Process for the production of ethyl tert.-alkyl ethers

The present invention is a cyclic process for the preparation of ethyl tert.-alkyl ethers by the reaction of an alcohol, ethanol, with an iso-olefin such as isobutylene or isoamylene wherein an effluent from the reaction zone is separated in a distillation column to provide an overhead effluent stream and a bottoms effluent stream comprising ethyl tert.-alkyl ether and unreacted ethanol. The unreacted ethanol is recovered in an adsorption zone comprising a selective adsorbent selected from the group consisting of zeolite 13X, sodium zeolite Y, alumina, silicalite and mixtures thereof. The invention is useful in recovering unreacted ethanol from the bottoms effluent stream and returning the unreacted ethanol to the reaction zone. The invention reduces the cost of this separation which is complicated by the formation of an azeotrope between the unreacted alcohol and the ether.

FIELD OF THE INVENTION 
The present invention relates to a process for the production of ethers by 
the reaction of an alcohol with an isoalkene. More particularly, it 
relates to an improved process for the production of ethyl tert.-butyl 
ether (ETBE) by the reaction of ethanol with isoalkene. The invention 
specifically relates to improvements in the recovery and recycle to the 
reactor of unreacted ethanol without loss of ETBE product. 
BACKGROUND OF THE INVENTION 
The production of gasoline motor fuel requires consideration of the balance 
between the specifications provided by the automobile manufacturers and 
the concern for the environment as controlled by the governmental 
regulations on automobile emissions. Renewed environmental awareness and 
the desire for cleaner air on the pan of the public has encouraged 
gasoline producers to develop reformulated grades of gasoline to reduce 
emissions from automobiles. Government has supported this reformulation 
initiative with new regulations which will result in the addition of 
oxygenates such as alcohols and ethers to the gasoline pool in an effort 
to reduce the level of CO and hydrocarbon emissions compared to emissions 
from conventional gasoline grades. The reformulated grades of gasoline, 
often referred to as oxyfuels, must meet all the typical gasoline 
specifications, and in addition must contain a minimum amount of oxygen. 
In the United States, according to current regulations, this oxyfuel must 
be sold in those areas of the country which do not meet minimum standards 
for ozone pollution. 
Automotive gasoline is usually sold by a grade such as regular, or premium, 
according to its octane rating. This octane rating is a measurable quality 
and is derived from a laboratory measurement of octane number. The octane 
number is a rating of the performance of a sample of the gasoline in a 
standard test engine. Typically, two types of octane numbers are used to 
characterize the octane rating (i.e., a research octane (RON) and a motor 
octane (MON). These are determined separately according to well-known 
laboratory methods and averaged (RON+MON)/2 to provide an octane rating 
for a particular grade of gasoline. 
Oxygen may be added to gasoline in the form of an oxygenate such as an 
alcohol including methanol, ethanol, or isopropanol and the like, or an 
ether including methyl tert.-butyl ether (MTBE), ethyl tert.-butyl ether 
(ETBE), tert. amyl-methyl ether (TAME), and the like. Oxygenates are added 
to the gasoline pool comprising hydrocarbons in amounts such that the 
octane rating and oxygen content of the blend increases, without exceeding 
vapor pressure limits. Vapor pressure is a physical property which 
reflects the amount of volatile material in the motor fuel. A high vapor 
pressure can result in hydrocarbon emissions to the atmosphere. Although 
alcohols such as methanol and ethanol have favorable octane numbers when 
blended with other gasoline components, the alcohols generally have a 
higher vapor pressure than ethers. Therefore, the gasoline producers have 
sought to increase the oxygen content of fuels by incorporating more 
renewable resource materials such as ethanol into the gasoline by 
converting the alcohols into ethers by combining the alcohols with C.sub.4 
and C.sub.5 iso-olefins over an acid catalyst. 
The production of ethers by the reaction of an iso-olefin and an alcohol is 
a well-known commercial operation. A number of detailed descriptions of 
such processes, particularly as they relate to the production of methyl 
tert.-butyl ether (MTBE) appear in the technical and patent literature. 
Exemplary of patent disclosures are U.S. Pat. No. 3,726,942 issued Apr. 
10, 1973, to K. E. Louder; U.S. Pat. No. 4,219,678 issued Aug. 26, 1980, 
to I. Obenaus et al; U.S. Pat. No. 4,447,653 and U.S. Pat. No. 4,575,567 
issued to B. V. Vora on May 8, 1984, and Mar. 11, 1986, respectively; and 
U.S. Pat. No. 4,876,394 issued to M. M. Nagji et al Oct. 24, 1989. These 
ethers are useful as high octane blending agents for gasoline motor fuels 
by virtue of their high Research Octane Number (RON) of about 120 and 
their low volatility. 
