Note: Descriptions are shown in the official language in which they were submitted.
l3791~
F ~ OF T~.E INVENTION
This invention relates generally to a process for the prepara-
t~on of aminotriazine-aldehyde resins having improved adsorption character-
istics, and more particularly to a process for the condensation of polyamino-
triazines and formaldehyde in the presence of an acid cstalyst and a porogen
to form macroporous resins having high surface area.
BACKGRO~ND OF THE INVENTION
The preparation of amino resins by the reaction of amino-bearing
material with aldehyde to form a reactive monomer, followed by condensa~ion
polymerization to a thermosetting resin, is well-known. Perhaps the most
common resins of this type are the melamine resins resulting from the con-
densation of melamine and formaldehyde. These resins are widely used as
molding compounds, adhesives, paper wet strength agents, and fabric treat-
ment compositions.
Conventional amino resins do not display a useful sorption capac-
ity and are relatively unstable under conditions of use as adsorbents. It
would therefore be desirable to produce macroporous amino resins which have
increased mechanical and osmotic stability while maintaining fluid perme-
ability. Such permeability facilitates the flow and diffusion of ]iquid
phases through the resin and enhances its usefulness for processes such
as absorbing, adsorbing, catalysis, and the like.
SU*~RY OF T~E INVENTION
It has been discovered that highly adsorbent macroporous amino
resins can be prepared by reacting polyamino-triazines and formaldehyde in
a molar ratio of about 1:2 to 1:7 in the presence of a miscible organic
porogen and an acid catalyst. The reaction mixture is agitated and heated
to at least about 65C until gelation occurs. The resin is then cured to
produce a material having high porosity and surface area on the order of
10 m2/g and up.
1~3'7~5r3
Resins prepared by the process of the invention have high mechan-
ical and osmotic stability, and greatly improved adsorption characteristics
in comparison with conventional non-porous amino resins. The macroporous
resins have demonstrated excellent adsorption capacity for the removal of
color and organic matter from solutions such as wood pulp bleach effluent,
and are also useful as support materials for enzymes, catalysts, biocides
and the like.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention a polyamino-triazine, i.e. a
triazine having a plurality of substituted or unsubstituted amino groups
attached, is reacted with formaldehyde to form the basic resin. Numerous
polyamino-triazines are suitable for use in the process,such as melamine
(2,4, 6-triamino-1,3,5-triazine), benzoguanamine, dia]lylmelamine, and
mixtures of these and other such polyamino-triazines. The term formalde-
hyde includes not only formaldehyde itself, but also compounds yielding
formaldehyde, for instance paraformaldehyde and the like. Formaldehyde
is generally preferred for use as the aldehyde component, usually in the
form of an aqueous 30-45% solution since the resin preparation is gener-
ally carried out in an aqueous medium.
The mole ratio of polyamino-triazine to formaldehye is not par~
ticularly critical, and may range from about 2 to about 7 depending on the
particular polyamino-triazine employed and the characteristics desired in
the final product. For the preferred system of melamine and formaldehyde,
a ratio of 3-5 moles formaldehyde per mole of melamine has been found most
suitable for the process of the invention.
The condensation reactions of polyamino-triazines and formaldehyde
are considerably influenced by pH, and the optimum pH range for the pre-
cipitation of macroporous resins has been determined to be from about 2 to
about 5. Consequently, the use of a condensation-catalyzing acid in the
1137~5~3
f
process is recommended. Catalysts such as formic acid, sulfuric acid,
hydrochloric acid, and acetic acid may be employed. Formic acid has proven
to be most effective in thc process, and is the preferred catalyst. The
amount of acid catalyst may range from about 0.01 to about 0.10 moles per
mole of melamine, with 0.04-0.06 moles being the usual concentration.
The use of an effective miscible organic porogen is essential to
the preparation of macroporous resins having the desired characteristics of
high adsorptivity and large surface area. The porogen should be miscible
with all of the reactants. During the condensation it serves as an inter-
nal diluent to introduce the desired sponge-like macroporous structure into
the finished resin. The porogen may be selected from organics such as alco-
hols, thiols, amides, ethers, esters, or mixtures thereof. The preferred
porogen for the process of the invention is n-propanol, which is miscible
with all of the initial reactants in the process and has an appropriate
boiling point (97) which is above the normal polymerization temperature
yet is low enough to allow eventual removal at the usual drying temperatures.
