DOI: 10.1002/ente.201402079 Synthesis of a Renewable Oxygenated Diesel Additive in an Adsorptive Reactor Nuno S. GraÅa,* Aida E. Delgado, Dânia S. M. Constantino, Carla S. M Pereira, and Alírio E. Rodrigues [a] Introduction One of the main global environmental concerns nowadays is global warming attributed to the increase of the atmospheric concentration of CO 2 . Among the anthropogenic CO 2 emis- sions, 82 % are caused by fossil-fuel combustion. [1] Therefore, the search for alternative fuels has become one of the great trends in energy-sources research. Moreover, several studies predict the shortage of fossil fuel reserves in the next 20 to 30 years. In addition, the International Energy Agency (IEA) predicts an increase in the demand for fossil fuel in coming years; however, it also predicts the increase of the use of renewable sources of energy. [2] As a result of these economic and environmental concerns, research on alterna- tive fuels for automotive engines is increasing. Biofuels, such as bioalcohols and biodiesel, are a renewable alternative to conventional fossil fuels. The most common bi- oalcohol today is ethanol, which can be used in car engines pure or blended with conventional fuel; its high octane number and high heat of vaporization make ethanol a suita- ble biofuel for transportation. [3] Another renewable biofuel is the biodiesel constituted by methyl or ethyl esters of long- chain fatty acids produced by a transesterification reaction between methanol or ethanol with vegetable oils. Its renewa- ble origin makes biodiesel an attractive alternative to con- ventional diesel. However, its use presents some drawbacks such as high NO x and particle emissions. [4] Furthermore, bio- diesel is inferior in terms of oxidation stability, energy con- tent, and cold-weather operability relative to conventional diesels. [5] One possibility to overcome these drawbacks is the use of a suitable additive. However, the additives used in conventional diesel are less effective in biodiesel. [5] The use of the acetal 1,1-diethoxyethane (DEE) as diesel- fuel additive shows a marked reduction of exhaust smoke. However, the blends present a flash point below the Europe- an regulation limit (55 8C). [6] Therefore, the use of acetals with a higher molecular weight could be a solution. Acetals can be produced by the acid-catalyzed reaction be- tween two molecules of a monohydric alcohol and one mole- cule of an aldehyde (Figure 1). This reaction has been report- ed previously for the synthesis of different acetals such as 1,1-dimethoxyethane (R 1 = CH 3 and R 2 = CH 3 ), [7] 1,1-dieth- oxyethane (R 1 = CH 3 and R 2 = C 2 H 5 ), [8] and 1,1-dibutoxy- ethane (R 1 = CH 3 and R 2 = C 4 H 9 ). [9] The acetalization reaction can be performed under homo- genous catalysis using a strong acid such as H 2 SO 4 , HF, or HCl. [10] However, some drawbacks such as separation prob- lems caused by the miscibility with the reaction medium and equipment corrosion at high catalyst concentration are asso- ciated with its use. [11, 12] Therefore, the use of a heterogeneous The synthesis of the acetal 1,1-diethoxybutane (DEB) was studied by the first time in a fixed-bed adsorptive reactor packed with the commercial ion-exchange resin Amber- lyst 47. The adsorption equilibrium was investigated at 30 8C by frontal chromatography with nonreactive binary pairs. The experimental determination of DEB viscosity, the hydro- dynamic study of the fixed-bed column, and the study of the butanal/water liquid–liquid equilibrium were performed. DEB production and column regeneration were performed in the fixed-bed adsorptive reactor. Simulation results showed the feasibility of the synthesis of DEB in a simulated moving-bed adsorptive reactor to obtain a conversion and purities in both extract and raffinate above 97 % with a pro- ductivity of 10.04 kg L 1 d 1 and a desorbent consumption of 4.42 L kg 1 . Figure 1. Overall acetalization reaction. [a] Dr. N. S. GraÅa, A. E. Delgado, D. S. M. Constantino, Dr. C. S. M. Pereira, Prof. A. E. Rodrigues Laboratory of Separation and Reaction Engineering (LSRE) Associate Laboratory LSRE/LSM Department of Chemical Engineering, Faculty of Engineering University of Porto, Porto (Portugal) Fax: (+ 351) 225081674 E-mail: nunopsg@fe.up.pt Energy Technol. 2014, 2, 839 – 850  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 839