Selective permeation of aromatic hydrocarbons through polyethylene glycol impregnated regenerated cellulose or cellulose acetate membranes

Aromatic hydrocarbons present in a hydrocarbon feed stream containing a mixture of aromatic hydrocarbons and non-aromatic saturated organic components are separated from said hydrocarbon feed stream by selective permeation of the aromatic hydrocarbon through a regenerated cellulose or cellulose acetate membrane which has been impregnated with polyethylene glycol. The thus treated membrane possesses high selectivity for aromatic hydrocarbons at a high flux. The amount and type of polyethylene glycol impregnated into the membrane is carefully controlled in order to achieve high aromatic selectivity and high flux.

BRIEF DESCRIPTION OF THE INVENTION 
Hydrocarbon feed streams containing aromatic and saturated components are 
selectively separated into aromatic rich and aromatic lean phases by the 
selective permeation of the aromatic components through specially treated 
hydrophilic membranes selected from regenerated cellulose and cellulose 
acetate under pervaporation conditions. Regenerated cellulose as such has 
little selectivity for aromatic hydrocarbons in preference to non-aromatic 
components of a feed stream, and has a low flux. However, it has been 
discovered that regenerated cellulose membranes can be rendered selective 
and permeable to aromatic hydrocarbons by impregnating the regenerated 
cellulose, prior to use, with carefully controlled quantities and types of 
polyethylene glycol. Similarly, cellulose acetate membranes containing 
polyethylene glycol exhibit very high selectivities for aromatic 
hydrocarbons. 
In its preferred embodiment, the hydrocarbon feed stream being separated is 
made up of a mixture of aromatic and saturated hydrocarbons and is most 
typically a reformate stream such as a gasoline reformate stream. Such 
streams are presently separated by solvent extraction using solvents such 
as sulpholane, glycols, SO.sub.2, etc or they can be enriched in aromatics 
by distillation. 
The present process employing polyethylene glycol impregnated regenerated 
cellulose and cellulose acetate membranes can selectively remove aromatics 
from these mixed feed streams to reduce the severity of solvent extraction 
or eliminate distillation. This reduces the high energy consumption 
requirements of the conventional processes augmented or replaced by the 
membrane separation process.

BACKGROUND OF THE INVENTION 
The separation of aromatics from saturates is desirable in many processes. 
An increase of aromatics content in reformates leads to a higher octane 
rating motor fuel. Aromatics are also recovered from other similar streams 
for the preparation of various arylalkylates and for aromatic solvent 
production. 
The separation of aromatics from saturates is presently achieved using a 
variety of techniques, e.g., distillation (conventional, vacuum, 
extractive or azeotropid); solvent extraction using sulpholanes, glycols 
or SO.sub.2 ; adsorption using molecular sieves such as natural or 
synthetic zeolites. Other techniques have also been proposed including 
complexation of aromatics with various chemicals such as cyclodextrins, 
and membrane separation processes. 
Membrane separation processes are attractive due to their simplicity and 
low energy consumption. In separating aromatics from saturates various 
constraints are imposed on the membrane process by the very nature of the 
feed streams involved such as physical and chemical similarities. 
In light of these restrictions and obstacles, pervaporation has come to be 
recognized as a suitable membrane separation process for the separation of 
aromatics in low molecular weight hydrocarbon streams (&lt;C.sub.10). 
Pervaporation is a process in which specific components of a liquid feed 
stream selectively dissolve into and diffuse through a thin film. 
Downstream of the film, these components are removed by evaporation from 
the surface by applying vacuum or sweeping with an inert fluid. 
Various polymeric films have been used under pervaporation conditions. 
These include hydrophobic polymers such as polyethylene, polypropylene and 
polyvinylidene fluoride, hydrophilic polymers such as ethyl cellulose and 
cellulose acetate butyrate and aromatic containing polymers such as 
polyethylene styrene copolymer, aromatic polyurethanes, crosslinked 
polystyrene, and aromatic polyphosphonate-cellulose acetate polymeric 
alloys. Separation factors ranged from 1 to 20 and flux ranged from 
1.times.10.sup.-2 to 1.times.10.sup.-5 m.sup.3 /m.sup.2 day. Aromatic 
containing polymers generally showed high selectivity for aromatics but 
had moderate fluxes. (See U.S. Pat. No. 2,970,106; U.S. Pat. No. 
3,043,891; U.S. Pat. No. 2,958,656; U.S. Pat. No. 2,947,687; U.S. Pat. No. 
2,958,657; German Pat. No. 2,626,629; and U.S. Pat. No. 3,930,990). 
