US2249192A - Sulphuric acid concentration - Google Patents

Description

y 1941- N. TITLESTAD EI'AL 2,249,192

SULPHURIC ACID CONCENTRATION Filed Jan. 31, 1939 l4 CONCENTRAT'O F? DENITRATED H2504 65% AE'RATOR SUPERHEATED STEAM COOLER E :5 i g k i INVENTORS' /V/COA4V 7/72 F3740 BY 4 00/6 /V. fil-Zf/V, MA B Qfimm o M ATTORNEY.

Patented July 15, 1941 Nicolay Titlestarl, White Plains, N. Y. and Louis Nathan Allen, Jr., Nutley, N. J., assig'nors to Chemical Construction Corporation, New York, N. Y., a corporation of Delaware Application January 31, 1939, Serial No. 253,796 I In Great Britain March 18 1938 2 Claims. (01. 23-7307) 7 This invention relates to the concentration and decolorization of denitrated spent sulphuric acid, for example the sulphuric acid remaining after driving off the nitric acid content from the spent or waste acid from the manufacture of nitrocellulose or of nitroglycerine in munitions plants. Such acid, as obtained from the denitrating towers, is usually of 65-70% concentration and contains appreciable quantities of dark organic compounds which are derived from the nitration process.

Heretofore this acid has been concentrated by boiling it in cast iron pots over an open flame to a final concentration of from 93-96%. In this way the dark organic compounds are broken down and the acid becomes very light in color, but the process is expensive and wasteful as the pots break very frequently and large charges of acid are lost. The fuel consumption is also extremely high because the heat transfer is limited to the surface exposed to the flame and the transfer coefiicient is low.

Wehave attempted to concentrate the spent acid by passing hot gases through it which has the advantage of reducing the boiling temperature of the acid due to the reduced vapor pressure caused by the passage of the hot gases. We found, however, that while this method of treatment would concentrate the acid satisfactorily, it would not decolorize it because this reduced boiling temperature is then toolow. We then found that superheated steam, either when used alone or in admixture with other hot gases, will decolorize the dark concentrated acid produced by concentrating denitrated spent acid to approximately the proper strength either by means of hot gases or in a vacuum concentrator or by other methods in which the concentration is effected at a temperature at or below the normal boiling point (i. e. the boiling point under atmospheric pressure) of the acid. Our invention consists, therefore, in concentrating denitrated spent acid with hot gases or otherwise and thereupon blowing superheated steam into it, either alone or in admixture with other hot gases. Satisfactory results have been obtained by the following methods: ,g

(a) Blowing superheated steam into the liquid whereby the steam is condensed and enters into the acid partly diluting it and raising its temperature to the boiling point by virtue of the heat evolved during dilution together with the latent heat of condensation; J

(b) 'Blow'ing superheated steam intothe liquid, condensing the steam and raising the temperature to somewhat below the boiling point, thereby diluting the acid correspondingly.

.(c)' Blowing an excess of superheated steam into the liquid, condensing part of the steam. The uncondensed part is removed and temperature is raised to the boiling point, with corresponding dilution of the acid;

d) Blowing an excess of superheated steam and hot combustion gases into the liquid, condensing part of the steam. The uncondensed 'part is removed and the temperature is raised to below the boiling point without diluting the acid.

(6) Blowing an excess of superheatedrsteam into the liquid without condensing any of the steam and raising the acid to the boiling point or slightly below, with or without concentrating the acid further.

A particularly effective method and apparatus constituting a specific feature of the invention is illustrated in the "accompanying drawing, in

which the single'figure is a diagrammatic illustration of the furnace, concentrators and piping system for'accomplishing the concentration and decoloriz'ation.

In this drawing the apparatus consists generally of, the combination of a furnace I, which may be of any known or approvied type, a concentrator 2 of the Mast type such as is described in Reissue Patent No. 19,064 and a decolorizer 3 together with an aerator or concentrator 4 for cooling'and further concentrating the decoloriaed acid obtained in the decolorizer 3.

In the modification shown the furnace l is of the oil or'powdered coal burning type, which is especially well suited for the generation and/or superheating of steam and the production of hot gases in accordance with the present invention. This furnace is equipped with a burner 5 having a fuel supply line 6, and an air supply line I, the latter being connected to an air blower 8. The furnace is divided by a baiile I0 into a fire box '9, which may contain water tubes in the usual manner for generating steam, and a dilution chamber ll for diluting the stack gases to suitable temperatures for use in acid concentration.

