Direct esterification process

PET is the polyester of terephthalic acid and ethylene glycol. Polyesters are prepared by either direct esterification or transesterification reactions. In the direct esterification process, terephthalic acid is reacted with ethylene glycol to produce PET and water as a by-product. Transesterification involves the reaction of dimethyl terephthalate (DMT) with ethylene glycol in the presence of a catalyst (usually a metal carboxylate) to form bis(hydroxyethyl)terephthalate (BHET) and methyl alcohol as a by-product. In the second step of transesterification, BHET... 

Reimschuessel, H. K Polyethylene terephthalate formation. Mechanistic and kinetic aspects of the direct esterification process, Ind. Eng. Prod. Res. Dev., 19, 117-125 (1980). 

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). 

One of the greatest difficulties with direct esterification processes has been the tendency for the olefins to polymerize at the temperatures and in the presence of the catalysts used in the process. Energetic reagents such as anhydrous zinc chloride, ferric chloride, sulfur chloride, aluminum chloride or bromide such substances as fullers earth forms of energy as light, heat, silent electric discharge and the alkali or alkali earth metals are all known to affect greatly the polymerization of olefins. 

The economic utility of the direct esterification process depends, of course, upon cheap acetic acid (if acetates are being sought). For the process to compete with the present method for esterification which uses calcium acetate of about 85 per cent purity a source of cheap acetic acid will be necessary. Although a price considerably lower than the present quoted price for acetic arid is necessary, it seems possible that it could be made from acetylene at a satisfactory price.82... 

PET is prepared commercially by either ester interchange (El) or direct esterification processes (11. 12). For many years, the El process was the only one practical because of the difficulties encountered in purification of terephthalic acid (TA). The dimethyl terephthalate (DMT) was much easier to purify, and therefore much more readily available as a raw material. In the normal El batch process, ethylene glycol and DMT are mixed in a ratio ranging from... 

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). 

Reimschuessel, H. K., Debona, B. T. and Murlhy, A. K. S., Kinetics and mechanism of tire formation of glycol esters benzoic acid - ethylene glycol system, J. Polym. ScL, Polym. Chem. Ed., 17, 3217-3239 (1979). Reimschuessel, H. K., Polyetliylene terephthalate formation. Mechanistic and kinetic aspects of tire direct esterification process, Ind. Eng. Prod. Res. Dev., 19, 117-125 (1980). 

In some cases it is possible to directly polycondense acid and phenols evolving water at about 300 C [41]. This process works well when catalysed with compoimds of group IV or V metals tin salts are preferred, especially dialkyl tin dialkanoates or oxides. The process is not really suitable if p-hydroxybenzoic acid is involved because this can imdergo decarboxylation at >200 "C. The polymerisation is not affected because the phenol formed volatilises at the high temperatures involved, but the resultant polyester will contain less than the anticipated mole ratio of hydroxybenzoate-derived units. Hydroxynaphthoic acid does not suffer from this problem, and direct esterification processes may be used if non-benzoate copolymers are required [42]. 

C. S.Wang, and C. S. Lin, Catalyst composition for production of polybutylene terephthalate via direct esterification process, US Patent 5,900,474,1999. 

Yamada et al. [136] and more recently Kang et al. [137] have presented models of the direct esterification process of terephthalic acid (TPA) with ethylene glycol (Figure 3.10). As TPA has a low solubility because of its high melting point, the first reactor in the train ( esterification reactor) is operated at a higher pressure and... 

Fig. 3. 10. Simple model for WFR used for the direct esterification process of terephthalic acid (TPA) with ethylene glycol.

An alternative process (97) for direct esterification of cresols using phosphoric acid, a slow reaction, was developed in Israel, where phosphoms oxychloride is not locally available. 

Most large-scale industrial methacrylate processes are designed to produce methyl methacrylate or methacryhc acid. In some instances, simple alkyl alcohols, eg, ethanol, butanol, and isobutyl alcohol, maybe substituted for methanol to yield the higher alkyl methacrylates. In practice, these higher alkyl methacrylates are usually prepared from methacryhc acid by direct esterification or transesterification of methyl methacrylate with the desired alcohol. 

On the basis of bulk production (10), poly(ethylene terephthalate) manufacture is the most important ester producing process. This polymer is produced by either the direct esterification of terephthaHc acid and ethylene glycol, or by the transesterification of dimethyl terephthalate with ethylene glycol. In 1990, poly(ethylene terephthalate) manufacture exceeded 3.47 x 10 t/yr (see Polyesters). Dimethyl terephthalate is produced by the direct esterification of terephthaHc acid and methanol. 

There are two main processes for the synthesis of ethyl alcohol from ethylene. The eadiest to be developed (in 1930 by Union Carbide Corp.) was the indirect hydration process, variously called the strong sulfuric acid—ethylene process, the ethyl sulfate process, the esterification—hydrolysis process, or the sulfation—hydrolysis process. This process is stiU in use in Russia. The other synthesis process, designed to eliminate the use of sulfuric acid and which, since the early 1970s, has completely supplanted the old sulfuric acid process in the United States, is the direct hydration process. This process, the catalytic vapor-phase hydration of ethylene, is now practiced by only three U.S. companies Union Carbide Corp. (UCC), Quantum Chemical Corp., and Eastman Chemical Co. (a Division of Eastman Kodak Co.). UCC imports cmde industrial ethanol, CIE, from SADAF (the joint venture of SABIC and Pecten [Shell]) in Saudi Arabia, and refines it to industrial grade. 

