Double metal cyanide catalysts

Double metal cyanide catalysts, prepared by drying a catalyst slurry by a non-agglomerative drying method such as spray drying or freeze drying, directly produces catalyst particles of fine particle size such that intensive grinding is not required. The catalysts thus produced are different from conventionally dried particles in that polyoxyalkylation may be conducted with less reactor fouling and a polyoxyalkylene product of lower unsaturation and narrower polydispersity may be obtained.

TECHNICAL FIELD 
The present invention pertains to double metal cyanide catalysts. More 
particularly, the subject invention pertains to a process for the 
manufacture of double metal cyanide complex catalysts which exhibit 
unexpectedly improved properties. The process involves catalyst 
preparation followed by a non-agglomerating drying step. 
BACKGROUND ART 
Double metal cyanide complex catalysts were discovered in the decade of the 
1960s, and were found to have significant catalytic activity in a variety 
of reactions, particularly polymerizations. Although double metal cyanide 
salts themselves were found to have little or no catalytic activity, 
non-stoichiometric complexes formed from the double metal cyanide salt and 
an organic complexing agent were found to possess high activity. The 
activity was found to vary with the identity of the metals contained in 
the complex, and also with the organic complexing agents. The chemical 
makeup, effects of varying metal ions, and differences in reactivity due 
to the complexing agent are discussed in U.S. Pat. No. 3,427,335, herein 
incorporated by reference, which further indicates that polymers of 
different intrinsic viscosities, and therefore of differing molecular 
weight, may be obtained by suitable selection of organic complexing agent. 
According to the '335 disclosure, excess complexing agents can be removed 
by extraction with a low boiling, non-complexing solvent such as pentane 
or hexane. In a typical laboratory catalyst preparation, a solution of an 
alkali metal hexacyanometallate salt, e.g. K.sub.3 Fe(CN).sub.6 is added 
slowly to a stirred solution of metal chloride salt, e.g. zinc chloride, 
in slight molar excess. The precipitated zinc hexacyanoferrate(III) salt 
is washed thoroughly with water, and then washed with three portions of 
anhydrous dioxane. In an optional procedure, the dioxane washed 
precipitate is slurried in dioxane/hexane and refluxed, water being 
removed as an azeotrope. The moist solid is dried under vacuum of c.a. 1 
torr. The dry catalyst may be crushed to a fine powder. 
The catalytic activity of catalysts of the type disclosed by the '335 
patent and other related disclosures such as U.S. Pat. Nos. 3,427,256, 
3,427,334, 3,829,505, and 3,941,849, although high, was not high enough to 
overcome the high cost of such catalysts relative to other catalysts 
traditionally utilized. For example, in conventional oxyalkylation 
reactions useful in preparing polyoxyalkylene polyols and polyoxyalkylene 
block surfactants, potassium hydroxide had long been the catalyst of 
choice due to its low cost. Moreover, removal of catalyst residues from 
double metal cyanide catalyzed polyols also proved to be problematic and 
to add additional expense to the production process. As a result, little 
if any commercialization of double metal cyanide catalysts of the types 
disclosed by the aforementioned patents occurred. 
In the 1980's, double metal catalysts were revisited, spurred on in part by 
the desire to manufacture polyether polyols with lower unsaturation and 
higher equivalent weights. In base catalyzed polyoxyalkylation, a 
competing rearrangement of higher alkylene oxides into unsaturated 
alcohols continuously introduces monofunctional, oxyalkylatable species 
into the oxyalkylation reactor. For example, propylene oxide, the most 
widely used higher alkylene oxide, rearranges to allyl alcohol. 
Oxypropylation of this monohydric species results in polyoxyalkylene 
monols. Continued generation of allyl alcohol and the continued 
oxyalkylation of it and the previously generated and oxyalkylated monols 
results in a considerable proportion of monohydric species spanning a 
broad molecular weight range. 
For example, in the manufacture of polypropylene glycols, the base 
catalyzed oxypropylation of a propylene glycol initiator results in a 
mixture of polyoxypropylene glycols and oxypropylated allyl alcohol 
polymers and oligomers. As oxypropylation continues, the mol percentage of 
monofunctional species steadily increases. In a 2000 Da equivalent weight 
polyoxypropylene "diol," the monofunctional species content may range 
between 30 and 40 mol percent, and the functionality reduced from the 
"nominal," or theoretical functionality of 2.0 to an actual, measured 
functionality in the range of 1.6 to 1.7. In the case of a 2000 Da 
equivalent weight triol, e.g. an oxypropylated glycerine polyol, the 
actual functionality will be closer to two than the nominal, or 
"theoretical" functionality of three. 
