US2414972A - Conversion of hydrocarbons - Google Patents

Description

Jan. 28, 1947. E. F. NELSON 2,414,972

' CONVERSION oF HYDRocARBoNs Filed Sept. 28, 1942 7 llw Patented Jan. 28, 1947 CONVERSION F HYDROCARBONS Edwin F. Nelson, Chicago, Ill., assigner to Universal Oil Products Company, Chicago, Ill., a corporation of Delaware Application September 28, 1942, Serial No. 459,938

The invention is particularly directed to an improved process ior the thermal or catalytic conversion of relatively light, normally liquid hydrocarbons, such as naphtha, gas oil and the like, or normally gaseous hydrocarbons, such as butanes and butylenes, to produce more valuable normally gaseous fractions, such as butadiene, acetylene, etc.

Processes of the type to which the present invention is directed employ high conversion temperaures, short conversion time and low effective operating pressure. For example, in the thermal cracking of naphtha to produce butadiene, temperatures of the order of 1400 to 1600" F. are usually employed with a conversion time of the order of 0.1 second or less and an effective pressure corresponding to substantially atmospheric or subatmospheric pressure. In the catalytic conversion of butane to butylene, the preferred operating conditions will vary somewhat with the particular catalyst employed and the purity of the charging stock, but are usually within the range of 1050 to 1150 F., with a short conversion time of the order of 0.1 second or less and an effective pressure corresponding, for eX ample, to about mm. of mercury. For the catalytic conversion of butylene to butadiene, the operating conditions may be much the same as those employed for the conversion of butane to butylene, but even lower effective pressure corresponding, f-or example, to about 5 mm. of mercury is preferably employed.

The dehydrogenating and/or cracking reactions which predominate in operations of this type are of a highly endothermic nature and the problem of maintaining the reactants to be converted at the required high conversion temperature for the necessarily short conversion time, While supplying the required endothermic heat of reaction thereto, is complicated by the necessity for maintaining a low effective operating pressure in the reaction zone; `f

Theobvious method of obtaining loweffective pressure in the reaction zone by the use of` a vacuum pump or exhauster makes the operation costly, particularly in View of the fact that the reaction also produces normally gaseous and/or liquid fractions other than those which are especially desired, and to recover the desired fractions in relatively pure state requires fractionating equipment for the conversion products which is rather expensive and costly, even when operated at substantial superatmospheric pressure, and would require larger Aand more 'expensive equipment, in addition to provision iol; ref rigerr 1 Claim. (Cl. 1556-52) ation, if operated at atmospheric or atlsubatmospheric pressure.

. The use of diluents, such as steam or' other rel atively inert gas in the reaction zone,k to give a low effective pressure by its partial pressure effeet and permit operation of the reactor atsuperatmospheric gauge pressure, involves a high expenditure of heat to bring the steam or other gaseous diluent to the high temperature required: for conducting the reaction.

It is common practice in catalytic operations of` the type above mentioned to employ a bed of granularor subdivided solid catalyst, upon which deleterious heavy combustible conversion prodr ucts of the reaction are deposited, and to periodically burn the combustible contaminants therefrom in a stream of oxygen-containing gases. This willresult in the storage of considerable heat in the catalyst mass whichxis given up to the conversion reaction in the subsequent period during which the regenerated catalyst is again employed for promoting the conversion reaction. However, the vcombustible deposits are usually not as lgreat in the conversion of' light distillates and gases as in the catalytic cracking of heavier oils, for example, and since the reaction is of a highly endothermic nature, there is usually no excess ofheat generated during reac-I tivation and stored in the catalyst mass over that required to supply the hydrocarbon reactants with the endothermic heat of reaction. It is therefore impossible to store sulcient heat in the catalyst mass to bring the `relatively large quantities of steam or other gaseous diluent employed to produce/the desired partialpressure effect to the high temperature of 4thefreation. Superheating steam or heating othergas-to such high temperatures by conventionalmethods also involves expensive equipment employing consider-A able strategic War materials, such as high chromium steel or chromium nickel steel which' are:

diilicult, if not impossible, to obtain at the present time.

