AU427199B2 - Continuous process for preparing extruded alumina bodies - Google Patents

Description

75 i,

The present invention relates to a continuous process for preparing extruded alumina bodies and more particularly to alumina bodies suitable for use as a carrier for hydrotreating catalysts.

The present invention provides a continuous process for preparing alumina which comprises continuously reacting together an alkaline aluminate, an acidic reagent, and from 0-20% based on the dry weight of AI 0 produced 2 3 of an alkali silicate, in an aqueous medium while maintain- ing a pH of from 5-12 the concentration of the aluminate being 1-25% by weight as AI 2 03 of the slurry; filterinr the resultant precipitate; drying at a temperature of from 200-1000°F.; recovering the dry powder; washing the powder; prewetting the powder to form a slurry mix; extruding the slurry mix and recovering the extruded

pellet.

The use of synthetic sillca-alumina compositions as carriers for catalysts is well known. Certain types of clay carriers, such as acid activated montmorillonite, have also been used in the refinery processes.

Hydrotreating is a process designed to remove sulfur, nitrogen and metals from feedstock and finished products, and some hydrogenation of olefins occurs. An important use is to remove catalyst poisons from catalytic reforming feed and it has been proposed for catalytic cracking feed. The removal of nitrogen compounds from

29,0O7 5171 catalytic reforming feed Is desirable because these compounds decrease the isomerization efficiency of the dual-functional catalysts used in catalytic reforming. The sulfur compounds decrease the hydrogenation function.

Four general catalysts are used in hydr'otreating: Oxides or sulfides or molybdenum, tungsten cobalt and

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29,075/71 nickel or any combinations of these. These catalysts are usually on an alumina or zeolite support and the metal oxides are sulfided before use by treatment with hydrogen sulfide In the presence of hydrogen. The catalysts are ac- tive for the three primary reactions of hydrotreating: sulfur and nitrogen removal and olefin hydrogenation. In general, catalytic processes may be described as fixed bed processes, moving bed processes, or fluid bed processes. In the fixed bed processes the catalyst particles, meaning the catalyst and the carrier, are placed In a column and the gases or vapors to be cracked are passed therethrough. In the fluid bed pro- cesses the catalyst particles remain suspended in the gas or vapor stream and are maintained in a fluidized state.

In fixed and moving bed cracking, macrosized particles in the form of pellets or tablets are often used and these particles are subjected to stresses from the weight of the catalyst disposed above them and the pres- sures used in the process. These macrosized particles, therefore must be physically strong and resistant to at-

trition. Alumina, or combinations of alumina and silica, have been used as catalyst carriers or extenders for a considerable time. In many instances, the physical char- acteristlcs of prior art alumina or alumina and silica carriers have-left much to-be desired.- For example, it Is often found to be impossible to extrude the carriers into pellet form. Carriers that have been extruded into pellet form have the undesirable characteristics of having an excess of a glassy phase, a relatively low porosity, or

A 427.199

2 075m7 of being exceedingly difficult and expensive to manufac- ture. It would be an advantage to the art if a method could be found for preparing alumina that could be easily extruded. A further advantage to the art would be a con- tinuous process for preparing alumina. Extruded alumina bodies would find ready acceptance for use in conjunction with various catalytic promoters in operations such as hy- drocracking, desulfurizatlon, hydrogenation, and similar catalytic operations. It, therefore, becomes an object of the subject invention to provide a continuous process for preparing alumina that can be easily extruded. It is a further object of this invention to provide extruded alumina bodies that can be used as a car- rier for fixed bed catalysts. Other objects will appear obvious to those skilled in the art. In accordance with the invention, a continuous process for preparing an extruded alumina carrier has been discovered. The carrier is characterized as being suit- able for carrying various catalytic promoters for use in operations of a general type which includes hydrocracking, desulfurization, hydrogenation, and similar operations. The synthetic alumina or silica-alumina compositions are prepared by a continuous process of pumping the reactants into a reaction vessel and withdrawing the precipitate product. This process enables alumina or silica-alumina compositions to be produced which can be extruded to form pellets or tablets that can be used in a fixed bed process.

427.199

2 075,71 The following Is a brief outline of the steps and conditions essential to practice this invention: I. -The alumina or alumina and silica are pre- cipitated from an alkaline aqueous solution at a pH be- tween about 5 and 12.0 and preferably 6.5 to 8, using an' alkali metal aluminate, an acidic reagent, and if desired, an alkali metal silicate, as the reactants.

