Hydration of acrylonitrile to acrylamide

An improved process for the hydration of acrylonitrile to acrylamide where nitrile and water are contacted with a heterogeneous hydration catalyst and the process is improved by utilizing as feed acrylonitrile and water which are substantially free of oxazole. Acrylamide monomer of enhanced stability against premature polymerization is obtained.

BACKGROUND OF THE INVENTION 
The invention relates to an improved process for hydration of acrylonitrile 
to acrylamide where oxazole is excluded from the reactant feed streams, 
acrylonitrile and water. The acrylamide produced in this improved 
hydration process exhibits exceptionally improved stability and low 
content of soluble and insoluble polymeric impurities without need for 
posthydration treatment such as that described in U.S. Pat. No. 3,923,741 
or Japanese Pat. Nos. Kokais 113,913 (1977); 116,410 (1977); 83,323 
(1975); and 82011 (1975). Acrylamide polymers prepared by the 
polymerization of acrylamide monomer from the improved process exhibit 
higher viscosity in aqueous solution than polymers prepared from 
acrylamide produced from acrylonitrile containing substantial oxazole. 
The removal of oxazole from acrylonitrile is taught in U.S. Pat. Nos. 
3,541,687 and 3,574,687 by contacting the acrylonitrile with a water-moist 
cation exchange resin in the hydrogen form. Regeneration is accomplished 
with deionized water or steam. It is suggested in U.K. Pat. No. 1,131,134 
that oxazole may be removed from acrylonitrile by hydroextractive 
distillation. It has also been taught in U.S. Pat. No. 3,146,258 and other 
patents that methylvinyl ketone impurity is removed from acrylonitrile by 
contacting with a strong acid cation exchange resin in its hydrogen form 
previously treated with a lower alkanol. In U.S. Pat. No. 2,444,589 an ion 
exchange material in conjunction with a decolorizing agent such as 
charcoal is utilized to purify acrylonitrile. The resultant purified 
acrylonitrile may be utilized in the preparation of acrylonitrile polymers 
to avoid discoloration of the ultimate product and therefore enhance the 
desirability of fibers or other colorless plastic articles prepared from 
such polymers. Acrylonitrile supplied commercially for heterogeneous 
catalytic production of acrylamide has commonly contained about 200 to 300 
ppm (by weight) of oxazole, based on acrylonitrile. 
SUMMARY OF THE INVENTION 
In a process for hydration of acrylonitrile to acrylamide comprising 
contacting acrylonitrile with water at a temperature between about 
50.degree. C. and about 175.degree. C. in the presence of a heterogeneous 
nitrile hydration catalyst, the improvement wherein the acrylonitrile and 
water are substantially free of oxazole, whereby the acrylamide produced 
exhibits enhanced stability against premature polymerization. Preferably 
the total oxazole content of the acrylonitrile and water is initially less 
than about 100 ppm based on the weight of acrylonitrile, more preferably 
initially less than about 50 ppm and most preferably less than about 25 
ppm. The process is preferably carried out at a temperature above 
75.degree. C., more preferably above 90.degree. C. and is preferably 
carried out at a temperature below 150.degree. C. and more preferably 
below 135.degree. C. The catalyst is preferably a metallic copper-based 
catalyst, more preferably a reduced copper catalyst or a Raney copper 
catalyst. Preferably the catalyst has a surface area greater than 0.2 
square meters per gram. More preferably a catalyst having a surface area 
of at least 0.5 square meters per gram and most preferably greater than 5 
square meters per gram is desired.

DETAILED DESCRIPTION OF THE INVENTION 
Heterogeneous catalytic processes for the hydration of nitriles to amides, 
specifically acrylonitrile to acrylamide, in the presence of various 
metallic catalysts have been widely described in the art. For example, 
Japanese Pat. No. Kokai 83,323 (1975) lists catalysts based on metals such 
as copper, silver, zinc, cadmium, mercury, barium, galium, indium, 
thallium, tin, lead, tellurium, chromium, molybdenum, tungsten, iron, 
cobalt, nickel, ruthenium, rhodium, platinum, lanthinium, cerium, thorium 
and the like in the form of metal, metal oxides, metal salts or compounds 
bonded to other metals. Numerous other heterogeneous metal catalysts are 
also taught in the art, for example, U.S. Pat. Nos. 3,597,481; 3,631,104; 
3,758,578; 3,696,152; 3,366,639; and 4,036,879. 
