US2361149A - Sulphur corrosion in cracking - Google Patents

Description

Oct 24, 1944 J. N. J. PERQUIN SULPHUR CRROSION IN CRACKING Filed March 25, 1945 lnvzn'or: Johannes N. J. -Perqul'n Patented Oct. 24, 1944 2,361,149 SULPHUR CORROSION IN CRACKIN G Johannes N. Jacobus Perquin,

Teddington, England, assigner to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application March 23, 1943, Serial No. 480,244

('Cl. 19e-1) 9 Claims.

, The present invention relates to a process for inhibiting corrosion. More particularly, it relates to a process for inhibiting the corrosion of metallic surfaces used in the construction of equipment wherein hydrocarbons containing hydrogen sulphide Contact said equipment at elevated temperatures.

It is well known that metallic surfaces such as furnace tubes corrode when they are contacted with hydrocarbons containing hydrogen sulphide at elevated temperatures, such as may occur, for example, in the cracking, reforming, etc. of hydrocarbons.

It is an object of the present invention to reduce corrosion of metallic surfaces in cracking, reforming, and other thermal processings of hydrocarbons. Another object is to reduce the corrosion of surfaces composed of ferrous metals which are contacted at relatively high temperatures with hydrocarbons containing hydrogen sulphide. A further object is to prevent hydrocarbons containing HzS from contacting metallic surfaces at critical corrodng temperatures which are described below.

This invention isv based upon the discovery that hydrogen sulphide in hydrocarbon fractions such as are derived, for example, from petroleum, exhibits a maximum degree of corrosion of ferrous metal surfaces at temperatures ranging from about 300 to 425 C., with the highest degree of corrosion at about 370 C. t

In processes in which it is desired to heat a hydrocarbon mixture containing HzS to temperatures above about 400 C., the method of this invention provides a mode for preventing hydrogen sulphide from contacting metallic surfaces at temperatures `Within this range of maximum corrosion and for times longenough to cause damage. To achieve this, the HzS-containing hydrocarbons are kept relatively cool, e. g. are heated to temperatures below this critical temperature range, and then are admixed rapidly with hydrocarbons poor in hydrogen sulphide having a temperature substantially above the critical temperature range to produce a mixture having a temperature above the critical range. In this manner, the hydrogen sulphide is heated so rapidly through the dangerous zone that it has no chance to come in contact with metallic surfaces for a time long enough to cause material corrosion.

The accompanying drawing is a flow diagram to illustrate the improvement of this invention, or it may be applied, for instance, to a cracking process. Referring to the drawing, a hydrogen sulphide-rich hydrocarbon feed which it is desired to treat at an elevated temperature is introduced into furnace I through valved line 2, line 3, valved line 4 and lim 5, at a temperature not exceeding about 325 C. and preferably not exceeding 300 C. This feed may, however, be preheated to just below these temperatures by passing through valved line 6, preheater I and valved line 8, around valved line '4, to join line 5. The preheater 'I may be heated in any suitable manner such, for example, by the flue gas from furnace I in its stack 9.

This hydrogen sulphide-rich feed upon introduction into furnace I is rapidly mixed at the junction I3 with a hydrogen sulphide-poor hydrocarbon feed in such an amount and having such temperature substantially in excess of 400 C. and preferably in excess of 425 C., so as to produce a mixture having a temperature above 400 C. and preferably above 425 C.-say, for example, a temperature of about 480 C. 'I'his hydrogen sulphide-poor feed may be introduced into furnace I through valved line I0 and line I I and pass through heater I2, wherein it is heated to a temperature substantially above 425 C. before reaching junction I3 in said furnace.

Mixing at junction I3 must be rapid, and it is therefore desirable that an effective mixing device be installed at this point. If the heating of the I-lzS-rich stream is very rapid, little or no corrosion will occur at junction I3. However, there is danger that some corrosion may occur at this onepoint, in which case it is desirable to use a metal, such as high chromium nickel steel, in the construction of this mixing device which is relatively resistant at sulphide corrosion.