The use of liquid membranes to separate aromatics from saturates is an 
alternative to pervaporation through polymeric films. Liquid membranes are 
made up of hydrocarbon/surfactant/water emulsions in heavy mineral oils. 
The hydrocarbon mixture is emulsified in an aqueous phase composed of a 
surfactant (e.g., saponin), a water soluble polar compound (e.g., 
glycerol, polyethylene glycol), and water. When this emulsion is dispersed 
in a heavier oil solvent, stable drops are formed such that the aqueous 
phase forms a thin film between the two hydrocarbon phases. The glycerol 
(or PEG) used to increase the drop stability and overall separation 
efficiency. The glycerol (or PEG) also enhances the solubility of the 
aromatics in the aqueous phase and hence their migration through the 
liquid membrane. Separation factors up to 20 have been achieved. The 
drawbacks of this process are the low stability of the droplets, the 
complexity of the operation and problems associated with recovery and 
recycle of the constituents making up the liquid membrane droplets. 
To overcome the problems and limitations associated with liquid membranes 
while taking advantage of their high selectivity, the immobilization of 
the liquid membranes in a porous matrix was developed. Immobilized liquid 
membranes are extractive liquids trapped in the porous matrix or on the 
surface of a solid such as a polymer membrane. 
Several methods for immobilizing a liquid in the matrix of a membrane to 
form an imobilized liquid membranes have been described in the prior art. 
See for example, Chemistry Letters, 1980, pg. 1445-1448; U.S. Pat. No. 
3,625,734; U.S. Pat. No. 4,039,499; "Membranes for Pressure Permeation" by 
Friedlander and Lutz, Membrane Processes in Industry and Biomedicine, M. 
Bier, ed., Plenum Press, N.Y.-London 1971 (pg. 73-99); U.S. Pat. No. 
3,447,286; U.S. Pat. No. 3,335,545; Recent Developments in Separation 
Science, Volume I, CRC Press (1973), pg. 153 ff, Recent Developments in 
Separation Science, Volume V, CRC Press (1979), pg. 11 ff; U.S. Pat. No. 
3,450,631; U.S. Pat. No. 4,060,566; Ind. Eng. Chem. Process Dis. Develop 
12(3) 1973; Japanese Kokai Sho 53 (1978) 70084. Methods include: 
1. Supporting the liquid film on a porous unwet backing. 
2. Supporting the liquid film on a non-interacting polymer film. 
3. Swelling the polymer film with liquid. 
4. Casting the polymer and liquid together into a film. 
5. Forming a gel using the liquid. 
6. Supporting the liquid film in a porous polymer film. 
An immobilized liquid membrane has been used for aromatic/saturate 
separation by pervaporation. This membrane was prepared by casting a 
mixture of polyvinylidene fluoride and 3-methyl sulfolane, which is an 
aromatic extraction agent. (J. of Applied Polymer Science, Volume 26, 
489-497 (1981)). Pure polyvinylidene fluoride membranes have high 
selectivity (18 for benzene/cyclohexane) but low flux (of 10.sup.-5 
m.sup.3 /m.sup.2 day at 60.degree. C.). Incorporating 3-methyl sulfolene 
up to 25 wt.% decreases the selectivity to 8 and increases the flux to 
10.sup.-3 m.sup.3 /m.sup.2 day at 60.degree. C. 
Schordinger .alpha.- and .beta.-cyclodextrins in a hydroxylpropylmethyl 
cellulose membrane have also been used for the separation of aromatics by 
pervaporation (J. Applied Polymer Science Volume 26, pg. 489-497 (1981)). 
Polyethylene glycol has been extensively used for the treatment of 
membranes and as an immobilized liquid in various polymeric membranes. 
Polyethylene glycol and glycerol are used as pore stabilizers for 
hydrophilic menbranes such as regenerated cellulose and cellulose acetate 
(U.S. Pat. No. 3,772,072) to prevent drying and pore collapse. Wet 
membranes from the casting solution are treated with aqueous solutions of 
PEG or glycerol then dried, leaving PEG or glycerol behind in the pores of 
the membrane. 
Polyethylene glycol has also been used as a substitute for swelling agents 
or non-solvents in casting solutions for the production of reverse osmosis 
cellulose acetate membranes (U.S. Pat. No. 3,878,276). Polyethylene 
glycols have also been used as a plasticizer to improve the flux of low 
flux cellulose acetate membranes and hollow fibres (U.S. Pat. No. 
3,873,653) as well as some other synthetic organic polymer membranes (U.S. 
Pat. No. 4,087,388). 
