Increasing Methanol Concentration Research Articles

The mass transport based on convection effects in a passive DMFC under open-circuit conditions

The study investigates the open-circuit characteristics of a passive direct methanol fuel cell (DMFC) based on temperature-induced convection effects, including the reactants distributions at anode, the non-uniform temperature distribution and the methanol crossover. A two-dimensional, well-thought-out numerical model coupling with mass transfer and momentum transfer is exploited for DMFC to investigate its inner component and temperature distributions under open-circuit condition. In addition, a 4.0 cm2 passive DMFC has been designed and manufactured by the laser-cutting technology for experimental verification. The average methanol crossover flux, methanol diffusion coefficient and crossover current are obtained, which coincide with the simulation data well. The temperature-induced convection simulation results show that the distorted temperature distribution becomes more obvious with higher methanol concentration. Furthermore, the polarization curve, cell temperature and open-circuit voltage (OCV) are measured by varying the methanol concentration to conduct more in-depth research on DMFC performance at open circuit state. The results indicate that the temperature is increased, whereas the OCV is decreased with the increase of methanol concentration, accompanied by the phenomenon of methanol crossover is aggravated. The paper provides the theory basis and the optimal operating parameters for safe start-up of DMFC.

Quenching for Microalgal Metabolomics: A Case Study on the Unicellular Eukaryotic Green Alga Chlamydomonas reinhardtii.

Capturing a valid snapshot of the metabolome requires rapid quenching of enzyme activities. This is a crucial step in order to halt the constant flux of metabolism and high turnover rate of metabolites. Quenching with cold aqueous methanol is treated as a gold standard so far, however, reliability of metabolomics data obtained is in question due to potential problems connected to leakage of intracellular metabolites. Therefore, we investigated the influence of various parameters such as quenching solvents, methanol concentration, inclusion of buffer additives, quenching time and solvent to sample ratio on intracellular metabolite leakage from Chlamydomonas reinhardtii. We measured the recovery of twelve metabolite classes using gas chromatography mass spectrometry (GC-MS) in all possible fractions and established mass balance to trace the fate of metabolites during quenching treatments. Our data demonstrate significant loss of intracellular metabolites with the use of the conventional 60% methanol, and that an increase in methanol concentration or quenching time also resulted in higher leakage. Inclusion of various buffer additives showed 70 mM HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) to be suitable. In summary, we recommend quenching with 60% aqueous methanol supplemented with 70 mM HEPES (−40 °C) at 1:1 sample to quenching solvent ratio, as it resulted in higher recoveries for intracellular metabolites with subsequent reduction in the metabolite leakage for all metabolite classes.

Hydrogen transfer versus olefins methylation: On the formation trend of propene in the methanol-to-hydrocarbons reaction over Beta zeolites

Beta zeolites with similar textural properties but variable Brønsted acid site (BAS) densities in the range of 25.5–203.8 μmol g−1 were fabricated and investigated as catalysts in the methanol-to-hydrocarbons reaction. The intrinsic influence of BAS amount, BAS density and methanol conversion on the reaction mechanism was investigated. Interestingly, methanol conversion depends on the BAS amount regardless of the BAS density. The increase of methanol concentration could modulate the product distribution by promoting the methanol-induced hydrogen transfer reaction and enhancing the olefins methylation as well as inhibiting the cracking of higher olefins. As the BAS density decreases from 203.8 to 56.6 μmol g−1, hydrogen transfer reaction is gradually restrained while the olefin interconversion is enhanced, leading to gradual replacement of aromatics-based cycle by the olefins-based cycle and thus increasing the propene selectivity. However, as BAS density further decreases from 56.6 μmol g−1, the propene selectivity declines because the methylation route in the olefins-based cycle is much more favoured than the cracking route. After detailed investigation of the deactivation behaviours of involved Beta zeolites, it has been found that the accumulation of long-chain alkanes and large polycyclic aromatics is responsible for the catalyst deactivation. These results provide further insights into the effect of BAS density on the reaction mechanism and product selectivity.

