阅读说明：本技术 使用高活性和选择性催化剂在丙烯酸生产中减少醛副产物的方法 (Method for reducing aldehyde by-product in acrylic acid production using high activity and selectivity catalyst ) 是由 徐金锁 N·I·基罗斯 D·A·博尔施 J·F·德威尔德 于 2020-04-20 设计创作，主要内容包括：催化剂组合物包含丙烯醛氧化催化剂,该催化剂包含通式(I)的混合金属氧化物催化剂：MoV-(a)A～(1)-(b)A～(2)-(c)A～(3)-(d)O-(m) (I)其中A～(1)包含至少一种选自W和Cu的元素；A～(2)包含选自由Sb、Fe和Nb组成的组中的至少一种元素；A～(3)包含选自由Y、Ti、Zr、Hf、Ta、Cr、Mn、Re、Ru、Co、Rh、Ir、Ni、Pd、Pt、Ag、Au、Zn、B、Al、Ga、In、Ge、Sn、Si、Te、Pb、P、As、Bi、Se、稀土元素、碱元素和碱土元素组成的组中的至少一种元素；a范围为0.01至1.0；b范围为0.01至1.5；c范围为0至1.5；d范围为0至1.0；m取决于其他元素的氧化态。催化剂组合物进一步包含精加工催化剂,其包含通式(II)的混合金属氧化物催化剂：MoV-(w)Nb-(x)X～(1)-(y)X～(2)-(z)O-(n) (II)其中X～(1)包含至少一种选自Te和Sb的元素；X～(2)包含选自由Y、Ti、Zr、Hf、Nb、Ta、Cr、Mn、Re、Fe、Ru、Co、Rh、Ir、Ni、Pd、Pt、Ag、Au、Zn、B、Al、Ga、In、Ge、Sn、Pb、P、As、Bi、Se、稀土元素和碱土元素组成的组的至少一种元素；w范围为0.01至1.0；x范围为0.01至1.0；y范围为0.01至1.0；z范围为0至1.0；n取决于其他元素的氧化态。精加工催化剂不含W或Cu,并且X射线衍射图显示斜方晶相为主晶相,主峰2θ分别为6.7°、7.8°、22.1°和27.2°。丙烯醛氧化催化剂具有与精加工催化剂不同的化学组成。还公开了生产丙烯酸的方法。(The catalyst composition comprises an acrolein oxidation catalyst comprising a mixed metal oxide catalyst of formula (I): MoV a A 1 b A 2 c A 3 d O m (I) Wherein A is 1 Comprises at least one element selected from W and Cu; a. the 2 Comprises at least one element selected from the group consisting of Sb, Fe and Nb; a. the 3 IncludedAt least one element selected from the group consisting of Y, Ti, Zr, Hf, Ta, Cr, Mn, Re, Ru, Co, Rh, Ir, Ni, Pd, Pt, Ag, Au, Zn, B, Al, Ga, In, Ge, Sn, Si, Te, Pb, P, As, Bi, Se, a rare earth element, an alkali element and an alkaline earth element; a ranges from 0.01 to 1.0; b ranges from 0.01 to 1.5; c ranges from 0 to 1.5; d ranges from 0 to 1.0; m depends on the oxidation state of the other elements. The catalyst composition further comprises a polishing catalyst comprising a mixed metal oxide catalyst of formula (II): MoV w Nb x X 1 y X 2 z O n (II) wherein X 1 Comprises at least one element selected from Te and Sb; x 2 Comprising at least one element selected from the group consisting of Y, Ti, Zr, Hf, Nb, Ta, Cr, Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Ag, Au, Zn, B, Al, Ga, In, Ge, Sn, Pb, P, As, Bi, Se, rare earth elements, and alkaline earth elements; w ranges from 0.01 to 1.0; x ranges from 0.01 to 1.0; y ranges from 0.01 to 1.0; z ranges from 0 to 1.0; n depends on the oxidation state of the other elements. The finished catalyst contained no W or Cu, and the X-ray diffraction pattern showed an orthorhombic phase as the main crystal phase, and the main peaks 2 θ were 6.7 °, 7.8 °, 22.1 ° and 27.2 °, respectively. The acrolein oxidation catalyst has a different chemical composition than the finishing catalyst. A process for producing acrylic acid is also disclosed.)

1. A catalyst composition, comprising:

a) an acrolein oxidation catalyst comprising a mixed metal oxide catalyst of formula (I):

MoV_aA¹ _bA² _cA³ _dO_m (I)

wherein:

A¹comprises at least one element selected from the group consisting of W and Cu;

A²comprises at least one element selected from the group consisting of Sb, Fe and Nb;

A³containing at least one element selected from the group consisting of Y, Ti, Zr, Hf, Ta, Cr, Mn, Re, Ru, Co, Rh, Ir, Ni, Pd, Pt, Ag, Au, Zn, B, Al, Ga, In, Ge, Sn, Si, Te, Pb, P, As, Bi, Se, a rare earth element, an alkali element and an alkaline earth element;

a ranges from 0.01 to 1.0;

b ranges from 0.01 to 1.5;

c ranges from 0 to 1.5;

d ranges from 0 to 1.0;

m depends on the oxidation state of the other elements;

b) a finished catalyst comprising a mixed metal oxide catalyst of formula (II):

MoV_wNb_xX¹ _yX² _zO_n (II)

wherein:

X¹comprises at least one element selected from the group consisting of Te and Sb;

X²comprising at least one element selected from the group consisting of Y, Ti, Zr, Hf, Nb, Ta, Cr, Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Ag, Au, Zn, B, Al, Ga, In, Ge, Sn, Pb, P, As, Bi, Se, rare earth elements, and alkaline earth elements;

w ranges from 0.01 to 1.0;

x ranges from 0.01 to 1.0;

y ranges from 0.01 to 1.0;

z ranges from 0 to 1.0;

n depends on the oxidation state of the other elements;

the finishing catalyst contained no W or Cu, and the X-ray diffraction pattern showed an orthorhombic phase as the main crystalline phase, with main peaks 2 θ of 6.7 °, 7.8 °, 22.1 ° and 27.2 °, respectively; and

the acrolein oxidation catalyst and the finishing catalyst have different chemical compositions.

2. The catalyst composition of claim 1, wherein:

w ranges from 0.1 to 0.5;

x ranges from 0.01 to 0.5;

y ranges from 0.05 to 0.3; and

z ranges from 0 to 0.2.

3. The catalyst composition of claim 1 or 2 wherein the polishing catalyst comprises less than 20 wt% of the total weight of the acrolein oxidation catalyst and the polishing catalyst.

4. A catalyst composition according to any one of claims 1 to 3 wherein the polishing catalyst comprises less than 10% by weight of the total weight of the acrolein oxidation catalyst and the polishing catalyst.

