Patent Abstract:
A method for producing high porosity boehmite alumina wherein an aqueous boehmite slurry is mixed with an effective amount of a modifier comprising a hydroxide or oxide of an element of group IIIA-VIA on the Periodic Table of Elements and having a pKsp of greater than 11 to produce a precursor mixture and hydrothermally aping the precursor mixture at an elevated temperature under agitation with an effective consumptive power of greater than 1 kW/m 3 .

Full Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority of U.S. Provisional Application No. 60/711,295 filed on Aug. 25, 2005, the disclosure of which is incorporated herein by reference for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a process for producing boehmite aluminas and, more specifically, to a process for producing high porosity boehmite aluminas. 
         [0004]    2. Description of Prior Art 
         [0005]    U.S. Pat. No. 6,048,470 discloses an alumina sol of high transparency and porosity, the alumina sol being prepared by stirring a dispersion of an alumina hydrate having a solids content of from 1 to 40 wt. % at a pH of from 7 to 12 with an effective consumptive power of at least 0.5 kW/m 3  for aggregation, and then adding an acid for peptization. The process preferably includes the addition of a base, preferably a water soluble base such as an alkali metal hydroxide, to adjust the pH of the alumina hydrate dispersion to the desired pH range. 
         [0006]    EP 0934905 discloses a process for producing a boehmite alumina wherein an alumina hydrate is dispersed in an acidic solution at a pH of about 3 to 4. The acidic dispersion is adjusted to a pH of 10 with an alkaline reagent such as sodium aluminate, sodium hydroxide, potassium hydroxide or the like. The dispersion is then heated to 80EC and stirred for a period of 4-20 hours following which the pH level is adjusted to 8 with an acidic reagent to prepare a colloidal sol. 
         [0007]    High surface area gamma aluminas which are produced from boehmite aluminas are commonly used as catalyst supports. For example, catalysts comprising relatively small amounts of precious metals deposited on high surface gamma aluminas are commonly used in catalytic converters for the auto industry. Increasingly, the catalytic converters are being placed closer and closer to the engine exhaust to more quickly reduce emissions. This close proximity to the engine exhaust subjects the catalyst to higher operating temperatures requiring that the support, e.g., the gamma alumina, be stable, i.e., retains a high amount of surface area and does not convert to alpha-alumina, at these higher temperatures. 
       SUMMARY OF THE INVENTION 
       [0008]    In one aspect, the present invention provides a process for producing a high porosity boehmite alumina. In a preferred embodiment of the process, an aqueous boehmite alumina slurry is mixed with, prior to and/or during a hydrothermal aging step, a modifier or additive comprising a water insoluble hydroxide or oxide of an element of Group IIIA-VIII of the Periodic Table of Elements. The hydrothermal aging is preferably conducted at a temperature in the range of 100-160EC, more preferably at 130-160EC, under agitation with an effective consumptive power of greater than 1 kW/m 3 , preferably from 5-12 kW/m 3 . Aging (residence) times in the aging step can range from 1 hour to 24 hours. The pH of the slurry during the hydrothermal aging will range from 8 to 10 and the modifier is one which has a pKsp of greater than about 11 and does not alter the pH, either of the feed slurry or of the product from hydrothermal aging step. 
         [0009]    In another preferred aspect of the present invention, the above process is carried out using certain insoluble or sparingly soluble hydroxides or oxides of metals which impart enhanced thermal stability when the boehmite aluminas are converted to gamma aluminas. While it is known that the thermal stability of gamma aluminas is enhanced by high porosity, the addition of certain metal dopants further enhances this thermal stability. 
         [0010]    The process of the present invention can produce boehmite aluminas of comparable crystal size, morphology and porosity as many commercially available aluminas using much shorter hydrothermal aging (residence) times than are conventionally used. 
         [0011]    A feature of the present invention is that the metal oxides and hydroxides which are added to the feed slurry of alumina to be hydrothermally aged cause little to no effect on the pH of the slurry, i.e., there is no change in pH sufficient to change reaction conditions. This is desirable as it is known that highly soluble basic materials such as potassium hydroxide, sodium hydroxide, etc. can result in undesirable thickening of the slurry requiring either that the hydrothermal aging be conducted at high temperatures and/or dilution of the slurry to reduce viscosity. 
         [0012]    A further feature of the present invention is the finding that by using the additives of the present invention in combination with high agitation energy, e.g., greater than about 8 kWm 3  the porosity that is achieved is much greater than what can be obtained without the additive. Effectively, a synergistic effect exists between the use of the additives of the present invention and effective energy consumption. 
         [0013]    According to an especially preferred embodiment of the present invention, it has been found that the addition of 0.1 to 5% wt., based on alumina content of the slurry, of certain insoluble or sparingly soluble metal oxides or hydroxides (modifiers) to the alumina slurry charged to a reactor for hydrothermal treatment reduces the residence time for achieving desired crystallite size and high porosity. Further since such modifiers do not have any appreciable effect on the pH of the slurry, the viscosity of the slurry is unaltered. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a graph showing the effect of various additives on crystallite growth of alumina. 
           [0015]      FIG. 2  is a graph showing the effect of various additives on total pore volume. 
           [0016]      FIG. 3  is a graph showing a comparison of the effect of KOH and aluminum oxide/hydroxide on crystallite growth. 
           [0017]      FIG. 4  is a graph showing a comparison of the effect of KOH and aluminum oxide/hydroxide on total pore volume. 
           [0018]      FIG. 5  is a graph showing a comparison of using aluminum hydroxide with medium porosity alumina and normal aluminas. 