The resulting heated mixture may then further be heated in coil I4 located in furnace I and withdrawn through `valved lines I5 and I 5 into a suitable reactor I'I wherein the proper time for the desired reaction-for whatever purpose it may be-is allowed to elapse. The residue of liquids and tars is withdrawn from the bottom of reactor I'I through cooler IB and line I9 and the reacted vapors are withdrawn from the `top of the reactor I1 through lines 20 and 2I wherein they are quenched at junction 22 by a suitable quenching fluid introduced through line 23 before passing on through line 24 to the fractionators and/or treaters. Alternatively the reactor I1 may be bypassed through valved line 25 directly to the quenching junction 22 with line 23. Also heater I4 may be by-passed through valved line 26 and the heated fluid passing through this line may proceed through reactor I1 or through the bypass 25 to the quenching junction 22.

The quenching fluid may consist of an inert cold gas, hydrocarbon liquid, Water or other inert liquid whereby the temperature of these vapors is reduced instantaneously from above the critical temperature range to below about 325 C. and preferably below about 300 C.

In a special modification, the I-IzS rich feed may be introduced through valved line 21 into fractionator 28 (which may be a fractional disbe applied to the treatment mixtures which it is desired to heat and which must be maintained for various lengths of time at elevated temperatures in contact with a ferrous metallic surf ace, which hydrocarbon mixtures contain H28 in amounts sufficient to cause corrosion underthese conditions. The HzS content of various hydrocarbon mixtures from petroleum is known to range between Wide limits, occasionally being as high as 5% or even higher, although in general it is below about .5%. However, it is particularly applicable to the treatment of hydrocarbons or mixtures thereof comprising components of relatively low boiling point, for example methane, ethane, propane, butane, isobutane, the pentanes, various gasoline distlllates and naphthas, etc., which are commonly derived from petroleums containing appreciable quantities of sulphun Processes in which such hydrocarbon mixtures are heated to above the critical corrosion temperatures com? prise thermal and catalytic cracking, reforming, high temperature alkylation, `isomerization, hydrogenation, hydroforming, hydroiining, isoforming, dehydrogenation, cyclization, etc.

By ferrous metal surfaces are meant those surfaces of any apparatus with which the hydrogen sulphide-containing hydrocarbons come in contact at elevated temperatures.

vary with the equipment under consideration but, in general, iron is the principal constituent, such as in steels of various hardness containing c arbon, and alloy steels containing molybdenum, chromium, nickel, aluminum, silicon, etc.

Since the rate of corrosion of equipment by hydrogen sulphide-containing hydrocarbons is a function of the concentration of hydrogen sulphide as Well as the temperature, itis impossible to `state precisely the maximum hydrogen sulphide content permissible in the HzS-poor feed. In general the lower its content the lower will be the rate of corrosion. Therefore it can only be said that the hydrogen sulphide content of this HzS-poor feed or fraction should not be greater than, or should be reduced to, the lowest practicable value. As a rule, it is desirable that the-HzS content be below about .2% and preferably below about .05%.

Although the present invention has been particularly described with reference to reducing the corrosion of heating elements, it is evident that it can be equally well applied to the protection The chemical composition of such apparatus and surfaces will from corrosion of blowers, heat exchangers, conduits, valves, reaction chambers, and the like; in short, any apparatus in which it is necessary to contact corrosive hydrocarbon mixtures containing hydrogen sulphide at elevated temperatures.

The following example represents an actual embodiment of this invention.

Example A propane-propylene fraction containing about 3% by volum'e hydrogen sulphide was admixed with a naphtha having a temperature of between about 10G-200 C. and the mixture was run through the tubes of a reforming furnace for a period of about four months, after which the furnace was shut down and the tubes were inspected. These tubes were made of a 4% to 6% chromium and .5% molybdenum steel. It was found that only those tubes were corroded which during operation were at temperatures between about 300 and 425 C. and a maximum corrosion was noticed in tubes which were at a temperature of about370o C. The corrosion decreased the wall thickness of these tubes as much as 4 mm. Those tubes which were above the temperature .of 425 C. were found to be substantially free from corrosion, as were those tubes at temperatures below 300 C.

