USRE23145E

USRE23145E - Two-stage synthesis of

Info

Publication number: USRE23145E
Authority: US
Publication date: 1949-09-06

Description

Reicsued Sept. 6, 1949 TWO-STAGE SYNTHESIS OF HYDROCABBONS Frank T. Barr, Summit, and Walter G. Sammann, Westfield,

Delaware Original No. 2,434,537,

Dec

Serial No. 568,514, cation for reissue 70,566

Our invention relates to the novel features hereinafter disclosed in the following specification and claims, reference being had to the accompanying drawing.

' The synthesis of hydrocarbons, including oils, from carbon monoxide and hydrogen is a matter of record. Our improvements involve a two-stage process in which we employ a fluid catalyst reactor in the first stage bed reactor in the second stage. Since the fluid catalyst type of operation is more flexible than the stationary bed type of process, we are enabled to secure the benefits of our invention which will be described presently. We so control the process that in the first stage of our process, only those hydrocarbons which are gaseous or exist as vapors under the conditions of operation are formed in the first stage of our process. The reason underlying this technique is that we desire to avoidwax or liquid formation on the powdered catalyst employed in the fiuid" stage of the process. As is known, wax is formed in the normal synthesis and this wax deposits on the catalyst requiring washing to remove the same. It is difficult to remove wax from a powdered catalyst. But more important perhaps,- is the fact that it is difficult to carry out a fluid catalyst type of operation in the presence of a liquid and hence we operate the process so as to limit the operation to the formation of hydrocarbons which are vaporized at operating temperaturesand then discharge the products of this first stage into a second, fixed bed stage where the conversion is continued.

It is one of the objects of this invention, therefore, to conduct the synthesis of hydrocarbons from C and hydrogen in a process where advantage is taken in both the fixed or stationary bed type of operation and the fluid catalyst type of operation, 1, e., in which the catalyst is suspended in'the reaction gases. Another object of our present invention is to provide means for effecting the synthesis of hydrocarbons, including normally liquid hydrocarbons, by reacting together CO and hydrogen in the presence of a suitable catalyst so as to produce maximum quantities of desired hydrocarbons in an expeditious and relatively cheap manner.

A further object of our invention is to provide means for synthesizing normally liquid hydrocarbon oils by reacting CO and hydrogen in the presence of a catalyst under conditions aflording rigid temperature control.

Other and further objects 0!. the inventlonwlll 55 a fluid catalyst reactor N. J., assignors to Standard Oil Development Company, a corporation 01 dated January 13,1948,

and a fixed or stationary ordinary means of temperaturecontrol.

ember 16, 1944. January 12, 1949, Serial No.

carbons higher than methane.

Appli- 13 Claims. (Cl. 260-4495) 2 appear from the'iollowing more detailed description and claims.

In the accompanying drawing, we have shown diagrammatically a combination of apparatus elements in which a preferred modification of our invention may be carried into practical effect. Explaining at first, in a general way, the flow of reactants through the system illustrated in the accompanying drawing, we wish to point out the theory upon which our improvements are based. In the synthesis of hydrocarbons from carbon monoxide and hydrogen over stationary catalyst, the reaction in the inlet at rates suificiently high so that temperature control is diflicult and expensive equipment is necessary to prevent temperature runaway from occurring. At the end of the reaction, however, the decrease of concentration of reactants together with higher thermal stabilizing effect of the inerts makes the fixed bed operation more amenable to Fluid catalyst operation for hydrocarbon synthesis, on the other hand, provides a means of temperature control suflicient to prevent runaway operation at any reactant concentration, but formation of liquid sometimes tends to coat the catalytic particles and reduce their activity. Inasmuch as the fluid catalyst technique does not lend itself readily and economically to the removal of the liquid material from the catalyst, such formation is distinctly disadvantageous.

As indicated we have found that it is advantageous to combine the two types of operation. The fluid catalyst operation is used on the fresh synthesis gas under conditions such that only a portion of the synthesis gas is converted to hydro- Conversion is limited so that materials liquid under the conditions of operation are not formed. The tail gas from this stage is led to fixed catalyst synthesis reactors. The concentration of reactants is now suiliciently low that satisfactory temperature control in fixed bed operation is obtained as described above and liquid products such as may be formed drain from the catalyst without impeding theprogress of the reaction. The tail gas from the second stage is led to a cooler-condenser and naphtha recovery plant. Tail gas from the fluid catalyst section may be cooled if desired but operation taking the gas directly from the separating system is simpler and ordinarily superior.

