US3120455A

US3120455A - Method for the removal of deposited crude maleic acid

Info

Publication number: US3120455A
Application number: US48843A
Authority: US
Inventors: Gans Manfred
Original assignee: Halcon International Inc
Current assignee: Halcon Research and Development Corp
Priority date: 1960-08-11
Filing date: 1960-08-11
Publication date: 1964-02-04
Anticipated expiration: 1981-02-04
Also published as: DE1443118A1; CH405279A; SE312795B; BE607012A; LU40491A1; ES269737A1

Description

United States Patent 3,129,455 METHUD FQR THE REMQVAL (3F DEPDSETED RUDE MALEIC ACID Manfred Gans, Leonia, Nd assignor to Halcon llnternatienai line, a corperation of Delaware No Drawing. Filed Aug. 11, 1950, Ser. No. 48,843 1 Claim. (Cl. 13430) This invention relates to the manufacture of maleic anhydride, including the dehydration of maleic acid by distillation in the presence of a water azeotroping agent to form maleic anhydride, and especially to such a process wherein the formed maleic anhydride is supersaturated with crude maleic acid which may include fumaric acid and resins and tars which tend to settle out and form a tenacious strongly adherent coating on steel equipment and the material is brought to or maintained at a temperature of at least 185 C. to render the crude maleic acid relatively non-adherent, and more particularly to such a process wherein a formed adherent solid deposit of the crude on the equipment is rendered relatively nonadherent by heating to a temperature to at least about 185 C. and then dispersed in a liquid such as water and removed.

Maleic anhydride is a commercially important material and it may be prepared by the catalytic partial oxidation of benzene or the like hydrocarbon in the presence of a catalyst such as vanadia or the like which may be supported on a carrier. The hot gaseous reaction mixture may be cooled to partially condense some of the maleic anhydride, and the remainder may be absorbed in Water to make maleic acid. The latter is converted to maleic anhydride by dehydration; e.g. by distillation in the presence of an azeotroping agent such as xylene or the like. The maleic anhydride obtained may contain some of the azeotroping agent and it may be stored for considerable time prior to further distillation to produce specification grade product. The maleic anhydride may be supersaturated with crude maleic acid which may include a large portion of fumaric acid together with some resins and tars and this may settle out to form a tenacious and ad herent solid deposit on or in the steel equipment used. Removal of this deposit is a major manufacturing problem, inasmuch as the solid is very tough and cannot be broken up easily. In addition, attempts to remove it by means of high pressure steam and water are extremely time consuming. Even the use of hot water alternated with hot aqueous caustic has been found to be ineffective for removal of the hard deposit formed in a storage tank.

The discoveries associated with the invention and relating to the solutions of the above problems, and the objects achieved in accordance with the invention as set forth herein include the provision of:

A process for rendering crude maleic acid non-adherent to steel which method comprises maintaining the steel at a temperature of at least 185 C. during contact thereof with a super-saturated solution or mixture of the crude acid in maleic anhydiide;

Such processes for removing a solid crude maleic acid deposit including heating the deposit to a temperature of at least about 185 C. and then dispersing it in water maintained at a temperature of about 100 C;

Such processes wherein the deposit has been precipitated onto steel equipment from a solution thereof in maleic anhydride;

Such processes wherein the deposit is submerged in liquid during the heating step;

Such processes wherein the liquid is predominantly maleic anhydride;

Such processes wherein the heating is at a temperature in the range of 185 C. to 200 C.;

And other objects which will be apparent as details or embodiments of the invention are set forth hereinafter.

In order to indicate still more fully the nature of the present invention, the following examples of typical procedures are set forth in which parts and percent mean part and percent by weight, respectively, unless otherwise indicated, it being understood that these examples are presented as illustrative only and are not intended to limit the scope of the invention.

Example 1 A benzene air mixture containing 1.21 mol percent of benzene is fed downward through a tubular reactor at a volume space velocity of 2500 per hour (volume of feed gas per volume of catalyst per hour), at a reaction temperature of 365 C. (using a modified vanadia catalyst as described in the Robert B. Egbert and Mitchell Becker Patent, 2,777,868, issued January 15, 1957).

The reactor tube may be of inch internal diameter and the catalyst bed height may be 10 ft. The tube may be surrounded by a temperature regulating medium such as molten salt, molten metal or a copper jacket.

The gaseous reaction mixture is passed through a partial condenser containing one or more vertical tubes of about one inch internal diameter and about 8 feet in length. The tubes are surrounded by a temperature regulating medium maintained at 53 to 58 C., e.g. circulating water. About one third of the maleic anhydride content of the gas is condensed and drains out as a liquid. The remainder of the gas is passed to a water scrubbing column or tower wherein it is contacted countercurrently with Water or aqueous maleic acid, so as to provide a 40 percent by weight aqueous maleic acid solution.

