METHOD AND SYSTEM FOR DISTRIBUTING LIQUID IN
(METH)ACRYLIC MONOMER PROCESS VESSELS
FIELD OF THE INVENTION
The present invention relates to chemical processes and the associated processing
equipment, in particular methods and process equipment for the preparation of
(meth)acrylic monomer.
BACKGROUND OF THE INVENTION
In the preparation of (meth)acrylic monomers, there are many vapor-liquid
contacting operations in which it is necessary to uniformly distribute a liquid stream over a
large cross-sectional area within a process vessel. The majority of these process operations
involve the collection or purification of (meth)acrylic monomer streams, such as for
example quenching, condensing, absorbing, and distilling operations. These operations are
typically performed in process vessels resembling upright cylinders, such as towers and
columns. Such process vessels commonly range in diameter from about 0.3 meter ( 1 foot)
up to about 9.2 meters (30 feet).
Liquid distribution equipment is generally located in the upper part of the process
vessel above any contact-enhancing internal components that may be present. In operation,
process liquid passes through the distribution equipment, is divided and broken into a series
of sheets, streams, and droplets, and then flows downward through the vessel under the
influence of gravity, while vapors simultaneously pass upward through the vessel. Mass
and energy transfer between the liquid and vapor occurs across the surface of the liquid;
process efficiency is enhanced when there is a high liquid surface area to promote contact
with the vapor, such as when a large number of liquid droplets are uniformly distributed
throughout the cross-section of the vessel.
Various types of liquid distribution devices include pipes, trays, troughs, rotating
armatures, and spinning disks. Such devices are intended to distribute liquid flows over a
large area and frequently are combined with other internal components, such as packed
beds, structured packing, or distillation trays, which serve to further distribute liquid flow in
an effort to maximize coverage and generate large amounts of liquid surface area. These
devices include stationary distributors, such as those described in U.S. Patent No. 3,969,447,
which describes a typical piping-based distributor comprising bottom-mounted spray
nozzles, and U.S. Patent No. 3,392,967, which describes a typical trough-type distributor.
Distributors are also described that revolve about a central axis by means of being mounted
to a rotating shaft (U.S. Patents No. 3,079,092; No. 1,464,816; No. 470,375; GB 1161560).
Examples of such distributors are also described in GB 726151, which describes a rotating
trough comprising bottom drain tubes, and U.S. Patent No. 3,353,802, which describes a
combination of a rotating distribution armature and baffles for use in vessels of rectangular
cross-section. Finally, spinning disks of various configurations have also been proposed as
means for distributing concentrated liquid feed streams; such devices are for example
described in US Patent application No. 201 1/144384, in which a Continuous Stirred Tank
Reactor (CSTR) feed stream is vigorously deflected by a spinning disk mounted on the
agitator shaft.
Current liquid distribution devices, however, have a disadvantage in that they
provide large process-facing surfaces within the vapor spaces of (meth) acrylic monomer
process vessels on which monomer vapors may condense and form polymer accumulations.
The accumulation of polymeric solids is a common problem for the preparation of
(meth)acrylic monomers because the foulants may interfere with the proper operation of the
vessel and disturb the intended chemical processes occurring within the vessel. Eliminating
the foulants may require costly cleaning operations and process downtime. In particular,
the formation of condensation polymer in the vapor spaces of (meth)acrylic monomer
process vessels, such as quench vessels, absorbers, contact condensers, scrubbers, heat
exchangers, distillation columns, reactors, and storage tanks, is a well-known and ongoing
problem. A quench vessel may also be known as a quench column, spray cooler, quench
cooler, contact cooler, and quench system.
Condensation polymer forms within process vessels when (meth)acrylic monomer
vapors condense on process-facing surfaces in the absence of polymerization inhibitors.
Process-facing surfaces on which condensation polymer accumulations are known to occur
include the top head and walls of process vessels; the interior surfaces of vessel nozzles and
manways; instrumentation and emergency pressure relief devices; internal structures such
as distillation trays, packing, baffles, and support structures; and even on the interior
surfaces of process piping directly connected to such vessels. For example, U.S. Patent No.
3,717,553 teaches that dry wall regions under distillation trays are prone to polymer
accumulation and recommends wetting them; U.S. Patent No. 7,892,403 teaches that the
supports for stationary spray nozzles can accumulate condensation polymer & recommends
placing such support members outside of the vessel; and U.S. Patent No. 6,983,758 teaches
that the presence of stationary spray nozzles and associated supply lines provides surfaces
for the accumulation of condensation polymer and that low flow regions such as nozzles
and manways are also prone to condensation polymer accumulations.
There are many variations of tank cleaning nozzles used to clean process vessels. A
common feature of tank cleaning nozzles is the reliance on highly pressurized sprays or
liquid jets to dislodge accumulated foulants through liquid impact. These devices are
intended to be used intermittently, during cleaning periods when process equipment is not
operating. Furthermore, any fouling-material dislodged must still be removed from the
process vessel, or it will merely transfer the fouling problem to a different part of the
process.
Thus, there is a need for liquid distribution equipment and/or methods which can
uniformly distribute liquid over the internal cross-section of (meth)acrylic monomer
process vessels while suppressing the formation of condensation polymer.
