USOO6281,384B1

(12) United States Patent (10) Patent No.: US 6,281,384 B1

Contracter et al. (45) Date of Patent: Aug. 28, 2001

(54) WAPOR PHASE CATALYTIC OXDATION OF FOREIGN PATENT DOCUMENTS

PROPYLENE TO ACRYLIC ACID
0 034 442 8/1981 (EP) .............................. CO7C/45/34
(75) Inventors: Rashmikant Maganlal Contracter, 0861819 * 2/1998 (EP).
Wilmington, DE (US); Mark William 0861821 * 2/1998 (EP).
0861819 A1 * 9/1998 (EP) .............................. CO7C/45/28
Andersen, Charlottesville, VA (US); 0861821 A1 * 9/1998 (EP) .............................. CO7C/57/04
Jean B. Myers, Wilmington, DE (US); 2227 257 * 4/1974 (FR) .............................. CO7C/57/04
Gerard Hecquet, Bethune (FR); 1307936 2/1973 (GB) ............................. CO7C/47/22
Roland Kotwica, Pontpoint (FR); 1490489 11/1977 (GB) ............................. CO7C/47/22
Mireille Stojanovic, Paris (FR); 3-170445 7/1991 (JP) ............................... CO7C/27/12
Charlotte Pham, Saverne (FR); Michel O5301051 of 1996 (JP).
Simon, St. Avold (FR) WO99/03809 * 1/1999 (WO) ........................... CO7C/45/28
OTHER PUBLICATIONS
(73) Assignees: E. I. du Pont Nemours and Company, Advertising, Chemicals Technologies Worldwide, 1973.
Wilmington, DE (US); Atofina, Paris James L. Callahan et al., Oxidation and Ammoxidation Of
(FR) Propylene Over Bismuth Molybdate Catalyst, Ind. Eng.
Notice: Subject to any disclaimer, the term of this Chem. Prod. Res. Develop., vol. 9, No. 2, 134-142, 1970.
patent is extended or adjusted under 35 Robert K. Grasselli et al., Selective Oxidation and Ammoxi
U.S.C. 154(b) by 0 days. dation Of Propylene By Heterogeneous Catalysis, Academic
Press, Inc., vol. 30, 133–163, 1981.
(21) Appl. No.: 09/105,497 G. S. Patience et al., Modelling Of Propylene Oxidation. In
A Circulating Fluidized-Bed Reactor, Elsevier Science B. V.,
(22) Filed: Jun. 26, 1998 1-18, 1994.
Primary Examiner-Gary Geist
(51) Int. Cl. ................................................. C07L 51/235 ASSistant Examiner Robert W. Deemie
(52) U.S. Cl. .............................................................. 562/535 (57) ABSTRACT
Field of Search ............................................... 562/535 An improved method for manufacturing acrylic acid by
(58) vapor phase oxidation of propylene in a single step or
(56) References Cited reaction Stage using as Solid phase oxidant a mixture of two
U.S. PATENT DOCUMENTS
particulate Solids comprising a bismuth molybdate multim
etal oxide (e.g., Mo12 CossBi. Feos.Wols.Si. KoosO) and a
3,487,109 12/1969 Kurata et al. ........................ 260/533 molybdenum Vanadate multimetal oxide (e.g.,
3,631,099 12/1971 Eden ................. 260/533 N. MoVSros.W. Cu2O). Such a process is advanta
3,639,269 2/1972 Koberstein et al. .. ... 252/437 geously carried out in a recirculating Solids reactor System
3,761,424 9/1973 Koberstein et al. .. ... 252/437 wherein the particulate mixture of Solids in an oxidized State
3,799.979 * 3/1974 Hensel et al....... ... 260/533 reacts with a feed gas containing propylene in a vertical riser
3,875,220 4/1975 White et al. ... ... 260/.530 N reactor and after Separation from the acrylic acid gaseous
4,102.914 7/1978 Beuther et al. ... 260/.465.3 product the particulate mixture of Solids in a reduced State is
4,152,393 5/1979 Callahan et al. ..................... 422/144 regenerated by contact with an oxygen containing gas in a
4,341,717 7/1982 Callahan et al. .. ... 260/.465.3
4,442,308 4/1984 Arntz et al. ........ ... 568/480 Separate regeneration reactor before recirculation to the riser
4,604,370 8/1986 Sarumaru et al. ..................... 502/38 for further reaction.
(List continued on next page.) 8 Claims, 1 Drawing Sheet

PRODUCT

REACTOR
FEED
 US 6,281,384 B1
Page 2

U.S. PATENT DOCUMENTS 5,072,052 12/1991 Boeck et al. ......................... 568/479

