5 Principle and Processing of Biodiesel Production
133
different points along C Me and taking the logarithm of C M and dC Me /dt, we will
get a graph log
−
dc Me
dt
∼ log(C Me ). Accordingly, α (reaction order of methanol)
and K (reaction speed constant) can be calculated based on slope and intercept,
respectively.
According to Arrhenius equation
k = k 0 e
En
RT
k reaction speed constant
k 0 frequency factor
E α activation energy.
Take the logarithm on both sides of the equation to get the following result:
log k =
E α
2.303R
×
1
T
+ log K 0
According to this equation, if we draw a graph showing the relationship between
lgk and 1/T, we will get a straight line, its slope representing activation energy E α
and its intercept representing frequency factor k 0 .
(1) Measuring methanol
Gas chromatography and colorimetry are most widely used to measure methanol.
Gas chromatographic analysis is easy to operate, but it has a low sensitivity and
is not suitable for measuring methanol in aqueous solutions. Colorimetric analysis,
however, is more complicated. It has high sensitivity and is particularly suited to
measure methanol in aqueous solutions. The methods and principles of colorimetry
are presented as follows:
In acid solutions, methanol is oxidized into formaldehyde by potassium permanganate, and then forms a purple compound by reaction with chromotropic acid in
sulfuric acid medium. At this point, the colorimetry method can be applied at a
wavelength of 580 nm.
The equation is described as follows:
At different time points and for different reaction time, reaction speed −dC Me /dt
and methanol concentration C Me can be described as follows (Table 5.1):
133
different points along C Me and taking the logarithm of C M and dC Me /dt, we will
get a graph log
−
dc Me
dt
∼ log(C Me ). Accordingly, α (reaction order of methanol)
and K (reaction speed constant) can be calculated based on slope and intercept,
respectively.
According to Arrhenius equation
k = k 0 e
En
RT
k reaction speed constant
k 0 frequency factor
E α activation energy.
Take the logarithm on both sides of the equation to get the following result:
log k =
E α
2.303R
×
1
T
+ log K 0
According to this equation, if we draw a graph showing the relationship between
lgk and 1/T, we will get a straight line, its slope representing activation energy E α
and its intercept representing frequency factor k 0 .
(1) Measuring methanol
Gas chromatography and colorimetry are most widely used to measure methanol.
Gas chromatographic analysis is easy to operate, but it has a low sensitivity and
is not suitable for measuring methanol in aqueous solutions. Colorimetric analysis,
however, is more complicated. It has high sensitivity and is particularly suited to
measure methanol in aqueous solutions. The methods and principles of colorimetry
are presented as follows:
In acid solutions, methanol is oxidized into formaldehyde by potassium permanganate, and then forms a purple compound by reaction with chromotropic acid in
sulfuric acid medium. At this point, the colorimetry method can be applied at a
wavelength of 580 nm.
The equation is described as follows:
At different time points and for different reaction time, reaction speed −dC Me /dt
and methanol concentration C Me can be described as follows (Table 5.1):