In the drawing similar reference characters refer to similar parts.

. Referring in detail to the drawing, i represents and 2 and 2M represent section tends to proceed threere'actors of which sans 2!! indicates the internal structure and shows the reactor to contain tubes t terminating in tube sheets .5, the catalyst being disposed in the tubes and for circulating a cooling medium from pipes 4 through the several reactors in parallel and withdrawing the cooling medium through pipes 5. In the drawing the cooling medium is indicated as water. but obviously anycooling mediummay be used such, as molten salts, mercury, etc.

The drawing has been provided with suflicient legends and arrows to enable ease in reading and mere inspection is nearly suflicient to understand the operation thereof.

The synthesis gas enters the system proportioned in the ratio of about 2 mols of H: per mol oi-.C0, and then is discharged into the bottom or fluid" reactor I where it passes upwardly in contact with powdered cobalt catalyst containing thoria or magnesia and supported on carriers such as silica gel or kieselguhr. This catalyst is known to the art. Other catalysts known to the art, such as iron promoted by alkali, may also be used. Proportion of H: to CO in the synthesis gas may not be the same as required for cobalt catalysts, and is preferably adjusted to the optimum, which for iron catalysts'is about 1:1. The catalyst size averages 200 mesh, although it may vary from 100 to 400 mesh, As a matter or fact, a substantial portion say 20% or the catalyst may have a size of low than 20 microns. Depending on the size of the particles 01' catalyst, the velocity of the gases in reactor l is controlled within the limits of 0.25 to 5 feet per second preferably from V to 3 feet per second. There results a fluid mass, i. e., a dense suspension of catalyst in gas. Also depending on the weight or amount of catalyst in the reactor, there will be an upper dense phase level at L and above L, adlsengaging space S where the concentration 01 catalyst drops sharply so that when the gas enters the solid-gas separating device(s) I (which may be one or more" "cyclone separators) the concentration oi. catalyst is low (ranging from 0.075 to 0.003 lb. per cubic foot) As indicated thegas passes through the separatofls) 1 wherein is removed and finally exits via line 6. Separated catalyst is returned from the separator(s) 3 via dip pipe I. 1

Since the reaction between CO and H2 is exothermic, it is advisable the manifolds M: and pipe I. Very accurate and rigid temperature control may be achieved by the method indicated due to the turbulent state of the fluidized catalyst constantly particles or a gas, thus provision being made 0 additional catalyst The scrubbed vapors leave scrubber ll via line It, then are forcedthrough a cooler ll, thence pass into a separator Ila and thence pass to the stationary catalyst via line II. In separator lIa,

' water and hydrocarbons (boiling below about 400 F.) collect at the bottom or the separator and may be recovered therefrom.

As indicated, the

the bottom by operation 'of product is cooled in i1 and colsuits First, in reactor 1 Preferred Range Broad Range Cobalt Iron Catalysts Catalysts Pressure in lbs. per sq. in..- mos-360 15-125 40-250 Temperature in (1 cos l 850-700 400- 600-050 Through ut (cubi i eet CO 500 at 60 and i atmos. per

lb. of catalyst) hour)? l-15 1-15 V onversion 0 .per can 6 35-00 35-00 Catalyst In powder form Second, in reactor z on original gss) .per oent-. 70-100 -100 80-100 Catalyst In the tom of pill; pellets, granules,

It is not necessary that the same composition of catalyst be used in the above two stages.

ereas conditions of operation operation, cooperating in conjunction with each other We have found that the combination of the two methods of oplexiting is advantageous for the reasons set forth In fixed catalyst operation for the synthesis of hydrocarbons from carbon monoxide and hydroen. it has been ioundthat reaction rates near the entrance of inert materials builds u tion rates are slower to:- given exigencies oi temperam lince it is ordinarily necessary to adiust conditions to those required at the point of maximum reaction rate, operation of the remaining catalyst volume is sometimes at conditions far removed from optimum eillciency. We avoid this diillculty by using the field catalyst technique for operation on fresh synthesis gas, whence the critical initial conditions are better controlled, and the fixed catalyst reactors operate at conditions nearing optimum efficiency for all parts of the bed.

