USOO890 1359B2

(12) United States Patent (10) Patent No.: US 8,901,359 B2

BrOWn et al. (45) Date of Patent: Dec. 2, 2014

(54) ADSORPTION PROCESS FOR THE (52) U.S. Cl.

DEHYDRATION OF ALCOHOL CPC ...................................... C07C29/76 (2013.01)
USPC .......................................................... 568/916
(76) Inventors: Christopher Brown, Buffalo, NY (US); (58) Field of Classification Search
Marion Simo, Kenmore, NY (US) CPC ....................................................... CO7C 29/76
(*) Notice: Subject to any disclaimer, the term of this USPC licati - - - - - file? - - - - - - - - - - - - -i - - - - - - - - - - - - - -h hist 568/916
patent is extended or adjusted under 35 See application file for complete search history.
U.S.C. 154(b) by 320 days. (56) References Cited
(21) Appl. No.: 13/499.940 U.S. PATENT DOCUMENTS
(22) PCT Filed: Sep. 3, 2010 4,351,732 A * 9/1982 Psaras et al. .................. 210,689
4,407,662 A * 10/1983 Ginder ............................ 95/105
(86). PCT No.: PCT/US2010/047918
* cited by examiner
S371 (c)(1),
(2), (4) Date: Sep. 26, 2012 Primary Examiner — Elvis O Price
(87) PCT Pub. No.: WO2011/029071 74). Att
(74) Attorney, Agent, or Firm
Agent, or Firm —
— Paul
Paul T.
T. Lavoie.
Lavoie, EEsq.
PCT Pub. Date: Mar. 10, 2011 (57) ABSTRACT
65 Prior Publication D The present invention includes a process for the dehydration
(65) rior Publication Data of ethanol by adsorption of water at elevated pressure and for
US 2013/022.5880 A1 Aug. 29, 2013 the regeneration (purging) of adsorbent at a lower pressure
O O than the pressure used for the adsorption of water where the
Related U.S. Application Data ratio of the duration of the regeneration (purge) step to the
(60) Provisional application No. 61/239,585, filed on Sep. duration of the water adsorption step is higher than 0.1 and the
3, 2009. temperature of adsorption is greater than 260 degree Fahren
heit.
(51) Int. Cl.
C07C 29/76 (2006.01) 23 Claims, 3 Drawing Sheets
U.S. Patent Dec. 2, 2014 Sheet 1 of 3 US 8,901,359 B2

FGURE

E - Astorf FEEE E-Adsorritor FEE

3E2. WOWN BE) 2. FRE
time: C-210s tire 21-225 s

PRDuc
Ep 1. ADSCRPTIN FE Bed-slow of Fees
set 2. PRESSJRIZATION BE2-A80RPTION
the 225 - 34s time: 343 - 555 s

Ill.) ROUc
IV.)
FEED: wet ethanol span waive
PRO.DUCT: dry ethanol, desirably 29.95% ethang ised yaw.
EXHAUS, ethan-water fixtue recycled back...to distication
U.S. Patent Dec. 2, 2014 Sheet 2 of 3 US 8,901,359 B2

100°C
148"C
187"C
200°C
167°C (1/16"pelety
O
'6 12 14 f6 8 20 22 24 25 28 3) 55,
3. ka P(kPa) 3. Pa
Ji TET wk' INTE.