5. A method of producing acrylic acid, the method comprising:

a) contacting a gas stream comprising acrolein with an acrolein oxidation catalyst to form a product stream a, wherein at least one aldehyde by-product is present in the product stream a;

b) contacting the product stream a with a finishing catalyst to form a product stream B comprising acrylic acid, wherein the product stream B comprises a lower weight percentage of at least one aldehyde by-product than product stream a;

wherein:

i) the acrolein oxidation catalyst comprises a mixed metal oxide catalyst of formula (I):

MoV_aA¹ _bA² _cA³ _dO_m (I)

wherein:

A¹comprises at least one element selected from the group consisting of W and Cu;

A²comprises at least one element selected from the group consisting of Sb, Fe and Nb;

A³containing at least one element selected from the group consisting of Y, Ti, Zr, Hf, Ta, Cr, Mn, Re, Ru, Co, Rh, Ir, Ni, Pd, Pt, Ag, Au, Zn, B, Al, Ga, In, Ge, Sn, Si, Te, Pb, P, As, Bi, Se, a rare earth element, an alkali element and an alkaline earth element;

a ranges from 0.01 to 1.0;

b ranges from 0.01 to 1.5;

c ranges from 0 to 1.5;

d ranges from 0 to 1.0; and

m depends on the oxidation state of the other elements;

ii) a polishing catalyst comprising a mixed metal oxide catalyst of formula (I):

MoV_wNb_xX¹ _yX² _zO_n (II)

wherein:

X¹comprises at least one element selected from the group consisting of Te and Sb;

X²comprising at least one element selected from the group consisting of Y, Ti, Zr, Hf, Nb, Ta, Cr, Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Ag, Au, Zn, B, Al, Ga, In, Ge, Sn, Pb, P, As, Bi, Se, rare earth elements, and alkaline earth elements;

w ranges from 0.01 to 1.0;

x ranges from 0.01 to 1.0;

y ranges from 0.01 to 1.0;

z ranges from 0 to 1.0;

n depends on the oxidation state of the other elements;

the finishing catalyst contained no W or Cu, and the X-ray diffraction pattern showed an orthorhombic phase as the main crystalline phase, with main peaks 2 θ of 6.7 °, 7.8 °, 22.1 ° and 27.2 °, respectively; and

the acrolein oxidation catalyst and the finishing catalyst have different chemical compositions.

6. A method according to claim 5 wherein the acrolein oxidation catalyst is located upstream of the polishing catalyst.

7. A process according to claim 5 or 6 wherein the acrolein oxidation catalyst and the polishing catalyst are formed as a single catalyst bed in a reactor.

8. A process according to claim 5 or 6 wherein the polishing catalyst is present in a reactor subsequent to a reactor containing the acrolein oxidation reactor.

9. The method of any of claims 5 to 7, further comprising:

prior to step a), a gas stream comprising acrolein is prepared by oxidizing propylene in the presence of a propylene oxidation catalyst.

10. A method according to any one of claims 5 to 9 wherein the polishing catalyst comprises less than 20% by weight of the total weight of the acrolein oxidation catalyst and the polishing catalyst.

Technical Field

The present invention relates to a catalyst and a process for producing acrylic acid, and more particularly to a high activity and selectivity catalyst and a process for reducing aldehyde by-products in the production of acrylic acid using the same.

Background

Acrylic acid and its esters are industrially important and can be used to make polymers for a wide range of applications including, but not limited to, adhesives, coatings, films, biomedical supports and devices, and adhesives. Acrylic acid can be produced by, among other methods, the catalytic gas phase oxidation of alkanes, alkanols, alkenes, or alkenals.

One widely practiced process is the catalytic gas phase oxidation of, for example, propane, propylene or acrolein. These feedstocks are typically diluted with an inert gas such as nitrogen, carbon monoxide, carbon dioxide, saturated hydrocarbons, and/or steam, and then contacted with a mixed metal oxide catalyst (e.g., a mixed metal oxide catalyst containing one or more of molybdenum (Mo), vanadium (V), tungsten (W), and iron (Fe)) with or without molecular oxygen at elevated temperatures (e.g., 20 ℃ to 400 ℃) to be oxidized to acrylic acid.

Mixed metal oxide catalysts based on Mo and V have been used for the oxidation of acrolein to acrylic acid. For example, the oxidation of acrolein to acrylic acid is the second step in the manufacture of acrylic acid using propylene. The mixed metal oxide catalyst generally contains one or more elements selected from W, copper (Cu), nickel (Ni) in addition to Mo and V, and has a high selectivity for the oxidation of acrolein to acrylic acid, with a yield generally above 92%. However, since such exothermic reactions lead to high temperatures and the formation of "hot spots" (i.e., locations within the catalyst bed where the temperature is higher than the bath temperature), the activity and selectivity of the mixed oxide catalyst may deteriorate over time, resulting in decreased acrylic acid yield and frequent catalyst replacement.

Improvements have been made to reduce catalyst deactivation and extend catalyst life. For example, european patent No. EP 0792866 reports the use of catalyst pellets of different sizes such that the particle size becomes smaller from the inlet side to the outlet side of the raw material gas to reduce the reactor temperature and hot spot, thereby extending the catalyst life.

European patent application publication No. EP 1749573a1 discloses the use of at least two reaction zones of different activity by varying the catalyst composition to reduce the rate of temperature rise over time to extend catalyst life. The catalyst comprises Mo, V, antimony (Sb), Cu, and at least one of niobium (Nb) and W, and may further comprise silicon (Si) and carbon (C).

Us patent No. 7,365,228 discloses the use of a layer of inactive material alongside the catalyst layer that creates "hot spots" to reduce the peak temperature between hot spots, thereby increasing the lifetime of the catalyst and achieving higher acrylic acid yields.

U.S. patent No. 8,623,780 discloses the use of organic reducing agents including C2-C6 diols or polyols and silicon powder in the preparation of mixed metal oxides and/or in the formation of catalysts to increase the activity of the catalyst and to increase the efficiency of heat transfer along the catalyst bed. As a result, "hot spots" are reduced and catalyst life and acrylic acid yield may be increased.

U.S. patent No. 9,181,169 discloses hydrothermal synthesis of mixed metal oxides to improve their activity and yield to acrylic acid.

In summary, these efforts are effective in improving the life of mixed oxide catalysts. However, there are other problems in using those catalysts and methods.

Since many parallel and subsequent reactions occur during the catalytic gas phase oxidation and since an inert diluent gas is used, the resulting mixed gas product contains not only acrylic acid but also inert diluent gases, impurities and by-products from which acrylic acid must be separated. Thus, the mixed product gas is typically next absorbed to remove acrylic acid from some by-products and impurities and form an acrylic acid solution. It is known to use absorption solvents such as water or hydrophobic organic liquids such as, but not limited to, toluene, methyl isobutyl ketone (MiBK and diphenyl ether) or acrylic acid itself (e.g. in a fractionation column) for the absorption step. The resulting acrylic acid solution is then subjected to further separation and purification steps, for example by azeotropic or simple distillation, or crystallization or extraction, to produce a crude acrylic acid product, which may or may not be subjected to further purification or reaction as desired, depending on the intended end use.

