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Патент USA US2116881

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May 10, 1938.
2,116,881
H. W. DE ROPP
I
UREA SYNTHESIS
Filed Feb. 2, 1934
Y
4 Sheets-Sheet 2
May 10, .1938.
’
|-|_ w, DE ROPP
2,116,881
~ URBA sYNTHEsis
Filed Feb. 2, 1954
4 sheets-Sheet 3
Vliv
ÍKWW
'
ATTORNEY.
May 10, 1938. Y
H. w. DE RoPP
2,1 16,881
UREA SYNTHESIS
Filed Feb.> 2, 1934
4 Sheets-Sheet 4
BY
îxßíûwv ’
`
ATTORNEY
Patented May `10, 1938
» 2,116,881 " "
, UNITED »STATES PATENT i 4.OFI-"ICE '
' _2,116,881
Unas SYNTHESIS
,
Harald W. de Ropp, Wilmington, Del., assign'or
to E. I. du Pont de Nemours & Company, Wil
mington, Del., a corporation of Delaware
Application February 2, 1934, Serial No. 769,423
(Cl. 260-125)
18 Claims.
This invention relates to the synthesis ofurea
excess ammonia has been accomplished, it is _
from ammonia and carbon dioxide or compounds e found that the amount _of _water carried over in
thereof and more particularly to an improved this distillationand/orV required to absorb and
method for reutllization of reactants unconverted
i
maintain the distillation products in liquid form,
when returned with the unreacted constituents 5
It is known that when ammonia and carbon to the reaction zone for further conversion to
dioxide, or compounds of the‘same, are heated in urea is of ‘ an order such as'to decrease greatly
a closed system a `partial conversion to u'rea' the conversion efllciency of the synthesis.
in urea synthesis.
"
_
takes place. The reaction mixtures' obtained,
According to my invention, however, the
amount of water carried. _over in distillation '1'0
to as “urea synthesis melts” may vary widely in _ and/ or required to absorb and maintain the prod
uct's of distillation in liquid form is considerably
composition with varying proportions of react
lessened ‘and higher >conversion eflìciency with
ants and/or with the extent to which the con
versionto urea has taken place. The synthesis consequent smaller over-all cost is obtained.
_ Pursuant to this invention, therefore, urea is 15
5 melts, for example, may contain various propor
0 which for convenience will hereinafter be referred
tions of urea, ammonia, „ammonium carbamate,
carbonates, and' water.
,
`
'
One of the uneconomical disadvantages hereto
synthesized at high temperatures and pressures
from ammonia and carbon dioxide, or compounds
thereof, in a closed reaction vessel, utilizing an
excess of ammonia over the stoichiometrical refore attendant on the synthesis of urea from am
‘0 monia and carbon >dioxide has been the.diñì- quirements, and the ureaY synthesis melt compriscult'y of returning the unconverted reactants to ' ing urea, ammonia, ammonium carbamate, and
the synthesis autoclave.
~
>
It is an object of this invention to provide an
- improved process for the removal from the urea
,
0
water passed to Aan ammonia still wherein-the
major part of the excess unreacted ammonia is
distilled. This ammonia is preferably utilized in
any desired manner and may be substituted for 25
, byffresh ammonia and/ or returned, together with
vessel of the reactants unconverted to urea.
Other objects and advantages of this invention a quantity of added ammonia, to the autoclave
will be ,apparent by reference to the following for 'further reaction with carbon dioxide to form
specification wherein the details and preferred urea, while the distillation residue'in the am
monia'still is _conducted to a' first ammonium 30
embodiments are described.
.
' '
\
.l I have found that great efficiencies in the ureav carbamate still and subjected to further distilla
tion at- a lower pressure than in the ammonia
synthesis may be accomplished, after synthesiz
ing- urea from ammonia and c‘arbon dioxide, on still with a resultant evolution of the major part
compounds thereof, whileutilizing- an excess of of the residual excess ammonia, a major part of
:5' synthesis melt and recirculation to the synthesis
g5 ammonia over the stoichiometrical requirements
at high temperatures `and~elevated pressures. by,
the ammonium carbamate and a relatively small 35
quantity of water.
