US2598449A

US2598449A - Purification of naphthalene

Info

Publication number: US2598449A
Application number: US42036A
Authority: US
Inventors: Scott Roland; Eric H Joscelyne
Original assignee: Midland Tar Distillers Ltd
Current assignee: Midland Tar Distillers Ltd
Priority date: 1947-08-13
Filing date: 1948-08-02
Publication date: 1952-05-27
Anticipated expiration: 1969-05-27
Also published as: NL70551C; FR970090A; GB630397A

Description

May 27, 1 R. SCOTT ET AL PURIFICATION OF NAPHTHALENE Filed Aug. 2, 1948 6 Z a x m a w m 5 W (m MW w M ow Q W Q 1 r l l l L l l lH (A. HI I I I I I l h h l H h O\ i rney Patented May 27, 1952 PURIFICATION OF NAPHTHALEN E Roland Scott and Eric H. J oscelyne, Oldbury,

Birmingham, England, assignors to The Midland Tar Distillers Limited, flldbury, Birmingham, England, a British company Application August 2, 1948, Serial No. 42,036 In Great Britain August 13, 1947 4 Claims.

This invention relates to the crystallisation of chemical compounds from liquid form and to apparatus for use in such crystallisation.

An object of this invention is to provide an improved process for crystallising chemical compounds from liquid form without allowing a mass of crystals to form by caking.

Another object is to obtain technically pure crystals from impure materials in an improved manner.

A further object is to improve the production of technically pure naphthalene from crude naphthalene.

Yet another object is to provide an improved combination of apparatus for use in crystallising and purifying chemical compounds.

Broadly stated, in the process of the present invention the liquid compound from which crystals are to be formed is introduced into a stream of liquid in which the desired crystals are either insoluble or have low solubility and which is at a temperature low enough to cause crystals to form; this liquid may conveniently be described as the precipitating liquid. The crystals and the precipitating liquid flow together while the crystals grow and then the crystals are conveyed upwards out of the liquid and while being so conveyed are washed by a downwardly flowing stream of the same (or precipitating) liquid. This stream of liquid serves to wash the crystals, and on arriving at the point at which the crystals are taken out of the first stream it meets and moves with the latter and the two streams are removed together as a common stream.

The apparatus we use consists of the combination of a crystallising apparatus and a washing apparatus. The crystallising apparatus comprises a tube or trough containing a conveyor, and the washing apparatus comprises an upwardly inclined conveyor screw or the equivalent. These two pieces of apparatus are united by a common chamber in which the two liquid streams mix and which is furnished with an outlet for the removal of the mixture as a common stream.

The invention is particularly applicable to processes in which crude naphthalene is simultaneously crystallised and purified by introduction into a precipitating liquid which is a solvent for the impurities in the crude naphthalene and which may advantageously be methyl alcohol, as described in our application Serial No. 8,298, dated 13th February, 1948, now abandoned. We have found that on introducing naphthalene at a temperature in the order of 100 G. into cold methyl alcohol at, say, room temperature, shock cooling takes place and many very small crystals are produced. These crystals tend to become caked into" a solid mass and this caking is prevented by means of the invention because the crystals are immediately engaged by the conveyor in the crystallising apparatus and carried along and in contact with the methyl alcohol. While they are so carried they tend to grow, i. e. naphthalene not crystallised upon immediate contact with the methyl alcohol crystallises out on to the crystals already formed. This growth may advantageously be controlled by appropriate cooling of the crystallising apparatus, the temperature being maintained at about 35 to C'. at the inlet and being reduced from the inlet to the outlet end, where it may be about 16 C. The growth of the crystals is advantageous because we have found that if they are tobe successfully washed clean of adherent impurities they should be relatively large, say, notless than two millimetres along their sides. Moreover, the crystals must grow to about this size if they are to be carried upwards by the conveyor screw of the washing apparatus instead of slipping backwards along the screw. The higher the temperature of the methyl alcohol at the inlet end of the crystallising apparatus, the greater is the crystal growth, and far more saisfactory results are obtained when this temperature is in the order of 35 to 40 C. than when it is only 20 0. Moreover, the larger crystals emerge from the washing apparatus in a dryer state.

An apparatus suitable for use in such a process is shown in the accompanying diagrammatic drawing. This apparatus consists essentially of a crystallising apparatus l and a washing apparatus 2 united by a common chamber 3 The crystallising apparatus l consists of a tube 4 with an inlet 5 for crude naphthalene and an inlet 6 for methyl alcohol and its outlet end delivers into the chamber 3. A conveyor consisting of a shaft 1 with a helical blade 8 is mounted in bearings 9 and H1 at the two ends of the tube 4 and in operation is driven slowly, say at the rate of ten revolutions per minute, by an electric motor II.