In addition to by-products (e.g., acetic acid) which are relatively easy to remove from the acrylic acid, the mixed gas product also contains aldehyde compounds which are at boiling points and/or dissolved in the acrylic acidThe solubility aspect is closely related to acrylic acid, and thus may be difficult to separate from acrylic acid. The aldehyde by-product formed in the oxidation product can include, for example, one or more of the following: formaldehyde, acetaldehyde, acrolein, propionaldehyde, benzaldehyde, phthalaldehyde, furfural, protoalbuterol, and possibly maleic anhydride or an acid thereof. The total amount of aldehyde component present in the mixed gas product may be up to or even greater than about 2 wt.% based on the total weight of the mixed gas product obtained from the oxidation reaction. Aldehydes, especially low molecular C, are reported to be₁To C₃The analogs (formaldehyde, acetaldehyde and propionaldehyde) can initiate polymerization of acrylic acid in separation equipment such as distillation columns, reboilers and heat exchanger equipment. In particular, it has been shown in the art that solids are produced when formaldehyde is contacted with common polymerization inhibitors such as Phenothiazine (PTZ), Hydroquinone (HQ), and hydroquinone monomethyl ether (MeHQ) (see, e.g., U.S. patent application publication No. 2007/0167650). Furfural and acrolein are also reported as fouling contributors in acrylic acid processing.

To produce Glacial Acrylic Acid (GAA) or Flocculant Glacial Acrylic Acid (FGAA), the amount of certain aldehydes, such as acrolein, furfural, and benzaldehyde, must be reduced to less than 1 ppm.

Attempts have been made to reduce the amount of aldehydes formed during the production of acrylic acid. These processes use chemical scavengers selected from primary and secondary amines or salts thereof, such as hydrazide or m-phenylenediamine (m-PD)), to react with aldehydes and form adducts with higher boiling points, thereby reducing the aldehyde impurities in the crude acrylic acid. The high boiling adducts remain in the distillation column bottoms stream, and purer acrylic acid is obtained as distillate. Such methods are disclosed, for example, in U.S. patent No. 7,048,834 and U.S. patent application publication No. 2013/0281737.

However, these methods require an excess of chemical scavenger to reduce the aldehyde concentration to the desired level, which adds additional cost to the acrylic acid production in addition to increasing dimer formation. Increased fouling of these chemical scavengers is also observed in downstream processes such as distillation or esterification.

In addition, chemical scavengers can cause other problems in addition to increased cost and/or fouling. For example, m-PD is difficult to handle because it is a solid at ambient conditions and is easily oxidized to complex with the color.

A new class of mixed metal oxide catalysts containing the elements Mo, V, Nb and tellurium (Te) or Sb has been found to be active and selective for the oxidation of propane to acrylic acid. For example, U.S. Pat. nos. 7,875,571, 7,304,014 and 9,616,415 disclose compositions and methods of preparation of MoVTeNb oxide catalysts for the direct oxidation of propane to acrylic acid. U.S. patent application publication No. 2009/0076303 reports the use of a MoVTeNb oxide catalyst to reduce propionic acid, an impurity in acrylic acid from direct propane oxidation. While MoVTeNb oxide can be used for the oxidation of acrolein to acrylic acid as reported in U.S. patent No. 6,812,366, the yield (89.4%, example 7) is lower than the reported 92% + yield when using a MoV-based mixed metal oxide catalyst optimized for selective acrolein oxidation to acrylic acid.

Therefore, there is a need for a catalyst and a method for producing acrylic acid with high yield, which can reduce the temperature and/or amount of aldehyde.

Disclosure of Invention

One aspect of the present invention relates to a catalyst composition comprising:

a) an acrolein oxidation catalyst comprising a mixed metal oxide catalyst of formula (I):

MoV_aA¹ _bA² _cA³ _dO_m (I)

wherein:

A¹comprises at least one element selected from the group consisting of W and Cu;

A²comprises at least one element selected from the group consisting of Sb, Fe and Nb;

A³containing at least one element selected from the group consisting of Y, Ti, Zr, Hf, Ta, Cr, Mn, Re, Ru, Co, Rh, Ir, Ni, Pd, Pt, Ag, Au, Zn, B, Al, Ga, In, Ge, Sn, Si, Te, Pb, P, As, Bi, Se, a rare earth element, an alkali element and an alkaline earth element;

a ranges from 0.01 to 1.0;

b ranges from 0.01 to 1.5;

c ranges from 0 to 1.5;

d ranges from 0 to 1.0;

m is an oxidation state dependent on the other elements;

b) a finished catalyst comprising a mixed metal oxide catalyst of formula (II):

MoV_wNb_xX¹ _yX² _zO_n (II)

wherein:

X¹comprises at least one element selected from the group consisting of Te and Sb;

X²comprising at least one element selected from the group consisting of Y, Ti, Zr, Hf, Nb, Ta, Cr, Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Ag, Au, Zn, B, Al, Ga, In, Ge, Sn, Pb, P, As, Bi, Se, rare earth elements and alkaline earth elements;

w ranges from 0.01 to 1.0;

x ranges from 0.01 to 1.0;

y ranges from 0.01 to 1.0;

z ranges from 0 to 1.0;

n depends on the oxidation state of the other elements;

the finished catalyst contained no W or Cu, and the X-ray diffraction pattern showed an orthorhombic phase as the main crystalline phase, with main peaks 2 θ of 6.7 °, 7.8 °, 22.1 ° and 27.2 °, respectively; and

the acrolein oxidation catalyst and the finishing catalyst have different chemical compositions.

