Note: Descriptions are shown in the official language in which they were submitted.
~WO 94/29010 PCT/US94/05621
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CATALYTIC DISTILLATION STRUCTURE
BACKGROUND OF THE INVENTION
f Field of the Invention
.
The invention relates generally to a structure that
performs the dual function of reaction catalyst and mass
transfer surface for distillation. More particularly, the
invention relates to a fixed distillation structure which
contains a solid particulate catalyst.
Related Art
The concurrent reaction and separation of products from
reactants has been practiced for some time, and the
advantages have been recognized. Examples of the use of
concurrent reaction and distillation are disclosed in U.S.
Pat. Nos.:(etherification) 4,232,177; 4,307,254; 4,336,407;
4,504,687; 4,918,243; and 4,978,807; (dimerization)
4,242,530; (hydration) 4,982,022; (dissociation) 4,447,668;
and (aromatic alkylation) 4,950,834 and 5,019,669.
Several different catalytic distillation structures have
been ~~roposed. See for example U.S. Pat. Nos. 4,302,356
and 4,443,559 in which a particulate catalyst is contained
within the pockets on a cloth belt wound with demister wire
to form a catalytic distillation structure and U.S. Pat.
No.4,731,229 which discloses a packing with corrugated
elements and tape form catalyst member. More recently
high efficiency packing has been modified to contain
catalyst as is disclosed in U.S. patent 5,073,236. In the
latter each of the structures, comprising two parallel gas
permeable plates having the catalyst between them, are
vertically placed within a column directly adjacent another
pair of the plates containing the catalyst. The close
packing of plates containing the catalyst when placed into
the column may present too dense a catalyst bed in some
instances and thus increase the residence time beyond that
necessary for a given reaction. It is an advantage of the
present invention that greater mobility of fluids within
the columns can be obtained in some of the embodiments. It
is a further advantage that the catalytic distillation
structure offers better distillation characteristics than
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many of those of the prior. It is a feature of the
present invention that less catalytic material may be
employed with the present structures.
SUMMARY OF THE INVENTION
The present invention provides a more versatile system
by separating at least one pair of adjacent elements
containing catalyst with a spacing element comprising an
inert element. For example, the spacing element may be a
flat plate (gas permeable or solid), an element similar to
the catalyst containing element containing inert particles
or an element similar to the catalyst containing element,
only void. By varying the number of spacing elements the
desired volume of catalyst may be placed in a column while
utilizing a standard catalyst containing element. In one
embodiment the catalytic elements may be spaced apart to
allow open space between some or all of the structures.
If consistent flow characteristics are desired across
the diameter of the column, the spacing elements can be
identical with the particulate catalytic material of the
catalyst containing elements being replaced with inert
packing of similar size and shape. Additionally the
catalyst or other packing may simply be omitted to provide
alternative flow characteristics.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a top view in partial cross section of a
structure showing catalyst containing elements and spacing
elements of the present invention.
Fig. 2 is a side view of one catalytic element of Fig. 1.
Fig. 3 is a cross section of one package element of the
invention.
Fig. 4 is the package element according to the present
invention containing particulate material. t
Fig. 5 is a structure comprising a plurality of catalytic
elements spaced apart.
Fig. 6 is a plurality of catalytic elements with only one
adjacent pair spaced apart.
Fig. 7 is a plurality of packages each touching and
contiguous to any adjacent package unit.
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Fig. 8 is a partial side view of a reaction distillation
column with the structure according to the present
invention in place.
.,
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the present invention a catalytic structure is
comprised of at least two catalytic elements in one or more
of the following configurations:
A. spaced apart
B. contiguous with an inert element selected from:
1. the package element
2. the non-catalytic element
3. a flat plate (gas permeable or impermeable)
Preferably the catalytic structure will contain a
plurality of catalytic elements in the configuration
described above. For example, in one preferred embodiment
as shown in Fig. 6 the catalytic structure is comprised of
two groups of contiguous catalytic elements separated by a
space. In another preferred configuration shown in Fig. 5
there is a plurality of catalytic elements in the
2o structure, each separated by a space so that there are no
contiguous catalytic elements and no adjacent catalytic
elements are in contact. These two configurations are an
advantage over structure as shown in U.S. Pat. No.
5,073,236, because they allow more open space within the
catalytic structure. In many applications a dense structure
having contiguous catalytic elements would be a barrier and
in effect act more like a packed bed of particulate
catalytic material with consequent high pressure drops of a
packed column.
The catalytic structure depicted in Fig. 7, however,
supplies the denser packing, but with an important
distinction from the prior art. Some of the packages shown
are void of any particulate material and/or contain inert
particulate material. The void packings are less dense and
provide excellent distillation characteristics with a great
deal of open space and surfaces. The inert elements are
the packings filled with inert particulate material that
may be the same size, smaller or larger than the catalytic
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2~.~~~'~~
particulate material. The inert elements allow for all of
the same hydraulic characteristics of the catalytic
elements but reduce the catalytic reactions, which in
catalytic distillation also designated reactive
distillation (U.S. Pat. No. 5,019,669) is frequently a
reversible reaction. Hence, by diluting the reactive
elements but maintaining the distillation elements a higher
degree of the separation aspect of the catalytic
distillation is obtainable. In other words, by dispersing
the inert elements between the catalytic elements, is a
given structure the fractional separation is emphasized,
while in the system as a whole comprising a column with a
plurality of the catalytic structures the force of the
reaction is maintained.
