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  • C07C45/34—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen of CHx-moieties in unsaturated compounds
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  • C07C45/32—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen
  • C07C45/33—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen of CHx-moieties
  • C07C45/34—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen of CHx-moieties in unsaturated compounds
  • C07C45/36—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen of CHx-moieties in unsaturated compounds in compounds containing six-membered aromatic rings
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  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
  • C07C51/21—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen
  • C07C51/215—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of saturated hydrocarbyl groups
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  • C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
  • C07C51/21—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen
  • C07C51/25—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of unsaturated compounds containing no six-membered aromatic ring
  • C07C51/252—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of unsaturated compounds containing no six-membered aromatic ring of propene, butenes, acrolein or methacrolein
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  • B01J2208/00106—Controlling the temperature by indirect heat exchange
  • B01J2208/00168—Controlling the temperature by indirect heat exchange with heat exchange elements outside the bed of solid particles
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  • B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
  • B01J2208/00008—Controlling the process
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  • B01J2208/023—Details
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Definitions

• the present invention relates to a process for producing unsaturated aldehydes and/or unsaturated acids from olefins or alkanes in a fixed bed shell-and-tube heat exchanger-type reactor by catalytic vapor phase oxidation, as well as a heat exchanger-type reactor for use in the same process.
• a process for producing unsaturated aldehydes and/or unsaturated acids from olefins or alkanes in vapor phase by using a catalyst is a typical process of catalytic vapor phase oxidation.
• catalytic vapor phase oxidation examples include a process for producing acrolein and/or acrylic acid by the oxidation of propylene or propane, or a process for producing methacrolein and/or methacrylic acid by the oxidation of isobutylene, isobutane, t-butyl alcohol or methyl t-butyl ether.
• catalytic vapor phase oxidation is carried out by charging one or more kinds of granular catalysts into a reaction tube (catalytic tube) , supplying feed gas into a reactor through a pipe, and contacting the feed gas with the catalyst in the reaction tube.
• Reaction heat generated during the reaction is removed by heat exchange with a heat transfer medium whose temperature is maintained at a predetermined temperature.
• the heat transfer medium for heat exchange is provided on the outer surface of the reaction tube so as to perform heat transfer.
• the reaction mixture containing a desired product is collected and recovered through a pipe, and sent to a purification step.
• the catalytic vapor phase oxidation is a highly exothermic reaction, it is very important to maintain reaction temperature within a certain range and to reduce the magnitude of a hot spot occurring in a reaction zone. It is also very important to disperse heat at a site where heat accumulation may occur due to the structure of a reactor or a catalyst layer.
• the partial oxidation of olefins or alkanes corresponding thereto uses a multimetal oxide containing molybdenum and bismuth or vanadium or a mixture thereof, as a catalyst.
• (meth) acrylic acid a final product
• ⁇ propylene or the like' a two-step process of vapor phase catalytic partial oxidation. More particularly, in the first step, propylene or the like is oxidized by oxygen, inert gas for dilution, water steam and a certain amount of a catalyst, so as to produce (meth) acrolein as a main product.
• the (meth) acrolein is oxidized by oxygen, inert gas for dilution, water steam and a certain amount of a catalyst, so as to produce (meth) acrylic acid.
• the catalyst used in the first step is a Mo-Bi-based oxidation catalyst, which oxidizes propylene or the like to produce (meth) acrolein as a main product. Also, some acrolein is continuously oxidized on the same catalyst to partially produce (meth) acrylic acid.
• the catalyst used in the second step is a Mo-V-based oxidation catalyst, which mainly oxidizes (meth) acrolein in the mixed gas containing the (meth) acrolein produced from the first step to produce (meth) acrylic acid as a main product.
• a reactor for performing the aforementioned process is provided either in such a manner that both the two- steps can be performed in one system, or in such a manner that the two steps can be performed in different systems.
• a catalyst for use in producing unsaturated acids such as (meth) acrylic acid from alkanes such as propane or isobutane via a single-step process has been developed.
• (meth) acrylic acid manufacturers now conduct diversified efforts either to improve the structure of the reactor so as to increase the production of acrylic acid by the reactor, or to propose the most suitable catalyst to induce oxidation, or to improve process operations.
• propylene or the like which is supplied into the reactor is used at high space velocity and high concentration.
• rapid oxidation occurs in the reactor, which makes it difficult to control the resultant reaction temperature.
• a hot spot is generated in the catalyst layer of the reactor, and heat accumulation occurs in the vicinity of the hot spot, resulting in increased production of byproducts, such as carbon monoxide, carbon dioxide and acetic acid at high temperature, and in a drop in yield of (meth) acrylic acid.
• the inventors of the present invention have made improvements in a fixed-bed shell-and-tube heat exchanger- type reactor for producing unsaturated aldehydes and/or unsaturated acids from olefins.
• at least one reaction zone of the first-step reaction zone and the second-step reaction zone was divided into two or more shell spaces along the axial direction by at least one partition, and the temperature of a heat transfer medium filled in each of the divided shell spaces was set to a temperature suitable for the activity of a catalyst and the degree of reaction.
