# The Optimized Production of 5-(Hydroymethyl)furfural and Related Products from Spent Coffee Grounds
## 1 Introduction  
Coffee is one of the most consumed beverages in the world and as such is becoming a daily commodity in most people's lives [1]. Such high consumption of coffee generates increasing amounts of spent coffee grounds (SCG). The United States Department of Agriculture estimate the yearly consumption to be 9.8 million tonnes of coffee beans worldwide [2], which has been increasing steadily since 2011 [2; 3; 4]. This demand for coffee demonstrates the lack of seasonality in the supply of coffee beans and the increasing availability of SCG to be industrially used and converted to fuels and higher value chemicals. SCG were initially considered a waste, being landfilled or disposed in the sea [5; 6]. However, the compositional analysis reveals the presence of carbohydrates (42-55% _w/w_), lignin (0-25% _w/w_), lipids (2-24% _w/w_), protein (10-18% _w/w_), caffeine (0-0.4% _w/w_), chlorogenic acids (1-3% _w/w_) and ash (1-2% _w/w_) [7; 8; 9; 10; 11; 12]. This composition lends itself to the production of fuels and higher value chemicals, and as such is a highly suitable feedstock to be used in the biorefinery industry. Initially, as the calorific value of SCG were considered to be similar to agro-chemical residues, SCG were used directly for heat generation in industrial boilers [13]. However, due to the increased heteroatom content, emissions from direct combustion are particularly hazardous. More suitably SCG have been pyrolyzed, yielding between 55% and 85% bio-oil, depending on the reaction conditions and moisture content [14]. The pyrolysis process is particularly attractive and as such higher value compounds such as diterpens can be extracted from the bio-oil. To this end, [PERSON] et al. added a downstream nanofiltration process that used the permeate and retentate in the production of further products [15; 16]. The pyrolysis yields are so high as SCG contain up to 15% triglyceride oil. Alternative work has therefore focused on the extraction and transesterification of these lipids into biodiesel [14; 17; 18; 19]. However, the low triglyceride oil content in SCG requires large amounts of SCG to produce considerable amounts of biodiesel, and as such cannot be produced as economically as from other glyceride sources. Due to the high carbohydrate content, SCG have also been used in the production of ethanol through fermentation. [PERSON] et al. used an acid pretreatment of the SCG, followed by enzymatic step to release the monosaccharides. The authors compared three different yeast strains on both SCG and coffee silverskin. The SCG used led to much higher ethanol productions (11.7 g/L) compared to the coffee silverskin (producing less than 1 g/L) [20]. [PERSON] et al., developed a biorefinery approach through fermentation of the SCG after the extraction of oil. This new design led to higher ethanol concentrations with a final titer of 19 g/L, while the extracted oil was used in the production of biodiesel. However, with the unique diversity of molecules present in SCG there is also a large potential to produce higher value chemicals alongside fuels. [PERSON] et al. developed a biorefinery design to produce chlorogenic acid and bioethanol [21]. The process included the extraction of phenolics to be converted into chlorogenic acid where the extraction residues were submitted to an acid hydrolysis, to depolymerize the sugars into monosaccharides, followed by fermentation to ethanol. [PERSON] evaluated a wide range of processes to come up with SCG-based biorefinery design [10]. The evaluated processes included: different oil extraction processes, the production of biodiesel through base, acid, lipase catalysis or in-situ transesterification of the extracted oils, the catalytic upgrading of the oils to renewable diesel, production of bioethanol through hydrolysis and fermentation of the carbohydrates. The author also reported additional products such as carotenoids, antioxidants and polymers, such as polyols, polylactic acid and polyhydroxyalkanoates. [PERSON] et al.