5,082,819 1/1992 Boeck et al. ......................... 502/212
4,621,072 11/1986 Arntz et al. .......................... 502/504 5,519,149 * 5/1996 Contractor et al..
4,668.802 5/1987 Contractor .. 549/259
4,677,084 6/1987 Bergna ..................................... 502/8
4,769,477 9/1988 Bergna ................................. 549/259 * cited by examiner
U.S. Patent Aug. 28, 2001 US 6,281,384 B1

|8010W38 03 3

10 } d

10 8d
 US 6,281,384 B1
1 2
WAPOR PHASE CATALYTIC OXDATION OF flow of active Solids and gases is other than vertically
PROPYLENE TO ACRYLIC ACID upwards. A transport bed reactor, as defined herein, includes
a riser reactor or pipeline reactor which also incorporates a
BACKGROUND OF THE INVENTION Zone for fluidization, i.e., a Zone where the gas Velocities are
1. Field of the Invention
Sufficiently high to carry out a Substantial portion of the
active Solids fed, but with more back-mixing of active Solids
The present invention relates to an improved vapor phase than would occur in plug flow. We will use the term
proceSS for the catalytic oxidation of propylene to acrylic “recirculating Solids reactor System' to mean a general
acid in a Single Step or Stage using as oxidant a mixture of reaction System with two reaction Zones, in which two
Solids in an oxidized State, and where the resulting reduced Separate reactions take place, and which uses a particulate
Solids is separately regenerated using molecular oxygen. Solid which circulates between the two reaction Zones and
More specifically but not by way of limitation, the invention takes part in both reactions. Optionally, either or both
relates to a process for performing this reaction in a recir reaction Zones may involve either a transport bed reactor or
culating Solids reactor System. a fluidized bed. Such reaction Systems have found use in
2. Description of the Related Art 15 catalytic cracking in petroleum refining and in other reac
An important route to acrylic acid is the vapor phase tions.
oxidation of propylene over a multicomponent catalyst U.S. Pat. No. 4,668,802 discloses a process for preparing
containing molybdenum and/or other metals, usually as their maleic anhydride by oxidizing butane using an oxidized
oxides. Typically, this is carried out in two steps. The first Vanadium-phosphorous oxide catalyst as oxidant rather than
reaction Step involves oxidation of propylene with air oxygen wherein the resulting reduced catalyst is separately
(oxygen) to form acrolein, often with a minor amount of regenerated, and the use of a recirculating Solids reactor
acrylic acid, along with carbon oxides, water and Smaller System for this reaction. Certain of the examples use a
amounts of other oxidized byproducts. The Second reaction transport bed or riser reactor for the butane oxidation
Step then converts acrolein to acrylic acid by a similar reaction.
oxidation Step, but typically using different reaction condi 25
Japanese Kokai 3-170,445 discloses a similar process for
tions and catalyst for optimum results. preparing a mixture of acrolein and acrylic acid by oxidizing
In Some proposed processes, the amount of acrylic acid propane using an oxidized bismuth-molybdenum catalyst or
co-produced with acrolein is large enough to merit isolating Vanadium pyrophosphate catalyst as oxidant. In Example 2,
it as product, and recycling the acrolein back to the oxidation a propane conversion of 55%, an acrylic acid Selectivity of
Step. These processes typically require the Separation and 65%, and an acrolein selectivity of 7% were obtained using
recycle of large amounts of acrolein. a catalyst consisting of Vanadyl pyrophosphate and tellurium
Typically these reactions are carried out in multitubular oxide.
fixed-bed reactors. The large exothermic heat of reaction and An advertising folder prepared by E.I. DuPont in 1973
the thermal Sensitivity of the propylene oxidation requires 35 titled “Chemical Technologies Worldwide” included a single
low feed concentrations, expensive heat transfer equipment, sheet titled “Transport Bed Reactor Technology for Selec
handling of a large Volume of gas, and good reactor tem tive Processes', which described the general advantages of
perature control. Low propylene concentration is also a transport bed or riser reactor, listing among typical appli
required to avoid flammability conditions. cations the reaction of propylene to make acrylic acid.
The magnitude of Some of these problems is reduced 40 None of the above references disclose the necessary
when fluidized-bed reactors are used. The temperature can information to enable the economical use of a vapor phase
be readily controlled within a few degrees because of the process for the catalytic Oxidation of propylene to acrylic
intensive catalyst mixing and the good heat transfer char acid in a Single Step or reaction Stage using as Oxidant a
acteristics. Higher propylene concentrations can be used combination or mixture of catalyst in a fluidized and oxi
because the danger of flammability is reduced by introduc 45 dized State, and where the resulting reduced catalyst is
ing the propylene directly into the reactor rather than pre Separately regenerated using molecular oxygen.
mixing it with air (oxygen). However, very high propylene The preparation of multicomponent compositions con
concentrations and low oxygen-to-propylene ratioS in the taining molybdenum, Vanadium and/or other metals and
reactor may result in the over reduction of the Solids and their use as catalysts in oxidation processes is well known in
reduced Selectivity to the desired products. Also, Significant 50 the art. For example, U.S. Pat. Nos. 4,677,084 and 4,769,477
back-mixing of gases in the fluidized-bed reactor results in disclose a proceSS for making highly attrition resistant
poorer Selectivity and makes it difficult to obtain high Silica-based catalysts containing molybdenum, Vanadium or
propylene conversion. other metals. Numerous other patents such as U.S. Pat. No.