The present invention is directed to a simple and advantageous solution of the problems above outlined in processes for the production of butadiene, acetylene and similar valuable products which must be produced in large quantities for military use. The features of the invention are not limited, however, to processes for the production of such materials, but are applicable to a Wide variety of oil refining and other chemical processes, both of a catalytic and non-catalytic nature, which involve the use of high temperatures and low effective operating pressures. It

is, therefore, not intended to limit the invention to any specific reaction of this general type since there are many applicabilities of its features which will be readily apparent to those familiar with the art.

The features and advantages of the invention are illustrated by the accompanying diagrammatic drawing and the following description thereof. The drawing is essentially a flow diagram of one embodiment of the process provided by the invention as applied to the endothermic conversion of normally gaseous or light normally liquid hydrocarbons, employing subdivided solid contact material of a catalytic or non-catalytic nature, upon which heavy combustible conversion products are deposited and from which the combustible contaminants are periodically burned to generate heat and restore the active surface oi the catalyst or contact material.

Referring to the drawing, the apparatus here illustrated comprises similar reaction vessels I and 2 which are each alternately employed as a zone in which endothermic conversion of the hydrocarbon reactants is accomplished and as a- Zone in which exothermic regeneration of the subdivided solid catalyst or contact material em ployed is accomplished. Each of the vessels i and 2 contains one or a plurality of fixed porous beds of solid catalyst or relatively inert contact material. The approximate upper and lower limits of the beds are indicated at 3 and 5 in vessel I and at tl and 6 in vessel 2.

As applied to the catalytic cracking of light normally liquid hydrocarbons or to the catalytic dehydrcgenation of hydrocarbon gases, the process permits the use of any of several Well known subdivided solid or granular catalysts capable of promoting dehydrogenating or cracking reactions and is not intended to limit the invention to the particular catalyst employed, except that it should be one which is not damaged or rendered inactive by steam, one which will successfully withstand the high reaction and regenerating temperatures employed without excessively reducing its porosity by melting or fusing of relatively low melting point components, or otherwise permanently impaired, and one which will successfully withstand frequent periodic regeneration without excessive loss of activity.

As applied t thermal cracking and dehydrogenating processes, the solid contact material in the reaction and regenerating vessels may comprise a checker-work of refractory shapes, such as fire-brick, calcined clays, silicon carbide, suitable metals or the like which will withstand the operating conditions encountered and will readily retain heat during the regenerating step and dissipate the same during the subsequent conversion step. Preferably I employ a porous bed or beds of relatively inert refractory material, such as crushed lire-brick, gravel, calcined clays or shales or particles of various metals, ores, quartz particles or the like.

The solid arrows adjacent the lines in the diagram indicate the flow through the system while vessel I is employed as the reaction zone and vessel 2 is employed as the regenerating zone. The dotted arrows adjacent the lines indicate the flow through the system while vessel 2 is employed as the reaction zone and vessel I is employed as the regenerating zone. The arrowheads on the lines themselves indicate flows which do not change with alternation of the reaction and regeneration zones.

Assuming, for the sake of illustration, that vessel I is being employed as the reaction zone and vessel 2 is being employed as the regenerating zone, the hydrocarbon reactants to be converted are directed in essentially vaporous or gaseous state, from suitable preheating equipment, not pertinent to the present invention and therefore not illustrated, through lines 'l and 8, valve 9 and line Iil into the reaction zone, wherethrough reactants and resulting fluid conversion products pass downwardly in contact with the solid catalyst or contact material and within which the conversion reaction is accomplished. Resulting iluid conversion products are directed from reu action vessel I through line II to stream-directing valve I2, wherefrom they are supplied through line I 3 to fractionating and recovery equipment of any suitable conventional form, not illustrated. rlhe heated products preferably are quickly cooled, in any well known manner, not illustrated, following their discharge from the reaction zone, in order to prevent excessive continued conversion thereof and substantially limit the conversion time to that obtained in the reaction vessel.