• the present inventors have found that a hot spot and heat accumulation in the vicinity of the hot spot could be inhibited.
• the present invention is based on this finding.
• the present invention may be applied to a single-step process for producing unsaturated acids from alkanes, for example, a process for producing (meth) acrylic acid from propane or isobutane.
• the present invention provides a process for producing unsaturated aldehydes from olefins, particularly a process for producing (meth) acrolein from propylene or the like, by fixed-bed catalytic partial oxidation in a shell-and-tube heat exchanger-type reactor, wherein the reactor comprises a reaction zone for producing the unsaturated aldehydes; the reaction zone is divided into two or more shell spaces by at least one partition; each of the divided shell spaces is independently heat-controlled; a heat transfer medium in the first shell space has a temperature ranging from the lowest active temperature of a catalyst layer packed in a reaction tube corresponding to the first shell space to [the lowest active temperature + 20 ° C], when referring to the two or more shell spaces sequentially as the first shell space, the second shell space, ... , the n th shell space; and the first shell space is controlled in such a manner that it provides an olefin conversion contribution per length as defined in the following equation of 1.2-2.5:
• Olefin conversion contribution per length (mole number of olefins that have reacted in the relevant catalyst layer zone / mole number of the total olefins supplied to the reaction zone) / volumetric ratio of the relevant catalyst layer zone to the total catalyst layer of the reaction zone.
• the present invention provides a process for producing unsaturated acids from unsaturated aldehydes or alkanes, particularly a process for producing (meth) acrylic acid from (meth) acrolein, propane or isobutane, by fixed-bed catalytic partial oxidation in a shell-and-tube heat exchanger-type reactor, wherein the reactor comprises a reaction zone for producing the unsaturated acids; the reaction zone is divided into two or more shell spaces by at least one partition; each of the divided shell spaces is independently heat-controlled; a heat transfer medium in the first shell space has a temperature ranging from the lowest active temperature of a catalyst layer packed in a reaction tube corresponding to the first shell space to [the lowest active temperature + 20 " C], when referring to the two or more shell spaces sequentially as the first shell space, the second shell space, ..., the n th shell space; and the first shell space is controlled in such a manner that it provides an unsaturated aldehyde or alkane conversion contribution per length as defined in the
• the present invention provides a shell-and-tube heat exchanger-type reactor which can be used in a process for producing unsaturated aldehydes and unsaturated acids from olefins by fixed-bed catalytic partial oxidation, the reactor comprising one or more catalytic tubes each including a first-step reaction zone for mainly producing the unsaturated aldehydes, and a second-step reaction zone for mainly producing the unsaturated acids, or both the two zones, wherein at least one of the first-step reaction zone and the second-step reaction zone is divided into two or more shell spaces by at least one partition; each of the divided shell spaces is independently heat-controlled; a heat transfer medium in the first shell space of the first-step reaction zone or the first shell space of the second-step reaction zone has a temperature ranging from the lowest active temperature of a catalyst layer packed in a reaction tube corresponding to the first shell space of the first-step reaction zone or the first shell space of the second-step reaction zone to [the lowest active temperature + 20 ° C
• the present invention provides a shell-and-tube heat exchanger-type reactor which can be used in a process for producing unsaturated acids from alkanes by fixed-bed catalytic partial oxidation, the reactor comprising one or more catalytic tubes each including a reaction zone for producing the unsaturated acids, wherein the reaction zone is divided into two or more shell spaces by at least one partition; each of the divided shell spaces is independently heat- controlled; a heat transfer medium in the first shell space has a temperature ranging from the lowest active temperature of a catalyst layer packed in a reaction tube corresponding to the first shell space to [the lowest active temperature + 20 " C], when referring to the two or more shell spaces sequentially as the first shell space, the second shell space, ... , the n th shell space; and the first shell space is controlled in such a manner that it provides an alkane conversion contribution per length as defined in Equation 2 of 1.2—2.5.
• the inventors of the present invention have conducted many studies and obtained the following results.
• a catalyst having a high activity corresponding to a conversion of 96% or more in the first-step reaction zone for example, a catalyst having a conversion of 96% at a temperature, where the highest catalytic activity can be obtained, under a space velocity of feed of 1500 hr "1 and that of an olefin of 100 hr "1 ) is packed in the first-step reaction zone and the reaction zone is operated with no temperature control along the axial direction, a hot spot having a temperature near the sintering temperature of the catalyst is generated in the front portion of the first- step reaction zone.
• a catalyst having a high activity corresponding to an acrolein conversion of 95% or more in the second-step reaction zone for example, a catalyst having a conversion of 95% at a temperature, where the highest catalytic activity can be obtained, under a space velocity of unsaturated aldehydes of 90 hr ⁇ ⁇ * ⁇
• a hot spot having a temperature near the sintering temperature of the catalyst is generated in the front portion of the second-step reaction zone.