SUMMARY OF THE INVENTION
One aspect of the invention provides a method for uniformly distributing a process
liquid within a process vessel, comprising;
a) providing a process liquid to a fouling-resistant liquid distributor comprising a
liquid distribution head, installed within a process vessel having a crosssectional
area;
b) causing rotational movement of the fouling-resistant liquid distributor; and
c) uniformly distributing the process liquid over the cross-sectional area within the
process vessel.
The method of the invention further comprises simultaneously self-rinsing the at
least one fouling-resistant liquid distributor with a portion of the process liquid during step
(c) and/or providing the process liquid during step (c) to a plurality of the fouling-resistant
liquid distributors, wherein each of the fouling-resistant liquid distributors simultaneously
rinse each other with a portion of the process liquid during step (c).
The simultaneously self-rinsing of the fouling-resistant liquid distributor with a
portion of the process liquid during uniform distribution has never been disclosed nor
suggested in prior art.
Another aspect of the invention, the rotational movement in step (b) is achieved by
supplying at least one of a motive fluid and the process liquid to the liquid distribution head.
Yet another aspect, the process vessel is a (meth)acrylic monomer process vessel
and the process liquid comprises one or more polymerization inhibitors.
Another aspect of the present invention provides a system for uniformly distributing
a process liquid within a process vessel comprising a supply of process fluid, a stationary
conduit, and a liquid distribution head attached to the conduit, preferably to an end of the
stationary conduit. The liquid distribution head is motive, powered by a fluid, preferably
by the process fluid, and comprises at least one process liquid delivery port, preferably a
plurality of liquid delivery ports. The at least one process liquid delivery port is configured
to provide a +10° or greater angle of liquid coverage when the liquid distribution head is
moving.
Yet another aspect of the present invention provides a process vessel comprising the
said system.
Yet another aspect of the present invention provides a simple and cost effective
method for uniformly distributing liquid over the internal cross-section of (meth)acrylic
monomer vapor-liquid contacting vessels, without accumulating condensation polymer on
the distribution equipment.
Yet another aspect of the present invention provides a method for collateral wetting
of process-facing surfaces within the vapor space of (meth)acrylic monomer process
vessels, such as quench vessels, absorbers, contact condensers, scrubbers, heat exchangers,
distillation columns, reactors, and storage tanks to further reduce the potential for polymer
accumulation within process vessels.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be more fully understood, the following figures are
provided by way of illustration, in which:
Figure 1 illustrates a vapor-liquid contacting vessel incorporating an embodiment of the
present invention;
Figures 2A-2G depict types of distributors which may be incorporated in various
embodiments of the present invention;
Figure 3 shows a vapor-liquid contacting vessel incorporating another embodiment of the
present invention; and
Figure 4A - 4C illustrate additional types of distributors which may be incorporated in
various embodiments of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The term "(meth)acrylic monomers," as used herein throughout the specification
and the claims, includes a , b-unsaturated carboxylic acids and esters, a group of compounds
which are known to form polymer when handled in the absence of polymerization
inhibitors. Such (meth)acrylic monomers are generally understood to include acrolein and
methacrolein, acrylic acid, and methacrylic acid, and also the esters of acrylic acid and
methacrylic acid. Specifically, the present invention relates to the preparation of one or
more compounds selected from the group consisting of acrolein, acrylic acid, methyl
acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-octyl acrylate, 2-
(dimethylamino) ethyl acrylate, methacrolein, methacrylic acid, methyl methacrylate, ethyl
methacrylate, butyl methacrylate, and 2-(dimethylamino) ethyl methacrylate. The present
invention may also be beneficially employed in the preparation of other (meth)acrylic
monomers not specifically named herein, including, but not limited to, so-called "specialty"
esters of acrylic acid and methacrylic acid such as those included in the product brochure,
Norsocryl ® SPECIALITY ACRYLIC AND METHACRYLIC MONOMERS. Arkema,
April 2005.
The present invention utilizes liquid distributors which may operate continuously,
whenever the process is operating, to uniformly distribute liquid throughout a process
vessel. By evenly supplying an adequate liquid volume, preferably with a high droplet
surface area, mass and energy transfer is enhanced in vapor-liquid contacting vessels, such
as (meth)acrylic monomer collection and purification equipment. According to various
embodiments of the present invention, self-rinsing of liquid distributors, as well as
collateral-wetting of process-facing surfaces, occurs prior to the accumulation of polymeric
solids, thereby preventing their formation.
Embodiments of the present invention may use a fouling-resistant liquid distributor
comprising a stationary conduit (pipe), which may be in any orientation (e.g. horizontal,
inclined, vertical), but is preferably oriented vertically within a vessel. The foulingresistant
distributor further comprises a motive fluid-powered liquid distribution head
attached to said conduit, the liquid distribution head comprising at least one process liquid
delivery port. The distribution head is capable of rotational movement and is attached to
one end of the vertical conduit. The distribution head is preferably compact for easy
installation/removal of the distributor for maintenance and inspection. A compact design
also allows the distributor to be installed with a minimum of supports or internal bracing,
which provides for a less complex and inexpensively installed distributor. A compact
design also allows for the option to install multiple distributors within a single vessel, if
desired.
