11250
Ind. Eng. Chem. Res. 2010, 49, 11250–11253
Effect of Reactive Distillation on the Yield of Tetraacetylethylenediamine (TAED) Eun-Seon Kim,† Kyun Young Park,*,† Jung-Moo Heo,‡ Byung Jo Kim,‡ Kyo Duck Ahn,‡ and Jong-Gi Lee‡ Department of Chemical Engineering, Kongju National UniVersity, 275 Budae-dong, Cheonan, Chungnam, 330-717, Republic of Korea and AK ChemTech Company Limited, 217-2, Shinseong-Dong, Yooseong-Ku, Daejeon 305-345, Republic of Korea
Tetraacetylethylenediamine (TAED) was prepared by acetylation of diacetylethylenediamine (DAED) with acetic anhydride in a 5 L reactor coupled with a packed distillation column, 2.5 cm in inside diameter and 1 m in length. The reaction temperature was set at 135 °C and the reflux ratio at 6. The molar ratio of acetic anhydride to DAED was varied from 3 to 5. A TAED yield as high as 80% was obtained, higher by 15% than in the absence of distillation. The temporal variation of the TAED yield was calculated using the kinetic parameters in the literature. Calculated and experimental values showed good agreement. Introduction Tetraacetylethylenedimine (TAED), (CH3CO)2NCH2CH2N(COCH3)2, is known to be the most important activator of sodium perborate, which is present in washing-machine detergents.1 TAED is generally produced from ethylenediamine in two stages. Initially ethylenediamine is reacted with acetic acid to form diacetylethylenediamine (DAED); then DAED is converted into TAED by reaction with acetic anhydride via the intermediate product triacetylethylenediamine (TriAED). The overall reaction can be represented by DAED + 2Ac2O ) TAED + 2CH3COOH
(1)
where Ac2O represents acetic anhydride, (CH3CO)2O. DAED is solid at ambient condition and melts at 170-172 °C. The boiling points of acetic acid and acetic anhydride are 118.1 and 139.6 °C, respectively. Many patents have been filed to improve the TAED yield and minimize the consumption of acetic anhydride.2-4 Academic studies on the specific subject are rare,5,6 although acetylation of alcohols and amines with acetic anhydride has been studied broadly.7-10 The conversion of DAED into TAED is known to be reversible.6 Removal of the acetic acid in the right-hand side of eq 1 should therefore shift the chemical equilibrium in the forward direction to increase the yield of TAED. The shift was experimentally verified; a considerable increase in the yield was observed by intermittent removal of the acetic acid during the reaction.3 Application of the reactive distillation,11 in which chemical reaction and distillation are combined, to the conversion of DAED to TAED would provide a continuous removal of the acetic acid during the acetylation reaction, leading to a higher TAED yield. We searched for previous works on TAED production with reactive distillation but could not find any published in the literature. In the present study, a packed distillation column was connected to the reactor in order to remove the acetic acid in situ by distillation. The reaction temperature was set at 135 °C. The ratio of DAED to acetic anhydride in the reactor was varied from 3 to 5. The method of acetic anhydride feeding to the reactor was varied from initial * To whom correspondence should be addressed. E-mail:
[email protected]. † Kongju National University. ‡ AK ChemTech Company Limited.