• Such problem of hot spots also occurs in a single-step process for producing unsaturated acids from alkanes .
• a hot spot refers to a site where the highest temperature peak is generated, and is formed by the generation of reaction heat caused by catalytic vapor phase oxidation.
• the hot spot is determined by the composition of reactants, the flow rate (L/min) of the reactants, the temperature of a heat transfer medium, etc., and has a certain position and magnitude under a certain process condition.
• each catalytic layer has at least one hot spot.
• the position and temperature of a hot spot may also be varied.
• a partition is disposed in such a manner that each shell space divided by the partition has at least one temperature peak, after the characterization of the temperature profile of a catalyst layer.
• each divided shell space indicates an internal space surrounded by a catalytic tube, a shell, a partition, a tube sheet, etc.
• the portions where heat control is problematic due to the hot spot include the front portion of a catalyst layer, in which main reactants including olefins, alkanes or unsaturated aldehydes, and molecular oxygen, are present at high concentrations. Also, if two or more catalyst layers are used in each step, such problematic portions include the vicinity of the boundary between the adjacent catalyst layers having different activities.
• the partition is preferably located at either a position where heat control is problematic due to the hot spot or heat accumulation caused by the hot spot, or a position allowing the largest possible removal of heat generation in each zone.
• each reaction zone is divided into two or more shell spaces by using at least one partition and is subjected to heat control, it is possible to provide the process with high flexibility under the variations in temperature profile characteristics.
• At least one of the first-step reaction zone and the second- step reaction zone is divided into two or more shell spaces by at least one partition; each of the divided shell spaces is independently heat-controlled; a heat transfer medium in the first shell space of the first-step reaction zone or the first shell space of the second-step reaction zone has a temperature ranging from the lowest active temperature of a catalyst layer packed in a reaction tube corresponding to the first shell space of the first-step reaction zone or the first shell space of the second-step reaction zone to [the lowest active temperature + 20 "C], when referring to the two or more shell spaces corresponding to the first-step reaction zone sequentially as the first shell space of the first-step reaction zone, the second shell space of the first-step reaction zone, ...
• a reaction zone for producing the unsaturated acids is divided into two or more shell spaces by at least one partition; each of the divided shell spaces is independently heat-controlled; a heat transfer medium in the first shell space has a temperature ranging from the lowest active temperature of a catalyst layer packed in a reaction tube corresponding to the first shell space to [the lowest active temperature + 20 ° C], when referring to the two or more shell spaces sequentially as the first shell space, the second shell space, ... , the n th shell space; and the first shell space is controlled in such a manner that it provides an alkane conversion contribution per length as defined in Equation 2 of 1.2-2.5.
• the term "the lowest active temperature of the first-step catalyst layer" refers to the lowest temperature where the olefin conversion
• Equation 3 (defined by the following Equation 3) in the relevant catalyst layer reaches 90%, when the olefins, such as propylene or the like, are allowed to react with the relevant catalyst layer at a space velocity of about 95-115 hr "1 .
• the above space velocity of the olefins ranging from about 95 hr “1 to 115 hr “1 corresponds to a space velocity of total reaction feed gas introduced to the first-step reaction zone of about 1300 ⁇ 1500 hr "1 , the feed gas comprising 7 —7.5% of olefins, 13 — 15% of oxygen, 7 ⁇ 10% of water steam and the balance amount of inert gas.
• Olefin conversion (%) [mole number of reacted olefins/mole number of supplied olefins] X 100
• the term "the lowest active temperature of the second-step catalyst layer” refers to the lowest temperature where the unsaturated aldehyde conversion (defined by the following Equation 4) in the relevant catalyst layer reaches 90%, when the unsaturated aldehydes are allowed to react with the relevant catalyst layer at a space velocity of about 75 — 100 hr "1 .
• the above space velocity of the unsaturated aldehydes ranging from about 75 hr “1 to 100 hr “1 corresponds to a space velocity of total reaction feed gas introduced to the second-step reaction zone of about 1050 ⁇ 1700 hr "1 , the feed gas comprising 5 ⁇ 6% of unsaturated aldehydes, 5.5 ⁇ .5% of oxygen, 2% of unsaturated acid, 12 ⁇ 17% of water steam, 1 2 % of byproducts and the balance amount of inert gas.
• unsaturated aldehyde conversion (%) [mole number of reacted unsaturated aldehydes/mole number of supplied unsaturated aldehydes] X 100
• the lowest active temperature of the catalyst layer for producing unsaturated acids from alkanes refers to the lowest temperature where the alkane conversion (defined by the following Equation 5) in the relevant catalyst layer reaches 60%, when the alkanes are allowed to react with the relevant catalyst layer at a space velocity of about 50 ⁇ 80 hr "1 .
• the above space velocity of the alkanes ranging from about 50 hr ""1 to 80 hr “1 corresponds to a space velocity of total reaction feed gas introduced to the reaction zone of about 1500 —2000 hr "1 , the feed gas comprising 3 ⁇ 5% of alkanes, 10—15% of oxygen, 30 ⁇ 50% of water steam and the balance amount of inert gas.