Several examples of the use of immobilized polyethylene glycol membranes to 
separate polar gases, e.g., SO.sub.2 or CO.sub.2 from gaseous mixtures 
have been demonstrated. Thus polyethylene glycol (MW 300 to 4000) has been 
cast with cellulose nitriate in tetrahydrofuran solvent to form a membrane 
used to selectively separate CO.sub.2 (Chemistry Letters, 1980, pgs. 
1445-1448). An immobilized film of polyethylene glycol was supported on a 
porous polymer membrane and used to separate SO.sub.2 from gas streams 
(U.S. Pat. No. 3,625,734). Diethylene glycol on a silicon rubber membrane 
was used to separate CO.sub.2 from O.sub.2 (U.S. Pat. No. 3,335,545). A 
rigid gel of polyethylene glycol and Cabosil or Cellosize supported on a 
porous backing was used for SO.sub.2 separation. (Recent Developments in 
Separation Science, Volume I, CRC Press, 1973 pg. 153 ff). Polyhydridic 
alcohols, including polyethylene glycol have been immobilized in porous 
polymer membranes and used to separate unsaturated compounds from a 
mixture of organic compounds (Japanese 53-70084, 1978). The concept of a 
semi-permeable membrane extraction using a porous absorbent barrier 
containing a selective solvent to separate aromatics from saturates (among 
other things) is described in U.S. Pat. No. 3,244,763. 
In summary, aromatic/saturate separation via membranes has been 
investigated using a variety of techniques. These include pervaporation 
through a polymeric film, extraction of aromatics from saturates by an 
emulsified liquid membrane and by pervaporation through immobilized liquid 
membranes. High selectivities were achieved in some of these cases, but at 
the expense of low fluxes. The present invention offers the opportunity to 
attain high selectivities at higher fluxes. 
THE PRESENT INVENTION 
The present invention relates to a process for the use of hydrophilic 
polymeric membrane selected from regeneraated cellulose or cellulose 
acetate, preferably regenerated cellulose, impregnated with from about 5 
to 30 wt.% polyethylene glycol having a molecular weight in the range of 
about 200 to 100,000 under pervaporation conditions to selectively 
separate low molecular weight aromatic hydrocarbons from saturated 
hydrocarbons. This separation using the PEG treated membranes is marked by 
high flux and high separation factors. This process using PEG impregnated 
hydrophilic membranes will find its broadest application in aromatics 
separation from reformate streams. Such a separation is important and 
useful in the production of high octane motor fuels, in the production of 
aromatic solvents, etc. 
It has been discovered that the selectivity and flux of aromatics through 
the membrane will be affected by varying the weight percent of 
polyethylene glycol in the membrane, the pore size of the membrane, the 
molecular weight of the polyethylene glycol, and the temperature. 
Membranes suitable for impregnation with polyethylene glycol are 
hydrophilic in nature such as the previously indicated regenerated 
cellulose and cellulose acetate membranes. Regenerated cellulose 
membranes, which offer the strongest hydrogen bonding between the glycol 
and the polymer are preferred because they resist leaching of the glycol 
from the membrane. 
Hydrophobic membranes do not hydrogen bond polyethylene glycol. The 
stability of the latter in the membrane matrix is therefore low. These 
membranes, therefore, are not useful for this invention. 
Useful hydrophilic membranes, preferably regenerated cellulose, are 
generally from about 10 to 25.mu. in dry thickness, have molecular weight 
cut offs as measured using aqueous solutions of from about 10,000 to 
50,000. Since the permeation rate of the membrane (flux) is inversely 
proportional to the membrane thickness, the thinner membranes are 
preferred. The MWCO of regenerated cellulose membranes may be modified and 
controlled by pretreatment with pore modifiers such as caustic (eg NaOH) 
or ZnCl.sub.2 solutions prior to impregnation with PEG. This is important 
to control flux and selectivity as described in detail in the examples 
presented below. Such treatment increases flux for a given PEG loading, 
but with an accompanying reduction in separation efficiency. 
The molecular weight of the PEG impregnated in the membrane should be in 
the range of about 200 to 100,000, preferably about 600 to 14,000. The 
useful concentration range of polyethylene glycol impregnated in the 
membrane varies from about 5 to 30 wt.%, preferably about 10 to 25 wt.% 
most preferably about 10 to 15 wt.%. Polyethylene glycol (PEG) impregnated 
regenerated cellulose membranes, (useful for the separation of aromatics 
from saturates in the present invention) can be prepared in a number of 
ways. Regenerated cellulose membranes are typically supplied by the 
manufacturer plasticized with glycerol or glycerin to prevent the membrane 
from drying out. This glycerol or glycerin must be removed, as by a water 
soak, before PEG impregnation. In the preferred method, a commercially 
available regenerated cellulose membrane, after removal of any glycerol or 
glycerin plasticizer, is impregnated with PEG by soaking, immersion, 
dipping, spraying, passage of the glycol across the membrane, etc. 