A second aspect of the present invention relates to a method for producing acrylic acid, the method comprising:

a) contacting a gas stream comprising acrolein with an acrolein oxidation catalyst to form a product stream a, wherein at least one aldehyde by-product is present in the product stream a;

b) contacting the product stream a with a finishing catalyst to form a product stream B comprising acrylic acid, wherein the product stream B comprises a lower weight percentage of at least one aldehyde by-product than the product stream a;

wherein:

i) the acrolein oxidation catalyst comprises a mixed metal oxide catalyst of formula (I):

MoV_aA¹ _bA² _cA⁴ _dO_m (I)

wherein:

A¹comprises at least one element selected from the group consisting of W and Cu;

A²comprises at least one element selected from the group consisting of Sb, Fe and Nb;

A³containing at least one element selected from the group consisting of Y, Ti, Zr, Hf, Ta, Cr, Mn, Re, Ru, Co, Rh, Ir, Ni, Pd, Pt, Ag, Au, Zn, B, Al, Ga, In, Ge, Sn, Si, Te, Pb, P, As, Bi, Se, a rare earth element, an alkali element and an alkaline earth element;

a ranges from 0.01 to 1.0;

b ranges from 0.01 to 1.5;

c ranges from 0 to 1.5;

d ranges from 0 to 1.0; and

m is an oxidation state dependent on the other elements;

ii) a polishing catalyst comprising a mixed metal oxide catalyst of formula (I):

MoV_wNb_xX¹ _yX² _zO_n (II)

wherein:

X¹comprises at least one element selected from the group consisting of Te and Sb;

X²comprising at least one element selected from the group consisting of Y, Ti, Zr, Hf, Nb, Ta, Cr, Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Ag, Au, Zn, B, Al, Ga, In, Ge, Sn, Pb, P, As, Bi, Se, rare earth elements and alkaline earth elements;

w ranges from 0.01 to 1.0;

x ranges from 0.01 to 1.0;

y ranges from 0.01 to 1.0;

z ranges from 0 to 1.0;

n depends on the oxidation state of the other elements;

the finished catalyst contained no W or Cu, and the X-ray diffraction pattern showed an orthorhombic phase as the main crystalline phase, and the main peaks 2. theta. were 6.7 °, 7.8 °, 22.1 ° and 27.2 °, respectively; and

the acrolein oxidation catalyst and the finishing catalyst have different chemical compositions.

Drawings

Fig. 1 shows an X-ray diffraction pattern of a MoVTeNb oxide finishing catalyst according to one embodiment of the present invention.

FIG. 2 shows Mo₃VO_xX-ray diffraction pattern of the catalyst.

FIG. 3 shows the packing of acrolein oxidation catalyst and finishing catalyst in the reactor tubes according to one embodiment of the invention.

FIG. 4 is a schematic diagram of a two-stage reactor process according to one embodiment of the present invention.

FIG. 5 is a schematic of a three-stage reactor process according to one embodiment of the present invention.

Detailed Description

As used herein, the terms "a/an", "the", "at least one", "one or more" and variations thereof are used interchangeably. Where the terms "comprise", "include", "contain" and variations thereof are presented in the specification and claims, these terms are not intended to be limiting. Thus, for example, a first mixed metal oxide catalyst composition comprising a polymerization inhibitor can be construed to mean that the composition comprises at least one polymerization inhibitor.

As used herein, the recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.). For the purposes of this disclosure, it is to be understood that the numerical ranges are intended to encompass and support all possible subranges subsumed within the range, consistent with what one of ordinary skill in the art would understand. For example, a range of 1 to 100 is intended to convey 1.1 to 100, 1 to 99.99, 1.01 to 99.99, 40 to 6,1 to 55, and so forth.

As used herein, recitation of numerical ranges and/or values, including such recitation in the claims, is understood to include the term "about". In this instance, the term "about" refers to a numerical range and/or value that is substantially the same as the numerical range and/or value described herein. When multiple endpoints are disclosed, the disclosure is intended to cover any range between any two of the disclosed endpoints.

As used herein, a mixed metal oxide catalyst refers to a catalyst comprising more than one metal oxide. Such mixed metal oxide catalysts may be formed on a support such as silica, alumina, silicon carbide or other materials known in the art that do not alter catalytic activity. The chemical formulas disclosed herein relate to the active catalyst material and do not include any support. For example, in the following formula (I), A³May comprise silicon. In formula (I), d includes only the amount of silicon (if present) in the active catalyst material and does not include any silicon in the support material.

Unless stated to the contrary or implied by context, all parts and percentages are by weight and all test methods are current as of the filing date of this application. For purposes of united states patent practice, the contents of any referenced patent, patent application, or publication are incorporated by reference in their entirety (or the equivalent us version thereof) especially with respect to the disclosure of limitations (to the extent not inconsistent with any limitations specifically provided in this disclosure) and general knowledge in the art.

The inventors have surprisingly found that a finishing catalyst comprising a mixed metal oxide comprising M, V, Nb and at least one element selected from Te and Sb can reduce the required temperature, which in turn can slow down the process for producing acrylic acid and extend the useful life of the catalyst. Surprisingly, the finishing catalyst can also reduce the amount of aldehyde by-product in the product stream and can increase the acrylic acid yield as compared to the use of conventional catalysts alone. The reduction of aldehyde by-products in the product stream can reduce the use of chemical scavengers and can mitigate fouling in downstream processes.

One aspect of the invention relates to a catalyst composition comprising two mixed metal oxide catalysts. The first catalyst is an acrolein oxidation catalyst, i.e., the main function of the acrolein oxidation catalyst is the gas phase oxidation of acrolein to produce acrylic acid. The second catalyst is a mixed metal oxide polishing catalyst. The polishing catalyst enables the catalyst composition to solve one or more problems of conventional mixed metal oxide catalysts used to produce acrylic acid while maintaining high yields of acrylic acid.

The acrolein oxidation catalyst has a different chemical composition than the finishing catalyst. As used herein, the term "different chemical compositions" means that the catalyst compositions have different molecular formulas. For example, the catalyst compositions may differ in the elements they contain, or the catalyst compositions may differ in the proportions of the elements they contain. Preferably, the acrolein oxidation catalyst differs from the polishing catalyst in the elements contained therein.

The finishing catalyst is preferably more active for aldehyde oxidation than the acrolein oxidation catalyst in the range of 200 to 350 ℃.

The acrolein oxidation catalyst may contain Mo and V as main elements. Preferably, the acrolein oxidation catalyst is a mixed metal oxide catalyst of formula (I):

MoV_aA¹ _bA² _cA³ _dO_m (I)

the mixed metal oxide catalyst of formula (I) comprises at least three metal oxides, including Mo and V oxides, i.e. a and b are greater than zero. Preferably, a is at least 0.01, such as at least 0.05, at least 0.1, at least 0.2, at least 0.3, at least 0.4 or at least 0.5. In formula (I), a is less than or equal to 1.0, such as less than 0.9, less than 0.8, or less than 0.7. Preferably, a ranges from 0.1 to 0.6.

In the general formula (I), A¹At least one element selected from W and Cu may be contained. When A is¹When more than one element is included, each elementThe amounts of (a) and (b) may be the same or different. A. the¹Is an essential element in the general formula (I). Thus, A in the formula (I)¹The amount b of (a) is greater than zero. For example, b may be at least 0.01, at least 0.03, at least 0.05, at least 0.1, at least 0.15, or at least 0.2. In formula (I), b may be less than or equal to 1.5, such as less than 1.0, less than 0.8, less than 0.6, or less than 0.5. Preferably, b ranges from 0.2 to 0.3.