In a preferred embodiment, the upper end of the vertically-oriented conduit passes
through a piping nozzle on the process vessel head, and the distribution head of the foulingresistant
distributor is attached to the lower end of the vertically-oriented conduit. When a
supply of process-compatible liquid is provided to the fouling-resistant liquid distributor,
the process liquid flows through the conduit to the distribution head, and is discharged
through one or more liquid delivery ports and into the process vessel. Referring to Figure 3,
a liquid distributor (301) according to the preferred embodiment of the present invention is
illustrated having a fixed vertical conduit (303) with a compact, moving distribution head
(304) attached to the lower end. It is preferred that the distribution head be small enough to
pass through a circular opening not more than 30cm (12") in diameter. The upper end of
the conduit (303) passes through vessel nozzle (302) in the process vessel top head and is
provided with a source of process liquid and, optionally, a source of motive fluid. As
previously mentioned, the liquid distributor may be oriented horizontally (i.e., the conduit
is horizontal) or at some other intermediate angle relative to the vertical plane; however, it
is preferred that a vertical orientation is used.
The distribution head comprises one or more liquid delivery ports through which the
liquid is discharged as a stream, a jet, or an atomized spray. The size, shape, and orientation
of the liquid delivery ports, as well as variables such as the liquid supply flow rate, pressure,
and viscosity, control the angle of liquid discharge, the distance that the discharged liquid
travels, and any geometric coverage pattem (e.g., circular, stream, flat fan, rectangular) that
the discharged liquid may create when it contacts a surface, such as the vessel wall.
Examples of liquid delivery port configurations include, but are not limited to, a cylindrical
hole, a port comprising a restriction orifice, a wedge-shaped slot, and a spray nozzle head.
In a distribution head comprising more than one delivery port, the configuration of each
port may or may not be the same.
Materials of construction for the liquid distributor (the conduit and the distributor
head) may include any process-compatible materials such as metals, plastics, ceramics,
composites, or combinations thereof. In one embodiment, the distributor comprises 300
series stainless steel, such as for example 304, 316, or 317 stainless steels. In another
embodiment of the invention, the distributor comprises both 300 series and 400 series
stainless steel components. In yet another embodiment, the distributor comprises polymerinhibiting
copper alloys, such as those described in U.S. Patent No. 7,906,679. In another
embodiment, the distributor comprises corrosion resistant materials, such as tantalum or
epoxy resins.
According to an embodiment of the invention, motive fluid flows through the
vertical conduit, and the distributor head, and is discharged during operation of the liquid
distributor. The motive fluid may be the process liquid or it may be a separate stream (e.g.,
compressed air, nitrogen, water, process liquid) used only for providing driving force for
movement. Motive fluid flows through the distribution head, driving continuous rotation of
the distribution head about the longitudinal axis of the conduit. In a preferred embodiment,
the distribution head smoothly and continuously revolves a full 360° around the conduit
axis in either a clockwise or counter-clockwise directions. Various drive mechanisms
known in the art, such as gears, internal turbines, or impulse paddles may be used to
operate the distributor. When the process fluid is not used as the motive fluid, the motive
fluid may alternatively be conveyed through means other than the conduit to the
distribution head or drive mechanism.
In an alternative embodiment of the present invention, the distribution head may
rotate through an arc of less than 360°, then reverse direction and retum to its initial starting
point; such movement would represent a continuously repeated, "cycling" form of
operation which may be beneficial in some processes. Additionally, in some embodiments,
the movement of the distribution head may be discontinuous, resembling the step-wise
movement of a rotary-impact lawn sprinkler. In another embodiment, the liquid stream
discharged from the distribution head may oscillate in a two-dimensional or even a threedimensional
wave-like pattern; such liquid discharges can be produced through the
incorporation of fiuidic oscillators within the distribution heads, such as those described in
US Patent No. 4,151,955.
In a preferred embodiment, the motive fluid is a process liquid, and the inertial force
of the process liquid discharging through the liquid delivery ports causes rotational
movement of the distribution head, such that the head moves in a direction opposite to the
direction of liquid discharge, i.e., discharging the process fluid causes propulsion of the
distribution head. The use of process fluid as the motive fluid is preferred because
movement of the distribution head is achieved without the need for a motor or a rotating
shaft and associated shaft seals, thereby reducing equipment costs, the potential for process
leaks through shaft seals, and maintenance issues, as well as lowering the total processfacing
surface area of the distributor on which monomer might condense.
The selection of the process liquid is determined by the process in which the liquid
distributor is to be used. Any liquid compatible with the process may be used. In instances
where the process is a (meth)acrylic monomer process, the process liquid may comprise
one or more of water, (meth)acrylic acid, (meth)acrylate esters, alcohols, solvents,
absorbents, and polymerization inhibitors. In a preferred embodiment, the (meth)acrylic
monomer process vessel is used in a process to produce one or more compounds selected
from the group consisting of acrolein, acrylic acid, methyl acrylate, ethyl acrylate, butyl
acrylate, 2-ethylhexyl acrylate, 2-octyl acrylate, 2-(dimethylamino) ethyl acrylate,
methacrolein, methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl
methacrylate, and 2-(dimethylamino) ethyl methacrylate. As it is common to operate
(meth)acrylate monomer process vessels at pressures other than atmospheric pressure (e.g.
sub-atmospheric pressure), it is generally desirable to supply process liquid to the liquid
distributor at a temperature below its boiling point at the operating pressure within the
process vessel. In some embodiments, the process liquid is supplied to the liquid
distributor at near ambient temperature (about 20°C). In some other embodiments, the
process liquid is supplied to the liquid distributor at, or even lower than, its condensation
temperature. Typically, the process liquid is supplied to the liquid distributor at a
temperature below its boiling point.
