US2394750A - Execution of catalytic conversions in the presence of ferrous metals - Google Patents

Description

Patented Feb. 12,- 1946 EXECUTION F CATALYTIC CONVEBSIONS IN THE PRESENCE QF FERBOUS METALS Robert M. Cole and Irving 1. Shultx, Long Calif., assignors to Shell Development Beach, Company, San Franclsco CaliL, a corporation of Delaware No I The present invention relates to the catalytic conversion of organic materials in the vapor phase at elevated temperatures in the presence of ferrous metals. A particular aspect of the invention relates to the treatment of hydrocarbon vapors at elevated temperatures, 1. e. from about 7 500 F. tq 1300' F., with dehydrogenation catalysts such, in particular, as those comprising an oxide of titanium, vanadium, chromium, man- 'sanese, molybdenum or tungsten, which arenormally substantially free of iron and which are ,subject to poisoning by iron.

As is well known, ,one of the most common and practical methods for executing .-"catalytic conversions of organic \materials in the vapor phase is to provide a porous bed of catalyst in a suit-' able reaction tube, converter, crcatalyst case,

' and (to pass the vapors of the carbonaceous reactant therethrough under appropriate conditions of temperature, pressure, etc. -In most cases when treating carbonaceous materials at temperatures in the order of 500 F. to 1300" F., the catalyst gradually loses its activity due to the deposition thereon of carbonaceous materials. This deactivation of the catalyst is temporary and Application Much as, 1042, sci-mm. 436,618

11 Claims. (01. zso-ssasi f versions are often executedunder pressure,

and since furthermore they generally require the introductlon or withdrawal of-considerable quantitles of heat to or from the reaction zone, usually 2 through the confining walls, it is usually impractical in these processes to employ apparatusconstructed of or lined with non-ferrous materials, such as silica, ceramic materials and the like,;

and the use of iron, steel or ferrous alloy equipment is practically unavoidable.

The industry has searched diligently for some practical method whereby the transfer of iron to these catalysts could be avoided, while at the same time using apparatus fabricated from ferrous metals. It has, for example, been proposed to employ apparatus plated with chromium, aluminum, copper, etc; Such apparatus sometimes may be indefinitely counteracted by periodically burning oil the deposited materials in situ. Catalysts usedin such processes, wherein they are periodically regenerated by burning carbonaceous deposits therefrom, are hereinafter referred to as regenerative catalysts.

Many of the most eflective catalysts for these various conversions are susceptible to poisoning by iron. These various catalysts, when used for the vapor phase conversion of organic materials at elevated temperatures in the presence of iron,

steel or ferrous alloys, besides undergoing the above-mentionedfltemporary deactivation due to an accumulation of carbon and tarry deposits,

undergo a permanent deactivation due to the accumulation of iron or iron compounds formed by works well for a short time. It is found, however, that these various linings invariably have minute pinholes or become scratched by the catalyst and after a short period of operation the under metal is attacked through these imperfections, with the result that the lining becomes pitted or peels and iron is transferred to the catalyst. The contamination of these catalysts by iron has also been "minimized .to a considerable extent by the use of certain alloy steels such,

in particular, as the more or less corrosion resistant steels containing chromium, nickel, etc.

It is found, for example,.that whereas iron and plain carbon steels are'praotlcally useless, the tendency to contaminate the catalyst with iron is considerably decreased by the incorporation of chromium. However, even chrome steel containing 27% chromium has not proved entirely satisfactory for the purpose. The reaction vessels fabricated from this material are both expensive and relatively short-lived. After a' period of use they suddenly begin to contaminate the catalyst with iron and must be discarded. It has also been proposed to employ ferrous metal equipthe oxidation or corrosion of the ferrous metal in contact therewith. Even traces of iron derived from various parts of the plant uch as preheating coils, etc., carried with the reactant vapors are often suilicient to cause a serious poisoning of these catalysts. Thus, in general'it is found that the activity of thesecatalysts is decreased approximately linearly from 80% of their initial activity with an iron content of 0.7%to40% when the iron content is increased to 1.3%, This deactivation of the catalyst, unlike that due to a deposition of tarry materials, is permanent and ment which has been pretreated with hydrogen sulfide,- This pretreatment is sometimes eifective in preventing carbon formation in non-catacannot becounteracted by any of the known regeneration processes. Since these various conlytic processes, and when employing catalysts which are not susceptible to iron poisoning. It does not, however, avoid or decrease iron contamination and in fact increases it. Thepretreatment of the ferrous metal equipment with hydrogen sulfide, when employing catalysts of the above-described type, is furthermore not suitable for use in such processes wherein the catalyst is periodically regenerated a above-described, due to the fact that upon regeneration the coating of protective sulfide formed on the.

hydrogenated to produce iso-octane.

