CN104649894B - Method for preparing acrylic acid by selective oxidation of acrolein - Google Patents

Abstract

The invention relates to a method for preparing acrylic acid by selective oxidation of acrolein, which adopts a fixed bed reactor, wherein reaction raw materials enter the reactor after being preheated by a preheater at the temperature of more than 150 ℃, the salt bath temperature is 240-270 ℃, and the airspeed is 800-2300 h^‑1The feed composition is as follows: 8-16% by volume of acrolein, 11-21% by volume of water vapor, 9-22% by volume of oxygen and 60-74% by volume of nitrogen; the fixed bed reactor is filled with an oxidation catalyst, the catalyst contains molybdenum, vanadium, nickel, copper, strontium and tungsten elements, and the catalyst also contains magnesium aluminate lanthanum oxide. The active component molybdenum of the catalyst is not easy to lose, the active phase is not easy to generate phase transition, and the method can stably produce the acrylic acid for a long period.

Description

Method for preparing acrylic acid by selective oxidation of acrolein

technical field

The invention relates to a method for preparing acrylic acid by selective oxidation of acrolein.

Background technique

The industrial reaction device for the selective oxidation of acrolein to prepare acrylic acid is mainly composed of multiple reaction tubes. On the premise of ensuring that the catalyst is not sintered and has a long service life, the selectivity and the yield of the target product are maximized to save raw materials. If the raw materials are converted Even if the yields of acrolein and acrylic acid are increased by 0.1 to 0.5 percentage points, the amount of products obtained will increase by hundreds to thousands of tons, and the economic benefits are considerable.

The catalysts for the partial oxidation of propylene to acrolein and acrylic acid are mainly molybdenum-based multi-component catalysts. Since the reaction of selective oxidation of propylene to prepare acrolein and acrylic acid is a strong exothermic reaction, water vapor with high specific heat is introduced during the reaction to effectively remove the heat of reaction. It is easy to lose under the washing. Moreover, under high temperature conditions, part of the active component molybdenum in the catalyst is lost from the surface of the catalyst due to sublimation. The loss of molybdenum, the active component, reduces the activity, selectivity, strength and service life of the catalyst, and the deposition of molybdenum in the downstream of the reaction system blocks the pipeline and affects the long-term operation of the system.

In addition, even if the active components such as molybdenum in the catalyst can not be lost, the content of molybdenum and the like does not change much before and after the reaction, but the active phase is prone to phase transition after long-term operation. The main components in the catalyst include Fe ₂ (MoO ₄ ) ₃ , α-Bi ₂ (MoO ₄ ) ₃ , CoMoO ₄ and NiMoO ₄ , where α-Bi ₂ (MoO ₄ ) ₃ is the surface active center and acts as a selective oxidation ; Fe ₂ (MoO ₄ ) ₃ promotes redox; CoMoO ₄ and NiMoO ₄ act as structural stabilizers. However, the catalyst prepared by co-precipitation method has many components, complex process, poor catalyst stability, high initial activity, but rapid deactivation. There are many factors that lead to the deactivation and stability reduction of multi-component Mo-Bi-Co-Fe-O catalysts and Mo-VO catalysts, including the loss of sublimation of Mo components due to local abnormal high temperatures (hot spots) and Irreversible crystal phase change, etc. These factors can cause changes in catalyst characteristics, resulting in reduced catalyst activity and shortened catalyst life. By characterizing the deactivated catalyst, it was found that Fe ₂ (MoO ₄ ) ₃ was reduced to FeMoO ₄ , and α-Bi ₂ (MoO ₄ ) ₃ was transformed into γ-Bi ₂ MoO ₆ .

To solve the above problems, there are many patents involved. For example, in order to suppress the loss of molybdenum, CN1583261 discloses a composite metal for the selective oxidation reaction of a gas containing unsaturated aldehyde and a gas containing molecular oxygen in the gas phase. An oxide catalyst whose catalyst composition is: [Mo _a V _b Cu _c X _d ]Y _m [Sb _e Z ¹ _f Z ² _g ] _n O _x where Mo is molybdenum, V is vanadium, Cu is copper, and Sb is antimony , X is at least one element selected from tungsten and niobium, Y is at least one element selected from titanium, antimony, Z1 is at least _one element selected from iron and nickel, _Z2 is at least selected from silicon, aluminum , an element of alkali metal and alkaline earth metal, a, b, c, d, e, f, g and x represent the atomic ratio of the element, when a=12 is the base, b is a number from 1 to 6, c is a number from 0.5 to 4, d is a number from 0.05 to 4, e is a number from 0.1 to 30, f is a number from 0 to 25, g is a number from 0.01 to 20; A number required for the composite oxidation state of a metal element; the catalyst is composed of its element oxides or composite oxides.

In order to improve the stability of the catalyst, CN1130172 discloses a catalyst for acrylic acid, using ammonium metavanadate and copper nitrate respectively, and partially replacing ammonium metavanadate and/or copper nitrate with low-valent vanadium oxide and/or low-valent copper oxide Catalysts obtained as raw materials for metal vanadium and copper or catalysts obtained using low-valent antimony oxides and/or low-valent tin oxides in addition to the above-mentioned raw materials show an intensity-enhanced peak at d=4.00 (vanadium-molybdenum active compound) and a _{V2O5 -} specific peak of reduced intensity at d = 4.38_. Thus, the above-obtained catalyst has improved catalytic activity and can exhibit stable performance over a long period of time. Similar also has patent document 1: Japanese Patent Application Publication No. 2002-233757, Patent Document 2: Japanese Patent Application Publication No. 8-299797, Patent Document 3: Japanese Patent Application Publication No. 9-194213, Patent Document 4: Japanese Special Table Publication No. 2004-504288; CN102066000A.