Figure 2: 3A Adsorption isotherm Data

U.S. Patent Dec. 2, 2014 Sheet 3 of 3 US 8,901,359 B2

Fig. 3
ra

8.
&ER388

388

34
 US 8,901,359 B2
1. 2
ADSORPTION PROCESS FOR THE U.S. Pat. No. 4,465,875 (“Greenbank’) and U.S. Pat. No.
DEHYDRATION OF ALCOHOL 4,407,662 (“Cinder') describe the use of molecular sieves to
dry the ethanol. U.S. Pat. No. 4,273,621 (“Fornoff)
FIELD OF THE INVENTION describes a process for the ethanol dehydration in the pres
ence of carbon dioxide using a crystalline Zeolite having a
This invention relates to the improvement of current pore size of 3 Angstroms with high affinity for water. The 3
adsorption process used for the alcohol dehydration in terms angstrom pore size is highly selective because the binding site
of new process arrangement and operation. for water is within a pore that is large enough to permit water
to enter into the pore, but is too small to allow ethanol to enter
BACKGROUND OF THE INVENTION 10 the pore.
United States Patent Application 20070000769 (“Brown
Lower alcohols (i.e. C 1-4 alcohols) are important compo I') incorporated by reference in its entirety discloses a pro
nents as reactants in a wide range of chemical processes and cess for producing fuel grade alcohol from a fermentation
as a fuel source. Ethanol has been mandated by the United process that includes use of pressure Swing adsorption. PCT
States government as a gasoline additive and/or as a major 15 Publication No. WO 2010/096626 (“Brown H') discloses the
component of automobile fuel. The use of ethanol as a fuel use of pressure Swing adsorption in a process for recovery of
additive has been gaining popularity because it is renewable methanol.
and is a cleaner burning fuel Source than most components of Common feature for all pressure Swing adsorption ethanol
gasoline. Particularly, production of ethanol worldwide has dehydration cycles encountered in the industry today is the
been steadily increasing over the past years. Ethanol is usu low value of the ratio of the purge time to the adsorption
ally produced by a fermentation process. The fermentation time—often about 0.05 or less. The other previously unsolved
broth, typically containing 5 wt.% to 13 wt.% ethanol, is constraint of the current-state-of-the-art is that the rate of the
distilled to increase the ethanol content beyond 90 wt.% and blowdown and the pressurization step is limited to ~25 Psia/
requires purification to greater than 99 wt.% to be useful as min. A faster rate will make the bed particles fluidize and thus
fuel grade alcohol. 25 cause irreversible damage to the adsorbent material.
Due to the existence of the ethanol-water azeotrope at a Thus, there is a need for a system of operation of an adsorp
concentration of about 95 wt.% ethanol, further ethanol tion bed for separation of water from lower alcohols that has
concentration is accomplished using azeotropic distillation or a greater Volume output without compromising purity, an
by adsorption separation process Such as a pressure Swing improvement in purity without compromising output, a
adsorption (pressure Swing adsorption) process. The dry etha 30 reduction in the blowdown or pressurization time without
nol stream preferably has less than 0.5% moisture content to increasing the loss of adsorbent. The present invention
meet the criteria for blending with gasoline. Azeotropic dis addresses these and other needs.
tillation requires the use of benzene to break the azeotrope.
Because of the carcinogenic nature of benzene, other efficient SUMMARY OF THE INVENTION
separation techniques are desirable. 35
Pressure Swing Adsorption (PSA) is a separation process The present invention includes a process for the dehydra
for selectively separating one component (“target compo tion of C 1-4 alcohol that increases the productivity or per
nent') from of a liquid mixture. The target component is formance of existing adsorption beds, particularly pressure
selectively adsorbed onto a solid adsorbent under relatively Swing adsorption beds. The present invention provides fuel
high pressure. At that pressure the other components are not 40 ethanol production facilities with increased ethanol yield.
adsorbed or is weakly adsorbed onto the solid adsorbent. With low operation pressure, less ethanol is used in regenera
After the capacity of the adsorbent to adsorb the target com tion. Additionally, the present invention provides protection
ponent is exhausted, the adsorbent is regenerated. Regenera against bed lift during depressurization and faster regenera
tion occurs by reducing the partial pressure of the target tion resulting from a bed design that introduces the alcohol
component in the adsorbent bed. This is accomplished by 45 feedstream from the bottom of adsorption bed. The present
lowering the total pressure of the vapor in the adsorption bed invention facilitates better interface with distillation resulting