Immersion is the preferred method. Typically the membrane is immersed in a 
PEG solution for a given period of time, generally until equilibrium is 
reached. Impregnation is a physical and not a chemical phenomenon and 
neither changes in temperature nor soak duration beyond the point of 
equilibrium will affect the final loading of PEG in the membrane. The 
amount of PEG trapped in the membrane (loading levels) is controlled by 
PEG concentration in the soaking bath solution and immersion time. Once 
equilibrium is reached, however, immersion for longer times has little 
effect; PEG loading will remain constant. At high loadings of PEG, smaller 
pore membranes are more selective to aromatics than larger pore membranes. 
The critical loading of PEG (i.e., the upper limit above which separation 
performance falls off) decreases as the pore size of the membrane 
increases. As the weight percent of PEG in the membrane is increased, the 
flux is increased and the selectivity is decreased until the critical 
concentration level is reached. Above the critical concentration level 
membrane performance falls off. For PEG 600 this critical loading ranges 
from about 13-25 wt.%, depending on membrane pore size. 
Polyethylene glycol impregnated cellulose acetate membranes can be prepared 
by dissolving the cellulose acetate and the polyethylene glycol in a 
solvent, such as methylene chloride, casting a thin film of the solution 
on a suitable substrate or casting plate (e.g., polished metal, glass 
etc.) and letting the solvent evaporate to produce a clear flexible film. 
The reformate streams which may be subject to the process of the present 
invention employing PEG impregnated regenerated cellulose or cellulose 
acetate membranes contain aromatic and saturate components, said streams 
typically being made up of components not greater than C.sub.9 -C.sub.10 
with molecular weight of not greater than about 150. Reformates may thus 
be beneficially upgraded by use of the present invention to obtain high 
octane motor fuels. 
By the process of the present invention aromatics are removed from 
feedstreams at permeation rates on the order of 10.sup.-2 m.sup.3 /m.sup.2 
d and separation factors of 7 or more. Flux and separation factors are 
directly associated with and dependent on pore size of the membrane, PEG 
molecular weight, PEG loading levels and operating temperatures and 
pressures. These relationships will be more fully described in the 
examples below. 
The separation is carried out under pervaporation conditions. The feed is 
in the liquid phase, its temperature and pressure range from 0.degree. to 
100.degree. C. and 0 to 1000 PSIG with a more preferred range being 
0.degree. to 100.degree. C. and 0 to 500 PSIG. Vacuum is applied 
downstream of the membrane such that the pressure is less than the 
equilibrium vapor pressure of the liquid feed. Separation is achieved by 
molecules diffusing through the membrane under a concentration gradient 
driving force caused by the downstream vacuum. The flow rate of the feed 
must be sufficient to ensure that no stagnant layer of feed accumulates 
over the membrane surface. 
A typical laboratory unit for this process is illustrated in FIG. 1. A 
hydrocarbon feed consisting of aromatic and saturated hydrocarbons is 
placed in the feed reservoir 1. The feed is circulated across the membrane 
holder 4 via pump 2 and line 3. The feed returns to the reservoir from the 
membrane holder via line 5. The membrane holder is of a plate and frame 
design in which the feed flows across the upper surface of the membrane 
and the permeate is removed under vacuum from the downstream side of the 
membrane via line 6. The permeate is trapped under liquid nitrogen in 
permeate trap 7. By means of valving, alternate permeate samples can be 
collected. 
A more complete demonstration of the process of this invention can be 
obtained by reference to the following examples which are illustrative 
only and are not meant to limit the scope of the invention. 
EXAMPLE 1 
The following example illustrates that hydrophobic polymeric porous 
membranes are not suitable for this invention. A polycarbonate porous 
membrane (pore size=0.2.times.0.04.mu.) and a polypropylene porous 
membrane (pore diameter=0.54.mu.) were impregnated with PEG 600 by 
spreading PEG 600 on the surface of the membranes. These membranes were 
then tested for their selectivity to aromatics under typical pervaporation 
conditions (upstream pressure=0 PSIG, downstream vacuum -10 mm Hg) and at 
22.degree. C. The feed used was a mixture of toluene/heptane. The results 
are listed below in Table 1. All of the PEG was leached from the membranes 
as indicated by the very high fluxes and no selectivity. 
