Figure 2. Formation of by-products with the high amount of acetone.
As known essentially in semi-batch systems, it is possible to manipulate the concentration of reactants in re-action media at the desired levels to obtain high yield and selectivity, also wild exothermic reactions can be controlled with these systems. There are different semi-batch studies based on yield and selectivity in literature. Because of its industrial importance, works conducted on BPA synthesis are generally encountered in the patent literature (Nowiǹska & Kaleta,2000; Jeřábek et al., 2002; Kawase et al., 1998; Chen et al., 2008; Hou et al., 2006; Singh , 1992; Das et al. 2004; Wang et al., 2013; Jia et al., 2004; Park et al., 2006; Laufer et al., 2002; Ouk et al., 2003; Al-Megren et al., 2013; Callanan et al., 2012; Tan et al., 2015; Santacesaria et al., 2011; Maestri & Rota, 2013). Nowinska and Kaleta synthesized a new catalyst with encapsulation of 12-tungstophos-phoric acid (HPW), ammonium and cesium salts on the MCM-41 for liquid phase BPA production. They compared yield and selectivity with synthesized catalyzer and zeolite (H-Y, H-DY). They carried out experi-ments at certain temperatures, reaction times and phenol-acetone molar ratios. They found highest selectivity (%60) with CsHPW/MCM catalyzer, feeding of 3:1 phenol-acetone molar ratio, at 160 in 6 hours (Nowiǹska & Kaleta, 2000). Jerabek and his colleagues used ion-exchange resins as catalyzer to synthesize BPA. They chose sulfonated divinyl benzene and Amberlyst as catalyzer. They investigated activity and the swelling prop-erties of these catalyzers. They used CSTR microreactor to prevent the problems that come with catalyzer swelling in batch systems. They achieved the highest reaction rate with sulfonated divinyl benzene (%1 by weight), feeding ratio of phenol to acetone 8:1 at 70 (Jeřábek et al., 2002). Lastly, Maestri and Rota, compared semi-batch reactors and semi-batch recycle reactors which designed for preventing the further reaction of main products with by-products hence selectivity loss. They developed boundary diagrams which can be used to identify selectivity and reactor productivity just using operating conditions and with these diagrams no need to solve mathematical model of the system (Maestri & Rota, 2013). However, in all of these studies, bisphenol a synthesis could not be synthesized in an appropriate yield or amount. It is not considered appropriate for them to be produced on an industrial scale. In addition, many by-products were obtained. Therefore, this study aims to eliminate the disadvantages (energy costs) of the pre-said situation. For this pur-pose, semi-batch reactor type was selected and experiments were conducted at stoichiometric ratio in various feeding modes. Acetone was fed as pulsed flow in a semi-batch operation. Feeding and waiting time were changed systematically and best result was explored for high yield and selectivity. Besides, batch and semi batch studies results, which were conducted in stoichiometric and over stoichiometric ratios were compared. The effect of mercaptoethanol as a catalyst enhancer, the amount of catalyst on product yield and selectivity was also investigated. As a result, the optimal feeding mode was determined to achieve high efficiency and selectivity with stoichiometric ratio aimed the minimum operating cost.
2 | Materials and Methods