دانلود رایگان مقاله لاتین سوئیچینگ ناهمزمان شبیه سازی شده از سایت الزویر
عنوان فارسی مقاله:
استفاده از دوازده وجهی برای توصیف استراتژی سوئیچینگ ناهمزمان شبیه سازی شده بستر در حال حرکت
عنوان انگلیسی مقاله:
Application of dodecahedron to describe the switching strategies of asynchronous simulated-moving-bed
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
Among various separation techniques, the simulated moving bed (SMB) process has attracted special attention in the past decades (Sa Gomes and Rodrigues, 2012). In the early stage, SMB was used in petroleum and sugar industries (Beste et al., 2000; Broughton, 1984; Lim, 2012; Ruthven and Ching, 1989). After its successful application in enantioseparation in 1990s, the application of SMB in pharmaceutical and fine chemical separation fields has been further explored (Negawa and Shoji, 1992; Rajendran et al., 2009) and nowadays it becomes a popular technique in bioseparation processes (Gueorguieva et al., 2011; Houwing et al., 2003; Li et al., 2007; Paredes et al., 2005; Wellhoefer et al., 2014; Xie et al., 2002). In the traditional four zone SMB process, the four ports connecting desorbent, extract, feed and raffinate lines are switched at the same time. Hence, the four zones have fixed number of columns throughout the whole switching period. In 2000, Novasep changed the situation by proposing an asynchronous SMB known as Varicol, in which the inlet/outlet ports are shifted asynchronously (Ludemann-Hombourger et al., 2000). Due to different switching time for inlet/outlet ports, the number of columns in a zone may ∗ Corresponding author. E-mail address: cyao@xmu.edu.cn (C. Yao). vary over time and hence the average number of columns can be a non-integer. Thus in Varicol, the allocation of the columns in the four zones is much more flexible. Varicol has been successfully applied in different separation systems, such as the chiral separation of 1,2,3,4-tetrahydro-1-naphthol (Ludemann-Hombourger et al., 2000), SB-553261 (Ludemann-Hombourger et al., 2002), propranolol(Toumi et al., 2003), pindolol(Zhang et al., 2007), mitotane (da Silva et al., 2012), and albendazole sulfoxide enantiomers (Lourenco et al., 2012). Moreover, it gives a higher productivity or lower desorbent consumption compared with traditional SMB (Ludemann-Hombourger et al., 2000, 2002; Toumi et al., 2003, 2002) especially when a low total number of columns is considered (Pais and Rodrigues, 2003). However, a big challenge for asynchronous SMB is thatits design and optimization becomes complicated due to the increased degree of freedom (Toumi et al., 2002; Yao et al., 2014). Though the equivalent true moving bed and the triangle theory, which are usually used to assistthe design oftraditional SMB (Biegler et al., 2005; Yao et al., 2014), in principle can be considered but they are not appropriate for the design of asynchronous SMB (Toumi et al., 2003). The first important decision in optimizing the asynchronous SMB process is to select the appropriate decision variables. Besides the flow rates QI–QIV and switching period ts, the decision variables related to switching strategy include also the four switching times of the four ports (Toumi et al., 2002) and three average column length (Toumi et al., 2003). These two options have the discrepancy on how many variables that influence the system performance. This discrepancy was unified in our previous work (Yao et al., 2014), where the parallel shifting of switching times was proved to have no influence on system performance, in other words, only three of the four switching times of four ports influence the system performance independently. Based on this finding, we defined three new variables (relative switching times) to describe asynchronous SMB. By using the relative switching times, it is easy to transform the switching times to the average zone lengths or vice versa, and a systematic method for this kind oftransformation was also developed. A preliminary optimization of operation conditions by using the relative switching times was already verified in our previous work (Yao et al., 2014), but the optimization method based on relative switching times needs to be further investigated. In the present work, possible strategies to optimize asynchronous SMB have been completely explored and a dodecahedron is used to describe all the applicable optimization strategies for asynchronous SMB. The dodecahedron not only offers a concise graphical way for description of the strategies explored, but also simplifies the design and optimization of asynchronous SMB. The optimization based on the dodecahedron and relative switching times is further verified by two case studies for maximization of throughput.
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