# The Optimized Production of 5-(Hydroymethyl)furfural and Related Products from Spent Coffee Grounds
## 3 Results
### Lignin Enriched Fraction (LEF)  
LEF Characterization  
In the fractionation, the lignin component is depolymerized into a thick bio-oil which is recovered from the MIBK. The main use for the LEF is as a biofuel component for combustion to be used to recover process energy on site or potentially to be used as a liquid fuel in a static combustion engine. As such, the high heating value (HHV) of this fraction is one of the most important features. Initially, elemental analysis was used to assess the LEF fraction (Table 3). This analysis not only helps to characterize these samples but can also be used in the calculation of the theoretical HHV. According to [PERSON] and [PERSON], lignin is composed of approximately 63% carbon, 5-6% hydrogen, 0-1% nitrogen and 1.5-3.5% sulfur [32]. In the samples obtained from the solvent systems MEW and MAW in Table 3, the carbon content is far lower than these values while the nitrogen content is higher. This may indicate the presence of protein in these samples. The samples obtained with MW show similar content to the one expected from lignin samples. This suggests that molecules such as protein and lipids must have migrated to the other fractions (CEF or HEF). However, the extremely low percentages of LEF obtained when using the MW solvent system suggest that most of the lignin present in both biomass sources may have also deposited in the CEF fraction. The experimental HHV was determined using a bomb calorimeter while the theoretical HHVS's were calculated using the percentages of elements obtained in the elemental analysis and Equations (1)-(3). \[HHV\;[Btu/lb]\;=145.44C\;+620.28H\;+40.55\;-77.54O \tag{1}\]  
\[HHV\;[Btu/lb]\;=151.2C\;+499.77H\;+45S\;-47.8O\;+27N \tag{2}\]  
\[HHV\;[Btu/lb]\;=\left(\frac{654.3H}{100-A}+424.62\right)\times\left(\frac{C}{3 }+H-\frac{O}{8}+\frac{S}{8}\right) \tag{3}\]  
Equations (1)-(3) are given in British thermal unit per pound which were then converted to Joule per gram to be in the same units as the value obtained from the bomb calorimeter [33; 34; 35]. Note that \(C\), \(H\), \(S\), \(O\), \(N\) and \(A\) are the contents of carbon, hydrogen, sulphur, oxygen, nitrogen and ash in weight percentage. The value of ash was assumed to be null in Equation (3). The models show highly similar results to one another, although were not as accurate as predicting the calculated HHV values, with the largest discrepancies being observed for the SCG LEF fractions (Table 4). This suggests that in the LEF fraction of SCG there are numerous biomolecules present that the simplistic models cannot account for. Additionally, the high error between the models and the experimental results for the MW samples indicates once more that this solvent system leads to fractions with a higher percentage of impurities. Figure 3: Growth of _Metschnikowia pulcherima_ in HEF substrate obtained from the fermentation of SCG. Where (**a**) is the logarithm of the number of cells per mL obtained over three days, and (**b**) shows the final cell count as a function of the initial sugar loading in the hydrolysate. The HHV is substantially higher for the SCG components than for the pistachio hulls, and higher than is typically found for lignin components alone. Lignin is also a valuable source of aromatics, and as such could be used for further chemical production. The LEF samples were therefore analyzed by 2D NMR and GC-MS to understand the functionality present in the fraction. All the spectra obtained in this analysis were compared with previous literature reports [29] (Figures 4-7, Table 5). The 2D NMR demonstrates the presence of aromatic species in the phase for all species examined. Furthermore, the presence of tricin and syringl are the most prominent units in the pistachio hull, normally observed in woody biomass [36]. In the SCG spectra for all fractions, the presence of \(p\)-coumarate and freulates were observed, these are commonly found in food wastes [37].