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Dec. 3, 1946.
T. K. sHi-:Rwoon
MANUFACTURE Ior’ Fo:umLmmf'nla4
Filed Nov. 19, 1943>
2 Sheets-Sheet l
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Dec.> 3, 1946.
Filed Nov. 19, 1943
2 Sheets-Sheet 2
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j 2,412,014
Patented Dec. 3, 1946
Thomas K. Sherwood, Wellesley, Mass.. anignor
to Godfrey L. Cabot, Inc.,`Bolton, Maas., a cor
poration of Massachusetts
`Application November 19, 1943, Serial No. 510,898
s claims. (q1. 26o-co4)
This invention consists in improvements in
processes of producing formaldehyde from
edly higher temperature, for example at least
natural gas. It has been known for many years
As a result of the rich air-gas mixture I employ
that methane may be converted into formalde
hyde by mixing natural gas with nitrogen oxides
as a gaseous catalyzer and heating, thus induc
ing an oxidizing reaction in the mixture result
ing in the formation of formaldehyde. Processes
of this character as heretofore carried out have
1200° F.
and .the lincreased working temperature, I find
that the process may be very appreciably speeded
up. For'example, in processes heretofore prac
ticed a contact time of about 8 seconds for re
. acting the methane has been considered neces
sary, whereas the contact time of my lnovel
not been entirely satisfactory for large scale pro-A 10 process is in the order of 1A to 1/2 second. '
Another extremely important advantage of my
duction and have been carried out only under
improved process is that the amount of catalyzer
, conditions of high pressure with poor efficiency
employed may be very substantially reduced. For
in respect both to time and materials used. The
present invention consists in improvements by
example', heretofore it has been considered-neces
which .the output of formaldehyde maybe greatly 15 sary to employ NO2 in amounts between 4.5 and 9
lbs. per 1000 cu. ft. of methane. I have discovered
increased as compared to the output of previous
processes, the emciency of ¿the manufacturing ` -.that in practicing my process I require only about
process greatly increased in respect -to lthe use
.29 lb. of NO2 per 1000 cu, ft. of methane. I am
of gas and catalyzers, and the time for com
.thus able -to reduce by more than one-half the
pleting the process substantially reduced as com 20 amount of the most expensive item required in
carrying out my process.
pared .to the time formerly required. Moreover,
the process of my invention may be advanta
A characteristic feature of the process of my
geously carried out in apparatus of compact de
invention comprises the step of cooling the -vapo
rized formaldehyde as it leaves the reactor' by
sign at atmospheric pressure and in a continuous
manner of operation.
25 direct contact ' with a formaldehyde solution.
Formaldehyde will decompose rapidly at the tem
Heretofore it has been considered necessary to
peratures at which the gasesmust leave the re
employ an air-gas mixture containing a large ex
actor station. Ii' the yield of formaldehyde is rto
cess of air, for example, .to five parts Aof air one
be appreciable, therefore, it is necessary to cool
par-t of methane. In accordance with my novel
process however, we require a much smaller pro 30 the gases very rapidly. The rate of heat transfer
portion of air, and may employ about equal parts
‘ between a hot gas and a solid surface is rela
tively slow, and it is well known in engineering
of air and methane or 30 to 50 parts methane
practice that .the rapid cooling of large quantities
With 70 to 50 parts air. From this striking dif
of hot gases by -the use of ordinary heat transfer
ference in procedure flow several extremely im
portant advantages. In the ilrst place, the less 35 apparatus involves `very large surfaces and cor
respondingly expensive equipment. The 4formal
air used lthe higher the yield of formaldehyde -per
dehyde decomposes so rapidly at the elevated
volume treated and per volume of methane. This
.temperatures .that a cooler is not practical if a
advantage results partly from the fact that when
metal wall is interposed between the cooling me~
a larger proportion of air is used in the processl
a very appreciable amount oi' methane is neces
40 dium and the gas.
sarily burned up and wasted. In the second place,
It is not uncommon to quench the` hot gases
by the use of water sprays. Such >procedure has
the -smaller volume of air used results in less
two principal advantages: (1) the provision of a
dilution of lthe product than heretofore, so that
recovery is more complete and cheaper. In the
large area of contact between the gas and the
third place, the reaction rate is faster and the 45 cooling medium, and (2) .the maintenance of a
-maximum temperature (the boiling point of the
process therefore is more emcient in -respect .to
time than heretofore. Finally, since‘the dilution
Water) 'of the cooling medium. However, if the
of the gas is less, I come out with a more com
gas contains a constituent soluble in water and
bustible waste gas mixture and this may be
if this constituent is present in small amounts
utilized as an efficient fuel for heating the re
relative to the total heat carried by the gas, then
lthe amount of water needed will be large and the
resulting solution objectionably di1ute`.~ This is
Heretofore a. minimum .temperature of about
1000° F. has been employed for inducing the de
the problem to be solved in the present instance
for. since the desired product is a relatively c_on
sired oxidizing reaction, whereas I find that im
proved results are attained by employing decid 55 centrated solution, the use of water would lead to
considerable added expense for concentration.