TABLE 1 
______________________________________ 
Wt. % Toluene Flux 
Membrane in Feed m.sup.3 /m.sup.2 Day 
S.F.* 
______________________________________ 
Polypropylene 
50 very high 1.0 
Polycarbonate 
50 2.7 1.0 
______________________________________ 
##STR1## 
EXAMPLE 2 
The following example illustrates that polyethylene glycol impregnated 
regenerated cellulose membranes selectively permeate aromatic hydrocarbons 
under pervaporation conditions and the performance of the membrane depends 
both on the concentration of PEG in the membrane as well as the pore size 
of the membranes. In Table 2 is listed the physical characteristics of the 
regenerated cellulose membranes that were used in these tests. The 
regenerated cellulose membranes were impregnated with PEG-600 by soaking a 
wet membrane in aqueous solutions of varying PEG concentrations for 
varying times. After treatment, the membranes were dried at 60.degree. C. 
to remove the water. The weight percent PEG-600 in the membrane was 
measured in the following fashion. After drying in the oven, the membranes 
were soaked in toluene for fifteen minutes to remove any excess glycol, 
dried and weighed. The membranes were then soaked in water, dried and 
reweighed. The difference in weight yields the percentage of PEG in the 
membrane. Regenerated cellulose membrane type 5 (PM-100 from Enka A.G.) 
was treated with zinc chloride to enlarge its pores in the following 
manner. A wet membrane was soaked in a concentrated aqueous solution of 
zinc chloride at room temperature for 15 minutes. The use of zinc chloride 
to expand the pores of regenerated cellulose is well known (J. Phys. Chem. 
2257 [40] 1936). After this treatment, the membrane was soaked in water 
for at least one day to remove the zinc chloride. Following this, the 
membrane was treated with polyethylene glycol in the previously recited 
manner. These membranes were then tested for their selectivity to 
aromatics under typical pervaporation conditions, downstream pressure of 
about 2 to 3 min. Hg, and at 22.degree. C. The feed used was a mixture of 
toluene/heptane. In none of these runs using PEG-600 impregnated 
regenerated cellulose was any leaching of the PEG-600 from the membrane 
observed. The results are listed below in Table 3. Tables 4 and 5 present 
the results of the investigation of the effect of temperature and 
aliphatic component concentration in the performance of a PEG 600 
impregnated Type 1 (50,000 MWCO) regenerated cellulose membrane while 
Table 6 and 7 report the effect of temperature and aliphatic compound 
concentration on the performace of a ZnCl.sub.2 treated Type 5 (PM100) 
regenerated cellulose membrane. 
TABLE 2 
______________________________________ 
Regenerated Dry Pore 
Cellulose Porosity Thickness 
Size 
Membrane Type 
MWCO % .mu.m .ANG. .+-. 2 
______________________________________ 
1 50,000 16.5 25.0 29 
2 25,000 15.5 25.0 23 
3 15,000 14.7 25.0 19.7 
4 (PM-250) 10-12 .times. 10.sup.3 
16.8 17.5 19 
5 (PM-100) 10-12 .times. 10.sup.3 
16.3 10.0 18.5 
______________________________________ 
A control blank experiment was performed (repeated in Table 3) using 
membrane Type 1 (50,000 MWCO) with no PEG-600 present. For that membrane 
flux was very low and there was no selectivity. The other membrane samples 
in this example were impregnated with various weight loadings of PEG-600. 
As can be seen, as the weight percent PEG-600 in each membrane decreased, 
the flux decreased and selectivity increased until a certain optimum 
loading level is attained for a given membrane. Further, as the flux rate 
is inversely proportional to the membrane thickness, it is seen that 
thinner membranes yield a higher flux for a given PEG loading and 
selectivity. The flux of Type 4 membranes (PM250 which is about 17.5.mu. 
thick) is almost doubled that of Type 3 membrane (25.mu. thick) for the 
same value of selectivity and PEG loading (.about.24%). 
TABLE 3 
______________________________________ 
Wt. % Wt. % 
Membrane Run PEG 600 Toluene 
Flux 
Type # In Membrane 
Feed m.sup.3 /m.sup.2 day 
S.F. 
______________________________________ 
1 a 0 53.9 0.001 1.0 
b 9 54.5 0.002 5.2 
c 9 52.5 0.04 2.9 
d 11 55.9 0.039 2.0 
e 12 55.9 0.047 1.81 
f 13 55.9 0.064 1.5 
g 11 55.9 0.087 1.5 
h 14 55.0 0.17 1.3 
i 34 50.5 0.23 1.2 
2 a 10 55.0 nil -- 
b 14 54.5 0.04 2.3 
c 24-34 50.0 0.25 1.4 
3 a 24 50.0 0.04 2.3 
4 a 15 55.0 nil -- 
b 22 55.0 nil -- 
c 24 54.0 0.07 2.5 
5 a 17 55.0 nil -- 
5 a &lt;12.7 56.9 0.013 7.1 
ZnCl.sub.2 
b 12.7 51.8 0.013 6.0 
treated c 15 56.1 0.008 3.3 
d 19 53.1 0.10 2.1 
e 26 56.0 0.14 1.7 
5 a 19.4 48.5 0.091 2.33 
ZnCl.sub.2 
b 19.4 45.5 0.050 3.15 
treated c 19.4 45.3 0.054 3.16 
(Temp 22.degree. C. 