           [0019]      FIG. 6  is a graph comparing KOH and aluminum hydroxide on pore volume. 
           [0020]      FIG. 7  is a graph showing a comparison of KOH and aluminum oxide/hydroxide on pore volume. 
           [0021]      FIG. 8  is a bar graph comparing residual surface areas of prior art, doped aluminas and aluminas made in accordance with the present invention. 
           [0022]      FIG. 9  is a graph comparing the viscosity of aluminas made using soluble and insoluble hydroxides. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0023]    It has been found that when certain insoluble hydroxides or oxides of certain elements are added to a feed slurry of boehmite alumina prior to hydrothermal aging and/or to such a feed slurry which is being hydrothermally aged, crystallite growth is accelerated, the hydrothermal aging or residence time necessary to achieve a desired crystallite size is reduced and, in the case of certain modifiers, the aluminas produced exhibit exceptional thermal stability when converted to the gamma form. 
         [0024]    The amount of modifier or additives employed in the process of the present invention will generally range from about 0.1 to 5 wt. % of the alumina charged to the reactor in which the hydrothermal aging is conducted. A feature of the modifiers of the present invention is that their addition does not alter the pH of the slurry or the product produced thereby. Additionally, as compared to a process wherein a soluble hydroxide e.g., potassium hydroxide, is employed, such as is done in the prior art, the process of the present invention employing the modifiers does not alter the viscosity of the slurry. In the case of soluble, basic materials such as the alkali metal hydroxides, which do result in increased viscosity and concomitant thickening of the slurry, low aging temperatures cannot be used. Further, in certain cases using these soluble alkali metal hydroxides it is also necessary to dilute the slurry to permit processing because of such high viscosity. 
         [0025]    It is known that soluble, basic hydroxides such as the alkali metal hydroxides do enhance the rate of crystallite growth and porosity development under hydrothermal aging conditions conducted with agitation. However, the use of these soluble basic materials increases the pH of the slurry with the result, as noted above, that the slurry may become unprocessable due to high viscosity. Furthermore, alkali metal hydroxides such as potassium and sodium hydroxide are catalytically undesirable metals and the alumina dispersions made using them tend to have high dispersion viscosities due to the effect of the metal ions in solution. Although basic materials such as ammonium hydroxide do not result in this effect since the ammonia is removed when the process slurry is dried, the ammonia does present an air emission problem. 
         [0026]    All of the above problems of using water soluble hydroxides are eliminated by using the modifiers of the present invention while still achieving the desired acceleration of crystallite growth and enhanced porosity. The alumina product produced according to the present invention is highly dispersible in water. 
         [0027]    The process of the present invention employs an aqueous slurry of a boehmite alumina containing from about 9 to about 12 wt. % alumina, calculated as Al 2 O 3 . In general, the process is conducted at a temperature of from 100-160EC, preferably from 130-160EC. The process is conducted with agitation at a consumptive power input of greater than 1 kW/m 3 , more preferably from 5-12 kW/m 3 . In the process, from 0.1 to 5 wt. %, based on the weight of the alumina in the slurry, of the modifier of the present invention is added, either to the feed slurry to the reactor or to the slurry being aged in the reactor. Hydrothermal aging is generally conducted for a period of from 1-24 hours, preferably from 2 to 6 hours. Generally, the pH of the slurry will range from about 8 to about 10 and, as pointed out above, the modifiers of the present invention do not alter the pH of the slurry in terms of changing reaction conditions. 
         [0028]    The modifiers of the present invention are water insoluble or sparingly soluble hydroxides and/or oxides of Group IIIA-VIII of the Periodic Table of Elements. Generally speaking, the modifiers employed will have a pKsp of greater than about 11. As noted, unlike water soluble hydroxides and other basic materials used in prior art processes, the modifiers of the present invention do not alter the pH, either of the feed slurry or of the product produced from the hydrothermal aging step. Generally, using the modifier of the present invention, the pH of the slurry will not be effected by more than about 0.2 pH units and in the case of most modifiers, the pH change is even less. In any event, the modifiers of the present invention cannot be considered as pH altering additives of the type used in the prior art processes. Stated differently, the modifiers of the present invention do not have any pH effect that could be considered to alter the reaction conditions, a necessary requirement of typical pH modifiers used in prior art processes. Non-limiting examples of modifiers useful in the process of the present invention include aluminum hydroxide, aluminum trihydrate, lanthanum hydroxide, lanthanum oxide, cerium hydroxide, etc. In particular, the use of lanthanum hydroxide produces a product which can be converted to a gamma alumina exhibiting enhanced temperature stability. 
         [0029]    The alumina used in the feed slurry of the present invention can be derived from a variety of sources. In particular, a boehmite alumina obtained from the hydrolysis of an aluminum alkoxide is preferred although boehmite aluminas derived from other sources can be used as well. 
         [0030]    To demonstrate the present invention, the following, non-limiting examples are presented. 
       Example 1 
       [0031]    A series of runs were made on various aqueous alumina slurries where no modifier, soluble or insoluble, was employed in the hydrothermal aging. The aqueous alumina slurries contained 12 wt. % boehmite alumina produced from the hydrolysis of aluminum alkoxides. In all cases, the hydrothermal aging was conducted with stirring at an effective consumptive power of 8.3 kW/m 3  (agitator speed of 600 rpm). The reactor employed was a 5 gallon, laboratory reactor, and was operated in a batch mode although the process can be conducted in a continuous mode if desired. The results are shown in Table 1 below: 
         [0000]    
       