In addition to thesteam generating equipment,

which'is not shown, the fire box 9 also contains steam superheating coils or tubes which are 11-- lustrated diagrammatically by the steam tube 12, and it is understood that these coils are connected directly with the steam generating equipment if this is also contained in the boiler. 'on the other hand, steam such as waste steam from any suitable outside source may be introduced to the coils [2, as through an inlet pipe l3, and it is operates.

understood that the invention is not limited in this respect.

As has been stated, the acid concentrator 2 is of a known type, and need not be described in detail. It consists generally of a plurality of drums or concentrating chambers I4 and I5 in which the acid to be concentrated is passed in countercurrent contact with hot products of combustion from the furnace I which are admitted through pipes I6 and I1. nitrated sulphuric acid of about 65% strength is fed to the drum or concentrating chamber I4 by inlet pipe and is heated and Partially concentrated by the gases entering through the pipe I6 which then leave through gas outlet pipe I9. The partially concentrated acid then overflows through the outlet 2| into the second drum or concentrating chamber I5 Where it is further concentrated by a second flow of hot gases entering through pipe I'I. Although the acid concentrator is shown as consisting of only two drums or concentrating chambers, it is understood that further stages of concentration may be employed if desired, the chief requisite being that the acid is finally brought to the desired concentration, such as 94-96% strength.

The decolo-rizing chamber 3 which in operation constitutes a principal feature of the invention is preferably similar in form and construction to one of the concentrating drums or chambers I4 and I5 and is made of acid-proof material adapted to withstand the high temperatures at which it In the modification shown it consists of a rectangular or cylindrical chamber provided with a steam inlet pipe 26 extending nearly to the bottom thereof and also preferably provided with an outlet pipe 21 for excess'steam. A liquid outlet 28 in the form of a pipe or channel is located at one side of the decolorizing chamber 3 at such a level as to" maintain therein a body of acid of substantial depth, thus retaining the acid within the chamber for a substantial period of time when the apparatus is in continuous operation. The volume of acid so retained in the chamber 3 is adjusted to the speed of decolorization by the superheated steam so that the'acid' is bleached as fast as it is concentrated in the concentrator 2.

As has been pointed out above the process of our invention may be operated with or Without a partial condensation of steam and consequent dilution of the acid in the decolorizer 3. In all cases, however, the acid leaving the chamber 25 is very hot and its high heat content may be used for purposes of further concentration by blowing Spent de-" air or other inert gases through it. For the accomplishment of this purpose the decolorizer 3 is directly connected with an aerator or concentrator 4, which consists of a chamber 30 preferabl similar in shape and construction to the chamber 25, but having an air inlet pipe 3| extending below the level of the acid therein. Decolorized acid enters this chamber through the pipe 28 and is maintained as a body of substantial depth by the location of an outlet pipe 32 which is provided at a suitable elevation in the side wall thereof. Decolorized and concentrated acid leaving the chamber 30 through this pipe is passed steam into a hot body of the acid. The necessity for this step arises from the fact that the concentration temperatures in a drum type concentrator such as the concentrator 2 are below those at which the organic colorizing impurities are decomposed or removed. Nitrating acid derived from the manufacture of nitrocellulose or nitroglycerine in munition plants contains or= ganic impurities of this nature which remain in the sulphuric acid after it is denitrated and result in a dark colored product when concentration is accomplished by the use of hot gases alone.

'Spent alcohol acid recovered as a by-product from the production of secondary alcohols by the absorption of olefins in sulphuric acid and subsequent hydrolysis also presents a similar problem, as it contains organic impurities which darken the acid when it is concentrated at low temperatures.

Accordingly, it will be seen that the process of our invention retains all the advantages accompanying the use of hot gases in concentrating dilute sulphuric acid containing organic impurities and simply adds the additional decolorizing step of blowing superheated steam into the acid. It is an additional important advantage of the invention that this steam can be superheated and/or generated in the same equipment that is ordinarily used for generating the hot gases used in concentrating, and therefore the fuel consumptionof the process is not materially altered. In fact, we have found that spent denitrating acid may be concentrated and decolorized to a strength and color suitable for reuse with an expenditure of fuel only 5% greater than that used in the concentrators alone. In other words, the

present invention provides light colored acid at a fuel cost of only 5% greater than that required for the production of dark colored concentrated acid, and with very little additional capital expenditure for equipment.

