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Ind. Eng. Chem. Res. 2009, 48, 9910–9914
Intrinsic Kinetics of Catalytic Hydrogenation of Cardanol Zhi-Bo Mao, Ting-Liang Luo, Hong-Tao Cheng, Miao Liang, and Guo-Ji Liu* College of Chemical Engineering, Zhengzhou UniVersity, Zhengzhou, Henan 450001, People’s Republic of China
The experiment of catalytic hydrogenation of cardanol was performed on a Raney nickel catalyst for the purpose of eliminating the effects of internal and external diffusion. The kinetics data have been collected experimentally over ranges of 2.5-4 MPa and 373.15-393.15 K, respectively. Then, the intrinsic kinetics of the catalytic hydrogenation reaction of cardanol was studied. It was proven that the catalytic hydrogenation of cardanol is a second-order irreversible series-parallel reaction under the experimental conditions. The kinetic parameters (Ea, K0) and kinetic equation were obtained through fitting, and the kinetic model was proven through testing to be reliable. Introduction The primrose liquid cardanol is the major component of cashew nut shell liquid,1 and the degree of unsaturation of the meta-position chain (C15H25-31) of cardanol is 0, 1, 2, or 3. Cardanol, which can be used to produce various required products, is abundant and inexpensive, and it has high values of development and application.2-6 However, cardanol will darken and degrade in quality, because the unsaturated side chain can be easily oxidized.7 As high-temperature distillation is adopted to refine cardanol, and cardanol with higher unsaturation is prone to form polymer that cannot be extracted, only cardanol with lower unsaturation can be obtained.8,9 However, the product of hydrogenation is an antioxidant and does not easily change color, and the possibility of side-chain polymerization is also eliminated during the course of distillation and follow-up synthesis. Consequently, the hydrogenation of cardanol has a very high value of practical application. However, the catalytic hydrogenation of cardanol and the related kinetics have rarely been studied and reported. In this work, intrinsic kinetics of catalytic hydrogenation of cardanol was studied, and the intrinsic kinetics model was constructed. The research of reaction mechanism provided the theoretical basis for the development of the industrial process. Experimental Section Experimental Materials and Apparatus. Refined cardanol, the content of which is >95% pure, was obtained from Shanghai Wujing Industrial Co., Ltd., China. High-purity hydrogen and high-purity nitrogen, the purity of which is >99.9% pure, were both obtained from Beijing Praxair Co., Ltd., China. Ni-Al alloy was obtained from Shanghai Sheenray Technology, Ltd., China. The Raney nickel catalyst was prepared from Ni-Al alloy, according to the literature.10 A high-pressure reactor was obtained from Dalian Tongda Reactor Plant, China. Highperformance liquid chromatography (HPLC) (Agilent 1100LC) was obtained from Agilent Technologies, Ltd., USA. Experimental Procedures. Three hundred milliliters of cardanol and 3.8 g catalyst were placed into a titanium alloy autoclave that had a capacity of 1 L and was equipped with a stirrer. The autoclave was tightened and nitrogen was charged three times to replace the air. Then, stirring began and the temperature was elevated. Hydrogen was charged three times * To whom correspondence should be addressed. Tel.: +86 37167781101. E-mail:
[email protected].
for replacement when the temperature reached a set value. Hydrogen was charged to the set pressure and the stirrer speed was adjusted to 400 rpm when the temperature was stable. During reaction, hydrogen was charged continuously to maintain the pressure. To study the influence of temperature on hydrogenation, five different temperatures were examined at a pressure of 3.6 MPa (namely, 373.15, 378.15, 383.15, 388.15, and 393.15 K), and the reaction time was in the range of 4.5-7 h. To investigate the effect of hydrogen pressure on hydrogenation, four pressures at 383.15 K were examined (namely, 2.5, 3, 3.6, and 4 MPa), and the reaction time was 5 h. The experimental flowchart is presented in Figure 1. Sampling and Analysis Methods. In this work, gas admission and sampling were conducted using the triple valve at the autoclave valve. Stirring was stopped and the admission valve was closed before sampling, and then the autoclave valve and the sampling valve were opened. After sampling, the sampling pipeline was swept to keep it clean and continue the reaction. The heater band, whose voltage was maintained at 80 V, should be bound among the admission valve, the sampling valve, and the autoclave valve, to prevent the pipeline from being jammed by the solid catalytic hydrogenation products. One milliliter of sample was extracted every 30 min, and then it was diluted by a factor of 500 with chromatographic-grade methanol. The concentrations of components in the diluted sample were measured via HPLC. The conditions for chromatographic analysis are as follows: chromatographic column, C-18 RHPLC silica gel; mobile phase, methanol (whose flux is 1.0 mL/min);
Figure 1. Schematic diagram of the experimental flow sheet. Legend: 1, outlet valve for nitrogen; 2, triple valve for hydrogen and nitrogen; 3, pipe valve; 4, triple valve for reactor intake and discharge; 5, sampling valve; 6, exhaust valve; 7, nitrogen cylinder; 8, hydrogen cylinder; 9, reactor; 10, stirrer; and 11, thermal couple.
10.1021/ie900655a CCC: $40.75 2009 American Chemical Society Published on Web 09/01/2009
Ind. Eng. Chem. Res., Vol. 48, No. 22, 2009
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C6H4OHC15H27 + H2 f C6H4OHC15H29 C6H4OHC15H29 + H2 f C6H4OHC15H31 When the reactions complete, the overall reaction equation could be expressed as C6H4OHC15H25 + 3H2 f C6H4OHC15H31
Figure 2. Relationship between granularity of the catalyst and conversion (T ) 393.15 K, t ) 3 h, PH ) 4 MPa, W(catal) ) 1.49%).
Kinetic Modeling. The catalytic hydrogenation of cardanol is not a simple consecutive reaction but rather a series-parallel reaction. It is indicated by previous study that hydrogenation is mainly composed of bimolecular reaction, and it has a tendency to be a second-order reaction.12,13 In this work, the kinetics of catalytic hydrogenation of cardanol C6H4OHC15H27 and C6H4OHC15H29 was investigated. The model of this reaction could be simplified as follows: k1
A + H2 98 R k2
R + H2 98 S
Figure 3. Effect of stirring speed on conversion (T ) 393.15 K, t ) 3 h, PH ) 4 MPa, W(catal) ) 1.49%).
where A is C6H4OHC15H27, R is C6H4OHC15H29, and S is C6H4OHC15H31. Because hydrogenation is irreversible, bimolecular, and of constant density, the rate equations could be written as follows: -
temperature of chromatographic column, 298.15 K; and wavelength of ultraviolet radiation used in diode array detector, 278 nm. Results and Discussion Eliminating the Effects of Internal and External Diffusion. The main factor that influences the internal diffusion is catalyst particle size. The relation between granularity of the catalyst and conversion is presented in Figure 2, from which it was observed that the conversion did not increase when the granularity of the catalyst is