         
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                   
                   
                   
                   
                 Crystallite 
                 Calcined at 
                 Calcined at 
               
               
                   
                 Aging 
                   
                 Agitator 
                   
                 Size 
                 1200° C./4 hrs 
                 1200° C./24 hrs 
               
             
          
           
               
                   
                 Time 
                   
                 Temp 
                 Speed 
                 Surface 
                 Pore 
                 Angstroms 
                 SA 
                 PV 
                 SA 
                 PV 
               
             
          
           
               
                 Test 
                 hours 
                 Modifier 
                 ° C. 
                 rpm 
                 Area m 2 /g 
                 Volume ml/g 
                 020 
                 120 
                 m 2 /g 
                 ml/g 
                 m 2 /g 
                 ml/g 
               
               
                   
               
             
          
           
               
                 A 
                 6 
                 None 
                 90 
                 600 
                 231 
                 0.785 
                 80 
                 81 
                   
                   
                   
                   
               
               
                 B 
                 8 
                 None 
                 90 
                 600 
                 230 
                 0.803 
                 76 
                 79 
               
               
                 C 
                 24 
                 None 
                 90 
                 600 
                 206 
                 0.985 
                 117 
                 107 
               
               
                 D 
                 6 
                 None 
                 130 
                 600 
                 183 
                 0.631 
                 78 
                 111 
                 39 
                 0.258 
                 8 
                 0.193 
               
               
                 D 
                 6 
                 None 
                 130 
                 600 
                 217 
                 0.6145 
                 59 
                 89 
                 45 
                 0.242 
                 24 
                 0.181 
               
               
                 F 
                 24 
                 None 
                 130 
                 600 
                 134 
                 1.031 
                 184 
                 179 
                 70 
                 0.849 
                 60 
                 0.695 
               
               
                   
               
             
          
         
       
     
       Example 2 
       [0032]    The procedure of Example 1 was followed with the exception that various water soluble as well as water insoluble modifiers of the present invention were employed. The results are shown in Table 2 below: 
         [0000]    
       
         
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
             
             
               
                   
                   
                   
                   
                   
                 Crystallite 
                   
                   
               
               
                   
                 Aging 
                   
                   
                   
                 Size 
                 Surface 
                 Pore 
               
               
                 Test 
                 Time 
                 Wt. % 
                 Water Solubility of 
                 Temp. 
                 Angstroms 
                 Area 
                 Volume 
               
             
          
           
               
                 ID 
                 hours 
                 Modifier 
                 Modifier 
                 Modifier 
                 ° C. 
                 020 
                 120 
                 m2/g 
                 ml/g 
               
               
                   
               
               
                 1 
                 24 
                 5.0 
                 Soluble 
                 Ammonium Carbonate 
                 130 
                 168 
                 156 
                 151 
                 1.129 
               
               
                 2 
                 6 
                 5.0 
                 Soluble 
                 Ammonium Carbonate 
                 130 
                 99 
                 122 
                 180 
                 0.842 
               
               
                 3 
                 6 
                 5.0 
                 Soluble 
                 Ammonium Hydroxide 
                 130 
                 175 
                 181 
                 140 
                 0.963 
               
               
                 4 
                 6 
                 1.0 
                 Soluble 
                 Cesium Hydroxide 
                 130 
                 129 
                 144 
                 154 
                 0.950 
               
               
                 5 
                 6 
                 1.0 
                 Soluble 
                 Potassium Hydroxide 
                 130 
                 202 
                 183 
                 141 
                 1.040 
               
