Biomedical Engineering Reference
In-Depth Information
Table 5. Surface area of the metal oxides
Surface Area (m
2
g
-1
)
Catalyst
PbO
0.55
MgO
157.4
MnO
2
50.55
BaO
0.76
CaO
61.39
Solid Super Base
According to Sun and Klabunde, “solid super bases are created when metal oxides are
treated with alkali metals; for example, Na-Al
2
O
3
or K-MgO.” [26] The result of the
treatment is highly active catalysts that are used for isomerization of alkenes or alkylation of
alkenes at moderate conditions (room temperature) [26].
Solid Catalyst
Solid catalysts create a high surface area for reaction to occur upon. Since solids can be
recovered easily, none of the water intensive washing needed in acid and base catalysis is
required here. Washing takes long time periods to complete which makes up for the slower
reaction time in solid catalysts. The glycerine product produced is also purer [1], which is
important for the economics of the plant. An example of solid catalyst is mesoporous silica
nano-particles [1]. There are also metal oxide based solid catalysts.
Enzymes
Enzymes are considered the environmentally friendly catalyst for this reaction. There is
no by-product generation, which reduces waste. Lipase is the most commonly used enzyme
catalyst [27-31], but enzymes have not been used commercially in biodiesel production to
date [7]. The product is easily recovered and mild reaction conditions can be used (room
temperature). Furthermore, the catalyst can easily be recycled. However, high conversions
Figure 8. Micrographs of a BSPs (a) before and (b) after cell immobilization [32].