• Alkane conversion (%) [mole number of reacted alkanes/mole number of supplied alkanes] X 100
• the lowest active temperature of a catalyst layer depends on the kind of the catalyst, content of the catalytic substance in the catalyst layer, ratio of main metal elements in the catalyst, presence of any alkali metal, kind of the alkali metal, mixing ratio with inactive materials, size of the catalyst, shape of the catalyst, sintering temperature of the catalyst, sintering atmosphere of the catalyst, and combinations thereof.
• the first-step catalyst layer has an active temperature of 280 ⁇ 450 ° C
• the second-step catalyst layer has an active temperature of 250 ⁇ 370 ° C
• the catalyst layer for producing unsaturated acids from alkanes has an active temperature of 350 ⁇ 420 ° C.
• the catalyst used in the first-step reaction zone is sintered generally at a temperature of 400 ⁇ 600°C
• the catalyst used in the second-step reaction zone is sintered generally at a temperature of 300 ⁇ 500 ° C
• the catalyst used in the reaction zone for producing unsaturated acids from alkanes is sintered generally at a temperature of 500 ⁇ 600 ° C. If the highest peak temperature of a catalyst layer exceeds the sintering temperature where the catalyst is sintered during the preparation thereof, the catalyst layer is deteriorated, resulting in a drop in yield of the target product.
• each front portion for example, the catalyst layer corresponding to the first shell space of each step shows a high concentration of reactants (olefins, unsaturated aldehydes or alkanes) and a high reaction pressure, and consequently leads to a severe reaction.
• reactants olefins, unsaturated aldehydes or alkanes
• a hot spot with a significantly large magnitude is formed in the front portion of each reaction zone. Therefore, it is preferable that the reaction in the above portion is controlled in such a manner that the peak temperature of the relevant catalyst layer is significantly lower than the sintering temperature of the catalyst.
• each catalyst layer corresponding to the first shell space of each step comprises 20 ⁇ 30% of the total length of the catalyst layer, conversion of reactants in the first shell space reaches 50% or more.
• the first shell space has an excessively high load of reaction in view of its proportion to the total catalyst layer, and thus may be thermally unstabilized with ease due to the high reaction heat.
• the temperature of the heat transfer medium in the first shell space of each step is decreased possibly to the lowest active temperature of the catalyst, according to the present invention.
• the temperature of a heat transfer medium is preferably controlled considering the characteristics and reactivity of the catalyst.
• temperature of a heat transfer medium may be controlled.
• shear pressure pressure of the reactor inlet
• space velocity may be controlled.
• the partition dividing the first shell space of each step from the second shell space of each step is disposed in such a manner that the first shell space includes a temperature peak occurring in the inlet portion of each reaction zone.
• the first partition dividing the first shell space from the second shell space is disposed in a position corresponding to 25% ⁇ 50% of the axial length of the reaction zone of each step. This indicates that contact time in the first shell space of each step corresponds to about 25% ⁇ 50% of the total contact time of each step.
• the first partition may be disposed at a point of 1200mm, which corresponds to 40% of the total length.
• the first partition should be in such a position with the proviso that the reactant conversion contribution (defined by Equation 3, 4 or 5) of the first shell space ranges from 1.2 to 2.5.
• the temperature of the heat transfer medium in each shell space is set as nearly as possible to isothermal conditions.
• the temperature difference between portions of the heat transfer medium, which correspond to both the ends of a catalyst layer in each of the divided shell spaces is preferably 0-5 0 C, and more preferably 0-3 0 C.
• the heat transfer medium examples include a very highly viscous medium, for example a molten salt which consists mainly of a mixture of potassium nitrate and sodium nitrite.
• a molten salt which consists mainly of a mixture of potassium nitrate and sodium nitrite.
• Other examples of the heat transfer medium include a phenyl ether medium (e.g., "Dowtherm") , polyphenyl media (e.g., "Therm S”), hot oil, a naphthalene derivative (S. K. oil) and mercury.
• the reaction throughout the tube corresponding to each of the shell spaces in the reactor can be carried out at substantially the same molten salt temperature.
• heat transfer media filled in shell spaces have different temperatures along the flow direction (also referred to as the axial direction hereinafter) of reactants, reactivity of the relevant catalyst layer varies in proportion to the temperature. It is preferable to set the temperature of the heat transfer medium (molten salt or heat transfer salt) in each of the divided shell spaces in such a manner that the relevant catalyst layer has optimal activity.
• the temperature of the heat transfer media can be varied in the axial direction according to the present invention.
• the temperature of the heat transfer media in the adjacent shell spaces in each of the reaction zones is preferably set to cause a temperature difference 0-50 0 C, and more preferably 5-15 0 C along the axial direction.
• the temperature of the heat transfer medium in each of the first shell space of the first step, the second shell space of the first step, ... , the n th shell space of the first step, divided by partitions is set in such a manner that the temperature of each heat transfer medium increases along the axial direction.