Thus as in the case of oil of bergamot, esterification is accompanied by a decrease in. the total proportion of linalol and in the proportion of free acid. These facts prove that, here also, the esters originate by the direct action of the acids on the alcohols. Under these conditions, as the plant develops, part of the linalol is esterified whilst another portion is dehydrated. So that not only does the proportion of free alcohol, but also that of the total alcohol decroase. But as the esterification process is completed, which happens when the flower commences to-fade, the total alcohols increase at a fairly rapid rate. 

This process differs from the direct esterification and the transesterification routes in that only ethylene glycol is released. In the former two routes, water or methanol are coproduced and the excess glycol released. 

As a historical note, SAI for Dove was made by this acyl chloride process until a commercial process for direct esterification of fatty acid and sodium isethionate was developed by Lever Brothers Co. in the late 1950 s. The SAI made by direct esterification is generally termed DEFI, an acronym for directly esterified fatty isethionate . The DEFI reaction is follows ... 

Sir A. R. Todd3 and his colleagues have exploited these phosphorylation processes with great success. It may be added parenthetically that the direct esterification of iZ OH with phosphoric acid would, in general, be a far too crude process for the production of (XIII). 

Meanwhile attempts to find an air oxidation route directly from p-xylene to terephthalic acid (TA) continued to founder on the relatively high resistance to oxidation of the /Moluic acid which was first formed. This hurdle was overcome by the discovery of bromide-controlled air oxidation in 1955 by the Mid-Century Corporation [42, 43] and ICI, with the same patent application date. The Mid-Century process was bought and developed by Standard Oil of Indiana (Amoco), with some input from ICI. The process adopted used acetic acid as solvent, oxygen as oxidant, a temperature of about 200 °C, and a combination of cobalt, manganese and bromide ions as catalyst. Amoco also incorporated a purification of the TA by recrystallisation, with simultaneous catalytic hydrogenation of impurities, from water at about 250 °C [44], This process allowed development of a route to polyester from purified terephthalic acid (PTA) by direct esterification, which has since become more widely used than the process using DMT. 

PCT, PETG, PCTG and PCTAs can all be prepared readily via standard melt-phase poly condensation processes [34, 35], The diacid can be delivered via transesterification of the dimethyl esters or via direct esterification of the diacids. Numerous conventional catalyst and catalyst combinations can be employed. The use of a catalyst or catalyst combination is important for the manufacture of polyesters via the melt-phase process and has been well reported in the literature [36-41], Appropriate catalyst systems enable the production of polyesters with high processing rates and high molecular... 

PTT is melt polymerized by either the transesterification of PDO with dimethyl terephthalate (DMT) or by the direct esterification of PDO with purified tereph-thalic acid (PTA). The process is similar to that for PET but with major differences, as follows ... 

Direct esterification of PDO with TPA is a more economical route than transesterification with DMT. However, it is also a more difficult technology to implement. Table 11.1 summarizes the reaction conditions, catalysts and additives for both the DMT and TPA processes [24-28], while Figure 11.2 shows the direct esterification reaction scheme. Only the TPA process will be described below. 

Figure 11.2 Polymerization of PTT by direct esterification of PDO with TPA using the heel process...

Direct esterification of PHBA monomer is problematic because the rate of decarboxylation is often comparable to the rate of (co)poly-merlzation (15,16). The problem seems largely overcome by two process refinements introduced here [1] Use of p-TSA apparently catalyzes esterification and more than it catalyzes formation of the undesirable by-product, phenol. [2] "Aromatic 150" solvent helps maintain constant reaction temperature and facilitates water removal. Refluxing solvent also prevents accumulation of sublimed PHBA in the upper parts of the reactor. 

Various combinations of reactant(s) and process conditions are potentially available to synthesize polyesters [Fakirov, 2002 Goodman, 1988], Polyesters can be produced by direct esterification of a diacid with a diol (Eq. 2-120) or self-condensation of a hydroxy carboxylic acid (Eq. 2-119). Since polyesterification, like many step polymerizations, is an equilibrium reaction, water must be continuously removed to achieve high conversions and high molecular weights. Control of the reaction temperature is important to minimize side reactions such as dehydration of the diol to form diethylene glycol... 

However, the lower fatty acid esters (particularly the acetates) of the acyclic terpene alcohols geraniol, linalool, and citronellol are extremely important both as fragrance and as flavor substances. The acetates occur in many essential oils, sometimes in rather high amounts. Formates, propionates, and butyrates occur less frequently. As a result of the development of large-scale production processes for terpenes, the esters of acyclic terpene alcohols are nearly always made synthetically. All acyclic terpene esters that are used as fragrance and flavor materials can be prepared by direct esterification of the appropriate alcohols. However, special precautions are required for the esterification of linalool. 

A process based on the use of an immobilized C. antarctica lipase (Novozym 435) has been developed in order to perform direct esterification of natural alcohols with carboxylic acids in a solvent-free system. Based on the system represented in Figure 11.2, the process had to overcome the problem of recycling the nitrogen, once the reaction was over. 

A. Riondel and J. Bessalem, Process for preparing butyl acrylate by direct esterification, US Patent 6 846 948, assigned to Arkema (Puteaux, FR), January 25, 2005. 

---