MTBE has become the most commonly used ether for gasoline octane 
improvement. For example, a typical reformulated gasoline grade would 
require about 11 volume % MTBE to provide a gasoline containing about 2.0 
wt % oxygen before reaching a vapor pressure limit. In a similar manner, 
if ETBE were used, the resulting blend with about 2.7 wt % oxygen would 
accommodate about 17 volume % ETBE at the same vapor pressure limit. ETBE 
has a higher octane value than MTBE and a blending vapor pressure of about 
one-half that of MTBE. In addition, ETBE like MTBE is miscible in gasoline 
in all proportions, but ETBE has a lower water solubility than MTBE, 
giving ETBE better fungibility in gasoline blends. ETBE is less likely 
than MTBE to be lost in pipeline transport. The cost of production is a 
major factor on the use of MTBE over ETBE. Methanol is typically derived 
from natural gas, while Ethanol is generally produced by fermentation of 
organic material. Given appropriate favorable price equalization of 
ethanol relative to methanol, the goal of encouraging the use of more 
regenerable material in the gasoline pool may be achieved. ETBE is 
produced by an etherification reaction of ethanol and an iso-olefin, such 
as isobutylene, wherein ethanol is present in an amount in excess of that 
required for the reaction. Typically, the reactor effluent is fractionated 
to produce a light stream comprising unreacted hydrocarbons and an ETBE 
product stream. Although some of the excess ethanol will be withdrawn with 
the unreacted hydrocarbon stream, at least a portion of the ethanol will 
remain in the ETBE product. The ethanol remaining in the ETBE product 
results in a loss of ethanol, and this ethanol significantly raises the 
vapor pressure and lowers the octane rating of the ETBE product. European 
Patent No. 542596 discloses the use of a costly and energy intensive 
extraction and three-stage fractionation scheme to separate the 
unconverted ethanol from the ETBE. Methods are sought to perform the 
separation of the ETBE from ethanol in the ETBE product in an efficient 
and low cost manner, without the loss of any valuable gasoline blending 
components. 
SUMMARY OF THE INVENTION 
It is the objective of the instant invention to provide a process for 
separating ETBE and other ethyl tert.-alkyl ethers from unreacted ethanol. 
The advantage of this process is that it provides an essentially pure 
ETBE, or ethyl tert.-alkyl ether product, containing less than about 100 
ppm-wt ethanol. This purified ether product adds flexibility to the 
production and blending of reformulated gasolines and eliminates the 
octane and vapor pressure limitations caused by presence of azeotropic 
mixtures of ETBE and ethanol in the ETBE product. 
In one embodiment, the invention is a cyclic process for preparing ethyl 
tert.-alkyl ethers comprising a series of steps. A reaction mixture formed 
by combining a feedstream comprising hydrocarbons having from 4 to 5 
carbon atoms per molecule and containing isoalkene is combined with a near 
stoichiometric milo of ethanol with respect to the isoalkene. The reaction 
mixture is contacted and reacted in a reaction zone to produce a reaction 
product effluent comprising ethyl tert.-alkyl ether, at least 10,000 ppm 
weight unreacted ethanol, and unreacted C.sub.4 -C.sub.5 hydrocarbons. The 
reaction product effluent from the reaction zone is separated in a 
distillation column to provide an overhead effluent stream comprising 
unreacted ethanol and unreacted C.sub.4 -C.sub.5 hydrocarbons, and a 
bottoms effluent stream comprising ethyl tert.-alkyl ether and unreacted 
ethanol. The bottoms effluent stream is passed to an adsorption zone 
containing a selective adsorbent to adsorb ethanol and an ether product 
stream comprising substantially pure ethyl tert.-alkyl ether is recovered. 
The selective adsorbent is regenerated with a regenerant stream to recover 
the ethanol to provide a recycle stream comprising ethanol, and the 
recycle stream is returned to the reaction zone. 