The process of our invention will be illustrated as being carried out in the apparatus which has been described, but it should be understood that in its broader aspects it is not limited thereto. On the contrary, it is understood that the substitution of alternative and equivalent steps may be resorted to within the scope of the claims appended hereto. Hot combustion gases produced in the furnace I by the burning of a fuel such as 'oil, gas or powdered coal are passed over the super-heating steam coils I2, and may then be passed over steam generating tubes in theusual manner if desired. The combustion gases then enter the chamber II where they are diluted with air from the blower 8 introduced through the branch pipe 35 in the air line 3|.

Sufiicient air is added from this source to cool the combustion gases to about 1100 F., and they pass at this temperature through the pipe I6 and through branch pipe I! into the concentrating drums or chambers I4 and I5 where they serve to concentrate spent denitrated sulphuric acid of about 65% strength introduced through the feed line 20 in the usual manner. In a, preferred method of operation the acid in the first concentrating drum or chamber I4 is held at -85% strength and the acid in the concentrating drum or chamber- I 5 is heldat 94-96% strength. The hot gases passing through these bodies-of acid evaporate water-therefrom, but atternperatures too low to decompose the impurities which they contain. Thus, for example, the acid in chamber. I5 is concentrated to 94-96% at a temperature of about 440- F., and therefore leaves this chamber as a dark colored concentrated acid which requires decolorization before it is suitable for reuse.

The dark colored acid leaving the concentrator 2 is preferably continuously introduced into the decolorizer 3 through a connecting pipe 36, at a temperature of 440-450" F. In the decolorizer it is maintained as a body of substantial depth and volume while steam which has been superheated in the coil i 2 to temperatures of about 1000 F. is passed into it through pipe 26. The temperature of the acid is thereby raised to about 520-530 FL, partly by taking up sensible heat from the steam and partly by the heat of dilution resulting from condensation of steam. At these temperatures the color forming impurities in the acid are rapidly decomposed. The size of the chamber 25 and the depth of acid therein are such that the acid is held for a sufficient length of time to remove substantially all of its colored and color forming impurities, after which it is discharged into the chamber 30 through the pipe 28 as a decolorized acid of 92-93% strength.

As has been pointed out above, it is not always necessary to condense a part of the steam into the acid. On the contrary, an excess of superheated steam may be blown through it without condensing any of the steam, and the acid is heated to temperatures near its boiling point simply by the sensible heat, or superheat, contained in the steam. In this way superheated steam at a temperature of 1000-1200" F. or more may be used to both decolorize and concentrate the acid. It is also possible, as is pointed out above, to employ a mixture of superheated steam and hot combustion gases in this stage of the process, in which case a further concentration of the acid maybe obtained in the chamber 25. It will be noted that when a mixture of hot gases and superheated steam is used the presence of the steam serves to ofiset the temperature reducing action of the 30. Acid from the chamber 25 is preferably continuously introduced into this chamber through the inlet pipe 28 and air from the blower 8 is passed through it by way of the pipe 3|. Since the acid enters at the extremely high temperatures of 5204530? F., its sensible heat content is suflicient to provide the heat necessary for vaporizing its excess content of water, and the acid is therefore concentrated by the passage of air through it to a concentration of about 93-94%. At the same time, the air stream also serves to cool the acid and to further bleach it by carrying away any volatile colored impurities which it may contain. The same result may be accomplished by using a vacuum evaporator at this details given above, which are primarily for pur-v poses of illustration.

What we claim is:

1. In a process of decolorizing dilute impure sulphuric acid containing organic coloringrimpurities in which the diulte acid is heated to concentrate and decolorize the same, the improve ment which comprises, concentrating the dilute acid to about 94-86% strengthby heating it to' temperatures which are below the normal boiling point, and thereupon blowing superheatedsteam into the hot concentrated acid to raise the acid temperature to about the normalboiling point to decolorize the acid, part of the superheated steam being condensed in and diluting the acid, and thereafter reconcentrating and cooling the hot decolorized acid by blowing cool air therethrough.

2. In a process of decolorizing dilute impure sulphuric acid containing organic coloring impurities in which the dilute acid is heated to concentrate and decolorize the same, the improvement which comprises, concentrating the dilute acid to about 94-96% strength .by the introduction of hot combustion gases thereinto, and

thereupon blowing super-heated steam into the hot concentrated acid to raise the acid temperature to at least about the normal boiling point to decolorize the acid.

NICOLAY TITLESTAD. IJOUIS NATHAN ALLEN, JR.

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