Alkali metal and ammonium dawsonites can be prepared by a nonaqueous process according to which equimolar quantities of the corresponding hydrogen carbonate and aluminum hydroxide in finely divided state are heated together to a tempeature within the range of 150 to 250 C, for a period of 1 to 6 hours under a carbon dioxide pressure within the range of 120 to 360 psig. Carbonates may be used instead of hydrogencarbonates

Altman, R. L.

English

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United States Patent 4,356,157 
Altman [45] Oct. 26, 1982 
1561 
SYNTHESIS OF DAWSONITES 
Inventor: Robert L, Altman, Berkeley, Calif. 
Assignee: The United States of America aa 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
Appl. No.: 178,192 
Filed: Aug. 14, 1980 
Int. ( 3 . 3  ........................ A62D 1/00; COlB 31/24; 
A61K 33/10 
U.S. c1. .................................... 423/419 P; 252/5; 
423/600; 424/156, 
Field of Search .................... 423/419 P, 600, 630; 
424/154, 156; 252/5 
References Cited 
U.S. PATENT DOCUMENTS 
2,783,124 2/1957 Grote .............................. 423/419 P 
2,783,179 2/1957 Grote .............................. 423/419 P 
3,360,345 12/1967 Lewin ................................. 424/156 
3,557,025 12/1971 Emerson et a]. ................ 423/419 P 
3,911,090 10/1975 Hem et al. ....................... 423/419 P 
4,053,579 10/1977 Kat0 et al. ........................ 423/419 P 
Primary Examiner-Gary P. Straub 
Attorney, Agent, or Firm-Darrell G. Brekke; John R. 
Manning 
1571 ABSTRACT 
Alkali metal and ammonium dawsonites can be pre- 
pared by a non-aqueous process according to which 
equimolar quantities of the corresponding hydrogen 
carbonate and aluminum hydroxide in finely divided 
state are heated together to a temperature within the 
range of 150" to 250" C. for a period of 1 to 6 hours 
under a carbon dioxide pressure within the range of 120 
to 360 psig. Carbonates may be used instead of hydro- 
gencarbonates. 
4 Claims, No Drawings 
https://ntrs.nasa.gov/search.jsp?R=19830025706 2020-03-22T01:05:04+00:00Z
436,157 
1 2 
The principal object of the present invention there- 
fore is to provide a process to manufacture a type of 
dawsonite that can be used successfully in fire extin- 
guishing operations, especially in extinguishing fires 
caused by hot surface ignition of hydrocarbon fuels. 
Another object is to develop a simple nonaqueous pro- 
cess for the manufacture of dawsonites. 
DISCLOSURE OF INVENTION 
The objects of the invention have been accomplished 
by calcining an intimate mixture of highly pulverized 
hydrogen-carbonate (MHCO,) and aluminum hydrox- 
ide at a temperature within the range of 150" to 250" C. 
for about 1 to 6 hours under a carbon dioxide pressure 
of 120 to 360 psig. A carbonate (MzCO3) may be used 
instead of the hydrogencarbonate. The chemical reac- 
tions involved in this process are: 
KHCO3 +Al(OH)34CAl(OH)2C03+ H20 (1) 
SYNTHESIS OF DAWSONITES 
ORIGIN OF THE INVENTION 
The invention described herein was made by an em- 
ployee of the United States Government and may be 
manufactured and used by or for the Government for 
governmental purposes without the payment of any 
royalties thereon or therefor. 
TECHNICAL FIELD 
This invention relates to a process for synthesizing 
sodium, potassium and ammonium dawsonite. 
BACKGROUND ART 
Dawsonite, sodium aluminum dihydroxide carbonate 
-NaAl(OH)2CO3, and its alkali metal analogs are use- 
ful compounds that either occur naturally or are synthe- 
sized by a variety of processes which take place in aque- 
ous medium. For instance, in the case of potassium 
dawsonite, the published procedures involve solution 
methods where the aluminum-containing component is 
derived from elemental aluminum, aluminum hydrox- 
ide, gibbsite, aluminum salts, or aluminum alkoxylates. 
The patents that have been issued for some of the syn- 
thetic processes range from c. Lorwig's German Pat. 
Nos. 19,784 (1882) and 70,175 (1892) to the Kat0 et al. 
U.S. Pat. No. 4,053,579 (1977). Typically, Grote (U.S .  
Pat. No. 2,783,124) discloses a method of synthesis 
based on the reaction AI(OH)3 +MHC03-+(HO)- 
zAlOC02M+H20 carried out in aqueous medium with 
a bicarbonate in which M is the sodium, potassium or 
ammonium ion. Grote (U.S. Pat. No. 2,783,179) also 
teaches the preparation of dihydroxy aluminum sodium 
carbonate by the reaction of an aluminum alkoxide and 
sodium bicarbonate in aqueous medium. More recently, 
a dihydroxy aluminum ammonium carbonate has been 
disclosed in the Kato et al. patent, involving the reac- 
tion of ammonium hydrogencarbonate with a soluble 