Investigations of other catalysts in attempting to lower monol production 
during oxyalkylation did not, in general, lead to commercially acceptable 
systems. For example, lowering the reaction temperature during base 
catalyzed oxypropylation was found to lower unsaturation, but at the 
expense of greatly increased process time. Levels of unsaturation in the 
range of 0.010 meq/g polyol, as measured by ASTM 2849-69, "Testing of 
Urethane Foam Polyol Raw Materials" could be produced, but with reaction 
times measured in days or even weeks rather than typical batch times of 8 
to 12 hours. Use of alternative catalysts such as cesium or rubidium 
hydroxide (U.S. Pat. No. 3,393,243); strontium or barium oxides and/or 
hydroxides (U.S. Pat. Nos. 5,010,187 and 5,114,619); and alkaline earth 
metal carboxylates (U.S. Pat. No. 4,282,387) have all been proposed. 
In U.S. Pat. Nos. 4,472,560 and 4,477,589, promoted double metal cyanide 
complex catalysts prepared by addition of inorganic acids or salts such as 
alkali metal hexafluorosilicates to double metal cyanide complexes were 
proposed. The promoter addition takes place in the presence of excess 
complexing agent, i.e. glyme, or in the presence of a liquid initiator, 
and following dehydration produces a catalyst/initiator slurry. However, a 
different slurry must be prepared for each different initiator desired, 
and the process cannot be used to prepare slurries of catalyst in volatile 
initiators. Moreover, the catalyst slurries are much more expensive to 
ship as compared to dry catalyst. However, the catalysts were stated to 
exhibit improved catalytic activity, and were also stated to be useful at 
temperatures in the range of c.a. 110.degree. C. to 120.degree. C., while 
prior DMC catalysts generally were rapidly deactivated at temperatures in 
excess of 100.degree. C. 
Further improvements in DMC catalysts are evidenced by the processes of 
preparation disclosed in U.S. Pat. No. 5,158,922, wherein modestly heated 
double metal cyanide-forming reactants, a relatively large stoichiometric 
excess of metal salt over metal cyanide salt, and a specific order of 
mixing these salts resulted in greatly improved catalytic activity. 
Japanese Patent Application Kokai No. 4-145123 disclosed that use of 
t-butanol as the organic complexing agent rather than glyme, the most 
common complexing agent, also resulted in improved catalysts, particularly 
with respect to catalyst longevity. These improvements, coupled with 
improved and less costly methods of removal of catalyst residues from 
finished polyether products as illustrated by U.S. Pat. Nos. 4,721,818; 
4,987,271; 5,010,047; and 5,248,833, led to commercialization of 
DMC-catalyzed polyether polyols for a short time. 
Most recently, discoveries by the ARCO Chemical Co. have resulted in double 
metal cyanide complex catalysts which not only offer polymerization rates 
which are considerably higher than prior catalysts, but moreover are far 
more easily removed from the polyoxyalkylene polyether product. While 
earlier DMC catalysts were able to produce polyols with levels of 
unsaturation in the range of 0.015-0.020 meq/g, these new catalysts 
consistently produce polyols with unsaturation in the range of 0.003 to 
0.008 meq/g. Such catalysts are disclosed in U.S. Pat. Nos. 5,470,813 and 
5,482,908, which are incorporated herein by reference. Double metal 
catalysts such as those disclosed by the 5,470,813 and 5,482,908 patents 
often allow for catalyst residue removal from polyol product by simple 
filtration. Moreover, the catalytic activity is so high in some cases that 
the low amounts of catalyst used, e.g. 10-25 ppm, does not require any 
removal process. 
However, the process of preparing the double metal cyanide complex 
catalysts themselves is lengthy, and involves numerous steps. While the 
process is easily done on a laboratory scale, on a commercial scale, 
catalyst preparation time increases dramatically. For example, in a 
commercial scale manufacturing process, catalyst preparation may consume 
in excess of 100 hours. Approximately 88% of this time is consumed in 
isolating the catalyst solids, drying the moist filter cake obtained, and 
grinding the catalyst into small particles. 