Modified forms of fluidized-bed reactor are known as 3.487,109, U.S. Pat. No. 3,631,099, GB 1490,489 or JP
recirculating Solids reactor, transport bed reactor, transport 55 05,301,051 also disclose specific catalyst compositions for
line reactor, riser reactor, fast fluidization reactor, multi use in the oxidation of propylene in a fixed-bed or fluidized
chamber fluidized bed reactor, and by other names, depend bed process.
ing on design and/or personal preference. In this application BRIEF SUMMARY OF THE INVENTION
we will use the term “transport bed reactor” to mean any
reactor in which Solid particles are injected at one end of the 60 The present invention relates to a proceSS for the Selective
reactor and carried along with gas reactants at high Veloci Vapor oxidation of propylene to acrylic acid in a single
ties and discharged at the other end of the reactor to a reaction Step or Single reaction Stage using a mixture of
gas-Solids Separation vessel. A riser reactor, in which the bismuth molybdate multimetal oxide and molybdenum
reactor is a vertical pipe wherein the active Solids and gases Vanadate multimetal oxide each in an oxidized form or State
are fed in at the bottom, transported in essentially plug flow 65 as the oxidant. Thus the present invention provides a process
and removed at the top, is one example of a transport bed for the oxidation of propylene to acrylic acid comprising the
reactor. Another example is a pipeline reactor, in which the Steps of: (a) contacting a feed gas comprising (i) from 1 to
 US 6,281,384 B1
3 4
100 mol % propylene, (ii) from 0 to 20 mol % oxygen, (iii) System which includes a transport bed reactor and a separate
from 0 to 70 mol % water, and (vi) the remainder inert gas regenerator. The transport bed reactor is preferably a riser
with an effective amount of an oxidant mixture comprising reactor in which particles are injected at the bottom of a
a particulate molybdenum Vanadate multimetal oxide in an Vertical pipe, carried upwards with gas reactants at high
oxidized State and a bismuth molybdate multimetal oxide in Velocities and discharged to a gas-Solids Separation vessel,
an oxidized state at a temperature from 250 to 450° C. and or a combination of a riser reactor with a fluidization Zone.
for a time Sufficient to convert a portion of Said propylene to The reaction between gas and Solids occurs in the riser pipe
acrylic acid, wherein the relative amount of Said molybde in a matter of Seconds, as distinguished from a conventional
fluidized bed reactor where the reaction time is a matter of
num vanadate multimetal oxide is from 5 to 50 percent by minutes. Gas Velocities in a riser reactor are about 2 to 15
weight total active ingredients and the remainder 95 to 50
percent by weight is Said bismuth molybdate multimetal times higher than in fluidized bed reactors, Solids concen
oxide; and (b) thereafter recovering the acrylic acid pro trations may be up to about 40 times lower. The product of
duced in Step (a). the above reaction is then Sent to a conventional processing
unit where the acrylic acid is Separated and recyclable
In one particular embodiment of the present invention the impurities Such as acrolein are returned for further proceSS
contacting of the feed gas and the particulate oxidant mix 15
ing.
ture in an oxidized State Such as to convert the propylene to The reduced Solids are then reoxidized in a separate
acrylic acid is performed in a transport bed reactor of a oxidation Step to enable their reuse for the oxidation of
recirculating Solids reactor System and wherein Said particu propylene. The reduced Solids from the riser Zone are first
late oxidant mixture in a reduced State after the conversion
of propylene to acrylic acid is separated from the acrylic acid Separated from the product gas, Stripped of any carbon
gaseous product and is then reoxidized in a regenerator aceous species in a separate Stripper Zone and then Sent to
reactor of the recirculating Solids reactor System by contact the regenerator for reoxidation. This proceSS permits inde
with oxygen containing gas before being recirculated to the pendent control of the reactant gas concentrations, the gas
transport bed reactor. In another preferred embodiment the residence time, and the Solids residence time in each Zone
Said transport bed reactor is a riser reactor and the particulate 25 for optimum operation.
oxidant mixture comprises particles from 10 to 300 micron There are Several advantages of the above reactive con
in size. Preferably in this embodiment the feed gas residence cept over the steady-state fixed bed or fluidized bed alter
time in the riser reaction Zone is from 1 Second to about 15 native. High Selectivity is achieved because of plug flow and
Seconds, and the particulate oxidant mixture residence time optimum oxidative State of the Solids. Significant reductions
in the riser reaction Zone is from 2 Seconds to 120 Seconds. are realized in product recovery costs because the regenera
Also, the particulate oxidant mixture residence time in the tion off-gas Stream is kept Separate from the product gas
regenerator reactor is from 0.5 minute to 10 minutes and the Stream, resulting in a highly concentrated product Stream.
OXygen-containing gas residence time is from 3 Seconds to High throughput rates are attributed to the independent
30 seconds at a temperature of about 250 to about 500 C. control of variables for the two steps of the operation,
It is an object of this invention to provide an improved 35 resulting in reduced investment and decreased multimetal
Vapor phase proceSS using a transport bed reactor for the oxide inventory.
oxidation of propylene to acrylic acid in a single Step using When a hydrocarbon oxidation reaction is carried out in
the oxidized form of attrition resistant multimetal oxide, and the absence of molecular oxygen, lattice oxygen from the
