Transesterification Equilibrium Research Articles

Modeling of biodiesel production in a membrane reactor using solid alkali catalyst

A mathematical model based on the pore model of membrane, liquid–liquid equilibrium model and reaction kinetics model for biodiesel production in membrane reactor was developed. The parameters of the model were calculated from the membrane reaction process of the transesterification between soybean oil and methanol catalyzed by KF/Ca-Mg-Al hydrotalcite. The biodiesel yield calculated by the model fitted the experimental data well. The model simulated results indicated that the membrane reaction system can be divided in biodiesel accumulation and membrane separation of biodiesel stage. In the studied temperature range, the biodiesel yield with the same reaction time increased with the increase in temperature. However, the maximum yields under of all temperatures were almost the same. The results proved that the membrane reactor can shift the transesterification equilibrium to the products side by continuously removing the products.

Thermodynamics and kinetics of transesterification reactions to produce diphenyl carbonate from dimethyl carbonate catalyzed by tetrabutyl titanate and dibutyltin oxide

AbstractThe transesterification reactions to diphenyl carbonate (DPC) from dimethyl carbonate (DMC) and phenol are the key steps to the green production of polycarbonate polymers (PC). The transesterification equilibrium constants were determined under temperatures from 453.2 to 493.2 K, and the reaction kinetics catalyzed by single tetrabutyl titanate, dibutyltin oxide, and their combinations was measured. By taking into account the effect of catalyst, the simplified kinetic model was developed involving the transesterification of DMC and methyl phenyl carbonate (MPC) with phenol, the disproportionation of MPC, and the formation of byproduct anisole. The kinetic model fitted experiments well under various temperatures and had an excellent predictive ability on the effect of catalyst concentrations. The reverse reaction of MPC transesterification with phenol, as well as that of the disproportionation of MPC, was found to be independent of temperatures within the investigated conditions. The thermodynamic information and kinetic model reported here will provide valuable insight into the understanding of the transesterification process from DMC to DPC.

Role of ultrasonic irradiation on transesterification of palm oil using calcium oxide as a solid base catalyst

Biodiesel production from transesterification of palm oil using a circulated continuous flow ultrasonic reactor was investigated. Transesterification was carried out at 60°C, 1atm and a methanol-to-oil molar ratio of 9:1. The highest reaction rate was achieved at the catalyst loading of 2wt%, and biodiesel yield constantly increased until transesterification equilibrium (about 80%) was reached. A higher ultrasonic frequency (50kHz) promoted the heterogeneously catalyzed transesterification of refined palm oil, because the three-phase system (packed solid catalyst, methanol and oil) required more spatial distribution by ultrasonic irradiation. Moreover, the highest ultrasonic power also provided highest transesterification rate and biodiesel yield due to cavitation activity enhancement. Reusability of calcium oxide catalysts was also investigated, and results showed that this can be reused to provide high biodiesel yield for at least three operations with slight decrease in the rate of reaction due to counter balance effect of organic compounds deposition on the catalyst surface. The results from this study can be a basis for scaling up of the process to industrial scale.

Multi‐Step Controlled Kinetics of the Transesterification of Crude Soybean Oil with Methanol by Mg(OCH3)2

AbstractThis work focuses on a kinetic model that can be expressed as three significant controlled regions, i.e., a mass transfer controlled region in the internal surface of a heterogeneous catalyst, an irreversible chemical reaction controlled region in the pseudo‐homogenous fluid body and a reversible equilibrium chemical reaction controlled region near to the transesterification equilibrium stage. With the help of MATLAB7.0 software, the apparent reaction rate constants, k2, k2+ and k2–, were calculated and the corresponding apparent activation energies were calculated to be 67.450, 60.680 and 58.279 kJ·mol–1, respectively. According to the confirmation experiments, it is indicated that the results can be applied for predicting the FAME yield at other reaction temperatures.