A²Sb, Fe, or Nb, or a combination of two or three of these elements may be contained. A. the²Is an optional component of formula (I), i.e. c is equal to 0. Alternatively, c may be greater than zero, e.g., at least 0.01, at least 0.02, or at least 0.05. In formula (I), c is less than 1.5, preferably less than 1.0, less than 0.5, less than 0.4, less than 0.3 or less than 0.2. Preferably, c ranges from 0.05 to 0.2.

In the general formula (I), A³At least one element selected from the group consisting of Y, Ti, Zr, Hf, Ta, Cr, Mn, Re, Ru, Co, Rh, Ir, Ni, Pd, Pt, Ag, Au, Zn, B, Al, Ga, In, Ge, Sn, Si, Te, Pb, P, As, Bi, Se, rare earth elements, alkali elements and alkaline earth elements may be contained. A. the³Is an optional element in formula (I), i.e. d may be equal to 0. Alternatively, d may be greater than zero. If present, A³Preferably selected from alkali metals or alkaline earth elements.

In the general formula (I), d is less than or equal to 1.0. Preferably, d is less than or equal to 0.8, less than or equal to 0.6, less than or equal to 0.5, less than or equal to 0.4, less than or equal to 0.3, or less than or equal to 0.25. d may be greater than or equal to 0, such as greater than or equal to 0.05, greater than or equal to 0.1, or greater than or equal to 0.2. Preferably, d ranges from 0.05 to 0.25

In the general formula (I), m depends on the oxidation state of the other elements.

The preparation of mixed metal oxide catalysts that may be included in formula (I) is described, for example, in U.S. patent nos. 5,959,143, 6,383,978; 6,641,996, respectively; 6,518,216, respectively; 6,403,525, respectively; 6,407,031, respectively; 6,407,280, respectively; and 6,589,907; U.S. published application No. 20030004379; U.S. provisional application serial No. 60/235,977; 60/235,979, respectively; 60/235,981, respectively; 60/235,984, respectively; 60/235,983, respectively; 60/236,000, respectively; 60/236,073, respectively; 60/236,129, respectively; 60/236,143, respectively; 60/236,605, respectively; 60/236,250, respectively; 60/236,260, respectively; 60/236,262, respectively; 60/236,263, respectively; 60/283,245, respectively; and 60/286,218; and european patent No. EP 1080784; EP 1192982; EP 1192983; EP 1192984; EP 1192986; EP 1192987; EP 1192988; EP 1192982; EP 1249274; and EP 1270068. The synthesis of such mixed metal oxide catalysts can be accomplished by any of several methods well known to those skilled in the art.

The acrolein oxidation catalyst is preferably highly selective in the oxidation of acrolein to acrylic acid in a yield of at least 90%, for example, in a yield of at least 91%, at least 92%, at least 93%, or at least 94%.

The finishing catalyst may comprise a mixed metal oxide catalyst of formula (II):

MoV_wNb_xX¹ _yX² _zO_n (II)

in the general formula (II), X¹Comprising at least one element selected from the group consisting of Te, Sb, and a combination of Te and Sb.

For the mixed metal oxide of formula (II), w, x and y are all greater than zero. Thus, the mixed metal oxide catalyst of formula (II) includes an oxide based on MoVNbTe and an oxide based on MoVNbSb. Preferably, the mixed metal oxide catalyst of formula (II) consists of a MoVNbTe oxide or a MoVNbSb oxide, i.e. z is 0.

The polishing catalyst of formula (II) comprises V in an amount w of 0.01 to 1.0 inclusive. Preferably, w is at least 0.1, such as at least 0.2, at least 0.3 or at least 0.4. w is less than or equal to 1.0, such as less than or equal to 0.8, less than or equal to 0.6, or less than or equal to 0.5. Preferably, w ranges from 0.2 to 0.4.

In the general formula (II), the amount x of Nb in the mixed metal oxide catalyst is in the range of 0.01 to 1.0, inclusive. Preferably, x is at least 0.05, such as at least 0.1, at least 0.15, or at least 0.2. Preferably, x is less than or equal to 0.8, less than or equal to 0.6, less than or equal to 0.5, less than or equal to 0.4, or less than or equal to 0.3. Preferably, x ranges from 0.1 to 0.3.

X¹Can be selected from Sb, Te, and combinations of Sb and Te, and can be present in an amount y in the range of 0.01 to 1.0. Preferably, y is at least 0.02, such as at least 0.03, at least 0.04, at least 0.05, at least 0.06, at least 0.07, at least 0.08, at least 0.09, or at least 0.1. Preferably, y is less than or equal to 0.5, such as less than or equal to 0.4, or less than or equal to 0.3. More preferably, y ranges from 0.1 to 0.3.

X²At least one element selected from the group consisting of Y, Ti, Zr, Hf, Nb, Ta, Cr, Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Ag, Au, Zn, B, Al, Ga, In, Ge, Sn, Pb, P, As, Bi, Se, rare earth elements, alkali elements and alkaline earth elements may be contained. Preferably, X²Including Pd.

In the mixed metal oxide catalyst of the general formula (II), X²Is an optional component, i.e. z may be equal to 0. Alternatively, z may be greater than zero. Preferably, z ranges from 0.001 to 1.0. Preferably, z is greater than or equal to 0.001, such as greater than or equal to 0.002, greater than or equal to 0.003, greater than or equal to 0.004, or greater than or equal to 0.005. z is preferably less than or equal to 0.5, less than or equal to 0.4, less than or equal to 0.3, less than or equal to 0.2 or less than or equal to 0.1. More preferably, z ranges from 0.005 to 0.1.

The finishing catalyst of formula (II) does not contain W or Cu.

Preferably, the X-ray diffraction pattern of the finished catalyst of formula (II) shows an orthorhombic phase as the main crystalline phase, the main peaks 2 θ being located at 6.7 °, 7.8 °, 22.1 ° and 27.2 °, respectively. As used herein, the term "main peak" refers to the peak intensity that is clearly observed in the X-ray diffraction pattern, i.e., the signal intensity with at least 1% of the highest intensity peak.

The catalyst composition may comprise a layer of acrolein oxidation catalyst and a layer of polishing catalyst. The finishing catalyst layer may be adjacent to the acrolein oxidation catalyst layer, or the finishing catalyst layer may be separate from the acrolein oxidation catalyst layer.

Alternatively, the catalyst composition may have a gradient distribution of the catalyst. For example, one end of the catalyst composition may consist essentially of the acrolein oxidation catalyst and the other end may consist essentially of the polishing catalyst, and the ratio of the two catalysts may vary from one end to the other.

The weight percent of the finishing catalyst in the catalyst composition can be less than the weight of the acrolein oxidation catalyst, e.g., the finishing catalyst comprises less than 50 weight percent of the total weight of the acrolein oxidation catalyst and the finishing catalyst. Preferably, the weight of the finishing composition is less than 40 wt.%, less than 30 wt.%, less than 25 wt.%, less than 20 wt.%, less than 15 wt.%, or less than 10 wt.% of the total weight of the acrolein oxidation catalyst and the finishing catalyst.

