Ind. Eng. Chem. Res. 1987, 26, 194-198
194
Unsaturated Polyester Resins from Poly(ethy1ene terephthalate) Waste. 1. Synthesis and Characterization? Utpal R. Vaidya and Vikas M. Nadkami* Polymer Science and Engineering Group, Division of Chemical Engineering, National Chemical Laboratory, Pune 41 1 008, India
Fiber-grade poly(ethy1ene terephthalate) waste was depolymerized by using different amounts of propylene glycol. These glycolyzed products were reacted with maleic anhydride and mixed with styrene monomer to get unsaturated polyester resins. T h e processing characteristics like viscosity, gel time, and exotherm temperature of the resins were investigated with respect to the amounts of styrene monomer, initiator, and accelerator. The resins were compared with the conventional general purpose resin and were found t o be comparable in their processibility. T h e resins offer a new class of unsaturated polyesters to the fiber-reinforced plastics (FRP) processors. Fiber-reinforced plastics form a versatile class of materials that are increasingly replacing conventional structural materials such as metals, wood, and concrete in engineering applications. These materials, commonly termed FRP, offer a high strength-to-weight ratio, excellent corrosion resistance, ease of fabrication, and versatility of product design in comparison with metals. Although both thermosets and thermoplastics are used as matrix materials for fiber reinforcement, the thermosets constitute the major segment. Among the thermoseting resins, unsaturated polyesters and epoxies are the most commonly used matrix materials for FRP. The world consumption of unsaturated polyester resins in composites was of the order of about 1 X lo6 metric tons in 1985, whereas that of epoxies in FRP uses was only about 1.5 X lo5 metric tons in the same year (MPI, 1986). The unsaturated polyester (UP) resins are thus commercially important for the reinforced plastics markets. Besides their low cost, the UP resins can be tailor-made to meet specific requirements by proper choice of their chemical building blocks. The UP resins are made by the reaction of aliphatic diols with unsaturated and saturated diacids. The most commonly used diols &e ethylene glycol (EG), propylene glycol (PG), and neopentyl glycol (NPG). The use of PG offers better hydrolytic resistance relative to EG, since the ester linkages are shielded by the pendant methyl groups. A further improvement in hydrolytic resistance is achieved by using NPG because of the presence of two pendant methyl groups in its structure that enhances the steric protection for the ester linkage. The saturated diacids used as monomers in UP resins include phthalic anhydride, isophthalic acid, adipic acid, succinic acid, etc. The aromatic acids impart rigidity, whereas the aliphatic acids are used to give flexibility. The choice of the acid monomer is governed by the desired combination of properties in the final product. The unsaturated acid monomers used are maleic anhydride and fumaric acid. Of the two, the former is more common because of its higher reactivity. It is thus possible to achieve a wide range of properties by proper selection of the monomers. The general purpose (GP) resin is prepared by polycondensation of PG, maleic anhydride, and phthalic anhydride (Parkyn et al., 1967). When phthalic anhydride is replaced by isophthalic acid, certain properties such as heat distortion temperature
* To whom
correspondence should be addressed.
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(HDT) and chemical resistance are improved (Boeing, 1969). This effect is expected to be more prominent when terephthalic acid (TPA) is used as the diacid. This is because the chain linearity increases as one goes from ortho to meta and from meta to parQnkages, thereby improving the packing ability of the polymer chains. However, the direct use of TPA in the synthesis of UP resins is restricted due to its high melting point and processing difficulties arising from its sublimation during the course of the reaction. The major use of TPA is in the manufacture of poly(ethylene terephthalate) commonly termed as PET, which is a versatile thermoplastic that is used in synthetic fibers, extruded films, moulded engineering components, and blow moulded bottles. The worldwide production of P E T is above 1 X lo6 metric tons/year. With such a large consumption, the effective utilization of P E T waste is of considerable