In order to improve the activity, selectivity and catalyst life of the catalyst, CN200980112659.3 discloses a coated catalyst comprising the following components: (a) a carrier, (b) a second molybdenum oxide or a precursor compound that forms a molybdenum oxide One layer, (c) a second layer comprising a multimetal oxide comprising molybdenum and at least one other metal. Preferably, the molybdenum oxide of the first layer is MoO ₃ , and the multi-metal oxide of the second layer is a multi-metal oxide represented by general formula II: Mo ₁₂ Bi _a Cr _b X ¹ _c Fe _d X ² _e X ³ _f O _y . The catalyst is a coated catalyst including a carrier. The object of the invention is to suppress the deactivation of a coated catalyst for heterogeneously catalyzed partial gas-phase oxidation of acrolein to acrylic acid, with improved deactivation performance. This invention does not clearly record the reaction performance evaluation data of the catalyst used to catalyze the oxidation of propylene to acrolein and acrylic acid, such as conversion rate, selectivity, yield, etc. CN87103192 discloses a method for producing a composite oxide catalyst, wherein the production method of the Mo-Bi composite oxide catalyst represented by the following chemical formula includes mixing related element source compounds into an aqueous system to form a composite and subjecting the composite to heat treatment, Using as Bi source a compound of (a) Bi and Na or (b) Bi, Na and X or (c) bismuth carbonate complexes of Bi and X containing at least part of the desired Na and/or X Wherein: X represents Mg, Ca, Zn, Ce and/or Sm; Y represents K, Rb, Cs and/or Tl; Z represents B, P, As and/or W; aK represents respective atomic ratio, when a= At 12, b=0.5-7, c=0-10, d=0-10, c+d=1-10, e=0.05-3, f=0.01-1, g=0-1, h=0.04 -0.4, i=0-3, j=0-48, k is a number satisfying the oxidation state of other elements. Solve the problem that Bi can be uniformly dispersed in the composite oxide catalyst. The catalyst contains α-Bi ₂ (MoO ₄ ) ₃ , MoO ₃ Fe ₂ (MoO ₄ ) ₃ , β-CoMoO ₄ , y-Bi ₂ MoO ₆ and γ-Bi ₂ MoO ₆ . CN101690900A discloses a preparation method for preparing acrolein and acrylic acid catalyst, the catalyst is composed of active component carrier and inert alumina carrier; the main constituent elements of the active component are selected from Mo, Bi, Co and/or Ni, and Fe, It also contains K, Na, Rb, Cs, Mg, Ca, Zn, B, P, W and other trace elements; wherein the active components are represented by the following expression: Mo _a Bi _b Co _c Ni _d Fe _e X _f Y _g In Z _h O _i formula, X represents at least one of K, Na, Rb and Cs, Y represents at least one selected from B, P and W, and Z represents at least one selected from Mg, Ca, Zn . The proportion of active components loaded on the carrier accounts for 5-70% of the total weight of the catalyst; the active components are unevenly distributed, and aluminates of divalent metals such as CoMoO ₄ and NiMoO ₄ are located in the core of the active components of the catalyst; Fe ₂ (MoO ₄ ) ₃ and free MoO ₃ are attached to the outer layer of the inner core; while the outermost layer of the active component is bismuth molybdate, forming a state of core-shell layered distribution. The divalent molybdate in the active component mainly has a β-phase structure, and the content of the α-phase structure in the active component is very low or does not exist. The catalyst has high activity and high stability. CN1280036 A catalyst for producing unsaturated aldehydes and unsaturated carboxylic acids, the production is by making at least one compound selected from propylene, isobutylene, tert-butanol and methyl tert-butyl ether with oxygen molecules or oxygen-containing molecules Gas is carried out vapor phase oxidation and realizes, it is characterized in that this catalyst is a kind of composite oxide composition, contains: (A) the composite oxide containing molybdenum, bismuth and iron as main component, itself is known for A catalyst for the vapor-phase catalytic oxidation reaction, and (B) a composite oxide containing cerium and zirconium as main components. The catalyst has a long catalytic life and enables long-term stable operation. Component (B) is a composite oxide represented by the following general formula (2): Ce _p Zr _q F _r O _y . Highly dispersed zirconia inhibits the aggregation of cerium oxide to maintain the latter's function of promoting the absorption and release of oxygen significantly during the reaction process, thereby accelerating the oxidation reaction of isobutylene, thus improving the catalytic activity. In addition, the irreversible decrease in activity of the composite oxide of component (A) caused by excessive reduction over time (ie, the stability of the composite oxide is improved) is also suppressed, thereby prolonging the catalytic life. This enhanced catalytic activity and prolonged catalytic life suppresses the reaction temperature increase with time, thereby weakening the sublimation of molybdenum at the superheated sites. The catalyst is used for the oxidation reaction of isobutene.

