Development of a Continuous System Based on ... - ACS Publications

Subscriber access provided by UNIV OF NEWCASTLE

Article

Development of a continuous system based on azeotropic reactive distillation to enhance triacetin selectivity in glycerol esterification with acetic acid Hajar Rastegari, Hassan S. Ghaziaskar, Mohammad Yalpani, and Amin Shafiei Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b01068 • Publication Date (Web): 18 Jul 2017 Downloaded from http://pubs.acs.org on July 23, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Graphical abstract

The schematic diagram of the developed continuous system in this study.

ACS Paragon Plus Environment

Energy & Fuels

1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Development of a continuous system based on azeotropic reactive distillation to enhance triacetin selectivity in glycerol esterification with acetic acid

Hajar Rastegari a, Hassan S. Ghaziaskar a,*, Mohammad Yalpani b, Amin Shafiei a a

Department of Chemistry, Isfahan University of Technology, Isfahan, 84156-83111, I.R. Iran

b

R & D Department, Farzin Chemicals Sepahan Co., Montazerie Industrial Complex, Villashahr,

Isfahan, 85131-14461 I.R. Iran. *

Corresponding author Tel: 0098-31-33913260, Fax: 0098-31-33912350, Email address:

[email protected] (Hassan S. Ghaziaskar)


Page 2 of 28

Page 3 of 28

Energy & Fuels

2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Highlights •

Continuous esterification of glycerol with acetic acid was investigated using toluene

as entrainer. •

Selectivity of 80% to TA at complete glycerol conversion was obtained.

•

MA was synthesized at glycerol conversion of 97% with selectivity of 85%.

•

Entrainer based azeotropic distillation obtained DA with selectivity of 65% at 100% glycerol conversion.


Energy & Fuels

3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract Glycerol esterification with acetic acid was carried out in a continuous, easy to scale up, system using toluene as entrainer. A water separation system was designed and coupled to an optimized continuous system. The continuous system operated at temperature of 100 oC, with acetic acid to glycerol mole ratio of 7, pressure of 1 bar, and feed flow rate of 0.5 mL.min-1 over 3g Amberlyst 36. At these conditions, the glycerol conversion was 100% with 43%, 44% and 13% selectivity to monoacetin, diacetin and triacetin, respectively. Formation of byproducts was not observed at these conditions. By coupling this continuous system to designed simultaneous reactor and water separation system, containing 3g Amberlyst 36, these values changed to 0%, 15% and 80%, respectively. By-products formation was observed with the selectivity of only 5% after passing feed from the water separation system. Continuous removal of formed water in the reaction was done by toluene. As a result of this process the chemical equilibrium shifted toward the TA production. The maximum selectivities obtained from experiments were 85% for MA, and 65% for DA. Amberlyst 15 and Purolite PD206 also was used for esterification reaction. Amberlyst 15 and 36 had similar performance. A mixture of MA and DA obtained through esterification of glycerol with trapped acetic acid in Dean Stark. Keywords: Continuous esterification, Toluene entrainer, Monoacetin, Diacetin, Triacetin.


Page 4 of 28

Page 5 of 28

Energy & Fuels

4 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1.

Introduction

Due to the presence of three hydroxyl group in its structure, glycerol (Gly) has the potential of being an extremely versatile building block in chemistry 1. One of the important glycerol derivatives is triacetin (TA), a good bio-additive that could be used as an anti-knocking and an octane booster for gasoline 2, and also cold flow improver and viscosity reducer for biodiesel 3. Moreover, it has also been utilized in production of cigarettes’ filters and also as a gelatinizing agent 3. TA can be synthesized via direct esterification of glycerol with acetic acid (AA)/acetic anhydride or transesterification of glycerol with methyl/ethyl acetate. Whereas direct esterification has had better yields compared with transesterification 4, 5. Utilization of acetic anhydride could improve the reaction to yield TA with a selectivity close to 100%. However, this procedure is not convenient, due to much higher price of acetic anhydride in comparison with acetic acid and also its hazardousness to health. Hence it is not economically and environmentally acceptable 6. Esterification of glycerol with acetic acid is reported using several solid acid catalysts in general batch reactor set-up, however the TA selectivity were rather low 7-16. Glycerol esterification with acetic acid, is a reaction consists of three consecutive steps. Whereas, water is produced as an unavoidable by-product at each consecutive step and chemical equilibrium limits the extent of the reaction. Using excess amounts of acetic acid is one promising route to overcome this limitation. Continuous esterification of glycerol with excess of acetic acid was carried out in supercritical carbon dioxide 17. A 100% selectivity for TA with 41% yield was obtained. However, the mole ratio of acetic acid to glycerol, and pressure were reported 24 and 200 bar, respectively. Removal of water from reaction medium is another promising route to shift the equilibrium towards the products. This could be achieved using reactive distillation method, since it shifts


