Critical Temperature Of Methanol Research Articles

Extraordinary Properties of Alcohols from the Homologous Series of Methanol

Non-trivial properties of thermodynamic quantities such as the density, the critical and triple point temperatures, and their ratio, as well as the optical and dielectric properties, have been analyzed for primary alcohols from the methanol series. The aim is to reveal relationships among their values measured at the same temperatures for alcohols with different ordinal numbers m’s in the methanol series. It is shown that the non-monotonic character of the temperature dependences of alcohol densities is associated with methanol rather than ethanol, as may seem at first glance. The critical temperature of methanol also deviates from the quasilinear dependence of the critical alcohol temperatures on m. With the growing m, the ratio between the critical and triple-point temperatures for alcohols is shown to tend to the corresponding value for water. Simple linear dependences of the electronic and effective static polarizabilities of alcohol molecules on m are established. The transverse and longitudinal components of the polarizability tensor for alcohol molecules are found. The dipole moments of the closest neighbor molecules in the alcohols are proved to anticorrelate, i.e. to orient in opposite directions.

Vapor–Liquid Equilibrium for Methanol + Methyl Palmitate near the Critical Temperature of Methanol

The vapor–liquid equilibrium for a methanol + methyl palmitate system was measured using a flow-type method at a pressure range of 1.86–8.81 MPa and a temperature range of 493–543 K, which is near the critical temperature of methanol (512.64 K). The mole fractions of methyl palmitate in the vapor phase were nearly zero, and the errors were also close to zero at all temperatures. The measuring errors of the liquid phase were slightly higher than those of the vapor phase. The Soave–Redlich–Kwong equation of state (SRK EOS), the Peng–Robinson equation of state (PR EOS), and the Cubic-Plus-Association equation of state (CPA EOS) combined with the Adachi–Sugie (AS) mixing rule were employed to correlate the measured data. The correlated results are consistent with the measured data. Because of their accuracy and concise calculation, the SRK and PR EOSs are better choices for correlating the methanol + methyl palmitate system when considering the accuracy and conciseness of calculating.

Biodiesel production from coconut oil in supercritical methanol in the presence of cosolvent

The transesterification of coconut oil with supercritical methanol in the presence of cosolvent was carried out in a batch autoclave for production of biodiesel. The transesterification was found to be catalyzed by the surface of the autoclave. However, the catalytic activity of the autoclave dropped with great extent after a certain period of time. A 1.5 M oxalic acidic solution could be used to wash the surface to restore the catalytic activity of the autoclave. From the measured yields of biodiesel in a period of 20 min, ether was found to be the most effective cosolvent among eight cosolvents tested in this study. The effects of temperature, pressure, molar ratio of methanol to coconut oil, and molar ratio of methanol to cosolvent on methyl esters yield using ether as the cosolvent were examined. A temperature at least 30 °C higher than the critical temperature of methanol is essential for obtaining high biodiesel yield. The yield was also found to increase with increasing pressure, however, the extent of increase was reduced when the pressure was higher than 14 MPa. The most appropriate molar ratios of methanol to coconut oil and to ether were found to be 30/1/3. These molar ratios were observed invariant when CO 2 instead of ether was used as the cosolvent.

Calculation and analysis of sub/supercritical methanol preheating tube for continuous production of biodiesel via supercritical methanol transesterification