CN102489309A discloses a catalyst preparation and regeneration method for producing acrolein. The catalyst is a composite oxide with the following atomic ratio: Mo: Bi: Co: Ni: Fe=10-14: 1.2-2.0: 4.8-5.6: 2-3: 1-2; the catalyst has a relatively concentrated pore distribution , moderate total pore volume, in which mesopores around 5-10nm account for more than 70% of the total pore distribution, forming a short and thick pore structure. This feature endows the catalyst with strong anti-coking ability, and the surface of the catalyst is not easy to sinter. Can prolong the service life of the catalyst. However, through the regeneration method provided by the present invention, the deactivated catalyst is calcined for 1-3 days under an oxidative atmosphere, and the catalyst activity is equivalent to that of a fresh catalyst. CN87103192 The method for producing Mo-Bi-Na composite oxide catalyst products, the method includes mixing related element source compounds to form a composite, and then performing heat treatment, using bismuth subcarbonate with at least part of the required Na in solid solution as a Bi source compound. The activity of the catalyst is greatly improved by the introduction of Bi and Na into the catalyst formed by specific water-insoluble compounds.

CN1109803 relates to multi-metal oxide compositions, which have a two-phase structure and contain molybdenum, hydrogen, one or more elements phosphorus, arsenic, boron, germanium and silicon; Aspects of use, improve activity and selectivity. CN1109802 discloses a multi-metal oxide composition, which has a two-phase structure and contains molybdenum, hydrogen, one or more elements phosphorus, arsenic, boron, germanium and silicon, and copper to improve the activity and selectivity of acrylic acid. CN1298861A adopts the composite oxide of adding magnesium, aluminum and silicon. CN1321110A respectively uses antimony oxide and antimony acetate as the antimony source of the active composite metal oxide. In order to solve the problem of good mechanical strength and high activity of the catalyst under the condition of high load. CN200410048021.7 discloses a composite metal oxide catalyst, the catalyst is composed of ① molybdenum, vanadium, copper main active components and ② essential stable components consisting of at least antimony and titanium and ③ nickel, iron, silicon, aluminum, Composite oxides composed of alkali metals and alkaline earth metals. Among them, ② and ③ are composite oxides that can be calcined in the range of 120°C to 900°C. The catalyst exhibits high activity and long-term stability with good selectivity. CN1121441 discloses a catalyst for the production of acrylic acid by the oxidation reaction of acrolein or acrolein-containing gas with a molecular oxygen-containing gas in the vapor phase, the catalyst comprising (A) a composite oxide containing molybdenum and vanadium As essential components, and suitable for the production of acrylic acid by vapor-phase catalytic oxidation of acrolein, and (B) a solid acid having an acid strength (Ho) of not more than -11.93 (Ho≤-11.93). The invention combines molybdenum vanadium type composite oxide with a solid acid whose acid strength does not exceed -11.93 to improve the low temperature and high activity of the catalyst. CN200510059468.9 discloses a catalyst for the production of acrylic acid, which is characterized in that in the catalyst for the production of acrylic acid in which oxides and/or composite oxides composed of metal elements represented by the following general formula MoaVbWcCudOx (1) are essential catalyst components, it is necessary to control Tungsten is biased on the surface side of the catalyst and/or copper is biased on the core side of the catalyst to enhance catalyst activity. A bias of tungsten to the surface side of the catalyst, and/or a bias of copper to the core side of the catalyst is difficult to accurately control. CN102039143A discloses a method for preparing a catalyst for the oxidation of acrolein to acrylic acid, a) the method for preparing a composite oxide coating: dispersing water-soluble metal salts containing Mo, V, W, Cu, and Sb at 30-100°C In the water/organic phase mixed system; keep the weight ratio of organic solvent and water at 5-50%; react to generate composite oxide precursor slurry; then distill, dry, and roast to obtain catalyst active components; b) the above activity The main constituent elements of the component are selected from one or more of Mo, V, Cu, W, and Sb; the active component is represented by the following formula: Mo _a V _b Cu _c W _d Sb _e O _f , the catalyst adopts Prepared with a mixed system of water and lower alcohols, the catalyst has a higher specific surface area and a special microstructure, has a higher specific surface and is not easy to fall off, and the loading capacity can reach 50% or more, which solves the short service life of the coated catalyst The problem.

CN1647854 discloses a catalyst for the selective oxidation of methacrolein to synthesize methacrylic acid. The general formula of the catalyst is: x(Mo ₁₂ P _a K _b Sb _c Cu _d As _e A _f D _g Q _h O _i Mo _j ) /yZ, Z is the carrier diluting heat conducting agent; Mo, P, K, Sb, Cu and As are respectively molybdenum, phosphorus, potassium, antimony, copper and arsenic; A represents tungsten W, vanadium V, niobium Nb, iron Fe and lead At least one element in Pb; D represents at least one element in boron B, gallium Ga, indium In, germanium Ge and silicon Si; Q represents at least one element in rubidium Rb, cesium Cs and thallium Tl. Adding Sb, Cu and As to improve the activity and selectivity of the catalyst; on the other hand, by adding MoO ₃ and carrier thermal diluent to improve the thermal stability, thermal conductivity and mechanical strength of the catalyst, effectively inhibiting the active component heteropolyacid Decomposition of salt and reduction of catalyst bed hot spot temperature, avoiding the loss of Mo and As, prolonging the service life of the catalyst.