In a further embodiment, the present invention is a cyclic process for 
preparing ethyl tert.-alkyl ethers comprising a series of steps. A 
feedstream comprising hydrocarbons having from 4 to 5 carbon atoms per 
molecule and containing isoalkene is combined with a near stoichiometric 
ratio of ethanol with respect to the isoalkene to provide a reaction 
mixture. The reaction mixture is contacted and reacted in a reaction zone 
to produce a reaction product effluent comprising ethyl tert.-alkyl ether 
at least 10,000 ppm weight unreacted ethanol and unreacted C.sub.4 
-C.sub.5 hydrocarbons. The reaction product effluent from the reaction 
zone is separated in a distillation column to provide an overhead effluent 
stream comprising unreacted ethanol and unreacted C.sub.4 -C.sub.5 
hydrocarbons, and a bottoms effluent stream comprising ethyl tert.-alkyl 
alkyl ether and unreacted ethanol. The bottoms effluent stream is passed 
to an adsorption zone containing a selective adsorbent to adsorb ethanol 
and recover an ether product stream comprising substantially pure ethyl 
tert.-alkyl ether. The overhead effluent stream is passed to a separation 
zone to provide an unreacted C.sub.4 -C.sub.5 hydrocarbon stream depleted 
in ethanol and an unreacted ethanol stream. At least a portion of the 
unreacted C.sub.4 -C.sub.5 hydrocarbon stream is passed to the adsorption 
zone to regenerate the selective adsorbent and to recover a hydrocarbon 
stream comprising ethanol. The hydrocarbon stream comprising ethanol is 
recycled to the separation zone. 
In a still further embodiment, the present invention comprises a cyclic 
process for preparing ethyl tert.-alkyl ethers comprising a series of 
steps. A feedstream consisting essentially of hydrocarbons having from 4 
to 5 carbon atoms per molecule and containing isoalkene is combined with a 
near stoichiometric ratio of ethanol with respect to the isoalkene to 
provide a reaction mixture. The reaction mixture is contacted and reacted 
in a reaction zone, preferably in the liquid phase, to produce a reaction 
product effluent comprising ethyl tert.-alkyl ether, at least 10,000 ppm 
weight unreacted ethanol, and unreacted C.sub.4 -C.sub.5 hydrocarbons. The 
reaction product effluent from the reaction zone is separated in a 
distillation column. The distillation column contains at least a portion 
of the action zone. The distillation column provides an overhead stream 
comprising unreacted ethanol and unreacted C.sub.4 -C.sub.5 hydrocarbons 
and a bottoms effluent stream comprising ethyl tert.-alkyl ether and 
unreacted ethanol. The bottoms effluent stream is passed to an adsorption 
zone containing a selective adsorbent. The selective adsorbent is selected 
from the group consisting of zeolite 13X, sodium zeolite Y, alumina, 
silicalite, and mixtures thereof to adsorb ethanol. An ether product 
stream comprising substantially pure ethyl tert.-alkyl ether is recovered 
from the adsorption zone. The overhead effluent stream is passed to an 
adsorption zone to provide an unreacted C.sub.4 -C.sub.5 hydrocarbon 
stream depleted in ethanol and an unreacted ethanol stream. At least a 
portion of the unreacted C.sub.4 -C.sub.5 hydrocarbon stream is passed to 
the adsorption zone to regenerate the selective adsorbent and to recover a 
hydrocarbon stream comprising ethanol. The hydrocarbon stream comprising 
ethanol is recycled to the separation zone.

DETAILED DESCRIPTION OF THE INVENTION 
The following description of the present process with respect to the 
production of ETBE is made with reference to the flow diagram of the 
drawing. In the interest of simplifying the description of the invention, 
the process system in the drawing does not contain the several conduits, 
valves, heat exchangers, and the like which in actual practice would be 
provided in accordance with the routine skill in the art to enable the 
process to be carried out on a continuous basis. 