one-step feeding to intermittent feeding in 3 steps and further to continuous feeding during reaction; the total amount of acetic anhydride fed to the reactor was kept the same between feeding methods. The effects of the reactive-distillation variables on the yield of TAED are discussed in comparison with the yields in the absence of the reactive distillation. Experimental Section Figure 1 shows a schematic diagram of the experimental apparatus. It consists of a 5 L Pyrex reactor with a stirrer, two Pyrex packed distillation columns in series (Lenz Laborglas, 2.5 cm in diameter and 50 cm in height), a condenser, a graduated cylinder with a valve at the bottom, a reflux pump, a distillate transfer pump, a 5 L distillate storage tank, a 10 L buffer tank, a vacuum pump, and a NaOH scrubber. The reactor is equipped with a heating mantle and a K-type thermocouple. DAED was supplied by the Aekyung Chemical Co., and the acetic anhydride was of analytical grade and used without further purification. A 826 g amount of DAED is charged into the reactor with an amount of acetic anhydride predetermined to meet the ratio of acetic anhydride to DAED. The vacuum pump is then operated to bring the reactor pressure down to a predetermined level. The reactor is heated up to a boiling point of the reactant mixture. The generated vapor exits the reactor and rises through the packing of the distillation column on top of the reactor and is condensed in the condenser after the distillation column. The condensate is passed through the graduated cylinder and split into two. One is recycled to the top of the distillation column with a metering pump, and the other or the distillate is sent to the storage tank. The condensate flow rate is measured intermittently by closing the valve at the bottom of the graduated cylinder and measuring the build up of the condensate in the cylinder. The rate of vapor generation in the reactor can be deduced from the condensate rate and controlled by manipulating the power input to the heater. A 380 g amount of acetic anhydride at room temperature was poured into the reactor to terminate the reaction by cooling and to precipitate the produced TAED. The precipitated TAED was then separated from the mother liquor by filtration, washed, dried, and weighed. The yield was determined by dividing the number of moles of the obtained TAED by that predicted from reaction stoichiometry. The mole fraction of acetic acid in the distillate was determined by measuring the refractive index and converting
10.1021/ie100886n 2010 American Chemical Society Published on Web 10/14/2010
Ind. Eng. Chem. Res., Vol. 49, No. 22, 2010
11251
Figure 1. Schematic drawing of experimental set up. Table 1. Experimental Conditions for Preparation of TAED through Acetylation of DAED with Acetic Anhydridea
run no.
reactive distillation
acetic anhydride feeding method
1 2 3 4 5 6 7 8 9 10
no no no no yes yes yes yes yes yes
A B B B A A A C C C
molar ratio of acetic anhydride to DAED
distillate flow rate, ml/min
reflux ratio
5 5 4 3 5 4 3 5 4 3
0 0 0 0 3.5 3.2 2.3 3.5 3.2 2.3
0 0 0 0 4.3-5.4 5.0-8.4 4.8-7.4 4.3-5.7 5.9-7.5 4.8-7.4
a Method A: all acetic anhydride is charged initially. Method B: one-third the acetic anhydride is charged initially and the balance is charged in equal divisions at two reaction times, 4 and 7 h, respectively. Method C: 5.73 mols of acetic anhydride, equal to the moles of DAED, is charged initially and the balance continuously over the reaction time.
the index into mole fraction using a calibration curve obtained in advance from known mole fractions of acetic acid. The validity of this optical method was confirmed by gaschromatographic analysis, as shown in the Supporting Information. Results and Discussion Table 1 shows the operating conditions for a total of 10 runs. The reactor temperature was set at 135 °C, the absolute pressure at the top of the distillation column at 0.7 atm, and the reaction time at 10 h for each run. Runs 1-4 were performed in the absence of reactive distillation with the molar ratio of acetic anhydride to DAED varied from 3 to 5. In run 1, the ratio of acetic anhydride to DAED was 5 and all the acetic anhydride was fed to the reactor initially. The operating condition for run 2 is the same as that of run 1 except for the acetic anhydride feeding method. In run 2, the acetic anhydride was charged in 3 steps: 1/3 initially, 1/3 at the reaction time of 4 h after distilling off the mixture of acetic acid and acetic anhydride, and the last 1/3 at 7 h following removal of the acetic acid as in the preceding step. Runs 3 and 4 were carried out using the same feeding method as in run 2 but with a lower ratio of acetic anhydride to DAED, 4 and 3, respectively. In run 1, the TAED yield increased initially with time but leveled off beyond 5 h at 50.2%, implying that an equilibrium