The polishing catalyst comprises at least 5 wt% of the total weight of the acrolein oxidation catalyst and the polishing catalyst. Preferably, the polishing catalyst comprises at least 10 wt.%, at least 15 wt.%, or at least 20 wt.% of the total weight of the acrolein oxidation catalyst and the polishing catalyst.

Another aspect of the invention relates to a process for producing acrylic acid.

A method of producing acrylic acid includes contacting a gas stream comprising acrolein with an acrolein oxidation catalyst to form a product stream a. Product stream a comprises acrylic acid and at least one aldehyde by-product. The at least one aldehyde byproduct in product stream a can include, for example, acetaldehyde, benzaldehyde, or furfural. As used herein, the term "aldehyde by-product" refers to an aldehyde formed during the production of acrylic acid. Acrolein as an aldehyde is not an aldehyde by-product.

The product stream a is then contacted with a finishing catalyst to form a product stream B comprising acrylic acid. Product stream B comprises a lower weight percentage of at least one aldehyde by-product present in product stream a. Product stream B can comprise at least 25% less of the at least one aldehyde by-product than product stream a, preferably at least 30% less of the at least one aldehyde by-product, at least 40% less of the at least one aldehyde by-product, at least 50% less of the at least one aldehyde by-product, at least 60% less of the at least one aldehyde by-product, or at least 70% less of the at least one aldehyde by-product than product stream a.

Product stream B comprises at least 50% less acetaldehyde than product stream a. Preferably, product stream B comprises at least 60% less acetaldehyde than product stream a, e.g., at least 70% less, at least 80% less, or at least 90% less.

The acrolein oxidation catalyst and the polishing catalyst used in the present invention may be selected from embodiments of the catalysts disclosed herein. Preferably, the acrolein oxidation catalyst is a mixed metal oxide catalyst of formula (I) and the finishing catalyst is a mixed metal oxide catalyst of formula (II).

The weight ratio of acrolein oxidation catalyst to finishing catalyst is at least 1: 1. The weight ratio of acrolein oxidation catalyst to finishing catalyst may be at least 2: 1, for example at least 3: 1, at least 4: 1, at least 5: 1, at least 6: 1, at least 7: 1, at least 8: 1, or at least 9: 1. Preferably, the weight ratio of acrolein oxidation catalyst to finishing catalyst is no greater than 20: 1, such as no greater than 16: 1, no greater than 14: 1, no greater than 12: 1, or no greater than 10: 1.

The acrolein-containing gas stream may be produced, for example, by oxidizing a feed gas stream comprising an alkane, alkanol, alkene, or alkenal to form acrolein. Preferably, the feed gas stream comprises propane or propylene. More preferably, the feed gas stream comprises propylene. The feed gas stream may be contacted with a suitable oxidation catalyst known in the art. For example, suitable propylene oxidation catalysts may be selected from commercially available mixed metal oxide catalysts, such as Mo and Bi based mixed metal oxide catalysts.

The process may be carried out in a two-stage reactor system. A schematic diagram of this embodiment is shown in fig. 4. In fig. 4, a two-stage reactor system 100 includes a first stage reactor 101 and a second stage reactor 102.

The first stage reactor 101 contains a mixed metal oxide catalyst 115 of propylene oxide. The second stage reactor 102 contains an acrolein oxidation mixed metal oxide catalyst 125 and a polishing catalyst 135.

A gaseous feed stream 110 comprising propylene enters first stage reactor 101 where propylene is contacted with a mixed metal oxide catalyst of propylene oxide to form a first product stream 120 comprising acrolein.

The first product stream 120 enters the second stage reactor 102. Acrolein oxidation catalyst 125 and finishing catalyst 135 are disposed in second stage reactor 102 such that first product stream 120 contacts acrolein oxidation catalyst 125 before the gas stream contacts finishing catalyst 135. Within second stage reactor 102, the product formed when first product stream 120 contacts acrolein oxidation catalyst is equivalent to product stream a described above with respect to various embodiments. Exiting second stage reactor 102 is a product stream 150 comprising acrylic acid. The product stream 150 comprising the gaseous products of the product stream 120 that have been contacted with both the acrolein oxidation catalyst 125 and the finishing catalyst 135 is equivalent to the product stream B discussed in the various embodiments above.

Alternatively, the process may be carried out in a three-stage reactor system, such as the system schematically shown in FIG. 5.

In fig. 5, a three-stage reactor system 200 includes a first stage reactor 201, a second stage reactor 202, and a third stage reactor 203.

First stage reactor 201 contains propylene oxidation mixed metal oxide catalyst 215, second stage reactor 202 contains acrolein oxidation mixed metal oxide catalyst 225, and third stage reactor 203 contains polishing catalyst 235.

A gaseous feed stream 210 comprising propylene enters first stage reactor 201 where propylene is contacted with a mixed metal oxide catalyst of propylene oxide to form a first product stream 220 comprising acrolein.

The first product stream 220 enters the second stage reactor 202. First product stream 220 contacts acrolein oxidation catalyst 225 to selectively oxidize acrolein to acrylic acid. Second product stream 220 exits second stage reactor 202 and then enters third stage reactor 203, where second product stream 220 is contacted with finishing catalyst 235 to produce product stream 250.

In the process shown in fig. 5, product stream 230 corresponds to product stream a described in certain embodiments above, and product stream 250 corresponds to product stream B. Product stream 250 contains a lower amount of aldehyde by-product than product stream 230.

The following examples illustrate the invention but are not intended to limit the scope of the invention.

Examples

Preparation of fine catalyst for synthesizing 1 crystal MoVTeNb oxide

Containing Mo as the nominal composition_1.0V_0.285Te_0.21Nb_0.164Pd_0.01O_nThe finished catalyst of mixed metal oxide catalyst of (3) is produced in the following manner:

ammonium heptamolybdate tetrahydrate (35.7g from Fisher Scientific), ammonium metavanadate (6.74g from Sigma Aldrich) and telluric acid (9.74g from Sigma Aldrich) were added in succession to 200ml of Deionized (DI) water preheated to 70 ℃. The mixed salt solution was stirred at 70 ℃ for 20 minutes to ensure a clear solution was formed. Then, 5ml of concentrated nitric acid (70 wt% in water, from Sigma Aldrich) was added to the solution with stirring.

Separately, an aqueous solution containing ammonium niobium oxalate (15.24g from HC Stark, Goslar, Germany) and oxalic acid dihydrate (3.95g from Sigma Aldrich) in 180ml of deionized water was prepared at room temperature.

