Note: Descriptions are shown in the official language in which they were submitted.
~2~739~
The invention relates to a method for obtaining
low-molecular olefins by catalytic decomposition of methanol.
~ ow-molecular olefins, especially ethylene and
propylene, but also butylene, are important chemical in-
5. termediate products which are required in very large quantities.Conventional method for producing these olefins are based
upon the decomposition of hydrocarbons, for example ethane,
propane, light gasoline, naphtha or kerosine. The deccmposition
of mixtures of hydrocarbons having a boiling range ~elow
10. about 200C is particularly satisfactory, since such materials
produce relati~ely high yields of olefin and few unwant:ed
by-products.
Since there is a very great need for low-molecular
olefins, which may lead to a shortage thereof and to price
15. increases, attempts have been made~ for some time, to develop
methods based upon other materials. Consideration was given,
in this connection, to the use of heavy hydrocarbon fractions,
more particularly gas-oil ox vacuum-oil. ~owever, the oc-
currence of large quantities of unwanted decomposition-products
20. can be avoided, with these materials, only by adding steps
to the method, resulting in high costs. Methods of this kind
are described in German OS's 28 05 720,~8 15 859, 28 43 792
and 28 43 783.
During the production of low-molecular olefins, a
25. decomposition-gas is produced from the charge-materials used,
the said decomposition-gas containing further reaction pro-
ducts in addition to the desired olefins. The said de-
composition-gas therefore has to be subjected to costly
- 1 -
9L2~3~4
breaking down in order to separate these by-products and
to isolate the olefins.
Catalytically accelerated, exothermal decomposition
of methanolhas also already been considered in the search for
5. alternative raw-materials. The reaction is carried out at
temperatures of about 400C, for example between 300 and 500C
and at atmospheric or moderately increased pressure, for ex-
ample between 1 and 30 bars. For the production of light
olefins, preferance is given to the lower range of pressures,
10. for examp]e between 1 and 12, more particularly between 7 and
12 bars, since the use of higher pressures shifts the product-
spectrum towards less desirable components.
Methanol decomposition is carried out substantially
in two stages, the first stage involvlng the conversion of
5. methanol into dimethyl-ether according to the reaction equation:
2CH OH-~H C-O-CH + H O.
The dimethyl-ether, formed as an intermediate product is then
converted into the desired olefin-rich decomposition-gas, a
main reaction representing the conversion into ethylene ac-
20. cording to the equation:
H3C-O-CH ~ C2H4 + H2O-
Under avourable reaction conditions i-t is possible to pro-
duce decomposition-gases containing over 40% by weight of
ethylene and a comparable amount of propylene. In addition
25. to this, the decomposition-gas contains about 1 to more than
10% by weight of butylene. The methanol decomposition-gases
~ _
~2(173~L~
are also noted for their low methance and hydrogen contents
and, in the case of decomposition under low pressure, for
the small quantities of high-boiling hydrocarbons.
Up to now, the investigation of methanol decompo-
5. sition has been restricted mainly to a search or suitablecatalysts, in connection with which reference is made to
German OS's 29 09 927 and 29 12 068, for example. Although
this was an important step towards obtaining olefins by
methanol-decomposition, the peculiarities of processing the
10. methanol-decomposition gas were completely ignored.
Because of its extraordinarily high olefin content,
methanol-decomposition gas is particularly suitable for ob-
taining low-molecular olefins, sin~e a high concentration of
the products to be separated, and a small proportion of by-
15. products, are present in the gas~decomposition right fromthe start. The composition of the gas, diEfering from that
arisin~ in the conventional decomposition of hydrocarbons,
requires a special method of decomposition matching the
composition of the gas. As a result o this, conventional
20. gas-decomposition methods cannot be transerred directly to
the method according to the invention.
It was there-Eore a purpose of the invention to
develop a method for the satisfactory processing of methanol-
decomposition gas.
25. This purpose is achieved in that the methanol-
decomposition gas is cooled, cleaned, compressed if necessary
-- 3 --
~l2~*3~
and, after the separation of a C3~fraction, is passed to a
low-temperature gas-breakdown unit where a Cl/C2 separation
and a breakdown of the C2 fraction into an ethane-~low and an
ethylene product-flow is carried out.
5. In the method according to the invention, the de-
composition gas, unless it has already been produced at suf-
ficient pressure, is compressed and, after precooling to
temperatures of between -30 and -50, for example to -35C,
is subjected to separation of C3 hydrocarbons and high-boiling
10. components. It is then cooled to a temperature suitable for
isolating a fraction of C2 hydrocarbons, for example to tempe-
ratures of about -100C, as obtained by a C2 refrigerating
circuit. Ethylene is sepaxated as a desired product from
the separated C2 fraction which contains ethane in addition
15. to ethylene. I the C2 fraction contains small amounts of
acetylene, these are removed prior to the ethylene-ethand
separation for reasons of safety, for example by washing or
by selective hydrogenationO
A first special characteristic of the method ac-
20. cording to the invention is the small amount of methane and
hydrogen in the methanol-decomposition gas and the problems
arising from this during the C1/C2 separating process.
