STELLA BEZERGIANNI

2.1 INTRODUCTION

The depletion of world petroleum reserves and the increased concern on climate change has stimulated the recent interest in biofuels. The most common biofuels are based on energy crops and their products, i. e. veg­etable oil for Fatty Acid Methyl Esters (FAME) biodiesel [1] and sugars/ starch for bioethanol. However these first generation biofuels and associ­ated production technologies face several considerations related to their economic and social implications regarding energy crops cultivation, by­products disposal, necessity for large investments to ensure competitive­ness and the “food versus fuel” debate.

As a result, second generation biofuel technologies have been devel­oped to overcome the limitations of first generation biofuels production [2]. The goal of second generation biofuel processes is to extend biofuel production capacity by incorporating residual biomass while increasing

Stella Bezergianni (2013). Catalytic Hydroprocessing of Liquid Biomass for Biofuels Production, Liq­uid, Gaseous and Solid Biofuels — Conversion Techniques, Prof. Zhen Fang (Ed.), ISBN: 978-953-51­1050-7, InTech, DOI: 10.5772/52649. Licensed under Creative Commons Attribution 3.0 Unported License, http://creativecommons. org/licenses/by/3.0/.

sustainability. This residual biomass consists of the non-food parts of food crops (such as stems, leaves and husks) as well as other non-food crops (such as switch grass, jatropha, miscanthus and cereals that bear little grain). Furthermore the residual biomass potential is further augmented by industrial and municipal organic waste such as skins and pulp from fruit pressing, waste cooking oil etc. One such technology is catalytic hydro­processing, which is an alternative conversion technology of liquid bio­mass to biofuels that is lately raising a lot of interest in both the academic and industrial world and is the proposed subject of this chapter.

Catalytic hydroprocessing is a key process in petrochemical industry for over a century enabling heteroatom (sulfur, nitrogen, oxygen, metals) removal, saturation of olefins and aromatics, as well as isomerization and cracking [3]. Due to the numerous applications of catalytic hydroprocess­ing, there are several catalytic hydroprocessing units in a typical refinery including distillate hydrotreaters and hydrocrackers (see Figure 1). As a result several refinery streams are treated with hydrogen in order to im­prove final product quality including straight-run naphtha, diesel, gas-oils etc. The catalytic hydroprocessing technology is evolving through the new catalytic materials that are being developed. Even though hydroprocess­ing catalysts development is well established [4], the growing demand of petroleum products and their specifications, which are continuously be­coming stricter, have created new horizons in the catalyst development in order to convert heavier and lower quality feedstocks [5]. Furthermore the expansion of the technology to bio-based feedstocks has also broadened the R&D spam of catalytic hydrotreatment.

Catalytic hydroprocessing of liquid biomass is a technology that offers great flexibility to the continuously increasing demands of the biofuels market, as it can convert a wide variety of liquid biomass including raw vegetable oils, waste cooking oils, animal fats as well as algal oils into biofuels with high conversion yields. In general this catalytic process tech­nology allows the conversion of triglycerides and lipids into paraffins and iso-paraffins within the naphtha, kerosene and diesel ranges. The products of this technology have improved characteristics as compared to both their fossil counterparts and the conventional biofuels including high heating value and cetane number, increased oxidation stability, negligible acid­ity and increased saturation level. Besides the application of this catalytic technology for the production of high quality paraffinic fuels, catalytic hydroprocessing is also an effective technology for upgrading intermedi­ate products of solid biomass conversion technologies such as pyrolysis oils and Fischer-Tropsch wax (Figure 2). The growing interest and in­vestments of the petrochemical, automotive and aviation industries to the biomass catalytic hydroprocessing technology shows that this technology will play an important role in the biofuels field in the immediate future.

In the sections that follow, the basic technical characteristics of cata­lytic hydrotreatment are presented including a description of the process, reactions, operating parameters and feedstock characteristics. Further­more key applications of catalytic hydroprocessing of liquid biomass are outlined based on different feedstocks including raw vegetable oils, waste cooking oils, pyrolysis oils, Fischer-Tropsch wax and algal oil, and some successful demonstration activities are also presented.