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I'm not an expert teacher or lecturer of chemistry. I was only a student from SMA NEGERI 15 SURABAYA who had been one of the Bronze Medalist Participants of Olimpiade Sains Nasional X (2011) of Chemistry In Manado, North Sulawesi, 11 - 16 September 2011 and graduated in 2012. Now, I'm studying at Universitas Airlangga in Surabaya, Indonesia. I do love chemistry and I would like to help them who had difficulties in studying chemistry. That's why, please understand me if you found some misconcepts in my entries. Suggestions are always necessary in order to develop this blog. And I'm sorry because my English isn't so well.

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Wednesday, January 04, 2012

Green Chemistry - The Use of Supercritical Carbon Dioxide

At room temperature and pressure (25 OC and 1 atm), Carbon dioxide usually acts as gas and as solid (dry ice) when it is frozen. If the temperature and pressure both raised from the STP condition to a condition upper than critical point, Carbon dioxide will have the properties between gas and liquid. (Tc = 31.1 oC and Pc = 72.9 atm).


(Source: Wikipedia)



Supercritical Carbon dioxide is an important solvent, replaces organic solvents. In various industries, Supercritical Carbon dioxide acts as the chemical extractor and this Carbon dioxide is well-known as the green solvent because it is can be reused. One of the uses of this Carbon dioxide is "de-caffeine-ation" (eliminate caffeine) from coffees with left no residue after the separation.

Question:
(1 Bar = 0.986 atm)


1. State the temperature and pressure where the three phases of Carbon dioxide is in the equilibrium.

2. If the compound heated in isobaric process, what condition makes the Carbon dioxide sublimed (turned from solid to gas).

3. As solvent, what condition (temperature and pressure) that makes Carbon dioxide can extract caffeine?

4. In your opinion, what is(are) the weakness(es) of Carbon Dioxide as a solvent?

5. Calculate how much energy needed to compress Carbon dioxide from 1 bar to 50 bar (Final volume = 50 mL at 298 K and assume Carbon Dioxide as the ideal gas).


If Carbon Dioxide is a real gas, then the Van Der Waals Equation is applied.
For Carbon dioxide: a = 3.59 x 105 Pa dm6 mol-2 and b = 0.0427 dm3 mol-1


6. Calculate the pressure needed to make the density of Real Gas Carbon Dioxide become 440 g L-1 at 350 K.


In Supercritical Carbon Dioxide, benzyl alcohol can be oxidized by O2 become benzaldehyde. Reaction begins with the presence of Pd / Al2O3 as catalyst with selectivity percentage of 95%.


7. Write the important chemical equation for the reaction above.

8. If there is a minor product of the reaction, what that could be?

Source:
Final Test of Pelatnas I IChO 2012


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