions, the barriers decreased with the order of C–N > N–H > C–H on Ni(1 1 1) and Ni(1 0 0), whereas they decreased with the order of C–N > C–H > N–H on stepped Ni(1 1 1) and N–Ni(1 0 0).