Article pubs.acs.org/IECR
Direct Hydration of β‑Caryophyllene Gaodong Yang, Pingkeng Wu, Zheng Zhou,* Xiangpo He, Weimin Meng, and Zhibing Zhang* Separation Engineering Research Center, School of Chemistry and Chemical Engineering, Nanjing University, Hankou Road No. 22, Nanjing, 210093, PR China S Supporting Information *
ABSTRACT: This study of β-caryophyllene hydration to produce β-caryophyllene alcohol was carried out catalyzed by strong acidic cation exchange resin NKC-9. The effects of different parameters such as agitation speed, catalyst type, catalyst loading, mass ratio of the reactants, temperature, and reaction time on the conversion of β-caryophyllene and yield of β-caryophyllene alcohol in a stirred-tank reactor have been investigated to obtain the optimal conditions. Under the optimal conditions (catalyst loading 20%(w/w), nβ‑caryophyllene/nwater 1/1, reaction temperature 363.15 K, reaction time 30−40 min), the experiment was then carried out in a pilot-scale stirred tank reactor and in a novel pilot-scale jet reactor respectively to achieve excellent performance. The β-caryophyllene alcohol has been purified by rectifying column and recrystallized. A pseudohomogeneous (PH) model was used to correlate the kinetic data in the temperature range from 333.15 to 363.15 K. The estimated kinetic parameters make the calculated results in excellent agreement with the experimental results.
1. INTRODUCTION Caryophyllene, a kind of bicyclic sesquiterpenoid which includes three isomers of α-, β-, and γ-, was first known in 1834. Wallach and Walker1 obtained crystalline nitrosite (1,2nitro-nitroso derivative) of caryophyllene and characterized βcaryophyllene in 1892. β-Caryophyllene plays an important role in the chemistry of the sesquiterpenoids, which is one of the most abundant sesquiterpenes found in many essential oils. For example, it is the primary hydrocarbon component of clove (Eugenia caryophyllata) and copaiba (Copaifera) oils.2,3 It is known that natural caryophyllene compounds possess the bioactivity, for instance, copaiba extract has been used in folk medicine, which occupies an important place in Brazil’s pharmaceutical exports.3 β-Caryophyllene alcohol is a kind of tricyclic sesquiterpenoid, which is included in the high boiling point fractions of Asian peppermint oil or pepper mint oil4,5 It shows a different pharmacological activity6 and also is a strong attractant to some cotton beetles.7 In addition, it has been approved as a food spice in the USA.8 Therefore, the development of βcaryophyllene alcohol is of special economic value. According to the studies of Collado and his co-workers,9 the reactions of β-caryophyllene include isomerization, hydration, oxidation, and so on. Traditionally, sulfuric acid was a widely used catalyst in the hydration.10−13 However, there are many problems with this catalyst, such as serious corrosion and troubles in postprocessing. Up to the present, a number of researches on other catalysts for β-caryophyllene hydration have been reported, to name a few, organic acid catalyst,14 zeolites,15 super solid acidic catalyst,16 cation exchange resin catalyst.17 Cation exchange resins have been widely used in esterification,18−21 hydration,22,23 transesterification,24 hydrolyzation,25,26 etc. A number of studies on using cation exchange resins as catalysts for the hydration of olefins have been reported. Liu et al.27−29 studied the hydration of dihydromyrcene, turpentine, and camphene with Amberlyst 15 and D-72 as © 2012 American Chemical Society
catalysts, and the yield of the products reached more than 40%, 35%, and 26%, respectively. A jet reactor, as a new multiphase reactor, has many advantages, such as the fact that it is simple in structure and excellent in sealing and has good performance in heat and mass transfer and low energy consumption, etc. Because of its broad application prospects in the biochemistry, petrochemical, and metallurgical industries, it has already been widely used in process engineering, such as absorption, oxidation, hydrogenation, and hydration28,30−33 and gives much better performance than the ordinary stirred-tank reactor.34 In our previous work, it has been successfully applied in liquid−liquid−solid systems, such as the direct hydration of turpentine and dihydromyrcene.28,33 Also, the kinetics of direct hydration of dihydromyrcene to dihydromyrcenol in a pilot-scale jet reactor has been studied by using strong acid cation exchange resins as catalysts.33 In this work, the direct hydration of β-caryophyllene was first carried out in the stirred tank reactor and NKC-9 was used as a catalyst to obtain suitable reaction conditions, under which the experiments were then conducted in a pilot-scale stirred tank reactor and a new pilot-scale jet reactor, respectively. The reaction structure of the hydration is shown in Figure 1, and a simplified reaction scheme for reaction of β-caryophyllene is shown in Figure 2. The product of β-caryophyllene hydration has also been purified by the method of Liu35 to get β-caryophyllene alcohol with the purity above 99%. Until now, there has not been reported any kinetic studies on the direct hydration of β-caryophyllene using cation exchange resin as a catalyst. The kinetics of the hydration reaction was studied using NKC-9 as a catalyst, through which the reaction Received: Revised: Accepted: Published: 15864
May 17, 2012 November 20, 2012 November 21, 2012 November 21, 2012 dx.doi.org/10.1021/ie301294f | Ind. Eng. Chem. Res. 2012, 51, 15864−15871
Industrial & Engineering Chemistry Research
Article
1:1) and catalyst (catalyst loading 20% (w/w)) were added into the reactor and then agitated sufficiently by circulating pump and jet device. The liquid was heated by a heat exchanger. When the temperature of the reactor reached the desired value (363.15 K), the corresponding time was set as the starting point of the reaction. Samples can be taken at different intervals and analyzed by GC. 2.2.2. Separation and Purification. After the reaction, the crude product was added into a rectifying column with a 5000 mL kettle for separation. The distillate of the kettle was collected and kept still for crystallization and then the crystals from the solution filtered via a Buchner filter to obtain the coarse crystal of β-caryophyllene alcohol. After this separation through distillation, the coarse crystal of β-caryophyllene alcohol were crystallized repeatedly by nhexane about three to four times and then dried by infrared lamp. 2.3. Analysis. All the samples of reactions, distillations, and recrystallizations should be analyzed by GC (HP 6890, Agilent) equipped with a hydrogen flame ionization detector (FID) and a capillary column (30 m × 0.32 mm ×0.25 μm, HP-5). The structure of crystal was identified by 1H NMR, 13C NMR spectroscopy (BRUKER DR × 500), FTIR spectroscopy (NEX05870 FT-IR), and MS (GC-TOF).
