US1986194A - Conducting chemical reactions in alkaline media - Google Patents

Description

i without decomposition.

Patented Jan. 1, 1935 i l .1Q9sa194" v CONDUCTING CHEMICAL REACTIONS IN "ALKALINE'MEDIAV'V' 1 John J. Gr'ebeflana John H. Rant, Midland, Mich'., assignors to The Dow Chemical Company, MidlamLt Mich, a corporation of Michigan No Drawing. Application March 6, 1930,

Serial No. 433,807. '2 Claims. -(Cl. 260-154);

ing chemical reactions in alkaline media at elevatedtemperatures and pressures, and has for a particular object the preventionof stoppages therein of a scale or incrustation ofcrystallized products such as magnetic iron oxide. Other objects will appear as the description proceeds.

An example of an organic chemical reaction of the aforesaid character is found in the well? known process for the manufacture of a phenol by hydrolyzing a'halogenated aromatic hydrocarbon wherein the latter is heated under pres-- sure with an aqueous caustic alkali solution.

"When chlorobenzene and caustic soda aregemployed for the specific reactants the reaction, is

carried out at a temperature between about 300- and 400 C., preferably between 3.50? and 390 C.

On account of the high pressure developed at] the reacting temperature, between 3000 and.

5000 pounds per square inch, the process is most advantageously carried out in a tubular type of autoclave comprising steel pipe coils. Thecaustic V alkali solution at the high temperature to which it is heated attacks the steel coils and dissolves iron from the exposed surfaces thereof. When the reaction mixture is cooled down prior to dis:

charge from the tubular system, the dissolved M 7 iron is precipitated out as magnetic iron oxide, F9304. This oxide forms as a hard, coherent scale or incrustation which builds up in the tubes, causing obstruction and eventual stoppage. This latter circumstance greatly shortens, 'the useful life of the tubes, necessitating fre-; quent repairs and renewals, and-also .gives rise to the dangerof blowouts whenever stQPDage occur s.

'We have of a colloidal material, such as soap, which is capable of withstanding the reaction conditions I r I U The invention, then, consists of the method hereinafter fully described and particularly pointed out in the claims, the following description setting forth but a few of the various ways in which the principle of the invention may be practiced. I

Under actual operating conditions for the manufacture of phenol by the foregoing process as found in plant practice, the tubular system consists of three sections or, zones, the first being the preheating zone, the second the reacting zone This invention relates to methods for conduct; 1

ing zone the mixture of caustic soda solution IIQW'1fOl1I1d. that, the building up of the aforesaid incrustation of magnetic ironoxide may be substantially completely prevented; by adding to the reaction mixture ;;a-, small amount and the third the cooling zone. In the preheati and chlorobenzene is, heatedupto about 350? C. whereat the reaction proceeds ata: suitable rate.

In this zone the alkali solution attacks the iron 5 surface-exposed thereto and dissolves off some i of the iron until the. solution becomes saturated therewith. Due to such continuous attack and been reduced to thelimit of saftey. .By utilizing j certain corrosion-resistant alloy steels, however, a -lon'ger life for the tubes .may be attained. Within the reaction zone the attack upon the steel-tubes almost ceases, owing to the solution having become substantially saturated with re-- spect to-the iron compound before arriving inthe latter-zone. Toward the end of the zone,"how-- ever, where the temperature begins to drop, there is a tendency for some of the dissolved iron compound .to be precipitated out and deposited upon the tube walls as a hard; adherent scale of magneticiron oxide, which gradually buildsup and constricts the'bore of thetube until its use must. be discontinued in order to avoid dangerof complete stoppage. vIt has been found that the tubes may beIused about 1000 hours in the lasthalf of the reaction zone before the condition just mentioned becomes such that replacement may be necessary. In the cooling zone, however, where the temperature of the hot, mixture is reduced from about 350 to? as low as 100 C. the deposition of iron oxide. scale occurs much more rapidly, at times necessitating replacement of the tubes. after as little as about 200 hours use. The. scale may be removed more or less completely from used tubes byrsuitable treatment, but this involves disassembling the aparatus and considerable expense is incurred in the handling. The tubes likewise deteriorate rapidly under such treatment, 'and can safely be refitted for service only .two-or three times, after which theymust be discarded; The necessity for frequentirew placement and renewal of tubes places a heavy burden of expense upon the process.