• the heat transfer medium in each of the first shell space of the second step, the second shell space of the second step, ... , the n th shell space of the second step, divided by partitions does not increase or decrease monotonously, because the product of the first step is supplied to the reaction zone corresponding to the first shell space of the second step. It is preferred to set the temperature of the heat transfer medium in each shell space in such a manner that the temperature of the heat transfer medium increases monotonously from the second shell space to the n th shell space except the first shell space, and the temperature of the first shell space is set according to the manner as described hereinafter related to the temperature setting in the second-step reaction zone.
• T h i-T sa iti ⁇ 150 0 C more preferably T h i-T sa iti ⁇ 110 °C
• T hN -T salt N ⁇ 120 0 C more preferably T hN -T sa it N ⁇ 100 °C (wherein N is an integer of 2 or more)
• N is an integer of 2 or more
• T h i-T salt i ⁇ 130 °C, more preferably T h i-T sa i t i ⁇ 75 °C, and T h N-T S ai t N ⁇ HO 0 C, more preferably T hN -T sa i t N ⁇ 70 0 C (wherein N is an integer of 2 or more) , when referring to the shell spaces divided by partitions in the second-step reaction zone for producing unsaturated acids from unsaturated aldehydes sequentially as the first shell space, the second shell space, ..., the n th shell space.
• T h i is the highest peak temperature of a reaction mixture in the catalyst layer corresponding to the first shell space (the highest peak temperature of the catalyst layer)
• T h N is the highest peak temperature of the reaction mixture in the catalyst layer corresponding to the n th shell space (the highest peak temperature of the catalyst layer)
• T sa i t i is the temperature of the heat transfer medium filled in the first shell space
• T sa i tN is the temperature of the heat transfer medium filled in the n th shell space.
• the concentration and pressure of reactants are high, so that the temperature difference between the highest peak temperature of the catalyst layer and the temperature of the heat transfer medium is higher than that in the next shell space. For this reason, the temperature difference range in the first shell space will be surely wider than those in the next shell spaces.
• the present invention provides a method by which the magnitude of peak temperature in the first shell space is minimized while a temperature difference in the next shell space is limited in an extended range, thereby forming an overall temperature profile having a smooth shape.
• the temperature difference between the highest peak temperature of a catalyst layer in each reaction zone and the temperature of a heat transfer medium is controlled as described above, so that the catalyst can show uniform activity in the axial direction.
• it is possible to inhibit heat accumulation in a hot spot and suppress side reactions, thereby preventing a drop in yield.
• the catalyst layer in the first-step reaction zone may consist of one layer with axially uniform activity, or if necessary, two or more stacked layers with increasing activity.
• the catalyst layer in the second-step reaction zone may consist of one layer with axially uniform activity, or if necessary, two or more stacked layers with increasing activity.
• the catalyst layer of the reaction zone for producing unsaturated acids from alkanes may be formed in the same manner as described above.
• a layer formed of an inactive material or a mixture of an inactive material and a catalytic material i.e., a reaction inhibition layer, is disposed within a portion of the catalytic tube, which corresponds to a position where the partition is disposed.
• a reaction inhibition layer is disposed within a portion of the catalytic tube, which corresponds to a position where the partition is disposed.
• a commercially available shell-and-tube reactor for producing (meth) acrylic acid includes catalytic tubes in the number of several hundreds to several tens of thousands, and a partition disposed in such a reactor has a relatively large thickness of 50 ⁇ 100mm. Therefore, in the reaction zone of each step having two or more divided shell spaces, it is difficult to remove the reaction heat at the portion where a partition is disposed, thereby causing a problem in heat transfer. To solve this problem, it is preferred to dispose a layer formed of an inactive material or a mixture of an inactive material and a catalytic material, i.e., a reaction inhibition layer within a portion of the catalytic tube, which corresponds to a position where the partition is disposed.
• the volume ratio of an inactive material to a catalytic material in this reaction inhibition layer is 20 ⁇ 100%.
• the inactive material used in the reaction inhibition layer is designated as a material which is inactive to a reaction for producing unsaturated aldehydes and/or unsaturated acids from olefins and/or alkanes, for example, catalytic oxidation of propylene or the like and (meth) acrolein. It can be used in a sphere, cylinder, ring, rod, plate or wire mesh shape, or a mass shape with suitable size, or a suitable combination thereof. Widely known examples of the inactive material include alumina, silica alumina, stainless steel, iron, steatite, porcelain, various ceramics, and mixtures thereof.
• the reaction inhibition layer is packed to a height corresponding to 20 ⁇ 500% of the thickness of a partition.
• the heat control system according to the present invention can be applied not only to oxidation of olefins but also to a reaction system for carrying out different reactions along the axial direction in a stepwise manner and a reaction system requiring independent heat control of every reaction zone to the optimal temperature even if the reaction zones perform the same reaction.