Actually the gas contains both water and form
aldehyde, and the condensate naturally formed
:ticularly favorable since contact of the mixture
with S102 of the silica tube tends to retard oxi
dation of the formaldehyde which is formed in
on a cold surface would be a .fairly strong solu
the reaction.
tion, for example, as high as 19%. Consequently,
the use of a solution approximating the concen
tration of the condensible portion of .the gas re
The gaseousproducts of the reaction are de
livered from .the silica tubes I3 of the reactors
`through a manifold, not shown, into an outlet
sults in a, product which requires no greater ex
duct 24 in Vwhich they are Y_immediately cooled
pense for concentration .than if the condensate
by a spray of cool formaldehyde solution of ap
were formed directly on a cold surface. In prac l0 proximately 19.2% concentration supplied by a
tice, a slightly more dilute solution may be em
ì spray head 28. The prompt occurrence of this
ployed since the cold gas carries more water
step after ythe formation of the formaldehyde
vapor than the hot gases leaving the reactor.
vapor eliminates any substantial decomposition
By the spray-cooling step of my‘novel process
of the' formaldehyde which would otherwise
.- the solution picks up the heat and -this heat must 15 rapidly occur at .the .temperatures at which the
be removed in the liquid~ cooler. Heat exchangers
vapor must leave the reactor. ’I'he spray head
for this purpose are standard equipment items
' is connected through a pipe 21 and a vertical pipe
and relatively cheap. Therefore, the advantage
28 to a pump 29, which draws the cool formalde
of the spray-cooling step of my process is that it.
hyde solution from a storage tank 40, .the pump
makes possible the substitution of .a simple and 20 having an inlet connection 30 with the tank 40.. `
.cheap spray coolerlplus a standard-design liquid
'I‘he spray head 26 has' return connections 32,
cooler inv place of an expensive gas cooler which
33, 34 to a second pump 35 by which the form
is impractical for formaldehyde treatment. The
aldehyde solution, heated by contact with the
use of .the ~formaldehyde solution corresponding
vaporized product in its spraying operation, is
to the condensate concentration makes it possible 25 delivered to a hot solutionI cooler 36 and then
'-to do this without adding to the process the cost
forced from the cooler through a .ver-tical pipe
of concentrating an .aqueous solution.
31 and the horizontal pipe 38 to the storage
tank 40.
'I'he process of my invention will be best under
stood and appreciated by ñrst considering the
The outlet duct 24 leads from the reactor mani
accompanying diagrammatic flow sheet of ap 30 fold Ito the bottom of a packed cooler condenser
paratus which may be advantageously employed
-tower 25. That portion of the vaporized product
in carrying out my novel process, although it will
not condensed by the formaldehyde spray from
the spray head 26 now passes upwardly through
be understood that the process is not restricted to
this or to any speciñc type of apparatus;
In the accompanying drawings:
Fig. 1 is a diagrammatic flow sheet, and
Fig. 2 is a diagrammatic view in Vertical sec
.tion and in some `detail of a furnace having -tubes
the condenser 25. Formaldehyde solution con
densed in its progress through the condenser 25
is drawn off through pipe connections 4I-»42 and
delivered to the storage .tank 40. That part of
the vaporized product not condensed in the con
arranged in vertical position rather than hori
denser 25 passes into an outlet duct 43 which
zontal as in the conventional showing in Fig. 1. 40 leads from the top of the condenser'and is carried
through a refrigerated condenser 44. Formalde
The flow sheet of Fis. 1 illustrates one suitable
form of apparatus arranged compactly for carry
hyde solution condensed from this vapor passes
ing out the process of my invention in a con
down through the vertical pipe 45 and back to
tinuous manner. A furnace I0 is shown on the
the storage tank 4I), while gases still uncondensed
left hand side of .the assembly and this contains
are discharged -through the waste gas stack 23 or
a series of horizontal .two-pass reactors, only one
are drawn from this stack through .the connection
appearing in Fig. 1. Each reactor may comprise
22 for fuel.
