Bulk Methanol Research Articles

Application of Microwaves in the Production Process of Biodiesel from Bulk Oil

Abstract Using bulk oil as biodiesel fuel is a waste reduction opportunity that creates economic value and creates alternative fuels to replace diesel fuel. The research was conducted through the transesterification reaction of bulk oil and methanol in batches using microwave heating to speed up the reaction time. The research is expected to show the right performance and response time to achieve optimal biodiesel yield and biodiesel properties, according to the Indonesian Nasional Standard (SNI). The experiment used two power levels (100 and 400 watts) and three reaction times (5, 10 and 15 minutes). Based on the analysis of variance and extended Duncan’s test, microwave power and response time were found to have a significant <0.05 impact on product yield. The highest yield was 93.3%, achieved with a variation of 100 watts and a process time of 10 minutes. The results showed that, except for total glycerol, all quality criteria (density, acid number, saponification rate, methyl ester content, and iodine) met the SNI 7182:2015 standard [17]. It can be concluded that the use of microwaves has the potential to shorten the reaction time of biodiesel production while at the same time achieving high yield and good biodiesel quality.

Spectroscopic and Computational Study of ZnCl2-Methanol Low-Melting-Temperature Mixtures.

Alcoholic electrolyte mixtures have wide applications in industries. In this study, a series of mixtures composed of ZnCl2 and methanol (MeOH) with ZnCl2 mol % from 6.7 to 25 were prepared, and their spectral, structural, and thermodynamic properties were studied using infrared (IR) spectroscopy, differential scanning calorimetry (DSC), and density functional theory (DFT) calculations. The DFT-assisted analysis of excess spectra, supported by 2D-correlation spectroscopy, led to the identification of the major constituents of ZnCl2-MeOH mixtures, namely, MeOH monomer, MeOH dimer, and ZnCl2-3MeOH complex, produced after dissociation of MeOH trimer which represents the bulk methanol. The Hirshfeld charge analysis showed that in the competition between the O-H···Cl hydrogen bond (H-bond) and Zn ← O coordination bond to transfer charge in ZnCl2-MeOH complexes, the latter always dominates, making MeOH positively charged. The phase diagram of the binary system showed the presence of V-shaped glass transition temperatures (Tg), characteristic of low-melting mixture solvents (LoMMSs). The present study provides insights into the microscopic properties of the system and sheds light on the understanding of the general principles to prepare deep-eutectic solvents (DESs) or LoMMSs using inorganic salts and alcoholic compounds.

Anomalous proton transfer of a photoacid HPTS in nonaqueous reverse micelles.

The proton transfer reaction is one of the fundamental chemical reactions where the reaction dynamics strongly depend on solvent properties such as acidity or basicity. A photoacid 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) shows a sharp decrease of pKa (7.7 → 0.5) upon photoexcitation, and the excited-state proton transfer (ESPT) occurs with ultrafast time constants of 2.5 and 89 ps in bulk aqueous solution. However, the two-step proton transfers via the contact ion pair formation and the proton diffusion are strongly limited inside the nanopools of reverse micelles (RMs). The confinement in small RMs strongly impeded the proton transfer reactions. In this work, we report the ESPT of HPTS confined in methanol-in-oil RMs by steady-state and time-resolved electronic spectroscopy. Interestingly, HPTS shows substantial deprotonation in the excited state only in small RMs, while the ESPT of HPTS does not occur in bulk methanol solution due to the low basicity of aliphatic alcohols. The kinetic analysis of time-resolved fluorescence and transient absorption measurements will compare the proton transfer dynamics of HPTS in the water-in-oil and methanol-in-oil RMs. The ESPT of photoacids, especially in the nonaqueous RMs, can be crucial in understanding many important chemical reactions involving proton transfer in the confined environments of cells and membranes.

Excited-State Dynamics in 4-[4'(Dimethylamino)styryl]pyridine, a Photobase: Role of Photoinitiated Proton-Coupled Electron Transfer.

