Purification of methacrylamidopropyltrimethyl-ammonium chloride with nonionic organic resins

Methacrylamidopropyltrimethylammonium chloride or its free amine, dimethylaminopropylmethacrylamide, is purified by contacting aqueous solutions of the salt or the free amine with solid, nonionic organic resins. Such resins absorb the organic impurities, yet leave behind the polymerization inhibitor.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a new process for the purification of 
methacrylamidopropyltrimethylammonium chloride (MAPTAC) or of the free 
amine, dimethylaminopropylmethacrylamide (DMAPMA), through the application 
of adsorption techniques. The invention more particularly relates to the 
purification, by both batch and continuous processing, of aqueous 
solutions of MAPTAC or DMAPMA by passing such solutions over a bed of 
solid, nonionic organic resin or by stirring such solutions with the resin 
in a batch treatment tank. 
2. Description of the Prior Art 
Methacrylamidopropyltrimethylammonium chloride, among its other uses, is an 
important monomer in the synthesis of a class of water soluble cationic 
polymers which find application as flocculants and as retention aids in 
the production of paper as taught by U.S. Pat. No. 3,661,880. 
Aqueous solutions of commercially available MAPTAC or the free amine vary 
in color from light yellow to dark amber. This color, or impurity, is 
carried through upon polymerization of the monomer resulting in polymer 
products of low molecular weight and widely varying color. Widespread 
variations in product color or impurities result in polymers having 
unacceptable performance characteristics. Further, the impurity in the 
monomer also may cause other undesirable polymer variations such as 
variations in clarity and viscosity. 
While the impurities may be removed effectively from the free amine by 
vacuum distillation techniques leading to a preferential distillate which 
is clear and "water white" and which, upon subsequent polymerization, led 
to a clear and "water white" polymer product, such vacuum distillation 
techniques do not lend themselves readily to continuous processing and are 
prohibitively expensive as a commercial process. In addition, the amine is 
easily activated in this form and may polymerize at distillation 
temperature, creating additional and undesirable processing problems. 
The impurities may also be effectively removed by treatment with activated 
carbon as described in U.S. Pat. No. 3,907,891. However, as will be shown, 
the activated carbon treatment will remove the polymerization inhibitor, 
such as the methylether of hydroquinone (MEHQ), as well as the impurities. 
Therefore, there remains a need for a method which will remove the 
impurities from MAPTAC and DMAPMA but which will not appreciably eliminate 
the presence of any polymerization inhibitor. It is important to have a 
certain level of polymerization inhibitor in MAPTAC to prevent premature 
polymerization while the MAPTAC is being stored or shipped. 
The method of this invention uses solid, nonionic organic resins as means 
to remove the organic impurities. One kind of resin, used in the 
experiments described herein, is the AMBERLITE.RTM. XAD series of resins 
manufactured by Rohm and Haas Company. The Rohm and Haas technical 
bulletins describe the various uses of the AMBERLITE XAD resins which 
include water purification, phenol removal, and pesticide and narcotic 
detection. 
SUMMARY OF THE INVENTION 
The invention is a process for purifying aqueous solutions of 
methacrylamidopropyltrimethylammonium chloride or the free amine thereof, 
dimethylaminopropylmethacrylamide, which comprises contacting an aqueous 
solution containing from 1 to 99 percent by weight of 
methacrylamidopropyltrimethylammonium chloride or 
dimethylaminopropylmethacrylamide with a solid, nonionic organic resin. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Impurities which are harmful to the end uses of MAPTAC may be removed by 
treating the MAPTAC with organic resins. The resins rapidly absorb organic 
impurities from MAPTAC yet leave behind the polymerization inhibitor, 
methylether of hydroquinone (MEHQ). Activated charcoal, while absorbing 
the impurities, will also absorb the MEHQ inhibitor. One of the impurities 
found in MAPTAC streams is allyl methacrylamide (AMA) which can cause 
crosslinking in polymers. Color-causing compounds and other impurities 
which may interfere with subsequent polymerization are also removed by the 
method of this invention. 
Treatment may be conducted by continuously passing the MAPTAC or DMAPMA 
solution over a bed of organic resin. Stirring the resin with a MAPTAC 
solution in a batch tank is also effective in removing AMA. Preferably, 
the treatment level should range from 5 to 35 pounds of monomer per pound 
of resin. 
The solid, nonionic organic resins useful in the method of this invention 
include polystyrene-divinylbenzene and acrylic resins. Similar resins of 
crosslinked organic monomers should also be effective. Of particular 
utility are the AMBERLITE XAD brand of resins. The resin should have a 
mesh size of from about 20 to 60 mesh. The average particle diameter 
should be on the order of 0.30 to about 0.45 mm. The resin should be 
nonionic and hydrophobic. 
The resin should also be able to withstand elevated temperatures as the 
preferred temperature for this purification is from about -40.degree. to 
100.degree. C. The especially preferred temperature range for the method 
of this invention is from about -20.degree. to 80.degree. C., while the 
preferred pressure is from ambient to about 500 psi. 
It is anticipated that the method of this invention will work for all 
aqueous solutions of MAPTAC and DMAPMA in all soluble proportions. 