Of these catalysts, catalysts comprising metallic copper exhibit the best 
performance in terms of conversion, selectivity and activity for the 
hydration of acrylonitrile to acrylamide. Numerous copper-based catalysts 
are known in the art and include Raney copper, Ulmann copper precipitated 
by reducing a soluble copper salt with metallic zinc, and other reduced 
copper species prepared by reduction of various copper oxides or salts 
with any common reducing agent. The added presence of other metals or 
metal compounds is an acceptable variation. Metallic copper prepared by 
decomposing copper hydride is also suitable. The catalysts may be 
impregnated on various inert carriers or supports that are also described 
in the literature. Preferred for use in the invention are reduced copper 
catalysts prepared by reduction of mixtures of about 10 to 99 weight 
percent copper oxide or other copper compounds and 1 to 90 weight percent 
chromium oxide, zinc oxide, aluminum oxide, cobalt oxide, molybdenum oxide 
or iron oxide. 
After preparation of the active metallic catalysts, it is preferred to 
protect the catalyst from contact with oxygen. This generally entails 
blanketing the activated catalyst with an inert atmosphere such as 
nitrogen or argon after activation, e.g., reduction or precipitation, and 
by excluding oxygen from the acrylonitrile and water feed streams to the 
reaction process. 
The hydration process is carried out by contacting the acrylonitrile and 
water, in varying proportions, with one another in the presence of the 
heterogeneous hydration catalyst. The process can be carried out in either 
a batch or continuous manner but since the catalysts are essentially 
insoluble, heterogeneous catalysts, a continuous reaction is preferred. At 
higher temperature, the gaseous reactants are miscible in all proportions 
but for liquid reactants, sufficient contact of acrylonitrile and water 
should be maintained by dissolving one in the other. Outside of the limits 
of the solubility of one of the reactants in the other, the reactant 
mixture may be agitated and a suitable solvent, for example acrylamide, 
may be added. Excess water is a useful solvent since the product is 
commonly marketed as an aqueous solution. 
The catalyst, as previously mentioned, may be immobilized on an inert 
support or pelletized, if it is one of the less maleable catalysts, with 
suitable inert binders. In the case of a highly maleable catalyst such as 
Raney copper or copper powder, a countercurrent flow process where the 
catalyst is employed as an aqueous slurry or suspension may be used. 
However, because of the simplicity of operation, a fixed bed catalyst 
process is preferred. The product is ultimately recovered and separated 
from any unreacted acrylonitrile by steam stripping or vacuum distillation 
and concentrated if desired. 
The temperature of the reaction may vary from about 50.degree. C. up to 
about 175.degree. C. Preferably the reaction is maintained above about 
75.degree. C., more preferably above about 90.degree. C. and preferably 
below about 150.degree. C., more preferably below about 135.degree. C. 
The oxazole impurity in the acrylonitrile commonly available commercially 
is removed by contacting the acrylonitrile feed, preferably dried 
acrylonitrile, with a cation exchange resin in the acid form. It is 
preferable that the resin first be dried by heating or by passing a dry 
inert gas through the resin prior to contact with acrylonitrile. After 
breakthrough of oxazole is observed, the cation exchange resin is 
regenerated by contacting with water, hot water, steam, methanol or 
slightly acid aqueous solutions. The cation exchange resin to be used is 
suitably any commercial poly (vinylaromatic sulfonic acid) resin in the 
hydrogen form. Either a gel or macroporous type resin may be employed. 
Preferably the cation exchange resin is loaded in a column and the 
acrylonitrile to be purified is passed through this column. The removal of 
oxazole may be accomplished at a temperature between about 0.degree. C. 
and 100.degree. C., preferably at ambient temperature. 
The presence of oxazole may be determined by employing a gas chromatograph 
analytical apparatus. Oxazole in the purified acrylonitrile is preferably 
reduced to less than 100 ppm based on the weight of acrylonitrile, more 
preferably less than 50 ppm and most preferably less than about 25 ppm. By 
the term "substantially free of oxazole" we mean a water/acrylonitrile 
feed stream containing less than about 200 ppm oxazole based on the weight 
of acrylonitrile. 
