The chemical industry today is coming a full circle on its raw material resources. Till the early twentieth century, most industrial products were made from vege­table plants and crops. This situation changed after the 1970s when most of these natural products started being replaced by petroleum-based organic chemicals, and petroleum refineries acquired unprecedented importance. However, with rapid depletion of fossil fuels and the imminent danger of running out of fossil fuels completely, the biomass resources are once again gaining importance globally. Biorefineries, the counterpart of petroleum refineries, for generation of transpor­tation fuels and other chemicals are being set up and technologies for their improvement are being developed. However, there are some fundamental differ­ences between the two (Table 1.13), which need to be clearly defined and understood, if the future biorefineries are to completely replace the petroleum refineries.

The first and foremost difference is in the nature of the raw material used as feedstock. Raw material for an oil refinery, i. e., crude oil is usually rich in hydrocarbons and consists of mixture of different organic hydrocarbons, but has essentially no oxygen. Biomass, the raw material for biorefinery, on the other hand, consists of too little hydrogen, too much oxygen, and lower fraction of carbon compared to the crude oil. The presence of oxygen reduces the heat content of molecules and gives them high polarity, which makes blending with fossil fuel difficult. This becomes important while considering the power requirement and the cost efficiency of the processes used. Also, the composition of biomass varies with the source of feedstock. This has an advantage in that, this variety in composition

can be exploited to facilitate formation of more classes of products compared to those that can be obtained from an oil refinery. However, an associated disad­vantage is that a larger range of processing technology is needed for a biorefinery. Thus it is essential that a biorefinery be equipped to cope up with such drastic changes in the feedstock composition. The integrated biorefineries already dis­cussed above are a step toward this objective. The second fundamental difference lies in the availability of the feedstock. Feedstock for a petroleum refinery is available throughout the year whereas the biorefinery feedstock, especially that required for the first — and second-generation biofuels, is seasonal. Thus, a petro­leum refinery can be operated throughout the year, whereas a biorefinery has to essentially operate in a seasonal time frame. Again, the integrated biorefineries are a remedy to this limitation. Biorefineries which can switch over from one feed­stock to another, depending on its availability, without compromising on the efficiency and cost-effectiveness need to be developed. A third aspect, which goes in favor of biorefineries, is the fact that it is possible to set up these biorefineries in rural areas, and as dispersed industrial complexes, so that the feedstock is locally available, thus avoiding the complex logistics of feedstock transportation and associated costs. Petroleum refineries, on the other hand, are essentially large industrial complexes set up at locations distant from the oil resources, making the transportation costs of its raw material to the refinery location, indispensable. Lastly, though the products of both the refineries are almost comparable, the intermediate products, or the chemical and biorefinery platforms, which enable further processing of the intermediate products to other value-added chemicals differ [56]. Figures 1.31 and 1.32 give an overview of the chemical and biorefinery platforms and the products obtained from them.

Table 1.13 Comparison between a biorefinery and a petroleum refinery Biorefinery Petroleum refinery