In a later run the propane-propylene fraction containing the hydrogen sulphide was rapidly admixed with the naphtha after the naphtha had been heated to a temperature of 480 C. whereby a mixture was produced which had a temperature of about 430 C. This mixture was then further heated to a temperature of about 560 C. before being quenched. After about four months of such operation the furnace was again shut down and the tubes inspected and substantially no corrosion had occurred in any of them.

I claim as my invention:

1. In a process for treating a hydrocarbon containing hydrogen sulphide in a concentration sufficient to cause thermal corrosion to ferrous metals, wherein said hydrocarbon comes in contact with such a ferrous metal at a temperature above 425 C., the improvement comprising the steps of mixing an amount of said hydrocarbon having a temperature not exceeding 325 C. with an amount of a second hydrocarbon containing hydrogen sulphide in a concentration insufficient for thermal corrosion having a temperature substantially above 425 C., to produce a resulting mixture of hydrocarbons having a temperature substantially above 425 C., and contacting said hydrocarbons at a temperature substantially above 425 C. with said ferrous metal.

2. In a process for treating a hydrocarbon of f relatively high hydrogen sulphide content at elevated temperature wherein said hydrocarbon comes in contact with a ferrous metal surface, the improvement comprising the steps of mixing an amount of said hydrocarbon having a ternperature not exceeding 325 C. with an amount of a hydrocarbon of relatively low hydrogen sulphide content having a temperature substantially above 425 C., to produce a resulting mixture of hydrocarbons having a temperature substantially above 425 C., and contacting said hydrocarbons at a temperature substantially above 425 C. With said ferrous metal surface.

3. The process of claim 2 wherein said process for treating is a cracking process.

4. The process of claim 2 wherein the hydrogen sulphide content of the hydrocarbon of rela-l tively high hydrogen sulphide content is between about .2% and 5% by volume.

5. The process of claim 2 wherein the hydrogen sulphide content tively low hydrogen sulphide content is less than about .2% by volume.

6. In a process for treating a hydrocarbon of relatively high hydrogen sulphide content at elevated temperature wherein said hydrocarbon comes in contact with a ferrous metal surface, the improvement comprising the steps of mixing an amount of said hydrocarbon having a temperature not exceeding 300 C. with an amount of a hydrocarbon of relatively low hydrogen sulphide content having a temperature substantially above 425 C., to produce a resulting mixture of hydrocarbons having a temperature substantially above 425 C., and contacting said hydrocarbons at a temperature substantially above 425 C. With said ferrous metal surface.

'7. In a process for treating a hydrocarbon mixture containing hydrogen sulphide at elevated temperatures wherein said hydrocarbons come in contact with a ferrous metal surface, the improvement comprising separating from said mixture a rst fraction relatively rich in hydrogen sulphide and a second fraction relatively poor in hydrogen sulphide, mixing an amount of said rst fraction at a temperature not exceeding 325 C. with an amount of said second hydrocarbon fraction at a temperature substantially above of the hydrocarbon of relastantially above 425 425 C., to produce a resulting mixture of hydrocarbons having a temperature substantially in excess of 425 C., and contacting said hydrocarbons at a temperature substantially in excess of 425 C. with said ferrous metal surface.

8. In a process for treating a hydrocarbon of relatively high hydrogen sulphide content at an elevated temperature wherein said hydrocarbon comes in contact With a ferrous metal surface, the improvement comprising preheating said hydrocarbon to a temperature not exceeding 325 C., mixing said preheated hydrocarbon with an amount of hydrocarbon of relatively low hydrogen sulphide content having a temperature sub- C., to produce a resulting mixture of hydrocarbons having a temperature substantially above 425 C. and contacting said hydrocarbons at a temperature substantially above 425 C. with said ferrous metal surface.

9. A process for preventing corrosion of ferrous metals when contacted with hydrocarbons of relatively high hydrogen sulphide content at elevated temperatures comprising the steps of mixing an amount of said hydrocarbons having a temperature not exceeding 325 C. with an amount of hydrocarbons of relatively low hydrogen sulphide content having a temperature substantially above 425 C., to produce a resulting mixture of hydrocarbons having a. temperature substantially above 425 C.

JOHANNES N. JACOBUS PERQUIN.

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