# The Optimized Production of 5-(Hydroymethyl)furfural and Related Products from Spent Coffee Grounds
## 4 Discussion  
The similar masses obtained in the fractionation process for SCG and pistachio hull indicate that this process, initially developed for lignocellulosic biomass sources, can be efficiently used in the separation of the components present in SCG. The CEF mass yields obtained were approximately in accordance with the higher content of cellulose present in pistachio hull than in SCG (14% and 12%, respectively). Both the MAW and MEW solvent systems also deposit a range of other components, up to 60%, into this phase. Although this is in accordance with other lignocellulosic biomass separated through this method [28]. The poor performance of the MW system demonstrates how both ethanol and acetone aid in the fractionation process. When these solvents are not used, most of the lignin remains as a solid species and is deposited elsewhere in the system. This reduces the ability to use LEF for bioenergy. Despite of the better fractionation performance, the presence of ethanol and acetone in the HEF fraction, demonstrated by the increased TOC in the phase, make it unsuitable for fermentation. In contrast, the aqueous fraction produced with MW contained all the micronutrients necessary for growth and could be used to grow the oleaginous yeast _M. pulcherrina_; interestingly the growth of the yeast was only limited by the sugar present and not inhibited by the presence of anything in the broth. For all the samples, the HEF fraction had a higher total nitrogen content when SCG was used. While this will relate to bioactive compounds such as caffeine as well as the increased protein content, it did not seem to have an inhibitory effect on the yeast. The sugar content of the HEF fraction showed that, while HEF from pistachio hull can be used in the production of furfural, the absence of C\({}_{5}\) sugars in SCG means that furfural could not be produced as a co-product with HMF in a SCG biorefinery. Instead, the presence of C\({}_{6}\) sugars, such as galactose and mannose indicate that this fraction could potentially be used in the production of HMF, although with similar issues associated with the conversion of glucose. While the sugars in the HEF fraction could be fermented, to achieve a good fractionation in the overall system, ethanol and acetone must be used--this severely limits the use of these sugars without further costly separations. The LEF fraction, solubilized in MIBK, obtained using MEW and MAW had a reasonably high HHV (15-26 MJ/kg) when compared to the LEF fraction from MW (approximately 11 MJ/kg). For both the MEW and MAW solvent systems, the LEF fractions from SCG had higher HHV (22-26 MJ/g) than pistachio hull (15-19 MJ/kg). This suggests that this fraction of SCG has higher potential to be used as a biofuel component. However, both the GC-MS and 2D NMR analysis of this fraction demonstrated the presence of depolymerized lignin and fatty acids. Both materials have elevated lipids, though the SCG has more. This indicates that this fraction may also be used in the production of renewable biodiesel and polymers, however, similar to the HEF fraction, the fatty acids would need to be separated from the other components, which could limit the applicability for lower value uses. One possibility would be to extract the lipids prior to the fractionation. \begin{table}
\begin{tabular}{c c c c c} \hline
**Biomass** & **Glucose Yield (\%)** & **Fructose Yield (\%)** & **HMF Yield (\%)** & **Overall HMF Yield (\%)** \\ \hline \multirow{3}{*}{Cellulose} & - & - & 0.8 & 0.8 \\  & 60.8 & - & 24.3 & 14.8 \\  & 60.8 & 52.2 & 73.2 & 23.2 \\ \hline \multirow{3}{*}{CEF from Pistachio} & - & - & 0.1 & 0.1 \\  & 23.7 & - & 21.8 & 5.2 \\  & 23.7 & 48.3 & 69.6 & 8.0 \\ \hline \multirow{3}{*}{CEF from SCG} & - & - & 0.1 & 0.1 \\  & 25.9 & - & 22.0 & 5.7 \\ \cline{1-1}  & 25.9 & 44.9 & 70.3 & 8.2 \\ \hline \end{tabular}
\end{table} 
Table 8: Summary of the cellulose/CEF hydrolysis, glucose isomerization and fructose dehydration. The final fraction contains the solids left over from the process, predominantly cellulose (CEF).