PRODUCTION

Membrane Permeation—Cheaper than Hexane Azeotroping

TOWER OVERHEAD* Isopropyl Alcohol . . Ethyl Alcohol . . . . Water . . . . . -ψ.

12,350 1b. 1,339 lb, 1,900 lb,

PRODUCT* Isopropyl A lcoho l Ethyl A lcoho l . . Water

11,700 ib. 1,200 lb.

05 lb.

Isopropyl Alcohol Towor

RECYCLE PERMEATE* Isopropyl Alcohol . . 650 lb. Ethyl Alcohol . . . . 139 lb.

1,835 lb.

'Design figures on a per day basis

INVESTMENT FOR NEW EQUIPMENT

OPERATING COSTS PER YEAR*

' · Supervision • Maintenance labor • Labor benefits • Maintenance

materials • Hexane loss • Membrane

replacement • Utilities • General and

administrative overhead

• Property taxes and insurance

CAPITAL COSTSf UNIT COST, CENTS/LB.*

'Based on operating Mm· of 8 5 % . tBased on 10.470 lb/itr.am day of crude Isopropyl alcohol feed (dry bails).

PERMEATION

$76,000

6,570 990

1,900 1,890

1,140

220 740

6,240

1,140

$23,400

1.36

AZEOTROPING

$100,000

6,570 990

2,500 2,010

1,500 470

1,620

6,780

1,500

$30,800

1.68

fBased on now equipment cost of $76,000 f permeation. $100.000 for azeotropins, A * · * / · 1

payout. 1 0 % per year depreciation, 5 2 % I come tax.

Take a Look at Permeation Membrane permeation process wrests components out of difficult-to-separate liquid mixtures

Az EOTROPES and close boiling mix­tures may soon fall from the difficult-and expensive-to-separate class if mem­brane permeation reaches its apparent potential. While vapor phase permea­tion has been known experimentally for some time, liquid phase permeation is much newer, says American Oil, as it discloses some process details.

The company has pilot planted per­meation t o separate liquid mixtures at its Texas City, Tex., laboratories. With permeation, American Oil has taken a crack at upgrading an isopropyl alco­hol-ethyl alcohol-water azeotrope. Re­sult—a unit that turns out a salable product (having less than 0.5% water) for 1.36 cents per pound. A similar-size unit using hexane azeotroping would produce at 1.68 cents a pound.

Key to separating liquids by permea­tion is that one component of a mixture be preferentially soluble in the polymer of the membrane film, say researchers Robert C. Binning and Frank E . James of American Oil.' The process has unique selectivity, they say, because a

membrane film used can be tailored to the needs of a given separation.

Using nonporous plastic membranes, the process requires:

• That components passing through the membrane be soluble in the mem­brane polymer.

• That components diffuse through the polymer structure.

• T h a t the permeate (product) be removed from the outside of the mem­brane as a vapor.

Permeation rate is inversely propor­tional to film thickness. Selectivity and film thickness are independent. But as yet, optimum film thickness and com­position cannot be predicted for a mix­ture never run before without experi­mental work.

Film thickness ranges down to 0.001 inch, and rupture becomes a problem only when sharp or pointed objects accidentally contact t he films. The films are supported to enable them to with­stand the pressure differential during

operation. Positioning films in the cells compares to positioning stiff filter papers in a filter press.

• Two Compartments. Permeation cells used by American Oil contain two compartments, separated by the mem­brane. In the charge compartment, pressure maintains feed in the liquid phase. This pressure may be atmos­pheric or greater, but must be large enough to equal the feed's vapor pres­sure at operating temperatures.

The other compartment receives the permeate, which is now richer in one or more of the feed components than the feed. To keep the permeate vaporized, this compartment is kept a t a lower pressure than the charge compartment. Depending on operating conditions— especially the pressure differential wanted across the permeation film—less than atmospheric pressure may be held in the permeate compartment. Any necessary heat of vaporization is sup­plied by steam or hot water in a jacket around the film holder.