Generally, this may be expressed as an aqueous solution containing from 1 
to 99 percent by weight of MAPTAC or DMAPMA. While the acceptable solvents 
for MAPTAC and DMAPMA may include any protic solvent, it is preferred that 
the solvent is water. Other monomers containing quaternary ammonium salts 
can also be purified by resin treatment. For example, 
methacrylamidopropylhydroxyethyl dimethyl ammonium acetate (MAPHDA) is a 
monomer derivative of DMAPMA which may be purified by the resin treatment 
of this invention. DMAPMA itself may typically be prepared according to 
the method of U.S. Pat. No. 3,873,247 to Texaco Chemical Co.

The method of this invention is demonstrated in the following examples. 
Examples I through IV demonstrate a batch processing mode while Example V 
shows a continuous processing mode. 
EXAMPLE I 
A MAPTAC sample (50% aqueous) containing 62 ppm AMA and 658 ppm MEHQ 
inhibitor was stirred magnetically with 3% by weight of AMBERLITE XAD-2 
nonionic polymeric adsorbant. After one hour, the MAPTAC sample contained 
26 ppm AMA and 556 ppm MEHQ inhibitor. Thus, 58% of the AMA was removed 
but only 16% of the inhibitor was removed. This characteristic of the 
resin adsorbent of not removing the same proportion of polymerization 
inhibitor (i.e., removing less) as proportion of impurity is also seen in 
the following examples. Indeed, in all examples at least twice as much 
impurity as polymerization inhibitor is removed, on a percentage basis. 
EXAMPLES II-IV 
Similar treatments of MAPTAC were conducted with other adsorbents, as shown 
below. MAPTAC containing 62 ppm AMA and 658 ppm MEHQ was used, and 3 wt.% 
adsorbent was used. 
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Solution Analysis 
After 1 Hour 
Example 
Adsorbent ppm AMA ppm MEHQ 
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2 AMBERLITE XAD-7 41 544 
3 AMBERLITE XAD-4 21 459 
4 DARCO G-60* 17 100 
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*Powdered activated charcoal from ICI. 
Example IV is included for comparison to demonstrate the undesired excess 
removal of the MEHQ inhibitor by the activated charcoal. 
The AMBERLITE resins are macroporous organic resins of moderate surface 
area available from Rohm and Haas Company. The XAD-2 and XAD-4 resins are 
made from styrene, and the XAD-7 resin is an acrylic. 
EXAMPLE V 
This example will show the suitability of this method for use in continuous 
processing. A 3 cm ID glass column was packed with 90 g (about 130 cc) 
AMBERLITE XAD-2 resin. MAPTAC solution (50% aq., 62 ppm AMA, 658 ppm MEHQ) 
was passed over the resin bed at .about.0.1 ml per cc of resin per minute, 
although the rate near the beginning of the experiment was somewhat 
slower. Each 100 g of MAPTAC effluent was analyzed for AMA and MEHQ. No 
AMA was detected (detection limit=2 ppm) in the first 700 ml of effluent, 
and the MEHQ was never less than 100 ppm in any of the first seven 
fractions. The resin was essentially exhausted after 1600 g of effluent. 
When a similar experiment was done substituting granulated activated 
charcoal for the resin, the MEHQ inhibitor was completely removed from the 
early fractions. 
EXAMPLES VI AND VII 
To demonstrate the deleterious influence of AMA on the production of high 
molecular weight polymers, two experiments were performed. Both were 
identical except that one contained MAPTAC to which 400 ppm AMA had been 
added. 
To a resin kettle equipped with a high speed stirrer, dip tube, addition 
funnel, and nitrogen pad were charged 256 g of acrylamide (50% aqueous 
solution) 88.6 g MAPTAC (50% aqueous solution), 44 g deionized water, and 
1 ml citric acid solution (2.5% in water). To the addition funnel was 
charged 162 g n-heptane, 18.4 g SPAN 80 Sorbitan Monooleate, and 1.8 ml 
initiator solution [17.9% 2,2'-azobis(2,4-dimethylvaleronitrile) in 
toluene]. Nitrogen was purged through both solutions at 5 and 2.5 l/hr, 
respectively, for two hours. The nitrogen flow was reduced and the 
addition funnel contents added rapidly while stirring at 1800 rpm. After 
30 minutes of stirring to emulsify, the stir rate was reduced to 1200 rpm, 
and heating was begun. The temperature was regulated at 
50.degree..+-.2.degree. until the exotherm subsided. Then the reactor 
contents were heated one hour more at 50.degree. C. Solids were isolated 
by pouring the emulsion into toluene, then into methanol, and then 
filtering. Viscosities of 0.1% aqueous solutions of the polymes were 5.6 
and 14.1 cp* for the MAPTAC and the MAPTAC+AMA experiments. Thus, even a 
small amount of AMA can interfere with polymerization and give variable 
polymer properties. 
FNT *Viscosities measured by Nameter vibrating sphere viscometer. 
An examination of Examples I through V will show that the nonionic polymer 
resin effectively removes AMA impurity without removing an appreciable 
amount of MEHQ inhibitor. The result is in contrast to Example IV where 
activated charcoal is used. In that example, AMA is removed as in the 
resin examples, yet the activated charcoal removed much more of the MEHQ 
inhibitor than did the resin. 
Variations and modifications may be made by those skilled in the art 
without departing from the spirit and scope of the invention which is 
defined only by the appended claims.