During this separa-tion, a free C2 fraction is to be taken
~rom the top of the separating column, since the ethylene in
25. this fraction would lead directly to a decrease in product-
yield. To this end, the top of the separating column must
be adequately cooled, either by providing a cold return
-- 4 --
~2~73~L
liquid or by indirect cooling ln a top-condenser. For
example, the top may be cooled indirectly with ethylene
boiling under a low pressure. Another way of cooling the
head, to which preerence is given in implementing the method
5. according to the invention, consists in using as the coolant
methane separated from the decomposition-gas at temperatures
o below 95C. In addi-tion to indirect cooling in a top-
cooler, special preference is given to direct cooling in which
super-cold liquid methane i5 applied to the top of the sep-
10. arating column as a return. The liquid methane is separatedrom the decomposi~ion-gas at temperatures of less than about
-95C, i.e. at a temperature lower than that obtainable in a
C2 refrigerating circuit. The temperature of the coolant may
be between -120 and -150C, or example about -130C. Because
15. of the low methanol content o a methanol-decomposition gas,
it is not immediately possible to make available an adequate
amount of methane as a coolant for the Cl/C2 separating
column. It is therefore an essential characteristic of this
variant o the invention that at least a part of the methane
20. fraction removed from the top of the Cl/C2 separa~ing column
be returned again. Only the amount of methane not required
for the low-temperature part of the method is removed and is
used as heating gas, for example. The methane is returned,
after releasingits cold-content to process-flows to be cooled~
25. to a suitable pressure-stage in the decomposition-gas compres-
sing unit. Since the Cl/C2 separation is normally carried
out an elevated pressure, between about 8 and 15, for example
10 bars, the full compression-ratio is not required in re-
compressing the methane.
-- 5 --
~734~1L
Return of the methane may be effected in various
ways; for example it may be returned to the top of the Cl/C2
separating column in a separate circuit. This has the ad-
vantage of preventing the methane from being mixed with other
5. fractions, but requires a separate compressor, additional
heat-exchangers and separate heat-exchanger cross-sections.
In many cases, therefore, it is simpler to pass the return
medium to the decomposition-gas in a suitable pressure-stage,
and to process it further jointly therewith.
lO. According to one desirable development of this
variant of the invention, another part o the low-boilillg
component of the decomposition-gas is used to condense the
low-boiling component used as the return for the Cl/C2 sep-
arating column. In this connection, a suitable refrlgerant
15. is a condensate arisin~ during the cooling o~ the decomposition-
gas in the final pressure-stage of a multi-stage C2 refriger-
ating circuit, l.e. at temperatures of between about -80 and
about -95C. The condensate thus formed is rich in methane
and also contains small amounts of C2-hydrocarbons. This
20. condensate is cooled and expanded andr in indirect heat-
exchange with the remaining gaseous part of the decomposition-
gas containing only methane and possibly hydrogen, is reheated
and evaporated. After the said condensate has thus delivered
the amount of cold required to produce the methane-return,
25. it is preferably returned to the raw-gas compressor, after
further heating in indirect heat-exchange with process-flows
to be cooled, and is again subjected to decomposition. This
avoids any loss of the C2-hydrocarbons, especially ethylene,
-- 6 --
~12~
still contained in this fraction.
A second special characteristic of the method ac-
cording to the invention is the utilization of the ethane
arising during the ethylene-ethane separation. This gas,
5. relatively valueless per se, is a useful material for thermal
decomposition for the production of low-mGlecular olefins and
it is therefore subjected to such decomposition for the pur-
pose of increasing the olefin yield from the method according
to the invention. This decomposition, which is carried out,
10. for example, at temperatures of between 750 and 900C, in
a heated tube-reactor, with very hrie periodc of residence,
for example between 0.1 and 1 sec., and in~the presence of
water-vapour produces a decomposition-gas rich in ethylene
which is cooled very rapidly in order to prevent secondary
15. reactions, and is thereafter broken down jointly with the gas
from the methanol-decomposition.
According to a desirable development of this variant
of the method, a C3 fraction is obtained, in a corresponding
manner, from the C3+ fraction separated after precooling, and
20. is subjected to propylene-propane separation. ~hereas the
separated propylene is directly available as a product-flow,
the propane is used as a material for thermal decomposition,
in order to convert the propane which, like the ethane fraction,
is mainly useful only as a waste-gas, into an ethylene-rich
25. gas by thermal decompositionO Even the product-gas obtained
from propane-decomposition, which i5 carried out under conditions
similar to those obtained during the ethane decomposition,
is broken down, after cooling, jointly with the methanol
decomposition-gas.
-- 7 --
~2~7349~
Under certain circumstances, thermal decomposition
of the separated propane may be carried out jointly with that
of the ethane-fraction, which allows an installation for the
implementation of the method to be reduced by one thermal
5. decomposition stage. In many cases, the methanol decomposition
may also be combined with a conventional method for the de-
composition under normal conditions of gaseous or liquid
hydrocarbons. In such a case also it is desirable to process
the decomposition-gas, obtained by such additional thermal
10. decomposition, jointly with the gas from the methanol-de-
composition, since this eliminates the considerable expense
of an additional yas-breakdown. If such additional thermal
decomposition is provided, a possibly separated ~ropane-
fraction, to be subjected to thermal decomposition, may also
15. be processed jointly with the additional charge-10w to be
decomposed. Which ractions are to be subjected to thermal
decomposition jointly or separately may be determined in each
case from the nature of the charge-materials, and the quantity
of the flows arising, on the basis of a normal profitability
20. analysis.