Swelling and Diffusion during Methanol Sorption into Hydrated Nafion

Diffusion within polymer electrolyte membranes is often coincident with time-dependent processes such as swelling and polymer relaxation, which are factors that limit their ability to block molecular crossover during use. The solution-diffusion model of membrane permeation, which is the accepted theory for dense polymers, applies only to steady-state processes and does not address dynamic internal structural changes that can accompany permeation. To begin discovery of how such changes can be coupled to the permeation process, we have constructed a stochastic multiscale reaction-diffusion model that examines time-dependent methanol uptake into and swelling of hydrated Nafion. Several potential mechanisms of diffusion and polymer response are tested. The simulation predictions are compared to real-time Fourier transform infrared attenuated total reflectance spectroscopy (FTIR-ATR) absorbance reported in the literature [ Hallinan , D. T. , Jr. ; Elabd , Y. A. J. Phys. Chem. B 2007 , 111 , 13221 - 13230 ]. Of the proposed polymer response mechanisms, only one, a reaction-limited, local response to increasing methanol concentration that takes the entire experimental time frame of 600 s, produces simulated FTIR-ATR data consistent with experiment. The simulations show that water diffusion out of the membrane is minimal during methanol sorption and that changes in the measured infrared absorbances are due primarily to the increase in methanol concentration accompanied by dilution of water during swelling. Swelling involves densification of the polymer structure even as there is an overall volume expansion of the film. Potential connections between the polymer densification and molecular-level structural changes of Nafion in methanol are discussed. These results indicate that the interaction between methanol and Nafion serves to increase Nafion's capacity to accommodate large volumes of methanol-water solutions, facilitating increased permeation across the membrane relative to pure water.

Adsorption and dissolution of methane at the surface of the methanol-water mixture

Adsorption and dissolution of methane at its interface with methanol-water liquid mixture was studied by applying classical molecular dynamics simulations. The role of molecular level roughness of the liquid surface on the dissolution of methane was examined by determining the average density profile of methane along the direction perpendicular to the interface. It is revealed that a methane molecule is more likely to enter the bulk liquid through the humps of the rough liquid surface. The effect of composition of the liquid on the molecular level roughness of its surface was examined. The results indicate that with an increase in concentration of methanol in the liquid, its surface becomes more rough in terms of height and depth of the humps and wells. The larger humps at the surface of methanol rich mixture suggest an enhanced dissolution of methane into the liquid through these humps. The distribution of methane adsorbed above the liquid surface was also examined which indicated a larger methane density above the wells than the humps. The non-uniform distribution of methane is explained in terms of the potential energy of its interaction with the molecules of the liquid. The effect of methane on the orientation of interfacial methanol molecules was analyzed and it is revealed that the presence of methane enhances the tendency of these methanol molecules to have their methyl groups oriented towards the gas phase.

Highly effective enhancement of waste activated sludge dewaterability by altering proteins properties using methanol solution coupled with inorganic coagulants

Proteins are the dominant organic component of extracellular polymeric substances (EPS) in waste activated sludge (WAS), and play an important role during sludge dewatering processes. Methanol is a polar hydrophilic reagent and can denature proteins, which suggested to us that the modification of protein configurations with methanol could improve sludge dewatering performance.In this study, methanol was used to precondition WAS prior to adding inorganic coagulants for dewatering enhancement. The morphology and EPS properties (especially of proteins) were investigated to analyze and explain the effects of methanol in the sludge conditioning process. The results show that methanol performed much better than traditional inorganic coagulants in improving sludge dewaterability in term of specific resistance to filtration (SRF) and cake solid content (CSC). Extractable proteins in EPS increased to a maximum when the concentration of methanol reached 40% (w/w) because cell membranes were destroyed and intracellular substances and water were released. Floc protein content was reduced with the further increase in methanol concentration due to protein precipitation. Confocal laser scanning microscopy analysis indicated that proteins precipitated and formed larger aggregates because methanol destroyed both the hydration shell and the hydrophobic clusters of proteins and expanded the protein tertiary structure to release interstitial water and bound water. The combination treatment of methanol and inorganic coagulants (PAC or FeCl3) showed significant synergetic effects on enhancing sludge dewatering and cake drying. In practical applications, methanol from the dewatering sludge can be returned to the biochemical pool and used as the carbon source for nitrogen removal in the denitrification process. This integrated process is appropriate for sludge final disposal technologies that have high energy demands, such as incineration and pyrolysis. This paper describes a novel approach to improving sludge dewaterability through the alteration of protein properties by use of physiochemical techniques.

Recovery of Rutin from Labisia pumila Extract Using Solid Phase Extraction.