and/or by passing a purge gas over the Solid adsorbent. The from increased re-pressurization time which provides
target component is released by this combination of pressure steadier flow of dried alcohol product. The quality of bed
reduction and purge from the Solid adsorbent into the purge regeneration is improved which improves the dried alcohol
stream. The adsorbent bed is then re-pressurized and has a 50 yield and bed drying capacity.
regenerated capacity to adsorb more of the target component In one embodiment, the system allows better interface with
onto the surface of the solid adsorbent. downstream operations recovering heat from the dehydrated
The original pressure Swing adsorption cycle was invented ethanol stream.
by Skarstrom in 1960 (See U.S. Pat. No. 2.944,627). Accord In one embodiment, there is a process for the dehydration
ing to Skarstrom, the two steps of adsorption and regeneration 55 of a C 1-4 alcohol comprising the steps of: (1) providing an
(or purge step) are carried out in two adsorbent beds operated adsorption bed having an adsorbent material; (2) first contact
in tandem, enabling the processing of a continuous feed. ing a feedstream comprising C 1-4 alcohol and water at a
Since the introduction of the Skarstrom cycle, many more temperature above 260 F with an adsorption bed at a first
Sophisticated pressure Swing adsorption processes have been pressure for an adsorption phase time to produce a dehydrated
developed and commercialized. Such processes have 60 alcohol stream; (3) reducing the pressure of the adsorption
attracted increasing interest more recently because of their bed to a second pressure for a blowdown phase time; (4)
low energy requirements and low capital investment costs. second contacting the dehydrated alcohol stream with the
One of the earliest disclosures of removing water (target adsorption bed for a purge phase time at a second pressure
component) from ethanol by pressure Swing adsorption is wherein the ratio of the purge phase time to an adsorption
found in U.S. Pat. No. 2,137,605 (“Derr'). Derr describes a 65 phase time is greater than 0.1; and increasing the pressure of
method that uses freshly reactivated alumina to adsorb the the adsorption bed to the first pressure for a pressurization
moisture. phase time.
 US 8,901,359 B2
3 4
In one embodiment, the adsorption bed has a top end and a DETAILED DESCRIPTION OF THE INVENTION
bottom end and the feedstream enters the adsorption bed from
the bottom of the bed and the purge stream enters the adsorp Definitions
tion bed from the top of the bed. “C 1-4 alcohol is a hydrocarbon alcohol having one to
In another embodiment, there is a process for the dehydra- 5 four hydrocarbons in each molecule. For example ethanol is a
tion of ethanol. The process includes providing an adsorption C2 hydrocarbon.
bed having a water adsorbent material. A feedstream com “Dehydration' is the selective removal of water from a
prising C1-4 alcohol and water is contacted at a temperature composition resulting in a composition having a lower water
above 260 degrees F. with an adsorption bed at a first pressure 10 content after dehydration. Dehydration of alcohol involves
for an adsorption phase time to produce a dehydrated alcohol separation of water from a primary alcohol stream.
stream. The feedstream enters the bed from an inlet at the Adsorption bed” is a bed of solid material that selectively
bottom of the adsorption bed. The pressure of the adsorption binds to at least one component in a multi component system
bed is reduced to a second pressure for a blowdown phase over at least one or more other components in that system.
“Feedstream” as used in the present invention is the stream
time. The dehydrated alcohol stream is contacted with the 15 containing
adsorption bed for a purge phase time at the second pressure. or a portionalcoholof
and water that is processed to remove all
the water in a pressure Swing adsorption
The pressure of the adsorption bed is increased to the first system.
pressure for a pressurization phase time. The cycle is Adsorption phase, as used in this invention is the phase
repeated. where feedstream is passed through a bed in the pressure
In one embodiment, the ratio of purge phase time to the 20 Swing adsorption system to remove water at a pressure that
adsorption phase time is greater than 0.2, preferably greater favors the selective adsorption of water onto the adsorbent in
than 0.3, more preferably greater than 0.5 and optimally the system.
between 0.5 and 1.0. “Blowdown phase' is the phase typically following the
In another embodiment, the step of providing provides two, adsorption phase where the pressure is reduced from the
three or four adsorption beds in a pressure Swing adsorption 25 adsorption pressure to a lower pressure that favors removal of
