Process for recovery of acetone

This invention is a process for purifying crude acetone obtained by cleavage of cumene hydroperoxide, said crude acetone containing aldehyde impurities and appreciable amounts of unreacted cumene, by fractionally distilling the acetone in a multiple plate distillation column, said process comprising: continuously feeding crude acetone; continuously feeding a dilute aqueous solution of an alkaline material at a point above the crude acetone feed point; and controlling the temperature profile of the column by adjusting the amount of liquid acetone removed in step (c) to maintain a preselected temperature on a plate in the region between the crude acetone feed point and the alkaline material feed point.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The subject matter of the invention includes a process for recovery of pure 
acetone from the crude acetone containing aldehydic impurities and 
unreacted cumene which is obtained from the cleavage of cumene 
hydroperoxide. 
2. Description of Related Art 
An important process for production of phenol and acetone is the cumene 
hydroperoxide process wherein benzene is alkylated to cumene, which is 
oxidized to cumene hydroperoxide, which, in turn, is cleaved to produce 
phenol and acetone. 
Varying amounts of side products such as aldehydes, particularly 
acetaldehyde and propionaldehyde, and other materials such as mesityl 
oxide, dimethylphenylcarbinol, alphamethylstyrene and acetophenone also 
result. 
Phenol can be recovered by fractional distillation, with a crude acetone 
fraction removed from overhead. The crude acetone fraction contains those 
side products discussed above, as well as hydrocarbons such as unreacted 
cumene and alphamethylstyrene and traces of organic acids such as formic 
acid. 
U.S. Pat. No. 4,430,447 to Laverick et al. describes a process for recovery 
of pure acetone from a crude acetone fraction which requires partial 
condensation of the crude acetone fraction, then feeding the resulting 
vapor phase only to a second distillation column for treatment with an 
alkaline material and distillation. 
U.S. Pat. No. 3,668,256 to Brundege describes a process of fractionally 
distilling crude acetone in a single, multiplate column while continuously 
adding to the column aqueous alkali metal hydroxide at a specified ratio 
to reflux rate, in an amount and concentration sufficient to polymerize 
aldehyde impurities. Caustic strength is controlled by the ratio of reflux 
to caustic feed. 
In practice, problems are encountered with the Brundege process if the 
crude acetone feed stream contains appreciable amounts of hydrocarbons, 
particularly unreacted cumene, which are not first removed from the crude 
acetone feed. It is desirable from a process and economic viewpoint to 
introduce substantially the entire crude acetone fraction, vapor and 
liquid, including any hydrocarbons and side-products that may be present. 
However, the cumene present in the crude acetone creates a cumene-rich oil 
phase which causes problems in operation of the column. The presence of an 
oil phase creates difficulty in caustic/aldehyde contact since the 
aldehydes are soluble in the oil phase and the caustic must then diffuse 
into the oil phase for contact. In practicing the Brundege process, the 
oil phase must be drawn off as a sidedraw from a plate or plates below the 
point of crude acetone feed. The inevitable result of the sidedraw of the 
oil phase is that economically significant amounts of the liquid phase 
containing caustic and acetone is drawn off also which must be separated 
from the oil and recycled with the caustic feed. This, however, creates 
further problems by introducing aldol condensation products, for example 
diacetone alcohol and further degradation products such as mesityl oxide, 
into the caustic feed, which can contact the acetone and increase the 
chance of acetone quality upsets. 
The need exists for an efficient, economical process for the recovery of 
acetone from cumene-containing crude acetone. 
SUMMARY OF THE INVENTION 
Crude acetone containing water, cumene, and aldehydic impurities is fed to 
an intermediate point in a multiple-plate distillation column. A dilute 
aqueous alkaline solution is continuously fed at a point above the crude 
acetone feedpoint. The temperature profile of the column is controlled by 
adjusting product drawoff to maintain a preselected temperature on a tray 
in the region between the caustic and the crude acetone feed points. The 
oil, water and aldol condensation products discharge from the bottom and 
flow to oil/water separation facilities for recovery of cumene. Purified 
acetone substantially free from moisture and passing the standard 
potassium permanganate test is withdrawn from near the top of the column. 
Overhead vapors are condensed and returned as reflux. If necessary, a 
portion of the condensate can be returned to a point in the column between 
the crude acetone feed point and the alkali feed point to permit further 
contact of aldehydic impurities with caustic.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Crude acetone containing water, cumene and aldehydic impurities can be 
purified to an extent wherein it will pass the standard potassium 
permanganate test, by combination of chemical treatment and distillation 
effected in a single, multiple-plate distillation column. 
With reference to the Figure which shows a preferred arrangement of 
equipment useful in performance of the process, Column 1 is a single 
distillation column containing 60 plates or trays operating under reduced 
pressure. Heat source 2 supplies heat, for example in the form of steam to 
the bottom of the column. 
Crude acetone containing water, unreacted cumene, and aldehydic impurities 
is continuously fed through vapor feed 3 at the sixth tray and liquid feed 
4 at the seventh tray in any ratio of vapor to liquid. A dilute aqueous 
solution of alkali is continuously fed through feed inlet 5 at the 
nineteenth tray with alternate feed locations provided at the seventeenth 
and fifteenth trays. The alkali solution mixes with the down flowing 
liquid in the column and serves to scrub the upflowing vapors. This 
removes aldehydes by promoting aldol condensation reactions to produce 
high-boiling aldol condensation products which settle in the bottom of the 
column with water, any unreacted cumene, and the spent alkali. The bottoms 
are removed through discharge outlet 6 to oil/water separation facilities 
7 where cumene is recovered for the cumene hydroperoxide reaction process. 