CN1109800 discloses a multi-metal oxide material: in the formula, A is Mo ₁₂ V _a X _b ¹ X _c ² X _d ³ X _e ⁴ X _f ⁵ X _g ⁶ O _x (coexisting phase), and its part B contains at least A crystallite with the X-ray diffraction pattern of the following copper molybdate (the original data on the X-ray diffraction fingerprint are given in parentheses): Cu ₃ (MoO ₄ ) ₂ (OH) ₂ (Molybdenite, JCPDS-ICDD Index Cards 36-405 of the Index (1991), Cu ₄ Mo ₆ O ₂₀ (A. Moini et al., Inorg. Chem. 25(21) (1986), 3782-3785), Cu ₄ Mo ₅ O ₁₇ (JCPDS - Index Cards 39-181 of the ICDD Index (1991), etc. CN1462211 relates to a method for preparing heterogeneous multi-metal oxide materials containing Mo, V, Cu and optionally other elements. According to the invention, at least one phase is independently preformed and dispersed in the plastically deformable precursor material of the other phase. The mixture is then dried and calcined. Multimetal oxide materials are suitable as active materials for catalysts used in the gas-phase catalytic oxidation of organic compounds, in particular in the oxidation of acrolein to acrylic acid. [A]p[B]q[C]r(I), Phases A, B and C in the multimetal oxide composition may be amorphous and/or crystalline. It is advantageous for phase B to consist of crystallites of oxometallates, or to comprise a crystal structure class of oxometallate microcrystalline copper molybdates having an X-ray diffraction pattern and further at least one of the following crystal structure types of copper molybdates α-CuMo ₄ [JCPDS-ICDD Card Index Note Card 22-242, (1991)], Cu ₆ Mo ₅ O ₁₈ [JCPCS-ICDD Card Index Note Card 40-865, (1991)], Cu _4-x Mo ₃ O ₁₂ where x=0-0.25 [JCPCS-ICDD Card Index Record Cards 24-56 and 26-547, (1991)], et al. The catalyst is to increase selectivity.

CN1295499 discloses a multi-metal oxide material [A]p[B]q[C]r(I) of formula (I), which contains molybdenum, vanadium, copper and antimony and one or more specific other metals and has Multi-component structured multimetal oxide materials as catalysts for the preparation of acrylic acid by gas-phase catalytic oxidation of acrolein. In the formula, A is Mo ₁₂ V _a X ¹ bX ² _c X ³ _d X ⁴ _e X ⁵ _f X ⁶ _g O _x , B is X ¹ ₇ Cu _h H _i O _y , C is X ₁ ⁸ Sb _j H _k O _z , X ₁ is W, Nb, Ta, Cr and/or Ce. The cocatalyst phase B consists of or contains these copper molybdate crystallites: α-CuMoO ₄ [reference diffractogram in card 22-242 of JCPDS-ICDD retrieval 1991], Cu ₆ Mo ₅ O ₁₈ [reference diffraction pattern in card 40-865 of JCPDS-ICDD search 1991], Cu _4-x Mo ₃ O ₁₂ where x is 0-0.25 [card 24-56 and 26 of JCPDS-ICDD search 1991 - Reference diffractogram in 547], et al. Region C may have copper antimonate Cu ₉ Sb ₄ O ₁₉ crystallites or Cu ₄ SbO _4.5 crystallites. CN1093950 discloses a composition of various metal oxides, including Mo, V, W, Cu, Ni in oxidized form as basic components, provided that the following ratio exists between the elemental components: Mo:V=12 :1 to 2:1, Mo:W=60:1 to 3:1, Mo:Cu=24:1 to 2:1, Cu:Ni=5:1 to 1:3. X1 is _one or more alkali metals _; X2 is one or more alkaline earth metals; _X3 is Cr, Mn, Ce and/or Nb; _X4 is Sb and/or Bi _; X5 is Si, Al , Ti and/or Zr. CN1387945 relates to containing Cu, Mo and at least one is selected from element W, V, Nb and Ta in the oxo metal compound of HT copper molybdate structure type, its preparation method, and their preparation in containing molybdenum, vanadium, copper And the application in composite metal oxide materials with multi-phase structure containing one or more elements of tungsten, niobium, tantalum, chromium and cerium. CN1394812 is used in the multimetal oxide used in the catalyst of the catalytic gas phase oxidation reaction of organic compound, said multimetal oxide contains Mo, V and element W, Nb, Ti, Zr, Hf, Ta, Cr, Si and At least one of Ge, and has a special three-dimensional atomic arrangement. CN1500770 Containing molybdenum, vanadium, copper and containing one or more elements of tungsten, niobium, tantalum, chromium and cerium, the composite metal oxide material of multi-phase structure, which is used in the production of acrylic acid by gas-phase catalytic oxidation of acrolein Applications, and oxometallates of the HT copper molybdate structure type containing Cu, Mo and at least one element selected from the elements W, V, Nb and Ta.

