supercritical extraction of freebase pseudoephedrine?

loki · guinea pig

braindamage: the definition of supercritical is a substance which is retained in the liquid state via high pressure above the boiling point of the substance. pressure cookers are somewhat supercritical devices. that gas in compressed gas cylinders is supercritical, the gas in a cigarette lighter is supercritical. that last example, is particularly good for highlighting the fact that supercritical substances exist as two phases. even if the headroom space isn't big, it's still always gonna have some of the gas in gas phase, except maybe if you use a higher pressure vessel to fill another vessel designed to vent the gas at the very top of the liquid once the pressure exceeds a pressure just below the pressure of the feeding cylinder.

if you want to work with highly polar gases like butane/propane then you have to be using it on highly polar substances. just because it's supercritical does not change polarity issues. carbon dioxide has the greatest utility for this because it is essentially a diketone, which puts its polarity at about the middle range meaning it can dissolve the greatest number of things. Polar gases are good for polar material. Acidic gases for alkaline material. alkaline gases for acidic material.

In any case, the extraction is not going to work without the supercritical substance in liquid phase under pressure in sufficient quantity and degree of surface contact with the solute matrix to permit complete dissolution.

Here's a little set of rules about solubility of phases of substances that maybe you are not aware of:

gases only dissolve gases, although they may contain suspended liquids and solids which are light enough due to size and density (and if given time and a lack of agitation via temperature differentials or vibration will settle out at the bottom)

liquids can dissolve gases, liquids and solids. the degree of solubilities depends on the liquid and the solute substance's degree of polarity and affinity with the liquid. Solids increase solubility in liquids with elevated temperatures, gases decrease solubility with elevated temperatures.

solids cannot dissolve anything but can be produced out of appropriately compatible materials (which can be liquids to some degree and to a much lesser degree, gases) mixed in liquid state and cooled rapidly to ensure they do not separate according to density.

and something else which i got a vague concept of misunderstanding when discussing with a friend who was picking my brain about the subject: you cannot use pressure to convert a gas to solid phase. when a supercritical gas, in liquid state, is released into the atmospheric pressure environment, the liquid rapidly boils off, which causes a cooling effect on the still liquid part of the gas due to kinetic energy fractionation: the molecules in a liquid with the highest kinetic energy are the ones which come out first, this property is exploited by our bodies and evaporative cooling systems by using localised low pressure regions, the rear face of a droplet relative to an air current, to increase evaporation rates of the liquid, which then removes heat from whatever the liquid is in contact with. If you have ever vented butane gas into an open container at atmospheric pressure you may have seen solids crystallising in the process - these solids are ice which has condensed due to low temperatures out of the air and then frozen rapidly due to the temperature being below the freezing point of water (butane's boiling point is -5 degrees, thus when it boils out when released from a compressed cylinder it lowers the temperature of its liquid phase below 5 degrees - this appearance of ice i have witnessed from using a fan to evaporate naptha in a very humid and cool environment too)

braindamage · Thu Jul 14, 2005 6:19 pm

thats nice and all but,and this not me calling you ignorant,you are completely wrong on this issue.

loki · guinea pig

it would appear that you are correct. However at the same time, pressurised gas still in the two phase situation does extract substances, a la honey oil etc. What is the supercritical temperature of CO2, butane...

so um like... if you want it supercritical you have to heat it. my idea for the dry ice extractor probably isn't so stupid after all then. once its all melted into liquid state, then you just bring the temperature up to the supercritical temp. et voila.

from wikipedia:

http://en.wikipedia.org/wiki/Critical_point_%28chemistry%29

braindamage · Fri Jul 15, 2005 3:47 pm

to go above the critical point you have to go above the Tc and Pc,ie of CO2 above 30.9C and 78bar(these values may be a bit off im ripping them outta my very damaged memory),thats why you dont see liquid CO2 pouring out of chimneys,etc.Butane gas has even higher tc/pc but i dont know the values by heart,if you need them i could revisit my old thermo tables.

no your idea for a dry ice extractor isnt dumb at all!but thats a standard extr,followed by a flash separation.my guess that triprolidine would be very soluble in co2,and if you could make use of those complexing agents i mentioned before you coculd have a very efficient way of extr pse.hcl.or maybe combinig the co2/butane extr?
these things have been discussed for a long time,but yet no one has tried to experiment w them.

loki · guinea pig

sorting out tripolidine is easy anyway, just a presoak of the ground pill mass in dry ketones.

braindamage · Mon Jul 18, 2005 9:50 pm

yeahyeah but lets play around a min here;use your imagination what will a CO2/butane+complexin agents extr yield....any volunteers?