SPECIFIC EMBODIMENTS 
In the following examples, various metallic catalysts are employed for the 
hydration of acrylonitrile to acrylamide and the quantity of oxazole in 
the acrylonitrile feed is varied. The hydration reaction is carried out 
both as a continuous process and as a batch process. 
In the batch process, the reaction is carried out in a stirred, 1000 cc 
Parr pressure vessel reactor. The charge is about 50 g acrylonitrile, 325 
g water and 25 g catalyst. The catalyst, if available in pellet form, is 
crushed to about 20-60 mesh (U.S. Sieve), reduced and then added to the 
Parr vessel in a nitrogen-filled chamber to avoid air contact. In most 
instances, air is purged from the water and acrylonitrile feed also. The 
Parr vessel reaction is run for about one hour at about 
110.degree.-120.degree. C. Catalysts for the batch reactions are reduced 
(except Raney copper) at about 175.degree. C. for about six hours with 
about 2000 cc/min of a 20/80 (vol) hydrogen/nitrogen stream and maintained 
under nitrogen after reduction. 
In the continuous process, a series of three or four 150 cc adiabatic 
reactors, each filled with catalyst, is employed. The catalyst is reduced 
in situ at about 175.degree. C. to 225.degree. C. for about 20-30 hours 
with about 7000 cc/min of about 5/95 (vol) hydrogen/nitrogen stream and 
maintained under nitrogen after reduction. Deoxygenated water is fed to 
the first reactor of the series at a rate of about 500-600 cc/hr mixed 
with about 95-120 cc/hr of deoxygenated acrylonitrile. To the effluent 
stream from the first reactor, about 100-135 cc/hr deoxygenated 
acrylonitrile is added to enrich the feed to the second reactor. The 
metallic copper in the first reactor also scavenges any oxygen remaining 
in the feed and since the copper so oxidized is dissolved by acrylamide, 
acrylamide should not be added or recycled to the first reactor. The 
reactor series is run at a temperature between about 95.degree. C. and 
130.degree. C. with a back pressure of about 8 to 9 atmospheres. 
The product from the reaction is collected and vacuum distilled to remove 
acrylonitrile and water until the concentration of acrylamide in water is 
about 50 percent by weight. Cupric sulfate is added to give a copper (II) 
concentration of about 22 ppm, based on acrylamide, and air is sparged to 
saturate the solution. A sample of this concentrated acrylamide solution 
is placed in a commercial gel meter, a Sunshine Gel Time Meter No. 22 with 
a 4 mil wire substituted for the standard 10 mil wire, to measure the time 
that it takes for the solution to reach a predetermined solution viscosity 
at 90.degree. C. This gives the relative polymerization stability for a 
sample of acrylamide monomer solution. The gel time test is carried out 
while bubbling nitrogen through the acrylamide solution in the gel meter 
to remove dissolved oxygen and to exclude diffusing oxygen thus breaking 
down the copper (II)-oxygen inhibitor system and no polymerization 
initiators are added. The greater the gel time, the greater the stability 
of the acrylamide. 
The various metallic catalysts to be employed are designated: 
Catalyst A--a copper-based catalyst containing about 30-35 percent by 
weight copper combined in copper compounds in a magnesium silicate matrix, 
which is prepared in the fashion of U.S. Pat. No. 3,928,439 by reacting an 
aqueous solution of 128 g magnesium nitrate (6H.sub.2 O) and 179 g sodium 
silicate (12H.sub.2 O) to precipitate magnesium silicate, adding thereto 
an aqueous solution containing 141 g cupric nitrate (3H.sub.2 O) and 6.3 g 
chromium (III) nitrate (9H.sub.2 O) then precipitating copper and chromium 
carbonates on the magnesium silicate by adding an aqueous solution of 78 g 
sodium carbonate, washing the ultimate precipitate, pressing pellets from 
it and then drying at about 60.degree. C; 
Catalyst B--a commercial copper-chromite catalyst sold under the tradename 
Harshaw Cu 0203 T catalyst, which contains about 80 percent by weight 
cupric oxide and about 17 percent chromium oxide, in pellet form; 
Catalyst C--a copper-chromium catalyst which is prepared in the fashion of 
Examples 3-16 of U.S. Pat. No. 3,696,152 except that about 0.96 mole 
cupric nitrate and about 0.04 mole chromium (III) nitrate is employed, the 
resulting carbonates precipitated at about 20.degree. C. are pelleted then 
decomposed at about 250.degree. C. for about one hour; 
Catalyst D--a copper-chromium catalyst which is prepared in the manner of 
Catalyst C except that a 0.98/0.02 mole ratio of the copper 
compound/chromium compound is employed, the resulting carbonates 
precipitated about 10.degree.-15.degree. C., the pellets decomposed at 
about 250.degree.-300.degree. C. and thereafter annealed in nitrogen for 
about 6 hours at about 300.degree.-325.degree. C.; 
Catalyst E--a 0.96/0.04 mole ratio copper-chromium catalyst prepared in the 
manner of Catalyst D; 
Catalyst F--a copper-zinc catalyst of 0.96/0.04 mole ratio prepared in the 
manner of Catalyst E; and 
Catalyst G--a commercial catalyst sold by W. R. Grace Co. under the 
tradename Raney copper No. 29, essentially 100 percent metallic copper. 