has been reached. The yield was increased to 64.9% in run 2 due to the intermittent removal of the acetic that shifted the reaction in the forward direction. As the ratio of acetic anhydride to DAED was decreased from 5 to 3, the TAED yield decreased from 64.9% to 46.3% due to the decrease in acetic anhydride concentration, a reactant. By employing the intermittent feeding and removal of the acid, the reaction volume could be maintained lower than that required for the one-step feeding. This allows for incremental charge of reactants, leading to an increase in production capacity for a given reactor volume; this advantage of capacity increase may be particularly appreciable for commercial-scale operations. The intermittent removal of the produced acetic acid was thus not only effective in increasing the TAED yield but also allowed for an increase in production capacity. This implies that the yield and production capacity could be increased further by employing a continuous removal during reaction or the reactive distillation. Batch Reactive Distillation. Runs 5-7 were carried out with batch reactive distillation. All reactants were charged to the reactor initially and heated to the boiling point under a vacuum. The ratio of acetic anhydride to DEAD charged to the reactor differs between runs: the ratio was 5 in run 5, 4 in run 6, and 3 in run 7. As the acetic anhydride to DAED ratio was decreased from 5 to 3, the distillate flow rate was reduced from 3.5 to 2.3 mL/min. Otherwise, the acetic acid-acetic anhydride mixture in the reactor would have been dried up before termination of a reaction. The reflux ratio was set at 6 but actually fluctuated between 4 and 8 due to the rather incomplete performance of the manual controller employed in the present study. The TAED yield increased remarkably due to the reactive distillation, as shown in Figure 2. Compared to 50.2% in the absence of distillation, the yield increased to 80.5% at the same acetic anhydride to DAED ratio of 5. The yield decreased to 75.8% and 66.1%, respectively, with decreasing the ratio to 4 and 3, due to the decrease in acetic anhydride concentration. Figure 3 shows temporal variations of instantaneous acetic acid mole fraction in the distillate for two ratios of acetic anhydride to DAED, 3 and 5. For the ratio of 5, the acetic acid mole fraction was maintained at about 0.8 for the initial 3 h and then decreased continuously with time down to 0.49 at 8 h. The decrease of the mole fraction with time is primarily due to a decrease in the acetic acid concentration in the reactor. The
11252
Ind. Eng. Chem. Res., Vol. 49, No. 22, 2010
Figure 2. Comparison of TAED yield between with and without reactive distillation. The reactor temperature was set at 135 °C and the reflux ratio at 6 ((O) with reactive distillation; (0) without reactive distillation). The molar ratio of acetic anhydride to diacetylethylenediamine was 5.
Figure 3. Temporal variations of acetic acid mole fraction in the distillate for two ratios of acetic anhydride to diacetylethylenediamine, 3 and 5 ((0) molar ratio at 3; (O) molar ratio at 5). The reactor temperature was set at 135 °C and the reflux ratio at 6.
concentration of acetic acid in the reactor at the bottom should decrease in the later stage because the rate of reaction, through which acetic acid is produced, is lower and the more volatile acetic acid has vaporized faster than acetic anhydride. Such a decrease in acetic acid concentration in the reactor led to the decrease in the distillate; theoretically, a decrease in concentration of a component in the reactor is propagated through the distillation column toward lowering the corresponding concentration in the distillate. The boiling point rose from 135 °C at the start to 140 °C at the end or after 10 h. This indicates that the composition in the reactor varied with time. The variation in composition may also have contributed to the decrease of the acetic acid mole fraction in the later stage. The acetic acid concentration in the distillate increased with decreasing ratio of acetic anhydride to DAED from 5 to 3. For a given amount of acetic acid formed as byproduct the fraction of acetic acid in the acetic acid-acetic anhydride mixture in the reactor should be higher with the lower ratio of acetic anhydride to DEAD, thereby increasing the acetic acid mole fraction in the vapor generated in the reactor and passed to the distillation column and consequently resulting in an increase of acetic acid concentration in the distillate withdrawn from the top of the distillation column. Semibatch Reactive Distillation. In the batch distillation, all reactants were fed to the reactor initially. By comparison,
Figure 4. Comparison of TAED yield between batch and semibatch distillations for varying ratios of acetic anhydride to diacetylethylenediamine (the black bar represents batch distillation and the white one semibatch distillation). The reactor temperature was set at 135 °C and the reflux ratio at 6.