               
                 6 
                 24 
                 2.5 
                 Soluble 
                 Potassium Hydroxide 
                 130 
                 332 
                 229 
                 124 
                 0.992 
               
               
                 7 
                 6 
                 2.5 
                 Soluble 
                 Potassium Hydroxide 
                 130 
                 228 
                 173 
                 138 
                 0.882 
               
               
                 8 
                 6 
                 5.0 
                 Soluble 
                 Potassium Hydroxide 
                 130 
                 258 
                 186 
                 123 
                 0.954 
               
               
                 9 
                 6 
                 1.0 
                 Soluble 
                 Rubidium Hydroxide 
                 130 
                 123 
                 146 
                 159 
                 0.945 
               
               
                 10 
                 6 
                 1.0 
                 Soluble 
                 Sodium Hydroxide 
                 130 
                 213 
                 175 
                 141 
                 1.040 
               
               
                 11 
                 6 
                 2.5 
                 Soluble 
                 Sodium Hydroxide 
                 130 
                 263 
                 224 
                 110 
                 0.929 
               
               
                 12 
                 6 
                 5.0 
                 Soluble 
                 Sodium Hydroxide 
                 130 
                 251 
                 197 
                 114 
                 0.936 
               
               
                 13 
                 6 
                 5.0 
                 Partially Soluble 
                 Calcium Hydroxide 
                 130 
                 64 
                 105 
                 198 
                 0.714 
               
               
                 14 
                 6 
                 1.0 
                 Partially Soluble 
                 Lithium Hydroxide 
                 130 
                 165 
                 172 
                 141 
                 0.942 
               
               
                 15 
                 6 
                 1.0 
                 Insoluble 
                 Aluminum Hydroxide 
                 130 
                 145 
                 151 
                 149 
                 1.079 
               
               
                 16 
                 4 
                 1.0 
                 Insoluble 
                 Aluminum Hydroxide 
                 130 
                 109 
                 139 
                 161 
                 0.902 
               
               
                 17 
                 4 
                 1.0 
                 Insoluble 
                 Aluminum Hydroxide 
                 130 
                 119 
                 144 
                 165 
                 0.870 
               
               
                 18 
                 6 
                 1.0 
                 Insoluble 
                 Aluminum Hydroxide 
                 130 
                 125 
                 148 
                 156 
                 0.917 
               
               
                 19 
                 4 
                 5.0 
                 Insoluble 
                 Aluminum Hydroxide 
                 130 
                 99 
                 131 
                 167 
                 0.876 
               
               
                 20 
                 4 
                 1.0 
                 Insoluble 
                 Aluminum hydroxide - dried gel 80% 
                 130 
                 124 
                 141 
                 156 
                 0.951 
               
               
                 21 
                 4 
                 1.0 
                 Insoluble 
                 Aluminum hydroxide - gel 19.7% 
                 130 
                 134 
                 144 
                 152 
                 0.951 
               
               
                 22 
                 24 
                 1.0 
                 Insoluble 
                 Aluminum hydroxide - gel 19.7% 
                 130 
                 198 
                 194 
                 133 
                 1.100 
               
               
                 23 
                 4 
                 1.0 
                 Insoluble 
                 Aluminum Trihydrate (Hydral 710) 
                 130 
                 145 
                 149 
                 151 
                 1.070 
               
               
                 24 
                 4 
                 1.0 
                 Insoluble 
                 Aluminum Trihydrate Alcan 
                 130 
                 117 
                 145 
                 156 
                 0.835 
               
               
                 25 
                 6 
                 1.0 
                 Insoluble 
                 Cerium Hydroxide 
                 130 
                 114 
                 144 
                 156 
                 0.819 
               
               
                 26 
                 24 
                 0.5 
                 Insoluble 
                 Lanthanum hydroxide 
                 130 
                 183 
                 184 
                 138 
                 1.040 
               
               
                 27 
                 6 
                 0.5 
                 Insoluble 
                 Lanthanum hydroxide 
                 130 
                 137 
                 149 
                 154 
                 0.926 
               
               
                 28 
                 24 
                 0.5 
                 Insoluble 
                 Lanthanum hydroxide 
                 130 
                 183 
                 184 
                 138 
                 1.040 
               
               
                 29 
                 24 
                 1.0 
                 Insoluble 
                 Lanthanum hydroxide 
                 130 
                 119 
                 163 
                 153 
                 0.813 
               
               
                 30 
                 6 
                 1.0 
                 Insoluble 
                 Lanthanum hydroxide 
                 130 
                 116 
                 146 
                 154 
                 0.905 
               
               
                 31 
                 6 
                 1.0 
                 Insoluble 
                 Lanthanum hydroxide 
                 130 
                 126 
                 148 
                 159 
                 0.877 
               
