US2251571A - Catalytic treatment of hydrocarbons - Google Patents

Description

' AU@ 5, l94,1- F. A. HOWARD 2,251,571

CATALYTIC TREATMENT 0F HYDROCARBONS Filed Nov. 19, 1937 ZZ 5I fz 2a 1 www Patented 1941 OFFICE f CATALYTIC TREATMENT! 0F HYDE@- t CABBONS Frm A. nowara'auubeta; N. r., signor t@ Standard Oil Development ompany, a corporation or Delaware Application November l 8 Claims.

The present invention relates to the catalytic ltreatment oi hydrocarbons and particularly to endothermc treatments such as cracking and dehydrogenation.

One ot the major dimculties encountered in catalytic cracking and dehydrogenation is the maintenance of an optimum temperature throughout the catalytic mass The difiiculty has been that when enough catalyst is employed 4to provide a proper time of contact for the desired conversion of the hydrocarbons, by reason of the endothermiq nature of the reaction, the temperature of the hydrocarbons is rapidly diminished in its passage through thr` catalytic mass so that it is not in contact with the catalyst at the proper temperature for the whole time of its passage therethrough. If it be attempted to supply enough heat to the feed stock as preheat to keep the temperature within an optimum range throughout the entire catalyst mass, cracking to an undesirable extent occurs in the preheater and mre especially in the pipe connecting the preheater with the reaction chamber.

This has led to the practice of mixing the hydrocarbon feedstock with inert gas or vapor such as steam which can pass through thel catalytic bed without suii'ering any loss of heat other thanthat due to radiation, which loss lslargely eliminated by suitable insulation of the reaction chamber. The obvious drawback to this procedure is that it cuts down the capacity of the unit and requires the employment of a special procedure for the recovery of the products from inert gas.

According to the present invention, hydrocarbons, particularly those of normally liquid nature such as gas oils, are cracked or dehydrogenated by being preheated to a cracking temperature or thereabouts, and passed through a catalyst chamber to which is fed at suitably spaced points other hydrocarbons of greater therm'al stability against decomposition heated to a, temperature above the optimum cracking temperature of s aid first mentioned hydrocarbons. In general, for hydrocarbons of the same type, such as saturated hydrocarbons or olei'ins, the thermal stability against lcracking decomposition var es inversely with the molecular weight. In

`i other words, the lower the molecular weight,l the greater the stability. Moreover, saturated hydrocarbons are, in general, more stable than the corresponding oleilns. The hydrocarbons employed for the maintenance of the reaction temperature in accordance with my invention, are those of a materially lower molecular weight 9,- fi937,.Seriailda 75,359 (er. ies-it)v than the hydrocarbons undergoing reaction. For

example, when converting gas oils, normally gaseous hydrocarbons, such as butane, propane, ethane, methane and corresponding oledns may be employed. Likewise, light normally liquid hydrocarbons, such as the pentanes, hexanes and corresponding olens may be employed. .Any

hydrocarbonwhich has the requisite thermal stability may be utilized. Although these light 'hydrocarbons are relatively stable against thermal decomposition under temperature conditions for cracking of the heavier oils constituting the main charging stock, they nevertheless have a marked iniiuence on the yield and character of -l the gasoline produced.` While the exact cause has not been fully established, there is reason to believe that a portionv of the light hydrocarbons combine with the oleiins and aromatic products resulting from cracking the heavier oil.

In the preferred embodiment or the present invention the cracking or dehydrogenation catalyst is arranged on spaced trays in the reaction chamber which is highly insulated. The hydrocarbon feed stock. after passing through a preheater is fed into the reaction chamber above the top tray. The hydrocarbons employed for temperature maintenance are introduced into the reaction chamber between the trays.k This arrangement makes it lpossible to accurately control the catalyst temperature. 'Itis not necessary to arrange the catalyst in this manner in order to secure the advantages oi the present invention. The catalyst may also be employed in the form of a deep bed in which are arranged at spaced points inlets for the superheated'hydrocarbons utilized for the maintenance of the reaction temperature.

The catalyst to be employed in the reaction chamber will depend upon the reaction desired. For dehydrogenation, any well' known. dehydrogenation catalyst may be employed. Examples of these are metals of group 6 of the periodic system and their compounds, particularly the oxides `and sulphides thereof, and combinations of these substances with metals, or compounds thereof, of other groups of the periodic system,

such as groups 2 and 4.

I'he process of the present invention is more particularly applicable to the catalytic cracking of relatively high boiling hydrocarbons, since in this operation it is possible to use the higher pressures which accelerate the reaction between unsaturated compounds produced by the cracking of said hydrocarbons and low boiling or nor- 55 mally gaseous hydrocarbons utilized for the maintenance of the reaction temperature. 'I'he catalyst best suited for this cracking operation is a clay, particularly one of bentonitic character, which has been activated by treatment with a mineral acid. Catalysts which accelerate cracking may be associated with the clay. Among these may be mentioned metals of the iron group and their compounds, especially nickel and itsA compounds. It is of especial advantage to employ a clay containing an acid, such as phosphoric acid. A particularly suitable catalyst is one prepared by absorbing a metal halide such as aluminium chloride on an adsorbent support such as silica gel. When this vtype of catalyst is employed, it is advantageous lto introduce chlorine into the reaction chamber with the feed stock or with thei auxiliary hydrocarbons used for temperature maintenance.

