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ABSTRACT
The planned massive increase in the production of bio-diesel will inevitably lead to a large oversupply of glycerol. From each unit of vegetable oil that is converted to bio-diesel approximately 10% by weight will be recovered as by-product glycerol. Conventionally, the commercial propylene glycol production route is propylene-based, through propylene oxide, and therefore it is sensitive to the price of petroleum and associated products. There is clearly an attraction to de-coupling propylene glycol from petroleum and exploiting the predicted surplus of glycerol is one way of achieving this. The efficient catalytic conversion of glycerol, the main by-product from the biodiesel production, into valuable chemicals, can contribute to the promotion of bio-diesel utilization from both an economic and environmental point of view. Glycerol can be hydrogenated to propylene glycol using copper chromite catalyst with high yield and conversion under mild reaction conditions (20 bar, 200°C, 8 h) and basic aqueous solutions. The effect of the added base type was discussed in this paper. The highest conversion of glycerol and the highest selectivity to 1,2- propanediol were observed in presence of LiOH.
Keywords: hydrogenolysis, propylene glycol, copper chromite catalyst.
1. INTRODUCTION
The rapid growth in bio-diesel production from the last years, created a surplus of glycerol and, therefore the opportunity for using renewable resources as feedstocks.
Literature provides different alternatives to transform glycerol in various variable products. One of the most interesting possibilities is the conversion to propylene glycol, by an eco-friendly process. For this purpose, many types of solid catalysts have been explored [Dasari M. et al., 2005]. A variety of catalysts including palladium, platinum, nickel, copper have been used in the hydrogenolysis, but copper based catalysts is far the preferred catalyst [Moulton K., Beal R., 1974; Marinoiu A., et al., 2010; Suppes G. et al., 2005; Wang S., Liu H., 2007; Casale B., Gomez A.M., 1993; Marinoiu A. et al., 2009; Suppes G., Sutterlin W., 2007]. Copper chromite catalysts suitable for the using in hydrogenolysis reaction are of the type of copper-chromiumoxide. The superiority is connected to the effects given by the mixing of copper with chromite, namely the increasing of the intrinsic catalyst activity of Cu, and the stability action of chromium for preventing sintering [Chuang Wei Chiu et al., 2006] .