The results of cellulose conversion calculated by gravimetric and
TGA method and are presented in Table 1.
Each experiment was repeated multiple times varying between
2 and 5 repetitions. Using the gravimetric approach, the conversion
(G) was calculated as the average value. The normalized average
deviation (G) of each experiment was obtained and the uncertainty
was then determined considering the highest value obtained
[21]. For TGAthe uncertainty was determined from the propagation
ofthe uncertainty obtained in the linear regression ofthe analytical
curve. The highest value was considered for all experiments [21].
Conversion results shown in Table 1 are in agreement with
the trend of expected values for the catalytic conversion. Generally,
conversion increases with an increase in the reaction time
with conversion increasing even more so with higher temperature.
Moreover, the M-W2C/C catalyst was expected to exhibit better
catalytic performance compared to M/C with the conversion values
confirming this expectation.
In general, the TGA method shows higher conversion values
when compared to the gravimetric method. However, considering
the associated errors, both methods gave similar conversion
trends and values. It is important to consider that both methods
are not free from experimental errors which can affect the conversion
value. In the case of the gravimetric method, there are several error sources due to sample handling. Firstly the sample needs to
be recovered after the reaction as a suspension consisting of catalyst,
unreacted cellulose and the aqueous solution. Secondly, the
separation of the solid phase from the solution is required. Finally,
the process of drying and weighing the solid phase is carried out.
Any mass loss implies a reduction of unreacted cellulose and thus a
higher conversion value will result. On the other hand, if moisture is
absorbed during the weighing procedure and/or if the liquid phase
is not completely removed from the solid phase, this additional
mass will be interpreted as unreacted cellulose. The conversion will
then be calculated to be lower than the real value.
An important advantage of the TGA method is that sample
manipulation is not a primary error source, which indicates that
the errors involved in this method can be better identified, quanti-
fied and minimized. Sample handling errors can only occur during
the weighing and mixing of samples during the preparation of the
standard samples. However, the analytical errors and uncertainties
can be minimized by increasing the number of samples and
repetitions used to obtain the analytical curve as well as characterizing
the experimental samples. Additionally, this analysis allows
moisture content to be determined.