In a preferred embodiment, the process liquid comprises one or more
polymerization inhibitors. Said inhibitors are selected from compounds that inhibit the
polymerization of a- b-unsaturated compounds, such as (meth)acrylic monomers, and are
provided in an amount sufficient to prevent or reduce polymerization. Suitable
polymerization inhibitors include, but are not limited to, phenolic inhibitors (hydroquinone,
hydroquinone methyl ether, di-tert-butyl paracresol, etc.), phenothiazine, TEMPO nitroxyl
compounds of type 4-OH or 4-oxo TEMPO, or soluble manganese or copper salts, and their
mixtures.
According to one embodiment, the process vessel incorporating the present
invention may be a vapor-liquid contacting vessel selected from the group consisting of a
quench vessel, an absorption tower, a contact condenser, a fractionating condenser, a
dehydration tower, a finishing column, a scrubber, a distillation column, and a storage tank.
Alternatively, the process vessel may be an integrated process vessel comprising two or
more successive process sections selected from the group consisting of a quench section, an
absorption section, a partial condensation section, a scrubbing section, a packed section, a
contact condensation section, a trayed section, a stripping section, and a rectification
section. The process vessel may comprise one or more internal components selected from
the group consisting of trays, tray supports, structured packing, random packing, feed
distributors, demister pads, stationary spray nozzles, baffles, liquid distribution troughs, and
side draw collection trays.
According to various embodiments of the present invention, rotation of the
distribution head provides uniform liquid coverage, unlike stationary spray nozzles or
liquid distributor trays and contributes to optimal heat and mass transfer for vapor-liquid
contacting operations. In addition, the various embodiments of the present invention may
comprise a distribution head having one or more liquid delivery ports and/or a conduit
having one or more liquid delivery ports, such that the liquid distributor is self-rinsing.
"Self-rinsing", as used herein throughout the specification and the claims, means
discharging liquid from a liquid distributor onto the exterior surfaces of the distributor itself,
thereby providing a self-rinsing action. Preferably, a self-rinsing distributor included in an
embodiment of the present invention includes a distributor head with at least one delivery
port configured to provide a +10° or greater angle of liquid coverage when the distributor is
moving. The "angle of liquid coverage" is measured relative to the longitudinal axis of the
conduit, with 0° being parallel to the conduit and 180° being perpendicular to the conduit.
Positive angles signify liquid flows that are directed towards the point of attachment of the
conduit to the vessel wall. Negative angles signify liquid flows directed away from the
point of attachment of the conduit to the vessel wall. If the liquid distributor is not selfrinsing,
it is preferred that embodiments of the present invention include a plurality of
liquid distributors configured to discharge liquid onto each other, such that liquid expelled
from each of the liquid distributors is able to rinse the exterior surface of another proximate
liquid distributor.
Rinsing the exterior surfaces of the distributor (i.e., both the conduit and the
distribution head) prevents the accumulation of condensation polymer. The rinsing action
may be achieved, for example, by configuring individual distributor head ports to
continually discharge liquid onto itself or an array of distributors may also be configured to
rinse each other for greater reliability and more complete rinse-liquid coverage. The
movement of the distribution head also causes the shedding of liquid droplets from the
external surfaces of the distributor head, further reducing the tendency to accumulate
foulants.
The rotational movement of the distribution head of the fouling-resistant liquid
distributor also provides for collateral wetting, i.e. the distributor wets proximate processfacing
surfaces in the vapor space of the vessel with a portion of the process liquid within
the process vessel. Distributor movement assures uniform liquid coverage of large processfacing
surface areas, such as the vessel head and walls. Generally, the wetting liquid rate
resulting from collaterally-wetting the process-facing surfaces of the process vessel interior
is less than 0.5 m /m -hr. According to various embodiments of the present invention, it
may be possible to achieve highly efficient wetting by using a moving distributor which
requires a smaller volume of rinse liquid to keep surfaces free of condensation polymer
compared to previous systems.
In Figures 2A-2G, various embodiments of distributors are shown with varying
angles of liquid coverage. Embodiments 2A through 2D are self-rinsing, while
embodiments 2E through 2G are not. Figures 4A-4C represent additional self-rinsing
embodiments: 4A represents a configuration which combines two discharge ports, one of
which has a +60° and another which has a -90° angle of liquid coverage; 4B represents a
self-rinsing configuration in which the distribution head is at the upper end of the vertical
conduit, and the angle of liquid coverage is +270°; and 4C represents a self-rinsing
configuration in which the conduit is oriented horizontally and the angle of liquid coverage
is +180°.
It is recognized that a distributor head mounted on a conduit having a rotating shaft
may obtain some benefit with respect to a more-uniform liquid distribution within the
vessel. However, if the shaft and distributor head rotate in concert, self-rinsing may be
compromised if the distributor head does not include liquid delivery ports directed around
the circumference of the conduit. Rotating the shaft in concert with a distributor head
having an insufficient number or configuration of liquid delivery ports may create a dry
zone on the surface of the conduit because an area of the surface of the conduit may not
receive any liquid from upward-aimed discharge ports.
Thus, various embodiments of the present invention provide the benefit of improved
mass and/or heat transfer due to uniform distribution of process liquid. Also, because the
various embodiments of the invention may be self-rinsing, polymer accumulation on the
distributor may be prevented, as well as process-facing vessel surfaces which receive
collateral-wetting from the liquid distributor.