Surface morphology may also be of importance with respect to catalytic 
activity for double metal cyanide complex catalysts. For example, in U.S. 
Pat. No. 5,470,813, unique double metal cyanide catalysts were produced 
which differed from prior art catalysts by being substantially amorphous, 
rather than possessing significant amounts of highly ordered or 
crystalline material. The amorphous nature of these catalysts was 
demonstrated by the lack of certain sharp lines in the X-ray diffraction 
spectrum which are characteristic of crystalline double metal cyanide 
salts. 
The substantially amorphous catalysts exhibited surprising and unexpected 
increases in catalytic activity, yet the particle size was actually much 
larger than that of prior art catalysts, prepared from similar chemical 
constituents, which thus presented higher surface area. The catalytic 
activity of such substantially amorphous catalysts can be increased yet 
further by grinding the catalyst to smaller particle sizes. Particle sizes 
less than 10 .mu.m are desired. 
The grinding process is very time intensive. Moreover, the moist, bulk 
filter cake produced during catalyst preparation retains a substantial 
amount of complexing agent, even after considerable time drying in vacuo. 
During this intensive grinding, surface modifications to the catalyst 
particles due to the inherent nature of the grinding operation may cause 
changes in catalytic activity. Thus, an increase in activity due to 
smaller particle size may be offset, at least in part, by a decrease in 
activity due to changes in surface morphology. Surface morphology may also 
affect properties other than activity per se. For example, double metal 
cyanide catalysts produced in finely ground form may also exhibit reactor 
fouling, in which gel-like and presumably very high molecular weight 
products accumulate in the reactor. 
It would be desirable to provide a process by which double metal cyanide 
complex catalysts may be prepared with reduced processing time. It would 
be further desirable to be able to prepare double metal cyanide complex 
catalysts of small particle size without the risk of altering surface 
morphology by intensive grinding. It would be yet further desirable to 
prepare double metal cyanide complex catalysts which offer increased 
handling ease, increased storage stability, less reactor fouling during 
polymerization, and higher catalytic activity. 
SUMMARY OF THE INVENTION 
It has now been surprisingly discovered that double metal cyanide complex 
catalysts having improved catalytic activity, greater storage stability, 
and other desirable properties can be produced in very small particle 
sizes without intensive grinding, by slurrying the double metal cyanide 
complex catalyst into a volatile complexing agent and removing the excess 
complexing agent by a non-agglomerative removal method. As a result of the 
process, solid double metal cyanide complex catalysts of fine particle 
size are directly obtained. Preferred non-agglomerative methods of excess 
complexing agent removal include spray drying and freeze drying.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The double metal cyanide complex catalysts of the subject invention are 
non-stoichiometric complexes of a volatile organic complexing agent and a 
double metal cyanide salt, optionally containing activity promoters and 
optionally containing a further complexing agent as well. The double metal 
cyanide salts themselves are well known to the skilled artisan, and in 
general contain a negatively charged complex ion consisting of a first 
metal ion surrounded by a plurality of cyanide ions and complexing 
ligands, and a second metal cation which at least in part counterbalances 
the charge of the complex cyanide anion. Other anions, cations, activating 
agents, and the like, may also be present as well. The metals are, in 
general, transition metals or inner transition metals. Examples of double 
metal cyanide salts include zinc hexacyanocobaltates, nickel 
hexacyanoferrates, iron hexacyanoferrates, zinc hexacyanonickelates, and 
the like. Further examples of double metal salts may be found in the 
previously cited U.S. patents, which have been incorporated by reference, 
and in particular by U.S. Pat. No. 5,470,813, 5,482,908, and U.S. 
application Ser. No. 08/435,116, which is also incorporated herein by 
reference. 
The volatile organic complexing agent is a heteroatom-containing organic 
ligand which can be removed from the double metal cyanide complex by 
evaporation. Examples of such organic ligands include low boiling 
alkanols, glycols, esters, ketones, nitriles, amides, ethers, and the 
like. Examples include isopropanol, 2-butanol, t-butanol, glyme, diglyme, 
diglyet, and the many complexing agents disclosed in the aforementioned 
patents. The volatile organic complexing agent is generally used in 
considerable excess, with that portion not involved in complex formation 
being subsequently removed. More than one volatile complexing agent may be 
used. 