In the use of the fluid catalyst technique for synthesis of hydrocarbons from carbon monoxide and hydrogen another desirable process involves the passage of the synthesis gas with catalyst suspended therein through tubes whose walls act as heat transfer surface for removal of the heat of reaction. Optimum operating conditions are such that tubes of 3-4" inside diameter are used and the total passage length. is of the order of 400-1000 ft. Variation of capacity of the reactor is achieved by putting two or more of these elements in parallel. The relations indicated are based on obtaining optimum heat transfer rate together with the desired time of contact for the reaction.

Here, however, the same difficulty arises as when the synthesis is carried out using fixed catalyst as described above. Although various methods for obtaining control suited specifically to the reaction going on in that part of the equipment under consideration have been proposed, we have found that a particularly advantageous method of obtaining said control involves the charging to the fresh synthesis gas of relatively small quantitles of fluid catalyst, such as will promote the reaction only to a limited degree. Because of the high reactant concentration at this point, reac tion rate can be maintained at a reasonable level with a smaller proportion of catalyst than at subsequent. points in the reaction path. At the point where reaction with the amount of catalyst originally supplied has decreased to an undesirably low level, additional catalyst is supplied. The increased quantity of catalyst brings the reaction rate to the desired level. The charging of additional catalyst may be repeated a number of times as desired and conditions may be set so as to achieve high conversion of the reacting materials.

Construction of equipment having such relatively long passage length would normally entail the assembly in series of a number of units of shorter passage length. Thus, a passage length of 560 ft. is in one case achieved by putting in series 28 units, each having tubes 20 ft. in length. Transfer of the reacting materials, from one unit to another in this arrangement is disadvantageous, however, owing to the necessity for making the transfer tlmeas shcrtas possible, because of the absence of adequate cooling surface. Although satisfactorily short transfer time can be provided, velocities through the transfer lines are great and pressure drops are thereby large.

We have found that for fluid catalyst operation the employment of a large number of passes within one shell is more satisfactory and is feasible from a mechanical point of view. Whereas in fixed catalyst operation the use of several passes in one shell involves the necessity for providing means for removal of the return bends for charging and discharging catalyst, such arrangement is not required with fluid catalyst. It is therefore possible to assemble with welded or otherwise permanently secured return bends a large number of relatively short lengths of tubing in a single of travel. For example, the 560 ft. of travel referred to above may be achieved by inserting in one shell 28 lengths of 20 ft. tubing connected in series by return bends. The return bends as well as the tubes may be surrounded by the coolin medium which in tumis and is outside the tubes. Fixed connection with lines outside the shell is necessary only at the chanical allowance to take care of differential thermal expansion difllculties is not required. In

case it is desired to assemble a number of the multiple pass units in parallel in a single shell, inlet and outlet headers within the shell may be provided. It is again necessary to provide secure connection to the shell for only one inlet and one outlet pipe. This arrangement has the further advantage of making assembly and dismantling of the equipment simple, inasmuch as the entire tube bundle can be removed from the shell by breaking piping connections at only two points.

It is apparent that any combination of theseries and parallel arrangement within one shell may be made. Under certain conditions achievement of the 560 ft. passage may be obtained, for instance, by connecting '1 lengths of 20 ft. tubin in series in a. single shell and putting 4 such shells in series. The number of 20 ft. passes in each shell need not be the same but may be varied as desired, providing only that the required total passage length be obtained.

It is pointed out that more than one fluid or fixed bed may be employed in the combination of fluid and stationary catalyst operation disclosed herein, and temperature control provided for each bed. For the fixed bed operation, a suitable arrangement involves the assembling in a vertical tower of a plurality of thin beds of catalysts, the catalyst in all cases being disposed suitably close to aheat removal surface. for instance, in small tubes or annular elements, and suitable separators being inserted in the shell on the cooling medium side to make possible independent control of the cooling medium temperature at each level. Catalyst tubes may extend through several cooling sections if desired and would be limited only by the length of tube available. An alternate arrangement involves the use of short tubes, the length of each cooling section, but with succeeding sections superimposed so closely that a minimum of free space between catalyst sections is allowed. This arrangement has the ad- 55 vantage that sections are transferable and individually removed for maintenance. A crane may be provided for assembling and dismantling sections stacked as many on one another as is desired.