During operation of vessel i in the manner above described, the catalyst or contact material in vessel 2, which has accumulated heavy combustible deposits during prior use of vessel 2 as the reaction zone, is regenerated by directing a stream of hot oxidizing gas, such as air diluted with combustion gases, for example, through line if! to the stream-directing valve I2, wherefrom it flows through line I5 into vessel 2 and passes upwardly through this zone in contact with the contaminated catalyst or contact material, burning the combustible contaminants therefrom. Resulting hot combustion gases are directed from the upper portion of vessel 2 through line I 5 to a recuperative type heater which contains a mass of heat-retentive material, such as a checker-work or fire-brick or the like, not illustrated. The hot gases pass through the heater in Contact with the refractory mass and store a substantial quantity of heat therein. The resulting partially cooled combustion gases are directed from heater I'I through line It to stream-directing valve I9 from which they are discharged through line 20 and may, when desired, be recycled, by well known means not shown, after suitable puriiication and after their' oxygen-content has been adjusted to the desired value, back to line ill for further use as the regenerating gas stream.

After a relatively short period of operation in the manner above described, the position of the stream-directing valves I2 and I9 is reversed to give a flow therethrough as indicated by the dotted lines, oxidizing gas from line I4 being supplied through line II to vessel I and the preheated vaporous or gaseous hydrocarbon reactants being directed from line 1 through line 2l, valve 22 and line I to vessel 2. Thus, the catalyst or contact material in vessel I, which has now accumulated combustible containants, is regenerated, while the hot regenerated contact mass in vessel 2 is employed to catalyze and/or supply heat to the endothermic conversion reaction. During this phase of the operating cycle, hot combustion gases are directed from vessel I through line I0 to the recuperative heater 23, which is substantially the same as heater I'I, wherein they supply heat to the refractory mass, with which they come in intimate contact While passing therethrough, and are appreciably cooled. The resulting partially cooled combustion gases are .directed from heater 23 through line 24 .to

'angers the stream-directing valve I9 which is-nowin `a position to direct the combustion gases through line 20.

By the alternate operation of vessels l and 2 as reaction andregenerating zones in the manner above described, a considerable portion of the heat evolved in the regenerating step is stored in the mass of catalyst or contact material undergoing regeneration and is supplied to the endothermic conversion reaction during the subsequent conversion step in the same vessel. No novelty is herein claimed for this portion of the operation and, by Iproper selection of catalyst yor contact material, temperature and pressure conditions, and by selecting the proper length of time for the conversion and regenerating stages of the cycle, it is possible in some instances to store in the catalyst o-r contact material, Iduring regeneration thereof, sufcient heat to retain the hydrocarbon reactants a-t the desired high conversion temperature during the subsequent conversion step and supply the necessary endothermic heat of reactionv thereto. However, thermal balance of this nature in conventional operation of such processes precludes the use of inert diluents for producing a -partial pressure effect in the reaction zone unless this diluent is supplied to the reaction zone substantially at or above the temperature at which the reaction is conducted. In the process of the invention at least a substantial portion of the heat required for bringing a relatively inert diluent, such yas steam, for example, to the high temperature at which the reaction is conducted is recovered from the outgoing regenerating gases in recuperative heaters. The heat thus recovered from the hot gaseous products of the regenerating step is stored in the heat retentive mass which they contact in passing through the recuperative heaters and is subsequently transmitted to the ste-am or other inert diluent by passing the same in contact with the heated mass.

While vessel I is em-ployed as the zone in which the hydrocarbon conversion reaction is conducted, the relatively inert diluent employed is supplied through line 25 to the stream-directing valve I9 Wherefrom it is introduced through line 24 to he-ater 23, and the resulting highly heated diluent gas is thence directed through line IIJ wherein it commingles with the incoming hydrocarbon reactants from line 8 land passes through the contact mass or catalyst in reactor I with the reactants and resulting hydrocarbon conversion products. In .a similar manner, while vessel 2 is employed as the reaction zone, the position of switch valve I9 is reversed so that the steam or other gaseous medium employed as the inert diluent liows from line 25 through valve I9 and line I8 to heater I1, wherein it is heated to a high temperature by contact with the previously heated refractory mass in this Zone, and wherefrom it is directed through line I6 to vessel 2, together with the hydrocarbon reactants being supplied to this zone through line 2 I.