In addition to the volatile organic complexing agent, a substantially 
non-volatile complexing agent may be used as well. The non-volatile 
complexing agent is one which is oligomeric or polymeric in nature and 
generally has little vapor pressure at room temperature or below. The 
molecular weight of the non-volatile organic complexing agent is generally 
above 300 Da and often considerably higher, for example in the range of 
1000 Da to 10,000 Da. Examples of preferred non-volatile complexing agents 
include polyoxyalkylene glycols and polyols, particularly polyoxypropylene 
glycols and polyoxypropylene polyols. Particularly suitable are 
polyoxypropylene polyols end-capped with isobutylene oxide to provide 
tertiary hydroxyl group termination. 
A typical laboratory preparation of double metal cyanide complex catalyst 
is illustrated by Example 1 of U.S. Pat. No. 5,470,813, reproduced 
hereafter. 
Laboratory Preparation of Double Metal Cyanide Catalyst 
Potassium hexacyanocobaltate (8.0 g) is added to deionized water (1.50 ml) 
in a beaker, and the mixture is blended with a homogenizer until the 
solids dissolve. In a second beaker, zinc chloride (20 g) is dissolved in 
deionized water (30 ml). The aqueous zinc chloride solution is combined 
with the solution of the cobalt salt using a homogenizer to intimately mix 
the solutions. Immediately after combining the solutions, a mixture of 
tert-butyl alcohol (100 ml) and deionized water (100 ml) is added slowly 
to the suspension of zinc hexacyanocobaltate, and the mixture is 
homogenized for 10 minutes. The solids are isolated by centrifugation, and 
are then homogenized for 10 minutes with 250 ml of a 70/30 (v:v) mixture 
tert-butyl alcohol and deionized water. The solids are again isolated by 
centrifugation, and are finally homogenized for 10 minutes with 250 ml of 
tert-butyl alcohol. The catalyst is isolated by centrifugation, and is 
dried in a vacuum oven at 50.degree. C. and 30 in. (Hg) to constant 
weight. 
In the foregoing example, less than 10 g of catalyst is produced. Isolation 
of catalyst solids from the slurry of catalyst in t-butanol is performed 
in a laboratory centrifuge. The moist centrifuge cake is then dried under 
vacuum. 
The standard laboratory techniques illustrated in the laboratory catalyst 
preparation are more difficult to implement on an industrial production 
scale. For example, the initially produced catalyst solids in the catalyst 
slurry are of a particle size which does not lend itself to isolation by 
filtration. For isolation by centrifugation, large and expensive 
centrifuges, e.g. a high rotation solid ejecting centrifuge, must be used. 
For drying the moist centrifuge cake or pellets obtained, numerous types 
of vacuum driers may be used. However, most are bulky and expensive batch 
driers, which seal with some difficulty, and which do not always offer 
either the desired rate of heat transfer or obtainable vacuum. For 
example, in the industrial preparation of approximately 135 Kg of 
catalyst, a 7,000-8,000 l batch reactor is required. The total process 
time will vary with the particular mode of catalyst preparation, for 
example with the number of wash and complexing steps, activating agent 
addition steps, etc. In a typical process, precipitation, washing, and 
isolation consumes approximately 84 hours, while drying and grinding 
consume an additional 24 hours, for a total cycle of approximately 108 
hours. Thus, a considerable portion of the total time is directed to 
drying and grinding operations, while a further considerable portion 
involves isolation by centrifugation prior to drying. In the present 
process, the pre-drying centrifugation, moist centrifuge cake drying, and 
grinding operations are replaced by a non-agglomerative drying step. As a 
result, the process time is much shorter. A typical process utilizing 
spray drying as the means of catalyst isolation/drying consumes only about 
76 hours. 
The spray drying step has been found to produce catalyst with particle 
sizes less than 10 .mu.m, thus rendering grinding unnecessary. The 
modified process saves 32 hours (4 shifts) of production time, and the 
cost of catalyst is greatly reduced as a result. However, it has been 
surprisingly found that the catalyst produced has higher catalytic 
activity, produces polyoxyalkylene polyols with less unsaturation, and 
importantly, with less reactor fouling than compositionally similar 
catalysts produced in the conventional manner. These results are 
completely surprising and unexpected. Due to the greater dryness, the 
storage stability is expected to be higher, as is also the ease of 
handling and packaging. 