Energy & Fuels

5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

the chemical equilibrium toward the desired product through continuous removal of one or more products 18. Utilization of entrainer based reactive distillation for esterification of glycerol with acetic acid was reported, using Amberlyst 15 as catalyst and ethylene dichloride as entrainer 19. Results was reported for two different setups including semi-batch and continuous reactor. In the semi-batch setup, the selectivity toward TA reported to be about 100%. While using continuous setup only a selectivity of 40% was obtained with complete conversion of glycerol 19. In another work 20, continuous reactive distillation was used to synthesize TA from glycerol using sulfuric acid as catalyst without any entrainer. The process obtained 99% of glycerol conversion with 9% selectivity to TA. In another study toluene was used as entrainer for selective synthesis of TA 21. Esterification of glycerol with acetic acid was performed in a batch reactor set-up at temperature of 105 oC. Both catalysts, Amberlyst 15 and 70, obtained selectivity to TA more than 95% at complete conversion of glycerol after 10h of the reaction. In another work the same setup was used with the exception of heteropolyacids as catalyst. The best performing catalyst, H4SiW12O40/SiO2, resulted in a TA selectivity of 71% at complete conversion of glycerol within 24h 22. In our previous study 23, a limited selectivity to TA is obtained by single-pass esterification of glycerol with acetic acid. The aim of the present work is to reach the highest selectivity for TA. To this end, a water separation system (WS) was designed and coupled to the developed continuous system (CS) in the previous study23. Toluene was used as entrainer in WS to remove the by-product water by azeotropic distillation. Moreover, the entrainer based azeotropic reactive distillation was developed using toluene as entrainer and Amberlyst 36 as heterogeneous catalyst in WS. 2. 2.1.

Experimental Materials


Page 6 of 28

Page 7 of 28

Energy & Fuels

6 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Acetic acid (purity > 99.85%), glycerol (purity > 99.9%), TA (purity > 99%) and DA (purity = 50%), wet Amberlyst 15 and 36, Purolite PD206, absolute ethanol (purity > 99.9%) and 2ethylhexanol (purity > 99%), were purchased from Fanavaran Petrochemical Co. (Iran), Emery Oleochemicals (Malaysia), Fluka (Germany), Fluka (Germany), Sigma-Aldrich (Germany), Purolite Co. (USA), Bidestan Co. (Iran) and Tat Chemical Co. (Iran), respectively. MA (purity > 95%) was synthesized via described method in our previous study 24

. It must be noted that all the chemicals was used without further purification.

2.2.

Procedure

The schematic experimental set-up used for the process is shown in Fig. 1. The reaction mixture, left the CS and entered the WS for water removal and additional conversion of acetins mixture. The dimensions of WS were height of 210 mm, inner diameter of 11 mm and the wall thickness of 2 mm. For the entrainer based azeotropic distillation it was filled with stainless steel fillings while in the entrainer based azeotropic reactive distillation experiments it was filled with packing and catalyst. WS was immersed in an oil bath with temperature of 130 oC in all experiments to maintain distillation condition. An electrical heating element with power of 1500 W (Kalai Co., Isfahan, Iran) was used for heating the oil bath. To regulate the electrical power of the element, a PID temperature controller was connected to it via a K type thermocouple. The thermocouple was immersed vertically in the oil bath to measure the temperature of the outer wall of the WS with accuracy of ±1 oC. Teflon material was used to assemble a double-neck adaptor to connect the glass Dean-stark, and condenser at the top of the WS. The oil bath, double-neck adaptor and Dean-stark were insulated to reduce heat loss. Temperature of the vapors at the top of the WS was measured via a thermometer placed in the double-neck adaptor. Experiments were begun by pumping prepared feed mixture at room temperature. After passing the CS, the acetins mixture entered from the top of the WS (F1 in Fig. 2a) that was at a height of 140 mm. The introduction of