- ing conditions.

2 metal surface by the hydrogen sulfide treatment jg destroyed, liberating sulfur dioxide which then poisons the catalyst. t

In Patent No. 2,269,028, we have, with George E. Liedholm, described and claimed a simple, practical and eflective method whereby the contamination of these catalysts with iron when used in such processes in contact with ferrous metals may be substantially obviated. According to. the process of said patent, this is effected by maintaining in the reaction zone certain specified small concentrations of oxygenated sulfur compounds, such in particular as carbonyl sulfide. The desired results may also be obtained according to. the method describedand claimed in co-pending application Serial No. 391,748, also with George E. Leidholm. According to the processlof said co-pending application, iron contamination of the catalyst is prevented by maintaining in the re- 20- 1 oxygenated sulfur compounds. such in particular action zone small specified concentrations of nonas elemental sulfur and thiophenic sulfur compounds. 1 p Y These processes are very eflective in preventing iron contamination of the catalyst. It will be noted, however, that the elemental sulfur or sulfur compound added is found in the product. This, although it is not serious, is disadvantageous in certain instances since for many uses the product must be sulfur-free and this sulfur must be subsequently removed. For example, in the catalytic dehydrogenation of butane to butylene, the butylene is usually polymerized and the polymer For the production of is'o-octane by this method, it is desired to have butylene as free from sulfur compounds as possible. One of the advantages of the process of the above-mentioned application over that of the above-mentioned patent is that elemental sulfur and thiophenic sulfur compounds can usually be removed from the product. by a relatively simple treatment. Thus, elemental sulfur in the product can be substantially completely removed by thoroughly washing the product with ca tic solution. Thiophenic sulfur compounds c usuallybe substantially completely removed in the case of. the treatment of lower boiling hydrocarbons by extraction or by scrubbing with'a heavy oil. The recovered thiophenic sulfur compounds'can'be re-used.

I As pointed out, these processes are regenerative.

i. e. the catalyst is periodically regenerated in situ by burning carbonaceous deposits therefrom.

- This necessarily involves subjecting the catalyst and confining converter 'walls to alternate reducing conditions during the treatment and oxidizing conditions during the regeneration. This alternate changing from reducing to oxidizing and from oxidizing to reducing conditons is particularly prone to cause degradation of ferrous metals and contamination of the catalyst by iron. Under these relatively severe conditions a considerably greater concentration of sulfur or sulfur compounds is required to inhibit iron contamination of the catalyst than would be required if the prdcess were effected continuously under reduc- During, .the regeneration step most of the effect of the sulfur used in the feed is destroyed. 1

As shown in the above-mentioned patent and patent application, if the reactant is sulfur-free, iron transfer to the catalyst and catalyst poisoning therefrom are relatively severe. We have now found that the disadvantages arising from the addition of sulfur compounds to the feed may be 76 eliminated while avoiding iron contamination of the' catalyst and at the same time employing a P 10 lysts which are affected by contamination by iron.

The process is of particular advantage for such of these processes as are endothermic since in these processes the metal confining walls are usually heated and this increases the tendency of 15 the catalyst to become contaminated by iron.

Thus, for example, it maybe appliedfor the dehydrogenation of indene to thene to acenaphthylene, alcohols'to aromatic hydrocarbons, isopropyl benzol'to methylstyrene,

cyclopentane to cyclopentadiene, etc. The process is, however, especially suitable for the dehydroge'nation of petroleum hydrocarbons. Thus, it may be advantageously employed for the treatment of any of the common petroleum fractions 5 which are vaporizable, without decomposition.