The photoinitiated proton-coupled electron transfer (PCET) process in photoacid-based adducts is predominantly governed by the evolution of the electron-proton transfer state. However, such a process is underexplored in the case of photobases as the excited states evolve through multiple competitive channels. Here, we elucidate the excited-state dynamics of a photobase, 4-[4'-(dimethylamino)styryl]pyridine (DMASP), in the presence of hexafluoroisopropanol (HFIP) that enables PCET. Transient absorption measurements show the evolution of a protonated species in the excited state with a time constant of ∼2.5 ps. Fluorescence upconversion measurements reveal the signatures of an emissive intramolecular charge transfer state and a protonated state. The role of such states is further confirmed by time-resolved measurements in the presence of trifluoroacetic acid and computational analysis. Furthermore, the proton-abstraction dynamics of DMASP is analyzed in bulk methanol and butanol solvents. The extent of proton abstraction by DMASP is found to be higher in the presence of HFIP when compared with the normal alcohols over a time period of a few picoseconds.

Competitive adsorption of alcohols over heteroatom zeolites hinders the catalytic conversion of sugar

In the catalysis of glucose from bulk methanol to Lewis acid centers via zeolite pores, MES-ATR-IR and PSD detected competitive adsorption driven by hydrogen bonding ascribed to the hydroxyl of the solvent, substrate, and interface. The phase-resolved spectra show a change from methanol- to glucose-silicon hydroxyl bonds, which slows the rate of Lewis acid center carbonyl activation. Moreover, increased silicon hydroxyl binding to glucose results in lower acidity of metal centers in the process. It almost eliminates the variations in reactivity caused by metal identity. In contrast, the absence of hydroxyl at the solvent, substrate, or interface prevents competitive adsorption and brings out the acidity of different metal centers, with Sn > In > Hf > Ti > Zr being the order of binding ability to the carbonyl. This study contributes to the development of zeotype metal center local environments for substrate and solvent matching in various reaction networks.

Development of Two-Dimensional Electronic-Vibrational Sum Frequency Generation (2D-EVSFG) for Vibronic and Solvent Couplings of Molecules at Interfaces and Surfaces.

Many photoinduced excited states' relaxation processes and chemical reactions occur at interfaces and surfaces, including charge transfer, energy transfer, proton transfer, proton-coupled electron transfer, configurational dynamics, conical intersections, etc. Of them, interactions of electronic and vibrational motions, namely, vibronic couplings, are the main determining factors for the relaxation processes or reaction pathways. However, time-resolved electronic-vibrational spectroscopy for interfaces and surfaces is lacking. Here we develop interface/surface-specific two-dimensional electronic-vibrational sum frequency generation spectroscopy (2D-EVSFG) for time-dependent vibronic coupling of excited states at interfaces and surfaces. We further demonstrate the fourth-order technique by investigating vibronic coupling, solvent correlation, and time evolution of the coupling for photoexcited interface-active molecules, crystal violet (CV), at the air/water interface as an example. The two vibronic absorption peaks for CV molecules at the interface from the 2D-EVSFG experiments were found to be more prominent than their counterparts in bulk from 2D-EV. Quantitative analysis of the vibronic peaks in 2D-EVSFG suggested that a non-Condon process participates in the photoexcitation of CV at the interface. We further reveal vibrational solvent coupling for the zeroth level on the electronic state with respect to that on the ground state, which is directly related to the magnitude of its change in solvent reorganization energy. The change in the solvent reorganization energy at the interface is much smaller than that in bulk methanol. Time-dependent center line slopes (CLSs) of 2D-EVSFG also showed that kinetic behaviors of CV at the air/water interface are significantly different from those in bulk methanol. Our ultrafast 2D-EVSFG experiments not only offer vibrational information on both excited states and the ground state as compared with the traditional doubly resonant sum frequency generation and electronic-vibrational coupling but also provide vibronic coupling, dynamical solvent effects, and time evolution of vibronic coupling at interfaces.