where the resulting reduced Solids are Separately regenerated Surface layers of these mixed metal oxide Solids gets con
using oxygen containing gas. It is a further object of the 40 Sumed very rapidly, typically in a matter of Seconds. When
present invention to provide a mixed multimetal oxide that occurs, the activity of the Solids decreases dramatically.
System that will Serve as an oxidant for the vapor phase If the Solids are allowed to remain in the reducing
conversion of propylene to acrylic acid in a single Step or atmosphere, reduced Surface layers are built up on an
reaction Stage. Fulfillment of these objects and the presence oxidized core because diffusion of the bulk lattice oxygen to
and fulfillment of additional objects will become apparent 45 the Surface is generally very slow in most practical Situa
upon complete reading of the Specification and attached tions. These reduced layerS decrease Selectivity and cause
claims. excessive yield losses when they get oxidized in the regen
erator to carbon oxides. Previous proposals for the oxidation
BRIEF DESCRIPTION OF THE SEVERAL of propylene to acrylic acid using an oxidant and a separate
VIEWS OF THE DRAWING 50 regeneration Zone for the active Solids do not disclose the
Surprising benefit of a short residence time in the propylene
FIG. 1 shows a Schematic drawing of a recirculating oxidation/Solids reduction Zone.
Solids reactor configuration in which the reaction Zone is In carrying out the inventive process, the feed gas to the
comprised of two parts, a fluid bed Section and a riser Section propylene oxidation step contains about 1 mol % to 100 mol
and the regeneration Zone is comprised of a fluid bed 55 % propylene (preferably about 5 mol % to about 30 mol %
Section.
propylene) and 0 to 30 mol % acrolein. Some of the
FIG. 2 is shows a Schematic drawing of a recirculating propylene and acrolein used in the feed may be provided by
Solids reactor configuration in which the reaction Zone is the unconverted and partially converted propylene which is
comprised of a riser Section and the regeneration Zone is present in the recycled reaction gas. In Some cases, propy
comprised of two parts, a riser Section and a fluid bed 60 lene may be available as the predominant component in a
Section. mixture of gases including other hydrocarbons. AS long as
DETAILED DESCRIPTION OF THE
none of the other gases present significantly adversely affect
INVENTION the process, it may be more convenient to use this
propylene-rich mixture in the feed gas as the Source of
The present invention relates to an improved proceSS for 65 propylene. The oxygen concentration in the feed gas can be
the Selective vapor oxidation of propylene to acrylic acid in from 0 to 20 mol%. Air can be used as the source of oxygen.
a single reaction Stage or Step in a recirculating Solids reactor The remainder of the feed can be any inert gas, Such as
 US 6,281,384 B1
S 6
nitrogen or recycled reaction gas containing mostly water, reoxidation reaction is carried out in the regeneration Zone
carbon monoxide and carbon dioxide, and possibly uncon (as opposed to the reaction Zone), the amount of propylene
verted propylene and acrolein. to be reacted, the amount of mobile (or reactive) oxygen
The present invention uses an effective mixture of a contained by the Solids, and the reaction Zone process
bismuth molybdate multimetal oxide and a molybdenum conditions that determine the amount of catalyst oxygen
Vanadate metal oxide in oxidized form. The weight fraction used per pass. When oxygen concentration in the reaction
of the molybdenum Vanadate multimetal oxide expressed as Zone is low, or Zero, and Substantially all of the Solids
weight percent active ingredient in the total charge is 5 to reoxidation reaction is carried out in the regeneration Zone,
50%, preferably 10 to 50%, with the remainder being the a high catalyst circulation rate is required. This rate may be
relative amount of the bismuth molybdate multimetal oxide. reduced, to the extent that the Solids reoxidation reaction is
It should be appreciated that these respective weight frac carried out in the reaction Zone.
tions are numerically based on active ingredient and as Such A recirculating Solids reactor System can be operated
do not include the mass associated with the use or presence continuously to oxidize propylene without any gas-phase
of any Solid inert Support (e.g., Al-O, SiO or mixtures and
the like) or silica additive (either derived from silicic acid, oxygen in the reaction Zone. Such operation results in a
polysilicic acid, colloidal Silica or combinations thereof) 15 higher Selectivity to make acrylic acid than can be attained
asSociated with imparting attrition resistance. Preferably with conventional fluidized or fixed bed reactors, providing
these are Specially hardened Solids which resist attrition, an adequate Solids circulation rate is maintained to Supply
such as disclosed in previously referenced U.S. Pat. Nos. the needed oxidized Solids. In order to minimize the gas
4,677,084 and 4,769,477. Numerous other bismuth molyb phase OXygen in the reaction Zone, gas phase oxygen is
date metal oxide compositions are disclosed in the art for the Stripped from the oxidized Solids before recycling them to
Vapor phase oxidation of propylene to acrolein, and numer the reaction Zone.
ous other molybdenum Vanadate metal oxide compositions Alternatively, if a recirculating Solids reactor System is
are disclosed in the art for the vapor phase oxidation of operated So as to oxidize propylene under conditions of
acrolein to acrylic acid, and are also Suitable for the opera temperature, oxygen and propylene partial pressures and
tion of this invention. The solid particles are preferably 25 residence time in the reaction Zone identical to those used in
about 10 to about 300 micrometers in size.
The oxidation Step is carried out in the reaction Zone at a conventional reactors, Significantly higher conversion of