Energy & Fuels

7 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

the entertainer from the height of 40 mm (F2 in Fig. 2a) lifted water up and minimized its concentration in the bottom stream. The catalyst packing section was fixed in the lowermiddle part of the reactor with stainless steel fillings above and below the heterogeneous bed in the entrainer based azeotropic reactive distillation experiments (Fig. 2b). Residual acetic acid, water and entertainer would rise to the top of the reactor and then enter the Dean-stark and flow through the condenser where the stream would condense. The heavier constituent of azeotrope mixture, water and acetic acid, trapped in Dean-stark apparatus while the lighter constituent, toluene and some acetic acid flew back to the WS. In each experiment, samples were collected at different time intervals with collection efficiency of higher than 95%. It should be noted that under steady state, the total mass of material entering a reactor must equal to total mass leaving the reactor. The mass balance of the cascaded process was determined for the optimized conditions of operation and temperature of 104 oC for azeotropic mixture, and is shown in Fig. 3. 2.3.

Analytical method

GC-FID (model 3420, BEIFEN, China) was used for the sample analysis. It was equipped with a capillary column of HP-5 (i.d. = 0.25 mm, length = 30m, film thickness = 0.25 µm). 2ethylhexanol and absolute ethanol were used as an internal standard and solvent, respectively. The injector and detector temperatures were set to 280 oC and 300 oC. The oven temperature program was began at 80 oC, ramped to 90 oC at the rate of 3 oC.min-1 and from 90 oC to 280 o

C at the rate of 30 oC.min-1 and held there for 5 min. All injections were made in the split

mode (split ratio of 1:30). GC-MS (model 6890N, Agilent technologies) was used for identification of the products. The glycerol conversion, each product selectivity and yield were calculated as mentioned by Morales et al 4. 2.4.

Characterization


Page 8 of 28

Page 9 of 28

Energy & Fuels

8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

FT-IR spectrometry was used for catalysts characterization. Spectra were recorded on a JASCO FT-IR-680 plus spectrometer in the region of 400-4000 cm-1 with a resolution of 4 cm-1. KBr pellets prepared by mixing 5 mg of each sample with 100 mg of dried KBr. 3. 3.1.

Results and discussions Entrainer based azeotropic distillation

Glycerol esterification with acetic acid is a consecutive reaction with stepwise formation of MA, DA, and TA 24. Each step is controlled by chemical equilibrium and water is an unavoidable by-product. Due to existence of water, the maximum selectivity for the resulted TA is low. Continuous removal of water from reaction medium is a strategy to shift the chemical equilibrium towards higher selectivity for TA. However, separating water from reaction medium by distillation is a challenge as the relative volatility of water and acetic acid is almost the same 21. Entrainer could help to facilitate the separation of acetic acid from water by increasing the relative volatility of one of these two components. To investigate the effect of water removal, the entrainer based azeotropic distillation setup showed in Fig. 1, was developed. Two experiments, with their results reported in Table 1, were conducted in the absence and presence of toluene. The reaction conditions were as follows. Acetic acid to glycerol mole ratio of 7, temperature of 100 oC in the CS and 130 oC in the oil bath, pressure of 1 bar, and flow rate of 0.5 mL.min-1. When glycerol esterification with acetic acid was performed in the CS, the selectivities for MA, DA, and TA were 43%, 44%, and 13%, respectively 22. Whereas, using WS for water removal at the end of the CS, has improved desired products selectivities to acceptable amounts. For the both experiments performed in the new developed system, the conversion of glycerol was already 100%, and the formation of by-products was not observed. More over DA was the major product in both of these experiments. In the absence of toluene, the selectivity of 29%, 48%, and 23% was obtained for MA, DA and TA, respectively. Comparison of these results with results obtained in the


