Reaction Parameters

Time TEMP PRESSURE A.V
(Min) C mm-hg meq/g,
0 20 760 104.2
15 71 760
30 111 760
35 121 760
45 140 760
60 166 760
75 180 760 83.1
90 180 760
105 180 760 64.6
135 180 760 50.0
145 180 350 38.0
165 180 350
195 180 350
200 180 250
225 180 250 24.0
230 180 160
235 180 100
255 180 100
285 180 100 14.0
290 180 40
345 180 40 6.7
405 180 40 2.07
465 180 40 0.46
525 180 40 0.39

Above, reaction parameters of esterification of acid oil with glycerol
Acid oil+Crude Glycerol <---> Triglyceride+H2O

Question 1- While reaction occurs in a CLOSED VESSEL and reach 100 C temperature, Vapor pressure of water will obviously begin to increase until 145 minutes, But, Why wacuum was not applied in after 30 minutes next to boiling point of water? In other words, why vacuum is applied after 135 minutes? And why vacuum is sharply reduced to 40 mm-hg?

Question 2; While reaction occurs, H2O yields and the amount of H2O is getting increased during reaction, the reason for reducing vacuum until 40 mm-hg, Is an increment in mole of friction of H20 inside solution in accordance with Raoults Law?

Question 3- in a closed vessel, between 0 and 135 minutes, as vapour pressure ascends, how was pressure kept constant at around 760 mm-hg?

Note that in order to run reaction towards right side, water have to be boilled off under the vacuum.

Any comments would be appreciated

erdem_ozcan

You have outdone yourself with a lack of information with this question. However, I will take a stab at a few answers. I will add a few assumptions to help your understanding of what I am thinking.

I assume your question has to do with the physical reaction to convert high FFA to triglycerides. Your equation "acid oil + Crude Glycerol <---> Triglyceride + H20", to me, means add sulfuric acid to glycerol, then mix together with high FFA oil. Raise the temperature of the reaction to a minimum of 180C to speed the reaction and to drive off the water as it is formed. By removing one of the products of the reaction, the reaction continually proceeds to the right. Thereby, achieving, virtually, complete conversion of FFA to triglycerides.

If this is correct, then I will try answering your questions.

I'll start with Question 3. A pressure relief valve could have been used to control the internal pressure at 760 mm-hg during the early stage of the reaction.

I suspect the rate of water production is greatest at the beginning of the reaction. The boiling water is contained in the vessel until the desired initial operating temperature is established.

Question 2. It seams reasonable that the rate of production of H20 will decrease as the conversion of FFA to TG leaves ever smaller amounts of H2O to be converted.

It appears the controlling variable is temperature. As the rate of H2O production decreases, then it became necesssary to start a vacuum pump to withdraw smaller and smaller volumes of H2O. This doesn't exactly seam logical, but it fits the data presented.

As to Question 1, it looks like they tried to adjust vacuum pressure and heat input to control internal temperature. The size of the vacuum pump may have been limiting at first so they ran the pump "wide open" for a while. And, at the same time they probably adjusted the temperature controller to limit heat input to just compensate for the heat being lost with the water.

Later in the reaction, the rate of water production slowed to the point that the vacuum pump could remove all water as it was produced. They then just let the vacuum pump run wide open and returned to controlling the reaction temperature by adjusting the rate of heat input.

I am a little confused by the term "meq/g" and V. The volume of a substance can be calculated by measuring the meq/g. But, what volume is being measured? Perhaps the meq of the FFA is measured and compared to mass of the TG. If that is what is happening, then would the sulfuric acid interfere with the measurement?

Responding to your posts is always an adventure, but I seam to always learn something from the excercise. In this case, I have learned I should not respond to what I do not fully understand - but when has that ever stopped me.

Regards.

Dear Producer;
Thank you very much for your valuable comments.

A.V : Acid Value
meq: Mili equivalent gram for FFA.
The column that you caused confusion show that acid value, which is the amount of NaOH requried in grams is to neutralize 1 miligram FFA.
I know you know. But I want to remember it so my english is poor. Thank you very much again.

quote:

Originally posted by erdem_ozcan:

I know you know.

You are too kind. I did not know that.

There is a technique using meq/g to calcualte a volume, but that was not used here.

With this information, it is doubtful that any sulfuric acid was used as a catalyst.

The reaction, then, is FFA + Alcohol <---> "glyceride" + water; with the driving force being heat. I placed "glyceride" in quotes because I wonder if the reaction would drive the FFA all the back to TRI glycerides, or if the reaction would favor the only the formation of MONO glycerides.

In any event and assuming full conversion of FFA then the resulting; TRI, MONO, or DI; compounds will all participate in the transesterification reaction.

erdem ozcan,
I believe you can interpet the data file as follows:
1) Time (in min.), Temp ( in deg C), Pressure (in mm-hg) and Acid Value (or A. V in meg/g)
2) Acid value is a way to monitor the completeness of the reaction without having to specify the particular fatty acids. When the acid value goes to zero all the FFA's are assumed converted.
3) 760 mm-hg is atmospheric pressure. They simply increased the temperature with the reactor open to the atmosphere and held it at 180 deg C until 135 minutes. This gets any initial water contaminating the oil vaporized before they start the vacuum pump in order to minimize the amount of water they need to remove through the vacuum pump (saves the pump).
3)They purge the vessel with nitrogen in order to help move the water vapor through the vacuum system and prevent oxidation by oxygen. They use the rate of nitrogen flow to control the vacuum at any given time.
Hope this helps.

quote:

Originally posted by erdem_ozcan:

Question 1- While reaction occurs in a CLOSED VESSEL and reach 100 C temperature, Vapor pressure of water will obviously begin to increase until 145 minutes, But, Why wacuum was not applied in after 30 minutes next to boiling point of water? In other words, why vacuum is applied after 135 minutes? And why vacuum is sharply reduced to 40 mm-hg?

Question 2; While reaction occurs, H2O yields and the amount of H2O is getting increased during reaction, the reason for reducing vacuum until 40 mm-hg, Is an increment in mole of friction of H20 inside solution in accordance with Raoults Law?

Question 3- in a closed vessel, between 0 and 135 minutes, as vapour pressure ascends, how was pressure kept constant at around 760 mm-hg?

Note that in order to run reaction towards right side, water have to be boilled off under the vacuum.

Any comments would be appreciated

My take:

Question 1:
Vacuum was not applied initiallly due to thermodynamic work requiremennts.

Question 2:
Pass for now. I'm not familar with Raoults Law.

Question 3:
I suspect that their "closed vessel" was not truly closed in a thermodynamic 'control volume' sense. In fact I suspect that The vessel was vented to allow water vapor to escape, which is the only way you can have a water-producing side reaction, 180C and 760mm Hg pressure.

I further suspect that vacuum was only applied, after 135 minutes, when a significant quantity of water had been rejected and now it would require less energy to sustain the vacuum (ref answer to question 1, above).

Horn