In addition, under high temperature conditions, part of the active component molybdenum in the catalyst is lost from the surface of the catalyst due to sublimation. The scouring of the mixed flow of acrolein, air (oxygen), nitrogen and water vapor will also cause the loss of active components in the catalyst. In order to suppress the activity decay caused by the loss of molybdenum sublimation, CN1121504 can suppress the dissipation and excessive reduction of molybdenum components by doping copper components and zirconium and/or titanium and/or cerium with specific particle size and specific surface area. The catalyst includes oxides or composite oxides composed of metal elements represented by the following formula (I) MO _a V _b W _c Cu _d X _e Y _f (I). CN1445020 adds a small amount of tellurium to stabilize the crystal structure of free molybdenum trioxide and copper molybdate, and suppresses the sublimation loss and excessive reduction of molybdenum; CN1583261 uses molybdenum, vanadium, copper, tungsten and/or niobium as main components, Composite oxides composed of other elements or mixtures of oxides constitute catalysts to suppress the loss of molybdenum.

Therefore, it is necessary to provide a catalyst for the selective oxidation of propylene to prepare acrolein and acrylic acid, and the oxidation reaction of acrolein can be carried out under low temperature and high load conditions. The temperature distribution of the reactor is more reasonable, the active components such as molybdenum are not easily lost, and the active phase is not easy to undergo phase transition, and the selectivity and yield of the target product are high.

For the selective oxidation of acrolein, it is first necessary to select an oxidation catalyst with excellent performance, and secondly to carry out the reaction under mild operating conditions to meet the industrial requirements of high space velocity and high selectivity. Therefore, it is necessary to develop a process for the selective oxidation of acrolein with moderate reaction conditions, improve the selectivity and yield of the target product as much as possible, and operate stably for a long period to obtain greater economic benefits.

Contents of the invention

The purpose of the present invention is to provide a method for the selective oxidation of acrolein to produce acrylic acid. The reaction is carried out under low temperature and high load conditions, and the selectivity and yield of the target product are improved as much as possible, and the long-term stable operation is used to obtain greater economic benefits.

A method for the selective oxidation of acrolein to produce acrylic acid. The process conditions for the oxidation reaction are not particularly limited. For example, the following process conditions can be used: the reaction raw materials, acrolein, water, and oxygen, are preheated by a preheater above 150°C and then enter the reactor. , salt bath heating, salt bath temperature 240-270°C, preferably 245-265°C; space velocity 800-2300h ^-1 , preferably 900-1800h ^-1 , feed composition: acrolein 8-16% by volume, water vapor 11-1 21%, oxygen 9-22% by volume, nitrogen 60-74% by volume; the fixed-bed reactor is equipped with an oxidation catalyst, the catalyst contains molybdenum, vanadium, nickel, copper, strontium and tungsten elements, and the main composition is the following general formula (I) Said that the catalyst also contains magnesium lanthanum aluminate oxide (LaMgAl ₁₁ O ₁₉ ), molybdenum and vanadium-containing (I) and magnesium lanthanum aluminate oxide are mixed at 91-98% and 0.6-9% by mass percentage, kneaded, After forming, drying and roasting, the finished catalyst is obtained.

Mo _a′ V _b′ Ni _c′ Cu _d′ Sr _f W _h M _i N _{j Sik} O _y (Ⅰ), wherein: Mo is molybdenum, V is alum, Ni is nickel, Cu is copper, Sr is strontium, W is tungsten, Si is silicon, silicon is a carrier added to the catalyst, M is at least one element selected from calcium, zinc, and zirconium; N is at least one element selected from boron, rubidium, and lanthanum; O is oxygen ; a', b', c', d', f, h, i, j, k respectively represent the atomic ratio of each element, wherein a' is a number of 12-14, b' is a number of 0.2-5, c' is a number from 0.5-4, d' is a number from 1-5, f is a number from 0.1-2.5, h is a number from 0.05-3, i is a number from 0.05-3, j is a number from 0.05- A number of 3, k is a number of 0.2-30, and y is a value determined by the oxygen of each oxide.

The invention adopts a two-step oxidation method of propylene to prepare acrolein acrylic acid, one-stage selective oxidation of propylene to prepare acrolein, a molybdenum-bismuth catalyst is used as a catalyst, and two-stage selective oxidation of acrolein to prepare acrylic acid uses the catalyst of the present invention. Both the first and second stage reactors of the present invention are equipped with thermocouples inside to measure the temperature of each part of the reactor. In order to prevent the deep oxidation of acrolein on the lower layer catalyst from affecting the yield and causing the catalyst to coke, the present invention controls the oxidation of acrolein ( Stage 2) The temperature of the lower layer of the catalyst is lower than the temperature of the upper layer of the catalyst, and the temperature of the catalyst bed is adjusted by controlling the temperature of the salt bath. Long-term stable operation. The temperature of the lower layer of the acrolein oxidation (second stage) catalyst of the present invention is at least 3°C lower than the temperature of the upper layer of the catalyst.

The reaction temperature of acrolein selective oxidation to acrylic acid is basically above 260°C. Under such high temperature reaction conditions for a long period of time, the active component molybdenum in the catalyst is easy to lose due to sublimation. N in the catalyst of the present invention is preferably lanthanum, and lanthanum and molybdenum, nickel, copper, antimony, etc. can form a stable crystal phase structure, such as Cu ₂ La, LaNi ₅ , Cu ₂ La, Cu ₅ La, etc., which is beneficial to inhibit Part of the active component molybdenum is lost from the surface of the catalyst due to sublimation, and the content of the active component molybdenum remains basically unchanged before and after the catalyst reacts, which delays the rate of activity deterioration and has good catalyst stability. The ratio of lanthanum to molybdenum and vanadium is appropriate. In the general formula (I), N is lanthanum, and i is a number from 0.1 to 3.5. Too much lanthanum will compete with vanadium and nickel for molybdenum. Lanthanum nitrate is preferred as the lanthanum source in the present invention. The main composition is represented by the general formula (II): Mo _a' V _b' Ni _c' Cu _d' W _h M _i La _{j Sik} O _y (II).

