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Heterogeneous Azeotropic Dehydration of Ethanol to Obtain a Cyclohexane-Ethanol Mixture

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Heterogeneous Azeotropic Dehydration of Ethanol to Obtain a Cyclohexane-Ethanol Mixture HETEROGENEOUS AZEOTROPIC DEHYDRATION OF ETHANOL TO OBTAIN A CYCLOHEXANE-ETHANOL MIXTURE Chemical Engineering Department University of Alicante (Spain) e-mail: [email protected] Vicente Gomis Mª Dolores Saquete Alicia Font Ricardo Pedraza Victoria Pastor-Matea OBJECTIVE Study the viability of cyclohexane in the ethanol dehydration to obtain an ethanol + cyclohexane mixture from an azeotropic distillation column. EQUIFASE 2009 INTRODUCTION Key renewable energy policy documents of the EU 1997 White Paper "Energy for the future" •Doubling the share of renewable energy from 6% (1997) to 12% (2010) 2003 EU Biofuels Directive (2003/30/EC) •Target for biofuels in transport: 2% by 2005, 5.75% by 2010 2009 Directive „on the promotion of the use of energy from renewable sources“ (2009/28/EC) •Overall EU target : 20% renewable energy in gross final energy consumption in 2020 •Target of 10% renewable energy in transport in 2020 for all member states EQUIFASE 2009 INTRODUCTION Ethanol Production Sectored emissions in Europe Agriculture Waste Benefits of biofuels 8% 2% Industry • Reduce GHG emissions 8% Energy • Improve air quality 48% • Reduce petroleum dependence Transport 34% • Improve energy security EQUIFASE 2009 INTRODUCTION Ethanol Production EQUIFASE 2009 INTRODUCTION Ethanol dehydration Pressure Swing Adsorption Azeotropic distillation EQUIFASE 2009 INTRODUCTION Azeotropic distillation TERNARY AZEOTROPE (E) Ethanol 0 0 0 1 C D G (N) 2 5 5 (M) 7 A FEED (G) 5 Ethanol/Water (D) 0 0 + 5 Benzene (B) 7 5 5 ABSOLUTE 2 (C) ALCOHOL M E N Heterogeneous region 1 0 0 0 B Water 100 75 50 25 0 Benzene EQUIFASE 2009 INTRODUCTION Possible entrainers Benzene (Young, 1902) Gasoline components Pentane Acetone Hexane Heptane Toluene Isooctane Cyclohexane EQUIFASE 2009 INTRODUCTION Conventional Process Raw Ethanol Mixing Fuel materials Production with gasoline Proposed Process Raw Ethanol + Gasoline Fuel materials Production EQUIFASE 2009 INTRODUCTION Cost diminution of: - Mixing Advantages - Transportation - Storage EQUIFASE 2009 EXPERIMENTAL DESIGN Study in an experimental Simulation of the industrial process semi-pilot plant column EQUIFASE 2009 Semi-Pilot Plant Column study Cyclohexane EQUIFASE 2009 Semi-Pilot Plant Column study Operation Variables • Feed 1: pure cyclohexane . Temperature = 66 ± 1ºC Flow rate = 41.00 g/min • Feed 2: water + ethanol mixture (94% wt. of ethanol). Temperature: 63 ±1ºC Flow rate = 4.38 g/min • Condenser : Temperature = 35ºC • Heat exchanger 3 : Temperature of the stream leaving HE-3 = 66 ±1ºC Simulation Variables Simulated in Chemcad 6 Rigorous calculation using the SCDS module (simultaneous correction method for rigorous fractionation simulation) Thermodynamic model: UNIFAC EQUIFASE 2009 Semi-Pilot Plant Column study Bottoms Product 1.0 0.8 The trends 0.6 Ethanol Simulation observed in the Cyclohexane Simulation experimental Cyclohexane 0.4 Ethanol results resemble Weight Fraction their simulated 0.2 Optimal counterparts 0.0 0 50 100 150 200 250 Reboiler Heat Duty (W) • The ethanol concentration depends on the heat duty • Only values ranging from 80-100 W permit ethanol concentrations close to 5 % wt. EQUIFASE 2009 Semi-Pilot Plant Column study Bottoms Product 0.005 Water Simulation Water 0.004 The trends 0.003 observed in the experimental 0.002 results resemble WeightFraction their simulated 0.001 counterparts Too high < 50ppm 0.000 0 50 100 150 200 250 Reboiler Heat Duty (W) • The concentration of water in the residue stream does vary considerably with respect to the reboiler heat duty • As the heat duty increases, the concentration of the water gradually decreases, reaching values lower than 50 ppm. EQUIFASE 2009 Semi-Pilot Plant Column study Aqueous phase Water Simulation 1.0 Ethanol Simulation Water Simulation 0.8 Water Ethanol Cyclohexane 0.6 0.4 The simulation adequately Weight Fraction reproduces neither the flow 0.2 rate values of the bottom product and aqueous layer 0.0 0 50 100 150 200 250 obtained experimentally nor Reboiler Heat Duty (W) the composition of the streams • The composition of the aqueous layer is also dependent on the heat duty • The composition tends to approach that of the plait point of the system. EQUIFASE 2009 Semi-Pilot Plant Column study Flows 50 The simulation 40 adequately reproduces 30 neither the flow rate Simulation values of the bottom Aqueous decant 20 product and aqueous Flow (g/min) Flow Bottoms Product layer obtained 10 experimentally nor the 0 composition of the 0 50 100 150 200 250 streams Reboiler Heat Duty (W) • The flow rate of the residue is always higher than that of the aqueous layer • Both flow rates become more similar when the reboiler heat duty increases. EQUIFASE 2009 Semi-Pilot Plant Column study Ethanol 0 0 0 1 UNIFAC non isothermal binodal curve Experimental non isothermal binodal curve 2 5 5 7 5 0 0 5 UNIFAC phase split prediction 7 5 5 2 Plait Point 1 0 0 0 Water 100 75 50 25 0 Cyclohexane EQUIFASE 2009 Semi-Pilot Plant Column study Etanol 0 0 0 1 Experimental UNIFAC UNIFAC Dortmund 2 UNIFAC LLE 5 5 7 5 0 0 5 7 5 5 2 1 0 0 0 Agua 100 75 50 25 0 Ciclohexano EQUIFASE 2009 Semi-Pilot Plant Column study Etanol 0 0 0 1 Experimental UNIQUAC NRTL α constante NRTL α variable 2 5 5 7 5 0 0 5 7 5 5 2 1 0 0 0 Agua 100 75 50 25 0 Ciclohexano EQUIFASE 2009 CONCLUSIONS It is possible, through azeotropic distillation, to obtain a mixture of cyclohexane + ethanol with concentrations of water lower than 50 ppm without the need to distill absolute ethanol beforehand. Afterward, the mixture could be directly employed as a carburant in car engines with no further modifications. The most critical parameter of the process is the reboiler heat duty . At lower values, this produces a mixture of cyclohexane + ethanol with excessive amounts of water. Whereas, at higher values the azeotropic distillation column does not work properly, since the top stream condenses giving only one liquid phase. Significant differences in some values are encountered between experimental and simulated data which can be attributed to the calculation of the liquid-liquid equilibrium. It is therefore necessary to improve the correlation of the experimental equilibrium data for determined regions of the ternary system diagram. EQUIFASE 2009 CONCLUSIONS The production of dry mixture of ethanol + cyclohexane seems to be technically and economically viable EQUIFASE 2009.
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