Purified acetone, essentially free of water, i.e. less than 0.5 percent 
water and able to pass the standard potassium permanganate test, is 
withdrawn from the column through outlet 8, preferably located 3 to 5 
trays below the top. Overhead vapor is removed through pipe 9 to condenser 
10 and returned as reflux through pipe 11. 
A portion of the overhead reflux can be fed through pipe 12 to a point 
between the crude acetone feed and the caustic feed, for example the 
eighth or eleventh tray, to afford additional contact with the caustic 
solution to insure essential aldehyde removal from the product when 
necessary. 
The alkaline agent used to polymerize the aldehydes may be an appropriate 
inorganic basic material including alkaline earth oxides, carbonates and 
hydroxides and alkali metal oxides, carbonates and hydroxides. A dilute 
aqueous solution of about 0.2 to 2.0, preferably 0.8 to 1.5 percent sodium 
or potassium hydroxide is an example of an appropriate caustic solution. 
The control process of this invention has resulted in a substantial 
reduction over past practice in the amount of caustic solution added to 
the column. It is necessary to add only 1 to 5 percent caustic solution on 
a volumetric ratio to crude acetone feed. This provides substantial 
savings in caustic and in energy requirements since substantially less 
water is added with the caustic to the column. 
The process of the present invention offers important advantages when the 
crude acetone feed contains appreciable amounts of unreacted cumene. 
Experience has shown that amounts as low as about 0.5 weight percent 
cumene in the crude acetone feed has created substantial problems in the 
Brundege process discussed above necessitating a sidedraw to remove oil 
from the column. The process of the present invention has successfully 
produced purified acetone when the crude acetone feed has contained as 
much as 4 weight percent cumene and 10 weight percent water. 
Essential to the success of the process of this invention is control of the 
temperature profile of the column. The presence of the cumene creates an 
oil phase in addition to the aqueous caustic phase in the region between 
the caustic feed point and the crude acetone feed point. It is in this 
region that essential aldehyde/caustic contact occurs. However, the 
presence of two liquid phases interferes with the efficiency of this 
contact, and it becomes important to control precisely the temperature 
profile in this region. 
In a distillation process, where the distillate is the desired product it 
is conventional to control the column at a point near to the point that 
distillate is withdrawn from the column. In the instant process, the 
product draw-off of purified acetone is of course grossly ratioed to the 
feed rate of crude acetone. However, for precise control of the 
temperature profile of the column, the product draw-off is adjusted to 
maintain a constant preselected temperature on a tray or plate in the 
region between the caustic feed point and the crude acetone feed points. 
It will be understood that the preselected temperature is dependent on the 
pressure in the column at that tray, and thus the preselected pressure 
compensated temperature is an indication of the composition profile at 
that point. With the 60-tray column being utilized, it has been found that 
there is sensitive interaction between the water and acetone profiles 
around the tenth tray and the product draw-off rate. Steam input at 2 is 
ratioed to the vapor and liquid feeds, in accordance with the relative 
amounts of vapor and liquid flows. The product draw off at 8 is ratioed to 
the feed rates, with the ratio adjusted by the pressure compensated 
temperature on the tenth tray. In this manner, essentially only acetone is 
in the overhead, and the cumene can be forced to the bottom with water, 
spent caustic, and the aldol condensation products. 
The process of the instant invention has resulted in the elimination of the 
oil sidedraw necessary in the previously discussed U.S. Pat. No. 3,668,256 
process. This has contributed significantly to the simplification of 
control requirements necessary to maintain composition profiles within the 
column. Absence of the oil sidedraw has presented many advantages: 
equipment is not necessary to recover acetone withdrawn with the oil 
sidedraw, lower caustic feed rate reduces the amount of water inventory in 
the column and allows reduction in steam usage, and only fresh caustic 
free from aldol product contamination is introduced at 5, thereby 
lessening the chance of acetone quality upsets. The process has resulted 
in increased acetone recovery combined with lower steam and caustic 
requirements, thus providing substantial savings in energy and materials. 
EXAMPLE 
Crude acetone containing impurities such as 500 ppm aldehydes, about 2 
percent by weight cumene and about 10 percent by weight water was 
continuously fed to a 8 foot (2.44 meters) diameter 60 plate column. The 
overhead pressure was 360 mm Hg (48 kPa). The crude acetone was fed as a 
liquid to the seventh tray at a rate of 263 gallons per hour (994 liters 
per hour) and as a vapor to the sixth tray at a rate of 4602 liquid 
equivalent gallons per hour (17400 liters per hour). Steam was passed into 
the bottom of the column at a rate of 10,215 pounds per hour (4634 kgm per 
hour). 
An aqueous 1 percent solution of sodium hydroxide was continuously fed to 
the nineteenth tray at a rate of 50 gallons per hour (189 liters per hour) 
and the distillation was carried out continuously, with the overhead 
vapors being removed, condensed, and a portion of the condensate returned 
to the top of the column as reflux, with the remaining portion of 
condensate fed to the eleventh tray at a rate of 128 gallons per hour (484 
liters per hour). 
Purified acetone product was withdrawn from the fifty-fifth tray at a rate 
of 4005 gallons per hour (15140 liters per hour). The product draw-off was 
ratioed to the crude acetone feed rates, with the ratio adjusted by the 
pressure compensated temperature on the tenth tray. For the given overhead 
pressure, the temperature on the tenth tray was maintained at 55.degree. 
C. The acetone product contained 0.36 weight percent water and had a 
permanganate rating of 3.7. 
A residue fraction containing cumene, water, excess alkali, and aldol 
condensation products was withdrawn from the base of the column to 
oil/water separation facilities and the cumene recovered.