The magnesium lanthanum aluminate oxide of the present invention is prepared according to a conventional co-precipitation method. For example, the following method is used to prepare: mix magnesium nitrate, lanthanum nitrate and aluminum hydroxide according to the stoichiometric ratio of LaMgAl ₁₁ O ₁₉ , add deionized water and stir evenly, and then spray dry, and the obtained powder is dried at 160°C Calcining at 1000-1500°C for 3-12 hours, and then obtaining lanthanum magnesium aluminate LaMgAl ₁₁ O ₁₉ with a particle size below 20 μm by crushing or ball milling.

The preparation method of the catalyst of the present invention comprises preparing catalyst (I) and magnesium lanthanum aluminate oxide by co-precipitation method, and mixing catalyst (I) and magnesium lanthanum aluminate oxide according to 91-98% and 0.6-9% mass percentage After kneading, molding, drying and roasting, the finished catalyst is obtained.

More preferably, the catalyst contains 92-97% of (I) and 2-8% of magnesium lanthanum aluminate oxide.

Under the condition of oxygen, the active components such as molybdenum of the catalyst are not only easy to lose under high temperature conditions, but also the active phase is prone to phase transition, which leads to a significant decrease in activity selectivity. Such as the active phase VMo ₃ O ₁₁ into MoO ₃ , CoMoO ₄ into Co ₃ O ₄ , CuMoO ₄ into MoO ₃ and so on.

Even if the molybdenum and other active components in the catalyst can be kept without loss, the content of molybdenum and the like does not change much before and after the reaction, but the active phase is prone to phase transition after long-term operation. In the invention, the magnesium lanthanum aluminate oxide is added to the catalyst, so that the active phase of the catalyst is more stable, and the phase transition is not easy to occur so as to improve the activity and selectivity of the catalyst.

The composite multi-metal oxide catalyst (I) of the present invention can be prepared by using the usual preparation method, such as the following steps can be used to prepare: the compound containing Mo, V, Ni, Cu, Sr, W and M _i N _j is dissolved And mix evenly, form a slurry after co-precipitation, add one of silicon dioxide, silicon carbide, etc., dry, shape, and roast to obtain the catalyst (I).

Both the catalyst (I) and the finished catalyst of the present invention need to be calcined at 300-550° C. for 3-10 hours. Compared with the catalysts not calcined separately, multiple calcining can improve the activity and stability of the catalyst. It can be open roasting or closed roasting, and the roasting atmosphere can be helium, nitrogen, argon and other inert gases. As compounds of the constituent elements of the catalyst of the present invention, nitrates, ammonium salts, sulfates, oxides, hydroxides, chlorides, acetates and the like of each element can be used. Such as ammonium molybdate, nickel nitrate, strontium nitrate, ammonium paratungstate, calcium nitrate, lanthanum nitrate, zirconium nitrate, basic copper carbonate, copper nitrate, boric acid, titanium oxide, rubidium nitrate, zirconium oxide, etc.

After the catalyst slurry of the present invention is dried, it is usually preferably processed into a spherical shape, a hollow spherical shape, an elliptical shape, a cylindrical shape, a hollow cylinder, etc., preferably a hollow cylinder or a spherical shape, by extrusion molding, granulation molding, tablet molding and other molding methods.

In order to improve the strength and pulverization degree of the catalyst in the present invention, one or more of glass fiber, graphite, ceramics or various whiskers can be added to the catalyst (I).

The catalyst of the present invention can be used directly or supported on an inert carrier. The inert carrier involved may be one or a mixture of alumina, silicon dioxide, silicon carbide, etc.

Catalyst evaluation performance indicators are defined as follows:

detailed description

The method for preparing acrylic acid by the selective oxidation of acrolein is illustrated below with specific examples, but the scope of the present invention is not limited to these examples. The analysis method of product composition adopts the common method in this field.

Example 1

Under stirring conditions, take 202.7 grams of ammonium molybdate and 21.1 grams of ammonium metavanadate, and dissolve them in 500ml of pure water (water temperature above 65°C) to obtain a slurry (1), then take 4.3 grams of ammonium paratungstate, 49.6 grams of copper nitrate, and 50.1 grams of nitric acid Dissolve nickel, 25.6 grams of zinc nitrate, 2.1 grams of strontium nitrate, and 56 grams of lanthanum nitrate in 1000 ml of pure water (water temperature above 65°C), stir and mix well to obtain slurry (2). Then, mix the slurry (1) with the slurry (2) to obtain the active component slurry (a), add 22.1 grams of silicon dioxide to the active component slurry (a), stir vigorously at 85°C for co-precipitation reaction, and then heat and dry. Heat treatment at 160°C for 3 hours in nitrogen, calcined at 500°C for 4 hours, crush, grind, and sieve to obtain catalyst (I) powder with a diameter of less than 40 μm. The main composition is: Mo ₁₄ V _2.2 Ni _2.1 Cu _2.6 Sr _0.1 W _0.2 Zn _1.0 La _2.1 Si _4.5 O _y (Ⅰ).