The temperature employed for the, catalytic cracking of liquid hydrocarbons will vary with the boilingvpoint range of the feed stock. In general, it will be above about 700 F. and not higher A than about 900 F. For gas oil, a preferred operating temperature lies between 800 F. and 900 F. With a higher boiling feed stock the temperaturewill be somewhat lower within the broad range specified unless the feed stock is especially refractory.

The process may be carried out at atmospheric or moderate superatmospheric pressure.

In its preferred embodiment the process of the present invention includes the separation of the total reaction products into normally liquid constituents, which may be restricted to those having 6 or more carbon atoms, an intermediate fraction preferably containing Ca to C hydrocarbons,

which may in some instances include Cz hydrocarbons if the latter are composed mainly of ethylene, and a normally gaseous fraction composed of hydrogen, methane. and usually, ethane. The normally gaseous fraction and the normally liquid fraction are removed from the system while the intermediate fraction is recycled to the catalyst chamber. In lieu of passing the total intermediate fraction to the catalyst chamber, this fraction may be first subjected to polymerizing treatment to polymerize readily polymerizable oleflnic constituents, such as the butylenes which 'are relatively unstable thermally as compared with other hydrocarbons of similar boiling range. 'I'he polymerizing treatment may be accomplished by any of the methods well known in the art, such as, for example, in the presence of a catalyst such as sulphuric or phosphoric acid. v

The process of thepresent invention will be better understood from the following detailed description thereof in conjunction with the apparatus shown in the accompanying drawing, in which the single figure is a front elevation, partly in section, of one form of apparatus which may be employed.

Referring to the drawing in detail, I designates i a reaction chamber provided with trays 2 on which are arranged beds of catalytic-material 3.

Normally liquid hydrocarbon feed stock to be cracked or dehydrogenated is introduced into the system through feed line 4 and passed through hydrocarbons. Each of pipes B terminates inside the reactor in a distributing head I 0 which may be of any desired type. VArranged in feed line 3 is a heater I I.

When the catalyst has lost its activity it is regenerated by burning off the carbonaceous material deposited thereon. This is accomplished by passing a: stream of air, preferably diluted with steam or an inert gas, through the catalyst at a temperature of about l000 F. suitable for the combustion of the carbonaceous material. The regenerating medium may be introduced to the reaction chamber through line I2 connecting with line ,4 and the products of regeneration removed through line I4 branching from line 6.

It is advantageous to provide bailles between the catalyst beds 2 in order to insure a thorough and uniform mixing of the heating medium and the reaction material.- These baiiies may take the form of annular plates I6 and I1v spaced from 'each other with a central circular plate I8 beer materials pass off at the top through line 25..

It is to be understood that fractionator 22 may be so operated that only hydrocarbons boiling above the gasoline range are withdrawn at the bottom, gasoline is withdrawn as a side stream and lighter hydrocarbons are taken off at the top, When operated as illustrated, the liquid products withdrawn through line 23 are separated into gasoline and a recycle stock.

Line 25 is provided with a branch line 26, controlled by a valve 21, through which the hydrocarbon mixture carried oif from fractionator 22` may be introduced between the plates of a second fractionator 28 which is suitably refrigerated to cause the condensation of propaneand higher hydrocarbons. Fractionator 28 is provided with a liquid 'drawoff line 29 connected with line 9 and controlled by a valve 30 and a gas drawofl. line 3|. Line 25 is connected with line 29 below valve 30 in order that the fractionator may be bypassed in the event that the composition of the light fraction recovered from fractionator 22 is suitable for recycling without fractionation.

As before mentioned, the recycle gas may be first subjected to polymerization treatment to polymerize readily polymerizable constituents such as butylenes before being returned to the catalytic chamber. To this end, the return line 29 is providedv with a valve 32 and with a branch line 33 leading to a suitable polymerizing unit. For purpose of illustration, there is shown a polymerizing unit employing sulphuric acid as a catalyst, it being understood that other types of polymerizing units may be employed. i

With valve 32 closed and valve 34 in branch line 33 open,the recycle stock passes through line 33 to a polymerization chamber 35 to which sulphuric acid catalyst may be fed through line 33 so as to pass through chamber 35 concurrently with the recycle stock. It is to be understood that feed line 36 may be provided with a dispersing tom of whichacid is withdrawn through line I9A and from the upper end of which hydrocarbons are withdrawn through line 40 and discharged into a separator 4I held under conditions suitable for the condensation of Cs and higher hydrocarbons which are lwithdrawn from the bottom thereof through line IZ. The remainder ofthe recycle stock is conducted from separator l4I back to line 29 through line d3.

