esterification, and is then purified. The key stages of bioethanol production, however, are fermentation, sometimes preceded by pre-treatment to make cellulose more accessible, followed by separation – via distillation or rectification – and dehydration. For both types of biofuels, separation is essential to purify the end product and meet biofuel specifications, allowing biorefineries to deliver high-octane bioethanol or biodiesel free of water and other impurities. As a result, using top performance separation processes with state-of-the-art equipment that fully addresses specific plant needs is essential. In contrast to conventional refineries, where the structure of a distillation column and its internals is relatively standardised, the variability in bio-based feedstocks demands that biofuel producers adopt customised distillation set-ups. Therefore, it is crucial for businesses in this sector to choose separation specialists that can clearly identify what the process
requirements are and provide the most suitable system to fulfil them. Full-service providers that can combine separation and heat integration systems, for example, are extremely beneficial, as they can offer seamless and comprehensive solutions while reducing the number of contractors. Firstgeneration biorefineries can benefit from implementing heat recovery and integration practices, as these are particularly effective in reducing energy consumption – and accordingly environmental impact. Furthermore, due to separation specialists such as Sulzer, this first wave of greener fuels and energy was extremely successful. In 2013, approximately 86 million t (circa 95 million t) of first-generation biofuels were consumed globally, including 65 million t (nearly 72 t) of bioethanol.1 At the beginning of 2016, the volume of bioethanol contributed to more than 80% of the 113 billion l of biofuels produced worldwide.2
An evolving industry
Figure 1. Biomass ethanol lifecycle.
Figure 2. Corn crop and grain silos.
44 ENERGY GLOBAL SUMMER 2020
Nonetheless, the global production capacity of biofuels could be increased considerably by using lignocellulosic material as feedstock. In particular, a study from 2016 concluded that North American autochthonous herbaceous crops, such as switchgrass, could help the US produce at least 1 billion tpy of biomass that could be used as feedstock for biofuels.3 While this would not be able to replace the entire petroleum consumption of the US, it could allow the country to replace up to 30% with biofuels. This is why second-generation bioethanol plants incorporate the use of plant-based biomass and lignocellulosic residues, such as bagasse. In this way, more businesses can use their resources to deliver green energy and adopt circular bioeconomy approaches. In addition, this expansion in suitable resources can optimise the biofuel/land area ratio, reducing the land demand for crop fuels. Second-generation plants use different methods to convert biomass into biofuels. Pre-treatment is mandatory to break the hemicellulose-lignin complex cross-links and increase the accessibility of cellulose and hemicellulose. Subsequently, biorefineries can adopt various methods to produce bioethanol. The first route, commonly referred to as the biomassto-liquid (BTL) conversion process, subjects the biomass to pyrolysis or gasification to produce synthesis gas (syngas), which is purified. This is then reformed to fuels using either a catalytic process, such as Fischer-Tropsch reactions, or by a biological conversion. The second route is similar to the process used in first-generation plants, as it relies on the transformation of sugar polymers present in biomass, i.e. cellulose and hemicellulose to monomeric sugars. These are fermented using microorganisms and purified. The third route is a combination of the other two methods. A chemical intermediate is produced by a biochemical process, transformed into fuels via pyrolysis and purified. Another possibility is to utilise flue gas, for example, from steel mills, which is converted by micro bacteria into ethanol and then purified in highly heat-integrated distillation and dehydration steps into ethanol fuel.