The decomposition-gases from the method according
to the invention normally contain impurities which would be
detrimental to the breaking down of gas at low temperatures.
Whereas the gases from thermal decomposition contain high~
25. boiling hydrocarbons and sulphur compounds as unwanted com-
ponents, in the case of methanol-decomposition gas it is
dimethyl-ether in particular which is not reacted. The
amount of this component which can lead to difficulties during
~ _
b7344
low-temperature gas-hreakdown depends upon the prevailing
reaction conditions and may fluctuate considerably. For
example over the range between 1 and 25% by weight, or even
outside this range in many cases. It is therefore desirable
5. to separate these components from the relevant decomposition~
gases prior to th~ir joint treatment.
Whereas high-boiling components are separated from
the gas obtained by thermal decomposition by condensation
during cooling, and whereas acid gases, especially hydrogen-
lO. sulphide, are separated by washing, preferably carried outduring the compression of decomposition-gas, between two
compression-stages, at an intermediate pressure, dimethvl-ether
is preferably separated ~rom the methanol-decomposition gas
also at an elevated pressure. If the methanol-decomposition
15. is carried out at an elevated pressure, for example between
5 and 12 bars, it is possible to clean the decomposition-gas
at this pressure. If the thermally obtained decomposition-
gas is cleaned at a corresponding or lower pressure-level,
the cleaned decomposition-gases may then be further processed
20. during the compression process.
In order to eliminate the detrimental effect of
dimethyl-ether upon the breaking down of decomposition-gas,
the methanol decomposition-gas is subjected, according to
another special aspect of the method according to the invention,
25. to washing whereby, in addition to the dimethyl-ether, carbon-
dioxide, which is also detrimental to low-temperature gas
breakdown, is also washed out. The cleaned decomposition-gas,
which then contains substantially only Cl to C~ hydrocarbons,
g _
can then be processed in a low-temperature gas-breakdown
installation.
According to a preferred configuration of this variant
of the invention, washing is carried out at above-atmospheric
5. temperature, since this permits a substantial reduction in
the volume of gas to be cleaned and the amount of washing
liquid required which, in turn, leads to smaller components
and thus to cost-savings.
According to a further desirable configuration of
10. this variant, the washing agent loaded with dimethyl-ether and
carbon-dioxide is sub~ected, after it has been removed from
the washing stage, to partial regeneration by expansion or
heating. The dimethyl-ether and car~on-dioxide, which boil
easily, then gas at least partly out o the washing liquid.
15. A~ter the separation of these componenl:s~ which may then be
put to any suitable use, regeneration of the washing agent is
a relati~ely simpl~ matter. It is particularly desirable to
expand the washing agent down to the pressure of the methanol-
decomposition since, in this case, the dimethyl-ether-rich gas-
20- fraction,arising during the expansion, may be returned directly
to the decomposition process.
Separation of the dimethyl-ether and carbon-dioxide
from the decomposition-gas may be effected with any suitable
washing agent, for example methanol, ethanol, water or mixtures
25. thereof.
In one particularly preferred configuration, the
washing is carried out with methanol. Thus has the substantial
-- 10 --
3.;i:~73~
advantage that methanol is in any case used as the decomposition
material and is thus in any case introduced as a material into
the method. There is thus no need to have another substance
available as a washing agent. Washing with methanol is also
5. particularly favourable because the loaded washing agent
need not be regenerated in a separate stept but may be passed
directly to the methanol-decomposition unit. Since, in this
way, any unreacted dimethyl-ether is returned to the de-
composition unit, the yield of desired decomposition~products
10. is increased.
As already mentioned, methanol-decomposition comprises
essentially two partial reactions, to wit the conversion of
methanol into dimethyl-ether and the production of the de-
composition-gas rom the dimethyl-ether. By using a suitable
15. catalyst, these two partial reactions may take place in a
single reactor. It is, however, also possible largely to
separate the two reactions from each other and to carry them
out in different reactors. If the methanol-decomposition unit
contains a separate reactor for the decomposition of the
20. intermediate product dimethyl-etherJ it is particularly desirable
to pass the gas, arising during degasification of the washing
agent, directly to this second reaction-stage. r~he partly
regenerated washing methanol, arising as a liquid after de-
gasification of the washing agent, may then be passed, with
25. fresh methanol, to the first reaction-stage. The part-
fractions of washing agent, arising during expansion~ are thus
returned to favourable locations in the decomposition-process.
-- 11 --
73'~
If the methanol-decomposition is carried out in a
single-stage process, it is desirable in many cases to react
the dimethyl-ether-rich gas, arising during degasification of
the washing agent, in a separate decomposition-stage arranged
5. in parallel with the methanol-decomposition. This not only
provides optimal conditions for converting the dimethyl-ether
into the decomposition-gas, but the elimination of dimethyl-
ether from the first reaction-stage of the methanol decompo-
sition also has a favourable effect upon the reaction-
lO. equlibrium therein obtaining. Decomposition-gases formed in
units arranged in parallel may then be cleaned and processed
jointly.