EXAMPLES
In order that the invention may be more fully understood, the following Examples
are provided by way of illustration only.
Example 1
Referring to Figure 1, a 4.3 meter (14 feet) diameter dehydration tower ( 110) may
be used as a vapor-liquid contacting vessel. The overall height of the dehydration tower
( 1 10) may be more than 45 meters (146 feet). The dehydration tower may be part of a
process for the recovery of acrylic acid, such as the process disclosed in U.S. Patent No.
8,242,308.
The dehydration tower ( 1 10) may be configured as an integrated process vessel,
meaning that the vessel comprises multiple process sections: an upper packed bed section
(140), a middle trayed section (145), and a lower quench section (150). Similar processing
steps could be performed in two or more successive process vessels rather than a single
vessel as used in this example.
The flow rate intended for uniform distribution will be about 14,545 kg/hr (32,000
lbs/hr) of process liquid across a bed of Mellapak™ 250.Y structured packing
(commercially available from Sulzer Chemtech of Pasadena, Texas USA) occupying the
entire cross-sectional area in the upper section (140) of the tower. The process liquid may
be a mixture of a reflux liquid stream (107), comprising condensed lights, and an inhibitor
package stream (108) comprising one or more of manganese ions, hydroquinone (HQ), 4-
hydroxy TEMPO (4-HT), and phenothiazine (PTZ). The reflux liquid stream (107) may
also comprise over 80 wt% water, as well as acetic acid and acrylic acid. The process
liquid flows downward through the packing, coming into intimate contact with a rising
vapor flow stream from the trayed section (145) comprising ten MVG™ fixed valve trays
(Tl through T10) (also commercially available from Sulzer Chemtech).
The dehydration tower overhead stream (106), comprising nitrogen, water, and
acetic acid, may pass through condenser ( 1 13) and form the reflux liquid stream (107) as
well as a vapor stream (102). The vapor stream (102) split into recycle gas stream ( 114)
may be recycled to a propylene oxidation reactor and vent stream ( 1 15) may be sent to one
or more waste gas processing systems, such as for example a fired incinerator or a catalytic
combustion unit (CCU).
Two identical fouling-resistant liquid distributors (131 & 132) may be installed in
the dehydration tower ( 110). The distributors may be made of 316 stainless steel
distribution heads attached to 3.8 cm (1.5 inch) diameter stationary conduits. Specifically,
the distribution heads may be TankJet® model #18250A-316SS45 fluid-driven tank
cleaning nozzles (commercially available from Spraying Systems Co., Wheaton, Illinois
USA). The process liquid may serve as the motive fluid to drive continuous rotation of the
distribution heads about the longitudinal axis of the stationary conduit.
Two 5 cm (2 inch) diameter flanged nozzles (not shown in the figure) may be
mounted on the dehydration tower top head, one on either side of overhead vapor line (106),
in positions that are about 1 meter (3.3 feet) from the vertical process vessel wall. The
liquid distributors (131 & 132) may be installed through these flanged nozzles, such that
they are oriented vertically, with the distribution heads located on the lower end of the
conduit. This results in a spacing between the two distribution heads of about 2.3 meters
(7.5 feet). The distribution heads may be positioned at the same elevation of about 1 meter
(3.3 feet) above the top surface of the packing in upper packed bed (140) and about 1 meter
(3.3 feet) below the highest interior point on the vessel top head.
Each of the distribution heads may include three liquid delivery ports fitted with
spray nozzles and configured to provide a 360° angle of liquid coverage. When process
liquid is supplied at a pressure of about 20 psi (138 kPa) and a temperature of about 138°F
(60°C), each of the fouling-resistant liquid distributors (131, 132) may deliver
approximately 120 liters per minute (32 gpm) of process liquid flow, resulting in a uniform
360° liquid distribution over a spherical spray diameter of about 2.4 m (8 ft) and selfrinsing
operation. Because of the optimal vapor-liquid contacting resulting from uniform
distribution of liquid droplets over the packing, the acrylic acid content of the overhead
vapor stream (106) may be beneficially minimized, thus providing an opportunity to reduce
processing costs. Additionally, the uniform liquid distribution may limit the occurrence of
dry regions within the packed bed, thereby preventing polymer accumulations on the
packing.
From Example 1, it is clear that the uniform liquid coverage provided by the
inventive distribution method may provide the potential for efficient mass and energy
transfer within the packed section of the dehydration tower, while simultaneously avoiding
polymer buildup on the distributors, the packing, and the process-facing surfaces of the
dehydration tower head and walls.
As recognized by one of ordinary skill, Example 1 demonstrates that the liquid
distributor could be beneficially employed within a (meth)acrylic acid absorber in which an
absorbent is instead utilized as the process liquid. It is fully expected that process liquids
comprising water, or even organics such as high boiling solvents like, for example,
diphenyl ether or toluene, could be effectively utilized as absorbents and uniformly
distributed according to an embodiment of the present invention.
Example 2
A similar vapor-liquid contacting vessel as used in Example 1 may be used in
Example 2. The applicability of the present invention to a process for the recovery of
acrylic acid may be applied in the cylindrical space generally defining quench section (150).
