201231451 六、發明說明： 發明背景 【發明所屬之技術領域】 本發明係關於丙烧氧化。在一態樣中，本發明係關於 種經改良之丙烧氧化方法’而在另一態樣中，本發明係 關於一種使用減量蒸汽之丙烧氧化方法。 【先前技術】 在丙烷直接氧化為丙烯酸（AA)的方法中，丙酸（pA) 的形成係不希望有的副產物。在丙烷至AA方法之一個具體 實例中，較佳催化劑系統由鉬、釩、碲及鈮（M〇/v/Te/Nb) 之混合金屬氧化物組成。當在達到最大AA產率（等於或大 於（2) 85%氧氣轉化率）之條件下操作時，此等催化劑產 生可介於1，〇〇〇百萬分率（ppm)以上至1〇 〇〇〇ppm以下範 圍内之含量的PA。 另外，過量丙酸副產物可在AA產物酯化後賦予丙烯酸 酉旨（AE)及其相應聚合產物不希望有的特徵，諸如高揮發 性有機物含量（V0C)、氣味或顏色。在酯化前，習知丙烯 氧化之AA產物流的pa規格典型地介於5〇〇1〇〇〇叩爪之範 圍内，遠低於丙烷氧化產物中所見之含量。因此，為了使 丙烷氧化在經濟上更合乎需要，需要經由氧化步驟或在下 游分離步驟中減小PA副產物含量。 丙酸與丙烯酸的分離存在問題。兩者之沸點相隔小於 (< )1 C，且其不能夠藉由蒸餾分離。雖然現有用於分 離之方法（例如㈣結晶），但此等步驟藉由需要附加㈣ 3 201231451 及公共事業設備實現所需分離而實質 I貨上增加AA純化方法 之資本及操作成本。因此，能夠以使 风尸八形成減少的方式护： 制AA方法使得額外高成本純仆眘 二 凡个、也化霄質上得到減少應為有利 且合乎需要的。 【發明内容】 在本發明之一個具體實例中，丙烧氧化方法使用減量 蒸汽以減少該方法中PA之量。用於使丙烧氧化為丙烯酸之 方法典型地包含以下步驟：在氧化條件下，使@烧、氧氣、 蒸汽及視情況選用之稀釋氣體（例如氮氣）與丙烷氧化催 化劑接觸。由於蒸汽為丙烷經濟地轉化為AA所必需，故不 能直觀明顯地看出顯著減少該方法中蒸汽之量可為有利 的》然而，令人驚訝的是，當蒸汽進料濃度降低時，相當 高含量的PA會減少《雖然損失一些相應AA產量，但由於 減少使PA與最終產物分離所需之該方法之資本及操作成本 而帶來的經濟效益可補償產量損失。此方法亦可用於減少 習知丙烯或含有丙烷之丙烯流之產物中之PA含量。 在一個具體實例中’本發明為一種用於使丙烷直接氧 化為丙烯酸之方法，該方法包含以下步驟：在氧化條件下， 使包含5-10%丙烷、5-15%氧氣、1-20% (較佳10-15%)蒸 汽及餘量稀釋氣體之氣體混合物（以該混合物之重量計， 以重量百分比（wt% )表示）與丙烷氧化催化劑接觸。所產 生PA之量典型地小於1，〇〇〇 pprn或小於750 ppm或小於500 ppm 〇 【實施方式】 4 201231451 定義 除非相反地陳述、上下文所暗示或此項技術中所慣 用，否則所有份數及百分比係以重量計且所有測試方法為 到本發明申請曰期為止之現有方法。出於美國專利實務之 目的，任何所引用專利、專利申請案或公開案之内容係以 全文引用的方式併入（或其等效us版本如此般以引用的方 式併入），尤其關於此項技術中之定義（在與本發明中特定 提供之任何定義不一致的程度上）及常識之揭示。 除非另外指明，否則本發明中之數值範圍為近似的， 且因此可包括該範圍外之值。數值範圍包括來自且包括下 限值及上限值且以__個單位遞增的所有值，其限制條件為 任何下限值與任何上限值之間存在至少兩個單位的間隔。 舉例而言，若組成性質、物理性質或其他性質（諸如，例 如分子.量等）為100至^00,則明確列舉所有個別值（諸 如100、101、102等）及子區間（諸如1〇〇至144、155至 170、197至2〇〇等h對於含有小於i之值或含有大於i之 刀數（例如1 · 1、1.5等）的範圍而言，視情況而定，將一 個單位視為0.0001、0.001、0 01或〇丨。對於含有小於ι〇 之個位數（single digit number)之範圍（例如}至5 )而言， 將一個單位典型地視為。此等範圍僅為具體規定之實例 且所列舉之最低值與最高值之間的數值的所有可能組合視 為在本發明中明確地陳述。在本發明内提供尤其關於該方 去之氧化條件、AA流中之PA含量及其類似物的數值範圍。 方法反應物 201231451 ι始物質通常為丙烧氣體'至少一種含氧氣體、蒸气 及稀釋氣體。丙烷不必符合任何特別高的純度標準，且= 可能含有丙烯或其他烴或含有雜原子之烴作為雜質。在— 個具體實例中’丙烷不含有任何可評估量之丙烯，例如以 丙烷之重量計’小於丨wt%、或小於〇 5 wt%、或小於U外二 之。丙烯。在一個具體實例中，丙烷含有相對較大量（例如 wt%或以上）之丙稀，諸如低級丙院進料（諸如來自流 催化裂解器之低級丙烷進料）中所發現之情況。L氧 •本發明實踐中所用之含氧氣體可為純氧氣、諸如空^ 3氧氣體、虽氧氣體或包含兩種或兩種以上此等氣體： 混合物。稀釋氣體典型地為惰性氣體，諸如（但不限於 氮乱、風耽、氦氣及二氧化碳。稀釋氣體可用於稀釋 物質及/或調節空間速度、氧分壓及蒸汽分壓。此等。 ::者可單獨或與一或多種其他氣體組合添加至該方： 在-個具體實例中’丙炫可用適於氣相氧 醛或羧酸之另一烷烴補充或置換。 匕口 堂蛊η — t 矛、丙烷以外，該烷烴通 节為烧煙，典型地為異丁院或正丁炫。與丙通 此等其他烷烴不必符合任何特別高的純度標準箸， :可含有一或多種〜稀烴作為雜質。典型稀烴包括丙: 異丁烯、正丁烯、戊烯及其類似物。 丙烯、 在-個具體實例中’ c3-8缔煙進料置換丙燒 進，可含有大量燒烴，例如高達49重量百 席二 —個具體實例尹，該進料為異丁烯。 /0)。在 201231451 起始物質氣體混合物中丙烷/氧氣/稀釋氣體/水之合適 莫耳比以及丙烧/空氣/蒸汽之進料比為此項技術中已知。