GB2189780A

GB2189780A - A process for the preparation of alumina spheres

Info

Publication number: GB2189780A
Application number: GB08609792A
Authority: GB
Inventors: Herman Wouter Kouwenhoven; Johannes Martinus Nanne; Donald Reinalda
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1986-04-22
Filing date: 1986-04-22
Publication date: 1987-11-04
Also published as: GB8609792D0

Abstract

A process for the preparation of alumina spheres comprises drying alumina gels with a drying agent of the group consisting of a) isobutyl alcohol b) a higher than C4-alcohol c) an alkyl acetate, an alkyl propionate d) methyl proxitol acetate and e) acetyl acetone, for a sufficient time to extract at least part of the water from the alumina gels, separating said alumina gels from the drying agent and if desired further drying the obtained alumina gels and calcining the alumina gels to alumina spheres.

Description

SPECIFICATION A process for the preparation of alumina spheres The invention relates two a process for the preparation of alumina spheres and to alumina spheres prepared by such process.

It is known to prepare alumina spheres from alumina gels by drying the alumina gels and calciningthe resulting dried product. A disadvantage is that during the drying step clusters are formed, which makesthe spheres uneasy to handle.

In the US patent specification 3,972,990 is disclosed a process for the preparation of alumina spheres, whereby an alumina hydrosol is prepared by dissolving aluminium pellets in dilute hydrochloric acid under reflux conditions. The obtained hydrosol is admixed with aqueous hexamethylenetetramine and then dispersed as droplets in a gas oil suspension medium at95 C. The resulting hydrogel spheres are allowed two age in a hot oil and thereafter separate from the oil. The aged spheres are then treated in a wash column, absolute alcohol being perculated through the spheres. The spheres are further dried and calcined.Before the alcohol treatment the alumina spheres will already have lost a large part of the water and the perculation with alcohol serves to remove the wash-water from the previous step. The aging method is rathertime consuming and the whole process rather complicated.

Applicant has now found that specific drying agents can be used for quickly drying the alumina gels,which still contain the water, in which the alumina gels were formed. Generally the alumina gels contain from 300to 700 percentof water, calculated on the weight of solids. The hydrogels can bye treated after aging.

The invention therefore relates to a process for the preparation of alumina spheres which comprises drying alumina gels with a drying agent of the group consisting of a) isobutyl alcohol b) a higherthan C4-alcohol c) an alkyl acetate, an alkylpropionate d) methyl proxitol acetate and e) acetyl acetone, for a sufficient time to extract at least part of the water from the alumina gels, separating said alumina gels from the drying agent and if desired further drying the obtained alumina gels and calcining the alumina gels to alumina spheres.

Alumina sols are preferably prepared by mixing boehmite powder with a peptizing agent,waterand a compound which generates hydroxyl ions upon hydrolysis and dropping the obtained mixture into hot oil. In the hot oil the droplets take their spherical shape and solidify to a certain extent. The obtained spherical gels are separated from the oil. The gels may be aged preferably in dilute aqueous ammonia. The compound which generates hydroxyl ions in the preparation of the droplets, is preferably hexamethylenetetramine (HMTA), which latter compound already is hydrolysed at a temperature of 80"C underformation of ammonia.

The residence time in the hot oil bath is between 10 s and 1 min, preferably between 10 and 20 s. The obtained gelate may be aged in dilute aqueous ammonia between 2 and 24 hat room temperature. The obtained alumina gelsarethen changed into alumina spheres according to the process of the invention.

Gelation is effected by introducing the mixture of boehmite water, peptizing agent and HMTA into the upper end ofan oil column. The length ofthe oil column determines to a certain extentthe residencetimeof the droplets in the oil. Atthe bottom ofthe oil column the gel droplets are collected and aged. The spheroidal alumina gels are then treated with the drying agent according to the process ofthe invention.

The process according to the invention provides alumina spheres with a pore volume between 0.50 and 0.80 ml/g, an average pore diameter between 7 and 20 nm and a surface area between 100 and 350 m2/g.

The alcohols to be used in the process according to the invention include, among others, isobutyl alcohol, pentanol-1, hexanol-1, heptanol-1, octanol-1, nonanol-1, decanol-1, isomeric alcohols and branched chain alcohols. Preferred are the 0to to C8-alcohols.