This distillate is conducted
to a first carbamate absorber and thence re
first removing the greater part of excess unre
acted ammoniafrom the urea synthesis melt by` turned to the autoclave with or without added
distillation and subjecting the distillation residue .v water or utilized as- hereinafter described. The
distillation' residue is conducted to a‘ second still 40
i0 to a further two-stage distillation for theV re
' «moval of all or substantially all of the ammonium f wherein the remaining -excess ammonia, am
carbamate.' the residual free ammoniaf'and at
, least 4a part of the water.
Accordingto this invention, by the utilization`>
45 of va two-stage _ammonium carbamate and resid'
monium carbamate, and a somewhat larger
quantity _of water than ~in the ñrst carbamate
' _still are completely removed by distillation, at a
lower -pressurethan in the preceding still, and
ual ammonia distillation, following a‘preliminary ‘ conducted'to and condensed in a second carbam
distillation, of the greater part- of excess unre-`
acted-ammonia, the amount of water returned to
the=` reaction zone may be sufliciently lowered to
50 effectl considerably greater conversion efficiency
ate absorber or absorbed in Water contained in
- a second carbamate absorber maintained at a
lowertemperature and'pressure than the still
from which the reactants are distilled. The now
puriñed still residue comprising a urea-water
than heretofore possible. -If, for example, thedistillation of residual free or unreacted excess _solution may be treated in a known manner for
ammonia' and ammonium carbamate from the obtaining crystal-urea, and the solution -result
synthesis melt is attemptedœ‘in vone distillation ing from the absorption of the products coming
55 step, after distillation of the maior portion `of from the last described still passed _into the nrst ,
.
2
2,116,881
described absorber, therein to absorb the ñrst
carbamate still distillate previously described and
thence to the autoclave for further conversion,
with additional quantities of ammonia and car
water, comprising 11 parts ammonium carbamate,
bon dioxide, to urea.
The conditions of temperature and'pressure
followed in the urea synthesis, according to this
invention, may vary over a wide range, my proc
ess being applicable generally to urea synthesis
10 from ammonia and carbon Adioxide or compounds
from first carbamate still (3) to give a solution,
comprising 76.5 parts ammonium carbamate, 30
parts ammonia, and 58.8 parts water, which is
thereof.
8 parts ammonia, and 53.8 parts water, is con
veyed to the first carbamate absorber (4) and
there utilized for absorption of distillate evolved
returned to the autoclave (I) for reaction with
the previously described 100.7 parts carbon di
oxide and 214.5 parts ammonia to form further
Thus, for example, the synthesis may Y quantities of urea.
be satisfactorily accomplished at temperatures of
from about 17o-220° C., and pressures of from
about 3000-6000 pounds per square inch pressure
15 without departing from this invention or sac
riñcing any of the advantages thereof.
Various changes may be made in the details
and methods of procedure according to this in
vention without departing therefrom or sacrific
Example 2.-Referring to Figure II, into a pres
sure resistant urea converter (I), maintained at
20D-220° C.,~and 6000 pounds per square inch
absolute pressure, ther-eis introduced 214.5 parts
by Weight of ammonia,\100.7 parts of carbon di
oxide and 165.3 parts of a\`so1utìon comprising
ammonia, ammonium carbamate` and water,
described. The resultant» urea syn
y20 ingl any of the advantages thereof, as will be - hereinafter
thesis melt, comprising 76.5 parts ammonium
illustrated by reference to the following examples
read in conjunction with the accompanying dia
grammatic flow sheets.
Example 1.-Referring to Figure I, into a pres
25 sure resistant urea converter (I) there is intro-.
duced, in a cyclic system, 214.5 parts by weight
of ammonia, 100.7 parts carbon dioxide, and 165.3
parts of a solution comprising water, ammonia
and ammonium carbamate, hereinafter to be de
30 scribed.
These materials are caused to react at
a temperature of 20D-210° C., and about 6000
pounds per square inch absolute pressure to give
a. urea synthesis melt comprising '76.5 parts am
v monium carbamate, 137.3 parts urea, 166.7 parts
35 ammonia and 100 parts water. 'I'his urea
synthesis melt is led to an ammonia still (2)
where the melt is distilled at a -pressure of 185
pounds per square inch absolute and 120° C.,
evolving 136.7 parts of ammonia which is recon
40 ducted'together with 77.8 parts'additional am
monia, to the autoclave (I) for further synthesis.