• FIG. 1 is a schematic diagram showing the structure of a reactor according to Example 1, which illustrates the position of a partition and a catalyst layer disposed inside a catalytic tube
• FIG. 2 is a schematic diagram showing the structure of a reactor according to Example 3, which illustrates the position of a partition and a catalyst layer disposed inside a catalytic tube.
• Reference Example 1 Determination of Lowest Active Temperature of Catalyst Layer Corresponding to First Shell Space of First Step
• a pilot reactor in which the first step is conducted in one catalytic tube was provided.
• the catalytic tube had an inner diameter of 2 ⁇ mm.
• a catalyst layer was packed to a height of about 1200 mm.
• two kinds of catalysts having activity increasing along the axial direction from the inlet to the outlet were packed to a height of 320iran and 880mm, respectively (see “Method of Controlling Catalytic Activity” described in US3801634 and US4837360) .
• the catalyst was comprised of the first-step oxidation catalyst material obtained according to the method as disclosed in Korean Patent Publication No. 0349602 (Korean Patent Application No. 10-1997-0045132), the catalyst material being based on molybdenum (Mo) and bismuth (Bi) .
• the first catalyst layer (referred to as LGCl hereinafter) of the first-step reaction zone showed an activity corresponding to 85 ⁇ 90% of the catalytic activity of the second catalyst layer, when measuring the catalytic activity by propylene conversion (space velocity of propylene 98 hr-1, molten salt temperature of 300 ° C) .
• the first shell space included the peak portion of the second catalyst layer, and the catalyst layer of the first shell space had a length of 540mm.
• the starting materials introduced into the inlet of the reactor were comprised of propylene, oxygen, steam and nitrogen gas, wherein propylene content was 7% and the ratio of oxygen to propylene was about 1.80.
• space velocity was 1400 hr '1 (standard temperature and pressure, STP)
• space velocity of the olefins introduced into the first-step reaction zone was 98 hr '1 (STP) .
• the catalyst layer used in Reference Example 1 has the lowest active temperature of 290 ° C.
• Example 1 Variations in Yield and in Magnitudes of Temperature Peaks at Hot Spots Depending on Variations in Temperature Setting of Molten Salt
• a pilot reactor was provided in which each of first-step reaction and second-step reaction is conducted in one catalytic tube (included in zone 10 or 20 of FIG. 3) .
• the catalytic tube had an inner diameter of 26 mm, and the first-step catalytic tube was filled with catalyst layers to a height of about 1200 mm, and the second-step catalytic tube was filled with catalyst layers to a height of about 1100 mm.
• the catalyst layers of the first step reaction zone 10 two kinds of catalysts having activity increasing along the axial direction from the inlet to the outlet were packed to a height of 320mm and 880mm, respectively
• the catalyst layers of the first-step reaction zone were comprised of the first-step oxidation catalyst material obtained according to the method as disclosed in Korean Patent Publication No. 0349602 (Korean Patent Application No. 10-1997-0045132), the catalyst material being based on molybdenum (Mo) and bismuth (Bi) .
• the catalyst layers of the second-step reaction zone were comprised of a catalyst based on molybdenum and vanadium (V) , the preparation of which is described in Korean patent No. 0204728 or Korean patent No. 0204729.
• LGCl catalyst was used in the first catalyst layer of the first-step reaction zone.
• the catalyst showed an activity corresponding to 85 ⁇ 90% of the catalytic activity of the second catalyst layer, when measuring the catalytic activity by propylene conversion (space velocity of propylene 98 hr-1, molten salt temperature of 300 ° C).
• the first catalyst layer of the second-step reaction zone showed an activity corresponding to 85 ⁇ 90% of the catalytic activity of the second catalyst layer.
• a partition was disposed at the 600-mm position (central portion) of the first-step reaction zone, so that the first shell space of the first step covered both temperature peaks occurring in the first catalyst layer of the first step and the second catalyst layer of the first step.
• an inactive material layer was filled to a thickness corresponding 120% of the thickness of the partition.
• Reference numerals 11 and 12 in FIG. 1 illustrate the shell spaces divided in the first-step reaction zone. Each molten salt filled in each shell space was set to a temperature of 308 ° C and 315 ° C, respectively.
• Reference numeral 21 in FIG. 1 illustrate a shell space of the second-step reaction zone, the shell space being filled with a molten salt set to a temperature of 265 ° C.
• a pipe inducing a flow represented by reference numeral 2 in FIG. 1 serves to connect the two catalytic tubes and is surrounded by a heat insulation material.
• Starting materials comprising propylene, steam, oxygen and inert gas enter the reactor through a line 1, passes through the reaction steps, and then flows out from the reactor through a line 3.
• the starting materials were comprised of propylene, oxygen, steam and nitrogen gas, wherein the propylene content was 7% and the ratio of oxygen to propylene was about 1.80.
• Space velocity was 1400 hr "1 (standard temperature and pressure, STP) in the total first-step reaction zone, and 1530 hr "1 (STP) in the total second-step reaction zone. Also, the space velocity of olefins introduced into the first-step reaction zone was 98 hr "1 (STP) .
