US2417351A - Hydrofluoric acid resistant packing material - Google Patents

Description

March 11, 1947. J, D. CovlNGTQN 2,417,351

HYDROFLUORIG ACID RESISTANT PACKING MATERIAL Filed July 7, 1944 TMHMM ENQ@ NSU @su ZQNRU NN@ Patented Mar. 11, 1947 HYDROFLUORIC ACID RESISTANT PACKING MATERIAL James D. Covington, Dallas, Tex., assignor, by mesne assignments, to Socony-Vacuum Oil Company, Incorporated, New York, N. Y., a corporation of New York Application July 7, 1944, Serial No. 543,855

2 Claims.

This invention relates to packing materials, and particularly to packing materials employed in the control units of systems or processes utilizing hydrouoric acid, particularly to processes for the condensation of hydrocarbons, such as the alkylation f isoparaffins with olens, the polymerization of olens, the alkylation of aromatic hydrocarbons with olefins and the like.

-A typical application of my invention is its use in a commercial alkylation process, 'such as the alkylation of isoparaflins such as isobutane with oleiins such as the butenes. The invention will be illustrated as applied to an alkylation process of this type. It is to be understood, however, that the principles of my invention are applicable to any process or system wherein essentially anhydrous hydrogen iiuoride is utilized as a catalyst or other treating agent and/or wherein control of the flow of this acid or its agitation are required.

Hydrouoric acid exerts a strong corrosive action on many 0f the materials normally used in the construction of reiinery equipment. Also, the acid is highly toxic and is therefore a potentially hazardous chemical. For these reasons the use of hydrouoric acid asl an alkylation catalyst has introduced new problems in design, construction and operation of refinery equipment.

A particularly troublesome problem encountered in HF alkylation plants has been the frequent occurrence of leaks in circulating pumps and control valves and the like through which hydrofluoric acid, or mixtures of hydrofluoric acid and hydrocarbonsare conducted in the process. These leaks are caused mainly by deterioration of the packing used in these units due to the action of the hydroiiuoric acid, although infrequently, corrosion of the metal parts of such units, after prolonged exposure to the acid, is a contributing factor. These leaks are not only troublesome from an operational standpoint but they constitute a serious hazard to personnel because of the high toxicity of the acid.

It is an object of my invention to provide a novel compacted packing and lubricating material for use in flow control units, such as pumps, valves and the like which are employed in systems carrying hydrofluoric acid, said packing material being highly resistant to the action of hydrouoric acid. whereby the occurrence of costly and hazardous leaks, due to packing failure in such control units is substantially minimized.

I have discovered that when units such as pumps and valves, which handle hydroiiuoric acid or mixtures containing hydrouoric acid such as in the alkylation of isobutane with butenes,

are packed with a packing material comprising talc instead of the conventional packing materials the operating period during which no leakage will occur in such units is greatly increased.

In order that a full understanding of the invention and the advantages to be derived from its use may be had, reference is made to the accompanying drawing which is a iiow diagram of a conventional process for producing alkylated hydrocarbons from isobutanes and butenes utiliz- 'ing hydrogen fluoride as a catalyst.