Figure 5. Comparison of TAED yield between calculated and experimental values for batch and semibatch reactive distillations ((O) experimental yield with batch distillation; (0) experimental yield with semibatch distillation; solid and dotted lines represent calculated yields for batch and semibatch distillations, respectively). The reactor temperature was set at 135 °C and the reflux ratio at 6. The molar ratio of acetic anhydride to diacetylethylenediamine was 5.
in the semibatch distillation, equimolar acetic anhydride and DAED were charged initially and the balance of the acetic anhydride was fed to the reactor continuously at a constant rate until termination of a run. With the semibatch distillation, the reaction volume could be reduced at the expense of a potential reduction in TAED yield. Runs 8-10 were carried out under the semibatch distillation mode to compare with runs 5-7 that have been performed under the batch distillation mode. As shown in Figure 4, the semibatch distillation gave TAED yields lower by about 5% than those obtained with the batch distillation. Such a decrease in TAED yield may be due to the decrease in the time-averaged concentration of acetic anhydride in the reactor, as shown in the Supporting Information. The semibatch distillation, however, ensures a higher production capacity by allowing for an increase in the amount of DAED chargeable to the reactor due to the decrease in acetic anhydride volume in the reactor. Figure 5 shows a comparison in temporal variation of TAED yield between the batch and the semibatch distillations for a molar ratio of acetic anhydride to DAED at 5. In the early stage, the yield was apparently higher with the batch distillation due to the higher initial charge of acetic anhydride. In the later stage,
Ind. Eng. Chem. Res., Vol. 49, No. 22, 2010
11253
the TAED yield was lower by 5% with the semibatch distillation in which the acetic anhydride was fed to the reactor continuously. The semibatch distillation, however, would allow for a higher production capacity due to the reduction in reaction volume. The trade off between the yield and the capacity needs further consideration in practical applications. The temporal variation of the TAED yield was calculated using the kinetic parameters in the literature. Calculated values and experimental data showed good agreement but for a deviation over a specific range of reaction times. Further studies may be necessary to investigate the causes of the deviation. Acknowledgment
Figure 6. Calculated concentrations of DAED, TriAED, and TAED with time for a batch reactive distillation (solid line, DAED; dotted line, TriAED; dashed line, TAED). The reactor temperature was set at 135 °C and the reflux ratio at 6. The molar ratio of acetic anhydride to diacetylethylenediamine was 5.
the gap narrowed due to the continuous make up of acetic anhydride with the semibatch distillation. Ultimately the yield with the semibatch distillation came out to be quite close to that with the batch distillation. The temporal variations of the yield were calculated based on component mole balances for DAED, TriAED, TAED, acetic acid, and acetic anhydride using the kinetic parameters in the literature.6 The reaction volume change due to withdrawal of the distillate was considered. Details on the calculation can be found in the Supporting Information. Calculated yields are compared with experimental data in Figure 5. For the batch distillation, good agreement can be seen in the early stage. In the later stage, however, the calculation overestimated. A reason for the overestimation is that the rate constant for the reverse reaction from TAED to TriAED, which was adopted from the literature, may be underestimated. For the semibatch distillation, calculated yields agree with experimental data at the start and at the end but are lower than experimental values over a broad intermediate range of reaction times. Further studies may be necessary to investigate the causes of the deviation. Figure 6 shows the calculated concentrations for DAED, TriAED, and TAED for a batch distillation with varying reaction