(184c) Green Diesel Additive Synthesis: Elimination of Azeotropic Distillation by Coupling Simulated Moving Bed Reactor with Solvent Recovery Units

The use of green additives for diesel oxygenation offers the possibility of reducing emissions significantly, mainly Particle Matter (PM), improving even engines performance. Additionally, with the use of oxygenates fuel blends it is possible to introduce a considerable renewable fraction into the petroleum derived fuels, as recommended by the Directive 2003/30/EC. Acetals are recognized as diesel additives. In fact, 1,1-diethoyxethane (1,1-DEE), also known as diethylacetal, has only been reported as a good diesel additive in the 80's by Daimler Benz [1], and just in the most recent studies [2,3] it has been confirmed that 1,1-DEE reduces drastically particles emissions.

The synthesis of 1,1-DEE involves a chemical equilibrium limited reaction, and the reactive mixture exhibits three binary azeotropes (ethanol/water, ethanol/acetal and acetal/water) and one ternary azeotrope (ethanol/water/acetal), making its production and commercialization highly dependent on energy consumption. Those disadvantages led LSRE researchers to consider the Simulated Moving Bed Reactor (SMBR), which combines reaction and adsorption separation into a single unit, achieving complete reactants conversion and complete products separation [4]. As result, and for the first time, it was applied the SMBR technology for an acetalization process [5]. By this way, it is possible to obtain two outlet streams: (i) the extract stream comprising ethanol and water; and (ii) the raffinate stream comprising ethanol and acetal. Ethanol should be separated from each stream and recycled back to SMBR unit. Since distillation is the most widely used separation process in the chemical industry; the recovery of ethanol from each stream by distillation leads to a binary azeotrope (considering 100% purity of each stream in a base without ethanol). Reducing the purity criteria, the separation of each stream will also lead a ternary azeotrope. To break these azeotropes by selecting a proper entrainer is costly. Therefore, alternative strategies are essential for the economic viability of the process.

This work presents a methodology to avoid azeotropic distillation, and therefore avoiding the use of solvents to break the azeotropes and reducing the associated solvent distillation costs. The proposed methodology uses residue curve map (RCM) in order to define the distillation regions for the system ethanol/1,1-DEE/water and to set the minimum purity requirement of each SMBR outlet stream (raffinate and extract) which will be distillated. Thus, the RCM will enable to design the SMBR under reduced purity requirements in order to reduce the desorbent consumption and consequently the distillation cost. Moreover, a new strategy was developed and implemented to optimize the overall process: elimination of the azeotropic distillation by recycling back to the SMBR the azeotropic mixtures ethanol/ water and ethanol/acetal obtained in the distillation of extract and raffinate streams, respectively.

References:

1. K. Boennhoff, F. Obenaus, ?1,1-Diethoxyethane as diesel fuel?, CA Patent no. CA1141544A1 (1980).

2. F. Frusteri, L. Spadaro, C. Beatrice, C. Guido, ?Oxygenated additives production for diesel engine emission improvement?, Chem. Eng. J. 134 (2007), 239?245.

3. K. Nord, D. Haupt, ?Reducing the Emission of Particles from a Diesel Engine by Adding an Oxygenate to the Fuel?, Environ. Sci. Technol. (2005) 39, 6260-6265.

4. Silva, V.M.T., Rodrigues, A.E., ?Novel Process for Diethylacetal Synthesis?, AIChE J., (2005) 51, 2752-2768,.

5. A. E. Rodrigues, V. M.T.M. Silva, ?Industrial process for acetals production in a simulated moving bed reactor?, WO Patent 2005/113476A1 (2005), EP1748974 (2007).