Mix magnesium nitrate, lanthanum nitrate and aluminum hydroxide according to the stoichiometric ratio of LaMgAl ₁₁ O ₁₉ , add deionized water and stir evenly, then spray dry, the obtained powder is dried at 160°C and then calcined at 1100°C for 10 hours, then Lanthanum magnesium aluminate LaMgAl ₁₁ O ₁₉ with particle size below 20 μm is obtained by ball milling or other methods.

Take 95 parts of catalyst (Ⅰ), 5 parts of magnesium lanthanum aluminate oxide, add deionized water and knead in a kneader, extrude into hollow columnar particles of φ4.5×5mm, dry at 120°C, and dry at 450°C Catalyst 1 was obtained by calcining for 6.5 hours.

Comparative example 1

Comparative catalyst 1 was prepared according to the main composition ratio of Example 1, but magnesium lanthanum aluminate was not added to the catalyst in the form of solid solution oxide, but was prepared by co-precipitation method, and the reaction conditions were the same as the evaluation conditions of catalyst 1. The main composition of contrast catalyst 1 is:

Mo ₁₄ V _2.2 Ni _2.1 Cu _2.6 Sr _0.1 W _0.2 Zn _1.0 La _2.4 Si _4.5 Mg _0.3 Al _3.3 O _y

oxidation reaction

The internal diameter of the fixed-bed single-tube reactor is 25mm, and a thermocouple is installed inside. The reactor bed is filled with 45ml of the above-mentioned catalyst or the catalyst of the comparative example along the feeding direction, and the temperature of the salt bath is 245°C. A mixed gas of 9% by volume of acrolein, 16% by volume of oxygen, 16% by volume of water vapor, and 59% by volume of nitrogen enters from the inlet of the reaction tube at a space velocity of 1600h ⁻¹ . The catalyst of the present invention was reacted at a low temperature of 245°C for 24 hours. The hot spot temperatures of the catalyst beds in Example 1 and Comparative Example 1 were 269°C and 271°C respectively, the conversion rates of acrolein were 99.3% and 98.8%, and the selectivity of acrylic acid was 90.5% and 88.3%, acrylic acid yields 89.3% and 86.2%. Example 1 After 2000 hours of reaction, the local hot spot temperature of the bed was 270°C, the conversion rate of acrolein was 99.1%, the selectivity of acrylic acid was 90.5%, and the yield of acrylic acid was 89.2%. The molybdenum and other active components of the catalyst are not easy to lose, the active phase is not easy to undergo phase transition, the structure of the active phase of the catalyst is stable, the selectivity and yield of the target product are high, and the catalyst performance is stable. The comparative example has poor catalyst selectivity and low yields of acrolein and acrylic acid.

Example 2

Preparation of Catalyst 2

The preparation steps and main raw materials are the same as those of catalyst 1 in Example 1, and the catalyst (I) is obtained by calcining at 500°C for 4.5 hours. The main composition is: Mo ₁₃ V _4.8 Ni _3.8 Cu _2.2 Sr _0.5 W ₃ Ca _0..3 Rb _0.1 Si _2.3 O _y (Ⅰ). Take 98 parts of catalyst (Ⅰ), 2 parts of magnesium lanthanum aluminate oxide, add deionized water and knead in a kneader, extrude into hollow columnar particles of φ4.5×5mm, dry at 120°C, and dry at 500°C Catalyst 2 was obtained by calcining for 4.5 hours.

The internal diameter of the fixed-bed single-tube reactor is 25 mm, and a thermocouple is installed inside. 50 ml of the above-mentioned catalysts are loaded into the reactor bed along the feeding direction, and the temperature of the salt bath is 250 ° C. A mixed gas of 9% by volume of acrolein, 12% by volume of oxygen, 16% by volume of water vapor, and 63% by volume of nitrogen enters from the entrance of the reaction tube at a space velocity of 1350h ^-1 . After 24 hours of reaction, the hot spot temperature of the catalyst bed was 274°C, the conversion rate of acrolein was 99.2%, the selectivity of acrylic acid was 90.3%, and the yield of acrylic acid was 89.0%.

Example 3

The preparation steps and main raw materials are the same as those of catalyst 1 in Example 1, and the catalyst (I) is obtained by roasting at 400°C for 6 hours. The main composition is: Mo ₁₄ V _2.8 Ni ₄ Cu _4.8 Sr ₂ W ₁ Zr _2.5 B _0.1 La _1.1 Si _3.7 O _y (Ⅰ). Take 93 parts of catalyst (Ⅰ), 7 parts of magnesium lanthanum aluminate oxide, add deionized water and knead in a kneader, extrude into hollow columnar particles of φ4.5×5mm, dry at 120°C, and dry at 550°C Calcined for 4 hours to obtain catalyst 3.