The washing apparatus 2 consists of a tube 12 in which a conveyor screw 13 works, being driven by an electric motor [4. The tube l2 has an inlet l5 through which a washing stream of methyl alcohol is introduced and at the top an outlet I 6 through which the crystals conveyed upwards by the screw l3 are discharged to fall under gravity into any suitable container or on to a conveyor.

The chamber 3 has an outlet ll through which the two streams of methyl alcohol which meet in the chamber are removed as a common stream. The height of this outlet determines the level of the liquid in the tube 4.

The tube 4 is surrounded by a jacket 18 into which water for cooling purposes is introduced through an inlet l9, leaving by way of an outlet 20.

It will be seen that the methyl alcohol is introduced into the washing apparatus at a point well below the upper end of the conveyor screw 13 so that the latter carries the crystals out of the liquid and thus some at least of the liquid adherent to them drains away while they are still in the washing apparatus.

If the draining is inadequate the crystals may be passed towards a drying chamber, being maintained at a temperature low enoughon the one hand to prevent any distillation or sublimation of the crystals, but high enough on the other hand to bring about evaporation of the entrained liquid. The conveying apparatus in the drying chamber may comprise agitators which serve to turn the mass of crystals over so as to present as large an area as possible to the atmosphere inside the chamber.

In order to save fresh methyl alcohol, some of the impure stream removed through the outlet I! may be mixed with fresh methyl alcohol introduced into the inlet 6.

It will be understood that in simultaneously crystallising and purifying any other chemical a suitable precipitating liquid which is also a solvent for the impurities is chosen.

We claim:

1. A continuous process for purifying crude naphthalene comprising continuously introducing crude molten naphthalene into a flowing stream of precipitating liquid in which naphthalene is of low solubility and which is also a solvent for the impurities and is at a temperature of the order of 20-40 C. to cause naphthalene crystals to form at once, causing the mixture to flow a sufficient distance to allow the crystals to increase in size to not less than 2 millimeters and at the same time preventing agglomeration of the crystals by agitating the flowing mixture, separating the crystals from said mixture by conveying said crystals upwardly out of said mixture, washing said crystals being so conveyed with a downwardly flowing stream of the same liquid, directing said downwardly flowing stream into the liquid stream from which said crystals are upwardly conveyed to mix therewith, and removing the resultant mixed stream.

2. A process as claimed in claim 1 in which the temperature of said first mentioned mixture is reduced asthe flow proceeds.

3. A process as claimed in claim 1 in which the temperature of said first mentioned mixture is maintained at about 35 to 40 C. at a point of formation thereof and progressively reduced to about 16 C. at the point of separation of said crystals and said liquid.

4. A process as claimed in claim 1 and in which the precipitating liquid is methyl alcohol.

ROLAND SCOTT. ERIC H. JOSCELYNE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 848,484 Newnham Mar. 26, 1907 1,081,949 duPont Dec. 23, 1913 1,810,217 Lohmann June 16, 1931 1,906,534 Burke May 2, 1933 2,163,581 Boyd, Jr June 2'7, 1939 2,207,752 Miller July 16, 1940 FOREIGN PATENTS Number Country Date 260,129 Great Britain Oct. 28, 1926

Claims

1. A CONTINUOUS PROCESS FOR PURIFYING CRUDE NAPHTHALENE COMPRISING CONTINUOUSLY INTRODUCING CRUDE MOLTEN NAPHTHALENE INTO A FLOWING STREAM OF PRECIPITATING LIQUID IN WHICH NAPHTHALENE IS OF LOW SOLUBILITY AND WHICH IS ALSO A SOLVENT FOR THE IMPURITIES AND IS AT A TEMPERATURE OF THE ORDER OF 20-40* C. TO CAUSE NAPHTHALENE CRYSTALS TO FORM AT ONCE, CAUSING NAPHTHALENE FLOW A SUFFICIENT DISTANCE TO ALLOW THE CRYSTALS TO INCREASE IN SIZE TO NOT LESS THAN 2 MILLIMETERS AND AT THE SAME TIME PREVENTING AGGOLMERATION OF THE CRYSTALS BY AGITATING THE FLOWING MIXTURE, SEPARATING THE CRYSTALS FROM SAID MIXTURE BY CONVEYING SAID CRYSTALS UPWARDLY OUT OF SAID MIXTURE, WASHING SAID CRYSTALS BEING SO CONVEYED WITH A DOWNWARDLY FLOWING STREAM OF THE SAME LIQUID, DIRECTING SAID DOWNWARDLY FLOWING STREAM INTO THE LIQUID STREAM FROM WHICH SAID CRYSTALS ARE UPWARDLY CONVEYED TO MIX THEREWITH, AND REMOVING THE RESULTANT MIXED STREAM.