Supercritical Ethanol Conditions Research Articles

The bifunctional active sites on carbon supported Fe-Mo bimetallic catalyst to improve Kraft lignin liquefaction

Carbon-supported Fe-Mo bimetallic catalysts were synthesized for the thermal catalytic ethanolysis of lignin to liquid fuels composed of aromatic monomers. A yield of 40.7 wt % of lignin oil, consisting of 38.8 wt % phenol monomers and 39.3 wt % benzeneacetaldehyde monomers, was obtained in the presence of Fe-Mo-P catalysts (1:0.5) at 290 °C for 4 h in the supercritical ethanol solvent (6.5 MPa). The catalysts exhibited a rich distribution of α-MoC nanoparticles, Fe0 nanoclusters, surface oxygen defects, and active species of Mo6+ and phosphoric acid on the graphitized microporous carbon substrate. The synergistic effects of these active components were crucial for enhancing lignin liquefaction efficiency. The ethanolysis of the lignin model compound revealed that the Fe-Mo bimetallic catalyst can facilitate double cracking of C-C/C-O bonds under supercritical ethanol conditions. In situ Raman and FT-IR characterization were performed to monitor the transformation of the Fe-Mo bimetallic catalyst from the precursor to the carbon material, including the dehydration and carbonization of the organic precursor.

ZnO:V Nanoparticles with Enhanced Antimicrobial Activities

In this study, we used sol-gel to synthesize undoped and V-ZnO nanoparticles with different vanadium concentrations (1, 3, and 5 at.%) under supercritical dry conditions of ethanol. XRD spectra showed that the obtained powders are well crystallized in the hexagonal wurtzite structure of ZnO nanoparticles. The average crystallite size, estimated by the Debye-Scherer formula, was found to be equal to 31 nm for the pure sample, and it was decreased to 27 nm for the 3at.% vanadium-doped one. SEM and TEM photographs indicated the spherical and elongated shapes of the nanoparticles. The stretching bands located at 419 cm−1 confirmed ZnO material formation. The efficacy of the produced ZnO NPs against Gram+, Gram− bacteria, and fungi was tested. Vanadium-doped ZnO, with low concentrations (10 µg/mL), exhibited a large influence on bacterial and fungi growth inhibition. For example, the inhibition zones IZ of S. aureus and E. coli bacteria reached 16 and 15 mm, respectively, for ZnO:V1%, while the IZ of these two bacteria were 14 and 12 mm for the undoped ZnO. The use of V-dopant enhanced the production of the reactive oxygen species ROS by the photogeneration of electron-hole pairs due to light absorption by ZnO in the visible region.

Hydrodeoxygenation of lignin derived bio-oil into aromatic hydrocarbons over Ni-Cu-Ru/HZSM-5 catalyst

The complexity and diversity of lignin derived bio-oil (LDB) has posed a great challenge to the subsequent processing and utilization. In this work, HZSM-5 was modified by sodium hydroxide and followed by Ni, Cu and Ru species. LDB was used as the raw biocrude to prepare bio-oil rich in aromatic hydrocarbons with modified HZSM-5 catalysts under supercritical ethanol conditions (320 °C, 14 MPa). Results showed that the desilicated HZSM-5 with the loading of Ni, Cu and Ru (Ni-Cu-Ru/DeHZSM-5) exhibited the best catalytic performance with a high relative amount of aromatic hydrocarbons of 28.95%. After catalytic hydrodeoxygenation (HDO) of LDB, 80.40% upgraded bio-oil (UBO) with 96.32% energy recovery was obtained in the presence of Ni-Cu-Ru/DeHZSM-5. Demethoxylation and dehydration were the main reactions in the catalytic HDO process. Potential reaction pathways of guaiacol, syringol and creosol were also proposed in this paper. The heating value of UBO reached 35.22 MJ/kg compared with LDB, which was increased by 19.80%. The water content and viscosity of UBO were also significantly improved. The micro-mesoporous structure of modified HZSM-5 with loading of Ni, Cu and Ru was beneficial to promote the yield of the aromatic hydrocarbons.