Ethanol in the liquid phase enters the reaction zone through line 10 and 
enters the reaction zone 12 along with a feedstream comprising C.sub.4 
-C.sub.5 hydrocarbons, preferably in a liquid stream, comprising 
isobutylene entering through line 14. Advantageously, all fluid streams 
introduced into the system have previously been dried to a water content 
of about 1 ppm-wt to about 10 ppm-wt water at the operating pressure of 
the reaction zone. Reaction zone 12 is operated at a temperature which in 
large measure is dependent upon the particular catalyst employed, but is 
generally in the range of about 40.degree. C. to 90.degree. C., and using 
an internal system pressure sufficient to maintain the reaction mixture in 
the liquid phase. In the present embodiment, the catalyst is of the 
ion-exchange resin type and the temperature of the reactor is about 
60.degree. C. The isobutylene-containing C.sub.4 -C.sub.5 hydrocarbons 
include butene-1, cis and trans butene-2, butadiene, isobutane, n-butane, 
and n-amylenes along with isobutylene and isoamylenes. Preferably the 
isobutylene is present in an amount of at least 10 mole-% and preferably 
the near stoichiometric molar ratio of ethanol to isobutylene in the 
reaction zone ranges from about 0.95 to about 1.15. The effluent from the 
reactor comprises product ETBE, unreacted ethanol, unreacted C.sub.4 
-C.sub.5 hydrocarbons and diethyl ether in addition to other reaction 
by-products. This effluent is passed through line 16 to distillation zone 
18. In some embodiments, the reaction zone may be made up of a first 
reaction zone outside of the distillation zone and a second reaction zone 
comprising at least a portion of the reaction zone contained within the 
distillation zone. In addition, the first reaction zone may be further 
subdivided into two or more stages with interstage cooling to remove heat 
and maintain the reaction in the liquid phase. While in this illustration 
the reactor and distillation column are represented as two different 
zones, relatively recent advancements have made possible the combination 
of the function of the reactor and the distillation column into a single 
apparatus, examples of which are taught in U.S. Pat. No. 5,243,102, which 
is hereby incorporated by reference. For purposes of the present 
invention, either operational mode is suitably employed. As a result of 
the distillation zone, a bottoms effluent stream 20 comprising ETBE is 
recovered from the bottom of distillation column 18. The bottoms effluent 
preferably contains from about 0.5 to about 7 weight percent of ethanol, 
and more preferably the bottoms effluent stream contains from about 5000 
ppm-wt to about 2 wt % ethanol with the remainder being essentially ETBE, 
and is passed through line 20 to adsorption zone 22 containing a selective 
adsorbent which selectively adsorbs the ethanol. The selective adsorbent 
may be any of the commonly used solid adsorbents such as activated 
alumina, silicalite, silica gel or zeolitic molecular sieves. It has been 
found that zeolite X and Y molecular sieves offer particular advantages in 
adsorbing ethanol. More particularly, it was found that adsorbents such as 
zeolite sodium zeolite X, sodium zeolite Y, alumina, silicalite and 
mixtures thereof provide particular advantage for the selective adsorption 
of ethanol in the presence of ethyl tert.-alkyl ethers. The ether product, 
which is essentially pure ETBE, preferably containing less than 1000 
ppm-wt, and more preferably containing less than 100 ppm-wt, ethanol, is 
removed from the adsorption zone through line 24. The overhead effluent 
stream from the distillation column 18 comprises about 0.7 to 1.5 wt % 
unreacted ethanol, unreacted C.sub.4 -C.sub.5 hydrocarbons, 1 to 100 ppm 
diethyl ether as well as trace amounts of other volatile by-products. The 
content of the ethanol in the overhead effluent is dependent upon the 
formation of an azeotrope with the unreacted C.sub.4 -C.sub.5 
hydrocarbons. Thus, the amount of ethanol removed with the overhead 
effluent is limited by the formation of the azeotrope, and the remainder 
of the excess or unreacted ethanol is withdrawn in the bottoms effluent 
stream. This overhead effluent stream passes through line 26 to a 
separation zone, or water wash column 28, which adsorbs the ethanol. The 
non-adsorbed hydrocarbons, diethyl ether and other highly volatile 
impurities pass through water wash column 28 and, depending upon the 
intended utilization of this effluent, are optionally passed through line 
30 to a second adsorbent bed (not shown) containing a selective adsorbent 
to produce a relatively pure C.sub.4 -C.sub.5 hydrocarbon stream further 
depleted in ethanol. The particular selective adsorbent involved in the 
second adsorbent bed is also not a critical feature. Any of the commonly 
used solid adsorbents such as activated alumina, silica gel or zeolitic 
molecular sieves can be employed. It has been found that a sodium zeolite 
X is well suited to this application. Of the zeolite adsorbents, 
particularly zeolite 5A, zeolite 13X and zeolite D are preferred. More 
preferably zeolite 13X offers particular advantages in adsorbing trace 
amounts of oxygenales. In the present embodiment, on a cyclic basis, a 
portion of the C.sub.4 -C.sub.5 hydrocarbon stream is passed through line 
32 to the adsorption zone 22 as a regenerant for the adsorbent therein. 
The spent regenerant hydrocarbon stream comprising ethanol is returned to 
the water wash column 28 via lines 34 and 26. The substantially pure ethyl 
tert.-alkyl ether, or in this case ETBE, containing less than 100 ppm-wt 
ethanol, is recovered via line 24 for use in downstream processing or for 
blending into reformulated gasoline. A spent water wash stream is 
recovered from the water wash column in line 38. The spent water wash 
stream 38 may be passed to a water separation zone (not shown) for 
recovery of additional amounts of ethanol for recycle to the reactor 12 
and for regeneration of the wash water for return to line 36. In an 
alternative operation, the overhead effluent stream in line 30 may be 
passed to a second adsorption zone (not shown) containing an adsorbent 
selective for the further removal of oxygenales from the overhead 
effluent, to provide an overhead effluent, containing unreacted C.sub.4 
-C.sub.5 hydrocarbons, with an oxygenate content of less than about 100 
ppm-wt ethanol, prior to the use of at least a portion of the overhead 
effluent stream to regenerate the adsorption zone 22. The remainder of the 
overhead effluent stream may be passed to an alkylation zone for the 
production of alkylate or passed to a dehydrogenation zone for the 
production of additional amounts of iso olefin. 