In the drawing there is shown a reaction circuit I into which butene feed stock is admitted through line 2 -tted with valve 3. isobutane feed stock is fed to the reaction circuit through line 4 fitted with valve 5. Essentially anhydrous hydrouoric acid catalyst is delivered to the reaction circuit through line 6 provided with valve I by way of line 8. A circulating pump II) cir` culates the reactants and the hydrofluoric acid continuously around the reaction circuit. A cooler II is provided in order to maintain the reactants at the desired reaction temperature. The reactants may be by-passed through the cooler II in any desired proportion by means of ow regulation valve I2. Material is continuously withdrawn from the circulating mixture through line I3 provided with valve I4 to separator I5 where gravity separation of hydrofluoric acid from reacted and unreacted hydrocarbons occurs, forming an acid phase and a hydrocarbon phase. The heavier acid phase settles to the bottom of the separator I5 and is withdrawn through line 8 provided with valve I6 and recycled to reaction circuit I by means of a pump 20. The hydrocarbon phase is withdrawn from the top of separator I5 through line 2|' provided with valve 22 and passed to fractionating column 23 provided with reboiler 2li.v Small amounts of hydrouoric acid carried over in the eiliuent stream from the separator I5 may be removed from the process at this point by treatment in a suitable alkaline absorber or by means of a hydroiiuoric acid stripper (not shown). Liquid alkylate product is withdrawn from the bottom of fractionator 23 through line 25 fitted with valve 26 while the lighter components of the reacted mixture, comprising unreacted isobutane with small amounts of n-butane and lighter gases such as propane, ethane, etc., formed in the reaction circuit are taken o overhead in line 21. In line 21 the isobutane and normal butane-containing fraction is conducted to fractionator 28 in which the isobutane is separated and recycled to reaction circuit I by way of line 29 provided with compresser 30, cooler 3| and valve 32. Normal butane is withdrawn from fractionator 28 in line 33 fitted with valve 34, while the gases lighter than isobutane are vented through line 35.

In the operation of the hydrofluoric acid'alkylation process just described trouble has been encountered due to the frequent occurrence of `leaks in the hydrofluoric acid recycle stream pump 20 and in the circulating pump i0. Leaks were also encountered, though they were less frequent, in control valves 1, I4' and I6. All of these leaks were the result of deterioration of the conven` tional packing used in these units. The life of the packing material in the circulating pumps under conditions of continuous operation was only a few hours on the average and rarely exceeded a day after which time leakage occurred and repacking was necessary. However, when in accordance with my invention a packing composition comprising talcumpowder was employed in these umts leakage was prevented for periods' as long as from 3 to 5 weeks. under conditions of continuous operation. This represents about a thirtyfold increase in the length of the packing life. The fact that talc is so eiective for this purpose is surprising since it is essentially a silicious material (MgO.4SiO2.H2O) and there` fore would be expected to be attacked readily by hydrofluoric acid. Whether a reaction does occur between the talc and the hydrogen uoride to produce a substance which affords the talc its eectiveness as a packing in the presence of hydrogen fluoride is not known to me, the evident fact being. that'it is so eiective.

In order to reduce friction and a'ord a lubricating quality to the talc, I generally mix the talc with ilake graphite. I have found that best results are obtained by using a mi-xture of talc and graphite containing from about to about 25l percent by weight of graphite although mixtures containing as high as 50 percent may be employed.

Though I have described and illustrated my in-` vention in connectionwith an alkylation process, it should be understood that the principle of the invention is equally applicable to other hydrofluoric acid processes or to systems carrying hydrouoric acid or mixtures thereof in which circulating pumps, agitators and stirrers having packed shafts, bearings, etc., are exposed to hydrogen fluoride.

pacted packing and lubricating mass consisting of an intimate mixture of talc and ilake graphite,

said mass characterized by being highly resistant to the action of hydrogen uoride and the talc being present in an amount from about "I5k to about 90 per cent of the total weight of the mixture.

2. As a new article of manufacture a compacted packing and lubricating mass characterized by being highly resistant to the action of hydrogen fluoride consisting of an intimate mixture of talc and flake graphite in which the talc comprises from to about,90% by weight of the mixture.

JAMES D. COVINGTON.

REFERENCESy CITED The following references are of record in the le of this patent:

UNITED' sTATEs PATENTS Number Name Date 1,409,276 Benjamin Mar.- 14, 1922- 1,363,563 Calts Dec. 28, 1920 2,322,800 Frey June 29, 1943 2,363,597 Jones Nov. 28, 1944 2,357,753 Matuszak Sept. 5, 1944 FOREIGN PATENTS Number Country- Date 325,566 British Feb. 14, 1930 OTHER REFERENCES National Pet. News, Tech. Soc., June 2, 1943,

(Patent Office Library.) National Pet. News, Tech. Soc., Mar. 1, 1944,

Vpp. R-146, R-148, R-150, R-151, Elf-1.54, R455.

Chem. Abs., v01. 26, page 446.1, Aug. 2o, 1932, 252-29. (Copy in Div. 64.)

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