Most of the carbon-dioxide washed out o~ the de-
composition gas is contained in the components gassing out of
15. ~he washing agent. When this fraction is re-turned to the
decomposition unit, the presence of carbon-dioxide, within
certain limits, is very favourable, since this ma~es it pos-
sible to avoid premature carbonization in the decomposition-
reactor. ~owever, if so much carbon-dioxide is washed out
20. that there is too much in the reactor, it may be better to
separate the carbon-dioxidefrom the dimethyl-ether and to
reduce the danger of carbonization in the reactor by passing
to the decomposition-unit only a part of the carbon-dioxide or
water present.
25. Separation of carbon-dioxide from the gassed-out
fraction containing mainly carbon-dio~ide and dimethyl-ether
may be effected by washing with water. This produces a wash-
water loaded with dimethyl-ether which may be passed, after
- 12 -
73~4
expansion, directly to the decomposition-unit, any carbon-
dioxide not washed out being taken off as residual gas.
Another characteristic of the invention, finally,
relates to a special way of cooling the decomposition-gas in
5. cases where hydrocarbon-decomposition is carried out in parallel
with methanol-decomposition. In this case, the special im-
plementation of the method is characterized in that cooling
of the methanol-decomposition gclses is carried out at least
in part under production of steam at an elevated pressure; in
10. that the gas from the thermal decomposition is cooled at least
in part under the production of steam at an elevated pressure;
in that the cooled decomposition-gases are compressed if
necessary and are passed jointly to the decomposition-gas
breakdown unit, the steam obtained during cooling of the
15. decomposition-gases producing work upon being expanded, and
the energy thus obtained being used at least in part of com-
pressing the decomposition-gases.
This method~variant is based upon two different
decomposition processes, on the one hand from the conventional
20~ decomposition of hydrocarbons and, on the other hand, from
the catalytic decomposition of methanol. The use of the two
flows of material makes the method extremely flexible, since
rapid adaptation to differing conditions of raw-material supply
is made possible by varying the relative amount of material
25. used.
The thermol decomposition is carried out under usual
reaction conditions, i.e. in an externally heated tube-reactor,
- 13 -
at temperatures of between 750 and 900C, for example at830C, with short periods of residence of 0.1 to 1 sec., in
a decomposition furnace, and at atmospheric pressure or at a
pressure slightly there-above. The highly reactant gas arising
S. at this high temperature is immediately quenched down to
temperatures at which unwanted secondary reactions no longer
take place.
Compressing decomposition-gases to the gas~breakdown
pressure, for example to pressures of between 20 and 35 bars,
10. requires a considerable amount of energy. According to the
invention, at least a part of this energy is obtained in that
high-pressure steam, produced during cooling of the two
separately occurring decomposition gases, produces work while
being expanded. Steam may be produced from the ~hermal-
15. decomposition-gas in the usual way, i.e. by indirect heat-
exchange between evaporating water and hot decomposition-gases
emergi~g from the tube-reactor. The heat of reaction arising
during catalytic methanol decomposition may be used in various
ways for producing steam. For example, the reactor may be in
20. one or two stages, the emerging hot decomposition-gases entering
into indirect heat-exchange with a coolant, or cooling may
take place in the reactor itsel~, for example by arranging
cooling tubes in a heap of catalyst or by allowing a coolant
to flow over tubes filled with catalyst.
25. The production of steam in conjunction with methanol-
decomposition may be effected directly, i.e. by direct cooling
o~ the reactor, or of the hot decomposition-gases emerging
from the reactor, with boiling water. With this method, how-
ever, considerable differences may arise, under certain cir-
IL2~734~
cumstances between the heat-exchange media, resulting in high
thermal stresses in the heat-exchangers used. In many cases,
therefore, it is desirable to produce steam indirectly by
interposing a heat-carrier, the said heat-carrier being heated
5. by the heat of the reaction and being then cooled again in a
steam generator with water boiling under pressure. The cooled
heat-carrier may be reheated with reaction-heat and circulated.
Suitable heat-carriers for this configuration of
the invention are molten salts in circulation, for example.
lO. Another advantageous heat-carrier medium is quenching oil as
used for normal cooling of yases from thermal decomposition
of hydrocarbons. A quenching oil of this kind is a high-boiling
hydrocarbon fraction which is spra~ed into the already pre-
cooled thermal decomposition gas, producing a further drop
15. in the temperature of the decomposition-gas as a result of
condensation of high boiling decomposition-products. The
quenching oil is then removed from the decomposition gas and,
after cooling in an open circuit, is returned thereto.
According to one ~avourable configuration of the
20. method according to the invention, part of the quenching oil
used in cooling the thermal-decomposition gas is withdrawn and
is circulated as a heat-carrier for removing the reaction-
heat of the methanol decomposition~ Fresh quenching oil is
fed continously to this circuit, a corresponding amount of
25. excess quenching oil being removed therefrom. This prevents
a decomposition-products formed in the quenching oil cir-
culating at high temperatures from settling and causing in-
adequate heat-removal. The quenching oil taken from the circuit
may be returned to the quenching-oil circuit of the thermal
- 15 -
~L2~
decomposition unit. The amount of fresh quenching oil added
to the circuit, and the amount of quenching oil removed there-
from, may vary within wide limits in view of the special
conditions obtaining. The amount of fresh quenching oil in
5. the circuit may be between 3 and 30, preferably between 5 and
25, more particularly between 10 and 20% by weight.