Energy & Fuels

9 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

CS, showed that the selectivity to MA has reduced while selectivity to DA and TA have increased due to the water removal in WS. While in the presence of toluene as entrainer, these selectivities has changed to 17%, 65%, and 18%, for MA, DA, and TA, respectively. This high selectivity to DA is probably due to presence of toluene in the WS. Toluene has lifted water up and reduced its concentration in the bottom stream. So the equilibrium has shifted towards the 2nd step and the selectivity to DA, as the consecutively formed product, has increased. In the presence of toluene as entrainer, total selectivity of DA and TA has increased from 71% to 83%. These results showed that use of toluene as an entrainer, offers higher selectivity to more desirable products. It worth mentioning that the maximum value for DA selectivity, among all the performed experiments in this study was 65%. As the second step, all the performed experiments related to the system optimization in the CS 23 were repeated in the new developed system, with toluene introduced as entrainer. The experiment results are compared to the results of the CS as reported in Table 2. Glycerol conversion was 100% in all of the runs, except in run number 6 where acetic acid to glycerol mole ratio is 1, which is lower than the stoichiometric amount (3). At this run, the glycerol conversion was 97% and removal of water through azeotropic distillation has not significant effect on the products selectivity too. These observations could be due to the low mole ratio of acetic acid to glycerol (1) and also removal of acetic acid from reaction medium through azeotrope formation with toluene. It is well known that except removing water, an excess of acetic acid could shift the equilibrium limited reactions forward. But at this experiment the mole ratio of acetic acid to glycerol is lower than the stoichiometric one. On the other hand toluene can form two azeotropes in the reaction medium. The azeotropic mixture of toluene with water boils at 84 oC as well as with acetic acid at 104 oC 21. At the beginning of the experiment, the mixture started to boil at 84 oC while the temperature increased very fast to reach 104 oC as measured on top of the WS. Depending on the extent of water in the reaction


Page 10 of 28

Page 11 of 28

Energy & Fuels

10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

medium, the temperature changes. A maximum temperature of 104 oC indicates azeotrope formation between acetic acid and toluene. So removing water through azeotropic distillation is not effective on the reaction progress for mole ratios lower than the stoichiometric ones, due to the lack of acetic acid in the environment. It worth mentioning that the maximum selectivity of 85% was obtained for MA among all the performed experiments. According to Table 2, the only effective parameter on the products' selectivities is the extent of reaction progress in the CS. This could be justified as the reaction progress has a direct effect on the amount of remained acetic acid and formed water. As can be seen in Table 2, selectivity of by-products in the new developed system have not significant difference with results obtained in the CS. As mentioned in the previous study 23, the only effective variable on the by-products selectivity was reaction temperature. No byproducts were observed in the CS at temperatures lower than 120 oC. In the present work, toluene forms an azeotropic mixture with water at 84 oC as well as with acetic acid at 104 oC 21

. Either of these two azeotropic mixtures could be formed in this system. Depending on the

formed azeotrope, the boiling point of the mixture will be determined. Nevertheless, the temperature would remain under 120 oC, and therefore the formation of by-products in WS was not occurred. So by-products selectivity did not change in WS compared with the CS. Utilization of the entrainer based azeotropic distillation caused decrease in the selectivity of MA and increase in the selectivity of DA (Table 2). Whereas, changes in selectivity of TA was insignificant. Glycerol esterification is a chain of three consecutive reactions and water is produced as a by-product in all of these steps. Le Chatelier's principle states changes to a system in chemical equilibrium, concentration, temperature, volume or partial pressure, will shift the equilibrium to counteract the change. Consequently the new equilibrium will be established. Therefore, continuous removal of water had shifted the chemical equilibrium towards products. However, the major product was DA and changes in TA selectivity was not


Energy & Fuels

11 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

significant. This behavior could be attributed to reaction medium acidity. The only acid in the medium is acetic acid which molecules can catalyzes the esterification reaction homogeneously 25. But acetic acid is known to be weak which has not enough acid strength for rapid catalysis of the 3rd step. Hence it seems that incorporation of a strong acid catalyst is necessary in order to reach higher TA selectivity. 3.2.

Entrainer based azeotropic reactive distillation

It is well known that esterification reactions need acid catalysts. The acid strength is an important factor affecting the kinetics of the reaction 21. As mentioned in the section 3.1, the acid strength of acetic acid is not enough for catalyzing the 3rd step. To confirm this, 3g Amberlyst 36 was packed in the WS and an experiment was conducted in the developed system. The reaction conditions were acetic acid to glycerol mole ratio of 7, temperature of 100 oC, pressure of 1 bar, feed flow rate of 0.5 mL.min-1, while the temperature of oil bath was 130 oC. Glycerol conversion of 100% and selectivity of 15%, 80%, and 5% obtained for DA, TA, and by-products, respectively. At these conditions, the formation of MA was not observed. Using Amberlyst 36 at WS had changed MA, DA and TA selectivity from 17%, 65%, and 18% to 0%, 15%, and 80%, respectively. This results prove that esterification reaction is acid catalyzed. Consequently, increasing the reaction medium acidity has favored further esterification of MA and DA to form TA. In addition, using the heterogeneous catalyst produced by-products with a selectivity of 5%. Analysis of this sample with GC-MS showed that the major by-products were esters and cyclic ethers including propyl hexanoate, 4-acetoxy-5-methyl-3,6,8-trioxabicyclo (3.2.1) octane, 2,3-dihydro-1,4-dioxepin, 1,2,4-butanetriol triacetate, 1-O-(dec-1-enyl) glycerol-2,3diacetate, 2-methyl-4-methoxy-1,3-dioxane, 2-hydroxy-2,3-dimethyl succinic acid, 1,3dioxolane-2,2-diacetic acid diethyl ester, hexanoic acid pentyl ester. Although the reaction temperature was lower than 120 oC, but the formation of by-products was observed. This