The quench section (150) may have an internal vessel diameter "D " of 4.3 meters (14 feet)
and a height of about 20 meters tall (65 feet). The quench section (150) would not
comprise any internal trays or packing to promote vapor-liquid contact. Instead, a plurality
of fouling resistant liquid distributors may be used to provide uniform liquid distribution
within the quench section (150) resulting in intimate vapor-liquid contact (for optimal mass
and heat transfer), as well as self-rinsing of the distributors and collateral wetting of the
vessel walls for the avoidance of polymer accumulation. The fouling resistant liquid
distributors may be installed in a series of five distribution arrays (Al, A2, A3, A4, A5),
with each distribution array being placed at a specific elevation along the vessel wall.
Each distribution array may comprise five horizontally-oriented distributors,
removably attached to the vessel wall, for a total of twenty-five installed distributors.
Within each distribution array, the five distributors may be evenly spaced at 72° intervals
along the circumference of the vessel wall and positioned geometrically Normal to the
interior surface of the wall. The distributors within successive arrays may be vertically
offset in order to create a staggered arrangement down the wall; for example, the
distributors in array Al would not align vertically with those of array A2. Each successive
array would be offset by 36° relative to the previous array.
Although not required, each distributor in each array may be identical in design and
comprise a 15.3 cm (6 inch) long conduit section, to which a 3.8 cm (1.5") model HWS-50
Hydrowhirl S® slotted spray nozzle (commercially available from BETE Fog Nozzle, Inc.
of Greenfield, Massachusetts, USA) is attached. Distributors having Teflon® components
should be avoided.
Process liquid flow to each distributor may be controlled such that 278 liters/minute
(74 gpm) is provided to each of the twenty-five distributors. At a supply pressure of 40 psi
(276 kPa), this flow of process liquid discharging from the distribution heads may cause the
distributors to revolve about the longitudinal axis of the horizontal conduit to which they
are mounted, thereby achieving a 360° liquid coverage angle over a spherical spray
diameter (Ds) of about 5.5 m (18 ft).
The Ds at a given process liquid flow rate may be determined empirically by direct
observation or, in the case of commercially available nozzles, such data may be obtained
from the manufacturer. It is preferred that horizontally-oriented distributors in accordance
with the present method be selected and operated in a manner that conforms to the
relationship:
D < D
In Example 2, the five distribution arrays (Al, A2, A3, A4, A5) may be placed
within the quench section (150) with a 2.75 m (9 ft) vertical distance ("H") between each
successive level. It is not necessary for the vertical distance between successive arrays to
be constant. In general, it is preferred that the spacing between successive distribution
arrays conforms to the relationship:
H < Ds / 2.
Additionally, in embodiments such as Example 2 in which distributors within a
distribution array may be placed at regular intervals along the circumference of the vessel
wall, it is preferred that the number of distributors ( ) in a distribution array conforms to
the relationship:
6.28 x (D / Ds < N , where N is a positive integer.
The uppermost array (Al) may be positioned about 2.75 meters below the bottom-most tray
(T10) of trayed section (145) and the bottom-most array (A5) may be at least 3 meters
above the centerline of reaction gas line (101).
During operation, over 95,450 kg/hr (210,000 lbs/hr) of a gaseous reaction mixture
from the outlet of a propylene oxidation reactor may enter the dehydration tower via a
reaction gas line (101) at a temperature of about 182°C (360°F). Bottoms liquid ( 116) is
drawn from the dehydration tower ( 1 10). A portion of this stream may be transferred to a
finishing column (not shown) via line (103), with the remainder going to heat exchanger
( 1 12) via recirculation line (120). Condensed liquid stream (104) may also return from the
finishing column (not shown) via line (104).
Acrylic acid containing quench liquid may serve as both the process liquid and the
motive fluid for the distributors. A total process liquid flow of about 376,460 kg/hr
(828,210 lbs/hr) may exit exchanger 112 at a temperature of about 100°C (212°F) and flow
through each of the lines in the return piping network ( 1 11.1, 111.2, 111.3, 111.4, and
111.5) to supply each of the distributor arrays. The lines within this return piping network
may optionally include one or more ancillary components, including but not limited to flow
measurement devices, temperature measurement devices, pressure measurement devices,
flow control valves, restriction orifice plates, heat exchangers, and filters. The presence of
such optional ancillary components may allow process liquid flow rates to be varied from
one array to the next, or even allow the temperature of the process liquid supplied to
distribution arrays higher in the dehydration tower to be cooler than that supplied to the
arrays lower in the tower.
By way of this configuration, a copious quantity of liquid droplets may be broadly
and uniformly distributed throughout quench section (150), and these droplets intimately
contact the crude acrylic acid vapor, achieving excellent mass and energy transfer within
the quench section. Each of the distributors may be thoroughly self-rinsed, and the bottom
of tray T10 may also be collaterally wetted by the distributors in array Al . As a result, the
quenching step may be efficiently performed without the accumulation of fouling polymer
solids.
As understood by one of ordinary skill in the art, the use of the present invention in
a quench section does not require that the quench section be part of an integrated process
vessel. Operation of the quench section, as well as the present invention, will not
materially change if performed in a separate process vessel immediately upstream of an
alternative dehydration tower, such as the arrangement described in Figure 2 of U.S. Patent
No. 8,242,308.
Example 3
Referring to Figure 3, the vapor-liquid contacting vessel in Example 3 was a 2.75
meter diameter Glacial Acrylic Acid distillation column (300). Process gases (315) passed
out of the column via an overhead vapor line (310), which was mounted to the side of the
column top head. The column comprised a plurality of dual-flow trays (generally
represented as Tl, T2, T3, T4) on which intimate vapor-liquid contact occurred.