2. This precipitation takes place at a focal point where all the ingredients are introduced at the same 2 time. 3.The concentrations of the reactants employed are controlled and the concentration of alumina in the final slurry is within the range of from 1-25% as A12 03 and the most preferred concentration of the alumina in the slurry is within the range of 5-15% as A12 03 The slurry may then be washed and is filtered to increase the concentration of the A1 0 to about 2 3 10-2C. 4. The precipitate is then dried at a tempera- ture of from 200-1000F. Spray drying has been found very effective.

The dry powder may then'be washed and is prewetted with water to form a slurry mix. 6. The slurry mix is then extruded. The extruded bodies are then recovered asa 'fixed bed catalyst. The precipitation step should take effect at a temperature within the range of from 70-135"F., more pref- erably between 95 and 110 0F. The pH during precipitation Is critical in obtaining an alumina carrier with the desired physical characteristics. The precipitation must be ef-

427.199

2 9 0 75/71 preferably between fected at a pH between 5 and 12.0 but at a high pH, and 8. If the precipitation is effected glass-like in char- the resultant alumina composition is properties as to ex- acter and does not have the desired trudibility. in the sub- The acidic reagents which are useful aluminum salts of ject invention include mineral acids and are mineral acids. Typical mineral acids which are useful

hydrochloric acid, sulfuric acid, and nitric acid. acids are most useful. Alumina salts of the aforementioned solution The aqueous alkali metal aluminate of the subject in- which is most preferred in the practice vention is sodium aluminate. However, it is not intended to the use of sodium to limit the scope of the invention 13 aluminate. The term "alkali metal aluminate solution" the aluminum salts of the intended to include solutions of When an aqueous various alkali metals and of ammonium. in order to form alkali silicate is added to the solution of silicate added a carrier containing silica, the amount carrier contains an must be controlled so that the dry by weight. More amount of silica equal to from 0-20% in the carrier preferably, the amount of silica present silica, and expressed should be between 1-10% by weight of the in- as SiO 2 The most preferred silicate for use in the term "alkali vention is sodium silicate. However, is intended to metal silicate" as used in this invention of the alkali metals include the silicate salts from all and of ammonium. of the subject In a greatly preferred embodiment presence of invention the precipitation is effected in the

7. 427.199

29.07571 of aldonic a compound selected from a group consisting acid and aldonates. These compounds can be obtained by other suitable man- the oxidation of an aldose or in any used are ner. Examples of acids or salts which may be and mannonlc. gluconic, galactonic, arabonic, xylonic in Instead of employing the free aldonic acid a salt there- the preparation of the alumina composition, It will be of can be used, preferably the sodium salts. is not limited to understood, however, that the invention the type of aldonate employed. Typical other suitable and aldonates are potassium, zinc, magnesium, calcium, gluconic acid or other aldonic acids. The preferred pro- are within the portions of aldonic or aldonates employed calculated as range of about 0.5%to about 6% by weight gluconic acid based on the dry A12 0 3 content. Excellent results have been obtained with the calculated as use of about 2 to about 3% of the aldonate Although gluconic acid based on the dry weight of A12 0 3 the aldonic acid or aldonate is preferred in the practice

of this invention, it has been found that this chemical

can be eliminated from the production of the extruded alumina bodies. The time of the precipitation reaction may vary

over a considerable range. Preferably the reaction is

carried out almost instantaneously when the ingredients enter the reaction vessel. Therefore, the reaction vessel

need not be of a large volume. In fact, the reaction ves-

sel could consist of a pipe into which all the ingredients are being fed at the same time. The precipitate should be being forming immediately and therefore be capable of 8 427.199

29.o7517t. withdrawn so that it can be filtered and washed as out- lined in the process of the invention.

The washing step removes impurities, mostly sodium sulfate, from the precipitate or the dry powder. Therefore, this washing step is performed either after precipitation and filtering or after spray drying and before extrusion. The latter is preferred.