Although any other gaseous diluent which will not adversely affect the reaction may be employed in lplace of steam, within the scope of the invention, I prefer to employ steam due to the ease with which it may be separated, upon condensation, from the hydrocarbon conversion products of the reaction. When steam is employed las the ineri-I diluent, either steam or water vapor may be admitted through line 25 and lines I8 and 24 to the recuperatve heaters and, when desired, a

Waste-heat boiler, to which combustion gases from line 20 are directed, may be employed to generate the steam supplied to the recuperative heaters. i

In the case illustrated, a Waste-heat boiler 26 yof any suitable form is provided and combustion gases from the recuperative heaters are directed through line 20 to the waste-heat boiler and Ipass therethrough vin indirect -contact and `heat eX- change relation with water supplied tothe boiler through line 21. Combustion gases from which -additional heat has thus been abstracted are discharged from boiler 26 through line 28 and may, when desired, be recycled by well known means, not illustrated, through line I4 back to the vessel in which regeneration of the catalyst lor contact material is taking place. When combustion gases are recycled in this manner their temperature and oxygen content is readjusted to the desired value prior to their reintroduction into the regenerating zone. Steam generated in the waste-heat boiler 26 is directed therefrom through line 25 to the stream-directing valve I9 from which i-t is'supplied, as previously described, to the recuperative heaters.

When heat, in addition to that which can be recovered from the hot combustion gases discharged from the regenerating zone, is required for heating the gaseous diluent to the desired high temperature, it may be supplied to the system by commingling any desired type of fuel with the combustion gas stream passing from the regenerating zone to the recuperative heater and burning the fuel in the latter in contact with the heat-retentive mass therein. Burners 29 and 30 communicating with the respective lines I6 and it are provided, in the case illustrated, for introducing regulated amounts of a combustible mixture of fuel and air into the respective recuperative heaters i'I and 23. Thus, the heat content or both the heat content and the temperature of the combustion gases utilized to store heat in the recuperative heaters may be increased to any desired value.

Provision is also made for burning fuel, other than the contaminants deposited on the contact material, in the zone wherein the contact mass is regenerated. Burners 3| and 32 communicating with the respective lines I5 and II are provided for supplying the desired quantity of additional fuel to the regenerating zone, wherein it is burned in contact with the mass of catalyst or contact material. Thus additional heat may be stored in the contact mass, in addition to increasing the heat content of the combustion gases supplied to the recuperative heaters. The supply of fuel through burners 29 and 30 is, of course, discontinued while the respective heaters II and 23 are employed for superheating steam and the supply of fuel through burners 3l and 32 is discontinued while the respective vessels 2 and I are employed for conducting the hydrocarbon conversion reaction.

I claim as my invention:

A process of the character described which comprises subjecting hydrocarbons to endother mic conversion in a first reaction zone containing solid contact material; simultaneously burning carbonaceous matter from a body of solid contact material in a second zone; thereafter endothermically converting hydrocarbons in said second zone while burning carbonaceous matter from the contact material in the first zone; preventing admixture of the combustion gases formed by said burning and the hydrocarbon products formed by said endothermic conversion; passing hot combustion gases from said rst zone, during the burning operation therein, through a rst heatretentive mass to store heat therein; passing hot combustion gases from said second zone, during the burning operation therein, through a second heat-retentive mass to store heat in the latter; passing the combustion gases discharging from said heat-retentve masses in indirect heat exchange relation with a body of water to generate steam from the latter; throughout the hydrocar- 10 bon conversion in said first zone passing a portion of said steam through said rst mass and thence into the first zone to commingle with the hydrocarbons undergoing conversion therein; and, throughout the hydrocarbon conversion in said second zone, passing another portion of said steam through said second mass and thence into the second zone to commingle with the hydrocarbons being converted in the second zone.

EDWIN F. NELSON.

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