Enzyme‐catalyzed synthesis of aliphatic polyesters in organic media: Study of transesterification equilibrium shift and characterization of cyclic compounds

AbstractEnzyme‐catalyzed synthesis of aliphatic polyesters in organic media from methyl diesters and diols was carried out at stoechiometric ratio in the presence of supported lipases (li‐pozyme® and novozyme®). Two systems were studied to shift the thermodynamic equilibrium which limits the conversion. In the first one, the solution flows through a molecular sieve in which methanol is adsorbed. In the second one, methanol is eliminated by nitrogen bubbling. The system with nitrogen bubbling in hydrophobic solvents at 60°C works best when novozyme® is used as catalyst. Despite a high fractional conversion (p> 0.99), the number‐average molar mass is not very high (M̄;n = 3050 eq. PS). In relation to the nature of monomers, cycles with DP = 2–20 were characterized by chromatographic analyses and mass spectrometry. Their formation explains why high polycondensates cannot be obtained. © 1995 John Wiley & Sons, Inc.

Chemical reactions occurring in the thermal treatment of polymer blends investigated by direct pyrolysis mass spectrometry: Polycarbonate/polybuthyleneterephthalate

AbstractThe chemical reactions occurring in the thermal treatment of polycarbonate/polybuthyleneterephthalate (PC/PBT) blends have been investigated by gradual heating (10°C/min) using thermogravimetry and direct pyrolysis into the mass spectrometer. Exchange reactions occur already in the temperature range below 300°C but the transesterification equilibrium is affected by the evolution of thermal degradation products. Buthylenecarbonate, was detected in the first decomposition stage (320–380°C), which is evolved together with a series of cyclic compounds containing units of PC and PBT, in varying ratios. The overall thermal reaction evolves towards the formation of the most thermally stable polymer, i.e., a totally aromatic polyester (polymer III, Table I), which was found to be the end‐product of the thermal processes occurring in the system investigated. The thermal decomposition products obtained from the PC/PBT blends in the range 320–600°C have mass sufficiently high to be structurally significant, since they contain at least one copolymer repeating unit. The reactions occurring in the thermal treatment of the PC/PBT blend are discussed in detail. © 1993 John Wiley & Sons, Inc.

Chemical reactions which occur in the thermal treatment of polycarbonate/polyethyleneterephthalate blends, investigated by direct pyrolysis mass spectrometry

The chemical reactions which occur in the thermal treatment of polycarbonate/poly(ethyleneterephthalate) (PC/PET) blends have been investigated by gradual heating (10°C/min) using thermogravimetry and direct pyrolysis into the mass spectrometer. Exchange reactions occur even in the temperature range below 300°C, but the transesterification equilibrium is affected by the evolution of thermal degradation products. Ethylene carbonate was detected in the first decomposition stage (280–380°C), and is evolved together with a series of cyclic compounds containing units of PC and PET in varying ratios. The overall thermal reaction evolves towards the formation of the most thermally stable polymer, i.e. a totally aromatic polyester (polymer III, Table 1), which was found to be the end product of the thermal processes occurring in the system investigated. Several thermal decomposition products, originating from the PC/PET blends in the range 250–600°C, were identified. The compounds detected have masses sufficiently high to be structurally significant, since they contain at least one copolymer repeating unit. The reactions which occur during the thermal treatment of the PC/PET blend are discussed in detail.

Group 4 organometallic reagents. Part 6. The organotin-mediated monofunctionalization of diols: an insight into the selective monoesterification with acyl chlorides

The monoesterification of ethylene glycol with acyl chlorides through its dibutylstannylene derivative (1) has been selected as a model reaction to investigate, by n.m.r. spectroscopy, the origin of the organotin-mediated selective monofunctionalization of diols. The reaction has been found to take place in two separate steps, namely, an initial fast formation of a stannylated diol monoester followed by a slower intermolecular transesterification. The latter affords diester products and regenerates the starting dioxastannolane (1). Thus, the success of monoesterification depends on the timing of quenching the intermediate and is ensured by the large rate difference between the two steps. The above transesterification is an equilibrium reaction, shifted towards (1), that eventually leads to complete formation of diesters. Dynamic phenomena exhibited by n.m.r. spectra reveal that such a transesterification equilibrium also takes place intramolecularly at a much faster rate, showing intramolecularity factors of the order of 107 with respect to its intermolecular counterpart. Dibutyltin dichloride (3), which forms in the reaction, exerts a catalytic effect enhancing the reactivity of dioxastannolane toward the ester functionality. Such a catalytic effect may be accounted for by the very fast and strongly biased equilibrium reaction that occurs between (1) and (3), leading to ring-opening of the highly stable dioxastannolane. The generality of the stannylation method is further confirmed by monosilylation, carried out with silyl chlorides.