               
                 32 
                 6 
                 1.0 
                 Insoluble 
                 Lanthanum hydroxide 
                 130 
                 122 
                 155 
                 155 
                 0.870 
               
               
                 33 
                 6 
                 1.0 
                 Insoluble 
                 Lanthanum hydroxide 
                 130 
                 134 
                 148 
                 156 
                 0.957 
               
               
                 34 
                 6 
                 1.0 
                 Insoluble 
                 Lanthanum hydroxide 
                 130 
                 144 
                 155 
                 148 
                 1.017 
               
               
                 35 
                 6 
                 1.0 
                 Insoluble 
                 Lanthanum hydroxide 
                 130 
                 132 
                 153 
                 145 
                 0.903 
               
               
                 36 
                 6 
                 1.0 
                 Insoluble 
                 Lanthanum hydroxide 
                 130 
                 144 
                 160 
                 150 
                 0.948 
               
               
                 37 
                 4 
                 1.0 
                 Insoluble 
                 Lanthanum hydroxide 
                 130 
                 125 
                 138 
                 164 
                 0.897 
               
               
                 38 
                 6 
                 1.0 
                 Insoluble 
                 Lanthanum hydroxide 
                 130 
                 127 
                 155 
                 150 
                 0.999 
               
               
                 39 
                 6 
                 3.0 
                 Insoluble 
                 Lanthanum hydroxide 
                 130 
                 105 
                 145 
                 167 
                 0.744 
               
               
                 40 
                 4 
                 1.0 
                 Insoluble 
                 Lanthanum hydroxide - Molycorp 
                 130 
                 90 
                 127 
                 168 
                 0.754 
               
               
                 41 
                 4 
                 1.0 
                 Insoluble 
                 Lanthanum hydroxide - Molycorp 
                 130 
                 101 
                 135 
                 165 
                 0.895 
               
               
                 42 
                 6 
                 1.0 
                 Insoluble 
                 Lanthanum oxide 
                 130 
                 145 
                 153 
                 149 
                 0.996 
               
               
                 43 
                 4 
                 1.0 
                 Insoluble 
                 Lanthanum oxide 
                 130 
                 142 
                 146 
                 156 
                 1.009 
               
               
                 44 
                 4 
                 1.0 
                 Insoluble 
                 Lanthanum oxide - Molycorp 
                 130 
                 107 
                 131 
                 170 
                 0.945 
               
               
                 45 
                 4 
                 1.0 
                 Insoluble 
                 Lanthanum oxide - Molycorp 
                 130 
                 145 
                 157 
                 162 
                 1.072 
               
               
                 46 
                 6 
                 1.0 
                 Insoluble 
                 Lanthanum oxide - Molycorp 
                 110 
                 117 
                 117 
                 172 
                 1.071 
               
               
                 47 
                 6 
                 3.0 
                 Insoluble 
                 Lanthanum oxide - Molycorp 
                 110 
                 107 
                 117 
                 181 
                 1.000 
               
               
                 48 
                 4 
                 3.0 
                 Insoluble 
                 Lanthanum oxide - Molycorp 
                 130 
                 154 
                 153 
                 152 
                 1.010 
               
               
                 49 
                 6 
                 14% 
                 Insoluble 
                 SnO2 
                 130 
                   
                   
                 137 
                 0.900 
               
               
                 50 
                 6 
                 14% 
                 Insoluble 
                 SnO2 
                 130 
                   
                   
                 137 
                 0.900 
               
               
                   
               
             
          
           
               
                   
                 1200° C./4 hours 
                 1200° C./24 hours 
                   
               
             
          
           
               
                   
                   
                 Water 
                 Surface 
                 Pore 
                 Surface 
                 Pore 
                 Alpha 
                   
                   
               
               
                   
                 Test 
                 Dispersibility 
                 Area 
                 Volume 
                 Area 
                 Volume 
                 Conversion 
                 Slurry 
               
               
                   
                 ID 
                 % 
                 m2/g 
                 ml/g 
                 m2/g 
                 ml/g 
                 ° C. 
                 pH 
                 pKsp 
               
               
                   
                   
               
               
                   
                 1 
                 98.5 
                 69 
                 0.777 
                 49 
                 0.535 
                 1352 
                   
                   
               
               
                   
                 2 
                 96.1 
                 34 
                 0.345 
                 7 
                 0.029 
                 1295 
               
               
                   
                 3 
                 0.0 
                 63 
                 0.636 
                 49 
                 0.504 
                 1366 
               
               
                   
                 4 
                   
                 52 
                 0.458 
                 8 
                 0.036 
                 1364 
               
               
                   
                 5 
                 0.0 
                 63 
                 0.865 
                 59 
                 0.705 
                 &gt;1400 
                 10.83 
               
               
                   
                 6 
                 98.0 
                 74 
                 0.935 
                 66 
                 0.857 
                 &gt;1400 
               