We have now found that the deposition of magnetic iron oxide scale in the tubes in the reacting and cooling zones may be substantially prevented by introducing into the reaction mixture a colloidal substance stable under the conditions existing in the process, which has the effect of inhibiting i grain growth of the precipitated iron oxide. The action of the colloid may consist simply in interv posing a film between the individual particles of precipitated iron oxide which prevents their cohesion or agglomeration into larger masses and the building up into a hard scale, or the colloid may serve as a dispersing or defiocculating agent to reduce the size of particles and prevent their coalescence. The result in either case is that the black iron oxide is precipitated in a highly dispersed form which is carried along by the stream of liquid in the tubes and is discharged from the apparatus admixed with the reaction product.

As a suitable colloid for introducing with the reaction mixture we have found soap to :be particularly effective, although other colloids and peptizers such as sodium tartrate, chromic oxide, saponin, tannin, glycerine or glucose, have also or vegetable fats, the alkali salts of thefatty acids, such as sodium oleate or sodium stearate,

with equal advantage. The .amount of soap or other colloid to be added is about 0.025 to 0.1 per cent of the solids present, althoughsomewhat more or less may be employed without materially changing the result- It is sufficient to provide" enough of the soapto mix with-the precipitated black iron oxide and prevent crystal growth','and.

in practice the amount above mentioned has been found ample;

without affecting the action of the soap.

.When'strong alkali'solutions, i.'e. about 30 to 40 per cent;, are employed,-however, there is an added advantage from using the soap; sincef at tinctly claim as ourinventiomsuch concentration some of the salt formed in the reaction is crystallized out and the crystals have been found to exert a scouring or eroding action on the tubes due to the high velocity of flowthferein. .In the presence of soap or similar colloid, however, crystal growth is impeded or inhibited just as withthe magnetic iron oxide, the size of the precipitated particles is kept small and a.

crystal sludge of soft consistency is formedwhich does not abrade the tube walls as greatly as the,

larger crystals otherwise formed. By means of the improved procedure hereinbefore described it is possible substantiallyto pre-- vent scaling and incrustation of the tubesin' the reacting and cooling zones so thattheir'life is increased almost indefinitely. The'savings' there by effected are of material consequence in a commercial process, since not only is the frequent renewal of tubes largely eliminated but also delays any interruption of process incident thereto. 1

The separation of the magnetic iron oxide sludge'from the reaction product maybe carried out by usual means, such as filtration, or bydistilling off volatile products whereupon the sludge remains in the still residue. V

While our invention has been described illustratively by reference to, the manufacture of phenol by reacting chlorobenzene and an aqueous Thecon'centration of the caustic 1 alkali solution may be'varied within wide limits steps stated by any of the following claims or the caustic soda solution, it is broadly applicable to similar processes for the manufacture of phenolic compounds by reaction of a hydrolyzable substituted derivative of an aromatic hydrocarbon, e. g. a halogenated or sulphonate d aromatic hydrocarbon, and an aqueous caustic alkali solution at an elevatedtemperature and pressure. The invention still further is adapted for use in any chemical process wherein an aqueous caustic alkali solution is heated under pressure in a tubular or other form of autoclave. While greater advantage attaches to the use thereof in operationscarried out in tubular apparatus, due to the greater readiness with which passages of relatively small bore may be obstructed or stopped up completely, there is also advantage when used withother types of pressure apparatus, the operation of which may be deleteriously affected by the accumulation on the Walls thereof of a hard,

equivalent of such stated step or steps be employed. 4 i

We therefore particularly point out and dis- ;1. In a method of preparing phenol by heating underpressure at a temperature between 300 and 400 C. in contact with surfaces of ferrous metal a reaction mixture comprising chlorobenzeneand aqueous sodium hydroxide solution, the

improvement which consists in adding to the.

said reaction'mixture a relatively small amount of a soap, whereby to preventthe'formation on thew'alls of" the reaction vessel of a hard adherent scale of magnetic iron oxide formed by chemical action between the aqueous alkali and the iron container for the said reaction mixture."

2. Ina method of preparing phenol by heating under pressure at a temperature of between 300 'and400" C.in contact with surfaces of ferrous metal a reaction mixture'comprising chlorobenzene-and, aqueous sodium hydroxide solution, the improvement which consists in adding to the said I reaction mixture up to 0.1 per cent of a soap,

whereby to prevent the formation on the walls or the reaction vessel of a hard adherent scale of magnetic'iron oxide formed by chemical action betweenthe aqueous caustic alkali and the iron containerfor the said reaction mixture.

. JOHN J. GREBE.

- JOHN H. REILLY.