The distillation residue, comprising '76.5 parts
ammonium carbamate, 137.3 parts urea, 30 parts
ammonia and 100 parts‘water is thereafter con
45 ductedto a first carbamate still (3) and distilled
at a temperature of 120° C., and 60 pounds per
square inch absolute pressure to drive 0E 65.5
parts of ammonium carbamate, 22 parts am
monia, and \5 ‘parts water. 'I'his distillate is
50 thence conducted to a ñrst carbamate absorber
55
(I), maintained at 55° C., and 53 pounds per
square inch absolute pressure where _it is absorbed
by passage thru a receiving liquid coming from
a second carbamate absorber (6),v hereinafter to
be described.
i
carbamate, 137.3 parts urea, 166.7 parts am
monia and 100 parts water is then treated as
described in Example 1 for separation of re
actants unconverted in the synthesis operation,
except that the 15.8 parts of water which is de
scribed in Example 1 as being introduced to the
second carbamate absorber (6) is instead intro
duced into the first carbamate absorber (4), in
order to maintain liquid the distillate from the
first carbamate still when combined with the
liquefied distillate from the second carbamate
absorber (6).
Example 3.-Referring to drawing Figure III,
into a pressure resistant urea converter (I) there
is introduced, in a cyclic system as described in
Examples 1 and 2, 227.3 parts by weight of am
monia, 106.9 parts carbon dioxide, and 146.3 parts I
of a solution comprising water, ammonia and
ammonium carbamate hereinafter to be de
scribed. These materials are caused to react at
a temperature of 20D-220° C., and about 6000
pounds per square inch absolute pressure to give
a urea synthesis melt comprising 76.5 parts am
monium carbamate, 137.3 parts urea, 166.7 parts.
ammonia, and 100.0 parts water. This urea syn 45
thesis melt is then conducted to an ammonia still
(2) Where the melt is distilled as in Example 1,
at a pressure of 185 pounds per square inch ab
solute pressure and 120° C., evolving 136.7 parts
ammonia which is reconducted, together with 90.6 50
parts fresh added ammonia, to the autoclave for
further synthesis.
'
'I'he distillation residue,- comprising 76.5 parts
ammonium carbamate, 137.3 parts urea, 30 parts
ammonia and 100 parts water, is thereafter con 55
ducted to a first carbamate still (3) and distilled
'I‘he distillation residue in the carbamate still
(3), comprising 11 parts ammonium carbamate, ` at a temperature of 120° C., and 60 pounds per
137.3 parts urea, 8 parts ammonia, and 95 parts square inch absolute pressure to drive off 65.5
water, is conducted to a second carbamate still Vparts of ammonium carbamate, 22 parts am
(5) maintained at a temperature of 120° C. and monia, and 5 parts water. This distillate is
-20 pounds per square inch absolute pressure, thence conducted to a first carbamate absorber 60.
wherein the remaining'ammonium carbamate,A (4) maintained at, 70° C., and 53 pounds per
'ammonia and some water, ,comprising 11 parts, square inch absolute pressure, where it is ab
8 parts, and 38 parts respectively, are distilled sorbed in 53.8 parts of added water. The dis
65 aêid conducted to a second carbamate >absorber
tillation residue in the first carbamate still (3),
v( ).
comprising 11 parts ammonium carbamate, 137.3
'I'he solution of 137.3l parts urea in 57 parts parts urea, 8 parts ammonia, and 95 parts water,
water remaining in second carbamate still (5) is conducted to a second carbamate still (5),
is treated as desired for concentration and/or maintained at 120° C., and 20 pounds per square
'10 production of crystal urea, while the distillate inch absolute pressure,l wherein the remaining
just previously described is absorbed in a' second ammonium carbamate, ammonia’ and some water 70
.carbamate absorber (6), maintained at a »tem
are distilled and conducted to a second carbamate
perature'of 60° C., and 15 pounds per square inch absorber or condenser (6) , to beremoved there
`ìabsolute pressure, into which 15.8 parts of water from and utilized as desired, as, for example, to
75 is introduced.
condensate, with the added- prepare ammonium sulfate. The solution of 75
l
‘ 2,116,881'
3
low that existing during the urea synthesis, in
which
at least the major part of the 'excess am
desired for concentration `and/or production o! _.
monia is recovered and returned to the reaction
zone, and thereafter subjecting the resultant
' The distillate from the first carbamate still (3)
to atwo-stage secondary distillation at
previously described as absorbed in 53.8 parts material
succeedingly
lower pressures than that or the
water in the ñrst carbamate absorber (4), is re
conducted to the autoclave for further synthesis primary distillation4 in whichV the unconverted
ammonium carbamate, the remainder of excess
_ to urea as described in Example 2.