More general details of the permea­tion process are expected to be disclosed b y American Oil in a paper to be given a t the ACS national meeting in San Francisco next month.

• Commercial Unit. American Oil has designed a unit to remove water from a ternary azeotrope of isopropyl alcohol, ethyl alcohol, and water. The

5 8 C & E N M A R C H 3 1, 1958

azeotrope, produced in hydrocarbon synthesis, has little market value. How­ever, mixed alcohols containing less than 0.5% water can be sold. Permea­tion to remove water from this azeo­trope appears more attractive from an economic standpoint than two-tower azeotropic distillation using hexane as the entraîner—the usual way to make the separation.

American Oil's permeation unit was designed to separate the overhead from an alcohol distillation tower. Permeate, rich in water, goes back to the water injection tray of the tower. This per­mits recycling alcohols that permeate with the water. Auxiliary heat to in­crease rate comes from steam in a jacket around the cell.

Although conservatively designed, the unit's cell and auxiliary equipment fill relatively little space—6 by 6 by 8 feet—yet will process 15,600 pounds per day of the azeotrope.

American Oil estimates that a com­plete change of film should take no longer than one 8-hour shift. Films are precut and mounted on supports for easy placement in the cell. Total oper­ating life of the films has not yet been completely determined. Some films have operated continuously for several months without failure.

More research work may further in­crease the efficiency of permeation over that of azeotropic distillation for re­moving water from the azeotrope of isopropyl alcohol, ethyl alcohol, and water. But economic calculations show that permeation looks favorable now. Investment for azeotropic distillation is 3 1 % more than for permeation, by American Oil's estimates. Operating and capital costs are less for permea­tion, with the result that product cost per pound is about 20% less.

American Oil thinks permeation has a big potential for separating azeo-tropes. Perhaps designers will no longer need to plan carefully to avoid azeotropes in chemical and petroleum refining processes with high equipment costs that result from such plannning. The permeation process will be avail­able for license, says American Oil.

• First successful cold extrusion of hollow titanium shapes is reported by Battelle Memorial Institute. Battelle used a 700-ton hydraulic press for both forward and backward extrusion. Cold extrusion gives a finished surface, im­proves mechanical properties of un­alloyed titanium,· Battelle says.

A New Catalyst for Room or Low Temperature Polymerization

of Polyester Resins

^SBHC^IOATIONS/ ; ΐ&^ζ-β Ketone Peroxide # 6 Active Oxygen . . .

S 0 . 0 % Cnnin.> 6 . 2 5 % Cmln.)

P R O P E R T I E S : A white, fine powder with 6 6 - 6 8 ° C melting point. Solubility at 20°C. (weight percent) :

Slight solubility ( 1 - 5 % ) in water, glycerol ethylene glycol, most esters and hydrocarbons. Moderate solubility ( 5 - 1 5 % ) in alcohols, tricresyl phos­phate, ketones and chlorinated hydrocarbons. Soluble ( 1 5 - 5 0 % ) in ethers and methanol.

A P P L I C A T I O N S — W h e n LUCIDOL KETONE PEROXIDE #6 is used in conjunction with metallic promoters, faster gel times are obtained than with other commercial ketone peroxides. Workable pot life of polyester resins catalyzed with it is considerably lengthened providing no selective accelerators are present. Exotherm measure­ments (S.P.I, procedure) at 180°F. using unsaturated polyester resins show that it combines long cure time with fast gel time. A lower peak exotherm temperature is obtained with LUCIDOL KETONE PER­OXIDE #6 with some resins than with any other ketone peroxide. LUCIDOL KETONE PEROXIDE # 6 should prove advantageous in applications involving molding, casting or potting where crazing is to be avoided. Write for Data Sheet

L U C I D O l DIVISION Wallace and Tlernan incorporated

Dept. 2 1 7 4 0 M I L I T A R Y R O A O B U F F A L O S, ISI.Y.

M A R C H 3 I, I 9 5 8 C & E N