system preferably two beds in the system. the alcohol from the adsorbent.
In still another embodiment, the feedstream temperature is “Regeneration phase' or “purge phase' is the phase that
greater than 260 degrees Fahrenheit, preferably greater than typically follows the blowdown phase where the partial pres
300 degrees Fahrenheit, more preferably greater than 320 sure of water is sufficiently low to favor the separation of
degrees Fahrenheit. 30 water from the adsorbent.
In still another embodiment, the ratio of first pressure to “Pressurization phase' is the phase that typically follows
second pressure is greater than 10. In another embodiment the the regeneration phase where the pressure is increased from
pressure Swing adsorption system is a pressure vacuum Swing the regeneration pressure to the adsorption pressure.
adsorption system. Optionally, the feed pressure is less than 35 "Purge stream' is a stream that passed through and adsorp
25 psia (preferably less than 20 psia) and the reduced pressure tion bed during the regeneration phase to aid in the separation
of water from the adsorbent.
for blowdown is less than 2.5 psia (preferably less than 2 “Exhaust stream' is a stream that removes gas from the
psia). adsorbent bed during the blowdown phase, and purge phase.
In still another embodiment, the dehydrated alcohol stream Improved Pressure Swing Adsorption Process
produces an exhaust stream that is directed to a distillation 40 Without being limited to a particular theory of operation,
column. experimental and mathematical modeling studies of the etha
In yet another embodiment, the feedstream comprises less nol dehydration pressure Swing adsorption process have
than 10 wt.% water. revealed that by increasing the duration of the purge step
Optionally, the step of reducing pressure and the step of (terror) the ratio terror/tos will be increased and the pres
increasing pressure has a rate of pressure change that is 45 Sure Swing adsorption unit will have improved performance
greater than 30 psi per minute and preferably greater than 50 including: (1) better product quality without increased oper
psi/minute. ating cost; (2) higher throughput while delivering the product
Alternatively, the adsorbent has a pore size larger than the of the same quality (eg. 99.5% pure dry ethanol in one
average diameter of a water molecule but smaller than the embodiment) or (3) reducing capital expenses by using a
average diameter of the alcohol. Preferably, the pore size is 50 Smaller pressure Swing adsorption system to accomplish the
less than 4 angstroms, most preferably about 3 angstroms. same standard of drying that could previously be obtained
Optionally, the molecular sieve is a 3 angstrom Zeolite with a larger system. However, these benefits are non-limiting
molecular sieve catalyst available from various Suppliers. as there are more variables that can affect the performance of
In one embodiment, the C1-4 alcohol is methanol or etha a pressure Swing adsorption unit. For example one could
nol. In another embodiment, the C 1-4 alcohol is ethanol. 55 increase the purge flow rate while keeping the to con
Stant.
DESCRIPTION OF THE DRAWINGS A more general operating parameter is defined in order to
capture the idea of our invention:
FIG. 1 is a schematic of a two-bed pressure Swing adsorp
tion system illustrating the four stages of a pressure Swing 60
adsorption cycle which can be operated with more efficiency P Volume of Purge tpuRGE X Vp iPURGE X Fp X PH
according to one embodiment of the present invention. F T Volume of Feed T tADS X VF iADS X FF X PL
FIG. 2 is a chart showing adsorption isotherm data for a 3
angstrom Zeolite catalyst.
FIG.3 is a schematic of a pressure Swing adsorption system 65 where duration of steps was defined previously, V and V.
integrated with an ethanol distillation column according to correspond to the volumetric flow rate of the feed and purge,
one embodiment of the present invention. respectively (both in actual Volume units). After rearrange
 US 8,901,359 B2
5 6
ment and introduction of molar flow rates of the purge (F) adsorption step. In the example of FIG. 1, the adsorption time
and the feed (F) and the operating pressures we get the of BED 1 is 345 seconds, while the BED 2 undergoes blow
definition of P/F ratio (purge to feed ratio). down phase, purge phase and pressurization phase that total
This ratio is often utilized to characterize the operation of 345 seconds likewise. Afterwards the beds are switched and
a pressure Swing adsorption process. The recommended 5 the sequence repeats itself.
value for the efficient operation is usually close to unity. BLOWDOWN: Blowdown is illustrated in FIG. 1 part I
However, the value characterizing the operation of current and part IV. The bed 2 in part I and bed 1 in part IV is
ethanol pressure Swing adsorption process is close to 0.07. It depressurized from the relatively high pressure of part I to low