aluminum salt. Hem et al. synthesized a compound of 
the formula MalOH2CO3, where M is a sodium or po- 
tassium ion, by using a silicate anion as a nucleating 
agent (U.S. Pat. No. 3,911,090). 
Finally, Emerson et al. (US. Pat. No. 3,557,025) have 
prepared alkalized alumina composites containing 30 to 
80% of a dawsonite-MAl(OH)zCO3, by heating to- 
gether a selectively calcined transition alumina, mixing 
that with 0.5 to 2.5 molar equivalents of MHC03 and 
heating that together in the solid state or in aqueous 
conditions at a temperature of about 100" C. to a tem- 
perature below the decomposition point of the dawso- 
nite formed. Pressure is recommended to avoid losses to 
bicarbonate when the conversion temperature exceeds 
loo' C .  Pressure is obtained by using the bicarbonate as 
an aqueous suspension and carrying out the reaction in 
an autoclave. 
The dawsonites of the art made by the processes just 
reviewed have been used in several manners, including 
as drying agents and polymerization inhibitors for gase- 
ous organic compounds susceptible to polymerization, 
SO2 absorption, and as stomachal antacids. Yet, al- 
though some aluminum compounds have been disclosed 
to possess fire retardant properties, it has not been possi- 
ble heretofore to employ dawsonites as fire extinguish- 
ers. It must be kept in mind here that fire retardant and 
fire extinguishing are different processes that have their 
own individual requirements in order to operate. 
5 
10 
15 
20 
25 
30 
35 
40 
45 
50 
55 
60 
65 
or 
K2CO3 +COz +ZAl(OH)3-ZKAl(OH)zCO3 + H20 (11) 
In reactions (I) and (11), sodium or ammonium may be 
substituted for potassium. 
DETAILED DESCRIPTION OF THE 
INVENTION 
It is now possible to synthesize dawsonites of high 
purity by a novel high-temperature, high-pressure, so- 
lid-state procedure which involves the following opera- 
tions and criticalities: 
Equimolar quantities of aluminum hydroxide, e.g. 
gibbsite or bayerite, and an alkali metal or ammonium 
hydrogencarbonate in the form of a dry, ground pow- 
der with a particle size smaller than 90 pm, are inti- 
mately mixed and transferred to a cylindrical open-top 
vessel made of aluminum or other inert metal. The 
vessel is placed into a high pressure reactor. The reactor 
is flushed with gaseous carbon dioxide and pressurized 
with the same gas to a level within the range of 120 to 
360 psig. The reactor is then headed as quickly as possi- 
ble to a temperature within the range of 150" to 250" C., 
and it is maintained at that temperature for a period of 
about 1 to 6 hours. When sodium and potassium hydro- 
gencarbonates are used, the calcination is preferably 
carried out at a temperature within the range of 240" to 
250" C. for about 4 to 6 hours under a carbon dioxide 
pressure of 230 to 250 psig. After cooling and depressur- 
ization, the product is dried in a vacuum oven at 50" C .  
The above reaction can also take place with carbon- 
ates instead of hydrogencarbonates. 
The process of the invention will now be illustrated 
by the following examples which are not intended to 
limit the scope of the invention as stated in the ap- 
pended claims. 
EXAMPLE 1 
Aluminum hydroxide and potassium hydrogen car- 
bonate in equimolar weight ratio (78.00:100.12) were 
ballmilled together and passed through an ASTM #35 
sieve. The aluminum hydroxide used was equivalent to 
Kaiser Chemical's H-36 grade of alumina trihydrate. It 
had a particle size finer than 35 mesh and a purity of 
approximately 99%. The potassium hydrogen carbon- 
ate had a purity of 99.7% to 100.3%. It was thoroughly 
dried and ground to a particle size small enough to pass 
4,356,157 
3 4 
a 35 mesh sieve. It was kept dry until use and redried if 
necessary, since calcination reaction weight loss pro- 
vides a convenient measure of reaction extent. 
The intimately mixed materials were then placed in 
an open-top aluminum cylinder which, in turn, was 
placed in a Parr Corporation pressure reaction vessel. 
The sealed pressure vessel was flushed with carbon 
dioxide to remove most of the air from it and was then 
charged with carbon dioxide to a pressure of 240 psig. 10 
The pressurized assembly was heated quickly to 245" 
C., in approximately 60 minutes, without allowing any 
overshoot in the temperature. That temperature was 
maintained for about 5 hours. The reactor assembly Was 
The improved heat stability of the calcined product 
over that of the solution precipitated products is readily 
apparent from these data. 
A solution preparation of sodium dawsonite obtained 
5 from Kaiser Chemical was flaky rather than granular in 
nature and could not be pulverized in a ball mill as 