commercial and technological significance. P E T waste may be converted into extruded or moulded articles after repelletizing, or it may be depolymerized to yield raw materials for resin synthesis. Recycling of segregated waste by blending in small quantities with virgin monomer, bis(hydroxyethy1)terephthalate, is a possibility. However it often lowers the quality of the final product (Sittig, 1981). It is, therefore, desirable to break down the polymer into smaller fragments or oligomers. PET can also be fully depolymerized into dimethyl terephthalate (DMT) (Matsuura et al., 1975; Hemmi et al. 1973; Ligorati et al. 1972; Heinze et al., 1969; Sittig, 1981). This regenerated DMT can be recycled with fresh DMT. However, the regenerated DMT exhibits a significantly higher carboxyl content, adversely affecting the product quality. It is more economical to convert P E T into low molecular weight oligomers by glycolysis, in the presence of a transesterification catalyst (Matsuura et al., 1975; Etienne and Soulas, 1969; Miura et al., 1968; Rustagi et al., 1977; Mueller et al., 1972; Ostrowski, 1975). When glycolysis is carried out using EG, the oligomers may be directly recycled into the polycondensation stage in P E T manufacturing. However, this also lowers the prbduct quality. Glycolysis can also be carried out using other glycols such as PG, and the oligomers can be used in the synthesis of unsaturated polyesters by reaction with maleic anhydride (Toshima, 1975; Miyake et al., 1975; Makimura and Miyake, 1978; Tong et al., 1983). There are two distinct advantages of the process. Firstly, the P E T waste is converted into a commercial value added product, and 0 1987 American Chemical Society
Ind. Eng. Chem. Res. Vol. 26, No. 2 , 1987 195 secondly, TPA-based UP resins are obtained without the processing difficulties encountered with the use of plain
TPA. The present paper reports the results of synthesis and characterization of unsaturated polyester resins prepared from glycolyzed PET waste. PG was used for glycolysis, since preliminary experiments showed that the UP resins synthesized from EG-based glycolyzed PET were incompatible with styrene monomer. The effect of the amount of glycol on the extent of depolymerization and the nature of the glycolyzed PET were studied. The processing characteristics of the U P resins synthesized from the glycolyzed PET and maleic anhydride were investigated. These include viscosity, gelation behavior, exotherm temperatures, etc. The processibility of these resins was compared to the conventional general purpose resin. Experimental Section 1. Materials. Pigmented PET waste with a number average molecular weight (ATn) ranging between 18OOO and 20000 was obtained in the form of chunks from M/s Century Enka, Pune. LR-grade propylene glycol obtained from M / s Indian Drug and Pharmaceutical Ltd., Hyderabad, was used for glycolysis. Zinc acetate (LR) and maleic anhydride (LR) were supplied by M/s High Purity Chemicals Pvt. Ltd., Delhi. LR-grade hydroquinone, supplied by M / s Loba Chemie, Bombay, was used as the inhibitor in the polyester synthesis. Styrene monomer (LR) was procured from SD Fine Chemicals Pvt. Ltd., Boiser. Methyl ethyl ketone peroxide (50% solution) and cobalt naphthanate (-8% Co) supplied by Fluka AG, Switzerland, were used as initiator and accelerator, respectively, for curing the polyester resins. Commercially available general purpose UP resin was obtained from M / s Roplas India Ltd., Pune, for use as a reference sample. 2. Glycolysis of PET Waste. The PET waste was depolymerized at different weight ratios of PET to PG using 0.5% (by weight) zinc acetate based on the weight of PET, as the catalyst. The reaction was carried out at about 200 "C under reflux for 8 h in a nitrogen atmosphere. The reactor used was a four-necked, round-bottomed flask of 2-L capacity having a reflux condenser, gas bubbler, thermowell, and stirrer. Thus, the glycolysis was carried out with PG at 62.5%, 5070, and 37.5% w/w PET waste to get three oligomeric diols, coded GPET-1, -2, and -3, respectively. The total charge in the reactor was about 1200 g for all the batches. The glycolyzed produds were then analyzed for hydroxyl value and the amount of free glycol as follows. (a) Determination of Hydroxyl Value. The hydroxyl values were determined by the conventional acetic anhydride/pyridine mixture (Urbanski et al., 1977). (b) Determination of Free Glycol. A