Organotin-mediated synthesis of macrocyclic polyesters: mechanism and selectivity in the reaction of dioxastannolanes with diacyl dichlorides

The reaction of 2,2-di-n-butyl-1,3,2-dioxastannolane with diacyl dichlorides for the synthesis of macrocyclic tetraesters has been investigated to gain an insight into its mechanistic pathway and to ascertain the occurrence of genuine template effects. Experimental results show unambiguously that the reaction is a clean cyclo-oligomerization involving a fast transesterification equilibrium that affords a thermodynamic distribution of oligomeric esters. No evidence to support a structural or ‘covalent’ template effect by tin was found. Instead, dioxastannolane is not only the reagent, but also behaves as an efficient transesterification catalyst that equilibrates the macrocyclic ester mixture. In this context, the reaction can hardly be considered selective.

Hydrogenolysis of methyl formate over copper on silica: II. Study of the mechanism using labeled compounds

Deuterium labeling has been used to investigate processes occurring during the conversion of methyl formate to methanol over silica supported copper at 393 to 419 K. Unlabeled and labeled methyl formates (CH 3OCDO and CD 3OCHO) react with hydrogen and deuterium at identical rates. The product distribution is that expected for successive simple additions without exchange at methyl or aldehyde positions (e.g., the initial products of the reaction between CH 3OCHO and D 2 are CH 3OD and CHD 2OD). The only complication is a rapid transesterification equilibrium (e.g., CH 3OCHO + CHD 2OD CHD 2OCHO + CH 3OD). Control experiments show that this process, and a similarly rapid CH 3OH + D 2 CH 3OD + HD equilibration, are catalyzed by copper and not the silica support. The mechanism suggested for hydrogenolysis involves formation of a surface hemiacetal species which, on cleavage of the CO bond, gives surface methoxy groups and formaldehyde. It is unclear if the slow step is this bond cleavage or the addition step which forms the intermediate. During reaction between CH 3OCHO and H 2 D 2 mixtures equilibration to HD is 10 to 30 times faster than hydrogenolysis. Added CO inhibits both hydrogenolysis and equilibration but the latter is inhibited to a greater extent. Both effects can be explained in terms of the displacement of adsorbed hydrogen by adsorbed CO with equilibration being affected more because of its higher kinetic order in adsorbed hydrogen. The lower concentration of surface hydrogen concentration in the presence of CO also reduces the rate of hydrogenation of the formaldehyde intermediate causing its diversion into a polymeric by-product which poisons the catalyst.

Study of poly-ε-caprolactone bulk degradation

The thermal stability of poly-ϵ-caprolactone samples obtained by ring-opening polymerization in the presence of different metal alkoxides has been investigated. A significant degradation of the polyesters is observed under isothermal conditions at 120°C. The degradation is related to the nature of the endgroup, the presence of catalyst residues, and the presence of molecular oxygen. The hydroxyl endgroups play a determinant role in the process. They probably give rise, under the influence of catalyst residues, to hydroperoxides which are responsible for the polymer degradation by a radical reaction. It is shown that this is clearly different from the change in molecular weights distribution due to the well-known ester interchange reaction (transesterification equilibrium). Resulting methods for the polymers stabilization are indicated.

The reaction of ethylene oxide with oleic acid

AbstractThe base‐catalyzed reaction of ethylene oxide with oleic acid can be divided into two stages. The first stage consists of a slow reaction of oleic acid with ethylene oxide to form principally ethylene glycol monooleate; other reactions such as esterification, transesterification and polyglycol formation lag behind. In the second stage, after the addition of approximately one mole of ethylene oxide, the reaction accelerates and transesterification equilibrium is rapidly attained. The composition of products containing several molecules or more of ethylene oxide can be calculated satisfactorily on the assumption of random addition of ethylene oxide and random esterification of the hydroxyl groups. The uncatalyzed reaction is much slower and transesterification equilibrium is attained slowly, if at all. A reaction mechanism based on the difference in basicities of the carboxylate and alkoxide ions (and the relative rates of the competitive ethylene oxide reactions) is presented for the base‐cat‐alyzed reaction.