Conversion of Non-Homogeneous Biomass to Ultraclean Syngas and Catalytic Conversion to Ethanol

Reducing greenhouse gas emissions, rising energy prices and security of supply are reasons that justify the development of biofuels. However, food prices recorded in 2007 and 2008 affected more than 100 million of people that became undernourished worldwide (Rastoin, 2008) The food crisis has been caused by several factors: underinvestment in agriculture, heavy speculation on agricultural commodities and competition of biofuels vs. food. It is estimated that by 2050, it will be essential to increase by 50% the food production to support the 9 billion people living on the planet (Rastoin, 2008). Recycling the carbon from residual waste to produce biofuels is one of the challenges of this new century. Several companies have been developing technologies that are able to transform residual streams into syngas, which is subsequently converted into alcohols. "Green" ethanol plays an important role in reducing dependency toward petroleum and providing environmental benefit, through its role in the fuel additive market. Ethanol is an oxygenate and also serves as an octane enhancer. The waste-to-syngas approach is an alternative to avoid the controversy food vs. fuel whilst reducing landfills and increasing carbon recuperation. Using this approach, yields of ethanol produced are above 350 liters/dry tonne of feedstock entering the gasifier (Enerkem’s technology is taken as example). Residual heat, also a product of the process, is used in the process itself and, as well, it can be used for outside heating or cooling. Enerkem Inc. is moving the technology from bench scale, to pilot, to demo to commercial implementation (a 12,500 kg/h of sorted and biotreated urban waste, is being constructed in Edmonton, Alberta). Economics of the process are favorable at the above commercial capacity, given the modular construction of the plant, reasonable operational costs and a tipping fee for the residue going into the gasifier. The first part of this chapter will present feedstock preparation, gasification and gas conditioning. The characteristics of the heterogeneous feedstock will determine its performance during gasification for syngas production whose composition has the appropriate H2/CO ratio for downstream synthesis. The second part of the chapter will be directed at the methanol synthesis in a three-phase reactor using syngas. The third and last part of the chapter will focus on the catalytic steps to convert methanol into bio-ethanol.

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