It will be understood that periodically it may be necessaryto remove wax from the stationary beds of catalyst, for the said wax deposits on the catalyst and diminishes its activity. The cata- 'lyst may be washed with a hydrocarbon oil, dur- 65 ing a shut down period toeiIect this result. The

details of washing the catalyst to de-wax the same are known to the prior art.

Numerous modifications of our'invention will appear to those familiar with this art without 70 departing from the spirit thereof.

What we claim is: 1. In the process of synthesizing hydrocarbons. including hydrocarbon oils, by contacting carbon monoxide and hydrogen properly stoichiometri- 75 cally proportioned at elevated temperatures and 6 shell so as to obtain the desired length contained in the shell entrance and exit of the 28tube element. Mei can pressures with a catalyst, the improvement which comprises efl'ecting rigid temperature control by first suspending catalyst in the synthesis gases to form a dense suspension, maintaining said suspension at conversion temperature and under conversion pressure and limiting the time of contact or said gases with said catalyst in said suspension so that hydrocarbons which are liquid'at the operating conditions are not formedin sub-- stantial amounts while efiecting a substantial conversion of said carbon monoxide to hydrocarbans but not more than about 60% of the amount possible under the reaction conditions, withdrawing residualsynthesis gases from said suspension and discharging them into a zone containing at leastone stationary bed of catalyst maintained-at reaction temperature and under reaction pressure, holding said synthesis gases in contact with 500". F. and the pressure from about to 250 lbs. per sq. in. gauge. a

5. The method of claim 1 in which the tem- V perature in the first stage is from about 375 to said stationary bed of catalyst for a sufficient period of time to convert additional amounts of carbon monoxide into normally'liquid products and recovering said normally liquid products from the second reaction zone.-

2. The method of synthesizing hydrocarbon oils which comprises forcing a mixture of carbon monoxide and hydrogen into a first reaction zone maintained under reaction conditions and containing a body of powdered catalyst inthe form of a dense suspension, limiting contact; time of reaction material with catalyst and temperature in said first reaction zone to suppress substantial formation of hydrocarbons which are liquid at the operating temperature while effecting substantial conversion of said carbon monoxide to hydrocarbons but not more than about 60% of the amount possible under the reaction conditions, withdrawing gaseous reaction material from said first reaction zone and discharging it into a zone containing at least one bed of stationary catalyst maintained under reaction conditions, carrying the reaction in said second reaction zone to maximum production of normallyliquid products and recovering from said second zone a tainlng gasoline and gas oil.

3.-The method of claim 1 in which the temperature in the first stage is from about 350 to 500 F. and the pressure is from about 10 to 250 lbs. per sq. in. gauge.

4. The method of claim 2 in which the temproduct conperature in the first stage is from about 350 to 450 F. and the pressure from about 25 to lbs. per sq. in. gauge.

6. The method of claim 2 in which the temperature in the first stage is from about 375 to 450 F. and the pressure from about 25 to 100 lbs. per sq.'in. gauge.

7. The process specified in claim 1 in which the feed rate in the first stage is from about 1 to 15 cubic feet of CO per hour per lb. of catalyst.

The method specified in claim 2 in which the feed rate in the first stage is from about 1 to 15 cubic feet of CO per hour per lb. of catalyst.

9. The method of claim '1 in which the feed rate to the second stage is from 100 to 1000 volumes of gas per volume of catalyst per hour.

10. A method for synthesizing hydrocarbons which comprises forcing CO and H2 through a fiuid mass of powdered cobalt containing catalyst in a first reaction zone at temperatures within the range of from about 350 to 500 F. at feed rates of 1 to 15 cubic feet of CO per hour per lb. of catalyst whereby the formation of hydrocarbon liquid at operating conditions is suppressed, withdrawing the reactants and forcing them through at least one body of pilled catalyst in the form of a fixed bed in a second reaction zone at temperatures within the range of from about 350 to 500 F. at feed rates of from about 100 to 1000 volumes of gas per volume of catalyst per hour, causing a heat absorbing fluid to circulate in heat exchanging in relationship with the reactants in both zones and recovering hydrocarbons including gasoline and gas oil from said second zone.

11. The method of claim 10 including th step of cooling reactants during their passage from the first to the second zone.

12. The method of claim 10 in which the feed to the first zone contains 2 mols of H2 per mol No references cited.