As used herein, the terms "drying" and "moist" are not used in the same 
sense as in other areas of technology as pertaining to water content. 
Water is substantially removed from the double metal cyanide salt by the 
first centrifugation and successive washes with complexing agent(s) which 
serve(s) to dehydrate the double metal cyanide salt as well as complex 
with the salt. Rather, the terms "dry," "drying," "moist" and "wet" refer 
in the present invention, to catalyst containing liquid other than water. 
For example, in the conventional preparation of zinc 
hexacyanocobaltate-glyme complexes, the "moist" nature of the centrifuge 
cake is due to the presence of glyme beyond that which is involved in the 
formation of the complex. With t-butanol complexed catalysts, the presence 
of additional t-butanol produces the same effect. Following vacuum drying 
of moist centrifuge cake in the conventional process, a product which 
appears to be dry is obtained. This product can be easily crushed to 
powder. The majority of glyme or t-butanol still contained in the powdered 
catalyst is chemically bound in the double metal cyanide complex. However, 
a small proportion of complexing agent is still believed to be retained in 
non-bound form. 
The initial catalyst complex preparation may be performed in numerous 
manners. For example, the salt solution, i.e. aqueous zinc chloride, may 
be added to the complex salt solution, i.e. aqueous potassium 
hexacyanocobaltate, organic complexing agent added, the solids isolated by 
filtration or centrifugation and reslurried in additional or different 
complexing agent. Alternatively, and preferably, the organic complexing 
agent is present at the time the two salts are first contacted, i.e. by 
adding the organic complexing agent to the potassium hexacyanocobaltate 
solution prior to adding the zinc chloride solution to it. Most 
preferably, the mixing is by high shear stirring, impingement mixing, 
homogenization, and the like. 
Following initial preparation of the solid catalyst, the mother liquor is 
removed by filtration and/or centrifugation, and the catalyst is generally 
washed with water or water/complexing agent and/or reslurried in fresh 
complexing agent(s). This reslurrying may not always be necessary, but is 
generally desirable to produce catalysts of the greatest activity. The 
separation/reslurrying is generally performed twice, and may be performed 
numerous times. During the wash/reslurry process, substantially all water 
is removed from the catalyst. It may be appropriate at this time to add a 
second complexing agent, for example a polyoxypropylene polyol. Although 
such higher molecular weight complexing agents are generally only of 
limited solubility in water, many are of much higher solubility in lower 
molecular weight complexing agents such as glyme and t-butanol. 
The present process avoids collection of the completed catalyst as a moist 
cake, whether by filtration, centrifugation, or other liquid/solid 
separation method. Rather, the completed catalyst is maintained in its 
last slurried or dispersed form, and subjected to a non-agglomerative 
drying process. In the sense used herein, "completed catalyst" refers to 
the catalyst at the point where all chemical modifications, i.e. washing, 
complexing, etc., have been completed, and catalyst isolation in dry form 
remains to be accomplished. 
By "non-agglomerative drying" is meant a drying process in which particle 
agglomeration is substantially prevented. For example, examination of the 
catalyst particle size in a wet centrifuge cake indicates that the median 
particle size may be 1.5 .mu.m. However, after drying such a cake in the 
conventional manner, i.e. vacuum drying, the resulting particle size is 
much larger. A 135 Kg batch, for example, requires about 12 hours of 
intensive grinding to obtain a median particle size less than 10 .mu.m. 
Thus, during the drying stage, considerable particle agglomeration has 
occurred. By "non-agglomerative drying" is meant a drying process other 
than conventional vacuum drying of an isolated solid product such that 
significant agglomeration is prevented, and a powdered product of fine 
particle size may be directly obtained. 