Complex formation in methanol-chloroform solutions: Vibrational spectroscopy and quantum cluster equilibrium study

Methanol-chloroform solutions with different mixing ratios were studied using vibrational (ATR FTIR and Raman) spectroscopy. Obtained spectra were analyzed by different techniques such as excess spectroscopy and multivariate curve resolution. Analysis of vibrational spectra showed that the investigated solutions consist of four kinds of species: ‘pure’ methanol, ‘pure’ chloroform, and two types of ‘effective’ molecular complexes. Molecular complexes were present in the entire concentration range of methanol dilutions in chloroform. Obtained spectral profiles of ‘pure’ methanol and ‘pure’ chloroform were identical to spectra of bulk species which means that their structure in solution is similar to corresponding ones in bulk methanol and chloroform.Minimal sets of possible structures of associates and molecular complexes were calculated using density functional theory. Information about optimized structures was further used for quantum cluster equilibrium (QCE) calculations. These calculations allowed us to explain the concentration dependence of excess enthalpy of methanol-chloroform solution. It was demonstrated that obtained concentrations of mixture components correlate with experimental ones obtained by MCR-ALS.

Ordered Solvents and Ionic Liquids Can Be Harnessed for Electrostatic Catalysis.

Herein, we employ classical molecular dynamics simulations using the Drude oscillator-based polarizable force field, quantum chemical calculations, and ONIOM multiscale calculations to study (a) how an external field orders the solvent environment in a chemical reaction and then (b) whether in the absence of this same applied field the ordered solvent environment alone can electrostatically catalyze a chemical reaction when compared with the corresponding disordered solvent. Our results show that a 0.2 V/Å external electric field, which is below the threshold for bond breaking of solvent molecules, leads to significant ordering of bulk methanol solvent and the ionic liquid [EMIM][BF4]. Importantly, in the absence of this same field, the ordered solvent lowers the activation energy of the hydrogen-transfer reaction of o-alkylphenyl ketones in excess of 20 kcal/mol when the solvent is methanol and by over 30 kcal/mol for [EMIM][BF4]. Even a 0.1 V/Å external field has effects of ca. 10 and 20 kcal/mol, respectively. This work suggests a possible strategy for scaling electrostatic catalysis by applying a pulsed external field to the reaction medium to maintain solvent ordering while allowing the reaction to proceed largely in the absence of an external field.

Iridium-Catalyzed Selective Cross-Coupling of Ethylene Glycol and Methanol to Lactic Acid.

An atom-economic approach that has an unprecedented high selectivity for the synthesis of lactic acid (LA) based on a catalytic dehydrogenative cross-coupling by using inexpensive bulk ethylene glycol and methanol is described. This method relies on the synthesis and utilization of a novel iridium catalyst bearing three N-heterocyclic carbenes derived from 1,3-dimethylbenzimidazolium salts, and exhibits outstanding activity in the production of LA [turnover frequency (TOF) up to 3660 h-1 ] owing to an elegant metal-ligand cooperation.

Iridium‐Catalyzed Selective Cross‐Coupling of Ethylene Glycol and Methanol to Lactic Acid

AbstractAn atom‐economic approach that has an unprecedented high selectivity for the synthesis of lactic acid (LA) based on a catalytic dehydrogenative cross‐coupling by using inexpensive bulk ethylene glycol and methanol is described. This method relies on the synthesis and utilization of a novel iridium catalyst bearing three N‐heterocyclic carbenes derived from 1,3‐dimethylbenzimidazolium salts, and exhibits outstanding activity in the production of LA [turnover frequency (TOF) up to 3660 h−1] owing to an elegant metal–ligand cooperation.

Excited-state dynamics of 4-dimethylamino-4′-nitrobiphenyl confined in AOT reverse micelles

Abstract We report the excited-state intramolecular charge transfer (ICT) dynamics of 4-dimethylamino-4′-nitrobiphenyl (DNBP) in the reverse micelles (RMs) of bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT) by time-resolved fluorescence and transient absorption spectroscopy. The absorption and emission bands of DNBP in the RMs appeared as blue-shifted from the maximum wavelengths of bulk methanol solution, which can be understood as the decrease of solvent polarity in the RMs. The quantum yield and excited-state lifetime of DNBP in the RMs increase enormously upon the decrease of the micelle size, which is interpreted as the decrease of the micropolarity and the increase of microviscosity in the small RMs. The efficient intersystem crossing to the triplet states and strong phosphorescence of DNBP in the near-infrared region was also observed in the small RMs, which results from the strongly restricted torsional relaxation of biphenyl group in the confined environments of the small RMs. We have observed the site-specific and micelle size-dependent excited-state dynamics of DNBP in the methanol/AOT/isooctane RMs, which may originate from the less homogeneous environment of the confined solvent pools of the RMs than bulk.

