Note: Descriptions are shown in the official language in which they were submitted.
1~- S~79
BACKGROUND OF THE I~ENTION
The invention relates to a process for the
separation of one or more olefinic or aromatic unsaturated
compounds from a liquid, paraffin-rich hydrocarbon
mixture. The invention enables unsaturated compounds
to be almost completely separated from liquid hydrocarbon
mixtures whose components have only slight physical and
chemical differences from each other. The invention
is particularly, but not exclusively, applicable to the
separation of aromatic hydrocarbons from hydrocarbon
mixtures which consist almost wholly of paraffin.
The separation of unsaturated compounds from
paraffin-rich hydrocarbon mixtures is known and has been
carried out for a long time by treating the crude
hydrocarbon mixture with a liquid, such as concentrated
sulphuric acid or a selective solvent, such as liquid
sulfur dioxide or furfural. To achieve almost complete
separation of the unsaturated compounds, however, the
known refining processes involve considerable outlay.
For economic reasons these processes are therefore
usually only used for the primary purification of crude
hydrocarbon mixtures.
Liquid hydrocarbon mixtures which contain
only small amounts of unsaturated compounds can be
further purified in an economic way, as is well known,
by treating with solid adsorption agents. Thus, for
example, the German Offenlegungsschrift P 22 52 305.3
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~k
lQC~779
discloses a process for the production of purified n-
paraffins in which a technically accessible n-paraffin
mixture is freed of carcinogenic polycyclic aromatic
hydrocarbons by treatment with a certain aluminum-oxide
adsorption agent to such an extent that the purified n-
paraffins can be used for the production of biogenic
proteins for use in foodstuffs, In this process the crude
n-paraffins mixtures are passed through a fixed-bed of the
adsorption agent. However, it is difficult and costly to
completely free the adsorption agent again from the aromatic
compounds bound therein and to regenerate it for renewed use.
U. S, Patent 3,409,691 relates to another process
wherein ~he separation of mixtures containing substances
of different polarity is performed using dehydrated
macroporous cation exchange resins in the form of their metal
salts as selective adsorption agents. However this U,S.
patent makes as little mention of economic regeneration
of the used exchange resin as it does of separation, in
particular of polycyclic aromatic compounds which are
contained in only small amounts in a starting material
substantially consisting of higher paraffins,
East German Patent 62 385 discloses a process
by means of which polycyclic aromatics and other dist~rbing
substances can be removed from crude oil paraffins tslack
wax) by adsorption on zeolitic molecular sieves,
Our U,S~ patent 3,960,763 tequivalent to German
Offenlegungsschrift 23 64 333) describes a process for the
purification of crude oil paraffin ~slack wax~ in which
the liquified starting material is treated with a
779
dehydrated macroporous ion exchange resin which is
charged almost completely with metal ions, in particular
silver or copper ions, and which is expediently arranged
as a fixed-bed in a column. This process supplies a
product which fulfills the purity requirements of the
German Manual for Pharmacists and Pharmaceutical Industry
(DAB VII - Deutsche Arzneibuch VII~ and which is therefore
suitable for biogenic protein synthesis, for pharmaceutical
and cosmetic purposes as well as for use in the food in-
dustry. However, the regeneration of the ion exchange
resin used for separation is relatively involved, since
the ion exchange resin must be rinsed with an inert hydro-
carbon, thereafter treated with an alcohol, ether or ketone
in order to desorb the separated aromatics and finally
rinsed again with an inert hydrocarbon and dried.
Our U.S. patent 3,979,280 (equivalent to German
Auslegeschrift 23 64 306) describes and claims a process
for the separation of unsaturated olefinic or aromatic
compounds from liquid hydrocarbon mixtures containing them
wherein the physical-chemical properties of the components
of the mixture differ only slightly or wherein only traces
of the unsaturated compounds occur in the mixture, which
comprises adsorbing the unsaturated compounds on a
macroporous, dehydrated cation exchange resin laden with
a metal ion and having a specific surface area of at
least 1 m2/gram and a pore diameter greater than 10 A, and,
subsequently, displacing the unsaturated compounds using a
normally gaseous hydrocarbon.
The process of U.S. 3,979,280 simplifies the
process of U.S. 3,960,703 in that the unsaturated compounds
of the ion exchange resin are desorbed and displaced in
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6779
U.S. 3,979,280 at temperature of 10 to 40C and pressures
of 1 to 30 atmospheres by employing a normally gaseous
hydrocarbon in the liquid phase as the desorption agent.
Liquified propene or butene are disclosed as preferred
desorption agents. In this process the exchange resin
used for separating unsaturated compounds is rinsed once
only with an inert hydrocarbon and is thereafter
desorbed with the liquified olefin. The desorption agent
is then allowed to evaporate. A second rinsing of the
exchange resin can be dispensed with in this way.