is one object of the present invention to operate the ethanol the relatively low pressure of part II, typically 2.5 to 3.5 psia.
dehydration pressure Swing adsorption unit with higher val 10 The blowdown occurs by shutting off the feedstream to the
ues of P/F ratio than currently used. bed and withdrawing the gaseous content of the bed through
The definition of physically meaningful cycle requires that an exhaust stream until the desired pressure is reached. The
the condition taps tou--terce+teres is satisfied. To exhaust stream is recycled back to downstream distillation
increase the P/F ratio, while keeping the flows and pressures process. As noted, the system described in FIG. 1 has a net
constant, the following expression needs to be maximized:
15 fluid flow during the blowdown that is in the direction of the
top of the adsorbent bed. Thus, a blowdown rate of pressure
change cannot typically exceed 25 psia per minute. In one
iPURGE ADS - BLOW - PRES
embodiment, the blowdown time is about 210 seconds and
iADS iADS
corresponds to an adsorption time of 345 seconds.
PURGE: The purge step is illustrated in FIG. 1 part II. Bed
2 is regenerated (purged) using a portion of dry ethanol from
The higher the time required for the blowdown and pres the product stream and cycling it into the bottom of Bed 2 for
surization steps is, the lower the value of P/F ratio is found. a period of time. While the example of FIG. 1 shows a system
Thus, it is desirable to reduce the duration of blowdown and having a short purge time of 15 seconds with an adsorption
pressurization steps in order to increase the P/F ratio. Previ 25 time of 345 seconds, extending the adsorption time to 360
ously, pressure Swing adsorption operating conditions were seconds, doubles the purge time (30 seconds) and greatly
constrained to a rate of pressure change in the bed to less than improves the product quality as illustrated in Example 1
25 Psia/min. Pressurization rate above this would cause tur below.
bulence in the absorption bed. This in turn would cause the PRESSURIZATION: The pressurization step is shown in
adsorption particles to break down (disintegrate) more rap 30 FIG. 1 part III. The pressure in Bed 2 is raised from P, to P.
idly. The disintegration would increase operating cost making using a portion of the dry ethanol product stream. After the
operation above this threshold prohibitively expensive. In one pressurization is complete the bed is ready to be switched to
embodiment, the flow in the pressure Swing adsorption unit is the adsorption step. The pressurization time in one non-lim
reversed so that flow during the adsorption step is from the iting embodiment is 125 seconds. The pressurization rate is
bottom to the top of the adsorption bed. In contrast, flow 35 limited by the fact that the pressure change in the adsorbent
during the purge phase, blowdown phase and pressurization bed cannot exceed 25 psia per minute without introducing
phase is from bottom to the top. Thus, by increasing the rate destructive turbulent flow in the system.
of blowdown, the blowdown and pressurization steps can Improvements in Operation
occur more rapidly leaving more time in the desorption cycle In one preferred embodiment, when operatingatan adsorp
to purge the adsorption system. 40 tion pressure less than 40 psia and particularly less than 25
As a result, higher values of P/F ratio (closer to 1) can be psia or 20 psia a greater product yield can be obtained by
achieved in the pressure Swing adsorption unit. operating at a temperature that is greater than 260 degrees
Description of the present invention is made with reference Fahrenheit, preferably 300 to 330 degrees Fahrenheit. The
to FIG.1. An alcohol (eg. ethanol) dehydration process using higher temperature for one, permits operating at relatively
the pressure Swing adsorption system with 3A zeolite is illus 45 lower pressures as does developing higher purge Volumes.
trated. The ethanol dehydration pressure Swing adsorption The changes in temperature and pressure are permitted by
process utilizes two beds loaded with zeolite 3A. The three operating at a higher P/F ratio.
bed process is also used in the industry. Another preferred cycle reverses the flow of feedstream,
The below example have operating times that are a bench exhaust and product through the adsorbentbed system so that
mark by which process changes can be illustrated to improve 50 flow during adsorption occurs from bottom of the beds
performance. upward and flow during the blowdown, purge and pressuriza
ADSORPTION: The wet ethanol stream (feed), of one tion phases are downward. This permits more aggressive flow
embodiment, is introduced to the top of the bed at high pres during the blowdown and pressurization phases and ulti
