Fluid Phase Equilibria 336 (2012) 41–51 Contents lists available at SciVerse ScienceDirect Fluid Phase Equilibria j our na l ho me page: www.elsevier.com/locate/fluid Modeling of physical and chemical equilibrium for the direct synthesis of dimethyl carbonate at high pressure conditions B.A.V. Santos a , V.M.T.M. Silva a , J.M. Loureiro a , D. Barbosa b , A.E. Rodrigues a,∗ a Laboratory of Separation and Reaction Engineering, Department of Chemical Engineering, Faculty of Engineering of University of Porto, 4200-465 Porto, Portugal b Laboratory for Process, Environmental and Energy Engineering, Department of Chemical Engineering, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal a r t i c l e i n f o Article history: Received 29 June 2012 Received in revised form 16 August 2012 Accepted 25 August 2012 Available online 2 September 2012 Keywords: Equations of state Supercritical CO2 Dimethyl carbonate Vapour–liquid equilibrium a b s t r a c t The physical and chemical equilibrium for direct synthesis of dimethyl carbonate is studied using the Soave–Redlich–Kwong equation of state coupled with five different mixing rules: one fluid van der Walls (1PVDW), modified first order Huron–Vidal (mHV1), modified second order Huron–Vidal (mHV2), linear combination of Vidal and Michelsen (LCVM), and Wong–Sandler (WS). The models parameters were adjusted from experimental vapour–liquid equilibrium data, from the literature, for the relevant binary systems. The mHV2 mixing rule showed to be the best model to predict phase equilibrium for this system. Then, the DMC equilibrium yield was modeled based on the SRK/mHV2 model. The Gibbs free energy of formation, for DMC, was adjusted from our experimental reaction equilibrium data in order to predict the equilibrium constant. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Organic carbonates have caught the attention of scientific community due to their low volatility and, toxicity and high biodegradability [1], which makes them potential chemicals for alternative routes to replace existing hazardous and toxic pro- cesses, according to the 12 principles of green chemistry [2]. In particular, dimethyl carbonate (DMC) is one of the most versatile carbonates, which can be used as reactant in carbonylation and methylation reactions [3,4], replacing the toxic and corrosive phos- gene, dimethyl sulphate and methyl halide. Furthermore, DMC can be used as an alternative to volatile organic solvents, reducing VOC emissions [1], and as an additive for gasoline [5,6] due to its high oxygen content (53.3%) and high booster power, improving the performance of gasoline combustion. DMC was firstly produced by phosgenation of methanol [7], although this route was almost abandoned due to the high toxicity of phosgene. Nowadays the main routes to produce DMC are oxy-carbonylation of methanol [8–10] and carbony- lation of methylnitrile [11,12]; however these routes use toxic carbon monoxide, and have risk of explosion and use fluent to regenerate the catalyst. Therefore new alternatives have been developed, such as the carbonylation of methyl carbamate [13], the ∗ Corresponding author. Tel.: +351 225081671. E-mail address: arodrig@fe.up.pt (A.E. Rodrigues). transesterification of ethylene carbonate [14–20] and the carbony- lation of methanol [21]. Monteiro et al. [22] used measuring tools in order to assess the sustainability of those six routes, by economical and environ- mental aspects. For the economical assessment they compared the price of the product with the reactants cost in stoichiometric con- ditions, while for environmental assessment they considered two factors: the toxicity and the environmental impact. The environ- mental impact was measured by a waste reduction algorithm [23]. Table 1 presents the total score, which is inversely proportional to the sustainability of the process. It was considered an equal weight factor for the three indicators. The phosgenation of methanol is by far the worst solution, while carbonylation of methanol and methanol oxy-carbonylation present the best score, 0.12 and 0.07, respectively. However, the authors considered the transesterification of methyl carbamate and ethylene carbonate as the most sustain- able, since methanol oxy-carbonylation does not involve CO 2 sequestration and rejected carbonylation of methanol due to being not feasible industrially. The low DMC yields and low reactiv- ity of carbon dioxide are pointed out as the major drawbacks of the direct synthesis of DMC (CO 2 + methanol ↔ DMC + H 2 O). Besides, lots of efforts have been taken in order to develop new catalysts [24–34]. However, CeO 2 might be the reference cata- lyst for this reaction [35], further modifications have been done, in order to improve the catalyst activity, such as CeO 2 –ZrO 2 [36,37], H 3 PW 12 O 40 /Ce 0.6 Zr 0.4 O 2 [38] or 5Ga 2 O 3 /Ce 0.6 Zr 0.4 O 2 [32]. 0378-3812/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fluid.2012.08.022