Reflux extraction was used to prepare crude extract from the leaves of Labisia pumila var. Alata using 60% methanol. The crude extract was subsequently fractionated by C18 solid phase extraction to recover high yield of rutin using 20-100% methanol. The volume of eluent to recover rutin was found to decrease with the increase of methanol concentration. The recovery of rutin was increased from 20 to 80% methanol system, but slightly decreased in the 100% methanol system. Approximately, 70% of rutin could be recovered using the 80% methanol system. This solvent system also appears to have the lowest distance (9.44 MPa1/2) for rutin as estimated by Hansen solubility. The recovered rutin rich fraction could achieve up to 3.96 mg/g of fraction which was about 4-fold increment from the crude extract. The increment was also noticed for its antioxidant capacity expressed as scavenging activity which was 2 times higher than crude extract. A portion of water (20%) in the 80% methanol system is important to improve the yield of rutin. Rutin is a glycosylated flavonol, and therefore a small portion of water could enhance its elution compared to the lower performance of 100% methanol in rutin recovery.

Zinc modified cadmium titanite nanoparticles: Electrical and room temperature methanol sensing properties

In this work ZnxCd1−xTiO3 (x=0.25, 0.5, 0.75) nanoparticles were synthesized using solid state reaction method. Detailed investigation of electrical properties and room temperature methanol sensing characteristics of synthesized nanoparticles was carried out. X-ray diffraction (XRD) and Scanning Electron Microcopy (SEM) were used to determine the crystal structure and morphology of the prepared material. The transition from positive temperature coefficient of resistivity (PTCR) to negative temperature coefficient of resistivity (NTCR) was observed in Zn0.75Cd0.25TiO3, Zn0.50Cd0.50TiO3 and Zn0.25Cd0.75TiO3 nanoparticles at 268K, 248K and 278K respectively. Prototype sensors of prepared ZnxCd1−xTiO3 (x=0.25, 0.5, 0.75) nanoparticles were tested at 10ppm, 20ppm, 30ppm and 40ppm of methanol at room temperature. The Zn0.75Cd0.25TiO3 and Zn0.25Cd0.75TiO3 nanoparticles sensors exhibited fast response and recovery times and a linear response with increase in methanol concentration. The Zn0.5Cd0.5TiO3 nanoparticles sensors exhibited nonlinear response and slow response and recovery times. Response of sensors based on all compositions was stable over period of 30 days.

Effect of supercritical carbon dioxide on the enzymatic production of biodiesel from waste animal fat using immobilized Candida antarctica lipase B variant

BackgroundWaste animal fat is a promising feedstock to replace vegetable oil that widely used in commercial biodiesel process, however the high content of free fatty acid in waste fat makes it unfeasible to be processed with commercial base-catalytic process. Enzymatic process is preferable to convert waste fat into biodiesel since enzyme can catalyze both esterification of free fatty acid and transesterification of triglyceride. However, enzymatic reaction still has some drawbacks such as lower reaction rates than base-catalyzed transesterification and the limitation of reactant concentration due to the enzyme inhibition of methanol. Supercritical CO2 is a promising reaction media for enzyme-catalyzed transesterification to overcome those drawbacks.ResultThe transesterification of waste animal fat was carried out in supercritical CO2 with varied concentration of feedstock and methanol in CO2. The CO2 to feedstock mass ratio of 10:1 showed the highest yield compared to other ratios, and the highest FAME yield obtained from waste animal fat was 78%. The methanol concentration effect was also observed with variation 12%, 14%, and 16% of methanol to feedstock ratio. The best yield was 87% obtained at the CO2 to feedstock ratio of 10: 1 and at the methanol to feedstock ratio of 14% after 6 h of reaction.ConclusionEnzymatic transesterification to produce biodiesel from waste animal fat in supercritical fluid media is a potential method for commercialization since it could enhance enzyme activity due to supercritical fluid properties to remove mass transfer limitation. The high yield of FAME when using high mass ratio of CO2 to oil showed that supercritical CO2 could increase the reaction and mass transfer rate while reducing methanol toxicity to enzyme activity. The increase of methanol concentration also increased the FAME yield because it might shift the reaction equilibrium to FAME production. This finding describes that the application of supercritical CO2 in the enzymatic reaction enables the application of simple process such as a packed-bed reactor.