Surface solvation and hindered isomerization at the water/silica interface explored with second harmonic generation.

Resonantly enhanced second harmonic generation (SHG) spectra of Coumarin 152 (C152) adsorbed at the water-silica interface show that C152 experiences a local dielectric environment slightly more polar than that of bulk water. This result stands in contrast to recently reported time-resolved fluorescence experiments and simulations that suggest an alkane-like permittivity for interfacial water at strongly associating, hydrophilic solid surfaces. Taken together, these results imply that while the static electric field across the aqueous-silica interface may be large, restricted water dynamics lead to apparent nonpolar solvation behavior similar to that experienced by solutes in confinement. Resonance-enhanced SHG spectra and time-resolved fluorescence of C152 adsorbed to aqueous-hydrophobic silica surfaces show that when water's ability to hydrogen bond with the silica surface is eliminated, a solute's interfacial solvation and corresponding ability to photoisomerize converge to an intermediate limit similar to that experienced in bulk acetone or methanol. While water structure and dynamics at solid-liquid interfaces have received considerable attention, results presented below show how strong solvent-substrate interactions can create conflicting pictures of solute reactivity across buried interfaces.

The Influence of Sodium Iodide Salt on the Interfacial Properties of Aqueous Methanol Solution by a Combined Molecular Simulation and Sum Frequency Generation Vibrational Spectroscopy Study.

Understanding the influence of salt ions on the microscopic properties of liquid interfaces is of both fundamental and practical importance. A large number of previous experimental and theoretical investigations have explored the salt effects on the surfaces of either pure water or neat organic liquid. However, how the salt ions affect the interfacial structures of water/organic liquid mixtures has rarely been studied. Here, the molecular dynamics (MD) simulations and sum frequency generation vibrational spectroscopy (SFG-VS) were carried out to investigate the influence of sodium iodide (NaI) on the air/liquid interfaces of the methanol-water mixtures. The SFG-VS spectral intensities were discovered to increase with the addition of 3 M NaI, while the center frequencies of the C-H stretching vibrations at high methanol concentrations showed a ∼2 cm-1 blue shift compared with those obtained before adding NaI. The MD results indicated that Na+ and I- can only affect Part I (near the bulk phase) but not Part II (near the gas phase) of the interfacial region. It was also found that the average orientations of interfacial methyl groups were constant and not effectively disturbed by the changes of methanol concentrations or the addition of NaI. It is therefore concluded that the changes of the SFG-VS intensities upon the addition of NaI salts were mainly caused by the increasing number of interfacial methanol molecules. Further analysis showed that the existence of NaI affects the surface tensions more for the interfaces with higher bulk methanol concentrations, which is in agreement with the SFG-VS results. It is noteworthy that the maximum number density of methanol molecules with the net nonzero orientations is reached near the Gibbs dividing surface, the reasons of which are worth further investigating.

Molecular dynamics simulations of nano-confined methanol and methanol-water mixtures between infinite graphite plates: Structure and dynamics.

Molecular dynamics simulations are used to investigate microscopic structures and dynamics of methanol and methanol-water binary mixture films confined between hydrophobic infinite parallel graphite plate slits with widths, H, in the range of 7-20 Å at 300 K. The initial geometric densities of the liquids were chosen to be the same as bulk methanol at the same temperature. For the two narrowest slit widths, two smaller initial densities were also considered. For the nano-confined system with H = 7 Å and high pressure, a solid-like hexagonal arrangement of methanol molecules arranged perpendicular to the plates is observed which reflects the closest packing of the molecules and partially mirrors the structure of the underlying graphite structure. At lower pressures and for larger slit widths, in the contact layer, the methanol molecules prefer having the C-O bond oriented parallel to the walls. Layered structures of methanol parallel to the wall were observed, with contact layers and additional numbers of central layers depending on the particular slit width. For methanol-water mixtures, simulations of solutions with different composition were performed between infinite graphite slits with H = 10 and 20 Å at 300 K. For the nanoslit with H = 10 Å, in the solution mixtures, three layers of molecules form, but for all mole fractions of methanol, methanol molecules are excluded from the central fluid layer. In the nanopore with H = 20 Å, more than three fluid layers are formed and methanol concentrations are enhanced near the confining plates walls compared to the average solution stoichiometry. The self-diffusion coefficients of methanol and water molecules in the solution show strong dependence on the solution concentration. The solution mole fractions with minimal diffusivity are the same in confined and non-confined bulk methanol-water mixtures.