It is apparent that many changes can be made in the process above described without departing from the scope of the present invention. No

attempt has been made to indicate in the drawing the various points at which heat exchangers may be advantageously employed. It may be mentioned that considerable heat conservation may be realized by effecting heat exchange between the outlet or reaction chamber i and recycle feed line 29. In addition, as previously stated, the catalyst may be arranged in a single bed of considerable depth and the reaction material and the heating mixture introduced into the bed vthrough suitably arranged tubes. It is to be understood also that a plurality of reactors will be employed, with one or more reactors on regeneration while the others are on stream. In such an arrangement the products of regeneration are employed to preheat the feed stock to reactors on stream, preferably being first passed into heat exchange relation with the light hydrocarbon heating medium and then into heat exchange relation with the heavier feed stock.

The natureand objects of the present invention having thus been described and illustrated, what is claimed as new and useful'and is desired to be secured by Letters Patent is:

l. A process for cracking liquid hydrocarbons which comprises preheating said hydrocarbons substantially to the desired cracking temperature, passing the preheated hydrocarbons through a-plurality of spaced layers of a cracking catalyst contained in a reaction chamber, simultaneously preheating a mixture of light hydrocarbons, including hydrocarbons ranging from Ca to Cs, to

a temperature above the desired cracking temperature, introducing the preheated light hydrocarbons into the reaction chamber at points Vbetween adjacent layers of catalystand removing the reaction products from the reaction chamber.

2. A process for cracking liquid hydrocarbons which comprises preheating said hydrocarbons to substantially the desired cracking temperature, feeding the preheated hydrocarbons to a mass of cracking catalyst, removing the reaction products from the catalytic mass, recovering from -the reaction product a fraction boiling within the gasoline range and a separate fraction including Ca to Cs saturated and unsaturated hydrocarbons, subjecting the latter fraction to a treatment suitable f or the removal therefrom of unsaturated hydrocarbons, heating the residual light fraction to a temperature above the desired cracking temperature and feeding the heated light hydrocarbons to the catalytic mass together with the initial material.

3. A process, according to the preceding claim,

in which the unsaturated light hydrocarbons are 4removed bypolymerization by the action of an acid polymerizin'g agent.

4. A process for cracking liquid hydrocarbons to produce hydrocarbons boiling within the gasoline range which comprises preheating said hydrocarbons substantially to the desired cracking temperature, feeding the preheated hydrocarbons to a granular mass of cracking catalyst maintained at the desired reaction temperature, removing the reaction products from the catalyst mass, dividing the reaction product into a fraction containing only hydrocarbons boiling .at least in the gasoline range, a fracti'on composed mainly of Ca to Cs hydrocarbons and a lighter :traction mainly composed of permanent gases,

heating the intermediate fraction to a temperature above the desired cracking temperature but below the temperature at which any substantial decomposition of the intermediate fraction occurs and feeding the heated intermediate fraction into said reaction zone and into the catalyst at spaced points alon'g the length of said reaction zone to supply heat to said reaction zone without supplying heat by indirect heat exchange.

5. A process, according to the preceding claim, in which the catalytic mass employed is a clay containing phosphoric acid.

6. A process for cracking normally liquid hydrocarbons to produce motor fuels which comprises heating said hydrocarbons substantially to a cracking temperature, passing the heated hydrocarbons through a plurality of spacedbeds of granular cracking catalyst contained in a reaction chamber, introducing a mixture of heated relatively light hydrocarbons into said reaction chamber at points between certain adjacent beds of catalyst to supply additional heat to the normally liquid hydrocarbons'undergoingl cracking and to maintain them at cracking temperature, the 'light hydrocarbons consisting essentially of C: to C5 hydrocarbons and being heated to a higher temperature than the cracking temperature for the normally liquid hydrocarbons but below the temperature at which any Asubstantial (decomposition of the light hydrocarbons occurs tially of Ca to C5 hydrocarbons and Ahaving a y higher thermal stability than the normally liquid hydrocarbons, introducing the preheated light hydrocarbons into the catalyst mass at spaced points alongthe path of travel of the normally liquid hydrocarbons therethrough to supply heat lost during the-conversion as the normally liquid hydrocarbons pass therethrough and to maintain the desired extent of conversion without supplying heat by indirect heat exchange, removing the reaction products from the catalyst mass and recovering therefrom a hydrocarbon mixture boiling within the gasoline range.

8. A process for cracking hydrocarbons which comprises preheating a relatively heavy hydrocarbon oil substantially to the desired cracking temperature, passing the preheated hydrocarbon oil through a relatively large granular mass of particles of a cracking catalyst in a reaction chamber, providing a mixture of light hydrocarbons consisting essentially of C3 to C5 hydrocarbons and having a higher thermal stability than the normally liquid hydrocarbons, separately heating the light hydrocarbons to a temperature above the desired cracking temperature for the 10

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