(483c) Simultaneous Dynamic Optimization and Heat Integration for the Co-Production of Diesel Substitutes: Biodiesel (FAME & FAEE) and Glycerol Ethers From Cooking Or Algae Oil

Martín, M., University of Salamanca
Grossmann, I., Carnegie Mellon University

For some time glycerol has been a valuable byproduct of the biodiesel industry. However, the increase in the production of biodiesel results in an excess of glycerol with no market (Pagliaro & Rossi, 2010) reducing the price of glycerol, to values of $0.102 /lb (Ahmed and Papadias 2010). Under these expected revenues from glycerol the production cost of biodiesel will increase $0.15/gal from the values presented by Martín & Grossmann (2012). There are a number of options to use the glycerol to provide further value including its use to enhance the yield to fuels out of oil. One promising alternative consists of the transformation of glycerol into fuel oxygenates by means of etherification and etherification reactions is being explored (Gupta, 1995, Bradin, 1996, Noureddini,1998). In particular the ethers are excellent oxygen additives for diesel fuel. Oxygenated diesel fuels are of importance to both environmental compliance and efficiency of diesel engines which can be added to diesel or biodiesel increasing the production of biofuel from oil.

In this paper we optimize the integration of the etherification of the byproduct glycerol from the production of biodiesel either using methanol or ethanol thus increasing the production of diesel substitute.  The problem we deal with is the dynamic optimization of the glycerol etherification production integrated with the production of biodiesel from cooking and algae oil. The process involves algae production and extraction, oil transesterification using either methanol or ethanol, alcohol removal and recycle, biodiesel and glycerol purification, glycerol etherification using ibutene, phase separation of a complex mixture, ibutene recovery and recycle and high glycerol ethers purification. We use surface response models for the transesterification reactors, first principles, experimental results and short cut models based on process simulation results for separation stages and a differential equation model for the complex equilibrium during the etherification of glycerol. We discretize the differential equation to formulate the problem for the simultaneous optimization and heat integration (Durán & Grossmann 1986) of the production of biodiesel and diesel additives as an MINLP one.

 The production of glycerol ethers increase the production yield of diesel substitutes by 20% with respect to the stand alone biodiesel facility, while the energy and water consumptions are competitive with those of biodiesel when glycerol is the byproduct of the process. (Martín & Grosmann, 2012, 2013).  However, the current price of ibutene increases the production cost of biofuel up to $1.05/gal in the best of the cases in which we integrate the production of ethanol, biodiesel and glycerol ethers from algae.


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