temperature of about 250 to about 450° C. The reactor gas propylene and Significantly higher yield of acrylic acid are
obtained.
exit pressure is typically 0 to 50 psig (0 to 3.95x10 Pa). The The high Selectivity to acrylic acid attained in the trans
gas residence time in the reaction Zone is typically about 1
Second to about 15 Seconds, and the Solids residence time in port bed reactor is maintained even if the feed to the reaction
the reaction Zone is about 2 Seconds to 120 Seconds. The Zone has a very high propylene concentration. The gas feed
upper limit of Solids residence time will, of course, depend can be 100% propylene.
on their activity. If still active, the solids can be retained in Recirculating Solids reactor Systems can in general have
the reaction Zone for longer than 120 seconds. Preferably, 35 many different reactor/regenerator configurations. For
the Solids are removed from the propylene oxidation Step example, the reaction Zone of the System can be comprised
when the oxidative surface layer of the Solids has been of a transport bed reactor, a fluidized bed reactor or other
essentially reduced to a non-oxidized form. The Solids in the gas-Solid reactors, as can the regeneration Zone. The recir
reactor effluent are Separated from the effluent gases, and the culating Solids reactor System employed in this invention
acrolein and acrylic acid products are recovered from the 40 utilizes a transport bed reactor for the reaction Zone. Option
effluent gases, both Separations employing conventional ally the transport bed reactor may comprise a riser reactor,
techniques and equipment. The Separated Solids are referred a pipeline reactor, or a riser or pipeline reactor combined
to herein as the reduced Solids because they are in a lower with a fluidization Zone. The regeneration Zone of the
oxidation state than that of the fresh Solids which enters the regenerator can be comprised of a riser reactor, a pipeline
reaction Zone. When appropriate to the embodiment, the 45 reactor, a fluidized bed reactor of any type, or a combination
reduced Solids are preferably Stripped of any reactor gases of the above reactors. It is to be understood that the invention
and then transported to the regeneration Zone of the recir is not limited to the Specific combination of reactors listed
culating Solids reactor System. The Stripped reactor gases are above.
mixed with the reactor effluent gases. Acrylic acid and A transport bed reactor is characterized by high gas
optionally acrolein are recovered from the effluent gases of 50 velocities of from about 5 ft/sec (about 1.5 m/sec) to greater
the reaction Zone in conventional processing units, and than 40 ft/sec (12 m/sec). At the lower end of the velocity
remaining gases may be vented or recycled to the reaction range there can be a Significant amount of local back-mixing
Zone. Any off-gases from the regeneration Zone can be of Solids. Typically, the reactor line is vertically mounted
vented preferably after heat recovery. with gas and Solids flowing upward in essentially plug flow;
The reduced Solids are reoxidized in the regeneration Zone 55 i.e., a riser reactor. Preferably, the Superficial gas Velocity in
using an oxygen-containing gas Such as air, OXygen enriched the riser is maintained at 3 to 30 feet/sec (1 to 10 meters/sec).
air or the like. Preferably the regeneration Zone temperature The flow can also be downward and the reactor line can be
is maintained at about 250 to about 500 C. The Solids mounted other than Vertically, i.e., a pipeline reactor.
residence time in the regenerator Zone is about 0.5 minute to, The Solids concentration in the reaction Zone of the
typically, about 10 minutes. The oxygen-containing gas 60 reactor can range from, typically, about 1 lb/ft (16 kg/m)
residence time is about 3 seconds to about 30 seconds. Total to, typically, about 40 lb/ft (640 kg/m), depending on the
gas flow rate and oxygen concentration must be Sufficient to gas Velocity, Solids particle Size and density, and the Solids
provide the needed oxygen for Solids reoxidation to occur circulation rate. Preferably, the solids flux (mass flow rate
within the Selected gas and Solids residence time. The per unit area) is at 2.1 to 42 lbsift-sec" (10.2 to 204
oxidized Solids are then recycled to the reaction Zone. 65 kgm-sec").
The required amount of Solids and the required Solids FIG. 1 is a Schematic drawing of one of the recirculating
circulation rate depend on the extent to which the Solids Solids reactor Systems used in the example. The reaction
 US 6,281,384 B1
7 8
Zone is comprised of a fluidization Section 1 and a riser application Ser. No. 09/088,804 filed on Jun. 2, 1998,
Section 2. The feed gas enterS 1 and the oxidation of wherein Sufficient colloidal silica Solution was added to the
propylene takes place in Sections 1 and 2. The Separator Slurry of the multimetal Solid component and polysilicic acid
Stripper unit 3 Separates and Strips off the reaction Zone to result in an additional 30 wt % SiO in the final dry solids
effluent gases from the reduced Solids. The acrylic acid and again prior to Spray drying and Subsequent calcining. The
optionally acrolein product is recovered from the reactor use of the expression “Substantially following the proce
effluent gases leaving 3. The reduced Solids is transported to dures” is not intended as an implication that the same
the regeneration Zone which is comprised of the fluidized ingredients were employed, but rather that the same general
bed section 4. The reduced solids are oxidized in section 4 techniques were used to achieve attrition resistance Starting
and the oxidized (regenerated) Solids are then recycled to the with the two types of Solids; i.e., bismuth molybdate mul
fluidization section 1. The alternate/additional feed line 5 timetal Solids and molybdenum Vanadate multimetal Solids,
can be used to feed additional oxygen or oxygen containing respectively.