a lower tube I I of alloy steel connected outside
A portion of the formaldehyde solution pumped
the furnace wall by a metal U-bend I2 to .an
upwardly through the pipe 28 on its way to the
upper horizontal tube I3 of silica. Natural gas 50 vspray head 26 is .deflected lby a connection“ and
and air mixed in the proper proportions are de
conducted through a series of tubular coolers~48
livered to the apparatus Ithrough a horizontal
passing from these through the outlet pipe-48
supply pipe I4, the mixture being led down- '
which leads back to the top of the condenser
wardly through a vertical pipe I5 to a blower
tower 25. The cooled formaldehyde solution
I6 and forced by the blower through a vertical 65 passes downwardly through .the condenser 25 in
pipe I1 .to the right hand end of the tube II.v
counter-flow relation to the ascending vaporized
product. ~
Oxides of nitrogen are introduced into the vertical
pipe I5 from a catalytic ammonia combustion
An ammonia refrigeration unit 50 is provided
_ unit I9 through a horizontal pipe I8. The vapor
for the purpose of supplying a refrigerating me
of nitrogen oxides is thus drawn into the blower, 60 dium to the condenser 44. Liquiiied ammonia
forced by it into the air-gas mixture and then in
gas passes upwardly from the vertical pipe 5I
a turbulent current lthrough the tubes of the re
and the‘horizontal pipe 52 to the condenser 44,
and expanding into .the condenser, is returned
In -the apparatus herein shown the furnace is
.through .the vertical pipe 53 to the compressor
heated by natural gas fuel and the supply pipe I4
5.4. It is drawn from .the compressor 54 .throug
is shown as‘connected to a fuel inlet pipeA -2|
the horizontal pipe 55, to the unit 50.
through a connection 20. To this gaseous fuel
Cooling water for .the refrigeration unit is
may be added waste gas, uncondensed in its
drawn from a cooling tower 58 through an outlet
progress through the apparatus, taken from the
pipe 51 and forced by a circulating pump 58
waste gas stack 23 through the horizontal pipe 70 upwardly through the vertical pipe 59, horizontal
22 which leads directly to the fuel inlet pipe 2i. _
pipe 60 and the vertical pipe 6I, to the main
The furnace is regulated preferably so that the
solution coolers 46. It is discharged from these
steel tube ofthe reactor is heated to approxi
coolers through the pipes 82, 63, 64, and de
` mately 900° F. and the silica tube I3 to about
livered to the hot solution cooler 36. It leaves
1200° F. ‘I'hese conditions have been found par 75 the hot solution cooler through the vertical pipe
high operating pressure and the presence of solid
water is also taken _from the horizontal pipe 60
through the vertical pipe 61 toa condenser 68
connected .to the top of a rectifyingcolumn10,
while the spent cooling water is discharged from
the cooler 68 by the connection 82.
Formaldehyde which has been collected from
tofore attempted which have invariably required
i5 and is returned through the horizontal -pipe 68
through the top of the cooling tower. Cooling
The silica tubes and their employment in .the
process disclosed are not herein claimed but con
stitute the subject-matter of the co-pending ap
plication of Raymond P. Rossman, Ser. No.
509,733, flled November 10, 1943.
Having thus disclosed my invention and de
scribed an illustrative example thereof, I claim
the quenching station at the furnace and the two
condensers 25 and 44 in .the storage tank 40 at
a concentration of about 19.2% by weight is now
as new and desire .to secure by Letters Patent:
l. The ,process of making formaldehyde from
to beconcentrated to the 38% formalin solution
required in commerce. The solution withdrawnv
from the storage tank 40 contains upl to 1.5%
formic acid and a small amount of acetaldehyde.
The former should be removed or neutralized
before concentration in order to reduce corro-4
sion in .the concentration _equipment and to pro
mixture of methane and air with NO2 to a tern
natural gas which includes the steps of heating a
4perature above 1100° F., and then immediately
and before any substantial decomposition can
take place, cooling the vaporized product by direct
contact with a cool formaldehyde solution-_
2. The process of making formaldehyde from
duce an acceptable formalin product.