New Catalysts for Biodiesel Production under Supercritical Conditions of Alcohols: A Comprehensive Review

AbstractNowadays, due to detrimental carbon dioxide emissions and dwindling non‐renewable fossil energy from crude oil, biodiesel from green sources such as vegetable oils, animal fats, waste oils and microbial oils have been described as a promising non‐fossil fuel, renewable, sustainable, clean, and biodegradable. So far, transesterification is the most superior process for converting green resources into biodiesel by reacting with alcohol in the presence of a catalyst. This process is influenced by some considerations such as alcohol to oil molar ratio, reaction temperature, reaction pressure, reaction time and specifically the amount of catalyst, which greatly affect the reaction performance and the biodiesel production. In depth, this review will discuss novel catalysts for biodiesel production under supercritical methanol and ethanol conditions by reviewing published articles related to this field to date.

Contactless Visible Luminescence Thermometry Based on β-Phase Zinc Silicate Confined in Silica Glass Matrix

Nanophosphors zinc silicate β-phase in glass matrix with adequate manganese concentration were synthesized by a sol–gel method in three steps. In the first one, a sol-gel process was used for the synthesis of ZnO:Mn nanopowder. In the second one, the elaborated nanopowder was incorporated in silica aerogel monolith using supercritical conditions of ethanol and in the third step, a simple solid-solid reaction under natural atmosphere for 2 h at 1500 °C was performed. The obtained samples are composed by grains with an average size of about 70 nm in a triclinic phase dispersed in silica host matrix. This protocol leads to a very stable 15 at.% Mn doped zinc silicate β-phase at high temperature. The analysis of the obtained nanophosphor material showed a strong broad yellow emission at 584 nm attributed to 4T1(4G) to 6A1(6S) transition. The intensity and the time decay of this yellow emission depend on the measurement temperature. In fact, the decreases rate of the PL intensity is of 12.7% and the rate of lifetime change is of about 2.7%. These results are considered as promising values compared to those obtained until now. These two potential behaviours make it possible to predict the use of this material in various technological applications, particularly in contactless luminescence thermometry.

Facile synthesis of superparamagnetic Fe3O4 nanoparticles at therapeutic temperature range for magnetic hyperthermia therapy

Superparamagnetic Fe3O4 nanoparticles have been synthesized using simple and ecofriendly hydrothermal method at supercritical conditions of ethanol. The morphology and crystal structure reveal cubic-like shape with an average size of 63 ± 30 nm and formation of FCC Fe3O4 phase structure. The magnetic properties exhibit superparamagnetic-like behavior at room temperature with saturation magnetization (Ms) of 108 emu/g and coercivity (HC) close to 0 Oe. The temperature dependence on magnetization measurements has confirmed the superparamagnetic behavior with blocking temperature TB of 320 K at the therapeutic temperature range of hyperthermia therapy at 42–47 °C. Feasibility for magnetic hyperthermia has been tested under applied AC magnetic field and frequency ranges from 100 to 500 Oe and 147 to 304 kHz, respectively. The findings confirm that Fe3O4 nanoparticles are feasible for magnetic hyperthermia treatment of cancer.