Since, however, the more higher boiling 'of suchpetroleum fractions usually contain considerable amounts of sulfur compounds, the. process will find most application to the treatment ofthe appreciable amounts of sulfur compounds, it'is,

however, necessary to first submit them too. suitable desulfurization treatment to reduce the sulfur content to within the pe m sible limit. Any 7 of the conventional desulfurization treatments wen known in the art may be used for this pur- 40 pose. Suitable concentrations of sulfur in thefeed to be treated are, for-example, from O-to about 0.000996.

The various substantially sulfur-free materials are treated under known suitable conditions to effect the desired conversion; Any. of the regenerative oxide catalysts can :be employed. The

process is, however, very effective when employ-- ing catalysts ofthe dehydrogenation type such as the oxides of the metals selected from the left-hand members of Groups IV, V and VI of the Periodic System of the Elements, for example Tl,

V, Cr, Mo and W. These various catalytic oxides may, if desired, be employed in admixture with oxides selected from Groups I and/or For example, a very suitable catalyst comprises'an adsorptive alumina impregnated with '4-20% chromium oxide. Such catalysts are susceptible to poisoning by iron; they are strong dehydrogenation catalysts and are regenerative. In genera]; when employing catalysts of this type in the vapor phase treatment of the various mas terials, the temperature of the treatment is between about 500 F. and 1300 F. The use of these catalysts for the treatment of organic materials at these temperatures causes the catalyst to'be relatively quickly deactivated bythe deposition of carbonaceous deposits thereon. After a relatively short time, for example 2-12 hours, the

catalyst activity declines to an uneccnomical level. At this point the feed is stopped, and an inert gas is passed through the catalyst to flush out residual reactants, and hydrogen, if this isemployed in the reaction step. Carbon is next removed from the catalyst by combustion with a stream of an oxygen-containing gas. The gas senes, acenaphlighter more nearly sulfur-free fractions such, foremployed in this regeneration treatment is usually an inert'gas to which air has been added to bring the oxygen concentration" to a point where the heat of combustion can-be controlled, for example 1%-4%. In some cases pure air may be used. After the carbonaceous deposits have been sufnciently'removed, the oxygen-containing to a content of 0,0045% "(and in a similar experiment, 9.000%). The propane vapors cmtaining the specified, amounts of elemental sulfur were dehydrogenated under the above-degas is flushed from the catalyst with lnert'sas,

and the catalyst is put back on-stream. If hydrogen is recycled in the process, the hydrogen recycle can be initiatedprior to starting the feed. This series of steps is repeated at frequent interfeed iron transfer to the catalyst is substantially K inhibited. 1;, The product, however, contains sulvals. The inert gas used to flush the catalyst and/or to which oxygen is added to eflect the burning is hereinafter referred to as the regeneration gas.

Transfer of iron to the catalyst is inhibited, according to the process of the present invention,

by maintaining in the regeneration gas a low and controlled amount of sulfur in the form of sulfur dioxide. It is found that if the regeneration gases contain certain specific concentrations of sulfur dioxide, iron contamination of the catav lystis substantially inhibited even when employ- .ing sulfur-free feeds. The concentrations of sulfur dioxide in the regeneration gas employed in the present process must be carefully controlled,

.however, since insufficient concentrations will not prevent iron contamination of the catalyst and the use of excessive amounts of sulfur dioxide is not only detrimental to the activity of the catalyst but causes severe corrosion. Thus, when employing a substantially sulfur-free feed, 1. e. having a sulfur content below about 0.0009% suitable concentrations of sulfur in the form of sulfur dioxide are between 0.001%. and 0.019%. These various points are illustrated in the following examples. These examples, for the sake of comparison, all relate to the dehydrogenation of propane vapors under the following conditions:

Temperature 1140 F.

,Pressure 1 atm.

Space velocity..- 35 volumes propane-at normal scribed conditions. During 200 process cycles the iron transfer to the catalyst was in both cases not more than 0.015%. Similar results are obtained withother sulfur compounds in place.o f

' elemental sulfur. It is seen that by the application of specific concentrations of sulfur in the fur which, in most cases, must be removed by a separatef'treatment.