The alkyl acetates are, for example, methyl acetate, ethyl acetate, propyl acetate, butyl acetate and isomers therefrom.

Since the driers are quick drying agents the necessary extraction time is short and preferably ranges from 3 to 10 min. Drying time depends on temperature and water load in the drying agent. It should be noted that preferably the drying time should be rather short, since prolonged emersion badly effects pore size distribution and the spheres will swell and have a low density. The contact time is long enough to extract between 40 and 80 percent of the water from the alumina hydrogels. The temperature may be between 20"C and 10000, preferably between 40"C and 60"C. The higher the temperature is, the higher is the degree of dehydration in a fixed time.

After the alumina gels have been brought into contact with the drying agent they may befirstlyfurther dried bythe usual methods, such asforexample, in a hotairstream.To obtain the alumina spheres,thedried alumina gels are then calcined atatemperature offrom 400to 850"C. Atthisstagethegamma-alumina is formed. To obtain alpha-alumina, calcination at highertemperatures, preferably between 120000 and 170000, is necessary. The alumina spheres are suitable as carriers for catalysts in catalytical reactions. The alumina spheres are especially suitable to be used in bunkerflow reactors, also called moving beds.

Example The following slurry composition was prepared: boehmite 88.6 g nitric acid 19.5 g water 249.0 g hexamethylenetetramine 21.0 g The boehmite was mixed with an aqueous solution of nitric acid,aged for 17 h and mixed with hexamethylene tetramine. The obtained slurry was dropped into an oil column of 2.5 m at a temperature of 90"C. While the hexamethylene tetramine was hydrolysed, the gelate was formed during the residencetime of about 15 s in the oil. The spheroidal gelatewas collected in a 5% byweight of aqueous ammonia solution and aged for 17 hat room temperature.

The obtained alumina gels, after being dried in absorbent paper, were ready to be used in the process according to the invention. Forthis purpose enough alumina gels were prepared and 5 g portions ofthe alumina gels were contacted with 50 ml drying agent or 5 g portionsof the gel were contacted with 250 ml drying agent, after 5 min at 600C under stirring, the gels were collected, carefully dried with absorbent paper and weighed. The loss of water was determined and expressed in a weight percentage ofthe water in the untreated gel. In the following table, these weight percentage losses for a number of drying agents is given.

TABLE drying agent 5gin50ml 5g in250 ml pentanol-1 53 53 hexanol-1 50 54 heptanol-1 38 48 octanol-1 26 42 isobutyl alcohol 47 methyl acetate 44 52 ethyl acetate 49 62 butyl acetate 28 54 methyl propionate 43 methyl proxitol acetate 49 acetylacetone 42 ethanol 30 30 propanol 30 30 tert.butyl alcohol 36 36 The portions were further dried and calcined at 500 C.

It can be conciuded that the drying agents, used in the process of the invention, are effective driers, befter than ethanol, propanol ortert.butyl alcohol, all three being mentioned in the US patentspecification 3,972,990.

Claims

1. A processforthe preparation ofalumina spheres which comprises drying alumina gels with adrying agent of the group consisting of a) isobutyl alcohol b) a higherthan C4-alcohol c) an alkyl acetate, an alkyl propionate d) methyl proxitol acetate and e) acetyl acetone, for a sufficienttimeto extract at least part of the water from the alumina gels, separating said alumina gels from the drying agent and if desired further drying the obtained alumina gels and calcining the alumina gels to alumina spheres.

2. A process according to claim 1,wherein the drying agent under b is a C5to C8-alcohol.

3. A process according to claim 2, wherein the alcohol is pentanol-1, hexanol-1, heptanol-1 or octanol-1.

4. A process accordingto claim 1, wherein the alkyl acetate under c is methyl acetate, ethyl acetate our butyl acetate.

5. A process according to any one of the claims 1 -4, wherein the extraction time ranges from 3 to 10 min.

6. A process according to any one of the claims 1-5, wherein the alumina gels in the presence ofthe drying agent are dried at a temperature between 20"C and 1 OO"C.

7. A process according to claim 6, wherein the temperature is between 40"C and 80"C.

8. A process according to any one of the claims 1 wherein the alumina gels are calcined ata temperature of from 400 C to 850 C.

9. A process according to claim 1, as hereinbefore described with special reference to the example.

10. Alumina spheres, whenever prepared by means of a process according to any one of the claims 1-9.