The effect of rare earth element (Er, Yb) doping and heat treatment on suspension stability of Y2O3 nanoparticles elaborated by sol-gel method

Sol–gel processing was used to fabricate undoped and rare-earth (Er, Yb) doped very fine Y2O3 nanoparticles under supercritical drying conditions of ethanol using an autoclave and annealed at 500 °C and 800 °C for 2 h. The Er and/or Yb concentration is fixed at 5 mol % for doped and co-doped nanoparticles. The as-synthesized Y2O3 nanopowder was characterized by the X-ray diffraction, scanning electron microscopy and thermogravimetric analysis (TGA) coupled with differential thermal calorimetry (DTA). The effects of solvent, heat treatment and the doping on the suspension stability of yttrium oxide (Y2O3) nanoparticles doped rare-earth elements (Er and Yb) were evaluated by UV-Visible spectroscopy, zeta potential measurement and particle size in suspension, thus, Hamaker 2 software. During this work, the particle analysis showed that the resulting nanoparticles had a pure cubic structure and nano-sized crystallites of about 8–38 nm. The heat treatment of the nanopowders causes a rapid decantation of the suspensions and the Er doped nanoparticles suspension had a good stability.

Effects of Ti-precursor concentration and annealing temperature on structural and morphological properties of TiO2 nano-aerogels synthesized in supercritical ethanol

TiO2 nano-aerogels are elaborated by using acid-modified sol–gel approach from titanium tetra isopropoxide under supercritical drying conditions of ethanol. The effects of Ti-precursor concentration and annealing temperature on structural and morphological properties of TiO2 nanoparticles are investigated by XRD, infrared spectroscopy, SEM and specific surface area measurements. It was found, from XRD analysis, that pure anatase phase is obtained for the aerogels synthesized with various precursor concentrations. The increase of sol concentration leads to a slight and uniform variation of TiO2 cell parameters. The specific surface area of aerogels particles decreases and the pore volume increases with increasing of Ti-concentration. The presence of Ti–O and Ti–O–Ti bonds is confirmed by FTIR measurements. EDAX analysis shows that TiO2 nano-aerogels are oxygen rich. SEM images put into evidence the almost spherical elaborated particles with an enhanced agglomeration at high precursor concentration. With the increase of annealing temperature, the mixture of the phases did not happen and the pure anatase to pure rutile transition phase temperature is found to be around 900 °C. The Ti–O–C bonds disappear with annealing temperature. The heat treatment leads not only to the changes in crystal structure but also in morphology of the elaborated aerogels grains.

Catalytic Hydrotreatment of Industrial Wood Tar under Supercritical Ethanol Conditions

Catalytic hydrotreatment under supercritical ethanol conditions is an effective method for improving the performance of wood tar. In this study, the physicochemical properties of industrial wood ta...

Two-step sub/supercritical water and ethanol processes for non- catalytic biodiesel production

The catalyst-free two-step process has been developed for biodiesel production using low-grade feedstocks. The first step consists of triglycerides hydrolysis under subcritical water conditions to generate and increase free fatty acid (FFA) content for ethyl ester production. In its subcritical state, water can be used as both a solvent and a reactant for the hydrolysis of triglycerides. The hydrolyzed product mixture is separated by decantation into the oil phase of FFA (upper layer) and a water phase that contains glycerol (lower layer). In the second step, the hydrolyzed products of free fatty acids were successfully esterified to their ethyl ester in supercritical ethanol conditions without any catalyst. Under the sub- and supercritical conditions of water and ethanol, the hydrolysis and the esterification reactions proceed quickly, with a conversion of greater than 98 % after 10−20 min. This two-step process for biodiesel production offers several advantages, such as milder reaction conditions and pollution reduction due to the use of water instead of organic solvents. Also, the glycerol is removed after the hydrolysis reaction so that the backward reaction between the glycerol and the ethyl ester disappears, and lead to the biodiesel yield and quality improvement. The aim of this study is making a comparison between our previous one-step process and the two-step reaction process to find the best pathway for designing and building an integrated reactor. Indeed, the two-step process is more applicable for low-grade feedstocks with a high amount of FFA and water.

