Continuous esterification processes

The continuous esterification process is superior to the batch process, in that the same high yield can be obtained in a much shorter dwell time and with substantially... 

The alcoholysis process ulso is readily adaptable to continuous operation. Procedures in general are similar to those used for continuous esterification processes. 

Ravindranatli, K. and Mashelkar, R. A., Modeling of poly(ethylene terephthalate) reactors 4. A continuous esterification process, Polym. Eng. ScL, 22, 610-618 (1982). 

Yamada, T, and Y. Imamura, A Mathematical Model for Computer Simulation of a Direct Continuous Esterification Process Between Terephthalic Acid and Ethylene Glycol, Polym. Eng. Sci., 28, 385-392, 1988. 

The esterification process can be carried out in either batch or continuous mode, the final decision depending most likely on the size of the flow rates involved. For most commercial sizes of 15 MM gal/yr or higher, the continuous process is probably more cost effective and for this option, two additional options are available continuous stirred tank reactor (CSTR) or a fixed-bed reactor (FBR). 

Polycarbonates are manufactured via interfacial polymerization or through a melt esterification process. The properties of polycarbonate can differ greatly based on the method of polymerization. Specifically, the molecular weight distributions created by the two methods differ because of kinetic effects. Polycarbonates manufactured via interfacial polymerization tend to be less stable at high temperatures and less stiff than those produced via melt esterification, unless proper manufacturing precautions are taken. Therefore, when choosing a polycarbonate resin grade for a specific application, it is important to know the method by which it was produced. Either polymerization method can be performed as a continuous or batch process. 

Table 2.9 summarizes the kinetic data which were employed by Ravindranath and co-workers in PET process models. The activation energies for the different reactions have not been changed in a decade. In contrast, the pre-exponential factors of the Arrhenius equations seem to have been fitted to experimental observations according to the different modelled process conditions and reactor designs. It is only in one paper, dealing with a process model for the continuous esterification [92], that the kinetic data published by Reimschuessel and co-workers [19-21] have been used. 

The continuous polycondensation process consists of four main process units, i.e. (1) slurry preparation vessel, (2) reaction unit, (3) vacuum system, and (4) distillation unit. The molar EG/TPA ratio is adjusted to an appropriate value between 1.05 and 1.15 in the slurry preparation vessel. In most industrial processes, the melt-phase reaction is performed in three up to six (or sometimes even more) continuous reactors in series. Commonly, one or two esterification... 

Yamada, T. and Imamura, Y Simulation of continuous direct esterification process between terephthalic acid and ethylene glycol, Polym.-Plast. Technol. Eng., 28, 811-876 (1989). 

The benefits of using biodiesel as renewable fuel and the difficulties associated with its manufacturing are outlined. The synthesis via fatty acid esterification using solid acid catalysts is investigated. The major challenge is finding a suitable catalyst that is active, selective, water-tolerant and stable under the process conditions. The most promising candidates are sulfated metal oxides that can be used to develop a sustainable esterification process based on continuous catalytic reactive distillation. 

Ethyl Acetate. The production of ethyl acetate by continuous esterification is an excellent example of the use of azeotropic principles to obtain a high yield of ester (2). The acetic acid, concentrated sulfuric acid, and an excess of 95% ethyl alcohol are mixed in reaction tanks provided with agitators. After esterification equilibrium is reached in the mixture, it is pumped into a receiving tank and through a preheater into the upper section of a bubblecap plate column (Fig. 5). The temperature at the top of this column is maintained at ca 80°C and its vapor (alcohol with the ester formed and ca 10% water) is passed to a condenser. The first recovery column is operated with a top temperature of 70°C, producing a ternary azeotrope of 83% ester, 9% alcohol, and 8% water. The ternary mixture is fed to a static mixer where water is added in order to form two layers and allowed to separate in a decanter. The upper layer contains ca 93% ethyl acetate, 5% water, and 2% alcohol, and is sent to a second recovery or ester-drying column. The overhead from this column is 95—100% ethyl acetate which is sent to a cooler and then to a storage tank. This process also applies to methyl butyrate. 

Esterification Processes. There are two general methods used for esterification the batch process and the continuous process. Esterification can be done batchwise under pressure at a temperature of 200-250°C. As it is an equilibrium reaction, the water is removed continuously to obtain a high-ester yield (15). 

One of the first commercial-scale catalytic distillation processes was that for the production of methyl acetate [17]. In this esterification process the liquid acid catalyst is continuously added to the reactant mixture it finishes up in the bottoms and, following neutralization, in the wastewater from the plant. 

All esterification processes with acetic anhydride yield the fully esterified ester as the first soluble product. If the reaction medium is a solvent for the triester a solution is obtained, and if a reaction which retains the fiber structure is employed, samples taken at intervals are all insoluble in solvents until complete esterification is attained. The process in this way differs from nitration, in which soluble, partially esterified products are obtained by adjustment of the concentration of the nitration acids. In the etherification of cellulose, the ethers (e.g., methylated cellulose) prepared by partial substitution are also soluble products, exhibiting continuous, gradual changes in solubility characteristics with increasing substitution. 

Kang, C.-K., Lee, B. C., Ihm, D. W. and Tremblay, D. A., A simulation study on continuous direct esterification process for poly(etliylene tereph-tlialate) synthesis, J. Appl. Polym. ScL, 63, 163-174 (1997). 

As in the case of the esterification process presented before, we study first a one-stage column by singularity analysis to gain some physical insight and then continue with a numerical bifurcation study of an industrial size RD column. 

FIGURE 11 Example for a continuously working esterification process. [From Kaltschmitt, M., and Hartmann, H., eds. (2001). Energy from Biomass, Springer, Berlin, Heidelberg, Germany. (In German.)]... 

Yamada, T. (1996) Effect of reaction variables on TPA-EG continuous esterification with recycling in PET production process. Polym. React Eng., 4 (1), 1—45. 

If reactants A and B, and product C, are fluids, then continuous flow, solvent-free conditions may be suitable. This does, however, pose practical problems of efficient mixing between A and B, which can be made more difficult if either is viscous, or the reactions are fast. Within the polymer and food industries there are examples of both continuous solid and melt extrusion processes, though few involve reactive chemistiy. If the reaction is selective then product C can be isolated directly, otherwise its higher molecular weight may make it difficult to separate without using a solvent, negating the aim, unless it is a solid. An example of a solvent-free continuous flow process is the lipase-catalyzed esterification of fatly esters using alcohols, as shown in Scheme 12.1. ... 

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