The porogen may be present over a broad range of concentration in the re-
action mixture, usually from about 5 to about 30 percent of the total vol-
ume. Concentrations in the range of 16-20 volume percent have been fGund
to result in the optimum adsorptivity in the product resin for the pre-
ferred meiamine-formaldehyde system. Other specific porogens useful in
the process include ethoxyethanol and dimethylformamide.
Since the resin preparation is carried out in an aqueous medium,
the total quantity of solids in the initial reaction mix is not critical,
and normally ranges from 30-55 percent by weight of the total mixture. A
so].ids content of about 45 percent has been found to produce the most suit-
able resins with lower amounts resulting in a more friable resin and higher
amounts reducing the porosity of the product.
The monomers, catalyst, and porogen are all charged into an
appropriately sized reaction kettle, usually of glass or stainless steel
-- 4 --
L ~374SI~
construction and equipped with conventional heating and agitation means.
The pH of the reaction mix is in the range of 2 to 5 initially. The re-
action mix is gradually heated and agitated until solution of the initial
reactants is complete, then heating is continued until polymeri~ation begins
and a gel forms. This initial reaction may be carried out at temperatures
ranging from about 65C to about 95C, preferably at from about 70C to
about 85C. The initial reaction time is dependent upon the temperature
employed and on the rate of heat input into the reaction mixture. The
average rate of temperature increase in the reaction mix is preferably
maintained in the range of 0.5 to 5C/min. until gelation. Reaction times
will increase as the initial temperature is reduced. At 75C the reaction
may continue for more than 30 minutes. The reaction can be conducted under
pressure, which will affect the temperaturesand times recited.
After the initial reaction, the resin is cured at from ambient to
100C for about 2-20 hours. The cure time may be shortened by elevating
the temperature to the higher end of the range. During the curing step
the condensation goes to completion and the degree of cross-linking in-
creases. Completion of curing can be determined by measurement of the
resin stability to acid hydrolysis.
The product resin is then crushed, ground to the desired particle
si~e, and washed. The resin has the physical appearance of chalk. Char-
acteristic materials will have a surface area of over 10 m2/g and up to
about lOOOm2/g as measured by B.E.T. nitrogen multipoint analysis, and a
porosity of 0.2~1.0 as measured by heptane regain. Resistance to oxidation,
as measured by H202 oxidation, is 100% at ambient temperatures for up to 5
hours. The typical resin has an adsorption capacity of over 200 kg/m3 of
color as cobalt chloroplatinate for paper pulp mill "E" effluent compared
to conventional non-porous amino resin adsorptivity of less than 50 kg/m3.
The finished resin may be further treated by known methods, for
example reaction with epichlorohyd~in and/or amination, tc provide materials
f 1~l3~51~
having different characteristics.
The resins of the invention have particular utility in removing
organic materials from fluid media by adsorption. A typical application
is in the treatment of paper pulp mill effluent which contains color bodies
in the form of condensed guiacylpropane type structures, with carbonyl and
carboxyl groups as well as phenolic hydroxyl. Such materials are effectively
removed by contact with the macroporous resins of the invention. The resins
also exhibit equilibrium adsorptive capacities for typical organic materials;
i.e. 85-90% removal in a 0.01 M p-nitrophenol solution and 70% removal in
munitions plant red water effluent.
The invention is further illustrated by the following specific
examples.
EXAMPLE 1
225 g of melamine, 536 ml of formaldehyde (37%, aqueous), 240 ml
of n-propanol and 12 ml of 88% formic acid were mixed in a jacketed resin
kettle equipped with stirrer, condenser and thermometer. The mixture was
stirred and heated to 80C until gelation occurred, after about 20 minutes.
The temperature was held at about 80C for 16 hours to cure the resin.
After cooling the product was removed from the kettle, ground, and water
washed. The resin was an opaque solid with a pore volume of 0.6 ml/g,
a surface area of 160 m2/g andanadsorption capacity to paper pulp mill
effluent of 280 kg/m3 as cobalt chloroplatinate.
EXAM~LE 2
765 g of melamine, 1608 ml of formaldehyde (37%), 720 ml of
n-propanol and 36 ml of 88% formic acid were combined as in Example 1.