A wide variety of catalyst materials has been found to promote the 
etherification reaction including ion-exchange resins such as 
divinylbenzene cross-linked polystyrene ion exchange resins in which the 
active sites are sulfuric acid groups; and inorganic heterogeneous 
catalysts such as boric acid, bismuth molybdate, and metal salts of 
phosphomolybdic acids wherein the metal is lead, antimony, tin, iron, 
cerium, nickel, cobalt or thorium. Also boron phosphate, blue tungsten 
oxide and crystalline aluminosilicates of the zeolitic molecular sieve 
type have also been proposed as heterogeneous catalysts for the reaction 
of ethanol and isobutylene. 
The reaction conditions are not narrowly critical and depend in large part 
upon the particular catalyst composition employed. Thus, both vapor phase 
and liquid phase processes have been proposed in which reaction 
temperatures are from about 50.degree. C. to about 400.degree. C., 
reaction pressures vary from about atmospheric to about 1.04 MPa (1500 
psig) and stoichiometric molar ratios of ethanol to isoalkene range from 
0.2:1 to about 10:1 and preferably, according to a near stoichiometric 
molar ratio ranging from about 0.95 to about 1.15. Thus, the present 
process may employ a near stoichiometric ratio of ethanol with respect to 
the isoalkene. Both batch type and continuous process schemes may be 
suitably employed. In the present process the reaction can be carried out 
in either the vapor phase or the liquid phase, but the liquid phase is 
preferred. For reaction zone portions within distillation zones, the 
reaction proceeds primarily in the liquid phase. Isobutylene is the 
preferred isoalkene, although isoamylene may also be employed. 
The selective adsorbent for the process of the present invention will be 
understood by those skilled in the art to be any of the well-known 
adsorbents for selectively adsorbing ethanol from a mixture thereof with 
ethyl tert.-alkyl ethers such as ETBE, and the adsorbents can be employed 
whether in simple or in compound bed, provided only that these adsorbents 
exist and that they be maintained at a capacity for adsorbing essentially 
all of the ethanol from the distillation column bottoms to produce ETBE in 
the desired purity. A number of the typical adsorbents such as zeolite 4A 
and 5A were considered for the instant process, but were found to adsorb 
the ethanol too strongly to be regenerated completely. Silica gel was also 
considered, but silica gel was found not to be selective enough to adsorb 
much of the ethanol in the presence of ETBE. Silicalite was surprisingly 
found to provide a good capacity for the adsorption of ethanol with a 
relatively sharp mass transfer zone. A mixture of sodium zeolite Y in 
combination with alumina, similar to the adsorbents described in U.S. Pat. 
No. 4,725,361 to Fleming for the removal of trihalomethane from aqueous 
solutions, also was surprisingly found to exhibit high capacities for 
ethanol with a relatively sharp mass transfer zone and with the ability to 
be regenerated by a non-reactive gas or liquid. It is believed that when 
the proportion of the sodium zeolite Y in the adsorbent mixture, ranges 
preferably between 10 and 40 wt percent of the mixture, and more 
preferably when the proportion of sodium zeolite Y ranges between 15-30 wt 
%, the resulting adsorbent becomes isostructural, thus moderating the 
strength of the adsorbent by redistributing the number of sodium cations 
coming in contact with the ethanol. This isostructural form permits the 
adsorbent mixture to retain a high capacity and selectivity for the 
ethanol, but lowers the strength of the adsorbent mixture to permit the 
adsorbent admixture to be desorbed or regenerated with either a gas phase, 
or a liquid phase regenerant. Zeolite 13X also was found to have a high 
initial capacity for ethanol in the presence of ETBE; however, some 
degradation of adsorbent capacity was observed following subsequent 
regeneration. In commercial service, zeolite 13X should provide 
performance within an acceptable range. Thus, silicalite, zeolite 13X, 
sodium zeolite Y, alumina and mixtures thereof are preferred for use as 
the selective adsorbent with the instant invention when configured either 
as separate beds or in compound beds having multiple layers of adsorbents. 