To uniformly distribute a process liquid stream comprising acrylic acid and about
200 ppm MeHQ polymerization inhibitor (herein referred to as "GAA Inhibitor Solution")
onto the top tray (Tl) of the distillation column, as well as prevent accumulation of
condensation polymer on the process-facing surfaces of the distillation column top head or
the portion of the vessel walls located in the vapor space above the top tray (a total surface
area of about 30 m2 (317 square feet)), a fouling-resistant liquid distributor comprising a
single, spherical distribution head (304) with a plurality of liquid delivery ports was used.
This specific distribution head was a 316 stainless steel model #566.968. 17.BL nozzle,
commercially available from Lechler GmbH of Metzingen, Germany. This distribution
head was attached to the lower end of a stationary 19 mm (3/4 inch) diameter conduit (303)
via a NPT connection. The fouling-resistant liquid distributor (301) was inserted through a
standard 5 cm (2 inch) flanged vessel nozzle (302), located on the top center of the
distillation column head, and sealed in place using a standard bolted connection (not
shown).
Conduit (303) was of sufficient length to allow positioning of the distribution head
below the top tangent line of the column, within about 1 meter of the top interior surface of
the column head. GAA Inhibitor Solution was supplied at a rate of 1,600 kg/hr (3,520
lbs/hr) to the upper end of the conduit (303) and flowed downward through the conduit to
the interior of the spherical distribution head (304). In this way, the flowing inhibitor
solution served as the motive fluid for the distributor, causing the distribution head to
revolve continuously about the centerline axis of the conduit (generally indicated in the
figure by the circular arrow). When in motion, the distribution head discharged sufficient
liquid GAA Inhibitor Solution to provide uniform coverage over a +300° angle of liquid
coverage (305), uniformly distributing inhibitor solution over the entire circumference of
the top tray of the column, continually wetting all of the interior surfaces within the vapor
space above the top tray of the column at a wetting liquid rate of 0.05 m /m -hr, and
simultaneously self-rinsing the exterior surfaces of the conduit and distribution head. In
this way, the trays (Tl , T2, T3,. ..) and process-facing interior surfaces of the column were
reliably protected against polymer accumulation despite operation in (meth)acrylic
monomer process service.
Subsequent inspection of the distillation column after one year of continuous
operation verified that there was no polymer present in the top of the column. This
demonstrates that the inventive distribution method employed in this embodiment is highly
effective at preventing polymer accumulation at the top of the distillation column. Further,
given that the low wetting liquid rate which was employed provided satisfactory results (for
example, the wetting liquid rate used in Example 3 was one-tenth the minimum wetting
liquid rate taught in U.S. Patent No. 6,409,886), various embodiments of the present
invention may provide improved uniform liquid distribution over the previously used
process utilizing stationary spray-nozzles.
Example 4
In Example 4, the single fouling resistant liquid distributor of Example 3 was
retrofit to an existing dual-use acrylic ester distillation column that may be employed to
produce butyl acrylate or 2-ethylhexyl acrylate. The acrylate ester distillation column had a
1.96 meter ( 6.37 feet) diameter and included a plurality of trays on which intimate vaporliquid
contact occurred. The fouling resistant liquid distributor was used to uniformly
distribute a process liquid stream comprising polymerization inhibitor (herein referred to as
"Ester Process Inhibitor Solution") onto the top tray of the distillation column, as well as
prevent accumulation of condensation polymer on the process-facing surfaces of the
distillation column dome (or top head), as well as the portion of the vessel walls located in
the vapor space above the top tray, a total surface area of about 14 m (148 square feet).
Configuration of the system of Example 4 was similar to Example 3. The fouling
resistant liquid distribution head was attached to the lower end of a stationary 19 mm (3/4
inch) diameter conduit via an NPT connection. The upper end of the conduit was screwed
into a threaded connection on a standard D 100 (4 inch) flange. The fouling resistant
liquid distributor was then inserted through a standard 100 mm (4 inch) flanged vessel
nozzle located on the top center of the distillation column head, and the DN100 flange was
sealed in place using a standard bolted connection. The vessel nozzle had an overall length
of 0.565 meter (22 inches), which created a stagnant annular nozzle space between the
internal surface of the vessel nozzle and the exterior surface of the stationary conduit. Two
optional "conduit ports" were added to the upper end of the conduit within about 50 mm of
the D 100 flange. These conduit ports were positioned on opposite sides of the conduit
and were oriented perpendicular to the centerline axis of the conduit to direct a portion of
the ester process inhibitor solution radially outward onto the interior surface of the vessel
nozzle . Such optional conduit ports may range in diameter from about 1mm to about 10
mm (0.04 to 0.39 inch), dependent on variables such as the total number of ports, the
diameter of the stationary conduit, and the available process fluid supply pressure, and
selection of the specific number and diameter(s) of optional conduit port(s) is easily
determined by one of ordinary skill in the art. The use of optional conduit ports serves to
prevent the accumulation of foulants within the annular nozzle space.