               
                   
                 7 
                 0.0 
                 85 
                 0.816 
                 71 
                 0.728 
                 1324 
               
               
                   
                 8 
                   
                   
                   
                   
                   
                 1336 
               
               
                   
                 9 
                 0.0 
                 54 
                 0.522 
                 27 
                 0.265 
                 1362 
                 10.11 
               
               
                   
                 10 
                 0.0 
                 68 
                 0.778 
                 64 
                 0.748 
                 &gt;1400 
                 10.92 
               
               
                   
                 11 
                 0.0 
                 69 
                 0.818 
                 63 
                 0.740 
                 &gt;1400 
               
               
                   
                 12 
                 0.0 
                 78 
                 0.842 
                 68 
                 0.749 
                 &gt;1400 
                 10.92 
               
               
                   
                 13 
                 0.0 
                 27 
                 0.195 
                 25 
                 0.243 
                 1249 
                   
                 5.1 
               
               
                   
                 14 
                 0.0 
                 17 
                 0.185 
                 6 
                 0.041 
                 1316 
                 10.03 
               
               
                   
                 15 
                 98.9 
                 51 
                 0.526 
                 5 
                 0.016 
                 1330 
                 7.50 
                 33 
               
               
                   
                 16 
                 95.8 
                 37 
                 0.409 
                 6 
                 0.013 
                 1351 
                 6.5-7.5 
               
               
                   
                 17 
                 95.8 
                 34 
                 0.273 
                 6 
                 0.014 
                   
                 6.5-7.5 
               
               
                   
                 18 
                 95.8 
                 60 
                 0.534 
                 8 
                 0.377 
                   
                 6.5-7.5 
               
               
                   
                 19 
                 95.8 
                 32 
                 0.319 
                 6 
                 0.019 
                 1347 
                 6.5-7.5 
               
               
                   
                 20 
                 95.8 
                 55 
                 0.482 
                 9 
                 0.051 
                 1365 
                 6.5-7.5 
               
               
                   
                 21 
                 95.8 
                 52 
                 0.465 
                 7 
                 0.043 
                 1365 
                 6.5-7.5 
               
               
                   
                 22 
                 97.3 
                 65 
                 0.709 
                 34 
                 0.385 
                 1401 
                 6.5-7.5 
               
               
                   
                 23 
                 97.1 
                 58 
                 0.549 
                 6 
                 0.021 
                 1368 
                 6.5-7.5 
               
               
                   
                 24 
                   
                 41 
                 0.398 
                 6 
                 0.023 
                 1354 
                 6.5-7.5 
               
               
                   
                 25 
                   
                 9 
                 0.024 
                 5 
                 0.010 
                 1295 
                 7.90 
               
               
                   
                 26 
                 91.3 
                 65 
                 0.695 
                 44 
                 0.488 
                 1383 
                   
                 18.7 
               
               
                   
                 27 
                 96.8 
                 57 
                 0.475 
                 11 
                 0.037 
                 1324 
               
               
                   
                 28 
                 96.1 
                 65 
                 0.695 
                 44 
                 0.488 
                 1375 
               
               
                   
                 29 
                 99.2 
                 54 
                 0.451 
                 31 
                 0.362 
                 1360 
                 8.23 
               
               
                   
                 30 
                 97.0 
                 62 
                 0.522 
                 31 
                 0.249 
                 1320 
               
               
                   
                 31 
                 77.2 
                 62 
                 0.531 
                 34 
                 0.321 
               
               
                   
                 32 
                 77.2 
                 62 
                 0.543 
                 33 
                 0.288 
               
               
                   
                 33 
                 77.2 
                 64 
                 0.582 
                 32 
                 0.299 
               
               
                   
                 34 
                 77.2 
                 65 
                 0.614 
                 23 
                 0.213 
               
               
                   
                 35 
                 77.2 
                 63 
                 0.584 
                 41 
                 0.391 
               
               
                   
                 36 
                 77.2 
                 65 
                 0.598 
                 17 
                 0.147 
               
               
                   
                 37 
                   
                 65 
                 0.51 
                 30 
                 0.372 
                 1392 
               
               
                   
                 38 
                 97.8 
                 66 
                 0.602 
                 48 
                 0.474 
                 1364 
               
               
                   
                 39 
                 97.2 
                 57 
                 0.481 
                 37 
                 0.299 
                 1381 
               
               
                   
                 40 
                   
                 59 
                 0.396 
                 17 
                 0.287 
               
               
                   
                 41 
                   
                 64 
                 0.512 
                 24 
                 0.21 
               
               
                   
                 42 
                   
                 68 
                 0.649 
                 49 
                 0.478 
                 1376 
               
               
                   
                 43 
                   
                 71 
                 0.632 
                 58 
                 0.52 
                 1377 
               
               
                   
                 44 
                   
                 68 
                 0.548 
                 9 
                 0.192 
               
               
                   