A simple two dimensional model of methanol

Methanol is the simplest alcohol and possible energy carrier because it is easier to store than hydrogen and burns cleaner than fossil fuels. It is a colorless liquid, completely miscible with water and organic solvents and is very hygroscopic. Here, simple two-dimensional models of methanol, based on Mercedes–Benz (MB) model of water, are examined by Monte Carlo simulations. Methanol particles are modeled as dimers formed by an apolar Lennard-Jones disk, mimicking the methyl group, and a sphere with two hydrogen bonding arms for the hydroxyl group. The used models are the one proposed by Hribar-Lee and Dill (Acta Chimica Slovenica, 53:257, 2006.) with the overlapping disks and a new model with tangentially fused dimers. The comparison was done between the models, in connection to the MB water, as well as with experimental results and with new simulations done for 3D models of methanol. Both 2D models show similar trends in structuring and thermodynamics. The difference is the most pronounced at lower temperatures, where the smaller model exhibits spontaneous crystallization, while the larger model shows metastable states. The 2D structural organization represents well the clustering tendency observed in 3D models, as well as in experiments. The models qualitatively agree with the bulk methanol thermodynamic properties like density and isothermal compressibility, however, heat capacity at the constant pressure shows trend more similar to the water behavior. This work on the smallest amphiphilic organic solute provides a simple testing ground to study the competition between polar and non-polar effects within the molecule and physical properties.

Synergistic Enhancement of Electron-Accepting and -Donating Ability of Nonconjugated Polymer Nanodot in Micellar Environment.

Understanding the fundamental electron-transfer dynamics in photoactive carbon nanoparticles (CNPs) is vitally important for their fruitful application in photovoltaics and photocatalysis. Herein, photoinduced electron transfer (PET) to and from the nonconjugated polymer nanodot (PND), a new class of luminescent CNP, has been investigated in the presence of N,N-dimethylaniline (DMA) and methyl viologen (MV2+) in homogeneous methanol and sodium dodecyl sulfate (SDS) micelles. It has been observed that both DMA and MV2+ interact with the photoexcited PND and quench the PL intensity as well as excited-state lifetime in bulk methanol. While in bulk methanol, purely diffusion-controlled PET from DMA to MV2+ via PND has been observed, the mechanism and dynamics differ significantly in SDS micelles. In contrast to homogeneous methanol medium, a distinct synergic effect has been observed in SDS micelles. The presence of both DMA and MV2+ enhances the electron-accepting and -donating abilities of PND in SDS micelles. Time-resolved photoluminescence (PL) measurements reveal that the PET process in SDS micelles is nondiffusive in nature mainly due to instantaneous electron transfer at the confined micellar surface. These results have been explained on the basis of heterogeneous microenvironments of SDS micelles which compartmentalize the donor and acceptor inside its micellar pseudo phase. The present findings provide valuable insights into the intrinsic relation between redox and PL properties of nonconjugated PND.

Excess electrons in methanol clusters: Beyond the one-electron picture.

We performed a series of comparative quantum chemical calculations on various size negatively charged methanol clusters, CH3OHn-. The clusters are examined in their optimized geometries (n = 2-4), and in geometries taken from mixed quantum-classical molecular dynamics simulations at finite temperature (n = 2-128). These latter structures model potential electron binding sites in methanol clusters and in bulk methanol. In particular, we compute the vertical detachment energy (VDE) of an excess electron from increasing size methanol cluster anions using quantum chemical computations at various levels of theory including a one-electron pseudopotential model, several density functional theory (DFT) based methods, MP2 and coupled-cluster CCSD(T) calculations. The results suggest that at least four methanol molecules are needed to bind an excess electron on a hydrogen bonded methanol chain in a dipole bound state. Larger methanol clusters are able to form stronger interactions with an excess electron. The two simulated excess electron binding motifs in methanol clusters, interior and surface states, correlate well with distinct, experimentally found VDE tendencies with size. Interior states in a solvent cavity are stabilized significantly stronger than electron states on cluster surfaces. Although we find that all the examined quantum chemistry methods more or less overestimate the strength of the experimental excess electron stabilization, MP2, LC-BLYP, and BHandHLYP methods with diffuse basis sets provide a significantly better estimate of the VDE than traditional DFT methods (BLYP, B3LYP, X3LYP, PBE0). A comparison to the better performing many electron methods indicates that the examined one-electron pseudopotential can be reasonably used in simulations for systems of larger size.