Page 12 of 28

Page 13 of 28

Energy & Fuels

12 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

observation can be explained by the concentration of water molecules in the reaction medium. Water is the by-product of the side reactions. So removing water through heterogeneous azeotropic reactive distillation caused the formation of these by-products 26. FT-IR spectra of fresh and used Amberlyst 36 in the CS and WS are presented in Fig. 4. Amberlyst resins are co-polymeric ion exchange consisting primarily of styrene and di-vinyl benzene functionalized with sulfonic groups. All three samples exhibited typically one major band centered at around 3400 cm-1, attributed to the stretching vibration mode of the –OH groups. The appeared peaks at 2900 cm-1 could be assigned to the stretching vibration of CH. Observed peaks at around 1375 and 1700 cm-1 are due to C=C stretching vibrations. The characteristics peaks related to the sulfonic groups are clearly seen at around 1200 cm-1. These are characteristics peaks of symmetric and asymmetric vibrations of S=O bonds. The overall FT-IR analysis suggested that the catalyst had maintained its activity during the reaction both in CS and WS. 3.3.

Catalyst Study

To find the best acid catalyst for glycerol esterification with acetic acid, in the developed system, the catalytic activity of Amberlyst 15, and Purolite PD206 were also investigated. These acidic catalysts have different structures as well as different acid capacities. Amberlyst 36, 15 and Purolite PD206 specifications by the suppliers 27-29 are listed in Table 3. These experiments carried out at an optimized acetic acid to glycerol mole ratio of 7, temperature of 100 oC in the CS and 130 oC in the oil bath, pressure of 1 bar and flow rate of 0.5 mL.min-1. As reported in Table 4, in the CS high selectivities to MA and DA were obtained because, as stated earlier, the formation of MA and DA is much easier when compared to that of TA. But the selectivity toward TA was remarkably increased in WS, due to the water removal from reaction medium through azeotropic distillation and further consecutive reactions of MA and DA to yield TA. However water removal in WS lead to the formation of by-products through


Energy & Fuels

13 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

oligomerization and polymerization reactions 26. When the reaction was carried out in the absence of the catalyst (control reaction), the glycerol conversion was about 95% and 100%, in the CS and in WS, respectively. However the major products were MA and DA. The control reaction can proceed due to the activity of acetic acid protons as mentioned in the section 3.1. Despite lower acidity, Amberlyst 15 has the same activity as well as Amberlyst 36. This observation may be related to the larger average pore diameter which makes the reactants diffusion into the holes easier. Among different catalysts Purolite PD206 has the highest selectivity to the most desirable products, DA and TA, in the CS. However in the WS, this catalysts had the lowest activity to DA and TA. It could be suggested that the lowest crosslinked resin, Purolite PD 206, has the most availability to absorb water through swelling which makes the accessibility to catalytic sites easier 30, consequently favors the production of esters in the CS. However in the WS, this catalyst has the lowest activity. It was observed that some particles of Purolite PD206 was crushed at the end of the reaction. These observation is due to its lowest thermal and mechanical stability. As reported in Table 3 this catalyst has the largest pores, as a result of lower cross-linkages which decreases its mechanical stability. So among screened catalysts for esterification of glycerol with acetic acid, Amberlyst 15 and 36 exhibited best performance than Purolite PD206.

3.4.

