سنتز هم زمان دی متیل کربنات و پلی (اتیلن ترفتالات) با استفاده از فلزات قلیایی به عنوان کاتالیزور

Dimethyl carbonate (DMC) and poly(ethylene terephthalate) was simultaneously synthesized by the transesterification of ethylene carbonate (EC) with dimethyl terephthalate (DMT) in this paper. This reaction is an excellent green chemical process without poisonous substance. Various alkali metals were used as the catalysts. The results showed alkali metals had catalytic activity in a certain extent. The effect of reaction condition was also studied. When the reaction was carried out under the following conditions: the reaction temperature 250°C, molar ratio of EC to DMT 3:1, reaction time 3h, and catalyst amount 0.004 (molar ratio to DMT), the yield of DMC was 68.9%.

Dimethyl carbonate (DMC) is considered to be a benign carbonylation and methylation agent, substituting for poisonous phosgene and dimethyl sulfate. It can be used to enhance gasoline octane value and synthesize polycarbonate resins[ 1 -31. At present, three routes for production of DMC including the phosgene-methanol route, the oxidative carbonylation of methanol route and the transesterification route have been commercialized on a large scale[4,5]. In recent years considerable efforts have been put into the transesterification of ethylene carbonate (EC) with methanol [reaction (1) in Fig.11 due to its using simple equipment and little corrosion to equipment. Poly (ethylene terephthalate) (PET) is one of the most important engineering polymers, widely used in food packaging film and in beverage containers[6]. With the increase of demand to PET[7], there has been growing concern on the study of transesterification of ethylene glycol and dimethyl terephthalate (DMT) [reaction (2)], which is an important industrial route to produce PET. In this paper, reactions (1) and (2) were coupledto simultaneously synthesize dimethyl carbonate and poly (ethylene terephthalate) [reaction (3)]. This method improved the atom economy by avoiding by-products of methanol and ethylene glycol and decreased energy consumption. Because ethylene carbonate is a product of the reaction between C02 and ethylene epoxide, this method make good use of greenhouse gas C02. The reaction cannot proceed without catalyst. However, there are only a few catalysts that are reported, such as Ti(OC4H9)4[8-10], TiO2[9], Ti(OCH&[9] and various metal acetateslll]. Since alkali metals compounds are often applied in reaction (1)[12,13], it is presumed that it would also have catalytic activity in a certain degree for reaction (3). Therefore, various alkali metals compounds catalysts were developed.

3.1 Catalytic behavior To investigate the reaction of ethylene carbonate with dimethyl terephthalate, several experiments were carried out first to screen the catalysts. The reaction conditions are: temperature 250 "C , molar ratio of EC/DMT= 1, molar ratio of catalyst/DMT = 0.002, reaction time 3h, amount ofTable 1 shows alkali metals compounds are active in the reaction, indeed. The catalytic activity of LiN03, LiCl, CH30Na, CzH50Na, NaN03 and Na- HC03 is close to each other and their yields of DMC are above 37%. A small amount of methanol was also detected by the GC-MS analysis. Methanol might be intermediate product and was distilled slightly with DMC when the oligomerization of poly (ethylene terephthalate) occurred during the transesterification. LiCl is chosen as the catalyst and studied the effect of reaction conditions in detail. 3.2 Effect of catalyst amount on the reaction It can be seen from Table 2 that the catalytic activity was increased with increasing LiCl amount, but when the molar ratio of LiCl was above 0.004, the catalytic activity dropped to a slightly lower level. It seems likely that excess LiCl catalyst leads to polymerization of EC, disadvantageous to produce DMC. So, the optimal catalyst amount may be 0.004.3.3 Effect of molar ratio of EC/DMT on the reaction Table 3 presents the yield of DMC versus the molar ratio of EC to DMT. When EC and DMT were added according to the stoichiometric reaction, the yield of DMC is the lowest. This may ascribe that the reaction is reversible. It is more favorable to the yield of DMC when EC is in excess compared with the amount of DMT. When the molar ratio of EC/DMT was increased to 3 : 1, the yield of DMC increased greatly, but the increase thereafter became negligible. The appropriate molar ratio of EC to DMT was about3.4 Effect of reaction time on the reaction To investigate the catalytic activity at different time, more experiments was conducted in the range of 1-7h. The result is shown in Table 4. It can be seen that the yield of DMC increased with the reaction time, but the change was not significant after about 3h. So, the optimal reaction time for the reaction is 3h.3.5 FT-IR spectra about oligomer of PET The FT-IR spectra about PET are shown in Fig.2. The FT-ER spectrum of most PET produced by the transesterification of ethylene glycol and dimethyl terephthalate is shown as spectrum (1)[14]. The FT-IR spectrum (2) is the product that obtained using LiCl as catalyst and the reaction conditions were the same with those in section 3.1. It is interesting to see that spectrum (2) is almost identical to spectrum (1) and it can be concluded that the present product is the oligomer of PET. In spectrum (2), the characteristic bands are mainly derived from ester and aromatic ring groups. 1267cm-’ and 1128cm-’ are due to stretching vibration of C-0. The bands at 1719cm-’ and 728cm-’ are characteristic of C=O and benzene ring, respectively [14]. The band at 3432cm-’ indicates the oligomer of PET contains hydroxyl.In this work, the oligomer of PET was obtained, and the study of further polymerization is under way.