                 45 
                   
                 79 
                 0.7439 
                 67 
                 0.635 
               
               
                   
                 46 
               
               
                   
                 47 
               
               
                   
                 48 
               
               
                   
                 49 
               
               
                   
                 50 
               
               
                   
                   
               
             
          
         
       
     
         [0033]    The advantages of the present invention can be seen with reference to the various figures which graphically depict the data in Table 2. Referring first to  FIG. 1 , there is shown the effect of the additives or modifier on crystallite growth. As can be seen with respect to  FIG. 1  and with particular reference to the use of lanthanum oxide, without the use of the modifiers of the present invention, it would take in excess of 15 hours of aging time to achieve the same crystallite growth that is achieved in less than 5 hours according to the process of the present invention. As  FIG. 1  also shows, water soluble modifiers such as KOH, also dramatically increase the rate at which the desired crystal growth is achieved. However, as will be shown hereafter, the use of potassium hydroxide or similar water soluble hydroxides has a deleterious effect on viscosity. 
         [0034]    Turning to  FIG. 2 , the effect of using the additives of the present invention, as well as water soluble additives, on total pore volume is depicted. Basically,  FIG. 2  shows the same effect as  FIG. 1  vis-a-vis aging time to achieve desired pore volume. 
         [0035]    Whether the oxide or hydroxide is soluble or insoluble is not critical in determining its effectiveness in promoting crystallite growth or development of porosity as seen in  FIGS. 1 and 2 . In fact, as seen above, the insoluble aluminum hydroxide gives better porosity at the same aging time as soluble potassium hydroxide.  FIGS. 3 and 4  below show that while a soluble hydroxide, i.e., potassium hydroxide, gives faster crystallite development ( FIG. 3 ), porosity enhancement is comparable at short aging times and better at long aging times using aluminum trihydrate or aluminum hydroxide ( FIG. 4 ). 
         [0036]      FIG. 5  graphically depicts the synergistic effect between the additives and the agitation energy. When only high agitation energy, about 10 kW/m 3 , is used in the process a medium porosity alumina is obtained. As shown in  FIG. 5 , when an additive according to the present invention is added to the feed slurry in combination with high agitation energy, the porosity is much greater than can be obtained without the additive. As can be seen, total pore volumes can be up to 50% greater using the aluminum hydroxide as compared with just agitation alone. Effectively, there is synergism between the use of the additives of the present invention and effective energy consumption. It is well known that total pore volume varies as a function of the crystallinity of boehmite alumina.  FIG. 5  demonstrates that at the same crystallite size, the porosity of alumina produced according to this invention is increased by as much as 50% over aluminas produced at normal or high agitation levels without addition of the additives demonstrated in this invention. All results are at 2.3 hours aging time. 
         [0037]      FIG. 6  shows a similar comparison with respect to the use of soluble potassium hydroxide. In the case of the data depicted in  FIG. 6 , the residence time and agitation conditions are the same for the three sets of additives. Note that the addition of alumina hydroxide produced a high porosity alumina at a crystallite size below that which can be produced using potassium hydroxide. To make these low crystallite sizes, the reactor temperature must be relatively cool. When operated in this relatively low temperature range, potassium hydroxide makes the alumina slurry too viscous to process. 
         [0038]      FIG. 7  compares both the effect of adding aluminum hydroxide/oxide with potassium hydroxide and longer residence times than depicted in the previous two figures. Again, the use of the insoluble additives (aluminum hydroxide or aluminum trihydrate, ATH) produce results which are comparable to those obtained with the use of potassium hydroxide. However, as noted above, the use of additives such as aluminum hydroxide, alumina oxides or aluminum trihydrates does not result in undesirable increase in slurry viscosity in the reactor as is the case with the use of potassium hydroxide. Additionally, the insoluble additives of the present invention permit the production of smaller crystallite size high porosity aluminas than does the use of potassium hydroxide. 
         [0039]    As noted above, certain of the modifiers of the present invention can be used to produce aluminas which have a high degree of thermal stability. It is well known that a high porosity alumina can be doped with lanthanum in an additional step, i.e., after hydrothermal aging, and then calcined to produce a gamma phase alumina suitable for high temperature catalyst supports, e.g., catalytic converter supports. However, in the process of the present invention wherein an insoluble lanthanum compound is added prior to or during the hydrothermal aging, meaning that the subsequent step of combining a high porosity alumina with a water soluble lanthanum compound is unnecessary. Indeed, it appears that there is a synergy between the development of the high porosity and the increase in thermal stability of the subsequently produced gamma alumina produced from the boehmite according to the present invention. Thus a gamma alumina product produced using the process of the present invention has thermal stability equal to or greater than that used in the two-step doping process. Additionally, using the process of the present invention, calcination to achieve the gamma phase does not result in the emission of nitrogen oxides, hydrocarbon compounds or other gases that are released using traditional doping with water soluble lanthanum compounds. Thus, the present invention not only provides a process for making a high porosity alumina but, if the proper additive is chosen, the thermal stability of subsequently produced gamma aluminas is as good or better than that obtained with conventional doping processes involving subsequent steps.  FIG. 8  shows the surface area of various aluminas after they have been calcined at 1200EC for 24 hours. The surface area of calcined aluminas following calcination at the temperature and time listed above is referred to as Residual Surface Area. As can be seen, undoped high porosity aluminas (HP aluminas) do have enhanced thermal stability, but under the stringent testing applied herein, they lose most of their surface area as shown in  FIG. 8 . As  FIG. 8  also shows, if the HP aluminas are doped after they have been produced, aluminas of High Residual Surface Area can be obtained, using either lanthanum nitrate or lanthanum hydroxide as the doping. As  FIG. 8  further shows, using the process of the present invention wherein the lanthanum hydroxide is added to the feed slurry prior to or during hydrothermal aging, the high porosity aluminas produced have Residual Surface Areas that are comparable to post doped high porosity aluminas. As seen, the porosities of the aluminas are all greater than or equal to 1.0 ml/g. At lower porosity, aluminas tend to have lower stability as can be seen in Table 2. 
       Example 3 
       [0040]    This example demonstrates the effect on pH of adding water soluble hydroxide and the modifiers of the present invention to alumina slurries that are to be hydrothermally treated. In all cases, the additives were added at a 1% wt. level. The results are shown in Table 3 below: 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Additive 
                 Slurry pH 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Slurry with no Additive 
                 9.38 
               