• Equation 1 In the first shell space of the first step, the value defined by Equation 1 was about 2.
• a hot spot was generated in the zone corresponding to the first shell space of the first-step reaction zone, the hot spot having a temperature of 392.5 ° C. After the reaction in the first-step reaction zone, acrolein and acrylic acid were obtained in a yield of 80.33% and 11.37%, respectively. In the second-step reaction zone operated under isothermal conditions, a hot spot having a temperature of 320.5 ° C was generated. After the reaction in the second-step reaction zone, acrolein and acrylic acid were obtained in a yield of 0.631% and 86.83%, respectively.
• Example 2 Variations in Yield and in Magnitudes of Temperature Peaks at Hot Spots Depending on Variations in Temperature Setting of Molten Salt
• Example 2 This example was performed in the same manner as described in Example 1, except that the temperatures of the molten salt in the first-step reaction zone (first- step reactor) were set to 300 °C and 315 °C, respectively, in an axial direction. In the first shell space of the first step, the value defined by Equation 1 was about 1.9. In the zone corresponding to the first shell space in the first-step reaction zone, a hot spot with a temperature of 381.2 0 C was generated. The yields of acrolein and acrylic acid were 79.02% and 11.46%, respectively. In the second-step reaction zone operated under isothermal conditions, the temperature of a hot spot was 327.5 0 C, and the yields of acrolein and acrylic acid were 0.607% and 84.95%, respectively. Comparative Example 1
• This example was performed in the same manner as described in Example 1, except that the temperature of the molten salt filled in each shell space of the first-step reaction zone was set to 31O 0 C.
• the temperature, 310 ° C, of the molten salt in the first-step reaction zone is higher than the lowest active temperature by 20 ° C.
• Equation 1 After the analysis of the conversion in the portion corresponding to the first shell space of the first step according to Comparative Example 1, the value defined by Equation 1 was 2.7.
• This example was performed in the same manner as described in Example 1, except that the temperature of the molten salt filled in each shell space of the first-step reaction zone was set to 320 0 C.
• the temperature, 320 ° C, of the molten salt in the first-step reaction zone is higher than the lowest active temperature by 30 ° C.
• This example was performed in the same manner as described in Example 1, except that the temperature of the molten salt filled in each shell space of the first-step reaction zone was set to 312°C.
• the temperature, 312°C, of the molten salt in the first-step reaction zone is higher than the lowest active temperature by 22 °C.
• a hot spot with a temperature of 409.1 0 C was generated.
• the yields of acrolein and acrylic acid were 78.8% and 11.9%, respectively.
• the temperature of a hot spot was 329.2 0 C, and the yields of acrolein and acrylic acid were 0.367% and 85.08%, respectively.
• Equation 1 After the analysis of the conversion in the portion corresponding to the first shell space of the first step according to Comparative Example 3, the value defined by Equation 1 was 2.63.
• a pilot reactor in which the first-step reaction and the second-step reaction are conducted in one catalytic tube was provided.
• the catalytic tube had an inner diameter of 26mm.
• a first-step catalyst layer was packed to a height of about 3570 mm
• the second-step catalyst layer was packed to a height of about 3125 mm.
• the catalyst material filled in the first-step reaction zone was the first-step oxidation catalyst material obtained according to the method as disclosed in Korean Patent Publication No. 0349602 (Korean Patent Application No. 10- 1997-0045132), the catalyst material being based on molybdenum (Mo) and bismuth (Bi) .
• the three catalyst layers filled in the second-step reaction zone were comprised of a catalyst based on molybdenum and vanadium (V) , the preparation of which is described in Korean patent No. 0204728 or Korean patent No. 0204729.
• the second-step catalyst layers were comprised of three kinds of catalysts having activity increasing along the axial direction from the inlet to the outlet (see "Method of Controlling Catalytic Activity" described in US3801634 and US4837360) .
• the second catalyst layer of the second step (reference numeral 22 in FIG. 2) showed an activity corresponding to 87% of the catalytic activity of the third catalyst layer of the second step.
• the three catalyst layers of the second-step reaction zone were packed to a height of 500mm, 700mm and 1925mm, respectively, along the axial direction.
• the first catalyst layer of the second step was packed to a height of 250mm in the catalytic tube corresponding to the shell spaces of the second-step reaction zone, and the remaining 250mm was disposed in the partition (reference numeral 30 in FIG. 2), by which the first-step reaction zone was divided from the second-step reaction zone, and in the catalytic tube covering the shell spaces of the first-step reaction zone.
• the second-step reaction zone was divided into two independent shell spaces (reference numerals 24 and 25 in FIG. 2) by the partition (reference numeral 27 in FIG. 2) disposed in the boundary between the second catalyst layer of the second step and the third catalyst layer of the second step. Meanwhile, an inactive material layer was packed in the catalytic tube at the portion corresponding to the position of the partition to a height corresponding to 120% of the thickness of the partition.
