Simultaneous Production of Diacetone Alcohol and Mesityl Oxide from Acetone Using Reactive Distillation
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Simultaneous production of diacetone alcohol and mesityl oxide from acetone using reactive distillation Suman Thotla, Vishal Agarwal, Sanjay M. Mahajani∗ Department of Chemical Engineering, Indian Institute of Technology, Bombay, Powai, Mumbai 400 076, India Abstract Dimerization of acetone (Ac) yields diacetone alcohol (DAA), which on further dehydration gives mesityl oxide (MO) along with various side-products. The reacting system is a combination of various series and parallel reactions. In the present work, the reaction is studied using a cation exchange resin (Amberlyst 15᭨) as catalyst. The effect of catalyst loading and temperature on reaction kinetics was evaluated and three models based on simplified Langmuir–Hinselwood mechanism are proposed. Aim of the work is to minimize undesired side-products and understand the effect of different parameters and operating modes on DAA:MO product ratio in reactive distillation (RD). It has been shown that the reaction when operated in a reactive rectification mode offers flexibility in the relative production rates of DAA and MO. The experimental results obtained are explained by simulation. Keywords: Acetone; Diacetone alcohol; Mesityl oxide; Reactive distillation; Cation exchange resin; Kinetics; Selectivity 1. Introduction further produces heavier products, such as isophorone. Fig. 1 shows the reactions of interest. Diacetone Alcohol (DAA) and mesityl oxide (MO) are indus- In the present study, we explore the possibility of using reac- trially useful products derived from acetone. DAA is produced tive distillation (RD) to conveniently manipulate DAA:MO ra- by selective aldol condensation of acetone. It is an industrially tio. RD is a popular multifunctional reactor that has been used important compound which is mainly used as a solvent in pu- successfully for many commercial processes in the last two rification processes. It is also used as a component of solvent decades (Sharma and Mahajani, 2002). There are various mo- blends for nitrocellulose, acrylic, and cellulose acetate lacquers tives behind its several applications and selectivity engineering and thinners. Other applications of DAA include metal clean- to manipulate the product composition is one of them (Agarwal ing compounds, degreasers, stripping aids for textiles, gum and et al., 2006). With judicious choice of operating parameters, one resin removers in automobile carburetor cleaners. Dehydration can manipulate the composition profiles in the reactive zone of of DAA produces 4-methyl-3-penten-2-one, commonly known the column and obtain enhanced selectivity towards the desired as MO. MO is a useful compound with various applications, product(s). the most important being the precursor for the production of Various kinetic studies on this reaction using different cata- a popular solvent methyl isobutyl ketone (MIBK). Hydrogena- lysts have been performed in the past. The aldol condensation tion of MO under suitable conditions gives MIBK in high yields of acetone is commonly conducted in the presence of base (O’Keefe et al., 2005). Aldol condensation of MO and acetone catalyst such as NaOH, KOH, Ca(OH)2 and Ba(OH)2. Many other alternative catalysts such as metal oxides and hydroxides, which exhibit both acidic and basic properties, were found to offer less selectivity towards DAA as compared to that ob- tained by the homogeneous catalyst (Lippert et al., 1991). A detailed kinetic study of aldol condensation of acetone using 5568 O O Table 1 OH ᭨ K1 Properties of Amberlyst 15 1) 2 H3CHCH3 (H3C)2 C 2C CH3 K2 Acetone Diacetone alcohol Property Units Value OH O O Minimum exchange capacity (dry basis) eq/kg 4.7 2 K3 Internal surface area m /gm 50 2) (H C) C H C CH (H C) CHC CH + H O 3 2 2 3 3 2 3 2 Particle size mm 0.5(90%) Diacetone alcohol Mesityl Oxide Density gm/lit 780 Shape – Bead O O ◦ K Maximum operating temperature C 120 3) 4 Heavier products H3C CH3 + (H3C)2 CHC CH3 Acetone Mesityl Oxide O O K ties of the catalyst are listed in Table 1. Before its use, the fresh 4) (H C) CH + H 5 (H C) CH HC CH 3 2 CHC 3 2 3 2 3 catalyst was carefully washed with pure water, isopropyl alco- Mesityl Oxide MIBK hol, dilute hydrochloric acid and then again with pure water sequentially. It was then dried at 70 ◦C under vacuum for about Fig. 1. Reaction scheme for aldol condensation of acetone and related reac- tions. 