FIG. 2 illustrates an alternate embodiment of the instant invention. The 
ethanol is passed to the reaction zone 112 in line 110. A feedstream 
comprising C.sub.4 -C.sub.5 hydrocarbons including at least some 
proportion of isobutylene is passed to reaction zone 112 via feed header 
114. The reaction zone 112 contains a catalyst to produce a reaction 
product effluent comprising ethyl tert.-alkyl ether such as ethyl 
tert.-butyl ether, which is withdrawn from the reaction zone 112 and 
passed in line 116 to a distillation column 118. The distillation column 
118 separates the reaction product effluent into an overhead effluent 
stream 126 comprising unreacted C.sub.4 -C.sub.5 hydrocarbons and a 
bottoms effluent stream 120 comprising ethyl tert.-alkyl ether and meted 
ethanol. The bottoms effluent stream 120 is passed to an adsorption zone 
122 comprising at least two adsorption beds containing an adsorbent as 
described hereinabove and selective for the adsorption of ethanol. An 
essentially pure ethyl tert.-alkyl ether product is withdrawn in line 124 
for subsequent use in downstream processing or gasoline blending to 
produce reformulated gasoline. The adsorbent zone is periodically 
regenerated on a cyclic basis with at least a portion of the feedstream 
withdrawn from the feed header 114 in line 140 and passed to the 
adsorption zone 122. A spent regenerant stream 142 comprising unreacted 
ethanol is recycled to the reaction zone 112 via line 142 which returns 
the recycle stream to the feed header 114 prior to the reaction zone. The 
distillation column overhead effluent stream 126 is passed to a water wash 
column, or separation zone, 128 wherein the overhead effluent stream is 
contacted with a water wash stream 136 to provide an unreacted C.sub.4 
-C.sub.5 hydrocarbon stream 130, depleted in ethanol comprising less than 
500 ppm-wt ethanol and a spent water wash stream 138. 
The temperature within the adsorption beds of the adsorption zone is 
preferably within the range, initially, of about 30.degree. C. to 
50.degree. C., i.e., essentially the same as the temperature of the 
effluent from the fractionation (distillation) tower. The pressure in the 
beds is preferably maintained such as to cause the streams being treated 
to remain in the liquid phase. The regeneration of the beds is 
accomplished in the conventional manner by purging, preferably in a 
direction countercurrent to the direction of flow through the beds during 
the adsorption step therein. The purge stream, preferably in the liquid 
phase, is advantageously of the same or similar composition as the C.sub.4 
-C.sub.5 hydrocarbon stream feed to the etherification reactor. The 
temperature of the purge stream is not narrowly critical, but should be at 
least greater than the temperature of the feedstream being treated during 
the adsorption step, and is preferably at least 30.degree. C. to 
150.degree. C. higher. 
The following examples are only used to illustrate the present invention 
and are not meant to be limiting. 
EXAMPLES 
EXAMPLE I 
A stainless steel adsorbent column (approximately 6.4 mm (1/4 
inch).times.10 mm (4 inch) was filled with about 1.5 grams of adsorbent 
pellets having a particle size of about 177 to about 250 microns (60-80 
mesh) and was employed in a series of adsorption and regeneration tests to 
evaluate the suitability of a series of adsorbents for removing ethanol 
from ETBE in a liquid solution thereof and regenerating the adsorbent with 
a heated inert gas (helium) or hydrocarbon vapor (n-hexane). The liquid 
solution of ethanol in ETBE was a commercial sample obtained from an ETBE 
production facility with the azeotropic composition comprising about 2.2 
wt-% ethanol. During the adsorption step, the ethanol/ETBE solution was 
pumped with a low flow rate, positive displacement pump (Waters 510 HPLC) 
through the adsorbent column and 1 cc samples of the adsorption effluent 
were collected for 10 seconds in sealed vials at 30 second intervals for a 
period of up to about 5 minutes. During the regeneration step with helium, 
helium gas was passed through the column while gradually heating the 
column from about ambient temperature to about 230.degree. C. over a 
period of about 10 minutes. The passing of the helium gas at 230.degree. 