In Example 4, the conduit was of sufficient length to allow positioning of the
fouling resistant liquid distribution head within about 0.6 meter ( 2 feet) of the top interior
surface of the column head. Ester Process Inhibitor Solution was supplied at a rate of about
2,000 kg/hr (4,400 lbs/hr) to the upper end of the conduit and flowed downward through
the conduit to the interior of the spherical distribution head. In this way, the flowing
inhibitor solution served as the motive fluid for the distributor, causing the distribution head
to revolve continuously about the centerline axis of the conduit. When in motion, the
distribution head discharged sufficient liquid inhibitor solution to provide uniform coverage
over a +300° angle of liquid coverage, uniformly distributing inhibitor solution over the
entire circumference of the top tray of the column and continually wetting all of the interior
surfaces within the vapor space above the top tray of the column at a wetting liquid rate of
about 0.08 m /m -hr. Operation of the fouling resistant liquid distributor comprising
optional conduit ports also rinsed the annular nozzle space and simultaneously self-rinsed
the exterior surfaces of the conduit and distribution head. The trays, the vessel nozzle, and
the process-facing interior surfaces of the column were reliably protected against polymer
accumulation despite operation in (meth)acrylic monomer process service. Subsequent
inspection of the ester process distillation column after extended periods of continuous
operation producing butyl acrylate or 2-ethylhexyl acrylate verified that the fouling
resistant liquid distributor was effective at preventing the accumulation of polymer in the
top of the column.
While preferred embodiments of the invention have been shown and described
herein, it will be understood that such embodiments are provided by way of example only.
Numerous variations, changes, and substitutions will occur to those skilled in the art
without departing from the spirit of the invention. Accordingly, it is intended that the
appended claims cover all such variations as fall within the spirit and scope of the invention.

CLAIMS
A method for uniformly distributing a process liquid within a process vessel,
comprising:
a. providing a process liquid to at least one fouling-resistant liquid distributor
comprising a liquid distribution head, installed within a process vessel having a
cross-sectional area;
b. causing rotational movement of the fouling-resistant liquid distributor; and
c . uniformly distributing the process liquid over the cross-sectional area within
the process vessel;
the said method further comprising at least one of:
simultaneously self-rinsing the at least one fouling-resistant liquid distributor with a
portion of the process liquid during step (c), and
providing the process liquid during step (c) to a plurality of the fouling-resistant
liquid distributors, wherein each of the fouling-resistant liquid distributors
simultaneously rinses each other with a portion of the process liquid during step (c).
The method of claim 1, wherein said at least one fouling-resistant liquid distributor
comprises:
a. a stationary conduit, and
b. a motive fluid-powered liquid distribution head attached to said conduit,
wherein at least one of said stationary conduit and said liquid distribution head
comprises at least one process liquid delivery port.
The method of claims 1 or 2, wherein causing the rotational movement in step (b) is
achieved by supplying at least one of motive fluid and the process liquid to the
liquid distribution head.
4. The method of any one of claims 1 to 3 further comprising collaterally-wetting
process-facing surfaces within the process vessel with a portion of the process liquid.
5. The method of Claim 4, wherein the wetting liquid rate resulting from collaterallywetting
the process-facing surfaces of the process vessel interior is less than 0.5
m /m -hr.
6. The method of any one of claims 1 to 5, wherein the process vessel is a
(meth)acrylic monomer process vessel.
7. The method of claim 6, wherein the (meth)acrylic monomer process vessel is used
in a process to produce one or more compounds selected from the group consisting
of acrolein, acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl
acrylate, 2-octyl acrylate, 2-(dimethylamino) ethyl acrylate, methacrolein,
methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and
2-(dimethylamino) ethyl methacrylate.
8. The method of any one of claims 1 to 7, wherein the process vessel is a vapor-liquid
contacting vessel selected from the group consisting of a quench vessel, an
absorption tower, a contact condenser, a fractionating condenser, a dehydration
tower, a finishing column, a scrubber, a distillation column, and a storage tank.
9. The method of any one of claims 1 to 7, wherein the process vessel is an integrated
process vessel comprising two or more successive process sections selected from
the group consisting of a quench section, an absorption section, a partial
condensation section, a scrubbing section, a packed section, a contact condensation
section, a trayed section, a stripping section, and a rectification section.
10. The method of any one of claims 1 to 9, wherein the process vessel comprises one
or more internal components selected from the group consisting of trays, tray
supports, structured packing, random packing, feed distributors, demister pads,
stationary spray nozzles, baffles, liquid distribution troughs, and side draw
collection trays.
The method of any one of claims 1 to 10, wherein the process liquid comprises one
or more polymerization inhibitors.
A system for uniformly distributing a process liquid within a process vessel,
comprising:
a. a supply of process fluid,
b. a stationary conduit, and
c . a liquid distribution head attached to said conduit, wherein said liquid
distribution head is motive, powered by a fluid, and comprises at least one
process liquid delivery port, and
wherein the at least one process liquid delivery port is configured to provide a +10°
or greater angle of liquid coverage of the process fluid when the liquid distribution
head is moving.
A process vessel comprising a system according to claim 12.
Use of the process vessel of claim 13, for producing (meth)acrylic monomers.
Use of the process vessel of claim 14, wherein the (meth)acrylic monomers are
selected from the group consisting of acrolein, acrylic acid, methyl acrylate, ethyl
acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-octyl acrylate, 2-(dimethylamino)
ethyl acrylate, methacrolein, methacrylic acid, methyl methacrylate, ethyl
methacrylate, butyl methacrylate, and 2-(dimethylamino) ethyl methacrylate.