Highly sensitive NO2 gas sensor based on hematite nanoparticles synthesized by sol–gel technique

The sol–gel technique was utilized to synthesize α-Fe2O3 nanoparticles in supercritical conditions of ethanol. The morphology and microstructure were investigated by scanning and transmission electron microscopy (SEM and TEM) analysis and X-ray diffraction (XRD).The average crystallite size estimated by sherrer’s equation was 60 nm. TEM images show that the obtained powder is composed of agglomeration of irregular shaped (between oval and spherical) grains. The prepared nanomaterial was used as sensing layer in gas sensing device. The sensor has been tested towards low concentrations in air of NO2 at different temperatures from 200 to 350 °C. We noticed that 225 °C was the best operating temperature. At this temperature, the obtained results indicated that the realized sensor has a high response towards 1 ppm of NO2 gas. The response and recovery times are 26 and 48 s, respectively. To show the selectivity of the sensor, we have tested it with different gases such as CO, CO2, and NH3. We found that hematite sensor exhibits high selectivity towards NO2 gas.

PET depolimerization in supercritical ethanol conditions catalysed by nanoparticles of metal oxides

The depolymerization of the PET in supercritical conditions using ethanol and catalyzed by cobalt and nickel oxides was enough for the recovery of the DET monomer, allowing yields close to 100 % depolymerization. The formation of DET in the depolymerization process was characterized by 1H-NMR, DSC, FTIR, SEM, and HPLC. Cobalt oxide and nickel oxide were obtained through the Pechini method and characterized using DRX, SEM, and TEM. A factorial design 22 with a duplicate center point was applied to evaluate the reaction time and amount of the catalyst effects on yield. Through analysis of response surface methodology (RSM), the highest degree of PET conversion (%) was obtained in 90 min reaction time and a smaller amount of catalyst (10 mg) through analysis of response surface contour. The smaller quantity of catalyst was sufficient to accelerate the process of depolymerization reaching almost 100 % yield, obtaining the monomer DET as the main product.

Nucleation of Co3C Magnetic Nanoparticles Using Supercritical Condition of Ethanol

Co3C magnetic nanoparticles have been synthesized using supercritical conditions of ethanol. The phase structure of the samples has shown two phases of orthorhombic Co3C and Co structures. The morphology of the prepared nanoparticles reveals a spherical-like shape. Tailoring the synthesis parameters has led to controlling the magnetic properties depending on the ratio of Co3C:Co in the samples. The magnetic properties of the samples have been measured, revealing ferromagnetic behavior. The data yield coercivity (HC) was of 600–950 Oe and saturation magnetization (MS) of 20–38 emu/g. The results present alternative approach to nucleate Co3C magnetic nanoparticles. The synthesis method will be optimized in the future to produce a pure Co3C phase structure.

Elaboration and characterization of glass–ceramic enriched by heavily manganese doped zinc silicate nanoparticles for optoelectronic applications

Nanocrystallines Mn2+-doped zinc silicate (β-Zn2SiO4:Mn) embedded in SiO2 host matrix were synthesized in two steps. In the first one a sol–gel process was used for the elaboration of silica aerogel monolith enriched by ZnO:Mn nanoparticles using supercritical conditions of ethanol. In the second step a simple solid-phase reaction under natural atmosphere at 1500 °C was investigated. The structure and texture of the obtained nanocomposites were studied by X-ray diffraction and transmission electron microscopy respectively. The optical results indicate that the obtained nanocomposites have excellent luminescence properties in the visible range. In addition, the PL spectrum for the β-Zn2SiO4:Mn/SiO2 nanocomposite reveals a band centered at about 584 nm attributed to the 4T1–6A1 transitions of Mn2+ ions. The intensive yellow luminescence presents a red shift and the lifetime is relatively weak compared to the known luminescence properties of this material. The obtained results are attributed to the protocol used and the excess of Mn2+ ions. The linear diminishing behaviours of the PL integrate intensity with the operating temperature, and the variation of the time decay with the Mn2+ contents; make it possible to anticipate the utilization of this material in luminescence thermometry.