Example In Substantially sulfur-free propane was dehydrogenated under the above-described conditions. No sulfur or sulfur compound was added to the propane but0.000'7% sulfur'in the form of sulfur. dioxidewas added to the regeneration gas. After only 69 process cycles the tube wall was in very poor condition and the catalyst was found to be severely contaminated with iron (0.10%). It is thus seen that when-using a sulfur-free feed a concentration of sulfur dioxide in the regenera tion gas equivalent to 0.000'7% sulfur is insufficient to prevent iron poisoning of the catalyst.

. Example IV Substantially sulfur-free propane was dehydrogenated under the above-described conditions. No I wall was in perfect condition. Thus, it is seen that by the use of 0.005% sulfur in the form of sulfur dioxide in the regeneration gas, iron 'poi-' sonlng of the catalyst is substantially eliminated.

conditions per volume catalyst per hour Catalyst 8-14 mesh pieces of active chromium oxide (11% 0.025% Fe, 0.045% 3) Process period-.. 40 min.

The catalyst in each example was employed in a new sand-blasted KA2Ssteel tube.

Propane vapors substantially free of sulfur were treated under the above-described conditions. After only 19 (and 38) process cycles, i. e.

19.(and 38) -minute process periods followed 0.35% iron); In other words, in check runs during 19 and 38' process cycles iron was transferred from the new KAZS steel tube to the catalyst to' the extent of about 0.24% (and 0.33%) by weight of the catalyst. It is seen that when the feed is substantially sulfur-free and sulfur dioxide is not added to the regeneration gases, iron transfer to'the catalyst is severe even with a new chrome-nickel steel tube. I

. Example I I To the vapors of substantiallysulfur-freepro- Ipane there was added vapors of elemental sulfur alumina impregnated with,

by l9 (and 38) regeneration periods, the catalyst was found to contain about 0.26% iron (and Furthermore, since no sulfur is added to the sulfur free feed, the. product doe not require a subsequent treatment to remove sulfur.

Example V Substantially sulfur-free propane was dehydrogenated under the above-described conditions. Nosulfur was addedto the propane but 0.025% sulfur in form of sulfur dioxide was added to the regeneration gas. During 193 process cycles 0.20% iron was transferred. to the catalyst and the reaction tube was badly corroded. Thus, it is seen that 0.025% sulfur in the form of sulfur dioxide in the regeneration'gas doesnot inhibit iron contamination of the catalyst but, on the otherhand'increases it and causes severe corro sion of the chrome-nickel tube.

As explained above and illustrated in the examples, contamination ofthe catalyst withiron may be substantially inhibited either by the proper application of sulfur or sulfur compounds in the feed according to the above-mentioned patent and co-pending application or according to the present invention, by the use of suitable concentrations of sulfur dioxide in the regeneration gas.

It is also possible and often advantageous to apply both'of these methods simultaneously. It will be observed, however, that in this case the concentrations of sulfur inboth' the feed and the regeneration gas are diflerent than when 'applying either method alone. Thus, according to a The catalyst at the end.

more pd aspect of the ma a very small and allowable concentration of sulfur carbonyl sulfide, elemental sulfurand thiophenic.

sulfurcompounds, are employed, the transfer of iron .to the catalyst may be effectively inhibited with smaller concentrations of sulfur dioxide in the regeneration gas. Thus,-it is possible to effectively inhibit iron transfer to the catalyst with as low as about 0.000596 sulfur in the regenerat'ion gas. n the other hand, when employing Y feeds containing between about 0.0009% and 0.0029% sulfur, the maximum concentrations of sulfur dioxide in the regeneration gas which may be effectively employed are lower than when employing. sulfur-free feeds. Thus. the maximum concentration of sulfur in the regeneration gas is about 0.01%. In general, the concentrations of sulfur in the feed and in the" regeneration gas vary inversely, that is. the higher the concentrations of sulfur in the fed, the lowerthe concentrations of sulfur dioxide in the regeneration gas. For example, with a feed containing about 0.0006% sulfur a suitable concentration ofsulfur in the regeneration gas is about 0.005%, whereas with a feed containing 0.002% the concentration of sulfur in'the regeneration gas is preferably about 0.0007%. ,The application of very small amounts of sulfur in the feed along with the specified concentrationsof sulfur dioidde in the 85 regeneration gas, although it does not produce a totally sulfur-free product, produces a product having permissible concentration of sulfur and is furthermore somewhat more effective in preventing iron poisoning than either method alone.