In many such non-agglomerative methods, particle to particle contact is 
minimized. In others, for example fluidized bed drying, Therma Jet.TM. 
flash drying, vacuum stripping with plough and ribbon, or other similar 
methods, particle-to-particle contact occurs, but the manner and/or 
duration of contact prevents agglomeration. Preferably, the powdered 
catalyst isolated from such a method has a particle size less than 40 
.mu.m, more preferably less than 20 .mu.m, and most preferably about 10 
.mu.m or less, all without grinding. Most preferably, the particle sizes 
obtained from the non-agglomerative drying method will be of the same 
order of magnitude as those which would otherwise be contained in a wet 
filter cake obtained by centrifugation. Non-agglomerative processes which 
do not produce the smallest particles may require some grinding. However, 
the amount and intensity of grinding will be far less than that required 
when agglomerative drying operations are utilized, and any change in 
surface morphology accordingly minimized. Preferably, the 
non-agglomerative drying methods include spray drying and freeze drying. 
In both spray drying and freeze drying, the double metal cyanide complex 
particles are isolated from other particles by a separating matrix. In the 
case of spray drying, the separating matrix is hot gas into which the 
catalyst/complex slurry is atomized. In a suitable spray drying apparatus, 
the dryer is constructed so as to allow the safe spray drying of organic 
substances. For example, the process may employ nitrogen or other 
substantially inert atmosphere, and may also be operated at reduced 
pressure. An oxygen analyzer at the dryer outlet can be used to ensure 
that oxygen concentration is below the limit of flammability. The feed to 
the dryer can be shut off manually or automatically if the oxygen 
concentration exceeds desired limits. In the case of freeze drying, the 
separating matrix is additional, non-chemically bound complexing agent 
and/or solvent. In both cases, as the complexing agent and/or solvent is 
removed, there is minimal contact of double metal cyanide complex 
particles, and particularly, little pressurized contact. Thus, very little 
agglomeration occurs. 
BRIEF DESCRIPTION OF THE DRAWING 
A pilot scale spray drying apparatus is illustrated by FIG. 1. 
DETAILED DESCRIPTION OF THE DRAWING 
The double metal cyanide complex catalyst slurry 1 is contained in slurry 
feed tank 2 and pumped from the slurry feed tank to the inlet 5 of spray 
dryer 7 by a feed pump 3, which may be of the peristaltic type or other 
type. As the catalyst slurry passes through supply line 9, it may 
optionally be heated or cooled. Nitrogen or other relatively inert gas is 
fed through line 11 through regulator 12 to atomizing gas inlet 13 of 
spray dryer 7. The atomizing gas pressure and volume, the catalyst slurry 
feed rate, and the size and geometry of atomizing nozzle 15 of atomizer 17 
are adjusted to produce the desired degree of atomization. It is currently 
believed that a higher degree of atomization and a more dilute catalyst 
slurry both minimize agglomeration, and lead to finer particle sizes. The 
atomizer, nozzle, etc., may take numerous forms. For example, an atomizing 
nozzle which does not employ gas to assist in atomizing may be used. In 
lieu of an atomizer of the types previously described, a spinning disk 
atomizer, where a stream of catalyst slurry impinges upon a rapidly 
spinning disk may be used to implement atomization. 
Heated drying gas is fed from source 16 through pressure regulator 17 
through a heater 19 to supply heated gas to spray dryer 17 through drying 
gas inlets 18. From the spray dryer, the dried particulate catalyst passes 
to cyclone 21 where it is separated from the hot, vapor laden gas. Product 
22 is collected in drums, cans, or other appropriate product collection 
containers 23. Organic complexing agent/solvent vapors pass through filter 
25 to cold trap 27, which may be maintained at 0.degree. C. in an ice 
bath, or cooled to an appropriate temperature by a refrigerating device 
28. From the cold trap 27, the vapors pass to a further cold trap 29 
maintained at lower temperature by device 30. Aspirator pump 31 ensures 
mass flow in the proper direction. The pump output may be adjusted to 
enable operation at less than atmospheric pressure, which is preferred. 
Commercial spray dryers are readily available, and are commonly used for 
spray drying instant coffee, instant tea, dyes and pigments, synthetic 
elastomer particles, etc. The theory and operation are well known, and 
need not be described here. On a commercial scale, the ice bath and dry 
ice cold traps would likely be replaced by refrigerated units. Parameters 
such as gas flow, temperature, degree of atomization, slurry input rate 
and concentration, etc. can all be adjusted. The process has not been 
optimized, but as can be seen from the actual example, the non-optimized 
process already produces a surprisingly superior catalyst. 