The acrylonitrile feed, having reduced oxazole content, is prepared by 
passing it through a column loaded with a commercial sulfonated 
polystyrene resin, DOWEX MSC-1 cation exchange resin, in the acid form 
which has been dried prior to use. Acrylonitrile so treated contains less 
than the lower limit (about 20 ppm) of oxazole detectable by use of a gas 
chromatograph packed with Chromosorb 101 chromatographic packing 
impregnated with 1.5 weight percent dodecyl benzene sulfonic acid. 
Acrylonitrile so purified is mixed with a suitable quantity of untreated 
acrylonitrile to obtain feed with varying amounts of oxazole. 
BATCH PROCESS 
Example 1--Supported Copper-Chromium Catalyst 
A. In the Parr vessel reactor, as previously described, acrylonitrile 
containing about 300 ppm oxazole (based on acrylonitrile weight) is 
hydrated over Catalyst A which has been reduced as previously described, 
and the acrylamide produced is concentrated to about 49 percent and is 
measured for gel time. A gel time of about 70 minutes is exhibited by the 
acrylamide. 
B. In the same manner, acrylonitrile containing less than about 20 ppm 
oxazole is hydrated and the resulting acrylamide exhibits a gel time of 
about 260 minutes. 
EXAMPLE 2--Copper-Chromium 80/17 Catalyst 
A. In like manner Catalyst B, reduced as previously described, is employed 
in the hydration of acrylonitrile containing about 30-40 ppm oxazole. 
Acrylamide produced from such hydration exhibits a gel time of about 90 
minutes. 
B. In the same manner, acrylonitrile containing less than about 20 ppm 
oxazole is hydrated and the resulting acrylamide exhibits a gel time of 
about 150 minutes. 
Example 3--Copper-Chromium 96/4 Catalyst 
A. Catalyst C, reduced as previously described, is employed to hydrate 
acrylonitrile containing about 300 ppm oxazole. The acrylamide produced 
exhibits about a 70 minute gel time. 
B. In the same manner, acrylonitrile containing less than about 20 ppm 
oxazole is hydrated. The acrylamide produced exhibits a gel time of about 
120 minutes. 
Example 4--Raney Copper Catalyst 
A. Catalyst G is employed to hydrate acrylonitrile containing about 300 ppm 
oxazole. The resulting acrylamide exhibits a gel time of about 100 
minutes. 
B. In the same manner, acrylonitrile containing less than about 20 ppm is 
hydrated and the resulting acrylamide exhibits about a 200 minute gel 
time. 
CONTINUOUS PROCESS 
Example 5--Copper-Chromium 96/4 Catalyst 
A. In the three-reactor series described above filled with Catalyst E which 
has been reduced as previously described, a feed of about 509 cc/hr water 
and 107 cc/hr acrylonitrile is pumped to the first reactor. To the 
effluent stream from the first reactor is added about 118 cc/hr 
acrylonitrile. The acrylonitrile employed in both cases contains about 300 
ppm oxazole. The product from the three-reactor series is distilled and 
concentrated to about 47.5 percent aqueous acrylamide. The acrylamide 
exhibits a gel time of about 90 minutes. 