gas, propylene, or recycle gases to riser Section 2. The In the Example, the bismuth molybdate multimetal start
recirculation Solids reactor of this embodiment can also be ing Solids were obtained following the procedure described
operated with just the riser Section 2 as the reaction Zone. In 15 in French patent application 97 02343 filed on Feb. 27, 1997
this mode of operation the feed can be introduced into the in the name of Elf Atochem S.A., “Method for the Manu
riser section 2 through feed line 5. facture of Acrolein from Propylene by Redox Reaction and
FIG. 2 is a Schematic drawing of another recirculating use of a Solid Mixed Oxide Compositions as Redox System
Solids reactor System. The reaction Zone is comprised of a in the Said Reaction'. More specifically, the bismuth molyb
riser section 11. The feed gas enters 11 and the oxidation of date Starting Solids used in the runs of the Example of this
propylene takes place in 11. The Separator-Stripper unit 12 invention were obtained according to example 5 of this
Separates and Strips off the reaction Zone effluent gases from French patent application. These Starting Solids correspond
the reduced Solids. The acrylic acid and optionally acrolein to the formula: Mo CossBi. Feos Wos Si Koos O,
product is recovered from the reactor effluent gases leaving where X is the quantity of oxygen bonded to the other
12. The reduced Solids are transported to the regeneration 25 elements and depends on their oxidation State. The proce
Zone which is comprised of a riser Section 13 and a fluidized dure involved 60.9 grams of Co(NO), HO being dis
bed section 14. The reduced Solids are oxidized in this solved in 20 mL of distilled water. Also, 20.2 grams of
regeneration Zone and the oxidized (regenerated) catalyst is Fe(NO).9HO were dissolved in 15 mL of distilled water
then recycled to the riser section 11. and 31.2 grams of Bi(NO).5HO were dissolved in 30 mL
The reaction and regeneration Zones can be within a of distilled water acidified with 6 mL HNO at a concen
Single reactor, although better process control usually is tration of 68% by volume. Separately 127.4 grams of
achieved if the two are in Separate units. (NH), Mo.O.4HO were dissolved in 150 mL of water
with heating and Stirring and then 7.4 grams of WO were
The conversion of propylene in percent is defined as 100 added. The aqueous Solution containing the cobalt was
times the number of mols of propylene converted, divided 35 introduced dropwise over 20 minutes into the aqueous
by the number of mols of propylene in the feed. The Solution of the ammonium Salts. The ferric Solution was next
Selectivity to acrylic acid and acrolein in percent is defined introduced over 10 minutes and then the Solution containing
as 100 times the number of mols of propylene converted to the bismuth over 15 minutes. A solution obtained by dis
these products divided by the total number of mols of Solving 0.2 grams of KOH and 12.8 grams of colloidal silica
propylene converted. The yield of acrylic acid and acrolein 40 (at a concentration of 40 weight 9%) in 15 mL of water was
in percent is defined as 100 times the number of mols of added over 10 minutes resulting in gel formation. The gel
acrylic acid and acrolein formed divided by the number of thus obtained was blended for 1 hour at ambient temperature
mols of propylene in the feed. and then 1 hour at 70° C. The gel was next dried for 18 hours
AS indicated previously, there are a number of bismuth at 130 C. to obtain a solid precursor. The solid obtained was
molybdate oxidants disclosed in the art as suitable for the 45 precalcined at 225 C. in air and milled. Before calcination
oxidation of propylene to acrolein. Likewise there are a at 450° C. for 9 hours in air, this solid precursor correspond
number of molybdenum Vanadate type oxidants disclosed in ing to the above formula was then mixed with polysilicic
the art as Suitable for the oxidation of acrolein to acrylic acid solution as described in Example 10 of the U.S. Pat. No.
acid. The process of this invention is not limited to a 4,677,084 (to impart either 10 or 12 wt % silica in the final
particular method of making these oxidants, nor to a par 50 dry solids with the remaining 90 or 88%, respectively, being
ticular promoter; i.e., oxidants known in the art to contain the bismuth molybdate multimetal oxide component) and
Surface labile oxygen capable of converting propylene to further treated to produce the attrition resistant bismuth
acrolein and/or acrolein to acrylic acid. It should be further molybdate multimetal oxide component of the oxidant mix
appreciated that other transition metal oxidant System ture used in the following runs 1 through 8 of the Example.
known in the art to promote either the oxidation of propylene 55 The molybdenum Vanadate multimetal Starting Solids
to acrolein or acrolein to acrylic acid, Such as for example were obtained according to EXAMPLE 1(a) of French
but not by way of limitation the iron/anitimony metal oxide patent application 97 02344 filed on Feb. 27, 1997 in the
Solids, should be considered equivalent for purposes of the name of Elf Atochem S.A., “Process for Manufacture of
process of the present invention. Acrylic Acid from Acrolein by Redox Reaction and use of
The multimetal Solids used in the various runs of the 60 a Solid Mixed Oxide Composition as Redox System in the
Example of this invention were prepared by Substantially Said Reaction”. These starting solids correspond to the
following the procedure in U.S. Pat. No. 4,769,477, particu formula. MoVSros.W. Cu2O, where X is the quantity
larly the procedure of Example 10 wherein the multimetal of oxygen bonded to the other elements and depends on their
Solid component was slurried with Sufficient polysilicic acid oxidation State.
solution to result in typically 10 wt % SiO in the final dry 65 The procedure involved 3.6 grams of ammonium
Solids prior to Spray drying and Subsequent calcining or by paratungState, 3.0 grams of ammonium metavanadate and
