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Патент USA US2404576

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Patented July 23, 1946
William H. Hill and James H. F. Veltman, Mount
Lebanon, Pa., assignors, by mesne assignments,
to Koppers Company, Incorporated, Pittsburgh,
Pa., a corporation of Delaware
No Drawing. ' Application April 18, 1944,
Serial No. 531,644
11 Claims. (01. 23-75)
. The present invention relates in general to the
soluble mono~ and di-carboxylic acids of relatively
production of stable, colorless thiocyanates, and
low‘molecular weight. ‘As is often‘to be observed
in chemical phenomena, the leading members
of the group exhibit most strongly the common
the discoloration of ammonium thiocyanate which
has been manufactured from the gases produced 5 characteristic.’ which in the present case is their
capacity‘ in small quantities in thiocyanates to
by the destructive distillation of coal and found
prevent discoloration of the latter. Thus, formic
particularly in the scrubbing liquors used in re?n
has reference more particularly to prevention of
acid and its salts are especially bene?cial as in-_
hibitors and appearto lend the greatest stability
In the manufacture; distribution, and use of
to stored thiocyanates.
- ; ,
thiocyanates, there has often been observed in
Unless free alkalinity exists in the thiocyanate
these salts a formationrof reddish color varying
solution to which coloration-inhibitor is to be
in-intensity from faint pink to deep red. Trou
added, the salts of the above-mentioned inhibitors
blesome dyes or colored solutions often are found
rather than the‘ acids themselves are preferably
in the crude thiocyanate solutions associated with
coke oven gas puri?cation liquors. Even though 15 employed in order to avoid any deleterious effect
of the acid upon the so-treated thiocyanate, such
puri?cation steps, such, for example, as am
ing coke oven gas.
effect being, for example, the formation of yellow,
perthiocyanic acid. The selected salts are prefer-7
ably those having the same cation as the thiocya
thereafter treating the thiocyanate ?ltrate with
activated carbon‘have been employed in crystal 20 hate being treated, thereby to reduce the total
amount of impurities so-added to the technical
lization to' provide .a ‘clear, colorless crystalline
product, discoloration of the'so-produced colorless
The addition of such inhibitors can be made at
saltwill nevertheless occur in storage and espe
‘any time during or after the manufacture of the
cially ‘will it do so‘ whenthe ,salt'is exposed‘ to
moniating and'sulphiding the thiocyanate solu
tion,l ?ltering off insoluble iron 'sulphide'and
natural‘or arti?cialli-ght.
25 thiocyanates, and‘ even if the salt is discolored
' prior to the present treatment, an addition of
one or more of the above-mentioned inhibitors
will cause a material lightening of the said dis-_
An object of the present invention is to provide
economical means‘jof producing a clear, colorless
puri?ed thiocyanate salt'that‘. is 'color stable in
spite of protracted storage, exposure‘ to light or
contact with iron.
‘ *
A further object of the‘present' invention‘ isto
colored salt. Howevenaddition of the inhibitor
preferably made to the crude thiocyanate solu
30 is
tion prior to crystallization, whereby a more inti
mate mixture and a more thorough distribution
of inhibitor compound throughout the subse
prevent that discoloration of clear-white puri?ed
thiocyanates which occurs upon storage.
quently formed crystal is obtained thus providing
more comprehensive protection of the inhibited
It is a‘ further object of the present invention to
‘provide a colorless, technicalthiocyanate that is
not only inhibited against the above-described
In the hereinafter described examples illustrat
ing the present invention, the thiocyanate salt
discoloration but is also of such strengthened,
crystal structure as materially ‘to‘prevent size
' degradation of the salt during handling, or the
that has been employed for test purposes is an
- The invention has for further objects such other
ammonium thiocyanate obtained in impure state
40 in
approximately 30%" solution by the scrubbing
improvements and such other operative advan
of coke-oven 'gas- with ‘an aqueous suspension of
tages or results as may be found to obtain inthe
processes or apparatus hereinafter described or
often contains some iron- and other impurities
The said thiocyanate solution, which
45 such, for example, asthiosulphates, can be puri?ed
. ' ‘ According to the present invention thiocyanates
such for example as ammonium, sodium, ‘potas
sium, barium, calcium, guanidine,_ and other or
and concentrated according to known procedure
to produce a colorless, technical thiocyanate of
at least 95% purity. The soV-produced salt, how
ever, soon discolors in storage and darkens with
ganic amino thiocyanates are stabilized against
' color changes by addition thereto-‘of small quan 50 especial rapidity in ‘sunlight or in contact with
titieswof one or more of certain inhibitors which '
have been found to prevent discoloration of the
These ‘ inhibitorsfinclude
iron. Since the said ‘thiocyanate solution of the ‘V
following examples is slightly ammoniacal, the
inhibiting anions can be ‘added directly inacid
form and the acid will be neutralized
pounds offformidvoxalic and‘malonic acids, and
are selected from~ the group; consisting of water? is solution.