could sodium and potassium dawsonite materials pre- 
pared by calcination. 
EXAMPLE 2 
The preparation of Example 1 was repeated but with- 
out carbon dioxide. The reaction was carried out in a 
nitrogen atmosphere. Analysis of the post-reaction mix- 
ture showed that dehydration had taken place, forming 
allowed to cool towards room temperature, wkle h i n g  15 such compounds as potassium carbonate and boehmite, 
AIOOH, instead of the des kept pressurized until a temperature of 50" C. was 
reached. At that point, the pressure was released and 
the product removed from the reactor and dried in the 
aluminum cylinder in Vacuo 
ature of 40" to 50" C. for not less than 16 hours. A 96% 
yield of crude potassium dawsonite was obtained, as 
calculated from the weight loss accompanying the cal- 
cination reaction, A chemical analysis yielded the fol- 
lowing results: 25 
EXAMPLE 3 
The preparation of ~~~~~l~ 1 was repeated Once 
mmHg) at a temper- 20 more at 145" C. under a carbon dioxide pressure of 150 
psig. The product weight was practically identical with 
that of the starting materials, indicating no significant 
reaction. 
EXAMPLE 4 
Equimolar quantities of boehmite and potassium hy- 
drogencarbonate were calcined in a pressurized carbon 
KAl(0H)zCOj: K++ ~ 1 + 3  CO3= dioxide atmosphere, as in Example 1. No significant 
Calculated: 24.42% 16.85% 37.48% quantity of potassium dawsonite was obtained, although 
Found: 24.4 0.5% 16.97 0.5% 37.4 0.5% 30 interestingly, the "combined" empirical formulas 
KHC03 and AlOOH add up to the empirical formula 
for potassium dawsonite, KAl(OH)2C03. 
Replacing the hydrogencarbonate with potassium This product can then be pulverized by crushing and 
ball milling to a particle size for the use intended and it carbonate in the above preparation did not result in the 
can be intimately mixed with 1% by weight of a solid 35 production of the dawsonite. 
flow agent such as Tullanox 500 8, a 400-mesh hydro- 
phobic fumed silica powder to improve its flow proper- 
ties. The resulting product can be stored in a plastic bag. 
inside a sealed metal container until needed since it does 
not hydrate. 
The nature of the product was confirmed by various 
analytical techniques. Infrared analysis, for instance, 
produced a spectrum virtually identical with that re- 
ported for potassium dawsonite prepared by the 
tion processes of the art. Thermogravimetric analysis, 
on the other hand, showed that the product obtained by 
the calcination process of this invention possesses 1. A process for the preparation of dawsonites, which 
greater thermal stability prior to the major endotherms comprises (a) intimately mixing approximately equimo- 
and that the transition temperatures attending these 50 lar quantities of finely divided aluminum hydroxide 
decompositions are measurably higher. Some of the (Al(OH)3) and a finely divided salt selected from the 
evidence obtained from these thermogravimetric stud- class consisting of hydrogencarbonates and carbonates 
of sodium, potassium and ammonia; and (b) heating the ies appears in the following table. mixture in an atmosphere of carbon dioxide under pres- 
55 sure and at a temperature and for a period of time SUE- 
cient to form dawsonite. 
2. The process of claim 1 wherein the finely divided 
materials have particle sizes no larger than 90 pm. 
3. The process of claim 1 wherein the reactants se- 
(80' C.) (135' C.) Calcination 60 lected are gibbsite and a potassium carbonate and 
Temp Solution Solution (245' C.) wherein the reaction is carried out at about 240" to 250' 
WJ Preparation Preparation Preparation C. in a carbon dioxide atmosphere of about 230 to 250 
260 6 3 2 4. The method of claim 1 wherein the pressure is 
300 10 5 3 65 about 120 to 360 psig, the temperature is about 
350 23 1 1  8 150"-250' C. and the period of heating is about one to 
EXAMPLE 5 
Equimolar quantities of sodium hYdrogencarbonate 
and gibbsite were calcined as in Example 1, but with the 
40 following change in conditions: temperature: 200" C.; 
carbon dioxide pressure, 200 psig; and heating period, 
72 hours. After cooling, depressurization, and vacuum 
drying, sodium dawsonite was obtained in 66% yield 
based on initial A1(OH)3. A 50% of sodium hy- 
45 drogencarbonate gave a 77% yield, while a 25% excess 
gave an 87% under the Same conditions. 
I claim: 
Comparative Weight Loss Profiles of 
Potassium Dawsonite Prepared in 
Three Different Ways 
Low Temp High Temp 
psig for a period of about 4 to 6 hours. (Percent Weight Loss at T . )  
six hours. 400 31 27 24 * * * * *  


Synthesis of dawsonites

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