The dilution of the volume of catalyst present in any
given column may be insignificant given the dynamic nature
of catalytic distillation and the improved distillation
characteristics described above.
The catalytic and non-catalytic elements are bound
together to form a structure, usually by plastic or metal
bands at the upper and lower ends of each grouping of
elements. Where spaces are desired a spacer in the nature
of a frame is placed between the elements to be separated.
The term package is used to describe the corrugated
sheets joined to form containers for particulate catalytic
material and particulate inert material. The corrugated
sheets may be joined by welding or by weaving, crimping and
bending. The corrugated sheets are arranged in parallel to
a common axis and present open channels between the sheets
for the distribution and fractional distillation of fluid
streams.
The corrugations and the channels and pockets of
particulate material on each sheet are disposed at an
inclination from the common axis while being oppositely w
directed to the corrugations of an adjacent sheet.
For a detailed description of the preferred embodiments
the reader is referred to the attached figures in which
like components are given like numerals for ease of
_, WO 94!29010 r PCT/US94/05621
reference.
In Fig. 1 there is shown a top view in plan of a
catalytic structure 10 of the present invention, which is
comprised of a plurality of catalytic elements 12 aligned
5 along a common axis each being separated by a non-catalytic
sheet 14 which may be permeable or non-permeable. The
elements are held together by band 16. In Fig. 2 a
catalytic element is shown to comprise two layers 18 and 20
of gas permeable wire mesh which are joined in regularly
spaced intervals to form pockets 22 in which a particulate
catalyst may be disposed or which may be employed empty as
described hereafter. The joining can be effected by
weaving the two layers together at the joints 13. A
particular embodiment involves a double weave type process
in which the mesh is woven as a double weave with the
pockets integral with the weave. Additionally the pockets
are woven diagonally across the surface of the element as
shown in Fig. 3. The appearance of the elements is that of
a corrugated herring bone (see Figs. 3 and 4).
In Fig. 7 there is shown a view of several of the
catalyst containing elements 12 separated by inert spacing
24. In this preferred embodiment each catalytic element 12
is separated by a non-catalytic distillation structure 24
which may either be the empty pocket structure of Fig. 3 or
the pockets may be filled with particulate material 26 such
as Fig. 4. The pocket elements containing the particulate
material may contain either catalytic particulate material
or inert particulate material. The elements appear to be
the same and only the nature of the particulate material
distinguishes them. Fig. 6 shows a similar view of a
structure where all of the pocket elements are catalytic
elements 12 and the two portions of contiguous catalytic
elements are separated by a space 28 such that the
catalytic elements are not contiguous across the entire
catalytic structure.
In Fig. 5 a bundle of the catalytic distillation
structure is shown ready for placement in a distillation
column reactor. The catalytic elements 10 are shown to be
WO 94/29010 ~ PCTIUS94/05621
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spaced apart by an open space elements 28 and the whole
bound into a bundle by band 16. All of the elements bound
by the band are placed vertically within the column.
Referring now to Fig. 8 there is shown a distillation
column reactor 100 containing a bundle of catalytic
distillation structure 10 of the type shown in Fig. 7.
Preferably the hc5rizontal pocketed catalyst containing
elements are placed together such the pockets of one
element are at 90° to the pockets of the next adjacent
pocket element whether empty (no particulate material),
filled with particulate catalyst or filled with inert
material so that fluid streams flow along the channels at
angles to the vertical axis of the column. This feature is
illustrated in Fig. 8 where the slanted lines on the upper
and lower tower sections represent the ridges of the
sheets.
The structure 10 operates as a structured packing for
fractional distillation of fluid streams and concurrently
provides for catalytic reaction of the fluid streams. In a
typical installation, a plurality of structures 10 are
stacked one on top of the other inside the column on an
appropriate support structure. Each vertical row of
structures is placed with its sheets 18 and 20 parallel to
other sheets in the same row and at 90° relative to the
plane of the sheets in a vertically adjacent row. This
relative orientation of three vertically spaced rows of
sheets is illustrated in Fig. 8. The structure 10 has
particular applicability with liquid phase reactions having
products separable by distillation and counter current
gas/liquid contacting in liquid phase heterogeneous
catalyst systems. In operation, one or more fluid streams
are charged to the column 100 with liquid descending
through structure 10 and vapor streams ascending through
the structure. The liquid stream flow occurs in channels 32
along the surface of sheets 18 and 20 and through the
catalyst bed 30 and the inert bed in element 24. Liquid
distributors may be utilized at the upper end of structure
10 to preferentially direct the liquid streams as desired
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into either the channels 32 or catalyst bed 30.
The catalyst bed 30 forms a catalytic reaction zone for
catalytically reacting the descending liquid streams.
Concurrently, a vapor phase is formed by fractional
distillation of the liquid streams and preferentially flows
upwardly through channels 32 for mixing with descending
liquid streams. Mass transfer between the liquid and vapor
phases occurs primarily on the surfaces of the sheets 18
and 20 as well as on the catalyst.
Mixing of the liquid and vapor phases occurs in channels
32 as ascending vapor contacts descending liquid. The
liquid phase passes through the permeable elements 18 and
from the channels into the catalyst bed 22 for catalytic
reaction or into the inert bed of element 24 for further
15 separation. The reaction product likewise passes from the
catalyst bed into the channels where primary fractional
distillation occurs.
It will be appreciated that more than one bundle may
be placed in the column at various heights as desired.
20 Additionally the bundle or bundles may be supported in the
column in any efficient manner. For instance the bundles
may be supported and separated by inert distillation
packing such as Rashig rings or the like.
