[coolsuman]

hai all,
 i have a problem with condensation in my case. i had obtained permeate as vapor at vacuum conditons. now i want condense in that vacuum only. how it has to be done? which method has to be follow?
can any one give me suggestions?

[eugenedakin]

Hi coolsuman,

You have a couple of options:

1) increase the pressure.  If your product is stable with the introduction of atmospheric gas, or nitrogen, or some other gas, add it to lower the vacuum.  If you 'gas' is a liquid at atmospheric pressure, it will condense with the added pressure.

2) Lower the temperature. If you are not able to complete #1 due to contamination issues, lowering the temperature by immersing the vacuum in ice, or in dramatic circumstances, in a CO2 bath (about -40 C), or liquid nitrogen (really cold).

Caution should be exercised with any one of these methods, as the container may or may not be able to handle the added pressure or induced vacuum.

I hope this helps.

Sincerely,

Eugene

[coolsuman]

thank you very much my dear friend.
but i have another problem. after condensing it have only 30% methanol. i have to heat again and i have to do distillation. in this way, some of the energy is waste. how to overcome this problem?
is there any method of separation of methanol from that vapor

[eugenedakin]

Hi coolsuman,

Yes, there are a couple of options to help with the condensing of methanol.

1) If increasing the pressure, increase it in increments. This will cause one of the products to condense before the other one, minimizing cross contaimination (condensation at one pressure would be mainly methanol, while the other would be mainly your product).

2) Lowering the temperature in increments has the same similar effect as increasing the pressure.

I hope this helps.

Sincerely,

Eugene

[coolsuman]

thank you very much. i have another problem related to condensation in pervaporation process.
i had done pervaporation of methanol-water ( 5.7 wt%) , i left with 30 wt% methanol under vacuum 12 mbar. now i have to condense this vapor under vacuum. if i perform  condensation as u said, then it left with 30wt% methanol. but my requirement is 95- 98 wt%.
can u please give me any suggestions regarding this problem?
otherwise is there any other separation processes to solve this problem.

[eugenedakin]

Hi coolsuman,

If you are using pervaporation, why don't you just recycle to extinction? Place another pervaporization process in the system, and recycle the products until you get your 95-98% methanol?

Just a thought 

Sincerely,

Eugene

[technologist]

Hi Suman
Pls describe your experiment in more details with what are the inlet rates & composition, permeate pressure temp & all.

Then probable we can give you better solution.

Anyway U need to recycle your concentrate of 30% as eugene said but it will slowly reduce your output.

[coolsuman]

hai
actually after performing pervaporation, the permeate conditions are
permeate pressure : 12 mbar
permeate flow: 207.99
permeate composition of methanol: 0.242
permeate temperature : 278k
now, tell me how it has to make  98wt% methanol liquid.

[coolsuman]

hai friends,
 i want to do condensation of methanol-water mixture which was at 278k, 12 mbar , 25 wt% methanol to 98wt% methanol , 1 atm.
what are the energy requirements need to this operation?
and how it has to be calculate?

[technologist]

I did some calculation for U (It should have been done by U) that 24.2% by Wt (Dont forget to write units in your post - I dont know 207.99 flow is Kg/hr or gms/hr or anything else) methanol & balance water in vapor at 12 mbar will condense at ~6.3°C so U need a chilled brine supply at ~0°C or less.

Once U have 24-25% Wt methanol (from 5.7%) Probably one recyle will be sufficient.

Anyway what was the feed rate in this case? Just to have an idea about recovery. Because this can save lot of energy in the process.

[coolsuman]

hi technologist,
thank you very much, i will explain clearly to you, by that u can understand my problem.
my feed flow rate was 2230 kg/hr, 5.7 wt% methanol, i was fed into pervaporation unit, where i get the methanol was 24.2 wt%. according to literature i got that the permeate will be at dew point at permeate vacuum and composition. i had calculated that the dew point is 280k at 12 mbar. now i have to make it as 98 wt% methanol liquid. how it has to be done? if u know this please give me a suggestions.
i think now u got my problem.

[technologist]

OK I got it. Thats there 280 K is ~6.8°C I told U about 6.3°C. So its fine.

Now If you are doing this for experimental purpose or to collect the data on pervaporative separation of methanol & water...you have it with one pass ~40% recovery...So go for recycling of 207 Kg/hr of 24% Methanol mixing it with your feed & re-separate.....Probably U will get 30-35% methanol concentration with ~227 Kg/hr & total recovery shall increase to 55%. This is my preliminary estimate based on first principle--- It may be completely wrong also.

Then U can condense it at ~4.5°C. After condensation U need to consider its distillation for purification till 98%

Now the question is about the trade off between energy consumptions in two cases.

Currently I'm unable to see any other method. R U doing it for industrial use OR for academic use. R U working or studying?
Final method may change based on the size of plant.

Have U considered or explored any use of LLE for such a low concentration recovery. Bcoz for this system the chilling energy & then distillation energy requirement will make it unsuitable for industrial use.

[coolsuman]

hai technologist,
 iam doing this for the purpose of my M.Tech thesis. i didn't do any experiments related to this work, just by taking some experimental data (flux data), i am continuing the work to know how much energy required for recovery of 98 wt% methanol from 5.7 wt%. i had done already simulation using conventional distillation for getting 50 kg of methanol with 98 wt% it needs 253 kj/sec of reboiler duty. these data got from Aspen plus.
     i had done liquid-liquid extraction, using solvent as hexyl acetate, but there is no any use.
so, i chose pervaporation, many researchers had done work using different membranes. but, with zeolite membranes it has more selectivity than conventional VLE. so, i had done with zeolites, after doing the permeate conditions as said above,.
    when come to recycle, iam already doing recycle with retantate to make the continuous process.so, i have to make this permeate to the required condition as said above. now tell me what i have to do?
 why you are telling that chilling duty and distillation duty will make unsuitable for industrial use?
please explain me clearly . thanking you.

[technologist]

when come to recycle, iam already doing recycle with retantate to make the continuous process.so, i have to make this permeate to the required condition as said above. now tell me what i have to do?

So was this concentration of 24.2% with recycle or without recycle. If it was with recycle, U have less chance to gain from further recycling it. Then go for direct distillation.

i had done liquid-liquid extraction, using solvent as hexyl acetate, but there is no any use.

Probably, Hexyl acetate is the most common but not suitable. As I suggested on your other post try TOPO - Tri Octyl Phophene Oxide for LLE which is having more affinity for organics.

why you are telling that chilling duty and distillation duty will make unsuitable for industrial use?

Because in case of pervaporation with 208 Kg/hr with 24% Methanol & Dew point of 6.3°C U need ~126 Kj/sec in condensation which is ~45 TR with system efficiencies. This 45 TR requires ~450 Kg/hr LP steam. The energy consumption in LP steam shall be ~290 kj/sec in terms of total steam energy from waste sources. Else U need to consider boiler efficiency also.

Thus Refrigeration itself is costlier than direct distillation (If your energy requirement is correct.) Then U further need distillation energy from 24% to 98%.

[coolsuman]

hai technologist,
how do u get these numbers? i have done flash condensation by decreasing temperature at an interval of 2 deg k. while doing that, most of the methanol left in vapor. after doing 4 stages also 33 kg/hr is left in vapor.
can u please give me the full details.