weighed quantity of the glycolyzed product was extracted with water and filtered. The filtrate containing water, free glycol, and some water-soluble oligomers was concentrated by evaporation of water and then chilled to precipitate out the water-soluble oligomers. This was filtered again. The second filtrate thus obtained contained water and free glycol. The residues remaining after the first and second filtrations were dried and weighed together. The difference between the original and the final weights represents the amount of free glycol removed by water extraction. The glycolyzed products were also analyzed by thin-layer chromatography (TLC), using the chloroform/ethanol solvent system as the mobile phase and silica gel as the stationary phase. In order to check the extent of depolymerization, the
glycolyzed products were analyzed after the removal of free glycol, for hydroxyl values and the number average molecular weights (ATn). The hydroxyl values were determined as described earlier. The number average molecular weights were determined by vapor pressure osmometry (VPO) by using a Knaur Vapor pressure osmometer. Ethyl acetate was used as the solvent and benzil as the standard. All the sample solutions were filtered before the molecular weight measurements in order to remove the suspended particles comprised of pigment and a very small amount of high molecular weight PET. This suspension was of the order of 2 3 % w/w. The exact weights were determined by subtracting the weight of the insoluble portion from the initial weight. The temperature of the VPO chamber was 50 "C. 3. Preparation of Unsaturated Polyesters. The UP resins were prepared by reacting the glycolyzed products with maleic anhydride at a fixed ratio of 1.1/1 for the hydroxyl-to-carboxyl groups. The hydroxyl number of the glycolyzed product before separation of the free glycol was used for computing the amount of maleic anhydride. Thus, three UP resins, coded UVMW-57, -58, and -59, were prepared by reacting 1217.8 g of GPET-1 with 489.9 g of maleic anhydride, 1109.4 g of GPET-2 with 681.7 g of maleic anhydride, and 1012.6 g of GPET-3 with 750.3 g of maleic anhydride, respectively. The reaction was carried out in a 3-L round-bottomed flask having a distillation condenser, a thermowell, a gas bubbler, and stirring assembly. The reactants were heated from room temperature to 180 "C in N2 atmosphere in about l'/zh. Then the temperature was held a t 180 "C for 4 h and finally raised to 200 "C and maintained until the acid value reached about 32 mg of KOH/g. The water of the reaction was removed throughout the course of the reaction. The amount of water of condensation and the acid value were monitored throughout the reaction. At the end of the reaction about 0.425 g of hydroquinone was added to the liquid resin. The acid values were determined by titrating the solution of the resins in acetone, with 0.2 N standard alcoholic KOH solution using phenolphthalein indicator. The unsaturated polyester resins were analyzed for hydroxyl value and number average molecular weight as described earlier, before blending these with styrene monomer. The unsaturated polyester resins were dissolved in styrene monomer at 100 "C to get 30% w/w styrene in the resins. These were further diluted to get different concentrations of styrene. The processing characteristics such as viscosity, gel time, and exothermicity of all the resins were investigated. The viscosity measurements were carried out in a constant-temperature bath at 31 "C by using a Brookfield viscometer. The gel time and peak exotherm were determined using 1.5% MEKP as the initiator and 0.5% w/w cobalt naphthanate as an accelerator. The gel times were determined by using a Tecam gelation timer manufactured by M/s Techne (U.K.). Commercially available general purpose resin (GP), prepared from maleic anhydride, phthalic anhydride, and propylene glycol was used as the reference resin. One of the PET-based resins was characterized for gelation time by using different quantities of the initiator and accelerator. Results a n d Discussion 1. Glycolysis. Since U P resins made from ethylene
196 Ind. Eng. Chem. Res. Vol. 26, No. 2, 1987 Table I. Characterization of Glycolyzed PET Waste analvsis of elvcolvzed PET after free glycol removal before free glycol removal hydroxyl value hydroxyl value, mg of KOH/g M" (VPO) mg of KOH/g free glycol, 70 516 480 240 35 717 399 295 47 276 326 933 60 -
no.