It is not necessary for all of the preceding con~
figurations of the invention to be carried out for the method
according to the invention to be successful. Instead, each
10. configuration per se~ or in any desired combination with other
configurations, offers substantial advantages for the treat-
ment of methanol-decomposition gases.
Further details of the invention axe described here-
inafter in conjunction with examples of emb~diment illustrated
15. diagrammatically in the drawing attached hereto, wherein:
Fig. l is a block-diagram showing the essential steps
in obtaining olefins by methanol-decomposition;
Fig. 2 shows a special procedure applicable to Cl/C2
separation;
20. Fig. 3 show special procedures applicable to the cleaning
to 5~ of methanol decomposition-gases, the decomposition
being carried out in a single stage in Fig. 3 and
in two consecutive stages in Fig. 4; Fig. 5
showing a modification of the procedure according
25. to Flg. 4;
Fig. 6 shows a special procedure applicable to decompo-
sition-gas cooling.
~ 16 -
In the method according to Fig. 1, a mixture of
methanol and water is fed through line 1 to reactor 2 where it
is converted into a decomposition-gas catalytically, at
tem eratures of 400C and at a pre~sure of 3 bars. It is
5. desirable to add water to the methanol in order to prevent,
or at least delay, carbonization of catalyst particles in
the reactor. The methanol decomposition-gas is removed through
line 3, is raised to an intermediate pressure in compressor 4,
and is then passed, through line 5, to a cleaning stage 6 in
10. which the dimethyl-ether, and any carbon-dioxide present in
the decomposition-gas, are separated. The cleaned decomposition-
gas the passes through line 7 to decomposition-yas compressor
8 where it is raised to low-temperature-gas-breakdown pressure,
for example between 22 and 30 bars. The decomposition-gas
15. then passes, through line 9, to a precooling unit 10 where
it is cooled to a temperature o betwleen about -30 and -50C,
for example by a multistage propane circuit to a temperature
of -35C. The C3 hydrocarbons and high-boiling components
condensing during the precooling are then separated in Cl/C2
20~ separator 11 and are removed through line 12. The remaining
C2 fraction is passed to a low-temperature section 13 which
operates at temperature, below the precooling temperature,
down to about -120 to -150C. In the said low-temperature
section, a fraction of Cl and C2 hydrocarbons occurs in liquid
25. form and is removed through line 14. The remaining gaseous
components, containing mainly methane,hydrogen and small
quantities of C2 hydrocarbons, are removed through line 15
and may be used, after being heated, for various purp~ses,
- 17 -
~2C~73~
possibly separated from each other and at different temperaturelevels. For instance, a fraction containing C2 may be returned
to the decomposition-gas compressor to recover olefin contained
therein.
5. The fraction removed through line 14 is passed to
breakdown part 16 where demethanation is effected. Separated
methane is removed through line 17 and, after being reheated,
is used as a heating gas. The remaining C2 fraction passes,
through line 18, into a cleaning stage 19 where any acetylene
10. contained in the decomposition-gas is separated. The decompo-
sition-gas then passes, through line 20 into ethlene-ethane
separating unit 21 when e':hylene is carried away, through
line 22, as a product-flow and ethane is carried away through
line 23. The ethane is heated and is subjected, in an ethane-
15. decomposition furnace 24, in the presence of water-vapour,
at temperatures between 760 and 900C, and at a pressure o
about 7 bars, to thermal decomposition. After a period of
residence of 0.5 se~., for example, the hot decomposition-
gas emerges, through line 25, from heated tube-reactor 24 and
20. is immediately cooled, in a quenching unit 26, to such an
extent that no secondary reactions takes place. After further
cooling, and separation of high-boiling decomposition-products
in 27, the remaining decomposition-gas is passed to a fixst
compressor stage 28 and is compressed to an intermediate
25. pressure. Since the ethane-decomposition gas contains small
quantities of carbon-dioxide which are detrimental to the
low-temperature part, it is passed to a cleaning stage 29.
- 18 -
~2~7~4~
The cleaned decomposition-gas is then combined with the methanol-
decomposltion gas from line 7 and is broken down in the manner
already described.
In C2/C3 separating unit 11, there occurs in line 12 a
5. C3~ fraction which, at 30, is broken down in a C3 fr2ction and
into heavier hydrocarbons which are removed through line 31.
The C3 fraction is removed through line 32 and, if necessary
after selective hydrogenation of higher unsaturated compounds,
is passed to a propylene-propane separating unit 33. While
10. propylene is removed through line 34 as a method-product, the
propane passes, through line 35, into a thermal-decomposition
stage 36, and is reacted there thermaLly under conditions
similar to those of the ethane in decomposition-stage 24.
The decomposition-gas passes, through line 37, into quench-
15. cooler 26 where it is cooled jointly with the ethane-decompo-
sition gas from line 25 and is further processed.
Fig. 2 shows, in greater detail, the breakdown of
decomposition-gas in the low-tPmperature part. Cleaned
decomposition-gas, which may contain therma-decomposition gas
20. in addition to methanol-decomposition gas, is passed through
line 38 to compressor 8 and is compressed to the gas-breakdown
pressure, for example 25 bars. The decomposition-gas then
passes, through line 9, to precooling unit 10 where it is
cooled by product-flows to be heated and by a circulating
?5. refrigerating agent. C3 and high-boiling hydrocarbons are
condensed, are separated from the decomposition-gas in
separator 39, and are removed through line 40. The remaining
gaseous components are passed, through line 41, to a heat-
-- 19 --
exchanger 42 and are cooled by cold process-flows and by
ethylene evaporating at an elevated pressure, in a refriger-
ating circuit, to a temperature of about -60C. Components
thus condensed are separated in separator 43 and are fed,
5. through line 44 and valve 45, into the lower part of Cl/C2
separating column 46.