Biodiesel is an important renewable energy. Supercritical methanol transesterification for biodiesel has recently been concerned because of its obvious advantages. The tubular reactor is an ideal reactor for continuous preparation of biodiesel via supercritical methanol transesterification. A methanol preheating tube is necessary for the tubular reaction system because the reaction temperature for supercritical methanol transesterification is usually 520–600 K. Therefore, in the range of 298–600 K, changes of the density, isobaric capacity, viscosity and thermal conductivity of sub/supercritical methanol with temperature are first discussed. Then on the basis of these thermophysical properties, an integration method is adopted for the design of sub/supercritical methanol preheating tube when methanol is preheated from 298 K to 600 K at 16 MPa and the influencing factors on the length of the preheating tube are also studied. The computational results show that the Reynolds number Re and the local convection heat-transfer coefficient α of sub/supercritical methanol flowing in Φ6× 1.5 mm preheating tube change drastically with temperature. For the local overall heat transfer coefficient K and the average overall heat transfer coefficient Km, temperature also has an important influence on them when the inlet velocity of methanol is lower than 0.5 m/s. But when the inlet velocity of methanol is higher than 0.5 m/s, K and Km almost keep invariable with temperature. Additionally, both the outlet temperature and the inlet velocity of methanol are the key affecting factors for the length of the preheating tube, especially when the outlet temperature is over the critical temperature of methanol. At the same time, the increase of tin bath’s temperature can shorten the required length of the preheating tube. At the inlet flow rate of 0.5 m/s, the required length of the preheating tube is 2.0m when methanol is preheated from 298 K to 590 K at 16 MPa with keeping the tin bath’s temperature 620 K, which is in good agreement with the experimental results.

Measurement and correlation of vapor–liquid equilibria for methanol + methyl laurate and methanol + methyl myristate systems near critical temperature of methanol

A flow-type method was adopted to measure the vapor–liquid equilibria for methanol + methyl laurate and methanol + methyl myristate systems at 493–543 K, near the critical temperature of methanol ( T c = 512.64 K), and 2.16–8.49 MPa. The effect of temperature and fatty acid methyl esters to the phase behavior was discussed. The mole fractions of methanol in liquid phase are almost the same for both systems. In vapor phase, the mole fractions of methanol are very close to unity at all temperatures. The present vapor–liquid equilibrium data were correlated by PRASOG. A binary parameter was introduced to the combining rule of size parameter. The binary parameters of methanol + fatty acid methyl ester systems were determined by fitting the present experimental data. The correlated results are in good agreement with the experimental data. The vapor–liquid equilibria for methanol + methyl laurate + glycerol and methanol + methyl myristate + glycerol ternary systems were also predicted using the methanol + fatty acid methyl ester binary parameters. The mole fractions of methanol in vapor phase are around unity even if glycerol is included in the systems.

Analysis of a Two-Step, Noncatalytic, Supercritical Biodiesel Production Process with Heat Recovery

A two-step, noncatalytic process for the production of biodiesel is analyzed. The reaction of transesterification of triglycerides with methanol is carried out in supercritical conditions by adopting reaction temperatures of 250−300 °C, higher than the critical temperature of methanol (240 °C). Under these conditions, free fatty acids are converted into fatty acid methyl esters with similar or higher rates than the corresponding triglycerides, and therefore, the process can use high acidity, cheap feedstocks, like yellow grease or beef tallow. The reacting system is also tolerant to water, so it is much more robust than the acid or alkali catalyzed systems which need the removal of water or free fatty acids to prevent catalyst deactivation. In order to minimize the heat consumption and pumping power which are very high in the traditional one-step supercritical method, two reactors with intermediate glycerol removal are used and a heat recovery scheme composed of heat exchangers and adiabatic flash drums i...

Henry's law constants of 1-butene, 2-methylpropene, trans-2-butene, and 1,3-butadiene in methanol at 374–490 K

Henry's law constants of 1-butene, 2-methylpropene, trans-2-butene, and 1,3-butadiene in methanol in the temperature range of 374–490 K are experimentally obtained. A similar method to a gas stripping method is applied to measure the Henry's law constants at high temperatures up to the critical point of methanol. The rigorous formula for evaluating the Henry's law constants from these measurements is applied to the data reduction for these highly volatile mixtures. By using this formula, a volume effect of vapor phase is discussed. The plot of Henry's law constants versus temperature goes through a maximum and approaches an unique point at the critical temperature of methanol. The fugacity coefficient of the solute in the vapor phase at infinite dilution and the infinite dilution activity coefficient of the solute in liquid phase are evaluated from these experimental data.