Mechanism analysis on controllable methanol quick combustion

This paper explored the reason that the amount of methanol consumed is much lower than that of its theoretical value in terms of calorific value in diesel methanol dual fuel (DMDF) combustion by the means of engine bench test and modeling analysis. The results from experiments show that, the DMDF has much higher combustion rate than that of the correspondent diesel (D) mode and the accelerating effect caused by methanol changes with engine load, methanol-air mixture concentration and intake air temperature. At low load condition, the ignition delay caused by methanol is dominated while the accelerating effect is weak. However, this situation just turned upside down at high loads, to bring forth great improvement in isochoric degree. When methanol conducts quickly burning, both the combustion efficiency and the conversion efficiency from heat to work are improved, and the replacement ratio SR becomes much lower than its theoretical value 2.16. In order to reveal the mechanism of high efficiency DMDF at various running conditions, a 3-dimensional CFD model to simulate and analysis the process of methanol burning together with diesel was built. By fixing constant operating parameters and boundary conditions, both the putting off and accelerating effects caused by methanol are enhanced with increasing methanol concentration. The putting off effect weakens with rising air temperature, while the accelerating effect becomes more effective in this process. Hence, the isochoric degree for DMDF deteriorates with rising air temperature at lean methanol mixture but improves as the concentration increases. Finally, a relational graph among isochoric degree, heat release concentration degree, methanol-air mixture concentration and temperature are derived, from which we get the understanding of controllable methanol quick combustion (CMQC) to further improve the DMDF thermal efficiency.

A novel cathode gas diffusion layer for water management of passive μ-DMFC

Micro Direct Methanol Fuel Cell (μDMFC) has been a promising new type of portable energy device due to its high energy density, quick start features and simple operation environment. Water management is one of the most crucial problems for hindering the development of passive μDMFC. A novel cathode structure of passive μDMFC controlling water management and increasing methanol concentration is proposed and fabricated. The reduced graphene oxide deposited in stainless steel fiber felt (SSFF) as gas diffusion layer (GDL) and cathode electrode plate enhances water back diffusion which passively prevents water flooding in the cathode and promotes low methanol crossover in the anode at the same time. Contact angle indicates that the composite structure has a hydrophilic contact angle, spreading water adhering on it rapidly. The passive μDMFC with novel cathode structure exhibits significantly higher performance than traditional μDMFC, especially in high concentration, with peak power density of 23.8 mW cm−2 at 3 M at room temperature. EIS (electrochemical impedance spectroscopy, EIS) test results show that the novel structure helps reduce the internal resistance. The power density at 4 M and 5 M of novel μDMFC is distinctly higher than that of the conventional, which demonstrates that the novel μDMFC with novel cathode gas diffusion layer has a higher performance than the traditional one, especially at high concentration.

Synthesis and Characterization of 2-Pyridinylmethylene-2-quinolyl Hydrazone Cobalt(III) Complexes. Reactivity Trends and Solvent Effect on the Initial and Transition States of Base Catalyzed Hydrolysis

The complexes of pyridine-2-aldehyde-2-quinolylhydrazone Co(III) nitrate [Co(paqh)2](NO3)2, methyl-2-pyridylketone-2-quinolinhyrazone Co(III) nitrate [Co(mpkqh)2](NO3)2, and phenyl-2-pyridylketon-2-quinolinhyrazone Co(III) nitrate [Co(ppkqh)2](NO3)2 were prepared and characterized. Solubilities of Co(III)–hydrazone complexes were measured. Transfer chemical potentials were calculated from the measured solubilities of the Co(III) complexes in aqueous methanol mixtures at 25 °C. The reactivity trends in the transfer chemical potentials are discussed in terms of the nature of the bonded ligands. Kinetics of the base hydrolysis of Co(III)–hydrazone complexes in the aqueous methanol mixtures have been studied at 25 °C, and follow the rate law k obs = k 2[OH−]. The solvent effects on the reactivity trends of Co(III) complexes are analyzed into initial state (is) and transition states (ts) components. The reaction rates are reduced by the increase of methanol content. The destabilization of the transition state is remarkable compared to the initial state in the aqueous methanol mixtures. The initial state is more hydrophobic in nature than the transition state for Co(III) complex reactions.