d 19.4 38.1 0.038 .08 
Vacuum 3-5 
e 19.4 28.9 0.018 5.26 
mm Hg) 
______________________________________ 
TABLE 4 
______________________________________ 
TEMPERATURE STUDY 
Temper- Heptane 
Toluene 
ature Total Flux 
Wt. % Heptane Flux Flux 
.degree.C. 
kg/m.sup.2 d 
in Permeate S.F. kg/m.sup.2 d 
kg/m.sup.2 d 
______________________________________ 
23 50.2 34.0 1.53 17.1 33.1 
29.9 72.91 36.0 1.40 26.3 46.6 
30.5 69.8 34.3 1.51 23.9 45.9 
36.8 94.9 35.6 1.43 33.8 61.1 
40.2 92.51 35.6 1.43 32.9 59.6 
41.0 99.6 37.8 1.30 37.6 62.0 
45.0 131.7 36.9 1.35 48.6 83.1 
45.1 123.9 35.6 1.43 44.1 78.8 
50.0 200.7 37.4 1.32 75.1 125.6 
______________________________________ 
Membrane = regenerated cellulose MWCO 50,000 impregnated with 12% PEG 600 
.+-. 1% 
Feed = 44% heptane/56% toluene 
TABLE 5 
______________________________________ 
CONCENTRATION STUDY 
Membrane = regenerated cellulose MWCO 50,000 
impregnated with 11.1% PEG 600, deviation .+-. 1.3 wt. % 
Temperature = 23.degree. C. 
Feed = toluene/heptane 
Wt. % Total Heptane 
Toluene 
Heptane 
Flux Wt. % Heptane Flux Flux 
in Feed 
kg/m.sup.2 d 
in Permeate S.F.* kg/m.sup.2 d 
kg/m.sup.2 d 
______________________________________ 
44.1 31.7 28.3 2.00 9.0 22.7 
54.9 18.0 36.8 2.09 6.6 11.4 
64.4 13.5 44.5 2.26 6.0 7.5 
74.0 11.0 52.0 2.58 5.7 5.3 
85.6 7.3 70.9 2.44 5.1 2.2 
______________________________________ 
##STR2## 
TABLE 6 
______________________________________ 
TEMPERATURE STUDY 
Wt. % Heptane 
Flux Elapsed Temperature 
Feed m.sup.3 /m.sup.2 d 
S.F. Time (hr) 
.degree.C. 
______________________________________ 
44.1 0.025 1.96 1 26.8 
44.1 0.008 2.27 2 26.8 
44.1 0.008 2.92 3 26.8 
43.9 0.008 3.13 4 26.8 
43.9 0.008 3.38 5 26.8 
43.9 0.008 3.47 6 26.8 
43.9 0.008 3.29 7 26.8 
43.7 0.048 3.02 8 35.0 
43.7 0.025 3.02 9 35.0 
42.7 0.05 2.57 10 50.0 
42.7 0.08 2.64 11 50.0 
43.2 0.015 2.82 12 27.2 
______________________________________ 
Membrane = PM 100, ZnCl.sub.2 treat, 14.8% PEG 600, S = 3.1 
Feed = Toluene/Heptane 
Vacuum = 305 mm Hg 
TABLE 7 
______________________________________ 
EFFECT OF FEED CONCENTRATION 
Wt Percent X Heptane Flux 
Heptane Feed 
Feed M.sup.3 /m.sup.2 d 
S.F. 
______________________________________ 
46.9 0.448 0.099 2.11 
51.5 0.494 0.091 2.33 
54.5 0.524 0.050 3.15 
54.7 0.526 0.054 3.16 
61.9 0.593 0.038 4.08 
71.1 0.693 0.018 5.26 
______________________________________ 
Membrane: PM 100, ZnCl.sub.2 treat 19.4 wt % PEG 600 
Feed: Toluene/Heptane 
Temperature: 22.degree. C. 