The Mo/V/Te solution was kept under stirring under heating. Then, the heating was stopped and the Nb containing solution was added to the Mo/V/Te solution. Gelation occurred immediately after mixing of the two solutions. The mixture was stirred for 5 minutes and slurried before transferring to a round bottom rotating flask.

The water in the slurry was removed by a rotary evaporator at 50 ℃ under a vacuum of 10 to 50mmHg (1.33 to 6.67 kPa). The solid material was further dried in a vacuum oven at room temperature overnight.

The dried solid material was placed in the middle of a quartz tube and quartz wool was inserted into both ends of the solid material bed. The tube is placed in the center of the furnace. The material was calcined in flowing air from room temperature to 275 ℃ at a heating rate of 10 ℃/min (80-100 standard cubic centimeters per minute, hereinafter SCCM) and held at 275 ℃ for 1 hour. The flowing gas is then switched to an inert gas such as argon or nitrogen (80-100 SCCM). The furnace temperature was raised from 275 ℃ to 600 ℃ at a rate of 2 ℃/min and held at 600 ℃ for two hours in an inert gas atmosphere. This gives Mo with the nominal composition_1.0V_0.285Te_0.21Nb_0.164Pd_0.01O_nThe MoVTeNb oxide of (1).

The crystallinity and crystalline phase of the MoVTeNb oxide powder were analyzed by X-ray powder diffraction using Rigaku D/MAX 2500 under nickel filtered copper ka radiation of 50kV/200 mA. The sample was scanned from 5 to 50 degrees 2 theta in 0.03 degree steps at 2 theta of 2 degrees per minute to acquire a signal. Using the reflection geometry, the sample was rotated at 20 RPM. The samples were dry powder pressed and flattened into a standard volume XRD sample holder.

The X-ray diffraction pattern of the movtenenb oxide is shown in fig. 1, fig. 1 showing the orthogonal phase as the predominant crystalline phase, with the major 2 θ peaks at 6.7 °, 7.8 °, 22.1 °, and 27.2 °.

The MoVTeNb oxide was crushed to < 10 mesh particles after calcination. The particles were then ground in a "cryogenic grinder," which is a model 6850 freezer/grinder from SPEX CertiPrep (quintucun, new jersey, usa). About 5 grams of the small particles were placed into a cylindrical plastic tube along with a steel cylinder. The ends of the tube are capped with steel. The entire instrument was immersed in liquid nitrogen and the steel cylinder was then shuttled back and forth within the tube by the action of the magnet. The samples were pre-cooled for 5 minutes before grinding for 3.5 minutes. After cooling for 2min, the sample was ground again for 3.5 min. The milled powder was removed from the tube and pressed/sieved into 14-20 mesh particles for performance evaluation in example 1 below.

Synthesis of 2 crystalline Mo₃VO_xPreparation of the catalyst

Crystalline Mo₃VO_xThe catalyst was prepared according to the procedure reported below: catal. Sci. Technol., 2016, 6, 617-629 and references cited in the article. Similar hydrothermal synthesis procedures were used to prepare Mo-V based oxide catalysts as disclosed in WO 2005/120702 a1 and U.S. patent No. 9,181,169B 2.

Vanadyl sulfate (7.0g VOSO)₄·nH₂O) and ammonium heptamolybdate (14.5g (NH)₄)6M_o7O₂₄) Are all dissolved in 200ml of high purity water. Once completely dissolved, the blue vanadate solution was poured into the colorless molybdate solution, resulting in a dark brown suspension.

After stirring for 10 minutes, concentrated sulfuric acid was added dropwise to adjust the pH to 2.2. The mixture was stirred at ambient for 2 hours and then split into 5 125ml Parr digestion reactors.

Each reactor was sealed and placed entirely in an oven at 175 ℃. After 18 hours at a temperature of 175 ℃, the oven was turned off and allowed to cool to < 100 ℃. The reactor was removed and cooled in water. When opened, the clear, slightly colored supernatant was decanted, and the dark solid was scraped off with fresh water and collected. All products were combined and washed on the filter with a large excess of fresh water.

The solid was dried at 90 ℃. The dried solid was crushed and then suspended in 325ml of 0.4M oxalic acid (16.5g oxalic acid/325 ml water) for 30 minutes. The extracted solid was then collected by filtration and washed with excess water, then dried at 90 ℃.

Approximately half of the dried powder was placed in a quartz boat and inserted into a quartz tube in a tube furnace. A nitrogen purge was performed for 10 minutes, and then the system was heated to 500 ℃ for several hours, held at that temperature for 2 hours, and then slowly cooled to ambient temperature while maintaining the nitrogen purge. After collection of the heat treated solid, a second batch was run with the remaining untreated sample.

The solids were combined into a single sample. The samples were press screened to 14-20 mesh granules in preparation for performance evaluation.

Samples Cu Ka radiation (wavelength) was used on a Bruker D8 diffractometer) And (5) operating. The sample was scanned from 5 to 50 degrees 2 theta. Using the reflection geometry, the sample was rotated at 20 RPM. The samples were dry powder pressed and flattened into a standard volume XRD sample holder.

Nominal composition Mo₃VO_xThe XRD pattern of the oxide is shown in fig. 2, which indicates that the oxide contains an orthorhombic phase.

Comparative example 1 Oxidation of stage 1 reactor effluent from the Oxidation of propylene to acrolein Using a commercial R2 catalyst alone

Oxidation of propylene to acrolein and acrylic acid in twoAnd (4) carrying out the stage. The oxidation of propylene is carried out in a tubular reactor to produce a gaseous mixture analogous to the first step in a two-step propylene oxidation process to produce acrylic acid. 15ml of a Mo and Bi based mixed metal oxide catalyst R1 (propylene oxidation catalyst) from Nippon Kayaku Co. (Tokyo, Japan) with 15ml of 1/8 "Denstone^TM57 beads (Saint-Gobain Norpro, Stow, OH) were mixed and then charged into a 2.54cm (1 ') Outside Diameter (OD) Stainless Steel (SS) first stage tubular reactor (0.834' ID). The reactor tube was heated to > 340 ℃ in a clamshell electric furnace. The feed to the first stage tubular reactor was a mixture of 24.0ml/min propylene, 211.6ml/min air, 34.0ml/min N2, and 1.44 g/hr deionized water. All gas flow rate values were carried out at standard temperature (0 ℃) and standard pressure (101.3 kPa). Water was injected by a syringe pump into the SS mixer vessel heated to 160-. Other raw material gases are controlled by a mass flow controller. The effluent from the first stage reactor (designated as R1-Exit) was fed directly to the second stage reactor via an external heat transfer line with the skin temperature controlled at 170-200 ℃.

The temperature of the first stage reactor was adjusted to achieve propylene conversion consistently in the range of 96.0-97.5% and oxygen conversion in the range of 66-69%. The conversion of propylene and oxygen was calculated using the following formula.