However, a disadvantage of this process is that this
process must be carried out at excess pressure and the
liquified olefins used for desorption sometimes tend to
form polymers, which can impair the regenerability of the
exchange resin.
It is advantageous to further simplify and improve
processes for separating unsaturated compounds, in particular
polycyclic aromatic hydrocarbons, from paraffin-rich hydro-
carbon mixtures by treating with dehydrated macroporous
cation exchange resins in form of their metal salts.
SUMI!$~RY OF THE INVENTION
We have found that the process of separating
unsaturated hydrocarbons from paraffin-rich hydrocarbons
by use of a macroporous cation exchange resin can be
substantialIy improved by employing one or more
mononuclear aromatic hydrocarbons as the desorption agent.
779
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In accordance with the present invention, there
is provided a process for the separation of unsaturated
compounds from a liquid, paraffin-rich hydrocarbon
mixture comprising:
(a) contacting the hydrocarbon mixture
with a dehydrated, macroporous cation
exchange resin in the form of a metal
salt whereby the unsaturated compounds
are adsorbed by the resin,
~b) contacting the resin with a mononuclear
aromatic hydrocarbon at a temperature of
50 to 150C whereby the adsorbed unsaturated
compounds are desorbed.
The desorption of the cation exchange resin is
conveniently carried out at normal pressure.
The cation exchange resin is preferably in the
form of a copper or silver salt~
The process of the invention may be used to
separate unsaturated olefinic and aromatic compounds from
liquid paraffin-rich hydrocarbon mixtures whose components
have only slight physical and chemical differences from
each other.
It will be appreciated that the initial
hydrocarbon mixture may comprise only one paraffin hydro-
carbon.
i779
The unsaturated compounds being adsorbed by
the cation exchange resin may be a single olefin, a mixture
of olefins, a single aromatic, a mixture of aromatics, a
mixture of an olefin and an aromatic, a mixture of olefins
and an aromatic, a mixture of an olefin and aromatics or
a mixture of olefins and aromatics. The olefins may
have from ~ to 25 carbon atoms, The aromatic compounds
include isocyclic and heterocyclic carbon compounds to
which the Huckel rule may be applied, excluding, however
inorganic compounds which also are of an aromatic type,
e,g. borazin. Examples of isocyclic carbon compounds are
benzene and its derivatives, polynuclear aromatics such as
naphthalene, anthracene, phenanthrene, polycyclic aromatics
such as tetracene, pentacene, hexacene and the carcinogenic
hydrocarbons derived from chrysene and pyrene, respectively,
as well as, for example, aniline, nitrobenzene and phenol.
Examples of heterocyclic carbon compounds include pyridin,
furan, thiophene, quinoline and phenanthroline.
~e have found that the processes disclosed in our
U,S~ 3,960,703 and 3,979,280 can be simplified if mono-
nuclear aromatic solvents, such as benzene, toluene and
xylene, are used for the desorption of the ion exchange
resins loaded with the unsaturated compounds, This is
surprising since the adsorptive bonding of aromatic
hydrocarbons to dehydrated, macroporous cation exchange
resins, in particular in the form of silver and copper salts,
was known and had been used for the separation of
~QC~779
aromatically unsaturated compounds from hydrocarbon mixtures.
In view of the fact that particularly higher polycyclic
aromatic compounds are relatively firmly bonded to
such salts of cation exchange resins, it was not to
be anticipated that they could be desorbed and displaced
by mononuclear aromatlcs. In addition, even if the lower
aromatics were able to displace the higher aromatics, it
was to be expected that the desorption agent would be
bonded by the exchange resin and would not be removable
therefrom to a sufficient degree by means of the usual
rinsing treatment with lower aliphatic hydrocarbons.
Surprisingly, it has now been found that these
doubts are unfounded and mononuclear aromatic compounds such
as benzene, toluene and xylene are emminently suitable as
desorption agents. The cation exchange resin, which is
expediently used as a fixed-bed in a separating column, can
be purified prior to desorption in accordance with the
invention in the usual manner by rinsing with an aliphatic ~-
hydrocarbon, for example a C5-Clo saturated aliphatic
hydrocarbon, such as isooctane, Similarly, the cation
exchange resin desorbed in accordance with the invention
can be freed of desorption agent by rinsing with an
aliphatic hydrocarbon and prepared for a new separating
cycle~ As the following examples will show, however, it
is possible to dispense with one or both of these rinsing
stages without noticeably impairing the separating results.