Vacuum: 3-5 mm Hg 
EXAMPLE 3 
The following example illustrates that polyethylene glycol of molecular 
weight 200 and diethylene glycol are not stable at room temperature and 
that their performance in membranes under pervaporation conditions is 
inferior to the membrane performance of the same membrane impregnated with 
PEG-600. Regenerated cellulose membranes of Type 1 and a ZnCl.sub.2 
treated Type 5 were impregnated with various amounts of PEG, molecular 
weight 200 and 600. Regenerated cellulose membrane Type 5 treated with 
ZnCl.sub.2 was impregnated with diethylene glycol. The diethylene glycol 
rapidly leached from the membrane, causing the membrane to become 
impermeable as time elapsed. These membranes were tested for their 
selectivity to aromatics under typical pervaporation conditions at 
22.degree. C. The feed was a mixture of toluene/heptane. The results are 
listed below in Tables 8, 9 and 10. By comparing these results to those in 
Example 2, it is obvious that the lower molecular glycol impregnated 
membranes are inferior in comparison to the membranes impregnated with 
PEG-600. 
TABLE 8 
______________________________________ 
POLYETHYLENE GLYCOL IMPREGNATED 50,000 MWCO 
MEMBRANES (Type 1 RC Membrane) 
Molecular 
Wt. % Standard 
Weight Heptane Flux Wt. % Deviation 
PEG Feed m.sup.3 /m.sup.2 d 
S.F. PEG of Wt. % 
______________________________________ 
200 43.9 Nil -- 4.3 0.3 
43.9 Nil -- 10.8 1.1 
43.9 Nil -- 12.9 0.8 
43.9 Nil -- 14.1 1.0 
43.9 Nil -- 15.1 1.3 
43.9 0.025 1.54 16.2 0.6 
43.9 0.025 1.51 11.4 2.0 
43.9 0.023 1.43 13.3 1.0 
43.9 0.037 1.27 14.0 1.1 
43.9 0.075 1.20 16.0 1.5 
43.9 0.21 1.12 16.8 0.3 
43.9 0.25 1.08 22.5 0.8 
600 46.1 Negligible 1.05 0 -- 
45.5 0.002 5.2 9.3 -- 
43.9 0.11 1.32 14.2 0.4 
45.0 0.17 1.3 13.9 -- 
49.5 0.23 1.23 34 -- 
______________________________________ 
(T = 293K, Feed = Toluene/Heptane, Vacuum = 3-5 mm Hg) 
TABLE 9 
______________________________________ 
POLYETHYLENE GLYCOL PM 100 ZnCl.sub.2 
TREAT MEMBRANES (Type 5) 
Wt. % Standard 
Molecular 
Heptane Flux Wt. % Deviation 
PEG Feed m.sup.3 /m.sup.2 d 
S.F. PEG of Wt. % 
______________________________________ 
200 43.9 Nil -- 4.2 0.7 
43.9 Nil -- 4.4 -- 
43.9 Nil -- 5.0 1.8 
43.9 Nil -- 18.4 0.3 
43.9 Nil -- 22.8 2.1 
43.9 0.013 1.64 20.8 0.7 
43.9 0.18 1.40 33.8 8.6 
43.9 0.21 1.12 24.2 1.1 
600 43.9 Nil -- 8.5 0.9 
43.9 Nil -- 8.6 0.3 
43.9 Nil -- 14.1 0.9 
43.9 Nil -- 16.9 0.6 
48.2 0.01 5.9 12.7 -- 
43.9 0.008 3.3 14.8 3.1 
46.9 0.099 2.11 19.4 -- 
43.9 0.14 1.7 25.6 0.2 
______________________________________ 
T = 293K, Feed = Toluene/Heptane, Vacuum = 3-5 mm Hg 
TABLE 10 
______________________________________ 
DIETHYLENE GLYCOL (DEG) PM 100 
ZnCl.sub.2 TREAT MEMBRANES (Type 5) 
Standard 
Flux Elapsed 
Wt. % Deviation 
Run # m.sup.3 /m.sup.2 d 
S.F. Time (hr) 
DEG of Wt. % 
______________________________________ 
1 Nil -- 1 4.3 3.3 
2 Nil -- 1 10.8 1.5 
3 3.2 .times. 10.sup.-2 
1.38 1 2.6 1.2 
Negligible 2.38 2 
Nil -- 3 
4 5.0 .times. 10.sup.-2 
1.15 1 5.7 1.6 
1.0 .times. 10.sup.-2 
1.9 2 
Nil -- 3 
5 1.08 .times. 10.sup.-1 
1.76 1 7.4 1.3 
-- 1.92 2 
3.3 .times. 10.sup.-2 
1.92 3 
3.0 .times. 10.sup.-2 
2.1 4 
6.75 .times. 10.sup.-2 
2.0 5 
6 1.58 .times. 10.sup.-2 
1.51 1 8.4 0.9 
6.75 .times. 10.sup.-3 
2.27 2 
7.25 .times. 10.sup.-3 
2.38 3 
5 .times. 10.sup.-3 
2.54 4 
6 .times. 10.sup.-3 
2.8 5 
2 .times. 5 .times. 10.sup.-3 
2.8 6 
7 7.5 .times. 10.sup.-3 
1.1 1 11.2 1.2 
3.75 .times. 10.sup.-2 
1.0 2 
Nil 
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T = 293K, Feed = 43.95 wt. % heptane/56.05 wt. % toluene, Vacuum = 1.3 mm 
Hg 
EXAMPLE 4 
The following example illustrates that regenerated cellulose membranes 
impregnated with polyethylene glycol with higher molecular weights than 
600 can be used to separate aromatics from saturates at temperatures 
higher than room temperature. At temperatures above 50.degree. C., PEG-600 
leaches from regenerated cellulose membranes. Higher molecular weight 
glycols are more resistant to leaching at higher temperatures. In 
particular, membranes impregnated with PEG 14,000 yielded stable 
performance at higher temperatures. These membranes were tested for their 
selectivity to aromatics under typical pervaporation conditions at 
elevated temperatures. The feed was a mixture of toluene/heptane. The 
results are listed below in Table 11. 