Cononsolvency of poly(N‐isopropylacrylamide) in methanol aqueous solution—insight by dielectric spectroscopy

ABSTRACTBoth water and methanol are good solvents for poly(N‐isopropylacrylamide) (PNIPAM), while PNIPAM does not dissolve in their mixed solvents, this phenomenon is called cononsolvency. Cononsolvency is closely related to many phenomena in life but so far, its mechanism is still controversial. In this work, the dielectric behavior of PNIPAM methanol aqueous solution was studied in the frequency of 40Hz–40GHz. From lower frequency to higher frequency, four relaxations were found. They are, respectively, from global chain motion, local motion of backbone, motion of side chain group, and the dipole orientation of the solvent molecule. The solvent dependence of dielectric parameters for the chain motion implied that the PNIPAM chain has undergone the coil‐globule‐coil transition. Dielectric analysis to microwave frequency showed that the volume of the bound solvent units on PNIPAM chain increases with the increasing methanol concentration, which suggested that the structure of solvation units bound on PNIPAM side chains undergo a changing process experience from water to water‐methanol cluster to the ternary methanol cluster. This work reveals the structure and dynamics of the PNIPAM chain and the solvent unit that involved in the solvation of PNIPAM, and provides some new insight into the cononsolvency phenomenon. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1227–1234

Adsorption of Ten Microcystin Congeners to Common Laboratory-Ware Is Solvent and Surface Dependent.

Cyanobacteria can produce heptapetides called microcystins (MC) which are harmful to humans due to their ability to inhibit cellular protein phosphatases. Quantitation of these toxins can be hampered by their adsorption to common laboratory-ware during sample processing and analysis. Because of their structural diversity (>100 congeners) and different physico-chemical properties, they vary in their adsorption to surfaces. In this study, the adsorption of ten different MC congeners (encompassing non-arginated to doubly-arginated congeners) to common laboratory-ware was assessed using different solvent combinations. Sample handling steps were mimicked with glass and polypropylene pipettes and vials with increasing methanol concentrations at two pH levels, before analysis by liquid chromatography-tandem mass spectrometry. We demonstrated that MC adsorb to polypropylene surfaces irrespective of pH. After eight successive pipet actions using polypropylene tips ca. 20% of the MC were lost to the surface material, which increased to 25%–40% when solutions were acidified. The observed loss was alleviated by changing the methanol (MeOH) concentration in the final solvent. The required MeOH concentration varied depending on which congener was present. Microcystins only adsorbed to glass pipettes (loss up to 30% after eight pipet actions) when in acidified aqueous solutions. The latter appeared largely dependent on the presence of ionizable groups, such as arginine residues.

Syntheses and Controllable Self-Assembly of Luminescence Platinum(II) Plane–Coil Diblock Copolymers

Polystyrenes have been synthesized with terminal groups of luminescence square-planar platinum(II) complexes, which can be conceptually regarded as plane–coil diblock copolymers. They can self-assemble into spherical micelles with a core of polystyrenes and a corona of planar platinum(II) complexes in the chloroform/methanol mixture solvents, while free-standing bilayered sheets form in the toluene/methanol mixture solvents. With increasing methanol content in the latter case, where the solvent quality was highly deteriorated for polystyrene blocks, the sheetlike nanostructures are readily transformed into spherical micelles. Pt···Pt and/or π–π stacking interactions between the planar platinum(II) blocks contributed significantly to these aggregate morphologies and their evolutions, leading to remarkable luminescence enhancements. This work represents a novel approach to design and synthesize luminescence platinum(II) plane–coil diblock copolymers, in which the planar platinum(II) complexes are for the fi...

Molecular Simulation and Experimental Characterization of Ionic-Liquid-Based Cosolvent Extraction Solvents

The use of ionic liquid (IL)/polar covalent molecule (PCM) cosolvent mixtures is a significant new pathway to extract and separate oils and other high-value components from algae and other bio-oil-bearing biomasses. In this work, light-scattering and steady-state fluorescence polarization techniques were utilized to characterize cosolvent behavior at the micro- and macroscales, and their measurements correlated to lipid extraction yields. In addition, molecular dynamics simulations were employed to probe the fundamental interactions between IL and PCMs in solution. Both experimental and computational (radial distribution functions and clustering analysis) data confirmed the increased aggregation between IL cations and anions with increasing methanol concentration. For the 1-ethyl-3-methylimidazolium methyl sulfate/methanol (MeOH) system, this ion aggregation appears to correlate with experimentally observed decreases in the maximum lipid extraction yields for MeOH concentrations above 80 vol %. At these concentrations, MeOH appears to completely surround the aggregates, thereby removing the effect of the IL and diminishing the extraction yield. The successful simulation of experimental observations provides new knowledge on not only the relationship between a molecular-level cosolvent structure and its impact upon the solubility of the extracted material, which in this case are lipids, but also the ability to improve future designs of IL-based cosolvent mixtures for a broad range of extractable materials.