In a particularly simple embodiment of the process of the
invention rinsing of the cation exchange resin with the
aliphatic hydrocarbon prior to and subsequent to desorption
is dispensed with and the major portion of the desorption
779
agent left in the resin is expelled from the cation
exchange resin after desorption by passing nitrogen or
another inert gas through the cation exchange resin.
The thus treated cation exchange resin can be used
again immediately thereafter for separating unsaturated,
in particular aromatic, compounds from fresh charge
material.
By using this greatly simplified technique
inevitably a small amount of the desorption agent is left
in the purified product. The presence of minor amounts
of desorption agent in the purified product does not
constitute a significant disadvantage as regards the
recovery of, for example, paraffinum liquidum tliquid
paraffin~ or paraffinum durum thard paraffin) or pure
n-paraffin mixtures which are suitable for biogenic protein
recovery, since such pure paraffin products have a
considerably higher boiling point than the desorption
agents used in accordance with the invention. Desorption
agents, such as benzene, toluene and xylene, contained
~ in the purified product can be easily removed therefrom by
means of stripping, preferably by introducing steam, so
that despite the use of aromatic desorption agents and
the omission of the rinsing stages with aliphatic hydro-
carbons, paraffin products can be obtained by the process
of the invention, whose conte~ of aromatic hydrocarbon
compounds fully meets or is below the maximum ~alue of
the requirements of the German Manual for Pharmacists and
Pharmaceutical Industry, VII Edition.
lQ96779
The process in accordance with the invention is
preferably conducted with a cation exchange resin, which has
a specific surface area of 40 to 1000 square meters per
gram and a mean pore diameter of 20 to 250 A. Particularly
good results were obtained with a cation exchange resin
having a specific surface area of 500 to 750 m2tg and a
mean pore diameter of 40 to 60 A,
The invention is illustrated by the following
examples. The examples show the possibility of almost
quantitatively separating aromatic compounds and other
polar impurities in three types of purification, namely:
1. complete purification of deoiled slack
wax tExample 21,
2. production of paraffinum liquidum
tliquid paraffin) from hydrogenated
white oils tExample 1 and 4~, and
3. purification of n-paraffins which are
produced by means of the molecular sieve or
urea dewaxing processes tExample 3).
Due to the limited absorption capacity of the
exchange resin with respect to unsaturated compounds,
the aromatic content of the starting material is reduced
by hydrogenation tof the distillate) in the production
of paraffinum liquidum tas in Examples 1 and 4). The
can also be achieved by deoiling upon complete purification
of slack waxes derived from cold dewaxing (as in
Example 2). In the case of a higher content of aromatics
the adsorbent has to be regenerated frequently, thereby
779
reducing the useful life of the resin. N-paraffins
from molecular sieve dewaxing or urea dewaxing can be
employed without subjecting them to pretreatment (as
in Example 3). The cation exchange resin used in
examples,~n)amely a macroporous cation exchange resin,
''~t" Amberlitel~XE 284, has a silver content of 25 to 27% by
weight, based on the dried resin, and a surface area of
380 to 440 m2/g of dried resin tdetermined according to
the method of Brunauer, Emmet and Teller with N2).
The tests in the examples are performed with an
apparatus in which an adsorption tower is charged from
the bottom to the top with the starting material. After
adsorption is completed, the starting material is either
displaced from the adsorption resin with a saturated hydro-
carbon and thereafter with a mononuclear aromatic, or
desorption is directly performed without a rinsing stage.
The next adsorption can be directly performed after
desorption, or it can be performed after rinsing with the
saturated hydrocarbons.
The process parameters in the production of
paraffinum liquidum ~liquid paraffin~, paraffinum durum
thard paraffin) and n--paraffins in the examples
can be seen from Table 1. Toluene is employed as the
desorption agent at a temperature of 90C and a space
velocity of 0.5 V/V of resin/hour. Rinsing before and
after desorption is performed with a saturated hydro-
carbon, in this instance, isooctane.
The use of one or more aromatic compounds as the
desorption agent has the advantage that the useful life of
the ion exchange resin is considerably prolonged. In
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779
the case of the previously used ketone desorption agent
undesired side-reactions may take place in which poly-
condensates, inter alia, are formed, which reduce the
adsorptive capacity of the ion exchange resin. Thus,
when using a ketone as a desorption agent, the resin is at
only 50% of its full capacity after lO cycles of adsorption
and desorption. When using mononuclear aromatic compounds
as desorption solvents, the resin is at 90% of its
capacity after lO cycles and still has 75% of its initial
capacity after 40 cycles.