Propylene conversion (%) — (moles of propylene fed-moles of propylene in R1-EXit)/moles of propylene fed.

Oxygen conversion (%) — (moles of oxygen fed-moles of oxygen in R1-Exit)/moles of oxygen fed.

R1-Exit was used as feed to evaluate the performance of the second stage reactor for the oxidation of acrolein and acetaldehyde to the corresponding acids. A typical composition of R1-Exit is shown in Table 1, with a propylene conversion of 96.5% and O₂The conversion was 67.7%.

TABLE 1 typical concentrations of the major components in R1-Exit

15ml of a commercial Mo and V based R2 catalyst (acrolein oxidation catalyst) from Nippon Kayaku Co. (Tokyo, Japan) with 15ml of 1/8 "Denstone^TMAnd (4) mixing the beads. The mixture was charged to the feed side of a1 "OD and 0.834" ID U-shaped stainless steel tube. The other inner space of the U-shaped tube is filled with Denstone^TMBeads. The U-tube was placed in a fluidized sand bath furnace with the catalyst bed partially immersed in the sand bath. Air is used to fluidize the sand at a flow rate of 3.3-3.5 SCFM (standard cubic feet per minute). By maintaining a high air flow rate, the temperature difference in the bath is controlled to not exceed 3 ℃. The bath temperature is increased to achieve higher conversion of acrolein to acrylic acid and oxidation of other organic components (e.g., acetaldehyde in R1-Exit). The effluent from the second stage reactor was designated R2-Exit.

R1-Exit or R2-Exit were collected and analyzed separately. The effluent first flowed through Trap 1, which is a 100-and 500-ml stainless steel vessel, connected with 1/4 "copper coils to a recirculation cooler set at 0-1 ℃. The gas escaping from Trap 1 flows through the second Trap 2, is immersed in the water/ice and flows through the third and fourth Trap (Trap 3A and Trap 3B) and is immersed in the dry ice/isopropanol mixture. Trap 2 serves primarily as a protective trap to prevent large amounts of water or acrylic acid from entering the dry ice/isopropanol trap, as water/AA may freeze in the dry ice/isopropanol trap and cause a pressure increase. Trap collection times are typically 2-4 hours. Prior to sample collection, 6-12 grams of inhibitor solution was injected into Trap 2, Trap 3A and 3B to prevent polymer formation. In most cases, the trap 2 collects very little material. 0.2% by weight hydroquinone was used as inhibitor solution in isopropanol.

The waste gas of the dry ice/isopropanol catcher is passed through a thermal conductivity detector andGC on-line analysis of the mol-sieve/silica gel column. The main gas components in the tail gas usually include nitrogen, oxygen, unreacted propylene, monoCarbon oxide and carbon dioxide. The collected fluids from Trap 1 and Trap 2 (if any) were combined into one sample, labeled as the T-1 sample. The fluids collected from Trap 3A and Trap 3B were labeled as T-3A and T-3B samples, respectively. T-1, T-3A and T-3B samples were sent for off-line analysis by GC (DB-FFAP 123-3232E) equipped with a flame ionization detector and a capillary column. The amounts of main products such as acrylic acid, acrolein, acetaldehyde, acetone, propionic acid, acetic acid, etc. are obtained.

The yield of acrolein, acetaldehyde and acrylic acid and the balance of the carbonaceous mass after the second stage reactor were calculated using the following formula:

acrolein yield (%) - (moles of acrolein in R2-Exit)/moles of propylene fed x 100 acetaldehyde yield (%) - (moles of acetaldehyde in R2-Exit/1.5)/moles of propylene fed x 100

Yield (%) of acrylic acid (moles of acrylic acid in R2-Exit)/moles of propylene fed 100

Carbon balance (%) - (total amount of carbon from molecules in R2-Exit, including CO2, CO, propylene, formaldehyde, acetaldehyde, acrolein, acetic acid, propionic acid, acrylic acid)/(total amount of carbon from propylene in the feed) 100

The acrolein yield, acetaldehyde yield, and acrylic acid yield are listed in table 2 below. As the R2 reactor bath temperature increases, the acrolein and acetaldehyde yields decrease and the AA yields increase accordingly. However, even at 292 ℃, acrolein yield was 1.91%, acetaldehyde yield was 0.074%, and AA yield was as high as 86%.

Example 1 addition of MoVTeNb oxide finishing catalyst after commercial R2 catalyst bed in the oxidation of propylene to acrolein stage 1 reactor effluent

The test conditions remained the same as in "comparative example 1" except that 1.0 grams of 14-20 mesh MoVTeNb oxide particles (prepared in synthesis 1) and 9.0 grams of carborundum #12 particles (from Hengar co., Thorofare, NJ) were charged as diluents into the outlet arm of the "U-shaped" reactor tube, as shown in figure 3. The space above and below the catalyst bed was filled with Denstone^TM57 beads.

The yields of acrolein, acetaldehyde and acrylic acid are shown in Table 2. At a bath temperature of 277 ℃, acrolein yield dropped to 1.2% and acetaldehyde was below the detection limit (about 5ppm in the liquid sample). The acrolein yield is reduced to below 1% at bath temperature of 282 ℃, and the AA yield is 87%.

Comparative example 2 oxidation of the effluent from the stage 1 reactor for the oxidation of propylene to acrolein Mo after the bed of the commercial R2 catalyst₃VO_xAddition of oxide catalyst

The test conditions remained the same as in example 1 except that the MoVTeNb oxide layer was coated with 1.0 g of 14-20 mesh Mo₃VO_xOxide particles (prepared in synthesis 2) and 9.0 grams of carborundum #12 particles as a diluent.

The yields of acrolein, acetaldehyde and acrylic acid are listed in table 2. At the R2 bath temperature of 287 ℃, acrolein yield decreased to 1.05%, whereas acetaldehyde yield was 0.112%, and AA yield was only 85.2%.

TABLE 2 comparison of product yields at different bath temperatures in the second stage reactor

AA yield was adjusted to obtain a carbonaceous mass balance of approximately 99.5%.

It has been surprisingly found that the additional small amount of a MoVTeNb oxide finishing catalyst having an orthorhombic phase can significantly reduce the bath temperature required to reduce acrolein yield while increasing AA yield compared to the use of a commercial R2 catalyst alone. Lower bath temperatures can slow the deactivation of commercial R2 catalyst. In addition, reducing acetaldehyde below the detection limit (about 5ppm in the liquid sample) can mitigate downstream separation contamination by acetaldehyde.

Use of additional Mo compared to commercial R2 catalyst alone₃VO_xThe oxide (comparative example 2) reduces the bath temperature required to achieve lower acrolein yield. However, acetaldehyde yields are not preferably reduced and AA yields are slightly lower than with the commercial R2 catalyst alone.