Accord- _
ingly the 19.2% solution withdrawn from the 20
natural gas which includes the steps _of mixing
methane, air and NO2, heating the mixture above
1100° F., then immediately and before any sub
stantial decomposition can-take place, condens
ing a portion of the vaporized product by direct
storage tank 40 and pumped Íthrough the vertical
pipe 28 is drawn from this pipe by a horizontal
pipe 1I and conducted through the vertical pipe
12 to a boiler 13 where the formaldehyde solu
.tion may be boiled with caustic, for example, 100
contact with a cool formaldehyde solution, and
solution, and then passed through a connecting
subsequently cooling the uncondensed vapor and
thereby securing a further condensation-of form
pipe 14 to a condenser 15. From the condenser
aldehyde. .
- to 200 lbs. of caustic to 2000 gals'. of formalin
3._ The process ofvmaking formaldehyde from
it is delivered by a pipe 16 .to approximately the
center of the rectification column 10. The form 30 natural gas which includes the steps o_f mixing
natural gas and air in approximately equal pro
alin solution is collected from the bottom of the
portions, adding a nitrogen oxide as a gaseous
column and delivered by connecting pipes 11 and
catalyzer, subjecting the mixture to a .tempera
1l to a formalin storage tank 19. From .there it
may be pumped through a delivery pipe 80 as . ture of approximately 1200" F. for an interval
required. Instead of wasting the spent water 35 not longer than one second; and then rapidly
. cooling 4and ‘condensing the vaporized product.
from the condenser 88 by the connection 8| this
4. The process of making formaldehyde from ,
water may be passed through the connection si
natural gas which includes the steps of mixing
to the condenser 1I and returned from there
3 to 5 parts natural gas with 7 to 5 parts air> and
-through the vertical pipe '82 to the cooling
tower 56.
An alternative form of furnace of the vertical
.type suitable for carrying out the process of >our
invention is shown in Fig. 2. This comprises a
circular refractory body 90 having an outlet stack
ll for the products of combustion. Gaseous fuel
is conducted to the bottom of the furnace through
a duct 92 and delivered to its interior through
burner openings 83. The entire interior of the
furnace is ringed with a double bank of vertical
tubes. The tubes 95 of the inner -series are of
alloy steel and are connected outside the .top of
the furnace b'y metal U-bends .to the tubes 91 of
the outer series. These Aare preferably of silica
as already explained in connection with the fur-‘
nace of Fig. 1. The air-gas-NO: mixture is sup
plied to the tubes 85 through anannular gas inlet
manifold 84 which is located outside and below
the body of the furnace. The gases delivered
from the manifold $4 pass upwardly through the
tubes 8l where they may be heated to a tempera
-ture approaching 900° F. for example, and then
pass downwardly tothe tubes l1 where they are
heated to a temperature of approximately 1200’ F.
Reacted vaporized product is delivered to an
40 not over '2% NO2 by volume based on total
natural gas, air, and NO2, passing the mixture
through a reactor at an` emerging temperature of
about 1200° F., and immediately condensing a
portion of the yvaporized product by direct con
45 tact with aspray of cool formaldehyde solution
thereby substantially eliminating decomposition
of the formaldehyde which would otherwise _occur
at the temperature at which .the vaporized prod
uct issues from the reactor.
5. The process of making formaldehyde from
natural gas which 4includes the steps of mixing
natural gas with air in substantially equaLpro-4
portions,~adding not over 2% NO2 by volume
based on total natural gas, air, and NO2, pass-'
55 ing the mixture through a reactor at approxi
mately 1200° F., immediately condensing the
4vaporized product .by direct contact with cool
formaldehyde solution thereby eliminating de
composition of the formaldehyde which would
60 otherwise occur -at the temperature at which the
vaporized product issues from the reactor, and
then concentrating the solution by vacuum recti
6. The process of making formaldehyde from
annular outlet manifold Il and thence conducted 65 natural gas which includes thev steps of mixing
methane, airand NO2, heating the gas mixture
- to a station at which the quenching operation is`
above 1100‘I F., and then condensing .the vapo
effected by a spray of cool formaldehyde solution
rized gas mixture by direct and immediate con
as outlined in the explanation of the flow sheet of
tact with a formaldehyde solution of substantially
Pig. 1 or the quenching step may be carried outA
70 the same concentration'as that resulting from
directly in the manifold Il.
the condensation of the reacted gas mixture, and It will be noted that the apparatus above de
thereby eliminating 'decomposition of the re
'scribed is designed to be operated at atmospheric
pressure. This is a characteristic and very im
portant feature of the process of my invention
v acted mixture which would otherwise occur at
andonethstdistinnuishesltfromproccsles'here 76
awroximßml 1100° F.
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