Tables II, III and IV show the success attainable
with the present process for the almost quantitative
separation of unsaturated compounds from liquid hydro-
carbon mixtures. The n-paraffins from Table IV are
particularly suitable as the starting product for biogenic
production of protein~
Table V shows that omission of both rinsing
steps, as compared with the normal method of working
tadsorption, rinsing, desorption, rinsing~, does not
lead to reduction in separating capacity. The process
conditions correspond to those given in Table I
Referring to Table V, cycles l to 3 were performed without
rinsing with a saturated hydrocarbon (only adsorption/
desorption1, cycles 4 to 6 with rinsing tadsorption/
rinsing/desorption/rinsing). All cycles were performed
successively without changing the resin.
A comparison of cycles l to 3 with cycles 4 to
6 shows that they have almost the same throughput. Hence,
it is clearly demonstrated that, depending on the
requirements, the process can be performed with or without
1~96779
the rinsing stages,
The W extinction at 275 nm was used as a
measure of the aromatics content of the charge stocks
and products according to "DAB" VII. In the case of
charge stocks with UV extinctions in excess of 1, the
values were measured after dilution with isooctane and
thereafter converted.
The determination of the sulphur content was
performed with the aid of X-ray fluorescence.
The results of the examples show that the
present process can be particularly advantageously used
for removing traces of aromatic compounds. Hydrocarbon
mixtures preferably used as feed stocks preferably have
an aromatics content of less than 5,000 parts per million.
At a constant capacity for the aromatic compounds, the
purified product amount per cycle is conversely
proportional to the concentratlon of aromatic compounds.
~: ~ lQ96779
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-13-
lQq~77~
It will be appreciated that steps 2 and 4 in this
Table are not carried out in cycles 1 to 3 of Example 4.
EXAMPLE 1
Production of paraffinum liquidum (light)
The charge materials were white oils which
were produced from twice extracted spindle oil distillate
tboiling range: 400 to 450C) by refining several times
with oleum (20 % SO3). Three white oils were employed
which differed in their aromatics concentration (expressed
in terms of W extinction at 275 nm at a cuvette width of
0.5 cm).
In contrast to the adsorption treatment, the
respective charge oils were subjected to conventional
treatment with oleum t20 % SO3) in several stages, 7 % of
oleum being used at each stage: treatment was carried out
until the treated oils achieved the specifications in
accordance with DAB VII. The results are shown in Table II.
TABLE II
White Oil
I II III
Charge material
Extinction at 275 nm 9.6 18.6 27.6
~0.5 cm~
De-aromatization
V(feed//V~resin)/cycle 10.0 5.0 2.5
Extinction at 275 nm
(0.5 cm) 0.751) 0-751' 0 75 )
after de-aromatization
Treatment with 20~ 3 x 7% 4 x 7 % 5 x 7 %
strength oleum
Extinction at 275 nm
~0.5 cm) 0.41 0.48 0.69
after aleum treatment
1) result after 5th cycle
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lQ96i779
EXAMPLE 2
Production of high-purity paraffinum durum according to
the DAB VII (Deutsche Arzneibuch VII - German Manual
for Pharmacists and Pharmaceutical Industry)
Charge material: slack wax (from the solvent
neutral oil of the SAE Class 5), pretreated with 0.5% by
weight of tonsil, 2 to 3 ~ by weight of oil content.
The average charge for 10 cycles amounted per
cycle to 14 kg of pure paraffin~kg of resin. The charge
material and end product had the analytical data shown in
Table III.
TABLE III
Charge material Purified paraffin
Sulphur ppm 300 20
Ext, at 275 nm
~2 cm cuvette)
0.5 g of paraffin in 50 1.8 0.25*
ml of isooctane tDAB
VII specifications)
*The maximum extinction of 0.6 permissible per se in
accordance with DAB could not be fully used as the
required sulphuric acid reaction ~according to DAB VII)
does not take place in accordance with the specifications
when the extinction value exceeds 0.25,
EXAMPLE`3
Purification of n-paraffins from the molecular sieve
process
The process conditions are given in Table I.
The charge product and the end product had the
analytical data shown in Table IV below.
~Q~6779
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--16--
lQq~779
For the purpose of comparison with adsorption treatment,
the Cl3-Cl6 was treated with 33% by weight of oleum
(4.5 % SO3). The extinction in the case of the treated
product was 0.45 at 270 nm tCuvette 1 cm).
Example 4
Production of paraffinum liquidum (PL)
The same charge material was used as in the
Example I except that it has a somewhat lower content of
aromatic compounds tcf. white oil I).
The product after de-aromati2ation: extinction at
275 nm tO.5 cm) = 0.8 tin accordance with DAB VII for PL).
Results are shown in Table V below.
TABLE V
Cycle Vtfeed)/Vtresin)/cycle
1 11.2
2 10.9
3 lO.9
4 10.8
10.8
6 lO,9
Cycles l to 3 : without rinsing
Cycles 4 to 6 : with rinsing before and after
desorption.
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