Example 4.--Referring to Figure IV, into a ammonia, and at least a part of the water' con
137.3 parts urea in57 parts water is treatedas
crystal urea.
,
«
_
_
pressure resistant urea converter (I)' there is
tained therein are recovered and returned to
the reaction zone, with fresh ammonia and car
introduced, in a- cyclic system, 259.5 partsby
Weight of ammonia, 119.5 parts carbon dioxide,
bon dioxide, at urea-forming temperature arfd
and 172 parts of solution comprising water, am
pressure.
monia and‘ammonium carbamate hereinafterde- `
-
v
2. Process as in claim 1, in whichv the ammo
carbamate-residual .excess ammonia-water 15
scribed. These materials areA caused `to react at a nium
distillate from the second stage of the two-stage
temperatureof- 200-210° C., and about l600()
pounds per square inch absolute pressure to give a
urea synthesis melt comprising 91.0 parts am
monium carbamate, 163.0 parts urea, 1971.0 parts _
secondary distillation is utilizedas an absorbing
liquid for the ammonium carbamate-excess am
monia-water distillate of the iirst stage ofthe
two-stage secondary distillation.
v20
‘
ammonia, and 100 parts water. This urea syn
_3. Process as in claim 1, in which water is>
thesis melt is led to an ammonia still (2), where added
to the ammonium carbamate-residuale
the melt is distilled at a pressure of 1_85 pounds
ammonia-water distillate from the second stage , per square inch absolute pressure and 118° C., -of the two-stage secondary distillation and the
evolving 167.0 parts of ammonia which is recon
resulting solution is utilized as an absorbing liq
ducted, together with 92.5 parts additional am
uid
for the ammonium carbamate-excess’ammo
monia, to the autoclave' ( l) for further synthesis. nia-water
distillate of the iirst stage of the two
The distillation residue, comprising 91.0 parts
ammonium carbamate, 163 .parts urea, 30 parts
‘ammonia and 100 parts water, is thereafter con
ducted to a iirst carbamate still (3), and distilled
at a temperature of 120° C., and 69 pounds per
square inch absolute pressure to drive 0E 76 parts
of ammonium carbamate, 22.1 parts ammonia.
and 5 parts water. The distillate’ is thence con
ducted to a first carbamate absorber (4), main
tained at 55° C., and 64 pounds per square inch
absolute pressure where it-is absorbedin a re
. ceiving liquid hereinafter to be described.
stage secondary distillation.
_^
4. Process as in claim 1, in which at urea syn-`
thesis temperatures of about 170° to about 220° 30
C. and pressures of about 3000 to about 6000
pounds per square inch the ammonium carbam
ate residual-excess ammonia-Water distillate
from the second stage of the two-stage second
ary distillation is utilized as an absorbing liquid 35
for the ammonium carbamate-excess ammonìa-` .
water distillate of the iirst stage of the two-stage
secondary distillation.
5. Process as in claim l in which at urea ‘syn
.thesis temperatures of about 170° to about 220°
C. and pressures of about 3000 to about 6000
bamate, 163 parts urea, 7.9 parts ammonia, and pounds per .square >inch the water is added to the
95 parts water, is conducted to a second carbam
carbamate-residual ammonia-water _
'ate still <5) . maintained at a temperature of 120° ammonium
distillate from the second stage of the two-stage
C., and 14 pounds per square inch absolute pres y secondary distillation and the resulting solution"
sure wherein the remaining'ammonium carbam
is utilized as an absorbing liquid for the ammo
The 'distillation residue in the first carbamate
still (3), comprising 15 parts ammonium car
40
ate, ammonia and some water, comprising 15 l nium carbamate-excess ammonia-water distillate
parts, 7.9 vparts and 46 parts respectively, are
distilled and conducted to a second carbamate
of the ñrst stage of the two-stage secondary
distillation.
vabsorber (6) .