sure (P). The feedstream enters the bed and a product stream mately allows a longer purge time relative to adsorption and a
containing dry ethanol is withdrawn from the wet ethanol 55 greater P/F ratio. Adsorption occurs at 20 psia for 300 min
stream. Typically in one embodiment, pressure between 55 utes; purge pressure is less than 1.8 psia with a blowdown
psia and 100 psia is used in the adsorption stage. These time of 50 seconds, a purge time of 180 seconds, a pressur
operating parameters correspond to operating at a tempera ization time of 50 seconds. As a result a P/F ratio of between
ture that is a minimum of 260 degrees Fahrenheit, preferably 0.5 and 1.0 is easily obtained.
a minimum of 300 degrees Fahrenheit, most preferably a 60 The present invention entails the modifications of the cur
minimum of about 330 degrees Fahrenheit. Vapor flows rent PSA cycle sequence and of the operation arrangement in
downward through the bed. The water is being adsorbed and a way that will allow the PSA unit to operate more efficiently.
at the same time the high pressure dry ethanol product is The key elements of this invention include 1) a significant
withdrawn at the bottom of the bed. For a two bed system, the purge time to aid in bed regeneration, 2) a hot wet feed vapor
duration of adsorption step defines the half cycle time. The 65 above 300F flowing upwards through the adsorption bed, 3)
duration of the remaining steps (blowdown, purge and pres a downward flow for depressurization and pressurization to
Surization) together preferably equal to the duration of allow shorter times for these steps, 4) a long purge time also
 US 8,901,359 B2
7 8
in a downward flow and 5) as a consequence of better bed purge the water that is selectively adsorbed in the pores of the
regeneration from 1 through 4 a lower adsorption pressure molecular sieve and withdraw such purge stream along regen
becomes possible allowing the potential use of waste heat for erate product line 32 under vacuum conditions. This purge
vaporization. step will take 3 minutes in this example. Once the purge is
With reference to FIG. 3, an ethanol drying system 10 is 5 completed for the second molecular sieve unit 20B, depres
disclosed according to one embodiment of the present inven surization outlet valve 22B is closed while purge inlet valve
tion. It will be understood that this system can be modified to 25B is increasingly open so that dry ethanol from first
dry other alcohols, including alcohols that do not form azeo molecular sieve unit 20A can pressurize the second molecular
tropes with water or do not form constant boiling mixtures sieve unit 20B in less than 50 seconds to the same pressure as
with water. Thus, it is understood that any discussion relating 10 the first molecular sieve unit 20A. An extra 20 seconds in the
to ethanol in the description of the schematic process in this regeneration cycle is available for Switching valves and for
specification may apply to other alcohols also. A wet ethanol establishing a final equilibrium of pressures between the two
feed stream 11 is vaporized in an ethanol vaporizer 12 heated molecular sieve beds.
by a waste heat stream 13 which may be in vapor or liquid
form as long as ethanol feed stream 11 can be vaporized at a 15 Dehydration begins for the second molecular sieve unit
pressure above 18 psia. The vaporized ethanol is fed along a 20B with the following valve arrangement. The second
vaporized ethanol feed stream 14 to an ethanol superheater 15 depressurization outlet valve 228 remains closed. The second
which is heated by process steam supplied by steam feed 16 purge inlet valve 25B is closed. The second product outlet
and withdrawn from the superheater steam condensate 17. valve 24B is opened, and the first inlet valve 21B is opened to
The superheated ethanol feed steam 18 is fed into a pressure facilitate flow from the vaporized wet methanol feed 18 into
20 the
vacuum Swing adsorption system 19. The pressure Swing second molecular sieve unit 20Band flow of dried ethanol
adsorption system 19 has a first molecular sieve unit 20A and from the second molecular sieve unit 20B through second
a second molecular sieve unit 20B. Optionally, a third product outlet valve 24B and master product outlet backpres
molecular sieve unit 20O may be included. However, for the sure valve 27 into dry ethanol stream 30. The regeneration
sake of illustration, the fluid system is shown for a two-bed 25 process as described above for the second molecular sieve
system only. A person of ordinary skill in the art will readily unit 20B is repeated for the first molecular sieve unit 20A.
be able to adapt the flow diagram to accommodate a three-bed Preferably, the regeneration occurs at a pressure below
or greater bed number pressure Swing adsorption system atmospheric pressure under a vacuum created by the vacuum
without undue experimentation. system 50. The regenerate leaves the second molecular sieve
