High Pressure Phase Equilibria of the Related Substances in the Limonene Oxidation in Supercritical CO 2 Marcos L. Corazza, † Lu ´ cio C. Filho, † Octa ´ vio A. C. Antunes, ‡ and Cla ´ udio Dariva* ,§ Departamento de Engenharia Quı ´mica, Centro de Tecnologia, Universidade Estadual de Maringa ´, Bloco D90, Av. Colombo 5790, Maringa ´ , PR 87020-900 Brazil, Instituto de Quı ´mica, Universidade do Brasil, CT Bloco A, Lab. 641, Rio de Janeiro, RJ 21945-970 Brazil and Departamento de Engenharia de Alimentos, URI-Campus de Erechim, Av. Sete de Setembro, 1621, 99700-000, Erechim-RS, Brazil The use of supercritical CO 2 (SCCO 2 ) as an alternative solvent in reactional systems has received increased attention nowadays because of its favorable transport properties that can accelerate mass-transfer limited reactions and also because of imposed environmental restrictions. The comprehension of the phase behavior of the reaction mixture is of relevance to determine selectivity and yield of such reactions at high pressures. In this context, the main objective of this work was to investigate the high-pressure phase equilibrium behavior of binary systems formed by CO 2 with the reactant (limonene), the most common solvents (acetonitrile and dichloromethane), and catalysts and the main products (carvone and 1,2-limoneneoxide) of the limonene catalytic oxidation reactions. The experimental data were measured using the static synthetic method with a variable-volume view cell in the temperature range from (313 to 343) K. Experimental data obtained were corrected modeled with the Peng-Robinson equation of state with the classical quadratic mixing rules. 1. Introduction Supercritical fluid (SCF) technology has received great attention in the application and development of new processes and products. 1,2 For example, they have been used as solvents in chemical reactions, 3-7 chromatographic analysis, 8 polymer processing, 9,10 pharmaceutical and food processing, 9 coal and petroleum processing, 11 and for environmental purposes. 2,9,12 Supercritical fluids could be useful as an alterative medium for chemical reactions because of their unique properties. Their gaslike transport properties and liquidlike densities can be easily manipulated by changing pressure and temperature. 4 Besides environmental advantages, one additional attractive feature of SCFs as a medium for chemical reactions is that they can lower mass transfer limitations and allow a better control of selectivity and reaction yield. Also it permits us to combine advanta- geously the reaction, separation, and purification steps. 5,13 In this sense, the natural use of supercritical carbon dioxide (SCCO 2 ) becomes an interesting possibility to replace organic solvents in many chemical reactions, like the catalytic oxidation of monoterpenes. The limonene oxidation is an alternative route to carvone production compared with extraction from natural products such as caraway seeds. 14 Limonene oxidation is tradition- ally carried out in an organic solvent media (for example dichloromethane, acetonitrile, and acetone among others), by using Metal(SALEN) as catalyst and iodozilbenzene as oxidant, via a rebound mechanism. 15 The main products obtained in the catalytic oxidation of limonene are epoxides (1,2-limoneneoxide), ketones (mainly carvone), and alcohols (mainly carveol). 16 To improve the selectivity and yield of this reaction, SCCO 2 can be used totally or partially in place of organic solvents. From an engineering point of view, the knowledge of phase equilibrium behavior of the components involved in the reaction system plays an important role in selecting operating regions and process scale-up. In this work, vapor-liquid equilibrium of binary systems formed by the reactant (limonene), organic solvents (acetonitrile and dichloromethane), and products of the limonene oxidation (1,2-limoneneoxide and carvone) with SCCO 2 were mea- sured in the temperature range of (313 to 343) K. The literature presents some experimental data for CO 2 + limonene. 17-21 Gamse and Marr 18 presented a study of the system CO 2 -carvone from (303 to 323) K. 1,2-Limone- neoxide constitutes one of the major oxidation products, but there seems to be no experimental phase equilibrium data for this compound with SCCO 2 . Here, it may be important to notice that, even when using SCCO 2 as an alternative medium for the limonene oxidation reaction, it might be necessary the addition of organic solvents at small concentrations (cosolvent). In this context, this work also reports binary phase equilibrium data of acetonitrile and dichloromethane (most common organic solvents used in the reaction at low pressure) with SCCO 2 . Phase equilibrium information for the system CO 2 /acetonitrile has hardly been reported in the literature. 22,23 The results were modeled using the Peng-Robinson equation of state (PR- EOS) with the classical quadratic mixing rule. 24 2. Materials and Methods 2.1. Materials. R-(+)-Limonene (99%, Sigma), S-(+) carvone (98%, Aldrich), 1,2-limoneneoxide (99%, Aldrich), dichloromethane (99%, Carlo Erba), and acetonitrile (99%, Jonhson Mattey) were used without further purification. The CO 2 was 99.9% pure (liquid phase, AGA). The critical properties of pure compounds are presented in Table 1. When experimental values were not available in the literature, 25 they were predicted by the Joback group contribution method. 25 * To whom correspondence should be addressed. Fax: +55-54-5209090. Phone: +55-54-5209000. E-mail: cdariva@uricer.edu.br. † Universidade Estadual de Maringa ´. ‡ Universidade do Brasil. § URI-Campus de Erechim. 354 J. Chem. Eng. Data 2003, 48, 354-358 10.1021/je020150k CCC: $25.00 © 2003 American Chemical Society Published on Web 01/14/2003 Downloaded by UNIV FED DE SANTA CATARINA UFSC on July 26, 2009 Published on January 14, 2003 on http://pubs.acs.org | doi: 10.1021/je020150k