The solution of _163 parts urea in 49 parts water
is treated as desired for concentration and/or
production of crystal urea, `while the distillate
`
`
_
_
6. Process as in claim 1, in which at urea syn 50
thesis temperatures of about 200 to about 210°
C. and a. pressure of about 6000 pounds per square
inch the ammonium carbamate residual-excess
ammonia-water distillate from the second stage
in a carbamate absorber (6), maintained at a >oi? the two-stage secondary distillation is utilized 55
temperature of 35° C., and 9 poundsper square
as an absorbing liquid for the ammonium-car
just previously described is absorbed-or condensed
_ inch absolute pressure.
This condensate, com
ammonia-water distillate ofthe
prising 15 parts ammonium carbamate, 7.9 parts _' bamate-excess
ammonia and 46 parts water, is conveyed to first ñrst stage of the two-stage secondary distillation.
carbamateabsorber (4) and there utilized as the
60
receiving liquid previously described for absorp
tion of distillate evolved from (3), to give a so
lution comprising 91 parts ammonium carbam--
„ >7. Process as in claim 1 in which at urea syn
thesis temperatures of about 200 to about 210° 60
C. and a pressure of about 6000 rpounds per square
inch'the water is added to the ammonium car
ammonia-water distillate from
ate, 30 parts ammonia, and 51 parts water, which - bamate-residual
the second stage of the two-stage secondary dis
tillation and the resulting solution 4is utilized as
the previously described 119.5 parts carbon diox-V an absorbing liquid'for the ammonium carbam
is returned to the autoclave (I) for reaction with
ide and 259.5 parts ammonia to form
quantitiespof urea.
_
further
I claim:
1». In a cyclical process for the synthesis loi'
65
ate-excess ammonia-water distillate of the iirst .
stageof the two-stage secondaryl distillation.
8. In a cyclical process for the synthesis of
urea by heating ammonia and carbon dioxide
70
70 urea by heating ammonia and carbon dioxide at ' at urea-forming temperaturesand pressures in .
_urea-forming temperatures and pressures in the
presence of a substantial excess of ammonia'over
the stoichiometrical requirements, the steps which
comprise subjecting the urea synthesis melt to
75 a primary pressure distillation at a pressure be
the presence of a substantial excess of ammonia4
. over the stoichiometrical
requirements, the steps
which require subjecting` the urea synthesis melt
to a primary pressure distillation at a pressure
4
2,116,881
below that existing during the urea synthesis,
at about 125 lbs. per square inch and about 165
lbs. per square inch lower pressures, respectively,
in which at least the major part of the excess
ammonia is recovered and returned to the reac
than in the primary pressure distillation, in which
tion zone, and thereafter subjecting the result
ant material to a two-.stage secondary distilla
two-stage secondary distillation the unconverted
tion at succeedingly lower pressures than that of
the primary distillation, in which a part of the
unconverted ammonium carbamate, excess am »
monia, and water, being that part which is ob
tained from the ,ñrst stage of the two-stage sec
ondary distillation, is returned with added Water
to the reaction zone, with fresh ammonia and
ammonium carbamate, the remainder of excess
ammonia, and at least a part of the water con
tained therein are recovered and returned to the
reaction zone, the ammonium carbamate-residual
excess ammonia-water distillate from the second
stage of the two-stage secondary distillation being
utilized as an absorbing liquid for the ammonium
carbamate-excess ammonia-water distillate of the
carbon dioxide, at urea-forming temperaturesv iirst
stage of the two-stage secondary distillation.
and pressures.
15
9. In a cyclical process for the synthesis of
urea by heating ammonia and carbon dioxide at
urea-forming temperatures and pressures in the
presence of a substantial excess of ammonia over
the stoichiometrical requirements, the steps which
20 comprise subjecting the urea synthesis melt to
a primary pressure distillation at a lpressure be
12. The process for the synthesis of urea by
heating ammonia and carbon dioxide at urea
forming temperatures and pressures in the pres
ence of a substantial excess of ammonia over the
stoichiometrical requirements which includes the
steps of subjecting the urea'synthesis melt to a
primary pressure distillation at temperatures of 20
about 118 to about 120° C., and pressures of
about 185 lbs. per square inch absolute, in which
which at least a major part of the excess ammo
at least the major part of the excess ammonia
nia is.recovered, and thereafter subjecting the. is recovered, and thereafter subjecting the re
resultant material to a two-stage secondary'dis
sultant residual material to a two-stage second
tlllation at succeedingly lower pressures than that ary distillation at about the same temperature 25
of the primary distillation in which a part of the but at about 116 lbs. per square inch to about 125
low that existing during the urea synthesis, in
unconverted ammonium carbamate, excess am
monia, and water, being that part which is ob
30 tained from the ñrst stage of the two-stage lsec
ondary distillation, is returned with added Wa
ter to the reaction zone, with fresh ammonia and
carbon dioxide to urea-forming temperatures and
pressures.