Freeze drying is a further non-agglomerative means of drying catalyst in 
accordance with the subject invention. In the freeze drying process, 
solids, as a dispersion or dissolved in a liquid continuous phase or 
solvent, in this case complexing agent and/or solvent, are frozen, 
following which the normally liquid continuous phase or solvent is removed 
by sublimation at reduced pressure. Freeze drying has an advantage in that 
it avoids the higher temperatures associated with spray drying and other 
drying methods. For this reason, freeze drying is commonly used for 
temperature labile products such as biochemicals, pharmaceuticals, and the 
like. Freeze drying has been used for many years for the freeze drying of 
instant coffee. 
Freeze drying may be accomplished in a batch or continuous process. In 
continuous processes, the composition to be freeze dried must traverse a 
freeze drying chamber having means to seal the entry and exit so as to 
maintain suitable vacuum. In batch-type processes, the composition may be 
placed in metal trays in a vacuum chamber, frozen, and sublimed. In either 
case, the time in which freeze drying is accomplished is minimized by 
maximizing surface area of the frozen composition. The freeze drying 
process and equipment for its use are well known to those skilled in the 
art of freeze drying equipment. 
Having generally described this invention, a further understanding can be 
obtained by reference to certain specific examples which are provided 
herein for purposes of illustration only and are not intended to be 
limiting unless otherwise specified. 
EXAMPLE 1 
Catalyst Preparation 
A solution of 7.5 g potassium hexacyanocobaltate dissolved in 300 ml 
distilled water and 50 ml t-butanol was introduced into a 500 ml beaker. 
In a separate beaker, 75 g zinc chloride was dissolved in 75 ml distilled 
water. The solution of zinc chloride thus prepared was added to the 
potassium hexacyanocobaltate solution over a period of 30 minutes at 
30.degree. C. with intensive mixing using a Power-Gen.TM. homogenizer set 
at a 20% power level. Following completion of addition, the mixing 
intensity was increased to 40% and mixing continued for 10 minutes. The 
solids were then isolated by centrifuging at 17,000 rpm for 30 minutes. 
The centrifuge cake was reslurried in 155 ml t-butanol and 55 ml distilled 
water in a 500 ml beaker and homogenized at 40% power level for 10 
minutes. The solids were isolated by a centrifugation as previously done, 
and then reslurried in 185 ml t-butanol at a 40% power level for 10 
minutes. The centrifuge cake was divided into two halves. The first half 
(Catalyst A), was dried at 60.degree. C. under 30 in/Hg vacuum until a 
constant weight was obtained. The catalyst was then crushed into fine 
powder. The second half of the isolated moist cake was reslurried into 
1,000 ml t-butanol at 25% homogenizing power for 10 minutes. This slurry 
was frozen in an ice bath and then freeze dried under vacuum. A fluffy 
powder catalyst was obtained directly. This freeze dried catalyst is 
denoted as Catalyst B. 
EXAMPLE 2 AND COMATIVE EXAMPLE C2 
Polyol Synthesis 
The catalysts prepared in Example 1 were used to prepare 8,000 Da 
polyoxypropylene diols. A one liter stirred reactor was charged with 
catalyst (0.0166 g, 25 ppm relative to finished polyol) and a 785 Da 
molecular weight polyoxypropylene diol (65 g) prepared conventionally from 
propylene glycol, KOH, and propylene oxide was used as the initiator 
molecule. The mixture was well stirred and heated to 105.degree. C. under 
vacuum for about 30 minutes to remove traces of residual water. The 
reaction temperature was increased to 130.degree. C., and approximately 11 
g of propylene oxide added to increase the pressure in the reactor from 
vacuum to about 2 psig. 
An accelerated pressure drop was noted, indicating the catalyst had become 
active. After catalyst initiation was verified, additional propylene oxide 
(600 g total) was continuously added at a rate of approximately 1.7 g/min 
over 6 hours. The reactor was held at 130.degree. C. for 30-45 minutes 
until a constant pressure was obtained, which indicated that propylene 
oxide conversion was complete. The mixture was stripped under vacuum at 
60.degree. C. for 30 minutes to remove traces of unreacted propylene 
oxide. The product was cooled and recovered and its properties measured. 
The properties of the polyols prepared from Sample A and Sample B 
catalysts of Example 1 are presented in Table 1 below. 