~ aseous components remaining in separator 43 pass,
through line 47, to a further heat-exchanger 48 and are cooled
by cold process-flows and, in the case of ethylene evaporating
10. at an average pressure, in a refrigerating circuit, are further
cooled down to about -80C. Componen-ts thus condensing are
separated in separator 49 and are also fed to Cl/C2 separating
column 46 through line 50 and valve 51~ Because o its greater
content oi low-boiling components, the fraction is introduced
15~ into the Cl/C2 separating column at a location above the pre-
viously mentioned feed location.
The gaseous phase in separator 49 consists mainly
of components which boil at a lower temperature than C2
hydrocarbons, i.e. methane and hydrogen in particular, and
20~ also contains a small amount of C2 hydrocarbons. This gas
is removed through line 52 and is cooled in heat-exchanger 53
as ethylene evaporating without pressure in a refrigerating
circuit, and by cold process-flows, to a temperature oi- about
-95Co This produces a methane-rich condensate which also
25~ contains the C2 hydrocarbons still contained in line 52~ This
condensate is separated in separator 54~ is removed through
line 55~ is supercooled in heat-exchanger 56 and is then
- 20 -
34~1~
expanded and cooled in valve 57. The cold thus obtained isreleased to the gaseous fraction remaining in separator 54
which is removed through line 58 and is cooled in heat-
exchanger 56, by cold process-flows, before being further
5. cooledl in heat-exchanger 59, by the expanded evaporating
condensate and being fed to a separator 60. After being
heated in heat-exchangers 56, 53, 48, 42 and 10, the conden-
sate evaporating in heat exchanger 59 is returned to the
decomposition-gas in line 38. By returning this flow to the
10. breakdown-process, the C2 hydrocarbons still contained in the
condensate of separator 54 are made use of, and this increases
the yield of valuable components.
A condensate consisting mainly of methane occurs in
separator 60 at temperatures between about -120 and -150C,
15. for example at -130C. The uncondensed portion of the de-
composition-gas now contains only hydrogen and methane and
is removed through line 61. After releasing its cold-content
to heat-exchangers 56, 53, 48, 42 and 10, it may be used as
heating gas, for example. The condensed me~hane is removed
20. through line 62 and is introduced, through valve 63, into the
top of the Cl/C2 separating column as a return liquid. Using
a pure and super-cold methane fraction as the return to the
Cl/C2 separating column ensures that the methane fraction
removed, through line 46, from the top of the said separating
25. column, contains almost no C2 hydrocarbons. At the bottom
of separating column 46 there occurs a pure C2 fraction which
is fed, through line 65 and valve 66, to an ethylene-ethane
separating column 67. If the C2 fraction from the bottom of
- 21 -
73~
separating column 46 still contains traces of acetylene, a
device for separating the acekylene is arranged between the
two separating columns. In separating column 67, ethylene
is recovered as a top-product and is removed through line 68.
~- After heating by process-flows to be cooled, this fraction
is released as a product. At the bottom of product column 67
there occurs a pure ethane fraction which is removed through
line 69 and, after being heated, is subjected to thermal
decomposition, for example by the procedure illustrated in
10. Fig. 1.
The top-product from Cl/C2 separating column 46 is
removed through line 64 and, ater being heated in heat-
exchanger~ 53, 48, 42 and 10, is released as a heating gas.
Since the low methane ccntent of a methanol-decomposition gas
15. in separaters 54 and 60 results in only small amounts of
condensate which, on the one hand do not produce adequate
cooling in heat-exchanger 59 and, on the other hand, do not
provide an adequate return for the Cl/C2 separating column in
separator 60, part of the top-product from separating column
20. 46 is branched off, after heating, and is returned to the raw
gas through line 70. The return of this fraction is preferably
effected between two compressing stages in compressor 8, at
the pressure-level of separating column 46, for example at
about 10 bars. The methane returned through line 70 will
25. remain, during cooling in heat~exchangers 10, 42 and 48, largely
in the gaseous phase, thus increasing the amount of methane in
the low-temperature unit. As a result of this there are ample
amounts of cGndensate in separators 54 and 60.
- 22 ~
~L2C~73~
In the example of embodiment illustrated in Fig. 3,
fresh methanol is brough in through line 1 and is divided at
2 into a part-flow 3 for decomposition and a part-flow 4 to
be passed to a washing unit. The amount of the part-flow
5. removed through line 4 is governed by the amount of washing
agent required and may make up the entire flow of fresh methanol.
