[0001] The present invention relates to a process for the production of
hydrocarbons and to a corresponding plant according 5 to the preambles of the
independent patent claims.
PRIOR ART
10 [0002] Processes and plants for steam cracking hydrocarbons are described,
for example, in the article “Ethylene” in Ullmann's Encyclopedia of Industrial
Chemistry, online edition, April 15, 2009, DOI:
10.1002/14356007.a10_045.pub2. Steam cracking (in German also referred
to as “Dampfspalten”) is mainly used for the production of short-chain olefins
15 such as ethylene and propylene, diolefins such as butadiene, or aromatics, but
is not limited to the production of such compounds.
[0003] Steam cracking yields component mixtures (also referred to as cracked
gases or raw gases) that are subjected to suitable processing sequences to
20 recover the desired individual components. Typically, the front-end section of
a corresponding treatment sequence involves the removal of heavy
compounds, if any, followed by a so-called raw gas compression and acid gas
removal. After processing in the front-end section, a fractionation process
takes place, in which different fractions are formed by thermal separation
25 processes and are further separated as required. For details, please refer to
the mentioned article “Ethylene” in Ullmann's Encyclopedia of Industrial
Chemistry, particularly Sections 5.3.2.1, “Front-End Section,” and 5.3.2.2,
“Hydrocarbon Fractionation Section.”
30 [0004] In one embodiment of corresponding fractionation, which can also be
used in connection with the present invention, hydrocarbons having two
carbon atoms and lower-boiling components such as methane and hydrogen
2
are initially separated from hydrocarbons having three carbon atoms and
higher-boiling compounds in fractionation. Such a step is usually also referred
to as deethanization, the design of corresponding fractionation is referred to
as a “deethanizer-first” or “front-end deethanizer” process.
5
[0005] The fraction of hydrocarbons having two carbon atoms and lower boiling
components obtained in gaseous form in deethanization can be fed to a further
separation, in which the hydrocarbons having two carbon atoms are separated
from the also contained lower boiling components. Such a step is also called
demethanization. Thus, in a “deethanizer-first” 10 or “front-end deethanizer”
process, demethanization is downstream of deethanization.
[0006] In alternative processes, the deethanization and demethanization steps
can also be performed in reverse order. This is then referred to as
15 “demethanizer-first” or “front-end demethanizer” processes. Further process
variants are described in the mentioned technical literature.
[0007] The present invention relates to all processes and process variants with
which a component mixture containing hydrocarbons having two carbon atoms
20 and lower-boiling components, in particular methane and hydrogen, is used or
obtained at any point in corresponding fractionation, and with which such
component mixture, hereinafter also referred to as a “feed mixture,” is
subjected to demethanization. Depending on the design of fractionation and in
particular the use for steam cracking, the feed mixture can also contain smaller
25 or larger amounts of higher boiling components, in particular hydrocarbons
having three carbon atoms, hydrocarbons having four carbon atoms, and
possibly also hydrocarbons having more than four carbon atoms of the usual
type.
30 [0008] Typically, temperatures below -130°C to -150°C are required for
sufficient separation of the hydrocarbons having two carbon atoms from the
lighter components, irrespective of whether higher boiling components are also
3
contained in a corresponding feed mixture, i.e. in demethanization, and
comparatively complex separation apparatus is required, as explained in detail
below.
[0009] EP 1 024 187 A1 relates to a process for 5 recovering an ethylene-rich
fraction by means of combined adsorption and rectification from an olefincontaining
mixed fraction withdrawn from a cracking furnace, in particular from
an ethylene cracked gas, wherein a fraction substantially containing H2, CH4
and CO is separated from the olefin-containing mixed fraction by adsorption or
10 permeation, and then the fraction containing the remaining components is fed
to the rectification process. There, a fuzzy C1/C2 separation takes place in
rectification, and at least one fraction depleted in terms of C2 components is
recycled upstream of the adsorptive or permeative separation stage. The
adsorptive or permeative separation stage can be followed by at least one
15 further adsorptive or permeative separation stage, wherein in this stage, a
fraction rich in C2 components is separated from the fraction containing H2,
CH4 and CO separated in the first separation stage. The process proposed
here is to enable a reduction in the gas streams to be processed in the cold
separation section and a cut-back of low-temperature demethanization,
20 leading to an overall reduction in investment costs and refrigerant compressor
capacity.
[0010] Processes for the treatment of gas mixtures are known from other
technical fields, but they are not suitable for the treatment of gas mixtures from
25 a steam cracking process, in particular under the boundary conditions
explained below, or are not advantageous or obvious for this purpose.
[0011] For example, US 2016/146534A1 discloses a process comprising the
steps of: Treating a feed stream to obtain a treated gas stream; at least partially
30 cooling and condensing the treated gas stream in at least one heat exchanger
in order to form at least one column feed fraction; feeding the at least one
column feed fraction to a distillation column in order to recover an ethylene
4
stream at the bottom of the distillation column and an ethylene-depleted head
stream at the top; and heating at least one downstream stream derived from
the head stream in the heat exchanger. As explicitly stated in this publication,
this process is not directed to the processing of a product stream of a steam
cracker, but to other ethylene sources that provide 5 a feed stream of widely
varying composition. The feed stream is explicitly obtained from nonconventional
ethylene sources and not through a high temperature cracking
process of hydrocarbons in the presence of steam.