While the first molecular sieve unit 20A is in a dehydration 30 unit 20B as a vapor stream. It is cooled in a regenerate con
mode, the second molecular sieve unit 20B is in regeneration denser 60 Supplied by a cooling water source designated
mode where the second molecular sieve unit 20B is first CWS,
depressurized, then purged with the dry ethanol stream and Condensed regenerate product comprising mixed water
finally re-pressurized. The adsorption time for each bed is and ethanol is withdrawn along stream 33 by regeneration
generally from 4 to 10 minutes. For this example the time for 35 pump 55 and returned to other processes in the plant. Con
operating one bed under adsorption and the time to fully densed dry ethanol from product condenser 40 is withdrawn
regenerate the other bed will be taken as 5 minutes. During along stream 34 by product pump 45 and further cooled and
this part of the cycle, the first inlet valve 21A is open and the sent to storage. The vacuum system includes a water make 35
second inlet valve 21B is closed directing the vaporized wet up to assist in the vacuum operation and to control the con
methanol feed from line 18 into the first molecular sieve unit 40 centration of ethanol in the regeneration condensate 33 and
20A. As the ethanol passes upwardly through the molecular also includes a vent stream 36 to remove leakage air entering
sieve unit 20A, water is selectively adsorbed into the pores of the vacuum. Vacuum system condensate 37 is returned to the
the molecular sieve and the dry ethanol passes through a first regeneration condenser 60 while non-condensed vapor and
product outlet valve 24A and master product outlet backpres air 38 is sent from the regeneration condenser 60 to vacuum
sure valve 27 along dry ethanol stream 30 and to product 45 system 50.
condenser 40. During the entire regeneration process, second EXAMPLE 1.
product outlet valve 24B is closed to prevent flow of regen
erate into the dry ethanol stream 30. This example shows how the change in the P/F ratio can be
Under regeneration conditions, the second molecular sieve increased by increasing the purge step and adsorption step
unit 20B is first depressurized in a downward flow in less than 50
50 seconds to approximately 1.0 to 1.5 psia. During depres ues duration while keeping the other variables constant. The val
surization, both the first purge inlet valve 25A and second from the pressure Swing adsorption process described in
purge inlet valve 25B are closed to prevent purge from enter FIG. 1 were used for illustration.
ing the second molecular sieve unit 20B during depressuriza TABLE 1
tion. The first depressurization outlet valve 22A is closed to 55
prevent flow of the wet ethanol feed steam 18 into the regen OLD PROCESS NEW PROCESS
erate product line 32. The second depressurization outlet
valve 22B is ramped open allowing flow from the second tADss 345 360
tBLoWs 210 210
molecular sieve unit 20B along regenerate product line 32. tPURGE |s| 15 30
The regenerate product will contain a mixture of ethanol and 60 tPRESs) 120 120
water. The regenerate product line is under a vacuum condi tpURGE/tADS O.043 O.083
tion as a result of the vacuum system 50. Thus, regenerate Product 99.48% 99.68%
product flows freely from the pressurized second molecular wt % EtOH)
sieve unit 20B along the regenerate product line 32.
Once the second molecular sieve unit 20B is fully depres- 65 Only a 15 seconds increase in the purge step duration doubles
surized, the second purge inlet valve 25B is opened allowing the P/F ratio and as a result the quality of produced ethanol
a controlled flow of dry ethanol through control valve 26 to was improved.
 US 8,901,359 B2
9 10
EXAMPLE 2 5. The process of claim 1, wherein the ratio offirst pressure
to second pressure is greater than 10.
This example illustrates how the reverse flow operation 6. The process of claim 5, wherein the first pressure is less
(feeding from the bottom of the bed) of the ethanol pressure than 25 psia and the second pressure is less than 2.5 psia.
swing adsorption unit affects the P/F ratio and eventually the 7. The process of claim 1, wherein the step of reducing the
final product quality. Virtually 100% dry product can be pro pressure and contacting the dehydrated alcohol stream pro
duced by this simple adjustment of the process arrangement. duce an exhaust stream that is directed to a distillation col
By assuming the rate of pressure change in the blowdown and l
pressurization step 53 Psia/min, an order of magnitude 8. The process of claim 1, wherein the feedstream com
increase in the P/F ratio is observed, see Table 2. Alternative 10 prises less than 10 wt.% water.
option to exploit this benefit will be to operate with higher 9. The process of claim 1, wherein the adsorption bed has