Henry's law constants of propane, propene, butane, and 2-methylpropane in methanol at 374–490 K

Henry's law constants of propane, propene, butane, and 2-methylpropane in methanol in the temperature range of 374–490 K are experimentally obtained. A similar method to a gas stripping method is applied to measure the Henry's law constants at high temperatures up to the critical point of methanol. The rigorous formula for evaluating the Henry's law constants from these measurements is applied to the data reduction for these highly volatile mixtures. By using this formula, the effect of the vapor space of the cell is discussed. The plot of Henry's law constants versus temperature goes through a maximum and approaches an unique point at the critical temperature of methanol. The fugacity coefficient of the solute in the vapor phase at infinite dilution and the infinite dilution activity coefficient of the solute in liquid phase are evaluated from these experimental data.

Henry’s constants of carbon dioxide in methanol at 250–500 K

Henry’s constants of carbon dioxide in methanol in the temperature range of 250–500K are experimentally obtained. The Henry’s constants at low temperatures are measured by a gas stripping method, and a similar method is applied to measure the Henry’s constants at high temperatures up to the critical point of methanol. The rigorous formula for evaluating the Henry’s constants from these measurements is applied to the data reduction for these highly volatile mixtures. By using this formula, a volume effect of vapor phase is discussed. The plot of Henry’s constants versus temperature goes through a maximum and approaches an unique point at the critical temperature of methanol.

Chemical conversion of cellulose as treated in supercritical methanol

The chemical conversion of cellulose as treated in supercritical methanol was studied using a batch-type reaction vessel at temperatures from 220 to 450°C and pressures from 14 to 72MPa. Supercritical methanol treatment at 350°C and 43MPa for 7min was sufficient to convert microcrystalline cellulose (avicel) to the methanol-soluble. To study the kinetics of the decomposition of cellulose, the decomposition rate constants were obtained, and rapid increase was observed at about 270°C which was about 30°C higher than the critical temperature of methanol. The main products from cellulose decomposition were methylated cellotriose, methylated cellobiose, methyl α- and β-D-glucosides, levoglucosan and 5-hydroxymethylfurfural. Monomeric compounds such as methyl α- and β-D-glucosides were stable in supercritical methanol, allowing high yields of monomeric products by supercritical methanol treatment. Based on these results, a pathway of cellulose decomposition treated in supercritical methanol was proposed. These findings suggest that the supercritical methanol treatment of various cellulosic materials may be suitable to obtain useful chemicals and liquid fuels without using fossil resources.

Raman spectroscopic studies on hydrogen bonding in methanol and methanol/water mixtures under high temperature and pressure

The Raman spectral shifts of methanol in pure methanol and methanol/water mixtures have been measured from room temperature up to 600 K under pressures of 10 or 20 MPa. In pure methanol, the gradual spectral changes of individual vibrational modes against the temperature indicate weakening of the intermethanol hydrogen bonding with temperature, but imply that it still remains at the critical temperature of methanol. In the methanol/water mixtures with low methanol contents, the Raman peaks of methanol do not move appreciably at temperatures lower than 600 K, which indicates that the methanol molecule is isolated in a water cage and the structure remains as it is up to 600 K.

Excess molar enthalpies and the thermodynamics of (methanol + water) to 573 K and 40 MPa

Excess molar enthalpies H m E of (methanol + water) were measured from 298 to 573 K at pressures from 7 to 40 MPa. The observed H m Es are significantly negative at 298.15 K, near zero at about 398 K, and positive at higher temperatures. The composition dependence of H m E at low temperatures is much simpler than for (ethanol or propanol + water). The measurements reported here extend above the critical temperature of methanol. The very large changes in H m E with temperature and composition often observed near the critical conditions of the more volatile component were not observed under the conditions of this study. The results reported here were combined with available measured values of other thermodynamic quantities and represented with thermodynamically consistent empirical functions of temperature, pressure, and composition. Calculated excess molar Gibbs free energies, excess molar volumes, excess molar enthalpies, and excess molar heat capacities are tabulated.