B. The hydration of A is repeated with acrylonitrile containing about 50 
ppm oxazole. Such acrylonitrile is prepared by treating with a commercial 
cation exchange resin then blending with untreated acrylonitrile to attain 
the 50 ppm oxazole content. The resulting aqueous acrylamide product, 
concentrated to about 51 percent strength, exhibits a gel time of about 
180 minutes. 
C. In the same manner, acrylonitrile containing less than about 20 ppm 
oxazole is hydrated, the aqueous product distilled and concentrated to 
about 49 percent acrylamide. The acrylamide exhibits about a 1080 minute 
gel time. 
D. In the same manner a commercial acrylonitrile, containing less than 
about 20 ppm oxazole and designated for preparation of low color 
acrylonitrile polymers, is hydrated. Distilled and concentrated to 50 
percent acrylamide, a gel time of about 830 minutes is exhibited. 
E. To the acrylonitrile of D, oxazole is added until the acrylonitrile 
contains about 450 ppm oxazole. In the manner above, the acrylonitrile is 
hydrated, distilled and concentrated to 48 percent acrylamide. The 
acrylamide exhibits a gel time of about 50 minutes. The effect of 
decreasing oxazole content is readily observed in the following Table. 
TABLE 
______________________________________ 
Effect of Oxazole Content of Feed 
Oxazole (ppm Gel Time of 
based on Acrylamide 
Example Acrylonitrile) Product (min) 
______________________________________ 
5E 450 50 
5A 300 90 
5B 50 180 
5C &lt;20 1080 
5D &lt;20 830 
______________________________________ 
Example 6--Mixed Catalyst 
The three-reactor series of Example 5 is modified by addition of an 
identical fourth reactor. The first two reactors of the series are loaded 
with Catalyst E and the last two reactors are loaded with Catalyst F. All 
catalyst is reduced as previously described. Acrylonitrile containing 
about 25 ppm oxazole is fed to the first reactor and second reactor, as in 
Example 5, for the hydration reaction. The product is distilled and 
concentrated to 48.5 percent acrylamide. The acrylamide exhibits a gel 
time of about 260 minutes. 
Example 7--Copper-Zinc Catalyst 
A. All four reactors of Example 6 are filled with Catalyst F which is 
reduced. Acrylonitrile containing about 300 ppm is fed as in Example 6. 
The concentrated 49 percent acrylamide product exhibits about a 50 minute 
gel time. 
B. In the same manner, acrylonitrile containing less than about 20 ppm 
oxazole is hydrated. The concentrated 50.5 percent acrylamide product 
exhibits a gel time of about 150 minutes. 
Example 8--Copper-Chromium 98/2 Catalyst 
In the manner of Example 5, the three-reactor series is loaded with 
Catalyst D which is reduced as previously described. As in Example 5, 
acrylonitrile containing about 300 ppm oxazole is hydrated as is 
acrylonitrile containing less than about 20 ppm oxazole. The acrylamide 
derived from the latter exhibits a significantly improved gel time over 
the former, as in the previous examples. 
Example 9--Copper-Chromium 80/17 Catalyst 
A. In the manner of Example 6, the four-reactor series is loaded with 
Catalyst B which is then reduced as previously described. Acrylonitrile 
containing 30-40 ppm oxazole is fed to the first reactor, and to the 
effluent from the first and second reactors as well, in the amounts of 
about 55 cc/hr, 81 cc/hr and 123 cc/hr, respectively. Water is fed to the 
first reactor at about 275 cc/hr. The concentrated acrylamide product from 
the reactor series exhibits a gel time of about 700 minutes. 
B. In the same manner, acrylonitrile containing less than about 20 ppm 
oxazole is hydrated. The concentrated acrylamide product exhibits a gel 
time of about 1200 minutes. 
Example 10--Polymer Improvement 
Samples of acrylamide prepared in the fashion described above from 
acrylonitrile containing (a) about 30-40 ppm oxazole and (b) less than 
about 20 ppm oxazole, are polymerized as dilute aqueous solutions using 
redox initiator systems. Standard viscosity tests of the resultant 
polymers determine that about 35 percent higher viscosity is present in 
polymers of the acrylamide derived from low oxazole acrylonitrile, (b), 
compared to polymers of the acrylamide derived from the higher oxazole 
acrylonitrile, (a).