time. The reactor temperature was set at 135 °C and the reflux ratio at 6. The molar ratio of acetic anhydride to DAED was 5. The concentration of DAED decreases continuously. In contrast, the concentration of TriAED increases initially, reaches a maximum at 2 h, and then decreases. Such a concentration profile of TriAED is typical of the concentration of an intermediate product in series reactions. The present model is not fully based on first principles but utilizes the measured composition of the distillate withdrawn from the distillation column. To make the model predictive for the distillate composition, vapor-liquid equilibria for a system of five components (DAED, TriAED, TAED, acetic acid, and acetic anhydride) and mass transfer data for the packings used in the experiments should be available, for which further studies must follow. Conclusions The yield of TAED in the acetylation of diacetylethylenediamine with acetic anhydride increased by more than 15% through a reactive distillation. Compared to the batch distillation,
This research was financially supported by the Ministry of Commerce, Industry and Energy (MOCIE) and Korea Industrial Technology foundation (KOTEF) through the Human Resources Training Project for Regional Innovation. Supporting Information Available: The information includes a comparison of acetic acid mole fraction in the distillate between refractometry and gas-chromatography, mole balance equations and kinetic parameters to calculate temporal molar composition in the reactor, and time-averaged concentration of acetic anhydride in the reactor. This material is available free of charge via the Internet at http://pubs.acs.org. Literature Cited (1) Martin Davis, D.; Dreary, M. E. Kinetics of the hydrolysis and perhydrolysis of tetraacetylethylenediamine, a peroxide bleach activator. J. Chem. Soc., Perkin Trans. 1991, 2., 1549–1552. (2) Pontogilo, E.; Donelli, G.; Padori, S. (CAFFARO S.p.A., IT). Process for the purification of tetraacetylethylene diamine (TAED). European Patent 0,484,634, May 13, 1992. (3) Hannam, S. J.; Saynor, J. S.; Watling, A. D. (Warwick Chemical Ltd., UK) Process for making N, N, N’, N’-tetraacetylethylenediamine. U.S. Patent 4,054,042, Oct 12, 1982. (4) Muller-schiedmayer, G.; Aigner, R. (Hoechst Aktiengesellschaft, DE) Process for the manufacture of N, N, N’, N’-tetraacetylethylenediamine. U.S. Patent 4,240,980, Dec 23, 1980. (5) Antsyshkina, A. S.; Sadikov, G. G.; Solonina, I. A.; Rodnikova, M. N. Synthesis and crystal structures of tetraacetylethylenediamine and N-(2-Ammoniummethyl)carbamate. Russ. J. Inorg. Chem. 2007, 52, 1561– 1566. (6) Platonova, O. V.; AkhmetshinYu., G.; Kossoi, A. A.; Vdovets, M. Z.; Laskin, B. M.; Malin, A. S.; Sitdikov, A. T. Kinetic model of acylation of diacetylethylenediamine. Russ. J. Appl. Chem. 2008, 81, 1808–1812. (7) Satam, J. R.; Jayaram, R. V. Acetylation of alcohols, phenols and amines using ammonium salt of 12-tungstophosphoric acid: enviromentally benign method. Catal. Commun. 2008, 9, 2365–2370. (8) Yadav, J. S.; Narsaiah, A. V.; Basak, A. K.; Goud, P. R.; Sreenu, D.; Nagaiah, K. Niobium pentachloride: An efficient catalyst for the selective acetylation of amines and thiols under mild conditions. J. Mol. Catal., A: Chem. 2006, 255, 78–80. (9) Srikanth Reddy, T.; Narasimhulu, M.; Suryakiran, N.; Chinni Mahesh, K.; Ashalatha, K.; Venkateswarlu, Y. A mild and efficient acetylation of alcohols, phenols and amines with acetic anhydride using La(NO3)3 · 6H2O as a catalyst under solvent-free conditions. Tetrahedron Lett. 2006, 47, 6825–6829. (10) Das, B.; Thirupathi, P. A highly selective and efficient acetylation of alcohols and amines with acetic anhydride using NaHSO4•SiO2 as a heterogeneous catalyst. J. Mol. Catal., A: Chem. 2007, 269, 12–16. (11) Jan Harmsen, G. Reactive distillation: The front-runner of industrial process intensification. A full review of commercial applications, research, scale-up, design and operation. Chem. Eng. Process. 2007, 46, 774–780.
ReceiVed for reView April 14, 2010 ReVised manuscript receiVed July 23, 2010 Accepted October 4, 2010 IE100886N