85
10. The process for the synthesis of urea by'
heating ammonia and carbon‘ dioxide at urea
forming temperatures and vpressures in the pres
ence of a substantial excess of ammonia over
the stoichiometrical requirements which includes
40 the 'stens’ of subjecting the urea synthesis melt
to s. primary pressure distillation at tempera
tures of about 118° C. to about 120° C., and pres
sures of about 185 lbs. per square inch absolute, in
which at least the major part of the excess am
45 monia' is recovered, and thereafter subjecting the
resultant residual material to a two-stage sec
ondary distillation at about the same tempera
ture but at about 116 lbs. per square inch to about
125 lbs. per square inch and about 165 lbs. per
50 square inch to about 171 lbs. per square inch lower
pressures, respectively, than inthe primary pres
sure distillation, in w 'ch two-stage secondary
distillation the unconverted ammonium carbam
ate, the remainder of excess ammonia, and at least
55 a part of the water contained therein are recov
ered _and returned to the reaction zone, the am
monium carbamate-residual excess ammonia
water distillate from the second stage of the
' lbs. per square inch- and about 165 to about 171
lbs. per square inch lower pressures, respectively,
than in the primary pressure distillation, in lwhich 30
two-stage secondary distillation the unconverted`
ammonium carbamate, the remainder of excess
ammonia, and at least a part of the water con
tained therein are recovered and returned to the
reaction zone, and adding water to the ammonium 35
carbamate-residual excess ammonia-water distil
late from the second stage of the two-stage’sec
ondary distillation and utilizing the resultant
solution as an absorbing liquid for the ammonium '
carbamate-excess ammonia-water distillate of 40
the ñrst stage of the two-stage secondary dis
tillation. -
13. The process for the synthesis of urea by
heating ammonia and carbon dioxide in the pres
ence of a substantial excess of ammonia over the 45
stoichiometrical requirements at temperatures of
about 170° C. to about 220° C., and pressures of
about 3000 to about 6000 lbs. per square inch
which includes the steps of subjecting the urea
synthesis melt to a primary pressure distillation,
and a temperature of about 118 to about 120° C.
and a pressure of about 185 lbs. per square inch
absolute, in which at least the major part of the
excess ammonia is recovered and returned to the
reaction zone, and thereafter subjecting the re 55
sultant residual material to a two-stage second
ary distillation at succeedingly lower pressures
than that of the primary distillation in which the
two-stage secondary distillation being utilized as unconverted ammonium carbamate, the remain
60 an absorbing liquid for the ammonium carbam
, der of excess ammonia, and at least a part of
ate-excess ammonia-water distillate of the iìrst the water contained therein are recovered and
stage of the two-stagesecondary distillation.
» returned to the reaction zone. with fresh am
11. The process for the `synthesis of urea by
- heating ammonia and carbon dioxide at urea
65 forming temperatures and pressures in the pres
ence of a substantial excess of ammonia over the
stoichiometrical requirements which includes the
-steps of subjecting the urea synthesis melt to a ,
primary pressure distillation at temperatures of
70 about 118 'to about 120° C., and pressures of about
185 lbs. per square inch absolute, in which at
least the vmajor part of the excess ammonia ‘is
recovered, and thereafter subjecting the result
ant residual material to a two-stage secondary
75 distillation at about the same temperature but
monia and carbon dioxide.