               
                   
                 KOH 
                 11.97 
               
               
                   
                 Al(OH) 3  commercial grade 
                 8.70 
               
               
                   
                 Crystalline Aluminum 
                 9.35 
               
               
                   
                 Trihydrate 
               
               
                   
                 Lanthanum Oxide 
                 9.33 
               
               
                   
                 Tin (IV) Oxide 
                 9.35 
               
               
                   
                 Ammonium Hydroxide 
                 10.73 
               
               
                   
                 Slurry with no Additive 
                 9.53 
               
               
                   
                 Al(OH) 3  laboratory grade 
                 9.20 
               
               
                   
                   
               
             
          
         
       
     
         [0041]    As can be seen from the data in Table 3, the addition of water soluble hydroxides such as potassium hydroxide or ammonium hydroxide, has a dramatic effect on the slurry pH. This is to be compared with the use of the additives of the present invention which essentially have no effect on pH. Although Table 3 does show that the addition of aluminum hydroxide does lower the pH by about 0.3 to 0.6 units, it is to be understood that aluminum hydroxide which contains aluminum hydroxy carbonate as an impurity. Aluminum hydroxy carbonate is acidic which accounts for the drop in pH. However, if the aluminum hydroxide were free of the carbonate impurity, there would be little, if any, change in the pH. 
       Example 4 
       [0042]    This example demonstrates the effect on viscosity of two water dispersed aluminas using a water soluble hydroxide and an insoluble hydroxide according to the present invention. The water dispersion contained 33.3% wt. alumina calculated as Al 2 O 3 , and lactic acid was used to adjust the pH of both to about 3.1. Although as can be seen from the data in Table 4, the two aluminas have similar properties, it was found that the dispersion of the alumina made using potassium hydroxide had significantly higher viscosity than the dispersion made using the crystalline aluminum trihydrate. The relevant viscosity data is shown in  FIG. 9 . 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
             
             
               
                   
                   
               
               
                   
                 Surface 
                 Pore 
                 Crystallite Size 
                   
               
               
                   
                 Area 
                 Volume 
                 (Angstroms) 
               
             
          
           
               
                 Additive 
                 (m 2 /g) 
                 (ml/g) 
                 020 Reflex 
                 120 Reflex 
               
               
                   
               
               
                 KOH 
                 144 
                 1.04 
                 201 
                 222 
               
               
                 Crystalline 
                 147 
                 1.03 
                 173 
                 190 
               
               
                 Aluminum 
               
               
                 Trihydrate 
               
               
                   
               
             
          
         
       
     
         [0043]    Representative but non-limiting applications for the compositions obtained by this process includes catalysts and catalyst supports; coatings; adsorbents; surface treatments; ceramics and refractories; reinforcement of ceramics, metals, plastics and elastomers; scratch resistant coatings; agents for the delivery of pharmaceutically active materials; thickening agents and rheology modifiers; rinse aids; fabric treatment; paper treatment; inkjet recording media; soil resistant coatings; and barrier coatings. 
         [0044]    The foregoing description and examples illustrate selected embodiments of the present invention. In light thereof, variations and modifications will be suggested to one skilled in the art, all of which are in the spirit and purview of this invention.

Technology Classification (CPC): 2