The methanol enters into the upper part of washing column 5
and washes out the ascending decomposition-gases dimethyl-ether
and carbon dioxide arriving through line 6. The washing agent
10. loaded with these components is removed through line 7 and
is expanded, in valve 8 to the methanol-decomposition pressure,
for example between 1 and 2 barsO Components gassing out upon
expansion, consisting mainly o-E dimethyl-ether and carbon-
dioxide, are separated in separa~or 9. The methanol thus
15. partly regenerated is carried away through line 10 and is
passed, jointly with part-flow 3, through line 12, to methanol-
decomposition unit 11. Water is also fed into line 12 through
line 13 in order largely to prevent carbonization of the
catalyst during methanol-decomposition. P~eactox 11 contains
20. a catalyst which is suitable not only for converting methanol
into dimethyl-ether, but also for further conversion to the
desired decomposition-gas. The exothermal reaction is held,
by suitable regulating means, to a temperature of about 400C,
after which the decomposition-gas is cooled and is removed
250 through line 14. Water condensing during cooling of the de-
composition-gas is separated in separator 15 and is removed
through line 16. A part-flow of water passes through line 17
to the top of washing column 5 and washes methanol vapours,
- 23 -
3~
in the upper part of the said wash.ing column, out of thecleaned decomposition-gas, so that the decomposition-gas
removed through line 18 no longer contains any detrimental
contaminants. Another part-flow 19 of the separated condensate
5. may be passed, for example, to line 13 and may re-enter
methanol-decomposition 11. Gas emerging from separator 15
passes, through line 20, to compressor 21 where it is raised
to the pressure of the methanol ~ash, and then, through line
6, to washing column 5.
lO. The cleaned decomposition-gas removed through line
18 is then passed to a low-temperature gas-breakdown unit and
is separated into individual product-flows.
The gaseous raction occurring in separator 9, con-
sisting mainly of dimethyl-ether and carbon dioxide, is removed
15. through line 22 and is passed to a separate decomposition-
stage 23 where the dimethyl-ether is converted into decompo-
sition-gas. Decomposition is effected under conditions similar
to those in decomposition unit 11, but at lower reaction-
temperatures of about 300C~ The emerging decomposition gas
20. is removed through line 24 and is mixed with the decomposition-
gas in line 14.
The carbon-dioxide content of the gas in line 22
eliminates any tendency to carbonization in reactor 23. If
the amount of carbon-dioxide in this fraction is not enough
25. to ensure adequate protection against carbonization, a further
part-flow of the water obtained in separator 15 may be passed
to the gas in line 22.
- 2~ ~-
~æ~734~
According to another configuration of the inve~ion,
the methanol-water mixture separated in separator 9 may be
divided into two part-flows, the part removed through line 10
being returned to the methanol~decomposition unit, whereas a
5- part-flow removed through line 26 is delivered by pump 27,
as a preloaded washing agent, to an area in washing column 5
located below the point of entry of line 4.
The example of embodiment illustrated in Fig. 4
differs from that in Fig. 3 in that decomposition is effected
10. not in two reactors operated in parallel, but in two reactors
operated in series~ The mixture of methanol and water to be
~ed to the methanol-decomposition unit is sub~ected, in a
first reactor 28, to a dimethyl-ether synthesis, after which
the reaction-product passes, through :Line 29, into second
15. reaction-stage 30 where dimethyl-ether decomposition takes
place. The decomposition-gas thus prod~ced is further processed
in the manner already described The gas-fraction occuring
in separator 9 is passed, through line 22, to the inlet to
second reaction-stage 30.
20. The example of embodiment illustrated in Fig. 5
differs from that in Fig. 4 in that carbon-dioxide is separated
from the gas-fraction arising from partial regeneration of
the washing agent. The loaded washing agent removed from the
bottom of the washing column through line 7 is heated in heat-
25. exchanger 31, causing the carbon-dioxide and dimethyl-ether
to pass largely over to the gaseous phase. Separator 9, in
which separation of the components gassing out of the washing
agent is effected, may be in the form of a decanter for
separate removal of higher hydrocarbons washed out of the
- 25 -
decomposition gas. This design of separator 9 is also pO5-
sible in the preceding examples of embodiment.
The gaseous fraction removed from separator 9 through
line 22, and consisting mainly of dimethyl-ether and carbon-
5. dioxide, is fed to the lower part of a washing column 32.Dimethyl-ether is washed out of this gas with water supplied
through ]ine 33, so that carbon-dioxide is removed from the
top of column 32, through line 34, as a residual gas. The
water used for washing may be a part-flow of the water separated
10~ in column 15 from the decomposition-gas. At the bottom of
column 32 there occurs, in liquid phase, a mixture o water
and dimethyl-ether which is removed through line 35, is
expanded in valve 36 to the decomposition-pressure and, after
being mixed with the gas in line 29, is passed to decomposition-
15. stage 30.
Separation of the carbon-dioxide may be carried out
accordingly by a procedure according to the example of
embodiment illustrated in Fig. 3.