This solution is dehydrated in a column in the presence of xylene as an azeotroping agent (the distilled water being removed and the xylene being recirculated as reflux to the column). A crude maleic anhydride material is removed as bottoms, and may contain about 20 percent or more xylene.

If desired, a part of the bottoms from the distillation may be removed and passed to a cooling and settling tank, wherein it is subjected to a vacuum so as to flash a part of the xylene and more maleic anhydride (which is condensed and recycled) and the temperature of the mixture is lowered to about C. Solid crude maleic acid containing a substantial amount of fumaric acid settles out in such a treatment, and the supernated liquid may be decanted and recycled to the distillation column. This procedure is set forth more fully in co-pending application of Walter N. Alexander and Manfred Gans, entitled Chemical Process, Serial Number 44,687, filed on July 22, 1960, now abandoned.

The crude maleic anhydride material may contain up to about 50 percent xylene, and this material may be held in accumulation or storage tanks, and then subsequently refined or further distilled to make specification grade maleic anhydride. During the distillation, storage, and optional settling of crude acid, a tough adherent deposit may be formed. After accumulation of the deposit is substantial, the particular piece of equipment has to be removed or isolated from service and cleaned.

The invention is typified by the cleaning of a large horizontal cylindrical ordinary steel (or stainless steel) vessel used to store the crude maleic anhydride for a period of several days or weeks until the solid deposit therein occupies about 10-20 percent of the volume of the tank. The liquid is removed from the tank, and the residue is brought to a temperature of about C. using a heating coil supplied with steam at 350 p.s.i.g. pressure and having a condensation temperature of about 225 C. Then water is introduced into the tank (while heating of the coil is continued) so that the temperature in the tank is at about 100 C. The sticky hard solid deposit goes into dispersion or solution into the water rapidly with no agitation beyond that brought about by introducing the water and the inherent boiling thereof. Then the tank is drained, and may be washed with Water at about 100 C. As a result, the tank is cleaned in about two hours.

To remove the liquid before heating it may be drained or if the take-oil nozzles are plugged, a siphon may be used. Alternatively, the liquid is boiled out while heating the tank contents.

In a comparative run, except without preheating to about 190 C., repeated hot washes with Water at 100 C. do not remove the solid.

Example 2 The procedure of Example 1 is repeated, except that a series of steel pipes used to convey the crude maleic anhydride is maintained at a temperature of at least about 185 C. by means of a steam jacket supplied with 300 p.s.i.g. steam. These pipes show no fouling or formation of tough adherent solid deposits.

If flow of liquid is stopped for up to about ten hours, solid settles out, but it is removed promptly when flow is started up again.

In a comparative run, Example 2 is repeated except that the heating of the pipes is by means of copper tubing wrapped around the pipes and supplied with steam so as to maintain the pipe at a temperature of about 130 to 150 C. The pipes are gradually coated with tough adherent solids, and great difiiculty is experienced in removing these solids.

The preheating should be at a temperature of at least about 185 C. and about 200 C. is a practical upper limit, although higher temperatures may be used. The water is applied when the solid reaches this temperature, but a heating at this temperature for about thirty minutes before adding the water is preferred.

Any convenient heating means may be used, including a heating jacket or a heating coil (steam); of course, severe charring or coking is to be avoided.

The crude deposit is removed from steel (including the ordinary and stainless types) or other materials of construction used in chemical plants, which materials can Withstand the indicated temperatures.

The water azeotroping agent may be any such agent which is compatible in the system including xylene, toluene, and the like hydrocarbon, or halogenated or oxygenated hydrocarbon having equivalent solubility and distillation properties.

It is indeed surprising that crude maleic anhydride may be produced with high efiiciencies and that equipment in which it is stored can be cleaned rapidly and that the deposit of solids on walls of piping handling this crude can be avoided especially in view of experience with extremely troublesome deposits of crude maleic anhydride including fumaric acid, resins and tars in transmitting lines or storage tanks. 1

In view of the foregoing disclosures, variations and modifications thereof will be apparent to one skilled in the art and it is intended to include within the invention all such variations and modifications except as do not come within the scope of the appended claim.

What is claimed is:

A method of removing deposits containing maleic acid, fumaric acid, resins and tars from steel, said deposits being formed in the presence of a liquid containing maleic anhydride which comprises: separating said liquid from said deposits; heating said deposits to a temperature of at least 185 C. and thereafter dispersing said deposits by contact with Water at a temperature of about 100 C.

References Cited in the file of this patent UNITED STATES PATENTS 2,662,041 Dougherty et al Dec. 8, 1953 2,917,418 Cathcart Dec. 15, 1959 3,024,251 Feder et al Mar. 6, 1962 OTHER REFERENCES Handbook of Chemistry and Physics, 28 ed., 1944, Chemical Rubber Publishing Co., Cleveland, Ohio (pp. 868-869 relied on). (Copy in Sci. Library.)