12 h to remove moisture present in it. 2.1.2. Apparatus and procedure anion exchange resin (Amberlite IRA-900) has also been re- The reaction was performed in a 300 ml stainless steel batch ported in the literature (Podrebarac et al., 1997). This reaction is autoclave (Parr, USA) equipped with temperature and speed also catalyzed by acid catalyst, however, the rapid dehydration monitoring facility. The desired quantities of acetone (i.e. 190 of DAA to MO usually follows and DAA:MO ratio reduces to gm) and the catalyst were charged before the heating was a vanishing level (March, 1985; Panov and Fripiat, 1998; Flego started. The agitation was started, typically after 5 min, when and Perego, 2000; Kim and Hatfield, 1985). It is for this reason the desired reaction temperature was attained. This time was that the cation exchangers, as acid catalyst, have not attracted considered as the zero reaction time. The samples were re- much attention when the objective is to selectively produce moved after specific time intervals and were cooled through a DAA. To the best of our knowledge, barring few studies (Klein coil immersed in chilled water to prevent acetone evaporation and Banchero, 1956), there is not much information available during the sampling. Various experiments were carried out to on this reaction with cation exchange resin as catalyst. study the effect of different parameters like temperature and Podrebarac et al. (1998) used RD for this reaction with an ob- catalyst loading on the kinetics of the reaction. jective of selectively producing DAA from acetone, in the pres- ence of anion exchange resins. In the present study we address 2.1.3. Analysis the simultaneous production of DAA and MO from acetone in ᭨ A gas chromatograph (GC-911; Mak Anlytica India Ltd.) RD using cation exchange resin (Amberlyst 15 ) which has equipped with flame ionization detector (FID) was used to not been explored till date. The aim is to manipulate DAA:MO analyze the reaction mixture of acetone, MO and DAA. The ratio by conducting the reaction in a RD column, which oper- analysis was carried out in a 30 m long BP-5 column (SGE, ates close to or above the boiling point of acetone. To predict Australia) with an inner diameter of 0.55 mm. Elution was the performance of a catalytic distillation column, liquid phase established by nitrogen as a carrier gas at a flow rate of kinetic data for DAA and MO formation at temperatures near 0.5 ml/min. Methyl ethyl ketone (MEK) was used as an exter- the boiling point of acetone is required. The kinetic data was nal standard. The water concentration was calculated based on obtained in a laboratory batch reactor and a kinetic model has the material balance. The molar amount of water formed was been developed. Batch reactive distillation (BRD) and contin- assumed to be same as that of MO because the formation of uous reactive distillation (CRD) studies have been performed heavier side-products was negligible compared to the amount to demonstrate the potential of reactive distillation to enhance of acetone converted or MO formed. Klein and Banchero the selectivity towards the intermediate product(s). The results (1956) proved that this method of analysis is sufficiently of BRD and CRD are validated independently using simulation accurate over a temperature range of 30.75 ◦C. studies based on the kinetics developed in the present work. 2.1.4. Calculations for selectivity and conversion 2. Kinetic model development Conversion of acetone is calculated on the basis of initial moles of acetone 2.1. Experimental moles of acetone present X = 1 − . (1) 2.1.1. Materials and catalyst initial moles of acetone taken < . Acetone (AR grade, moisture 0 02%) was supplied by Selectivity towards DAA is calculated as Merck Ltd. The catalyst used in the experiments is commercial ᭨ 2 × moles of DAA formed strong-cation exchange resin, Amberlyst 15 and was obtained S = . (2) from Rohm and Hass, Philadelphia, PA. The physical proper- moles of acetone converted 5569 0.07 Table 2 UNIQUAC model binary interaction parameters (Aspen Technology Inc., Total 2001) 0.06 Towards MO Acetone DAA MO Water 0.05 Towards DAA Acetone 0 79.56 −30.80 642.7335 − 0.04 DAA 36.17 0 212.5 1188.5242 MO 61.65 −102.1 0 −56.94 Water −87.7160 −351.0861 1044 0 0.03 Conversion of acetone 0.02 water concentration may be different for the two different re- 0.01 actions taking place simultaneously. Such an observation has 0 also been reported by Lemcoff and Cunningham (1971). The 0 50 100 150 200 models considered for reactions (3) and (4) are as follows: Time (min) Model A: ◦ n M (k a2 − k a − k a ) Fig. 2. Conversion vs time at 55 C and 3.5% (w/w) of catalyst loading. d DAA cat f Ac b DAA MO DAA rDAA = = , (5) dt (1 + KW aW )2 2.1.5. General course of the reaction dnMO McatkMOaDAA Fig. 2 shows the general course of reaction with respect r = = . (6) MO dt ( + K a )2 to time in the batch reactor. Since the equilibrium conversion 1 W W of acetone to DAA is very low, DAA concentration does not Model B: rise beyond a particular limit.