Structural and optical characterizations of (Cu, Ce) iso-co-doped ZnO aerogel structures grown in supercritical ethanol

Undoped, Ce-doped, Cu-doped and (Ce, Cu) co-doped ZnO aerogels were synthesized by sol–gel process in supercritical conditions of ethanol. [Cu]/[Zn] and [Ce]/[Zn] atomic ratios were fixed at 0.02 (2%). The aerogels were investigated without any additional treatments by using X-ray diffraction (XRD), UV–visible spectrophotometry, scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), thermal gravimetric analysis (TGA), Fourier transforms infrared spectroscopy (FTIR) and photoluminescence spectroscopy. XRD results revealed that all the samples are well crystallized in hexagonal wurtzite structure. TGA and EDS measurements showed that highly pure aerogels are prepared. SEM analysis indicated that the morphology of the samples is dependent on Cu and Ce dopants. From UV–visible spectroscopy analyses, it was shown that the absorption and the band gap of the aerogels are strongly affected by Ce and Cu dopants. FTIR spectra demonstrated that co-doping induces a shift of Zn–O bond vibration band toward low wavenumbers. The room temperature photoluminescence spectra put into evidence that Ce and Cu doping influence the visible emission intensity. In particular, the iso-codoping leads to the appearance of a blue emission band at 443 nm.

Controlled pinewood fractionation with supercritical ethanol: A prerequisite toward pinewood conversion into chemicals and biofuels

Abstract The objective of this work was to investigate the ability of supercritical (SC) ethanol conditions to attack preferentially the lignin fraction against the carbohydrate fraction and their effects on the product distribution among gases, light products, bio-oils, and chars. In this study, the conversion of each pinewood component was determined by the analysis of solid residues to quantify cellulose, hemicellulose, lignin, and char contents. It is shown that, by tuning the temperature, hemicellulose and lignin are already transformed in subcritical ethanol conditions, lignin being more reactive than hemicellulose. In contrast, native wood cellulose is recalcitrant to liquefaction in SC ethanol near the critical point (Tc = 241 °C and Pc = 61 bar), but 20% of native wood cellulose is converted in SC ethanol at 280 °C. Besides, the severity of the conditions, in terms of temperature and treatment time, does not significantly influence the yields of gases, light products, and bio-oils but strongly enhances char formation. Interestingly, the increase in SC ethanol density does not change the conversion of biomass components but has a marked effect on bio-oil yield and prevents char formation. The optimum fractionation conditions to convert the lignin component, while keeping unattacked the cellulose fraction with a minimum formation of char, are dense SC ethanol, at 250 °C for 1 h, in batch conditions. However, although lignin is more reactive than hemicellulose under these conditions, these fractions are converted, in a parallel way, to around 50% and 60%, respectively.

Effects of (Ce, Cu) Co-doping on the Structural and Optical Properties of ZnO Aerogels Synthesized in Supercritical Ethanol

Undoped, Ce-doped, Cu-doped and (Ce,Cu ) co-doped ZnO aerogels were synthesized by sol-gel process in supercritical conditions of ethanol. [Cu]/[Zn] and [Ce]/[Zn] atomic ratios were fixed at 0.02 (2%). The aerogels were investigated without any additional treatments by using X-ray diffraction (XRD), UV–visible spectrophotometry, scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), Fourier transforms infrared spectroscopy (FTIR) and photoluminescence spectroscopy (PL). XRD results revealed that all the samples are well crystallized in hexagonal wurtzite structure. EDS measurements showed that highly pure aerogels are prepared. SEM analysis indicated that the morphology of the samples is dependent on Cu and Ce dopants. From UV-visible spectroscopy analyses, it was shown that the absorption and the band gap of the aerogels are strongly affected by Ce and Cu dopants. FTIR spectra demonstrated that co-doping induces a shift of Zn-O bond vibration band toward low wavenumbers. The room temperature photoluminescence spectra put into evidence that the visible emission intensity is influenced by Ce and Cu doping. In particular, the co-doping leads to the appearance of a blue emission band at 443 nm.