glycolyzed product
P E T / P G wt ratio in glycolysis
1 2 3
GPET- 1 GPET-2 GPET-3
62.5137.5 50/50 37.5162.5
Table 11. Characterization of the Unsaturated Polyester Resins analysis of resins without styrene glycocarboxyl hydroxyl value, mg value, mg lyzed of product of no. oolvester used KOHia KOHin (VPO) 1 UVMW-57 GPET-1 32 74 1045 2 UVMW-58 GPET-2 31 67 1325 3 UVMW-59 GPET-3 32 57 1269 4 G P resin 37 62 1300 (control)
1
I
-4-
UVMW-57
-0-
UVMW-58
-0-
UVNW-59
-X-
0
P resin
l500
a"
glycol are known to have poor compatibility with styrene and poor hydrolytic resistance, propylene glycol was used to depolymerize PET. The glycolysis was carried out at three levels of PG. The results of the characterization of the glycolyzed products are given in Table I. It is apparent that only about 2-4% of the glycol is used up in depolymerization. The number average molecular weight of the glycolyzed product decreases with increasing amount of PG varying from 480 to 270. This range is comparable to the molecular weights of bis(hydroxyethy1) terephthalate and bis(hydroxypropy1) terephthalate. This indicates that the extent of depolymerization is considerable and the glycolyzed products mainly consist of hydroxyl-terminated monomer, dimer, and trimer. The extent of depolymerization increases with increasing amount of PG. This trend is clearly seen from the hydroxyl value and the &In measurements (Table I). TLC analysis of the glycolyzed products showed five to six spots with extensive tailing. This suggests that there are a number of oligomers in the glycolyzed products, and the molecular weight distribution (MWD) is broad. The major fractions of the glycolyzed product could be represented by the following species: PG-TPA-PG, EG-TPA-EG, EG-TPA-PG, and PG. The moieties are linked through ester linkages. A small amount of EG.can also be present in the glycolyzed product as a result of the glycol-exchangereaction during chain scission. 2. Polyesterification. The glycolyzed products were polyesterified with maleic anhydride at a fixed ratio of hydroxyl to carboxyl with 10% molar excess of hydroxyl groups. The reaction was carried out until the acid value reached about 32 mg of KOH/g. In all three cases, unsaturated polyesters of number average molecular weight comparable to that of the GP resin were obtained (Table 11). Although a drop in the hydroxyl value of the resin is observed with an increasing amount of PG in the glycolyzed product (UVMW-57 > UVMW-58 > UVMW-59), the molecular weights do not exhibit a similar trend. This
28
30
32
34
STYRENE
36
*/a,
38
Figure 1. Effect of percentage of styrene on Brookfield viscosity of polyester resins.
may be because of the difference in the molecular weight distribution and sequence distribution of the glycolyzed products, which would be affected by the relative amounts of free PG and oligomers in the reaction mass and their relative reactivities toward maleic anhydride. The molecular weights may be expected to increase from UVMW-57 to UVMW-59 because of the increase in the quantity of free glycol which is more reactive than the oligomers and thus may lead to a greater extent of polymerization. 3. Resin Characterization. The resins containing different amounts of styrene, ranging from 30% to 40%, were investigated for their viscosities (Figure 1). These measurements are consistent with the molecular weight results. Nevertheless, at a given styrene amount, the viscosities of the polyesters containing higher aliphatic PG segments (UVMW-58 and UVMW-59) are significantly higher than the resin with the highest aromatic segment content (UVMW-57). These differences cannot be explained merely by the marginally (20-25%) higher &?, of UVMW-58 and UVMW-59 relative to UVMW-57. The higher viscosities thus may be the result of a broader molecular weight distribution of these polyesters and the higher contents of maleic anhydride moiety. The relative
Table 111. Chemical Constituents of the UP Resins % of different moieties before styrene addition
no. 1 2 ,i
4
polyester UVMW-57 UVMW-58 UVMW-59 GP resin
terephthalic 32 23 16
40
w/w
acid phthalic
glycol maleic 26 32 39
34
21.7
ethylene
propylene
14
28
10.6
34 4
1
38
44.3
Ind. Eng. Chem. Res. Vol. 26, No. 2, 1987 197 180-
251
I
-A-0-
-0-Y-
20
UVYW - 5 7 UVWW - 5 8 UVYW 59 G P ratin
-
-A-
UVYW-57 UVYW-58
-0-
-0-X-
vi
Y
UVYW-59 G P resin
c
L 3
x 5
I S -
Y
1
28 28
30
34 S T Y R E N E V . , */w
32
36
38
Figure 2. Effect of percentage of styrene on gel time of polyester resins when cured with 1.5% MEKP and 0.5% cobalt naphthanate.