The sulfur dioxide may be added to the regeneration gas in the desired amounts by simply mixing the desired amount of sulfur dioxide vapors with the regeneration gases entering the regeneration zone. In such cases where the regeneration gases are recycled, for instance according to the method of regeneration claimed in U. 8. Patent No. 2,225,402. the sulfur dioxide may be recycledand reused. If desired; however, in order to facilitate control, theregeneration gas may be scrubbed to remove sulfur-dioxide and then a measured amount of sulfur dioxide added. Since sulfur dioxide is very. cheap and only very small quantities are required, this does not involve any substantial loss. v I

The contamination of the catalyst by iron in the execution of these various reactions may be inhibited, according to the present process,;in the presence of any of the steels and common ferrous alloys. Iron and mild steel are not usually employed in these processes due to their lesserability to withstand themore or less severe conditions. Particularly suitable materials which may be used are the chrome steels such as KA2, KA2S, KA2ST,

. KA2Cb, KA2M0, KA2M0T, etc. Inthe past these otherwise excellent steels have not been found entirely suitable due to their tendency to cause iron contamination of the catalyst after a short'period of use-'and the industry has been forced to go to the more expensive and difiicultly workablehighchrome steel such as 27-Cr, etc. These latter materials, although definitely superior to most lowchrome steels, are nevertheless far from satisfactory and cause iron contamination after a rel'a tively short time. By utilizing the Process of the present invention. any of such steels maybe used indefinitely without any appreciable tendency to cause iron contamination of the catalyst. Particularly excellent results are also obtained using is nitrogen-' or aluminum-stabilized highchrome steels. For example, a particularly excellent steel 1. In a process for the conversion of carbonatemperatureat least equal to 500 F. wherein the reactant vapors are contacted with a catalyst susceptible to contamination by iron in the presence of a ferrous metal and the catalyst-is periodically regenerated in situ by oxidation of carbonaceous deposits therefrom with a stream of regeneration gas of low and controlled oxygen concentration, the step of inhibiting the contamination of the catalyst by iron which comprises maintaining in the feed to the reaction zone less than 0.0009% sulfur and maintaining in the regeneration gas to the regeneration zone between 0.001% and 0.019% sulfur in the form of sulfur dioxide. a

2. In a process for. the conversion of carbonaceous materials in the vapor phase at an elevated temperature at least equal to 500 F. wherein the reactant vapors are contacted with a dehydrogenating metal oxide catalyst susceptible to con- 0 tamination by iron in the presence of a ferrous metal and thecatalyst is periodically regenerated in situ by oxidation of carbonaceous deposits therefrom with a stream of regeneration gas of low and controlled oxygen concentration, the step of inhibiting the contamination of the catalyst by iron which comprises maintaining in the feed to the reaction zone less than 0.0009% sulfur and maintaining in the regeneration gas to the regeneration zone between 0.001% and 0.019% sulfur in the form of sulfur dioxide.

3. In a process for the conversion of carbonaceous materials in the vapor phase at an elevated temperature at least equal to 500 F. wherein the reactant vapors are contacted with a chromium as oxide catalyst in the presence of a ferrous metal situ by oxidation of carbonaceous deposits there from with -a stream of regeneration gas of low and controlled oxygen concentration, the step of a0 inhibiting the contamination of the catalyst by iron which comprlses maintaining in the feed to thereaction zone less than 0.0009% sulfur and maintaining in the regeneration gas to the regeneratioh zone between 0.001% and 0.019% sulfur in the form of sulfur dioxide.

4. In a process for the conversion of carbonsceous materials in the vapor phase at an elevated 7 temperature at leastequal to 500 F. wherein the reactant vapors are contacted with a catalyst ,70 susceptible to contamination by iron confined in a chrome steel reactor and the catalyst is periodically regenerated in situ by oxidation .of carbonaceous deposits therefromwith a stream of regeneration gas of low and controlled oxygen "concentration, the step of inhibiting the conceous materials in the vapor phase at an elevated and the catalyst is periodically regenerated in I assure tamination of the catalyst by iron which comprises maintaining in the feed to the reaction.

zone less than 0.0009% sulfur and maintaining in the regeneration gas to the regeneration zone between 0.001% and 0.019% sulfur in .the form of sulfur dioxide.