thesaid Y
To a technical ammonium thiocyanate
of the present invention that, when small
‘The following are examples of treatment of thi
ocyanate salts with discoloration inhibitor where
by puri?ed colorless thiocyanates will retain their
colorless appearance on storing.
Example 1
amounts of the above-mentioned inhibitors are
added to thiocyanates before or during crystal
lization, the habitus of crystallization is so
altered that a marked change in the physical ap
pearance of the thiocyanate salt is obtained. It
) again appears that the ?rst members of the
about 30% salt concentration such as is produced
chemical groups from which the inhibitors have
at by-‘product coke-plants by. scrubbing the "gas
been selected are the most effective and this is
coming from the primary coolers with a suspen'e 10" especiallytrue of formic acid, a notable example
being provided by the addition of 0.70% formic
sion of sulphur there was added 1.5% ammonium
acid to ammonium thiocyanate solution during
crystallization of the salt therefrom. Sparkling,
formate, 2% ammonia andv 1,__'%, hydrogen ‘sul
phide, the percentages being based on the _;net
weight of ammonium thiocyanate contained in
solution. The so-treated ‘solution was heated to,
colorless crystals were obtained which had sev
eral times the thickness of untreated ammonium
thiocyanate crystals, and which were uniform in
size and homogeneous in structure, and exhibited
no marked cleavage planes which could permit
ready fracture. .These so-produced crystals were
110° 0., treated with 2% Darco Ge-60 by weight.
of the said ammonium thiocyanate and ?ltered. 1
The solution was evaporated to a boiling temper;
ature of 128° C. and then ?ltered to remove pre
cipitated impurities. Upon cooling, clear-white
20 stored in the presence of light for more than a
crystals of ammonium thiocyanate were obtained
which proved color stable for more than a year.
Eztample 2_
year, and were subjected to intermittent han
dling, but at the conclusion of the test they nev
ertheless retained their original size and exhib
. ited the same sparkling, clear-white appearance.
Each of the hereinbelow listed inhibitors Were
' added to samples of 30% crude ammonium thio
the claims hereinafter made is intended to en
cyanate liquor, the various weights thereof which
were added being chemically equivalent. To the
compass not only the thiocyanates oi ther?xed
alkali metals such, for example, as sodium and
potassium, but also the thioc'yanate of ammonia,
solutions were then added 2% ammonia and 1%
hydrogen sulphide. After standing for onehour
the solutions were ?ltered.
30 which is ‘sometimes termed “volatile alkali.”
The ?ltrates were
The invention as herein‘above set forth is em
heated‘ to 110° C.,,treated with 2% by weight of
G-60 Darco and ?ltered. After cooling of the
bodied in particular form ‘and mannerzbut may be
variously embodied within the scope of the claims
solutions and crystallization of ammonium thio
hereinafter made.
cyanate therefrom, the crystals were ?ltered off,
placed in closed jars and exposed to daylight.
During the ensuing‘test period, the relative re-.
sistances to‘discoloration of the variously ‘inhib
ited ammonium thiocyanate crystals were com
The term “alkali thiocyanate” as employed in
Example v2.—Table
We claim:
1. Colorless’ technical ammonium thlo'cyanate
containing more than about 0.1% and less than
about 1% by Weight of a discoloration"inhibitor
selected‘frdm ‘the "group consisting in ‘the anions
of water-soluble mono- and di-fcarboxylic acids
of relatively low molecular weight.
_2. Colorless technical ammonium thiocyanate
. 1,...