contents of the chemical moieties in the polyesters are given in Table 111. In general, the waste-based polyester resin, UVMW-57, and the reference G P resin have comparable chemical composition in terms of the aliphatic and aromatic blocks and these two samples exhibited a similar viscosity behavior (Figure 1). The gel times of the resins were determined by using 1.5% w/w MEKP and 0.5% w/w cobalt naphthanate. The results are reported in Figure 2. The trend in the gel times of PET-based resins is consistent with the viscosity and molecular weight measurements. The gel times of PET-based resins are considerably lower than that of the reference GP resin. This suggests that the PET-based resins may be more reactive than the GP resin because of the reduced steric hindrance to the double bonds in para-para linkages than in ortho-ortho linkages. The peak exotherm temperatures decreased in the order UVMW-59 > UVMW-58 > UVMW-57 > G P resin as illustrated in Figure 3. This is to be expected since the maleic unsaturation is the maximum for UVMW-59 and the minimum for the GP resin (Table 111). It is interesting to note from Figure 3 that with G P resin the peak exotherm temperature levels off above 32% w/w styrene, whereas in the case of PET-based resin WMW-57 it levels off only above 36% w/w styrene and for UVMW-58 and -59 it is even higher. The shorter gel times and higher exotherm temperatures of the PET-waste-based resins may adversely affect their processibility. Therefore, the possibility of modifying the gelation characteristics of these resins by changing the amounts of catalyst and accelerator was investigated. Resin UVMW-57 was selected for this investigation because of its highest PET waste content and its comparable viscosity to that of the reference GP resin. The gelation data of the resin at different levels of catalyst and accelerator is presented in Table IV. Referring to the results, it is clear that the gelation behavior can be manipulated
I
I
30
32
I
34
S T Y R E N E '/. ,
I
I
36
38
3
Wfw
Figure 3. Effect of percentage of styrene on the peak exotherm of polyester resins when cured with 1.5% MEKP and 0.5% cobalt naphthanate. Table IV. Gelation Behavior of UVMW-57 with 36% Styrene cobalt peak MEKP, naphthanate, gel time, exotherm, no. % WJW % WJW min "C 0.2 52 120 1.5 125 29 0.3 1.5 0.4 20 130 1.5 11 152 0.5 1.5 120 26 0.5 1.25 45 0.5 110 1.0 105 80 0.5 0.75 105 90 0.2 1.0
as per requirement by varying the amount of the initiator and accelerator.
Conclusions When P E T is depolymerized by EG and the glycolyzed product as such is used for preparation of unsaturated polyester, the resins are not compatible with styrene. The PG-based glycolyzed products of PET waste can be further converted into unsaturated polyesters that are compatible with styrene. The degree of depolymerization depends on the amount of PG. UP resins based on PET waste, with viscosity and reactivity comparable to the GP resin, can be synthesized with a proper ratio of the aromatic acid moiety, the aliphatic anhydride, and the diol. Similarly the gelation cha,,acteristics of these resins can be manipulated per processing requirements by varying the relative amounts of the accelerator and initiator. The molecular weight distribution of the glycolyzed PET products as well as that of the resin affect the final properties like viscosity and gel time. Processing characteristics of PET-based resin, UVMW-57, are comparable with that of GP resins. Hence, it can successfully replace the conventional GP resin in FRP. The mechanical and dynamic mechanical
I n d . E n g . C h e m . Res. 1987, 26, 198-202
198
properties of the PET-based resins are being investigated and will be reported in a subsequent publication. PET-based resins would be best suited for processes like hot moulding, where a higher viscosity is desirable. These PET-based resins would definitely benefit the F R P industries by offering versatility in processing and properties over conventional resins. Registry No. PET, 25038-59-9; P G , 57-55-6; (EG)(PG)(TPA)(maleic anhydride)(copolymer), 30790-78-4;CsH5CH=CH2, 100-42-5.
Literature Cited Boeing, H. V. In Encyclopedia of Polymer Science and Technology; Wiley: New York, 1969; Vol. 11, p 150. Etienne, Y.; Soulas, R. US Patent 869017, 1969. Heinge, J.; Kuehnpast, W.; Ramm, H.; Richardt, H. Ger (East) Patent 68500, 1969. Hemmi, H.; Nagashima, H.; Kimura, Y.; Teresaki, I.; Satani, M. Jap. Kokai Patent 7 362 732, 1973. Ligorati, F.; Aglietti, G.; Nova, V. E. Ger. Offen. Patent 2' 158 560, 1972. Makimura, 0.; Miyake, H. Jap. Patent, 7 809 275, 1978.