10

I/We Claim:
1. A process (100) for the production of hydrocarbons, wherein a
component mixture containing the hydrocarbons is provided and, using at least
a portion of the component mixture, a feed 5 mixture containing hydrocarbons
having two, or two and more, carbon atoms and lower boiling compounds is
provided, and wherein a heavy fraction and a light fraction are formed using
the feed mixture, wherein the heavy fraction contains a portion of the
hydrocarbons having two, or two and more, carbon atoms from the feed
10 mixture and is poor in or free from the lower boiling components, and wherein
the light fraction contains a portion of the lower boiling components from the
feed mixture and is poor in or free from the hydrocarbons having two, or two
and more, carbon atoms, characterized in that the process comprises
providing the component mixture at least in part by steam cracking (1), that the
15 heavy fraction and a first intermediate fraction are formed in a low-temperature
separation process (10) using at least a portion of the feed mixture, that at
least a portion of the first intermediate fraction is subjected to a non-cryogenic
separation process (20) while obtaining the light fraction and a second
intermediate fraction, wherein the non-cryogenic separation process (20) is
20 downstream of the low-temperature separation process, and that at least a
portion of the second intermediate fraction is recycled to the process, wherein
the first and second intermediate fractions each contain a portion of the
hydrocarbons having two, or two and more, carbon atoms and the lower boiling
compounds from the feed mixture.
25
2. The process (100) according to claim 1, wherein an adsorptive
separation process, in particular a pressure swing adsorption, is used as noncryogenic
separation (20).
30 3. The process (100) according to claim 1 or 2, wherein said providing the
feed mixture comprises compressing (8) at least a portion of the component
mixture formed by the steam cracking (1).
26
4. The process (100) according to claim 3, wherein at least a portion of the
second intermediate fraction is recycled to the process (100) upstream of said
compression (8) and is compressed therein.
5
5. The process (100) according to any one of the preceding claims,
wherein the provision of the feed mixture comprises pre-cooling, drying and/or
hydrogenation (17) and/or at least partial removal (18) of hydrocarbons having
three or three and more carbon atoms.
10
6. The process (100) according to any one of the preceding claims,
wherein the low-temperature separation process (10) comprises forming one
or more condensates using one or more cooling apparatuses (11) and one or
more separation apparatuses (12, 13), and separating at least a portion of the
one or more condensates in 15 a separation column (14).
7. The process (100) according to claim 6, wherein forming the one or
more condensates using the one or more cooling apparatuses (11) and the
one or more separation apparatuses (12, 13) comprises single-stage or multi20
stage cooling to a temperature level of -60 to -80°C.
8. The process (100) according to claim 7, wherein at least a portion of a
residue remaining in gaseous form upon the formation of the one or more
condensates using the one or more cooling apparatuses (11) and the one or
25 more separation apparatuses (12, 13) and/or an overhead gas of the
separation column (14) is used at least in part to form the first intermediate
fraction.
9. The process (100) according to claim 8, wherein at least a portion of the
30 first intermediate fraction is heated using the one or more cooling apparatuses
(11) used in forming the one or more condensates before being fed to noncryogenic
separation (20).
27
10. The process (100) according to any one of the claims 6 to 9, wherein a
portion of the one, or at least one, of the plurality of condensates is expanded,
thereafter heated using the one or more cooling apparatuses (11) used in
forming the one or more condensates, 5 thereafter compressed and recycled to
the process (100).
11. The process (100) according to any one of the claims 6 to 10, wherein
the formation of the one or more condensates using the one or more cooling
10 apparatuses (11) and the one or more separation apparatuses (12, 13) is
performed at a pressure level of 25 to 40 bar, and wherein the separation
column (14) is operated at a pressure level of 20 to 35 bar.
12. The process (100) according to any one of the preceding claims,
15 wherein a refrigerant is passed through the one or more cooling apparatuses
(11).
13. A plant for the production of hydrocarbons, with means that are
configured to provide a component mixture containing the hydrocarbons and
20 to provide, using at least a portion of the component mixture, a feed mixture
that contains hydrocarbons having two, or two and more, carbon atoms and
lower boiling compounds, and with means that are configured to form, using
the feed mixture, a heavy fraction and a light fraction, wherein the heavy
fraction contains a portion of the hydrocarbons having two, or two and more,
25 carbon atoms from the feed mixture and is poor in or free from the lower boiling
components, and wherein the light fraction contains a portion of the lower
boiling components from the feed mixture and is poor in or free from the
hydrocarbons having two, or two and more, carbon atoms, characterized in
that the plant has means that are configured to recover the component mixture
30 containing the hydrocarbons at least partly by steam cracking, a lowtemperature
separation unit (10) that is formed and operated such that the
heavy fraction and a first intermediate fraction are formed therein using at least
28
a portion of the feed mixture, a non-cryogenic separation unit (20) is
downstream of the low-temperature separation unit (10) and is configured to
process at least a portion of the first intermediate fraction to obtain the light
fraction and a second intermediate fraction, and means that are configured to
recycle at least a portion of the second intermediate 5 fraction to the process,
wherein the first and second intermediate fractions each contain a portion of
the hydrocarbons having two, or two and more, carbon atoms and the lower
boiling compounds from the feed mixture.
10 14. The plant according to claim 13, which is configured to perform a
process according to any one of the claims 1 to 12.