Substantially following a related procedure in U.S. patent 12.4 grams of ammonium heptamolybdate being introduced
 US 6,281,384 B1
9 10
into 100 grams of water and heated to 100° C. Also, 3.0 regenerator was controlled by differential pressure control
grams of copper nitrate and 0.62 grams of Strontium nitrate between the Stripper and regenerator. Air was fed to the
were introduced into 5 grams of water and heated to 100° C. regenerator to re-oxidize the Solids. The off-gas from the
The Second Solution was added to the first and the resulting regenerator was fed to the regenerator quench System after
Slurry was then evaporated to dryneSS. The Solids were 5 disengagement from the Solids in a Series of cyclones.
precalcined at 225 C. in air to produce the desired precur From the regenerator, the oxidized catalyst was then fed
sor. Before calcining 400 C. for 4 hours in air, this solid back to the fluidization Section of the transport bed reactor.
precursor corresponding to the above formula was then The solids circulation rate was in the range of 15 to 30 kg/hr.
mixed with polysilicic acid Solution as described in Example The two quench Systems for the product and regenerator
10 of the U.S. Pat. No. 4,677,084 (to impart at least 10 wit off-gases were of identical design. A recirculating liquid
% silica, see Run 4 of the example) or mixed with polysilicic Served as a direct contact condenser/absorber for the prod
acid Solution and a colloidal Silica Solution as described in
U.S. patent application Ser. No. 09/088,804 to impart 10% ucts. Caustic was used on the product off-gas to absorb
organic products and to neutralize the acrylic acid produced.
silica from the polysilicic acid and 30% silica from the Water was used on the regenerator off-gas.
colloidal silica with the remaining 60% being the molybde 15
A hot gas Sample Stream for the product off-gas was taken
num Vanadate multimetal component (see Runs 1-3 and 5-8 to two static water absorbers. The first was used to absorb
of the Example) and further treated to produce the attrition C/C aldehydes and acids for quantitative analysis by an
resistant molybdenum Vanadate multimetal oxide compo off-line gas chromatograph. The Second was used as a
nent of the oxidant mixture.
The following example with several individual runs is pre-treatment absorber to remove aldehydes and acids which
presented to more fully demonstrate and further illustrate interfere with the analysis, prior to on-line gas chromato
various individual aspects and features of the present inven
graphic analysis of N, O, propylene, CO and CO.
tion. AS Such the examples are felt to be non-limiting and are The regenerator off-gas was Sampled down-stream of the
meant to illustrate the invention but are not meant to be water quench and analyzed for N, O, propylene, CO and
limiting in any way. 25 CO. Reactor performance was determined by on-line gas
chromatograph analysis for non-absorbed components in
EXAMPLE each of the two off-gas streams. Water absorbed products
were measured by off-line gas chromatograph analysis of the
A recirculating Solids reactor System of the type shown in liquid Sample absorber.
FIG. 1 was used to oxidize propylene to acrylic acid in a The primary process variables in the tables below are
Single Step. The transport bed reactor consisted of a Small defined as follows: Fluid. Bed Temp C. (fluidized bed
fluidization section surmounted by a 5/8 inch (1.59 cm) temperature in C.), CH Feed Conc. (propylene feed
diameter by 10 foot (3.05 m) tall riser tube. The recirculating concentration in mol%); Acrolein Feed Conc. (acrolein feed
mixture of Solids was transported up the riser tube with the concentration in mol %); Steam Feed Conc. (steam feed
reactant and product gases which are in plug flow. Reactant 35 concentration in mol%); Oxygen Feed Conc. (oxygen feed
gas contact times were on the order of 1 to 5 Seconds. concentration in mol %); Riser Gas Cont. Time (riser gas
Isothermal conditions (approximately 336+4 C.) were contact time in seconds); Fluid. Bed Gas Cont.Time
maintained by an electric furnace. Reactor pressure was (fluidized bed gas contact time in Seconds); Sol. Circ. Rate
maintained at 1 to 2 psig (6.89x10 to 1.38x10 Pa) at the kg/hr (Solids circulation rate in kilograms per hour);
top of the riser. Riser Superficial gas Velocity was in the 40 Mo-V/(Mo-V+Bi-Mo) Catal. in Chg (Wt %)
range of 6.6 to 10.5 ft/sec (2.67 to 3.02 m/sec). Riser gas (Molybdenum Vanadate type solids wt %, i.e. the weight
contact time was in the range of 0.9 to 1.5 seconds. Propy percent of total charge with the remainder being bismuth
lene and acrolein feed concentrations were varied as shown molybdate multimetal oxide).
in the following Table 1. Steam feed concentrations were in The primary responses were measured as key process
the range of 5 to 22.5 mol%. All feed flows were controlled 45 variables were changed. These primary responses are
by thermal mass flow controllers. Propylene and nitrogen defined as follows: Riser CH Conver. % (riser propylene
were fed to the fluidization Zone.
conversion 76); Acrol.+Acrylic Select. 9% (selectivity based
The product gas Stream leaving the riser was separated on the Sum of acrolein and acrylic acid selectivities); Acrylic
from the Solids in a two stage cyclone separator and fed to acid Select. 9% (selectivity to acrylic acid only); C. Select. 76
the product quench/absorption System. The Solids from the 50 (Selectivity to acetic acid and acetic anhydride); CO. Select.
Separator were transported to the regenerator via a 4 inch (10 % (selectivity to CO and CO); and Sol. Conver. Ratio kg/kg
cm) diameter fluidized bed Stripper. (Solids conversion ratio; i.e., kg Solids circulated/kg propy
The regenerator was a 4.5 inch (11.4 cm) diameter flu lene converted). Table 1 Summarizes the data associated
idized bed. Solids bed height (solids contact time) in the with runs 1 through 8.

