2 replies to this topic

[Annee]

Dear Friends,
I need your expertise comment over fractional column. I need to distilled out product (Pentafluoro Benzyl Chloride(PFBC), B.P 158 oC) from rxn mass Thionyl chloride (0.5 mole excess, B.P 78 oC)pluse PFBC. As we know on increasing the temp.(75 onward) first we get thionyl chloride and traces all and then we have to raise temp upto 157 oC to distilled out product. I am going for fractionating column to sort out problem of thionyl traces which may distilled out along with product even on higher temp. I need at least 95 % PFBC purity. My reaction mass volume is 70 L (app). I select Glass fractionating column with 1 meter height (600 mm packed height) with dia 100 mm and 10 mm Glass Rashing fill in it.

I need your comment over this and any suggestion or modification in this regard.

Thanks With
Warm Regards
-
Annee
( India)

[sgkim]

Annee,

You want a batch distillation. Then follow the following typical batch distillation procedure.
Ceramic Raschig Rings are better than glass in wettability which give effects on the column efficiency.

(1) put some part (say 20 L) of the mixtuer in a reboiler,
(2) heat the reboiler for heating up the whole column,
(3) reflux all the top distillate,
(4) if all the temperatures in the whole column are stabilized then
start to collect the distillate by reducing the reflux ratio to a starting point (say 1.5)
(5) Check the temperature of the top part of the column frequently.
(You'd better install a temperature recorder on top part of the column)
(6) Check the purity of the distillate. If the purity is OK then
(7) collect the distillate by keeping the temperature as far as possible (label this as "Fraction A")
(7) continuously feed the rest amount of the mixture.
(8) If the temperature begins to rise after all the rest is fed to the reboiler
then increase the reflux ratio slowly ( to 2, 2.5, to 5, 7,....)
(9) If it is hard to keep the temperature even with increased refluxes then
collect the distillate to a different bottle (label this as "Fraction B")
(10)Increase the reflux ratio by allowing the higher temperatures up to 155 ℃ or so.
(11)Chek the bottoms purity. if the bottoms meet the purity required say >98% then
(12) Stop the reflux, and cool.
(13) Drain the the bottoms and label as "Fraction C"
(14) Chek the yields and purities of PFBC and THC in Fractions "C", "A"
(15) If any of the yields PFBC or THC is not satisfactory, then rerun the "Fraction B"
(16) If the purity of PFBC does not meet the maximum allowable light- or heavy contents
rerun "stripping" or "vacuum evaporation" with respect to the former or latter case respectively.

Stefano

[Annee]

Dear Stefano,

Thank you very much for your comments in details. I will implement ur suggestion and share result with you. Now please let me know about designning part , what column parameters with i decide to go ahead, are you agree with that one e.g. column height,dia and rashing dia etc. Infact i want some more pratical practices literature which we can practically apply on batch distillation. Yes you are absolutely right i was talking about batch distillation in my previous mail.

I am looking for some practical designing guidline on distillation (Fractional distillation) which we can implement in plant. if you have anything to share please share with us. And if you donn;t mind interested to know more about you. my email id is anneepch@rediffmail.com

Thank you very much

Regards

Neeraj sharma