# Last edited on 2017-02-08 05:03:15 by jstolfi DEHYDRATING COMMERCIAL ETHANOL TO ABSOLUTE ETHANOL Inmetro's ethanol grades seem to be weight percentages. Thus 100 g of ethanol 92.8% should contain 7.2 g of water, and 100 g of ethanol 46.2% should contain 53.8 g of water. ---------------------------------------------------------------------- 2017-01-02 Trying to dehydrate with CaO Molar weights of CaO and Ca(OH)2 are 56.1 g and 74.1 g. Therefore 56.1 g of CaO should absorb 18.0 g of H2O. To dehydrate 100 g of ethanol 92.8% one would need ~23 g of CaO. To dehydrate 100 g of ethanot 46.2% one would need ~168 g of CaO. Not practical... First try: Put ~50 g of ethanol 92.8% in beaker. Added 25 g of CaO. Stirred. Filtered with 7 um paper, into filtrate (A1) and ppt (A2). Ppt (A2) was 32 g when wet (including 1 g of paper), 26 g when dry. Thus 25 g excluding the paper. Filtrate (A1) was clear mobile. The weight was 37 g. Together with the 10 g lost by (A2) in drying, that is 47 g. Thus 3 g were somehow lost. Added water to a bit of (A2), and it heated, showing that it still contained CaO. Since (A2) weighted the same as the initial CaO, the attempt failed. Maybe we did not wait long enough. Second try: Put 50 g of ethanol 92.8% in a beaker. Added 31 g of CaO. Waited for some time. Filtered the mixture in a covered funnel yielding filtrate (B1) and ppt (B2). Collected (B1) with a beaker in ice water to reduce evaporation. The ppt (B2) weighted 45 g wet, 31 g dry, excluding the paper. The filtrate (B1) weighted 34 g. Plus the 14 g lost by (B2) on drying, that is 48 g. There was still a loss of 2 g somewhere. Again (B2) weighted the same as the initial load. Failed again. Maybe should leave for a very long time (days). Perhaps try at higher temperatures, say 60 C. ---------------------------------------------------------------------- 2017-01-26 Wed Dehydrating with MgSO4 Attempting to dehydrate ethanol 92.8% with anhydrous MgSO4. Common hydrates are the heptahydrte MgSO4(H2O)7, which decomposes at ~150 C; and the monohydrate MgSO4(H2O), that decomposes at ~200 C leaving the anhydrous form. Molar mass of MgSO4 anydrous: 120 g. So 120 g of anhydrous MgSO4 would absorb 18 g of water to form the monohydrate, or 126 g of water to form the heptahydrate. Molar mass of MgSO4 monohydrate: 138 g. So 138 g of monohydrate should absorb 108 g of water to form the heptahydrate. Heated some MgSO4 (Agros quimica), in unknown hydration state, in a stainless steel cup. At some point, part of it "melted" into a thick concentrated solution, slightly pink (from corrosion of the steel?), boiling at ~98 C. The bottom of the mass was still solid. When bubbling stopped, it solidified into a waxy-looking solid. On further heating it turned white, opaque, and hard. ---------------------------------------------------------------------- 2017-01-27 Thu Removed with effort the MgSO4 (M11) from the cup. Ground it in a mortar, sifted, and stored in a jar with masking tape seal. Presumed to be a mix of anhydrous and monohydrate. ---------------------------------------------------------------------- 2017-01-31 Tue Placed 101 g of ethanol 92.8% in an erlen of 250 ml. Added 15 g of MgSO4 dehydrated as above. Stirred the mixture (E1). Filtered (E1) through paper Quanty JP41 12.5 cm (weight 1.25 g dry). Washed the erlen with ~9 ml of ethanol 99% Asher. (Bad; should have used the filtrate itself). The filtrate (E3), 67.5 g, was clear and left no residue on evaporation. The ppt (E2) was dried in the filter paper on warm plate. It weighted ~16 g with paper, i.e. ~15 g dry. Since the 101 g of ethanol had ~7.8 g of water, we expected ~23 g dry. So it seems that we failed too. Tried again: merged (E2) and (E3) back into (E1b), total 115 g. Left sit for some days in erlen closed with majipak. ---------------------------------------------------------------------- 2017-02-04 Filtered (E1b) that had been sitting for ~4 days, into clear filtrate (E3b), ~130 ml, and crystalline white ppt (E2b). The dry weight of (E2b) was still 16 g. So, failed again. To check the ppt (E2b), placed it in an erlen with ~100 ml H2O. Initially the mix (E2c) it did not dissolve completely. The water remained cloudy even after several minutes of agitation. Only after heating to ~80 C the solution became clear. Dehidrating with Na2CO3 See the "sodium_carbonate" notebook. Using the (E5) and (E6) anhydrous carbonate prepared there. Thus 106 g of anhydrous Na2CO3 should absorb 18 g of water to become the monohydrate, and 180 g of water (below 34 C) to become the decahydrate. Also 124 g of monohydrate should absorb (below 34 C) 162 g of water to become the decahydrate. Certain proportions of Na2CO3, water, and ethanol will form two separate liquid phases. Experiment run 1: Poured 100 g of ethanol 92.8% in an erlen. Addded 1 g of (E5). Left the mix (E6b) in a cool bath at first, then overnight, in the open erlen. The (E5) did not dissolve, but maybe the powder became crystalline again. Added more (E5) to (E6b), but forgot to weigh, darn! Cooled to ~10 C in ice bath. ---------------------------------------------------------------------- 2017-02-05 Sat Heated (E6b) to ~70 C and allowed it to cool to ~5 C. Did not seem to affect much. Filtered (E6c) at 5--10 C yielding clear filtrate (E8) and crystalline ppt (E7). Lost some ppt. Discarded the MgSO4 solution (E2c). ---------------------------------------------------------------------- 2017-02-07 Tue Another attempt with Na2CO3 Put 100 g (~120 ml) of ethanol 92.8% in an erlen. Added all the re-dried anhydrous carbonate (E6), 17g. Closed the erlen with alum foil. Swirled the mixture (Ed1) many times over a couple of hours. Cooled (Ed1) to ~10 C in ice bath. Filtered cold with W201 paper. Filtrate (Ed2) clear, colorless, very mobile. Spilled some of it. The ppt (Ed3) was white crystalline powder. Dried at ambient temp, ~29 C, by pressing in folded filter paper ("pastel") between paper napkins. Weigthed when still a bit moist: 25 g. Seems that it was a success: the ppt weights 8 g more than the anhydrous carbonate that was added. matches the 7.2 g of water expected in the ethanol.