feed flow rate and thus increasing the productivity of the a top end and a bottom end and the feedstream enters the
pressure Swing adsorption process (kg of EtOH/hr/kg of Zeo adsorption bed from the bottom of the bed and the purge
lite). stream enters the adsorption bed from the top of the bed.
15 10. The process of claim 6, wherein the step of reducing
TABLE 2 pressure and the step of increasing pressure has a rate of
pressure change that is greater than 30 psi per minute.
OLD PROCESS NEW PROCESS 11. The process of claim 1, wherein the C 1-4 alcohol is
tADssl 345 345 ethanol.
tBLoWs 210 60 12. A process for the dehydration of ethanol comprising the
tPURGE |s| 15 225 steps of:
tPRESs) 120 60 providing an adsorption bed having a water adsorbent
tPURGE/ADs O.043 O.652
Pressure change rate, 25 53 material;
Psia?min contacting a feedstream comprising C 1-4 alcohol and
Product wt % EtOH) 99.48% 99.999% 25 water at a temperature above 260 F with an adsorption
bed at a first pressure for an adsorption phase time to
Our experiments and data development for PVSA opera produce a dehydrated alcohol stream, wherein the feed
tions with 3A Zeolite have established an optimal tempera stream enters the bed from an inlet at the bottom of the
ture range for use in design of these systems in alcohol dehy adsorption bed;
dration. The following chart illustrates the point: 30 reducing the pressure of the adsorption bed to a second
The molar adsorption of 3A Zeolite, based on direct experi pressure for a blowdown phase time;
mental data we have collected demonstrates and proves that contacting the dehydrated alcohol stream with the adsorp
operation at 167 C (332 F) is far superior to the lower tem tion bed for a purge phase time at the second pressure;
perature specified by Ginder. The adsorptive capacity as increasing the pressure of the adsorption bed to the first
shown above is 3.8 times for 167 C (322 F) compared to 100 35 pressure for a pressurization phase time.
C (212 F). FIG. 2 shows the equilibrium water content of the 13. The process of claim 12, wherein the step of providing
Zeolite at 55 kPa partial pressure (inlet conditions) and 3.5 provides two adsorption beds in a pressure Swing adsorption
kPa partial pressure (outlet conditions). The difference system.
between the two pressures determines the overall Zeolite 14. The process of claim 12, wherein the purge phase time
adsorptive capacity and this pertains to any total pressure 40 to the adsorption phase time is greater than 0.2.
operation of adsorption and desorption. 15. The process of claim 12, wherein the feedstream tem
What is claimed is: perature is greater than 300 degrees Fahrenheit.
1. A process for the dehydration of a C 1-4 alcohol com 16. The process of claim 12, wherein the ratio of first
prising the steps of: pressure to second pressure is greater than 10.
providing an adsorption bed having an adsorbent material; 45 17. The process of claim 16, wherein the first pressure is
first contacting a feedstream comprising C 1-4 alcohol and less than 25 psia and the second pressure is less than 2.5 psia.
water at a temperature above 260 degrees Fahrenheit 18. The process of claim 12, wherein the feedstream is
with an adsorption bed at a first pressure for an adsorp from the overhead of a distillation column and the step of
tion phase time to produce a dehydrated alcohol stream; reducing the pressure and contacting the dehydrated alcohol
reducing the pressure of the adsorption bed to a second 50 stream produces an exhaust stream that is directed to the feed
of a distillation column.
pressure for a blowdown phase time;
second contacting the dehydrated alcohol stream with the 19. The process of claim 12, wherein the feedstream com
adsorption bed for a purge phase time at a second pres prises less than 10 wt.% water.
Sure wherein the ratio of the purge phase time to an 20. The process of claim 12, wherein the ratio of the purge
adsorption phase time is greater than 0.1; and 55 phase time to an adsorption phase time is greater than 0.1.
increasing the pressure of the adsorption bed to the first 21. The process of claim 16, wherein the step of reducing
pressure for a pressurization phase time. pressure and the step of increasing pressure has a rate of
2. The process of claim 1, wherein the step of providing pressure change that is greater than 30 psi per minute.
provides two adsorption beds in a pressure Swing adsorption 22. The process of claim 12, wherein the adsorbent has a
system. 60 pore size larger than the average diameter of a water molecule
3. The process of claim 1, wherein the ratio of the purge but smaller than the average diameter of the alcohol.
phase time to the adsorption phase time is greater than 0.2. 23. The process of claim 12, wherein the C 1-4 alcohol is
ethanol.
4. The process of claim 1, wherein the feedstream tempera
ture is greater than 300 degrees Fahrenheit.