TABLE 1.
SINGLE STEP 8 NCHRISERTEST:
ALL REACTANT FEEDS TO FLUIDIZED BED

PROCESS CONDITIONS

Run No. 1. 2 3 4 5 6 7 8

Fluid. Bed Temp C. 332 337 335 335 337 337 332 340
C.H. Feed Conc. 20.8 2O.O 19.2 15.O 2O.O 2O.O 2O.O 2O.O
Acrolein Feed Conc. O.OO O.OO O.OO O.OO 186 2.79 O.93 186
 US 6,281,384 B1
11 12
TABLE 1-continued
Steam Feed Conc. 11.9 5.6 22.5 20.1 2O2 2O2 2O2 2O2
Oxygen Feed Conc. O.O1 4.39 3.76 O.OO O.OO O.OO O.OO O.OO
Riser Gas Cont. Time 1.O O.9 1.2 1.2 1.2 1.2 1.2 1.2
Fluid Bed Gas Cont.Time 0.5 0.5 O.7 O.7 O.7 O.7 O.7 O.7
Sol. Circ. Rate(kg/hr) 27 24 15 3O 2O 21 22 22
Mo-VI(Mo-V + Bi-Mo) 15 15(a) O(a) 12(b) 20(a) 20(a) 20(a) 20(a)
Solin Chg(wt%)
(Mo-V is 60% active molybdenum vanadate component and 40% silica and Bi-Mo is 90% active bis
muth molybdate component and 10% silica.
(Mo-V is 90% active molybdenum vanadate component and 10% silica and Bi-Mo is 88% active bis
muth molybdate component and 12% silica.
RESPONSES

Riser C.H. Conver. % 6 11 16 1O 11 12 12 13

Acrol.+ Acrylic Select.% 76 77 76 77 78 81 82 78
Acrylic Acid Select.% 46 50 50 2O 78 81 62 78
C. Select.% 6 4 5 5 4 4 4 5
CO. Se1ect.% 17 17 19 17 17 15 14 17
Sol.Conv. Ratio kg/kg 1190 566 348 1486 636 583 660 575

The above results confirm the feasibility of conversion of State Such as to convert Said propylene to acrylic acid is
propylene to acrylic acid in a single Step and at low performed in a transport bed reactor of a recirculating Solids
selectivity to C and COX using a mixture of a molybdenum reactor System and wherein Said particulate oxidant mixture
Vanadate multimetal oxide and a bismuth molybdate multi 25 in a reduced State after Said conversion of propylene to
metal oxide as oxidant. With Some acrolein feed to the acrylic acid is separated from Said acrylic acid gaseous
reactor Zone, acrylic acid Selectivities are increased Substan product and is then reoxidized in a regenerator reactor of
tially by limiting propylene exposure and COX formation on Said recirculating Solids reactor System by contact with
the molybdenum vanadate multimetal oxide. This points to oxygen containing gas before being recirculated to Said
an advantage for acrolein (and propylene) recycle to the transport bed reactor.
reaction Zone, which is a likely operating mode on a 3. A process of claim 2 wherein Said transport bed reactor
commercial Scale. is a riser reactor and wherein Said particulate oxidant mix
ture comprises particles from 10 to 300 micron in size.
Having thus described and exemplified the invention with 4. A process of claim 3 wherein said feed gas residence
a certain degree of particularity, it should be appreciated that time in Said riser reaction Zone is from 1 Second to about 15
the following claims are not to be so limited but are to be 35
Seconds, and Said particulate oxidant mixture residence time
afforded a Scope commensurate with the wording of each in Said riser reaction Zone is from 2 Seconds to 120 Seconds.
element of the claim and equivalents thereof. 5. A process of claim 3 said particulate oxidant mixture
We claim:
1. A process for the oxidation of propylene to acrylic acid residence time in Said regenerator reactor is from 0.5 minute
comprising the Steps of: 40
to 10 minutes, and at an oxygen-containing gas residence
time of 3 seconds to 30 seconds at a temperature of about
(a) contacting a feed gas comprising (i) from 1 to 100 mol 250 to about 500 C.
% propylene, (ii) from 0 to 20 mol% oxygen, (iii) from 6. A process of any one of the preceding claims 1 through
0 to 70 mol % water, and (vi) the remainder inert gas 5 wherein said molybdenum vanadate multimetal oxide
with an effective amount of an oxidant mixture com corresponds to the formula: MoVSros W. CuO
prising a particulate molybdenum Vanadate multimetal 45
where X is the quantity of oxygen bonded to the other
oxide in an oxidized State and a bismuth molybdate element according to their respective oxidation States.
multimetal oxide in an oxidized State at a temperature 7. A process of any one of the preceding claims 1 through
from 250 to 450° C. and for a time sufficient to convert 5 wherein said bismuth molybdate multimetal oxide corre
a portion of Said propylene to acrylic acid, wherein the Sponds to the formula Mo CossBi. Feos Wols Sikoos.O.
50
relative amount of Said molybdenum Vanadate multi where X is the quantity of oxygen bonded to the other
metal oxide is from 5 to 50 percent by weight total elements according to their respective oxidation States.
active ingredients and the remainder 95 to 50 percent 8. A process of any one of the preceding claims 1 through
by weight is said bismuth molybdate multimetal oxide; 5 wherein said multimetal oxides are obtained by mixing of
and metal Salts, drying Said mixture and then precalcining Said
55
(b) recovering said acrylic acid produced in Step (a). dry mixture at 225 C. or above in air.
2. A process of claim 1 wherein Said contacting of Said
feed gas and Said particulate oxidant mixture in an oxidized