# Glycerol Steam Reforming in a Pilot Plant: Effect of Temperature and Catalyst Load
## 1 Introduction  
Global energy systems are dominated by fossil fuels, which currently represent around 85% of the total energy supply, whereas they will represent 90% of the total supply by 2030. Oil is the main energy source (34%), followed by coal (28%). Almost two-thirds of the increase in the coal supply between 2000 and 2030 will come from Asia. According to future trends, natural gas will represent a quarter of the total energy supply in 2030, on account of an increase in electricity generation [1]. Another environmental problem is oil consumption due to vehicles, which represents a considerable amount of evolved gases, contributing to the greenhouse effect. Apart from these factors, continuous changes in oil prices, as well as its questionable future availability, have contributed to the development of vehicles working with electric power or whose fuel is methanol or ethanol (or other natural sources) that can contribute to environmental protection, such as the use of vegetable oils to produce biodiesel, which is a perfect replacement for diesel as it presents many advantages such as biodegradability, higher lubrication efficiency and similar yields and efficiency in combustion engines, where it can be directly used if it complies with some quality standards [2]. In that sense, many vegetable oils, including safflower, rapeseed, cardoon or waste cooking oil, among others, have been successfully used for biodiesel production, withsuitable properties according to UNE-EN 14214 standard [3] in most cases, except for its low oxidative stability, which can be easily improved by an antioxidant addition such as tert-Butylhydroquinone (TBHQ) [4; 5; 6], butylated hydroxy anisole (BHA) [4] or propyl gallate (PG) [7]. Apart from that, genetically modified crops, with lower amounts of linoleic and linoleic acid (which cause a considerable decrease in oxidative stability), could be another interesting alternative to comply with the standard [8]. In any case, many studies have been carried out to optimize the effectiveness of biodiesel production and performance in diesel engines to make this process as competitive as possible, with the subsequent sustainable development [9]. This way, the role of biodiesel, especially when it comes to tribology [10] or pollutant emissions and efficiency [11], has been studied. Consequently, biodiesel production is going to play an important role in the short- and long-term, as observed in Figure 1 for global biodiesel production in million liters. This way, biodiesel production will triple in 15 years, pointing out the global concern about the replacement of petrol-based fuels for other sustainable alternatives. This could be due to the fact that many governments or international agencies (for instance, the so-called Sustainable Development Goals, SDGs [12]) are encouraging the use of these kinds of fuels in order to avoid environmental and sustainability problems. As commented above, biodiesel presents many advantages compared to conventional fuels, such as higher biodegradability (it comes from natural sources such as vegetable oils, and the chemical process produces similar molecular structures which are easily processed by microorganisms), zero-net CO\({}_{2}\) emissions, high flash and combustion points, the possibility of a sustainable economic growth in developing areas (as many oilseed crops can be easily adapted to extreme climate conditions such as drought or heat), etc. Biodiesel is mainly obtained from vegetable oils through transesterification with methanol, and triglycerides react with this alcohol to obtain fatty acid methyl esters (FAMEs) and glycerol, as observed in Figure 2. This global reaction takes place in three consecutive and reversible stages where one mol of triglyceride is converted to diglyceride, monoglyceride and glycerol, respectively, obtaining one mol of fatty acid methyl ester in each reaction.