TABLE 11 
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Mem- Temper- Wt. % Wt. % Flux 
brane Run ature PEG-14,000 
Toluene 
m.sup.3 /m.sup.2 
Type # .degree.C. 
In Membrane 
Feed day S.F. 
______________________________________ 
5 a 74 14 55.9 0.005 
3.2 
b 78 23 55.9 0.003 
2.9 
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EXAMPLE 5 
The following example illustrates that polyethylene glycol impregnated 
regenerated cellulose membranes under pervaporation conditions will 
selectively permeate the aromatics from an actual reformate stream. This 
example also shows that only aromatics containing up to ten carbons are 
selectively permeated across these membranes. The membrane used in this 
example is a type 5 regenerated cellulose membrane, treated with zinc 
chloride and impregnated with 18% of PEG-600. This membrane was tested for 
its selectivity to aromatics under typical pervaporation conditions at 
23.degree. C. Table 12 lists the compositions of the feed and permeate 
streams. As seen from the results, aromatics are selectively permeated 
across the membrane and the overall selectivity to aromatics is close to 
the value expected for the PEG concentration in this membrane. 
TABLE 12 
______________________________________ 
Wt. % Component 
Wt. % Component 
Component in Feed in Permeate S.F. 
______________________________________ 
C3 .04 0.00 
iC4 0.43 0.02 
nC4 .95 .10 
CP .03 .03 
iC5 2.25 .57 
nC5 1.66 .70 
Benz 2.21 4.02 
MCP .54 .33 
CH .29 .15 
iC6 4.46 2.39 
nC6 2.22 1.61 
To1 20.48 28.37 
DMCP 0.48 0.30 
MCH 0.17 0.11 
iC7 8.18 5.26 
nC7 9.26 4.55 
A8 19.35 28.58 
6N8 .39 .17 
5N8 .77 .48 
P8 7.33 4.7 
A9 12.14 13.13 
6N9 .62 .35 
5N9 .01 .01 
P9 2.1 1.4 
A10 1.87 1.3 
6N10 .02 .02 
5N10 .02 .02 
P10 .79 .68 
All .92 .64 
Total Paraffins 
39.69 21.99 0.43 
Total Naphthenes 
3.34 1.95 0.59 
Total Aromatics 
56.97 75.03 2.50 
______________________________________ 
EXAMPLE 6 
Polyethylene glycol impregnated cellulose acetate membranes were produced 
by dissolving cellulose acetate (acetyl content 39.8.+-.0.5%, viscosity 
(ASTM) 3.+-.1 sec) and polyethylene glycol 600 in methylene chloride. A 
thin film of the solution was cast on a glass plate and the solvent 
permitted to evaporate to produce a film (20.mu. thick). The membrane were 
tested under pervaporation conditions at 50.degree..+-.1.degree. C. with a 
feed of 53.+-.1% tolune/47.+-.1% heptane. The results are presented in 
Table 13 below: 
______________________________________ 
Flux 
Film Composition S.F. m.sup.3 /m.sup.2 .multidot. d 
______________________________________ 
13% PEG 600 12 3 .times. 10.sup.-3 
16.7% PEG 600 7 6 .times. 10.sup.-3 
20% PEG 600 9 6 .times. 10.sup.-3 
29.9% PEG 600 8 6 .times. 10.sup.-3 
______________________________________