Matsuura, M.; Habara, T.; Katagiri, Y.; Jap. Kokai Patent 7 571 639, 1975. Miura, K.; Kagiya, Y.; Ichikawa, T. Jap. Patent 6 823 449, 1968. Miyake, H.; Makimura, 0.;Tsuchida, T. Ger. Offen. Patent 2 506 744, 1975. Modern Plastics International; McGraw Hill: Switzerland, 1986; Vol. 16, No. 1, p 26. Mueller, W.; Groeger, C.; Schmidt, W.; Strobel, L. Patent Ger (East) 92801, 1972. Ostrowski, H. S. US Patent 3 884 850, 1975. Parkyn, B.; Lamb, F.; Clifton, B. V. Polyesters; American Elsevier: New York, 1967; Vol. 2, Chapter 2. Rustagi, S. C.; Dabholkar, D. P. A.; Niham, J. K.; Marathe, M. N.; Iyer, K. €5. Indian Patent 145323, 1977. Sittig, M. Organic and Polymer Waste Reclaiming Encyclopedia; Noyes Data: Englewood Cliffs, NJ, 1981; pp 41, 117. Tong, S . N.; Chen, D. S.; Chen, C. C.; Chung, L. Z. Polymer 1983, 24, 469. Toshima, H. Jap. Kokai Patent 7 564 382, 1975. Urbanski, J.; Czerwinski, W.; Janika, K.; Majewska, F.; Zowall, H.; Handbook of Analysis of Synthetic Polymers and Plastics; Ellis Horwood: Chichester, England, 1977.
Received for review May 7, 1986 Accepted August 14, 1986
Vapor-Phase Esterification of Acetic Acid with Ethanol Catalyzed by a Macroporous Sulfonated Styrene-Divinylbenzene (20 % ) Resin Jaime Gimenez,* Jose Costa, and Salvador Cervera Department of Chemical Engineering, Faculty of Chemistry, University of Barcelona, 08028 Barcelona, S p a i n
T h e kinetics of the vapor-phase (85-120 " C ) esterification of acetic acid with ethyl alcohol, a t atmospheric pressure, catalyzed by a macroporous sulfonated styrene-divinylbenzene (DVB; 20%) resin, has been studied. A simple first-order model (r = k iol) fits experimental kinetic data properly for a constant reactants ratio. Discussion by means of L-H-H-W models shows that the ratecontrolling step is the surface reaction with a single-site mechanism. The apparent activation energy is 4000 cal/mol. The esterification reaction of acetic acid with ethanol has been widely studied, mainly because of its industrial interest. Ethyl acetate is a very known solvent with many applications. This reaction has been studied in the vapor phase using solid catalysts, like silica gel, silica-alumina, aluminum orthophosphate, zeolites, several metal oxides, etc. (Amundson and Stusiak, 1959; Ballesteros et al., 1967; Buckley and Altpeter, 1951; Chashchin, 1963; Hoerig et al., 1943; Santacesaria et al., 1983; Sinisterra et al., 1979; Venkateswarlu et al., 1958). Its kinetics is still a matter of discussion, and the rate-limiting steps are not always clear enough. There are also a few kinetic studies done with ion-exchange resins as catalysts. In all of them, gel-type sulfonated styrene-divinylbenzene (DVB) resins have been used (Andrianova and Bruns, 1960; Andrianova, 1962, 1964; Herrman, 1955). Kinetic data interpretations are controversial, and modeling is far from being completed. Research in catalysis by ion-exchange resins is undoubtedly interesting, not only under a pure physicochemical point of view but because of the advantages of these types of catalysts over the conventional ones. Ionexchange resins increase the product yield, keep their activity a long time, and do not pollute; it is easy to separate them from reaction media and to regenerate them (Costa et al., 1984; Polyanskii and Sapozhnikov, 1977).
They also have some disadvantages: they are less resistant to temperature and abrasion and are more expensive. However, accounting for the savings of the advantages mentioned involve, it is not risky to predict an important growth in their industrial catalytic applications. Concerning the accessibility of the resin-active sites in vapor-phase reactions, the catalytic performance of resins has been improved with the use of the macroporous-type ones. Acetic acid-ethanol esterification had not been previously studied using macroporous-type resins. This fact and the preceding aspects were the starting point of this work. The aim of this study has been the kinetic study of this esterification reaction with a macroporous-type sulfonated resin, in order to obtain phenomenological rate equations and discuss them according to L-H-H-W models criteria.
Experimental Section (i) Apparatus. The experimental kinetic work was carried out in a continuous-flow device at atmospheric pressure (see Figure 1). The two liquid reactants were fed to the vaporizer with either a syringe pump or a Mariotte-type buret, depending on the flow rates used. A good performance of the vaporizer is paramount, given that this esterification reaction is autocatalytic when conducted in the liquid phase, and so condensation has to be avoided. Nitrogen was used as
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