'fhe mixture was stirred and heated to 75C until gelation (about 30 min-
utes). Heating was continued for an additional 12 hours at 80C. After
cooling, grinding and washing the product resin was a white opaque solid
1137~5~
with a pore volume of 0.74 ml/g, a surface area of 180 m2/g and an adsorp-
tion capacity to paper pulp mill effluent of 360 kg/m3 as cobalt chloro-
platinate.
EX~MPLE 3
44.3 g of melamine, 63.2 g of paraformaldehyde, 85 ml of water,
57 ml of n-propanol and 1.9 ml of 95% sulfuric acid were combined as in
Example 1. The mixture was stirred and heated to 78C until gelation oc-
curred. Heating was continued at about 80C for an additional 16 hours
after which the material was cooled, ground and washed. The product was
then heated at 100C for an additional 48 hours. The resulting resin was
a white opaque solid with a pore volume of 0.35 ml/g and an adsorption ca-
pacity for paper pulp mill effluent of 125 mg/m3 as cobalt chloroplatinate.
EXAMPLE 4
r
63 g of melamine, 150.5 ml of formaldehyde (37%), 25 ml of
ethoxyethanol, 75 ml of water, and 3.35 ml of 88% formic acid were mixed
as in Example 1. The mixture was agitated and heated to 80C until gela-
tion occurred. Heating was continued at 80C for an additional 23 hours.
The material was cooled, ground and washed. The resin was an opaque solid
with a surface area of 213 m2/g.
EXAMPLE 5
63 g of melamine, 150.5 ml of formaldehyde (37%), 25 ml dimethyl-
formamide, 75 ml of water, and 3.35 ml of 88% formic acid were mixed and
reacted as in Example 4. The resin product was an opaque solid with a
surface area of 211 m2/g.
EXAMPLE 6
The macroporous resins of the invention were prepared on a larger
scale, using a polymerization kettle with a capacity of 190 liters. The
.'l~l37~St~l
reactants were added in the following order with agitation -- 104.9 liter
formaldehyde (31%, aqueous, methanol inhibited), 4~.l kg melamine, 47
liter n-propanol, and 2.35 liter 88% formic acid. The contents of the
kettle were heated gradually, with stirring. The stirrer was removed
when the mixture reached about 65C, and heating was continued until gela-
tion occurred. A mild exotherm then raised the temperature to 80-85C.
The kettle jacket temperature was then raised to about 85C, and this
temperature was maintained for 4 hours. The resin product was then cooled,
gr~und and washed. Reaction conditions and product characteristics for
10 several batches are shown in the following Table.
TABLE I
Gel timeRate of heatSurface areaColor removal
Batch (min)to gel (C/min)(m2/g) (kg/m )
1 25 2.4 * 320
2 22 2.7 180 300
3 18 3.3 220 ~5
4 18 3.4 250 265
16 3.7 245 260
6 16 4.4 260 350
(* -- not measured)
EXAMPLE 7
The resin prepared in Example 1 was used in the decolorization
of tannin-containing surface water. A stream of 600 APHA surface water
was passed through a 50 ml volume of the resin in a 1 inch diameter column
at a rate of 11 ml/minute. A total of 12.5 liters of water was decolorized
to ar. average of 25 APHA units, with a maximum color of 75 APHA Imits.
EXAMPLE 8
A resin prepared as in Example 1 was used in the decolorization of
3745i~3
an NaOU extract of a bleached sulfate paper pulp mill liquor, termed the "E"
effluent. The caustic extract, having a total color of 5,355 APHA units,
was adjusted to pH 4. The solution was then passed through 50 ml of resin
in a 2 cm diameter glass column at the rate of 5 ml/minute (6 bed volumes/
hour). The column effluent was collected in aliquots, the pM was adjusted
to 7.6, and comparison was made with standards prepared from the feed solu-
tion to determine the percent of color removed. The run was terminated
at the arbitrary point where color removal had dropped to 70 percent. For
the resin of the invention this occurred after a total color throughput of
350 kg/m3, expressed as cobalt chloroplatinate.
Three other commercially available adsorbent resins were tested
in the same manner, and the results are shown in the following Table.
TABLE II
kg/m9 total color throughput
Resin to reach 70% removal
Example 1 350
Amberlite XAD-2 28
Amberlite XAD-7 120
Amberlite XAD-8 80
(Amberlite resins are available from Rohm and Haas Company)