Recovery of trapped acetic acid in Dean Stark

Trapped aqueous phase in Dean Stark apparatus titrated with standard solution of sodium hydroxide. It contained 70 wt.% acetic acid and 30 wt.% water. So the recovery of acetic acid from this high concentrated waste is important and essential from the economic and environmental points of view. Common method for acetic acid recovery from waste aqueous solutions is distillation which is not economical 31. So the effect of using this high concentrated acetic acid solution was investigated for esterification of glycerol. An


Page 14 of 28

Page 15 of 28

Energy & Fuels

14 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

experiment was performed and selected reaction conditions were those optimized before: acetic acid to glycerol mole ratio of 7, temperature of 100 oC in the CS and 130 oC in the oil bath, pressure of 1 bar, feed flow rate of 0.5 mL.min-1. At these conditions, a glycerol conversion of 90% was obtained with selectivities of 60%, 40% and 1% to MA, DA, TA, respectively, in the CS. While in WS a conversion of 95% obtained with selectivities of 40%, 55% and 5% for MA, DA, and TA, respectively. It must be noted that the formation of byproducts was not detected at these conditions. These observations are due to the presence of water in the reaction medium. Water is expected to promote ester hydrolysis and also adversely affect the catalytic performance due to its detrimental effect on the sulfonic acid sites of the catalyst 30. Higher amounts of water leads to a decrease in terms of both glycerol conversion and selectivity to desired products. Depending on the media composition, water molecules can form a humidity-rich microenvironment surrounding the sulfonic acid sites, thus hindering the accessibility of organic reactants to the acid centers 4. In conclusion, despite being the most desirable feedstock for the glycerol esterification, this aqueous solution of acetic acid cannot be directly used for TA synthesis. However a mixture of MA and DA was obtained in the CS. 4.

Conclusions

A continuous process for glycerol esterification with acetic acid using toluene as entrainer was developed. Entrainer based azeotropic distillation experiments were carried out without any solid acid catalyst in WS. Results showed that using toluene as entrainer was more capable of reaching the desired selectivity to TA in the designed continuous easy to scale up system. Also it was necessary to use solid acid catalyst in the WS, because acetic acid is weak and does not have the enough acid strength to catalyze this esterification reaction, especially the 3rd step. So entrainer based azeotropic reactive distillation was performed using acidic ion-exchange resin, Amberlyst 36 in the WS too, and high selectivity of 80% was


Energy & Fuels

15 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

obtained for TA. The maximum selectivity for MA and DA was 85% and 65%, respectively. It was observed that toluene forms two azeotropic mixture with water at 84 oC and acetic acid at 104 oC. The only effective parameter on the products selectivities in the entrainer based azeotropic distillation system, is the extent of reaction progress in the CS. Amberlyst 15, 36 and Purolite PD206 were used for glycerol esterification with acetic acid. The best performance exhibited by Amberlyst 36 and 15which showed similar activities. The formation of esters and ethers as the by-products was observed. A mixture of MA and DA obtained through glycerol esterification with trapped aqueous solution of acetic acid in Dean Stark. This study showed that the entrainer based azeotropic distillation is effective for DA synthesis, while removal of the formed water helps to shift the chemical equilibrium towards the 2nd and 3rd steps, so MA selectivity reduces. However the entrainer based azeotropic reactive distillation produces TA with high selectivity due to the acidity of the catalyst (kinetic effect) as well as removal of water (thermodynamic effect). Acknowledgement The financial support by Iran National Science Foundation (INSF) through the project number of 94018880, Isfahan University of Technology and Farzin Chemicals Co. are acknowledged.


Page 16 of 28

Page 17 of 28

Energy & Fuels

16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

References [1]

Samart, C.; Sreetongkittikul, P.; Sookman, C. Fuel Process. Technol. 2009, 90, 922– 925.

[2]

Pudi, S. M.; Biswas, P. Energ. Fuel 2015, 30, 584-593.

[3]

Silva, L. N.; Gonçalves, V. L. C.; Mota, C. J. A. Catal. Commun. 2010, 11, 1036-1039.

[4]

Morales, G.; Paniagua, M.; Melero, J. A.; Vicente, G.; Ochoa, C. Ind. Eng. Chem. Res. 2011, 50, 5898-5906.

[5]

Shafiei, A.; Rastegari, H.; Ghaziaskar, H. S.; Yalpani, M. Biofuel Res. J. 2017, 4, 565570.

[6]

Liao, X.; Zhu, Y.; Wang, S. G.; Li, Y. Fuel Process. Technol. 2009, 90, 988-993.

[7]

Melero, J. A.; Van Grieken, R.; Morales, G.; Paniagua, M. Energ. Fuel 2007, 21, 17821791.

