Synthesis of methyl orange in a micro reactor
Hamburger, L.J. and Koorn, I.
Huygens College, Heerhugowaard, the Netherlands
May 2012
Summary
The production of methyl orange in a micro reactor. When will there be the highest flow rate
of methyl orange? The variables that could be controlled were temperature and flow rate.
The results for the highest methyl orange production: put the flow rate to a low speed and
set the temperature at 80 degrees Celsius.
Introduction
Methyl orange is an azo-compound, what
is used as a PH meter in titrations and too
dye and print textile. Producing methyl
orange on a big scale, the temperature
needs to be kept low, because of risk of
explosion. This test is carried out on a
smaller scale so the production of methyl
orange in a micro reactor makes it possible
to let the temperature rise to a higher
value than producing on big scale.
this produces the methyl orange, see
figure 3.
Figure 3. (3)
This raises the question: At which
temperature and which flow rate will the
the highest concentration of methyl
orange be reached?
Figure 1. (1)
Methyl orange is produced by the reaction
of sulfanilic acid, sodium nitrite, and
dimethylaniline. First, sulfanilic acid is
dissolved in dilute aqueous acid. Sodium
nitrite is added to produce a diazonium
salt see figure 2.
Figure 2. (2)
After the diazonium salt is produced, the
salt is coupled with N,N-dimethylaniline,
Our hypothesis is: a high temperature and
a low flow rate will give us a maximum
concentration of methyl orange.
Expecting that a high temperature will be
better than a low temperature, because
particles collide harder in each other at
higher temperature than at low
temperatures. The higher temperature
makes particles move faster so there are
more collisions and they collide harder.(4)
The use of a low flow rate is better
because there will be more time for the
reaction to take place.
Experimental procedure and approach
The experiment was done in a micro
reactor which has 3 inlets. Two inlets are
used to inject the solution to make methyl
orange. The third inlet will stop the
reaction of methyl orange, after a
spectrometer and a photoelectric meter
will measure the concentration of methyl
orange. Inlet 1 contains a solution of
sodium carbonate, sulfanic acid and
sodium nitrate. Inlet 2 contains a solution
of N,N-dimethylaniline and hydrochloric
acid. Inlet 3 contains a solution of sodium
hydroxide. Those concentrations were not
changeable.
The changeable variables were the flow
rate and the temperature. The flow rate
could be varied between 1 µl/min and
1500 µl/min. The temperature in the
reactor was changeable between 8
degrees Celsius and 80 degrees Celsius.
Each experiment was done twice and if
necessary the measurements were done
three times to make sure the
measurements were reliable.
Measuring the best temperature was done
at a flow rate of 100 µl/min. The
temperature was varied with steps of 20
degrees Celsius. The results lead to a best
temperature of 80 degrees Celsius.
The optimum flow rate had to be found to
get the highest production of methyl
orange. The flow rate was varied from 50
µl/min to 800 µl/min.
Results
Temperature
in Celsius
Concentration of methyl
orange in M
20
0,000073
40
0,000333
60
0,000555
80
0,000611
Flow rate
in µl/min
Concentration of methyl
orange in M
50
0,000705
100
0,000612
200
0,000495
400
0,00039
800
0,0003 ± 0,00002
Looking at the results, the temperature
must be set at 80 degrees Celsius. The
flow rate looks like to be a nearly straight
line, when you keep on doubling the flow
rate. It cannot be concluded that it will
continue like a straight line. In this graphic
the straight line indicates the highest
concentration of methyl orange will be at
an optimum at to lowest flow rate that is
possible.
The highest production of methyl orange
would be at a flow rate around 1600
µl/min.
Conclusion and discussion
Concluded is that a low speed will give
more methyl orange. The temperature
must be set at 80 degrees to get the
highest concentration of methyl orange. In
combination with the lowest possible flow
rate. So recommend is to do the
experiment at the temperature close to 80
degrees Celsius. The measurement of the
concentration of methyl orange at a low
flow rate doesn't work as it should work it
the graph starts to jump from 0,0007 M to
0,002 M resulting in unreliable
measurements.
The high speed measurements are less
reliable, because there was no possibility
to fill the inlets with more than 1 ml. So it
was needed to stop quiet fast with the
measurement before it would shoot of the
scale.
Bibliography
1. Methyl orange,
http://en.wikipedia.org/wiki/File:Methylorange-sample.jp
2. Synthesis of diazonium salt
http://antoine.frostburg.edu/chem/senese
/101/index.shtml
3. Synthesis of methyl orange,
http://antoine.frostburg.edu/chem/
senese/101/index.shtml
4. Fourth class chemistry book