C. was continued for an additional period of 10 minutes. The adsorption 
column was allowed to cool to ambient conditions. The adsorption column 
was weighed after the adsorption step and after the regeneration step to 
determine the amount of material adsorbed or desorbed. When hydrocarbon 
vapor regenerant was employed, the hydrocarbon was vaporized at 
230.degree. C. and passed through the adsorbent column. The vapor flow was 
continued for about 60 minutes while effluent was collected at periodic 
intervals. The adsorption column was then isolated and cooled to ambient 
conditions. The samples were analyzed by gas chromatography and the 
analyses were plotted with time at the mean time during which the sample 
was taken to determine the ethanol breakthrough time and the 
stoichiometric time. The breakthrough time is determined when the ethanol 
concentration in the effluent reached 5% of the feed composition and the 
stoichiometric time is based on the time when the effluent is at 50% of 
the feed concentration. Table 1 presents the results of this experimental 
procedure for fresh activated adsorbent. The following adsorbents were 
considered: silicalite, zeolite 13X, zeolite 4A, zeolite 5A, silica gel 
and an adsorbent comprising caustic treated alumina and about 13 wt-% 
sodium Y zeolite. (Alumina/NaY) 
TABLE 1 
______________________________________ 
FRESH ADSORBENT CAITY 
Breakthrough 
Stoichiometric 
Weight of 
Adsorbent 
Loading, wt-% 
Loading, wt-% 
Unused Bed, % 
______________________________________ 
Silicalite 
6.0 7.2 17 
13X 10.5 13.0 19 
4A 1.0 2.3 57 
5A 4.4 7.9 44 
Silica Gel 
2.2 4.8 54 
Alumina/ 9.1 11.1 18 
NaY 
______________________________________ 
These results show that silicalite, 13X and the Alumina/NaY mixture 
demonstrate significant capacity (greater than 6.0%) for adsorbing ethanol 
from mixtures of ETBE and ethanol. 
The weight of unused bed, WUB, for the tube of Example 1 is determined 
experimentally from the following equation: 
##EQU1## 
The weight of unused bed, WUB, is a measure of the sharpness of the mass 
transfer zone. The lower the WUB, the more efficient is the use of 
adsorbent for the separation in the experimental column. Surprisingly, 
silicalite, 13X and the Alumina/NaY mixture displayed the lowest values of 
WUB and are therefore preferred for the adsorption of ethanol from 
mixtures thereof with ETBE in the present invention. 
EXAMPLES II 
The adsorption and regeneration steps of Example I were repeated following 
the regeneration of the samples of some adsorbents tested in Example I. 
The regeneration was carried out with helium, an inert gas, at 230.degree. 
C. as described in Example I. The results following this first cycle are 
shown in Table 2. 
TABLE 2 
______________________________________ 
ADSORBENT CAITY AFTER FIRST CYCLE 
Breakthrough 
Stoichiometric 
Weight of 
Adsorbent 
Loading, wt-% 
Loading, wt-% 
Unused Bed, % 
______________________________________ 
Silicalite 
7.4 8.4 12 
13X 8.7 11.2 22 
4A 0.5 1.5 67 
5A 1.2 2.8 57 
Silica Gel 
2.3 5.1 55 
Alumina/ 8.3 10.4 20 
NaY 
______________________________________ 
The adsorbent capacity for silicalite, 13X and the Alumina/NaY mixture 
showed some reduction in cycled capacity with a consistently sharp mass 
transfer zone as evidenced by the weight of unused bed remaining below 
about 20%. The 4A and 5A zeolites showed significant capacity reductions 
after one cycle, while the relatively weak and non-selective capacity of 
the silica gel adsorbent remained essentially the same with a long 
transfer zone. 
EXAMPLE III 
After the second or third regeneration cycle with helium according to the 
procedure described in Example I, a regeneration step using hexane vapor 
was employed. Pure n-hexane was employed to simulate the use of a 
hydrocarbon stream more consistent with industrial practice which may have 
some coadsorption effect. The results of this vapor phase hydrocarbon 
regeneration are shown in Table 3. 
TABLE 3 
__________________________________________________________________________ 
ADSORBENT CAITY AFTER N-HEXANE 
REGENERATION 
REGEN 
Breakthrough 
Stoichiometric 
Weight of 
Adsorbent 
Cycle # 
Loading, wt-% 
Loading- wt-% 
Unused Bed, % 
__________________________________________________________________________ 
Silicalite 
4 4.9 6.1 26 
13X 4 7.5 13.9 46 
Alumina/NaY 
4 8.2 10.2 20 
__________________________________________________________________________ 
The silicalite results indicated that the hexane regeneration caused a loss 
of capacity and a lengthening of the mass transfer zone. Because hexane is 
a non-polar material which should be a preferred adsorbate for 
silicalites, it appears that the ethanol is unable to easily displace the 
residual hexane, resulting in a lower breakthrough loading and a longer 
mass transfer zone. 
The use of hexane with 13X restored the capacity of the 13X to fresh 
capacity. However, the more difficult displacement of the n-hexane by 
ethanol appears to have resulted in a much longer mass transfer zone than 
with the helium regeneration of Example II. The use of n-hexane to 
regenerate the Alumina/NaY mixture restored the capacity without any 
change in the mass transfer zone. 