[8]

Rodriguez, I. D.; Adriany, C.; Gaigneaux, E. M. Catal. Today 2011, 167, 56-63.

[9]

Reddy, P. S.; Sudarsanam, P.; Raju, G.; Reddy, B. M. J. Ind. Eng. Chem. 2012, 18, 648654.

[10] Khayoon, M. S.; Hameed, B. H. Bioresour. Technol. 2011, 102, 9229-9235. [11] Liu, X.; Ma, H.; Wu, Y.; Wang, C.; Yang, M.; Yan, P.; Welz-Biermann, U. Green Chem. 2011, 13, 697-701. [12] Troncea, S. B.; Wuttke, S.; Kemnitz, E.; Coman, S. M.; Parvulescu, V. I. Appl. Catal. B: Environ. 2011, 107, 260-267. [13] Khayoon, M. S.; Hammed, B. H. Appl. Catal. A: Gen. 2012, 433-434, 152-161. [14] Zhu, S.; Zhu, Y.; Gao, X.; Mo, T.; Zhu, Y.; Li, Y. Bioresour. Technol. 2013, 130, 4551. [15] Zhou, L.; Al-Zaini, E.; Adesina, A. A. Fuel 2013, 103, 617-625. [16] Zhou, L.; Al-Zaini, E.; Adesina, A. A. Fuel Process. Technol. 2012, 104, 310-318.


Energy & Fuels

17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

[17] Rezayat, M.; Ghaziaskar, H. S. Green Chem. 2009, 11, 710-715. [18] Sharma, M. M.; Mahajani, S. M. Reactive distillation: status and future directions; Wiley-VCH, 2002; pp 3-29. [19] Hasabnis, A.; Mahajani, S. Ind. Eng. Chem. Res. 2010, 49, 9058–9067. [20] Mufrodi, Z.; Budiman, R.; Budiman, S.; Budiman, A. Mod. Appl. Sci. 2013, 7, 70-78. [21] Kale, S.; Umbarkar, S. B.; Dongare, M. K.; Eckelt, R.; Armbruster, U.; Martin, A. Appl. Catal. A: Gen. 2015, 490, 10-16. [22] Kale, S.; Armbruster, U.; Eckelt, R.; Bentrup, U.; Umbarkar, S. B.; Dongare, M. K.; Martin, A. Appl. Catal. A: Gen. 2016, 527, 9-18. [23] Rastegari, H.; Ghaziaskar, H. S.; Yalpani, M. Ind. Eng. Chem. Res. 2015, 54, 32793284. [24] Rastegari, H.; Ghaziaskar, H. S. J. Ind. Eng. Chem. 2015, 21, 856-861. [25] Saka, S.; Isayama, Y.; Ilham, Z.; Jiayu, X. Fuel 2010, 89, 1442-1446. [26] Blagov, S.; Parada, S.; Bailer, O.; Moritz, P.; Lam, D.; Weinand, R.; Hasse, H. Chem. Eng. Sci. 2006, 61, 753-765. [27]

Amberlyst

®

36 total pore volume 0.20 mL/g | Sigma-Aldrich.

http://www.sigmaaldrich.com/catalog/product/aldrich/436712?lang=en®ion=IR (accessed Jul 7, 2017). [28] Amberlyst ® 15 hydrogen form dry - multiple sizes available | Sigma-Aldrich. http://www.sigmaaldrich.com/catalog/product/sial/216380?lang=en®ion=IR (accessed Jul 7, 2017). [29] Product. http://www.purolite.com/product/pd206 (accessed Jul 7, 2017). [30] Rodriguez, I. D.; Gaigneaux, E. M. Catal. Today 2012, 195, 14-21.


Page 18 of 28

Page 19 of 28

Energy & Fuels

18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

[31] Singh, A.; Tiwari, A.; Mahajani, S. M.; Gudi, R. D. Ind. Eng. Chem. Res. 2006, 45, 2017-2025.