The limiting factor of the invention is the raw materials which are fed into the reaction vessel. As long as these are readily available and are being pumped into the reaction vessel the process should be continuous. In a preferred embodiment of the invention, the slurry is filtered after precipitation to increase the concentration of solids to approximately 10-20 by weight of A 0 3 The alumina carrier is then spray dried using either the countercurrent or the concurrent drying method. The temperature of spray drying can vary within the range of 200-1000*F. under conditions so that the temperature of the particles at completion of the spray drying process is within the range of 150-350 F. 0

.After spray drying, the alumina or alumina- silica particles are purified of excess alkali metal ions and sulfate ions by conventional methods. For best extru- sion results, a prewetting step is used. A carrier is ad- justed to a free moisture content of 48-56% and more pref- erably 52-54J% by weight. This prewetting step makes the slurry mix more susceptible to extrusion. If the process steps of the in- vention are carefully followed, excellent extrudates are formed, ranging in diameter from about 1/32 inch to about 9 427.199

29,075, 3/16 inch. The alumina or alumina-silica carrier prior to

the extrusion is in the form of a powder. The extrusion

can be accomplished by any of several well-known methods. All the methods involved forcing the powdery particles through openings in a die with sufficient water as men- tioned above, to provide the proper plasticity and lubri- cation for extrusion. The invention will be further il-

lustrated but is 'not limited by the following example. EXAMPLE I

Four tanks fitted 'with rotometers were set up to produce the alumina. Tank I contained 14.7 gallons of

Na2 AI2 04 solution containing 24.5% by weight calculated as A1 0 and containing 5% by weight in excess NaOH, 180 ml. 2 3

of 50% gluconic acid, and 19.5 gallons of water. The 0 temperature was maintained at 96 F. Tank 2 contained 1135 ml. Na2 SiO3 and 19.5 gal-

lons of water. The temperature was maintained at Tank 3 contained 5.1 gallons of an aluminum sul- fate solution containing 7.8% by weight calculated as A1 0 2 3and 19.5 gallons of water. The temperature was maintained at 900F. Tank 4 contained 3.6 gallons of 660 B6 sulfuric and 19.5 gallons of water. The tem- :acid (98% by weight) perature was maintained at IIOF, The rotometer settings of each cf the first

three tanks were set to deliver 0.4 gallons per minute. On the fourth tank, the settings were placed so as to de- liver 0.185 gallons per minute. All of the tanks fed directly into the reaction p27.199

29.07 5 /7 vessel. The alumina was produced almost instantaneously, and thus could be quickly withdrawn.

The pH of the precipitated mix was 9.2 when mea- sured by a pH meter and had a temperature of 1350F. The precipitated mix was collected at approximately 1.385 gal- lons per minute. This was then washed, filtered and spray dried at 3000F. using a conventional spray dryer. The powder produced was collected and prewetted with water to form a slurry; which was then extruded. Pellets of alumina were recovered as finished product. The pellets of alumina had a surface area of 360m2/g, a total pore volume of 0.56 cc/g and a crushing strength of 9.6 pounds. Based on these results, it would be obvious to one skilled in the at that these pellets would be of interest as a catalyst support.

427.199

Claims (1)

1. 29,075171 The claims defining the invention are as follows:-

   1. A continuous process for preparing alumina which comprises continuously reacting together an alkaline

   aluminate, an acidic reagent, and from 0-20% based on the dry weight of Al203 produced of an alkali silicate, in an aqueous medium while maintaining a pH of from 5-12

   the concentration of the aluminate being 1-25% by weight

   as Al 2 0 3 of the slurry; filtering the resultant precipitate; drying at a temperature of from 200-1000 0 F.;

   recovering the dry powder; washing the powder; prewetting the powder to form a slurry mix; extruding the slurry mix and recovering the extruded pellet.

   2. A process according to claim 1 which comprises

   continuously reacting together the alkaline aluminate,

   the acidic reagent, from 0.5-6% based on the dry weight

   of Al203 produced of a compound selected from the group

   consisting of aldonic acid and aldonates, and from 0-20%

   based on the dry weight of Al2 0 3 produced of the

   alkali silicate.

   3. A continuous process according to claim 2 wherein the aldonate is gluconic acid and ranges from

   2-3% based on the dry weight of A1 2 0 3 produced and the pH

   of the aqueous medium ranges from 6.5 to

   4. A continuous process according to claim 2

   427.199

   29,0O75/7f or 3 wherein the alkaline aluminate is sodium aluminate, the acidic reagent is aluminum sulfate, the aldonate i3 gluconic acid, and the alkali silicate is sodium silicate.

   The Process Of claim 1 substantially as described in the Example.

   DATED this NIIETrZTH day Of MAY, 1971

   14ALCO CHEIIC'U COmPANqY

   Patent Attorney for the 'SPRUStW& PERGUSO),a Applicant

   '-42799

   29,075/71

   42Z199--