TABLE 1 
______________________________________ 
Catalyst A Catalyst B 
Catalyst: (Conventionally Dried) 
(Freeze Dried) 
______________________________________ 
Polyol Properties 
Hydroxl No. 14.6 15.0 
Unsaturation (meq/g) 
0.0067 0.0061 
Polydispersity, M.sub.w /M.sub.n 
1.23 1.19 
Viscosity, cps, 25.degree. C. 
4150 3940 
Gel Formation? Yes No 
______________________________________ 
As can be seen, the freeze dried catalyst of the subject invention are 
capable of producing polyols with lower unsaturation, lower 
polydispersity, and lower viscosity, while not producing reactor fouling. 
These results are totally unexpected and surprising. 
EXAMPLE 3 
Spray Dried Catalyst Preparation 
A double metal cyanide catalyst is prepared substantially in accordance 
with Example 1, however, following reslurrying of the centrifuge cake in 
t-butanol, the slurry is divided into two parts. The first part is 
centrifuged and dried in the conventional manner, and is identified as 
Catalyst C. The second portion is introduced into a pilot plant scale 
spray drier as illustrated in FIG. 1, employing a feed rate of 10 ml/min 
of catalyst slurry. Approximately 7.5 liters/minute of nitrogen heated to 
a temperature of 106.degree. C. is used to dry the atomized catalyst 
slurry. The catalyst is collected from a cyclone, and its particle size 
and activity measured. Also measured are the catalyst particle sizes in 
the undried, wet centrifuge cake obtained from the first portion of the 
slurry (Catalyst C). Particle sizes were measured by conventional light 
scattering techniques in a Microtrac Full Range Particle Size Analyzer by 
volume distribution. The particles in the wet cake and the spray dried 
particles were found to have the particle sizes indicated in Table 2 
below. The particle sizes reported herein are in .mu.m (microns). 
TABLE 2 
______________________________________ 
Sample Particle Size (.mu.m) Distribution 
Description 10% 50% 90% 
______________________________________ 
Spray Dried 1.03 2.93 9.56 
Final wet cake 
0.65 1.50 3.10 
Conventionally Dried 
15.22 127.04 326.32 
and Ground Wet Cake 
______________________________________ 
As can be seen from the table, very little agglomeration occurred during 
the spray drying process over what was the particle size contained in the 
final wet cake. In contrast, during conventional vacuum drying of the wet 
cake, considerable particle agglomeration takes place resulting in the 
necessity of prolonged grinding to obtain a reasonable particle size. The 
spray dried particles have a median size of 2.93 microns as obtained from 
the spray drier. 
EXAMPLE 4 AND COMATIVE EXAMPLE 4 
Two 6000 Da polyoxypropylene triols were produced by oxyalkylating an 
oligomeric oxypropylated glycerine starter using the spray dried catalyst 
of Example 3 and the comparative catalyst prepared by conventional vacuum 
drying. The rates of oxypropylation, the unsaturation of the 
polyoxypropylated triol product, and degree of reactor fouling were noted. 
The results are presented in Table 3 below. 
TABLE 3 
______________________________________ 
4C 4 
Example Catalyst C Catalyst D 
Catalyst (conventional) 
(spray dried) 
______________________________________ 
Reaction rate (g PO/min) 
20.0 21.7 
Unsaturation meq/g 
0.0034 0.0032 
Reactor Fouling mild none 
______________________________________ 
As can be seen, the spray dried catalyst offered a slightly higher reaction 
rate, lower unsaturation, and eliminated reactor fouling. 
EXAMPLES 5 AND C5 
The procedure of Example 2 is followed to prepare 8000 Da polyoxypropylene 
diols using the spray dried, and conventionally dried catalysts of Example 
3. The viscosity and unsaturation are indicated in Table 4 below. 
TABLE 4 
______________________________________ 
Example 5C 5 
Catalyst Catalyst C 
Catalyst D 
______________________________________ 
Diol Viscosity (cps) 
3750 3780 
Unsaturation 0.0071 0.0051 
______________________________________ 
The viscosities of the polyol products are virtually identical, however the 
unsaturation of the polyol produced using the spray dried catalyst is 
considerably lower at 0.0051 meq/g as compared to 0.0071 meq/g for the 
conventionally dried catalyst. 
Having now fully described the invention, it will be apparent to one of 
ordinary skill in the art that many changes and modifications can be made 
thereto without departing from the spirit or scope of the invention as set 
forth herein.