The internal diameter of the fixed-bed single-tube reactor is 25mm, and a thermocouple is installed inside. The reactor bed is filled with 45ml of the above-mentioned catalyst along the feeding direction, and the temperature of the salt bath is 260°C. A mixed gas of 11% by volume of acrolein, 15% by volume of oxygen, 16% by volume of water vapor, and 58% by volume of nitrogen enters from the inlet of the reaction tube at a space velocity of 2000h ⁻¹ . After 24 hours of reaction, the hot spot temperature of the catalyst bed was 283°C, the conversion rate of acrolein was 99.4%, the selectivity of acrylic acid was 90.4%, and the yield of acrylic acid was 89.4%. After 2000 hours of reaction, the local hot spot temperature of the bed was 281°C, the conversion rate of acrolein was 99.3%, the selectivity of acrylic acid was 90.1%, and the yield of acrylic acid was 89.2%. The molybdenum and other active components of the catalyst are not easily lost, the active phase is not easy to undergo phase transition, the selectivity and yield of the target product are high, and the catalyst performance is stable.

Example 4

The preparation steps and main raw materials are the same as those of Catalyst 1 in Example 1, and the catalyst (I) is obtained by calcining at 480°C for 5 hours. The main composition is: Mo ₁₃ V _3.8 Ni _2.5 Cu ₃ Sr ₁ W ₂ Zr _1.1 Rb _0.1 La _0.5 Si _1.4 O _y (Ⅰ). Take 91 parts of catalyst (Ⅰ), 9 parts of magnesium lanthanum aluminate oxide, add deionized water and knead in a kneader, extrude into hollow columnar particles of φ4.5×5mm, dry at 120°C, and dry at 500°C Calcined for 5 hours to obtain catalyst 4.

The internal diameter of the fixed-bed single-tube reactor is 25mm, and a thermocouple is installed inside. The reactor bed is filled with 50ml of the above-mentioned catalyst along the feeding direction, and the temperature of the salt bath is 255°C. A mixed gas of 10% by volume of acrolein, 14% by volume of oxygen, 17% by volume of water vapor and 59% by volume of nitrogen enters from the inlet of the reaction tube at a space velocity of 1850h ^-1 . After 24 hours of reaction, the hot spot temperature of the catalyst bed was 280°C, the conversion rate of acrolein was 99.1%, the selectivity of acrylic acid was 90.2%, and the yield of acrylic acid was 89.2%. After 2000 hours of reaction, the local hot spot temperature of the bed was 279°C, the conversion rate of acrolein was 99.0%, the selectivity of acrylic acid was 90.1%, and the yield of acrylic acid was 89.0%. The molybdenum and other active components of the catalyst are not easily lost, the active phase is not easy to undergo phase transition, the selectivity and yield of the target product are high, and the catalyst performance is stable.

Claims (7)

1. A method for preparing acrylic acid by selective oxidation of acrolein, which is characterized in that the following process conditions are adopted: the reaction raw materials acrolein, water, and oxygen enter the reactor after being preheated by a preheater above 150°C, and the temperature of the salt bath is 240-270°C ℃, space velocity 800-2300h ^-1 , feed composition: acrolein 8-16% by volume, water vapor 11-21% by volume, oxygen 9-22% by volume, nitrogen 60-74% by volume; the fixed-bed reactor is equipped with Oxidation catalyst, the catalyst contains molybdenum, vanadium, nickel, copper, strontium and tungsten elements, and its main composition is the following general formula: Mo _a′ V _b′ Ni _c′ Cu _d′ Sr _f W _h M _i N _j Si _k O _y (Ⅰ ) means that the catalyst also contains magnesium lanthanum aluminate LaMgAl ₁₁ O ₁₉ , molybdenum and vanadium-containing (I) and magnesium lanthanum aluminate are mixed according to 91-98% and 2-9% by mass, and then kneaded, shaped, dried and roasted Finally, the finished catalyst is obtained; wherein: silicon is the carrier added in the catalyst, M is at least one element selected from calcium, zinc, and zirconium; N is selected from at least one element in boron, rubidium, and lanthanum; O is oxygen; a', b', c', d', f, h, i, j, k respectively represent the atomic ratio of each element, a' is a number of 12-14, b' is a number of 0.2-5, c' is a number from 0.5-4, d' is a number from 1-5, f is a number from 0.1-2.5, h is a number from 0.05-3, i is a number from 0.05-3, j is a number from 0.05-3 A number, k is a number from 0.2-30, and y is a value determined by the oxygen of each oxide. 2. The method according to claim 1, characterized in that the temperature of the salt bath is 245-265°C; the space velocity is 900-1800h ^-1 . 3. The method according to claim 2, characterized in that the temperature of the lower layer of the acrolein oxidation catalyst bed is lower than the temperature of the upper layer of the catalyst bed. 4. The method according to claim 1, characterized in that the preparation method of the catalyst used comprises preparing catalyst (I), magnesium lanthanum aluminate by co-precipitation method, and catalyst (I), magnesium lanthanum aluminate are mixed according to 91～98% After being mixed with 2-9% by mass, the finished catalyst is obtained after kneading, molding, drying and roasting. 5. The method according to claim 1, characterized in that N is lanthanum in the catalyst (I), i is a number from 0.1 to 3, and the lanthanum source is lanthanum nitrate. 6. the method according to claim 1 is characterized in that the catalyst preparation method represented by general formula (I) comprises the steps: the compound that will contain Mo, V, Ni, Cu, Sr, W and M _i N _j relates to Dissolving and mixing uniformly, forming a slurry after co-precipitation, adding one of silicon dioxide or silicon carbide, drying, shaping and roasting to obtain the catalyst (I). 7. The method according to claim 6, characterized in that the catalyst (I) and the finished catalyst are calcined at 300-550° C. for 3-10 hours.