Energy & Fuels

Page 20 of 28

19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 1. Experimental MA, DA, TA and by-products selectivity for continuous azeotropic distillation (WS) in absence and presence of toluene. Glycerol

Selectivity (%)

Conversion (%)

MA

DA

TA

By-products

Absence of Toluene

100

29

48

23

0

Presence of Toluene

100

17

65

18

0


Page 21 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Energy & Fuels

20

Table 2. Experimental MA, DA and TA and by-products selectivity for the CS [23] and the CS coupled with WS with temperature of 130 oC for oil bath, pressure of 1 bar, feed flow rate of 0.5 mL.min-1, and toluene as entrainer without any catalyst in WS. Glycerol conversion was 100% in all experiments except in experiment no. 6 which was 95% and 97% in the CS [23] and the CS coupled to WS, respectively. Run

Variables in CS

Selectivity (%) in this study

Selectivity (%) in previous study [23]

No.

X (Mole Ratio)

T (oC) P (bar)

MA

DA

TA

By-products

MA

DA

TA

By-products

1

5

100

100

26

59

15

0

45

46

9

0

2

3

80

159

51

42

7

0

62

34

4

0

3

3

120

41

47

44

8

1

63

32

4

1

4

3

80

41

52

41

7

0

67

30

3

0

5

5

100

100

29

55

16

0

46

45

9

0

6

1

100

100

83

15

2

0

85

14

1

0

7

7

120

159

24

55

18

3

30

50

17

3

8

7

120

41

26

50

22

2

37

47

15

1

9

5

66

100

39

47

14

0

56

39

5

0

10

7

80

41

36

51

13

0

47

44

9

0

11

5

100

1

40

49

11

0

50

42

8

0


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 22 of 28

21

12

9

100

100

27

51

22

0

40

45

15

0

13

5

100

199

23

58

19

0

41

49

10

0

14

5

100

100

29

55

16

0

43

48

9

0

15

5

100

100

27

58

15

0

44

47

9

0

16

3

120

159

46

43

9

2

61

32

4

3

17

5

134

100

32

46

14

8

45

38

9

8

18

7

80

159

27

53

20

0

49

43

8

0

19

5

100

100

29

56

15

0

45

46

9

0

20

5

100

100

28

57

15

0

46

44

10

0


Page 23 of 28

Energy & Fuels

22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 3. Characteristics of the catalysts used in this work. Data were taken from suppliers. Catalyst

Surface area

Average pore

Acidity

Thermal

(m2.g-1)

diameter (nm)

(eq.kg-1)

stability (oC)

Amberlyst 36

33

24

5.4

140

Amberlyst 15

50

30

4.7

120

Purolite PD206

-

>50

4.9

120


Energy & Fuels

Page 24 of 28

23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 4. Results obtained from catalytic experiments at optimized conditions of an acetic acid to glycerol mole ratio of 7, temperature of 100 oC and 130 oC in the continuous and the oil bath, respectively, pressure of 1 bar, feed flow rate of 0.5 mL.min-1, and toluene as entrainer. Glycerol conversion was 100% in all experiments except in the control experiment which was 95% in the CS. Selectivity (%) in the CS

Catalyst

Selectivity (%) in WS

MA

DA TA

By-products

MA

DA

TA

By-products

None (control)

75

23

2

0

17

65

18

0

Amberlyst 36

43

44

13

0

0

15

80

5

Amberlyst 15

42

44

14

0

0

16

80

4

Purolite PD206

30

54

16

0

10

43

47

0


Page 25 of 28

Energy & Fuels

24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 1. The schematic diagram of the set-up used; 1, feedstock reservoir; 2,7, HPLC pump; 3, air oven; 4, preheater; 5, reactor; 6, toluene reservoir; 8, back pressure regulator; 9,18, two way valves; 10, water separation system (WS); 11, oil bath; 12, thermocouple; 13, thermometer; 14, heat insulator; 15, Dean-stark; 16, condenser; 17, temperature controller; 19, collection vessel.


Energy & Fuels

25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 2. Schematic of (a) the filled WS with stainless steel fillings used in the entrainer based azeotropic distillation section (b) the filled WS with the heterogenuous catalyst and the stainless steel fillings used in the entrainer based azeotropic reactive distillation section.


Page 26 of 28

Page 27 of 28

Energy & Fuels

26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 3. Schematic diagram for mass flows of continuously operated reactors at optimized conditions of an acetic acid to glycerol mole ratio of 7, temperature of 100 oC and 130 oC in the CS and oil bath, respectively, pressure of 1 bar, and feed flow rate of 0.5 mL.min-1.


Energy & Fuels

27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 4. FT-IR spectra of Amberlyst 36 before reaction, and after reaction in the CS, and WS.


Page 28 of 28

Development of a Continuous System Based on ... - ACS Publications

Recommend Documents