The Effect of Solvents and Rare-Earth Element (Er, Yb) Doping on Suspension Stability of Sol-Gel Titania Nanoparticles.

The effects of solvent on the suspension stability of titanium dioxide (TiO2) nanoparticle (NP)-doped rare-earth elements (Er and Yb) were evaluated. Pure and doped TiO2 NPs were successfully prepared by the sol-gel method under the supercritical drying conditions of ethanol. Doped nanopowders were prepared with 5 mol% Er or 5 mol% Yb concentration, and co-doped nanopowders were prepared with fixed 5 mol% Er concentration and various Yb concentrations of 5 and 10 mol%. TiO2 NP suspensions with diverse solvents, such as water, ethanol, methanol, and butanol, were prepared. The nanopowders were characterized by studying their structural and morphology properties. The NP size analysis revealed the average size of TiO2 as approximately around 7-12 nm. Suspensions of TiO2 NPs in different solvents were prepared by a two-step powder dispersion process using several ultrasonication methods. The aim of this paper was to prepare a stable suspension for a certain time period and then to produce doped and undoped TiO2 NP coatings for photovoltaic application. The effects of concentration, dopants, and solvents on the dispersibility and stability of TiO2 suspensions were evaluated. The UV-visible spectroscopy, zeta potential measurements, particle size distribution, SEM, and Hamaker 2 software confirm that the 5%Er-10%:TiO2 suspension exhibits a good stability and stable suspension improved by co-doped rare.

Synthesis and characterization of antimony doped tin oxide aerogel nanoparticles using a facile sol–gel method

High purity antimony doped tin oxide (ATO) aerogel nanoparticles with various concentrations of Sb have been successfully synthesized using modified sol–gel method. In this process, hydrolysis was slowly released and followed by a thermal drying in supercritical conditions of ethanol. The aim of this study is to enhance the properties of nanoparticles with low doping concentration and low cost. The structural, morphological, optical and electrical properties were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, UV–Vis–IR spectroscopy, Fourier transform infrared spectroscopy (FTIR) and impedance spectroscopy, respectively. We show that ATO aerogels have a polycrystalline tetragonal rutile structure with a highly (110) plane preferred orientation. The grain sizes are in the range of 13–23 nm, dependending on the elaboration conditions. Raman spectra reveals fundamental peaks at 483, 633, and 770 cm− 1, corresponding to the Eg, A1g and B2g vibration modes, respectively, in a good agreement with those for the rutile bulk SnO2. The optical band gap of tin oxide increases slightly from 3.88 to 3.94 eV with the increase of Sb content. Impedance spectroscopy results indicate that the electrical properties are strongly dependent on temperature and doping rate. All results suggested that the as-prepared ATO nanoparticles were good quality material for thin film solar cell applications.

Catalytic upgrading of bio-tar over a MgNiMo/activated charcoal catalyst under supercritical ethanol conditions

Upgrading of bio-tar derived from fast pyrolysis of sawdust was performed over activated charcoal supported nickel-based catalysts (Ni/AC, NiMo/AC, MgNiMo/AC) under supercritical ethanol conditions. The catalytic activities of the catalysts was compared with those of representative bio-oil upgrading catalysts (Ru/AC, HZSM-5). The MgNiMo/AC catalyst exhibited the highest catalytic performance among the catalysts with a decrease of oxygen content in bio-tar from 31.3wt% up to 10.8wt% and the yield of liquid product (75wt%). The effects of reaction temperature (275–350°C), reaction time (0–120min) and bio-tar to ethanol ratio (1/9–4/6) were also studied over the MgNiMo/AC catalyst. In addition, reaction of vanillin which is one of major compounds present in bio-tar was carried out under the same bio-tar upgrading conditions in order to understand the production mechanism of phenolic chemicals.