- Inhibitor added
, Weightin per
" ‘cent oi'dry " '0
Coloraiter ap
‘Sim-S as
ye months’
ex osure to
'None _________ _________ __, ____________ __
Ammonium formate____
1. 58
Malonic acid.--_t ____ ._ ~,
1.30 _____ __
---_.d0 _____ ._
containing more than about 0.1% and less than
about 1% by ‘weight, as a discoloration inhibitor,
45 of an anion of a water-soluble ‘c'arboxylic v‘acid of
relatively low molecular weight,
Y ehltl o w w 1 e
Inrall the above examples the weight of in
hibitor remaining in each batch of crystals after
?ltration and crystallization of the treated solu
solution, less than one-tenth of one-percent in
4. wColorless technical’ammonium thiocyanate
containing 'more than about 0.1% and less than
about 1% by weight, as adiscoloration inhibitor, 1
tion was materially reduced, for example in one 55 of a ‘salt of formic acid.
'case where 0.70% of formic acid was added to the
‘ _
3. Colorless technical ammonium 'thio'cyahate
containing a discoloration inhibitor selected from
the group consisting in the anions of water-sol‘
50 uble mono- and di-carboxylic acids or relatively‘
5. Colorless technical ammonium thiocyanate
containing more than _about'0.1% and less than
hibitor, by weight of product, was found in the
0.7% by weight of ammonium formate.
salt. In every case, in fact, where analysis was
6. A method for preventing the discoloration
made of the inhibitor content of color-stabilized 60 of colorless, technical alkali thiocyanates, said
method comprising the steps of: purifying crude
salt‘, the inhibitor concentration was found to be
less than 0.1% by weight. It is apparent, there
thiocyanate salt and decolorizing the same; and
injecting into said salt prior to crystallization
fore, that the vso-added inhibitors are not present
in the treated thiocyanate to an extent su?i
minute quantities of a discoloration inhibitor
cient to a?ect thestandard of purity for tech 65 ‘selected from the group consisting in the anions
of water-soluble mono- and ‘di-carboxylic acids
of relatively low molecular weight.
‘Example 3
W 7.?A‘. method for preventing the discoloration
‘A technical ammonium thiocyanate (95 vper
of colorless, technical-grade, alkali thiocyanates,
cent) of deep brown-red color was tumbled in a 70 said ‘method comprising the steps of : purifying
glassjarv ‘for about ?ve minutes with 1.5% acid crude alkali thiocyanate ' and decolorizing the
ammonium oiralatetby'weight of said thiocyanate.
L'Ifhe color of thesalt was ‘reduced to a light green
It has been discovered during the development
same; and injectingu‘mto said salt small quantl-g
ties of adiscoloration inhibitor comprising the
> R salt having an anion that’is selected from ‘the
group consisting in the anions'oi water-soluble
10. A method for stabilizing colorless, techni- ‘
mono- and dicarboxylic acids of relatively low
molecular weight, where R is the cation of the
treated thiocyanate salt.
8. A method for preventing the discoloration of
cal grade ammonium thiocyanate against discol
oration and size degradation during handling,’
storage, and the like, said method comprising:
colorless, technical ammonium thiocyanate, said (A purifying crude ammonium .thiocyanate and de- ,
colorizing the same; adding to aqueous solution
method comprising the steps of: purifying crude
of said thiocyanate, as a discoloration'inhibitor,
ammonium thiocyana'te and decolon‘zing the
small quantities of a compound having as its
same; and injecting into said salt minute quan
anion the anion of a mono-carboxylic acid of less
tities of ammonium tomato.
than four carbon atoms; and thereafter crystal
9. A method for producing clear, colorless am
lizing from said solution, colorless ammonium
monium thiocyanate crystals that are stabilized
thiocyana‘te containing by weight thereof less
against color change by storage, contact with
than about 1% of the said added inhibitor.
metal, sunlight, and like discolorants, said
11. A method for preventing the discoloration
method comprising: treating crude ammonium
of colorless, technical ammonium thiocyanate,
thiocyanate solution with ammonia and hydrogen
said method comprising the steps of: purifying
sulphide and thereafter ?ltering off precipitates;
crude ammonium thiocyanate and decolorizing
heating so-derived ?ltrate and treatingthe same
the same; and injecting into the said salt small
with activated carbon; removing said carbon
quantities of a compound containing as an active
from so-treated thiocyanate solution; adding to
agent the formic acid anion.
the thiocyanate solution a salt of formic acid;
and crystallizing from the so-treated solution
clear, colorless ammonium thiocyanate crystals
containing the said 'formate in quantity at most
less than 1% by weight of the ammonium thio
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