In the example of embodiment illustrated in Fig. 6,
20. a hydrocarbon, for example ethane, propane, naptha or a gas-
oil, is fed, together with water-vapour, to a furnace 2 for
thermal decomposition. Furnace 2 is a tube-reactor in which
the decomposition-charge is passed through the externally
heated tubes. The energy required for endothermal reaction
25~ is obtained by the combustion of a heating medium supplied
through line 3. Hot combustion-gases emerge from the furnace
- 2~ -
i ~7~
through line 4 and pass to a stack 6 after recovery of heat
in a heat-exchanger 5 and, if necessary, additional heat-
exchangers not shown in the said -figure. Decomposition-gases
emerging from furnace 2 through line 7 are passed directly
5. to a first heat-exchanger 8 where they are cooled by water
boiling under high pressure to such an extent that no un-
wanted secondary reactions occur. Depending upGn the type of
decomposition-charge, the precooled decomposition-gas is usually
at a temperatuxe o between 350 and 480C. In order to produce~
10. from the decomposition-gas, as much energy as possible in the
form of high press~re, an attempt is made to keep the outlet
temperature from heat-exchanger 8 as low as possible, but this
must not be below the dew-point of the decomposition-gas, in
order to avoid contamination or obstruction o the heat-
15. exchanger and subsequent lines. Cooled quenching oil issprayed, at 10, or ~urther cooling, :into the precooled decompo-
sition gas removed through line 9. Direct heat-exchange with
the quenching oil produces further cooling of the decomposition-
gas down to below the dew-polnt, so that the high-boiling
20. decomposition-products condense. The mixture of decompo-
sition-gas and ~uenching oil passes to an oil-wash 11 in which
the condensed components are washed out of the flow of
decomposition-gas. To this end, a high-boiling hydro-carbon
fraction is fed to the top of oil-washing column 11. The
25. decomposition-gas, now at a temperature of between 100 and 120C,
is removed from the top of oil-washing column 11 through line 13
and, after further cooling and, if necessary, cleaning, is
passed through line 15 to decomposition-gas compressor 16. The
- 27 -
:lL2~3~4
compressed decomposition-gas then passes,through line 17, to
the low-temperature gas-breakdown unit not shown in the drawing.
Methanol-decomposition is carried out in parallel
with the decomposition of the hydrocarbons, to which end a
5. mixture of methanol and water is passed to reactor l9 through
line 18. Catalytic conversion is carried out at temperatures
of 400C, and at a pressure of 3 bars, in a reactor cooled
internally by coolant tubes 20. It is desirable to add water
to the methanol in order to prevent, or at least delay,
10. carbonization of catalyst particles in the reactor. The
methanol-decomposition gas is removed through line 21 andt
after cooling, is passed, i necessary9 through a cleaning
treatment 22, to decomposition-gas compressor 16 where it is
compressed jointly with the thermal-d~composition gas.
15. In order to cool the gases from the two decomposi-
tions 2 and 19, a quenching-oil circuit is maintained.
Quenching oil sprayed into the decomposition-gas in line 9
is separated in oil-washing column ll from the bottom of
which its is removed, through line 14, jointly with the con-
20. densed components of the decomposition-gasO ~hereas an
amount of quenching oil, corresponding to the amount of fresh
quenching oil in the decomposition-gas, is removed from the
part of the installation under consideration at this tim2,
the circulating quenching oil is passed, through line 25 and
25. by pump 26, to a heat-exch~anger 27 in which the decomposition-
gas is cooled by a coolant1 for example water boiling under
medium pressure, supplied through line 28 and removed through
line 29. The cooled quenching oil is then sprayed again,
through line 13 and valve 31, at lO, into the hot decomposition-
- 28 -
~2073~
gas in line 9. Before this, however, a part-flow is branched
off through line 32 and control-valve 33 and is passed to a
quenching-oil circuit flowing through heat-exchanger 20 in
the methanol-decomposition and carries away the reaction-heat
5. of the said methanol-decomposition. The quenching-oil circuit
consists of a circulating pump 34 followed by heat-exchanger
20, in which the quenching oil is heated, and by heat exchanger
35 in which the hot quenching oil is cooled by water boiling
under high pressure. A part-flow of cooled quenching oil
10. emerging from heat-exchanger 35 through line 36, is removed
through line 37 and valve 38 and is returned at 39 to line 30.
The amount of quenching oil removed from the circuit through
line 37 corresponds to the amount. of fresh quenching oil
suppli~d through line 32.
15. In the process illustrated i~ Fig. 6, the steam-
system contains a steam-drum 40 which is supplied, through
line 41, with water undQr high pressure which has been heated
almost to the boiling point by heat exchange with hot process-
flows. Water is passed, through line 42, to heat-exchanger 8
20~ where it is partly evaporated. The mixture of boiling steam
and water then passes, through line 43, back to steam drum
40. In the same way, water removed through line 44 is evapor-
ated in heat-exchanger 35 by not quenching oil and is returned,
through line 45 t to the steam-drum. The steam thus produced
25. passes, through line 46, to heat-exchanger 5 where it is super-
heated by hot combustion gases, after which it passes, through
line 47, to a turbine and rroduc~swork in expanding. The
expanded steam is removed through line 49O After complete
condensation, it may be preheated, for example, and pumped
- 29 -
73~
again through line 41 to s-team-drum 40.
The energy obtained by expansion of the steam in
turbine 48 drives decomposition-gas compressor 16 through a
shaft 50.
5. Decomposition-gas compressor 16, illustrated diagram-
matically in Fig. 6, and the work-producing expansion 48 of
the steam, may each be carried out is several stages. For
example, steam produced in drug 40 at a pressure of about 110
bars may be expanded, after being heated, initially to an
10. intermediate pressure of about 40 bars, then, in a further
e~pansion-stage, to a pressure of about 15 bars, and finally
to a low pressure, for example of the order o~ 2 to 5 bars.
In a similar manner, decomposition-gas compression may be
divided into three or four compressor-stages.
- 30 -