• the starting materials introduced into the inlet of the second-step reaction zone were comprised of acrolein, acrylic acid, oxygen, steam and nitrogen gas, more particularly, 5.5% of acrolein, 0.9% of acrylic acid, 5.0% of oxygen, 1.0% of byproducts such as COx and acetic acid, and the balance amount of nitrogen gas.
• space velocity was 1500 hr '1 (standard temperature and pressure, STP) .
• space velocity of the hydrocarbon reactant, i.e. acrolein introduced into the second-step reaction zone was 81 hr "1 (STP) and the feed gas mixture had a pressure of 0.4kgf/cm 2 G.
• the conversion defined by Equation 4 was 91.9% after the analysis of the gas obtained from the outlet of the first shell space of the second step.
• the catalyst layer has the lowest active temperature of 260 ° C.
• Example 3 (Use of Mixed Layers and Multi-step Heat Control System)
• a pilot reactor in which the first-step reaction and the second-step reaction are conducted in one catalytic tube was provided.
• the catalytic tube had an inner diameter of 2 ⁇ mm.
• a first-step catalyst layer was packed to a height of about 3570 mm
• the second-step catalyst layer was packed to a height of about 3125 mm.
• the catalyst material filled in the first-step reaction zone was the first-step oxidation catalyst material obtained according to the method as disclosed in Korean Patent Publication No. 0349602 (Korean Patent Application No. 10- 1997-0045132), the catalyst material being based on molybdenum (Mo) and bismuth (Bi) .
• the three catalyst layers filled in the second-step reaction zone were comprised of a catalyst based on molybdenum and vanadium (V) , the preparation of which is described in Korean patent No. 0204728 or Korean patent No. 0204729.
• the second-step catalyst layers were comprised of three kinds of catalysts having activity increasing along the axial direction from the inlet to the outlet (see "Method of Controlling Catalytic Activity" described in US3801634 and US4837360) .
• the three catalyst layers of the second-step reaction zone were packed to a height of 500mm, 700mm and 1925mm, respectively, along the axial direction.
• the first catalyst layer of the second step was packed to a height of 250mm in the catalytic tube corresponding to the shell spaces of the second-step reaction zone, and the remaining 250mm was disposed in the partition (reference numeral 30 in FIG. 2), by which the first-step reaction zone was divided from the second-step reaction zone, and in the catalytic tube covering the shell spaces of the first-step reaction zone.
• the second-step reaction zone was divided into two independent shell spaces (reference numerals 24 and 25 in FIG. 2) by the partition (reference numeral 27 in FIG. 2) disposed in the boundary between the second catalyst layer of the second step and the third catalyst layer of the second step.
• Each molten salt filled in each shell space was set to a temperature of 275 ° C and 270 ° C, respectively.
• an inactive material layer was packed in the catalytic tube at the portion corresponding to the position of the partition to a height corresponding to 120% of the thickness of the partition (reference numeral 26 in FIG. 2) .
• the starting materials introduced into the inlet of the second-step reaction zone were comprised of acrolein, acrylic acid, oxygen, steam and nitrogen gas, more particularly, 5.5% of acrolein, 0.9% of acrylic acid, 5.0% of oxygen, 1.0% of byproducts such as COx and acetic acid, and the balance amount of nitrogen gas.
• space velocity was 1500 hr "1 (standard temperature and pressure, STP) .
• space velocity of the hydrocarbon reactant i.e.
• two catalyst layers of the three catalyst layers except the mixed layer had a temperature peak.
• the two peak temperatures were 309.4 ° C and 321.7 °C along the axial direction.
• yield of acrylic acid was 86.2%.
• the reaction mixture arriving in the first catalyst layer of the second step along the axial direction had a temperature of 31 ⁇ ° C, and the temperature difference between the above temperature and the first heat transfer medium of the second step was 41 ° C.
• Comparative Example 4 This example was performed in the same manner as described in Example 3, except that the temperature of the molten salt filled in each shell space of the second-step reaction zone was set to 285°C. The temperature, 285 ° C, is higher than the lowest active temperature by 25 ° C, and thus is not included in the scope of the present invention.
• Equation 2 In the reaction zone corresponding to the first shell space of the second step according to Comparative Example 4, the value defined by Equation 2 was about 2.2, which was included in the scope of the present invention.
• two catalyst layers of the three catalyst layers except the mixed layer i.e. the first catalyst layer
• the two peak temperatures were 331.3 ° C and 328.1 ° C along the axial direction.
• Yield of acrylic acid was 83.8%, and the yields of byproducts, COx (carbon monooxide and carbon dioxide) and acetic acid were 11.3% and 2.12%, respectively.
• the present invention provides an improved system in which the temperature of a heat transfer medium in each shell space is controlled depending on the activity of a catalyst and the degree of reaction. By doing so, it is possible to inhibit heat accumulation in a hot spot and the vicinity thereof, and thus to ensure thermal stability, to reduce the production of byproducts and to improve the yield of a final product.

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