14. In a pro-cess for the synthesis of urea by
heating ammonia and carbon dioxide in the pres 65
ence of a substantial excess of ammonia over the
stoichiometrical requirements at temperatures of
about 170° C. to about 220° C., and pressures of
about 3000 to about 6000 lbs. per square inch
which includes the steps of subjecting the urea 70
synthesis melt to a primary pressure distillation
at a temperature of about 118 to about 120° C.
and a pressure of about 185 lbs. per square inch
absolute, in which at least the major part of the
excess ammonia is recovered and returned to 75
5
2,110,881
the reaction zone, and thereafter subjecting the
resultant-residual material to a two-stage sec
ondary distillation at about the same tempera
tures but at about 125 and about 165 lbs. per
square inch lower pressures, respectively, than
in the primary pressure distillation, in which the
unconverted ammonium carbamate, the remain
der of excess ammonia, and at least a part of the,"
water contained therein'are recovered and re
turned to the reaction zone, with fresh ammonia
and carbon dioxide.
ì
15. In a cyclical process for the synthesis of
urea by heating ammonia and carbon dioxide at
superatmospheric pressure in the presence of a
substantial excess of ammonia over the stoichio
metrical requirements at temperatures of about
170° to about 220° C. and pressures of about
3000 to about 6000 pounds per square inch, the
steps which comprise subjecting the urea synthe
sis melt to a primary pressure distillation at a
pressure below that existing during the urea
synthesis in which at least the major part of the
excess ammonia is recovered, and thereafter sub
4jecting the resultant material to a two-stage
secondary distillation at succeedingly lower pres
sures than that «lof the primary distillation in
is obtained from the ñrst stage'of the two-stage
secondary distillation is returned, with added
water, to the reaction zone, with fresh ammonia
and carbon dioxide. to urea-forming temperature
an`d pressure.
`
'
17. In a cyclical process for the synthesis of
urea by heating ammonia and carbon dioxide at
superatmospheric pressure in the‘presence of a
substantial excess of ammonia over the stoichio
metrlcal requirements' at temperatures of about 10
170° to about 220° C. and pressures 'of about
3000 to about 6000 pounds per square inch, the
steps which comprise subjecting the urea. synthe
sis melt to a primary pressure distillation at a
pressure below that existing during the urea syn 15
thesis in which at least the major part of the
excess ammonia is recovered, and thereafter sub
jecting the resultant material to a twoéstage
secondary distillation at succeedingly lower pres
sures than that of 'the primary distillation in 20
which a part of the -unconverted ammonium car
bamate, excess ammonia and water, being that
part which is obtained from the ñrst stage of the
two-stage, secondary distillation is returned, with
added water, to the reaction zone, with fresh am
monia and carbon` dioxide, to urea forming tem
which the unconverted ammonium carbamate,
perature and pressure.
the remainder of excess ammonia and at least
a part of the Water contained therein are recov
ered and returned to the reaction zone, and sub
mitting all said materials returned to the reac
metrical requirements at temperatures~v of about
tion zone,.with fresh ammonia and carbon diox
ide, to urea-forming temperature-and pressure.
16. In a cyclical process for the synthesis of
urea by heating ammonia and carbon dioxide at
superatmospheric pressure in the presence of a
substantial excess of ammonia over the stoichio
metrical requirements at temperatures of 'about
170° to about 220° C. and pressures of about
3000 to about 6000 pounds per square inch, the
steps which comprise -subjecting the urea synthe
sis melt to a primary pressure distillation at
a pressure below that existing during the urea
synthesis in which at least the major part of
the excess ammonia is recovered and returned
to the reaction zone, and thereafter subjecting
the resultant material to a two-stage secondary
' distillation at succeedingly lower pressures than
that of the primary distillation in which a part
of the unconverted ammonium carbamate, e_x«
cess ammonia, and water,_ being that part which
25
18. In a cyclical process for the synthesis of
urea by heating ammonia and carbon dioxide at
superatmospheric pressure in the presence of a 30
substantial excess of ammonia over the stoichio
200 to about 210° C. and pressure of about 6000
pounds per square inch, the steps which com
prise subjecting the urea synthesis melt to a 35
primary pressure distillation at a pressure below
that existing during the urea synthesis in which
at least the major part of the excess ammonia is
recovered and returned to the reaction zone, and
thereafter subjecting the resultant material tov
a two-stage secondary distillation at succeedingly
lower pressures in which a part of the u'ncon
verted ammonium carbamate, excess ammonia, f
and water, being that part which is obtained
from the first stage of the two-stageV secondary
distillation is returned, with added water, to the
reaction zone, with fresh ammonia and carbon
dioxide,V to urea-forming temperatures and pres
sures.
«
-
HARALD W; DE ROPP.
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