EXAMPLE IV 
The procedure of Example I for the regeneration with n-hexane was modified 
by not heating the regenerant and employing the n-hexane as a liquid at 
room or ambient conditions. This test was performed on the Alumina/NaY 
sample, following the vapor regeneration of Example 1II. The amount of 
ethanol desorbed from the Alumina/NaY material comprises one third of the 
adsorption capacity. Thus, liquid phase regeneration of the alumina/NaY 
adsorbent surprisingly also can be employed but at a reduced capacity (1/3 
of a heated regeneration). 
EXAMPLE V 
A series of Cases for the etherification of a hydrocarbon feed and the 
subsequent recovery of an ethanol free ETBE product are shown in Table 2. 
These were calculated from engineering design consideration and based on 
the performance of the 13X adsorbent in Example I. In all cases the 
regeneration was accomplished with a liquid regenerant at 110.degree. C. 
followed by cooling, and the ETBE product from the adsorption zone 
contained less than about 100 ppm-wt of ethanol. The flow schemes 
considered employed either a separate conventional etherification reaction 
zone and a distillation column, or a reaction with distillation, RWD, 
scheme wherein at least a portion of the etherification zone is contained 
in the distillation column. 
TABLE 2 
__________________________________________________________________________ 
REACTOR EFFLUENT 
REACTION 
STOICHIO- FEED % Wt-% Ethanol 
CASE 
FEED ZONE METRIC RATIO 
ISOBUTYLENE 
OVERHEAD 
BOTTOMS 
__________________________________________________________________________ 
A FCC CONV 1.01 15 1.5 1.65 
B FCC RWD 1.10 15 1.5 .66 
C DEHYDRO 
RWD 1.03 45 0.7 1.6 
D DEHYDRO 
RWD 0.95 45 0.7 .67 
__________________________________________________________________________ 
Case A, Table 2, represents the processing of about 45M metric tonnes/hour 
(100,000 lb/hr) of a C.sub.4 hydrocarbon feed from an FCC unit in a 
conventional etherification unit followed by the separation of the reactor 
effluent in a distillation column as shown in FIG. 2. The reactor was 
operated at an olefin conversion of 97%, and the ratio of ethanol to 
iso-alkene in the feed to the etherification reactor was 1% over the 
stoichiometric ratio. A three-bed adsorption system was employed for the 
removal of the 1.65% ethanol from the ETBE product, wherein each bed 
contained about 1.36 metric tons (3000 lb) of 13X adsorbent. The 
regeneration of the ethanol adsorption beds was accomplished with about a 
40% fraction of the feed; although about half of the distillation overhead 
could also be employed as the regenerant following a water wash step as 
shown in FIG. 1. 
Case B of Table 2 represents the processing of the same feed as Case A in 
an etherification unit wherein the distillation column contains an 
etherification reaction zone, operating at 98% olefin conversion with a 
stoichiometric ratio of ethanol to iso-olefin of 1.1. The resulting 
distillation column bottoms contained about 0.66 wt % ethanol as sent to a 
three-bed adsorption unit for the removal of the ethanol from the ETBE 
product. Each of the three adsorption beds contained about 0.9 metric 
tonnes (2,000 lb) of 13X adsorbent. The regeneration of the adsorbent beds 
was carried out with about a 27 percent of the feed, although about 30 
percent of the water washed distillation column overhead, comprising the 
unreacted C.sub.4 -C.sub.5 hydrocarbons, also could be employed as the 
regenerant. 
In case C, about 91M metric tonnes/hour (200,000 lb/hr) of a hydrocarbon 
feed comprising C.sub.4 hydrocarbon derived from a butane dehydrogenation 
process was passed to an etherification reaction zone and a distillation 
column wherein at least a portion of the distillation column contained 
second etherification reaction zone at an overall olefin conversion of 98% 
and a stoichiometric ratio of ethanol to iso-olefin of about 1.03. The 
resulting distillation column bottoms comprised about 0.67 wt-% ethanol. 
The distillation column bottoms was sent to a three-bed adsorption unit 
wherein each of the adsorption bed contained about 10.4 metric tonnes 
(23,000 lb) of 13X adsorbent. In this case C, almost all of the available 
feed was required to regenerate the adsorption beds. The results of this 
case C suggested that for this application, the etherification reaction 
zone should be operated at a lower stoichiometric ratio, even slightly 
sub-stoichiometric. 
Case D represented the same feed and reaction zone configuration of Case C, 
operated at a sub-stoichiometric ratio of 0.95 and at a corresponding 
olefin conversion of about 92%. The adsorption zone is the same as that of 
Case C; however, in Case D, the adsorption beds may be regenerated with 
essentially all of the water washed distillation column overhead.