There are several ways to convert isopropanol to acetone.
- Use of $\ce{Cr2O3}$ as catalyst[1]
The conversion of isopropyl alcohol to acetone has been studied over $\ce{Cr2O3}$ powder at 473 K in a flowing microcatalytic reactor. Appreciable steady-state catalytic activity was achieved only when oxygen was present in the reactant gas flow. The effect of mild pretreatment of $\ce{Cr2O3}$ in $\ce{O2–N2}$ at 473 K on the initial activity, and the observed dependence of the process on $\ce{O2}$ pressure has been related to the oxidation–reduction cycle of the surface chromium species. $\ce{Cr^{(3+n)+}}$ on the surface of $\ce{Cr2O3}$ have been considered to be the active species, where n= 1–3.
2 . Catalytic dehydrogenation of isopropanol
a) Source 1.
Catalytic dehydrogenation of isopropanol can be chosen as an
alternative synthetic route when high-purity acetone is required,
such as in biomedical applications. Turton et.al. mentions that a
single pass conversion of 85-92% with respect to isopropanol, with
reactor conditions of 2 bar and 350° C, is generally achieved. A
molten salt stream will be used a heat source for the endothermic
reaction:
$$\ce{(CH3)2CHOH -> (CH3)3CO + H2}$$
The acetone produced in the reactor passes into a phase separator and
then into a separation system that includes one stripping and two
distillation columns. A recycle stream takes a mixture of unreacted
isopropyl alcohol and water, with a trace amount of acetone, back into
a mixer that feeds the reaction system. Using the catalyst which will
be employed throughout this analysis, the reaction is first order with
respect to the concentration of isopropanol and has an Arrhenius
dependence on temperature with E=72.38 MJ/kmol and k=351,000 cubic m
gas/cubic m reactor sec.
b) Source 2
At the beginning of the process, feed including i-propyl alcohol and
water, and recycle stream are mixed in feed drum. From here, this
mixture is send to vaporizer to changestream’s phase as vapour. After
vaporizer, mixture is heated to reaction temperature in theheater.
Reactor used is a tubular flow reactor. Acetone, hydrogen gas (H2) are
produced andwater and i-propyl-alcohol are discharged. The mixture
with acetone, hydrogen, water, i- propyl-alcohol are sent to cooler
and then to condenser. After condenser the mixture is sent toflash
unit. Hydrogen, acetone, i-propyl-alcohol and water are obtained as
top product. This top product is sent to scrubber to remove hydrogen.
The bottom product of flash unit which isformed by acetone, water,
i-propyl-alcohol are mixed with the bottom product of scrubber before
acetone column. In acetone column, acetone is obtained from top
product with 99 wt%. i-propyl alcohol and water and also 0.1% of
acetone is sent to i-propyl-alcohol column from bottom product. The
top product of this column is sent to feed drum and bottom product is
thrown away as waste water.
- Using chromic acid [2]
Oxidation at 25' to 40' is accordingly specified, requiring the
mixture to be chilled in ice after each addition of oxidant. In 1926
the writer worked out a student experiment which involves the same
reaction, the oxidation being effected by gradual addition of chromic
acid solution to the boiling solution of isopropyl alcohol in water.
The reaction is carried out in a flask surmounted by a short
fractionating column, through which the acetone is distilled during
and after the oxidation. The crude acetone (collected below 65'), and
several subsequent fractions, are redistilled through the column,
permitting the easy isolation of a high yield (70% to 80% or more) of
acetone boiling 57' to 60' and over 99% pure, and also the isolation
of any unchanged isopropyl alcohol (76' to 82').
References:
- Ilyas, M.; Shah, S.; Nigar, R.; Khan, H. Conversion of isopropyl alcohol to acetone catalysed by Cr2O3 at 473 K: role of molecular oxygen. Faraday Trans. 1994, 90 (16), 2413. DOI: 10.1039/FT9949002413.
- Wagner, E. C. Oxidation of isopropyl alcohol to acetone. A student experiment. J. Chem. Educ. 1934, 11 (5), 309. DOI: 10.1021/ed011p309.
