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174 Advances in Eco-Fuels for a Sustainable Environment

energy, (i.e., low pressure and high retention time in association with the hydrolysis of
hemicellulose) while the optimal temperature and pH were found within the range of
45–50°C and 4.5–5, respectively. Therefore, enzymatic hydrolysis is advantageous
because it’s less corrosive, has low toxicity, and is also energy-wise and economically
efficient compared to acid or alkaline hydrolysis. The temperature is maintained by a
solar-assisted hot water system for the enzymatic hydrolysis process. Once hydrolysis
is completed, the resulting cellulose hydrolysate is fermented and converted into
ethanol [79].

6.10.1 Second-generation biofuel production from methane

The catalytic oxidation process is the conventional direct way to produce methanol
from methane. Recently, synthesis gas and steam reforming have become emerging
methods to convert methane into methanol. Sometimes methane can be directly
converted to methanol. The essential reaction mechanism of methanol production
is by partial oxidation of methane, as given below.

CH 4 +0:5O 2 ! CH 3 OH ΔH 298 ¼ 30:4kcal=molð Þ (10.1)
The oxidation reaction happens either in the liquid or gaseous phase. The operation
parameters for the gas phase reaction are 30–200bar pressure and 200–500°Cin
the presence of a catalyst [80]. With the help of a superacid catalyst, the methane
can be oxidized in the liquid phase reaction. In this process, CdH bonding is activated
and splitting of the covalent bonding occurs in the methane by electrophilic attack,
+
which produces the e and dCH 3 elements. Further, the oxidized products of methane
are produced by the oxidation reaction process. Until now, the conventional conver-
sion method of methane into methanol has been extensively used (Fig. 6.1).

6.10.1.1 Homogeneous catalyst

The homogeneous catalyst is the catalyst that exists in the same phase with reactants
and requires low temperature to convert the methane into methanol. The homoge-
neous catalyst reaction takes place at 35–700°C. The homogeneous catalyst does
not produce radicals as compared to the heterogeneous catalyst, and moreover, the
heterogeneous catalyst reaction requires a higher operating temperature. Temperature,
residence time, CH 4 /O 2 ratio, and OH concentration are the important process param-
eters, and by optimizing these, we can obtain maximum conversion yield. The opti-
mum temperature to achieve maximum conversion is 100°C. Many catalysts such as
as Pd(II), Pt(II), Pt(IV), and bipyrimidyl platinum(II) complex have been synthesized
and used in the methane conversion process. These are very efficient to activate and
functionalize the CdH bonds, which yield high partially oxidized products.

CH 4 +2H 2 SO 4 ! CH 3 OSO 3 +SO 2 +2H 2 O (10.2)