Article pubs.acs.org/IECR
Evaluation of Transfer Resistances in the Reactive Distillation Process for Phenol Production Yayun Zhuo, Yixing Zhong, Yale Xu, and Yong Sha* Department of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, Fujian, China ABSTRACT: The transfer resistances of the reactive distillation (RD) process for phenol production by using a dry resin called Amberlyst 35DRY as a catalyst were evaluated, including the transport resistance between vapor−liquid phases and the mass and heat transfer resistances of catalyst. The calculated results showed that the temperature of the reactive section in the RD column significantly increased after considering the influence of the transfer resistances between vapor−liquid phases. Subsequently, studies relevant to the catalyst showed that the catalytic packing with catalyst film grown on the conventional structured packing surface had significantly higher catalyst effectiveness, in comparison with other types (MULTIPAK-I, etc.). Results of this work indicated that transfer resistances cannot be neglected in the RD process for phenol production, and the evaluation of them is significantly beneficial to the design and development of the process.
1. INTRODUCTION As an important chemical product, the production of phenol has already reached a million tons per year. Over 90% of phenols are produced via a route based on the oxidation of cumene. Besides the industrialized reaction-separation process,1,2 a production process with a three-phase circulating fluidized-bed reactor3 and a reactive distillation (RD) production process were reported.4 Moreover, a novel phenol process by RD using resin as a catalyst was developed and surveyed in our previous work.5 In the novel phenol RD process, the unconcentrated cumene hydroperoxide (CHP) feed, containing cumene, dimethyl-benzyl carbinol (DMBA), and a small amount of acetophenone (AP), was directly sent into the reactive section of the RD column, where the CHP decomposed to phenol and acetone (reaction 1): C9H12O2 → C6H6O + C3H6O (CHP)
(phenol)
Although RD can significantly reduce the cost of process operation and equipment investment, the combination of reaction and distillation in the RD process may cause strong contradiction among various design variables.6−8 Therefore, the rigorous design of the phenol RD process is essential for the subsequent industrial developments. As an important factor, the transfer resistances that, between vapor−liquid phases and relevant to the catalyst, can significantly influence the RD process, and consequently the evaluation of them is significant for the process design. Because of the compromise between reaction and separation in RD column, previous studies concerned more about the impact of the transfer resistance on multiple steady states (MSS) or dynamic response.9−13 However, for the phenol RD process, the win−win situation between reaction and separation is very easy to achieve, because of the fast reaction rate and the large relative volatility, which indicates that the research priority should be converted to other aspects. For the phenol RD process, the decomposition heat of CHP is very large and the reaction rate is very fast, which is possible to be harmful for the normal operation of the RD column and the safety of the production process due to the dramatic increase of liquid temperature in the reactive section and the sharp decrease of the liquid flow rate. Moreover, the increase of liquid temperature could also accelerate the thermal decomposition of CHP. In the RD column, unfortunately, these adverse impacts could be aggravated by the mass- and heattransfer resistances between vapor−liquid phases and relevant to catalyst. Hence, the focus of this work should remain on these negative aspects. On the other hand, the selection of the catalytic packing is very important for the RD rigorous design,14−16 and it could be helpful to simultaneously improve the reaction conversion and
(1)
(acetone)
Meanwhile, CHP and DMBA would react to form dicumyl peroxide (DCP) and water (reaction 2), and then the former decomposed to α-methylstyrene (AMS), phenol, and cumene (reaction 3): C9H12O + C9H12O2 ↔ C18H 22O2 + H 2O (CHP)
(DMBA)
(DCP)
(water)
C18H 22O2 ↔ C6H6O + C3H6O + C9H10O (DCP)
(AMS)
(phenol)
(cumene)
(2)
(3)
Finally, the product streams of the column were sent to the subsequently refining and recycling process. A dry type of resin, Amberlyst 35DRY, was considered as the more suitable catalyst in that RD process, in comparison with the wet type of resin, and the corresponding reaction kinetic parameters that can accurately predict reaction rates under the given RD conditions were regressed. Subsequently, the laboratory-scale experiment preliminarily confirmed the high feasibility and energy efficiency of the novel RD process. © 2015 American Chemical Society
Received: Revised: Accepted: Published: 257
August 24, 2015 November 30, 2015 November 30, 2015 November 30, 2015 DOI: 10.1021/acs.iecr.5b03111 Ind. Eng. Chem. Res. 2016, 55, 257−266
Article
Industrial & Engineering Chemistry Research the degrees of separation of an RD process. Taylor and Krishna reviewed many different types of catalytic packings,6 for example, the catalytic packings with a sandwich structure and the catalytic bale licensed by Chemical Research and Licensing.17 Typical representatives of the former include the commercial MULTIPAK, KATAPAK-S, and KATAMAX. Another alternative is to make the packing itself catalytically active. A feasible configuration is the glass-supported precipitated polymer, and it has also been put into practice to make raschig ring-shaped packings.18−21 Another possibility is to coat packings with catalysts, although the amount of catalyst loaded in this manner is low.22,23 For the characteristics of the fast reaction rate and large reaction heat in the phenol RD process, the catalytic efficiencies of catalytic packings with different structure could differ greatly due to the resistances relevant to the catalyst. Therefore, this work is also focused on the performance of these different types of catalytic packings with the consideration of the resistances of the catalysts. In this work, by means of the commercial software Aspen Plus, the RD column for the phenol production with a capacity of 100 000 t/a, i.e. tons of phenol per year (1 year = 300 days) was preliminary simulated utilizing the equilibrium (EQ) stage model in order to provide a basis for the following studies. Subsequently, with the nonequilibrium (NEQ) stage model, the transfer resistance between vapor−liquid phases was investigated, and its impacts on the column temperature and liquid flow rate profiles were evaluated with the consideration of safety constraints. Subsequently, the mass- and heat-transfer resistances of catalyst were investigated, and the performance of different catalytic packing in the RD process were rigorously evaluated and compared.
Figure 1. Schematic diagram of the phenol reactive distillation (RD) column.
the stripping section were fixed to 13, 6, and 4, respectively, and the feed stage was set as 3 (not including the top condenser). According to our previous work,5 the temperatures at the first few trays in the reactive section cannot exceed the temperature limitation (398 K) to avoid the thermal decomposition of CHP, and the experimental results showed that the operating pressure should be