Wavelength Dependence of UV Photoemission from Solvated Electrons in Bulk Water, Methanol, and Ethanol.

We have measured the wavelength dependence (340-215 nm) of one-photon photoemission from the ground electronic state of solvated electrons in bulk water, methanol, and ethanol. In every case, the vertical electron binding energy (VBE) gradually increased with photon energy, indicating that the photoelectron kinetic energy diminishes as a result of electron-vibration inelastic scattering prior to emission from the liquid surface. In contrast, the VBE of the Rydberg electron in DABCO (1,4-diazabicyclo[2,2,2]octane), which has a surface-excess density, revealed no clear wavelength dependence. These results suggest that the solvated electrons are created predominantly in the bulk and that VBEs measured using UV photoemission spectroscopy of liquids generally require energy corrections to account for inelastic scattering effects. From the wavelength dependence, we have re-estimated the VBEs of solvated electrons in bulk water, methanol, and ethanol to be 3.3, 3.1, and 3.1 eV, respectively. Hydrated electrons were also identified by photoemission spectroscopy using 90 nm radiation.

Structural transformations in bulk and matrix-isolated methanol from measured and computed infrared spectroscopy

FTIR spectra of methanol trapped in an Ar matrix were registered during gradual heating of the sample. The spectral changes observed in these experiments indicate a transformation from isolated methanol monomers to small hydrogen-bonded clusters, allowing us to consider such experiments as an experimental model of the gas–liquid phase transition. The liquid–solid phase transition for methanol was investigated by analysing the temperature dependence of the registered FTIR spectra of methanol during cooling from −70°C to −115°C. Comparing the experimental spectra in the CO stretching region with results of quantum-chemical calculations using the method of principal component analysis we draw conclusions about the size and structure of the methanol clusters formed in the sample at different temperatures.

Adsorption and Aggregation at Silica/Methanol Interfaces: The Role of Solute Structure

Second harmonic generation (SHG) and time-resolved, total internal reflection fluorescence (TR-TIRF) spectroscopy were used to examine the adsorption, solvation, and aggregation of a coumarin solute, Coumarin 152 (C152), at the silica/methanol interface. Experiments were performed as a function of bulk C152 concentration with SHG data providing information about relative surface coverage and ground state solvation environment. TR-TIRF data measured emission lifetimes of C152 adsorbed to the silica/methanol interface. SHG spectra show strong resonance enhancement at 365 nm, a result that is blue-shifted considerably from C152’s electronic excitation of ∼400 nm in bulk methanol. Given C152’s solvatochromic behavior, this observation implies that C152 adsorbed to the silica/methanol interface experiences a local dielectric environment that is significantly less polar than in bulk methanol. TR-TIRF decays at sub-micromolar bulk concentrations were fit to two lifetimes: one assigned to C152 emission in bulk methanol (0.9 ns) and a longer lifetime assigned to contributions from adsorbed C152 (∼4 ns). The longer lifetime is similar to C152 in alkanes, a result that is consistent with SHG data. Isothermal data from SHG experiments show unusual behavior as bulk C152 concentration increases. Instead of approaching an asymptotic limit signifying monolayer coverage, the SHG response rises at the lowest C152 concentrations and then decreases dramatically, suggesting the onset of aggregate formation. Changes in the TR-TIRF emission behavior of C152 at higher C152 bulk concentrations support this hypothesis. These findings are interpreted in terms of C152’s ability to self-associate, and the energetics of dimer formation are explored using ab initio calculations and polarizable continuum models.