Figure 1. Hydration of β-caryophyllene.
3. RESULTS AND DISCUSSION 3.1. Structural Results of the Crystal. The results of 1H NMR, 13C NMR, FTIR, and MS of the crystal with purity above 99% are presented in the Supporting Information. The characteristic data are in good agreement with the structure of β-caryophyllene alcohol. 3.2. Effect of Catalyst Type. Two different dry cation exchange resins (NKC-9 and D-72) were used under the same experimental conditions. The physical properties of these catalysts are shown in Table 1 in the Supporting Information, revealing that the concentration of NKC-9’s active center (4.7 mol/kg) was higher than that of D-72’s (4.2 mol/kg). The surface structure of NKC-9, shown in Figure.3, is a solid
Figure 2. Possible reaction mechanism of the reaction of βcaryophyllene.
constants and activation energy could be determined for the reference by industrial application of β-caryophyllene hydration.
2. EXPERIMENTAL SECTION 2.1. Materials. β-Caryophyllene (β-caryophyllene, purity 82.5%), supplied by ShangHai Jorin N.E.L (China); NKC-9 and D-72, supplied by The Chemical Plant of Nankai University (China); n-hexane (purity ≥99%), supplied by Nanjing Chemical Reagent Co., Ltd. 2.2. Apparatus and Procedures. 2.2.1. Reaction. The hydration reactions were performed in both 500 and 5000 mL glass stirred tank reactors which are equipped with online measurements for the temperature and the agitation speed. The reactors were immersed in a water bath where the required temperature remained constant in for the reaction. The known amounts of reactants (reactant amounts 250 g in 500 mL glass stirred tank reactors, mole ratio of β-caryophyllene to H2O 1:1) were first charged into the reactors before the agitation started. The catalyst (catalyst loading 20% (w/w)) was then added into the reactors when the temperature reached the set point (363.15 K). Samples were taken and analyzed at regular intervals by a gas chromatography (GC, HP 6890, Agilent). In accordance with the rational condition of hydration reaction, the experiments were carried out in a stainless steel jet reactor (20 L). The schematic diagram of the jet reactor and jet device were shown in our previous work.21,22 The raw material (reactant amount 16 kg, mole ratio of β-caryophyllene to H2O
Figure 3. SEM of the surface of NKC-9: (a) 430 μm, (b) 10 μm.
spherical particle in shape with many micropores. The interior structure of NKC-9 was shown in Figure 4; there are many groups, which may be the active center of NKC-9, that were attached to the skeleton of the resin. The results are shown in Figure 5, revealing that the conversion of β-caryophyllene catalyzed by NKC-9 is higher than that by D-72. The reason may be that the reactants can much easily contact with NKC9’s active center. Therefore, NKC-9 was chosen as the catalyst for the kinetic study in this experiment. 15865
dx.doi.org/10.1021/ie301294f | Ind. Eng. Chem. Res. 2012, 51, 15864−15871
Industrial & Engineering Chemistry Research
Article
Figure 4. TEM of the interior of NKC-9: (a) 3 × 105, (b) 5 × 105.
Figure 6. Effect of the catalyst loading on the initial reaction rate (catalyst NKC-9; temperature 363 K; agitation speed 400 rpm; mole ratio of β-caryophyllene to H2O 1:1).
Figure 5. Effect of the catalyst type on the conversion of βcaryophyllene (temperature 363 K, agitation speed 400 rpm; catalyst loading 17% (w/w); mole ratio of β-caryophyllene to H2O 1:1).
3.3. Effect of Catalyst Loading. The effect of different catalyst loadings of NKC-9 on the conversion of βcaryophyllene was estimated by setting the catalyst loading at 6% (w/w), 10% (w/w), 13% (w/w), 17% (w/w), 20% (w/w), 23% (w/w), and 27% (w/w), respectively. The results were shown in Table 2 in the Supporting Information, which indicates that the conversion of β-caryophyllene increases along with the enhanced catalyst loading. A possible explanation is that more catalyst loading provides more acidic active sites, which result in a higher reaction rate for the conversion of βcaryophyllene. The initial reaction rate was shown to be a linear function of the catalyst loading, as shown in Figure 6. It was observed that the initial reaction rate increased together with the catalyst loading and there is a linear relationship between the initial reaction rate and the catalyst loading. This can be ascribed to the fact that the number of available active sites for the reaction is proportional to the catalyst loading. 3.4. Effect of Resins’ Particle Size. The particle size of NKC-9 is not totally the same, and the catalyst was sieved into four different sizes (