Solubility of cefoxitin acid in different solvent systems

Cefoxitin acid is one kind of important pharmaceutical intermediate. Its solubility is crucial for designing and optimizing the crystallization processes. In this work, the solubility of cefoxitin acid in organic solvents (methanol, acetonitrile, ethanol, isopropanol, n-propanol and ethyl acetate), water and water-methanol mixtures was measured spectrophotometrically using a shake-flask method within the temperature range 278.15–303.15K. PXRD data and the Karl Fischer method were used to verify the crystal form stability of cefoxitin acid in the solubility measuring process. The melting points, the enthalpy and entropy of fusion were estimated. Results showed that the solubility of cefoxitin acid increases with the increasing temperature in all tested solvents in this work, and the solubility of cefoxitin acid increases with the increasing methanol concentration in water-methanol mixtures. The experimental solubility values were well correlated using the modified Apelblat equation, NRTL model and CNIBS/R-K model. An equation proposed by Williamson was adopted to calculate the molar enthalpy during the dissolution process.

Effect of fabrication and operating parameters on electrochemical property of anode and cathode for direct methanol fuel cells

A quick and simple method for optimizing assembly force of the direct methanol fuel cell has been introduced. Meanwhile, the effect mechanism of operating parameters on fuel cell performance and the properties of single anode and cathode have been intuitively investigated by a three-electrode system in this paper. The impedance curves indicate that internal resistance is the suitable intermediate to connect assembly torque and assembly force. The cathode polarization curve and limiting current density of methanol crossover are shown that the increasing methanol concentration markedly exacerbates the polarization in cathode due to serious methanol crossover phenomenon. Also, the higher cathode backpressure mainly improves cathode property, and lowers methanol crossover simultaneously. Finally, the summaries of peak power densities prove that the main factor that affected the optimal flow rates of methanol and oxygen is not the concentration or backpressure, but the working temperature.

An effective and low cost Pd[sbnd]Ce bimetallic decorated carbon nanofibers as electro-catalyst for direct methanol fuel cells applications

In this paper, well decorated PdCe bimetallic on carbon nanofibers were synthesized by the cost effective electrospinning process and effectively applied as electro-catalyst for the detection of methanol fuel cells (MFCs). The synthesized PdCe bimetallic decorated carbon nanofibers were characterized in details using morphological, crystalline, structural, surface and electrochemical techniques. The crystalline and structural properties expressed the formation of PdCe alloys on the surface of carbon nanofibers during the electrospinning process. The PdCe bimetallic decorated carbon nanofibers were used to construct the effective anode for the high performance DMFCs and the cell performance evaluated by electrochemical measurements such as cyclovoltametry and electrochemical impedance. The PdCe bimetallic decorated carbon nanofibers based electrode presented the reasonable performance toward the methanol oxidation as increasing the current density with the increase of methanol concentration in alkaline medium. The addition of methanol in alkaline medium significantly increased the current density, which suggests that PdCe bimetallic decorated carbon nanofibers based electrode have excellent electrocatalytic activity towards the methanol.

Cation exchange resin catalysed biodiesel production from used cooking oil (UCO): Investigation of impurities effect

Converting used cooking oil (UCO) into biodiesel using solid acid catalysts shows good prospective for renewable and clean bio-fuel production. However, impurities (metal ion, water, etc.) contained in UCO will have effect on its biodiesel production as well as to affect the activity of solid acids. These effects were explored by selecting two UCOs and their model oils (same AV, without impurities) as feedstock, two typical kinds of cation exchange resins Amberlyst 15 and Amberlyst BD20 as solid acid catalysts. The result indicated that metal ion (Fe3+) not only showed deactivation effect on resin catalyst by cationic exchange but also exhibited catalytic activity as Lewis acid when it is in free form. The deactivation effect of water formed hydrated proton (–H3O+–SO3−) on resin catalyst cannot be alleviated by increasing methanol concentration but can be reduced through increasing reaction temperature. The organic acids, highly active in catalysing esterification reaction, showed synergistic effect with cation exchange resin. Under the co-effect of organic acid (UCO-1, 0.19mmol H+g−1; UCO-2, 0.12mmol H+g−1), metal ions (UCO-1, Fe: 0.6ppm, etc.; UCO-2, Fe: 9.4ppm, etc.) and other impurities, UCO-1/UCO-2 showed a FFA conversion of 1.2–14.1%/4.5–13.5%, compared with −4.35–9.36%/0.96–8.09% for their model oils at reaction condition of catalyst-free, 70–110°C, 3h, methanol-to-FFA molar ratio of 15:1.