5. In a process for the dehydrogenation of bu-.

zone less than.0.0009% sulfur and maintaining trolled oxygen concentration. the step of inhibiting the contamination of the catalyst by iron which comprises maintaining in the feed to the reaction zone less than 0.0009% sulfur and maintaining in the regeneration ga to the regeneration zone between 0.001% and 0.019% sulfur in the form of sulfur dioxide.

8. In a process for the dehydrogenation of propane in the vapor phase at an elevated temperature at least equal to 500 1". wherein propane v vapors are contacted with a dehydrogenating meta1 oxide catalyst susceptible to contamination by iron in the presence of a ferrous metal and the catalyst is periodically regenerated in situ by oxidation of carbonaceous deposits therefrom with a stream of regeneration gas of low and controlled'oxygen concentration, the step of inhibiting the contamination of the catalyst by iron which comprises maintaining in the feed to the reaction zone less than 0.0009% sulfur and maintaining in the regeneration gas to the regeneration zone between 0.001% and 0.019% sulfur in the form of sulfur dioxide.

7. In a process for the dehydrogenation of bu-, tane in the vapor phase at an elevated temperature at least equal to 500 I". wherein the butane vapors are contacted with'a chromium oxide catalyst in the presence of a ferrous metal and the catalyst is periodically regenerated in situ by oxidation of carbonaceous deposits therefrom with a stream of regeneration gas of low and controlled oxygen concentration, the step of inhibiting the contamination of the catalyst by iron which comprises maintalning in the feed to the reaction zone less than 0.0009% sulfur and maintaining in the regeneration gas to the regeneration zone between 0.001% and 0.019% sulfur in the form of sulfur dioxide.

8. In a process for the dehydrogenation of propane in the vapor phase at an elevated temperature at least equal to 500l". wherein the propane vapors are contacted with a chromium oxide catalyst in the presence of a ferrous metal and the catalyst is periodically regenerated in situ by oxidation of carbonaceous depositstherefrom with a 'stream of regeneration gas of low and controlled oxygen concentration, the step of inhibiting the contamination or the catalyst by iron which comprises maintaining in the feed to the reaction presence of. a ferrous metal and the catalyst is.

periodically regenerated in situ by oxidation of carbonaceous deposits therefrom witha stream of regeneration gas of low and controlled oxygen concentration, the step of inhibiting the contamination of the catalyst by iron which comprises maintaining in the feed to the reaction zone between .0009% and 0.0029% sulfur and maintaining in the regeneration gas to the regeneration zone between .0005% and 0.01 sulfur in the form of sulfur dioxide.

10. In a process for the dehydrogenation of butane in the vapor phase at "an elevated temperature at least equal to 500 F. wherein butane vapors are contacted with a dehydrogenating metal oxide catalyst susceptible to contamination by iron in the presence of a ferrous metal and the contamination of the catalyst by iron which comprises maintaining in the feed to the reaction zone between 0.0009% and 0.0029% sulfur and \maintaining in the regeneration gas to the re-- generation zone between 0.0005% and 0.01% sulfur in the form of sulfur dioxide.

11. In a process for the dehydrogenation of propane in the vapor phase at an elevated temperature at least equal to 500 F. wherein propane vapors are contacted with a dehydrogenating metal oxide catalyst susceptible to contamination by iron in the-presence of a ferrous metal and the catalyst is periodically regenerated in situ by oxidation of carbonaceous deposits therefrom witha stream of regeneration gas of low and controlled oxygen concentration, thestep of inhibiting the contamination of the catalyst by iron which comprises maintaining in the feed to the reaction zone between 0.0009% and 0.0029% sulfur and maintaining in the regeneration gas to the regeneration zone between 0.0005% and 0.01% sulfurinthe form of sulfur dioxide. i

' ROBERT M. COLE.

IRVING I. SHULTZ.