舉 例而吕，合適範圍揭示於USP 5,380,933中。典型範圍包括 丙烷.氧氣：水··稀釋氣體為1:(〇11〇):(〇_5〇):(〇_5〇)，更典型 地為1 .(0.5-5):(1-30):(0-30)。在一個具體實例中，起始氣體 犯合物包含5重量百分比（wt%)至1〇 wt%或6 wt%至8 wt% 之丙烧，l〇wt/i>至20 wt%之氧氣；1 wt%至wt%之蒸汽； 及餘量氮氣。 方法條件 使用氧化催化劑氧化起始氣體混合物。反應通常在大 氣壓下進行，但可在升壓或減壓下進行。反應壓力典型地 為〇磅/平方吋（psig)至100 psig，更典型地為〇 psig至 5〇Psig(0至0.70百萬帕（MPa)，更典型地為〇Μρ&至〇 35 MPa)。反應溫度通常為（^至woe，更典型地為2〇(rc至 5〇〇°C，甚至更典型地為3001：至48(rc且甚至更典型地為 350°C至440°C。氣體空間速度通常為1〇〇 hrl至1〇〇〇〇 更典型地為3〇〇hr-i至M00W且甚至更典型地為 300 hr·丨至3，_ hr·丨。反應器_起始氣體混合物之㈣時間 典型地為0.1秒至10秒、更典型地為1秒至4和、。 氧化催化劑 不贫明貫 ……η龙屬乳化 催化劑組成可變化很大，且可使用此項妯+丄 3孜術中已知用 於 烷烴氧化為不飽和醛及/或羧酸之任何催 之代表為式I之催化劑 化劑。此等催化劑 201231451 M〇iybMlcM2c〇n ⑴， 其中Ml為Te及/或Sb，M2為選自由Nb ' Ta、W、Ti、 A·1、&、^、_、Ga、Fe、^、Co、Rh、Ni、pd ' pt、La、201231451 VI. OBJECTS OF THE INVENTION: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the oxidation of propane. In one aspect, the invention is directed to an improved method of oxidizing propylene oxide' and in another aspect, the invention is directed to a method of oxidizing propylene oxide using reduced steam. [Prior Art] In the direct oxidation of propane to acrylic acid (AA), the formation of propionic acid (pA) is an undesirable by-product. In a specific example of the propane to AA process, the preferred catalyst system consists of a mixed metal oxide of molybdenum, vanadium, niobium and tantalum (M〇/v/Te/Nb). When operating at a maximum AA yield (equal to or greater than (2) 85% oxygen conversion), such catalysts can be produced from 1, 〇〇〇 parts per million (ppm) to 1 〇〇 PA in the range of 〇〇ppm or less. Additionally, excess propionic acid by-products can impart undesirable characteristics to the acrylic acid (AE) and its corresponding polymeric product, such as high volatile organic content (VOC), odor or color, after esterification of the AA product. Prior to esterification, the pa specification of conventional propylene oxidized AA product streams is typically in the range of 5 〇〇 1 〇〇〇叩 paws, well below what is seen in the propane oxidation products. Therefore, in order to make propane oxidation more economically desirable, it is necessary to reduce the PA by-product content via the oxidation step or in the downstream separation step. There is a problem with the separation of propionic acid from acrylic acid. The boiling points of the two are less than (<)1 C and they cannot be separated by distillation. Although existing methods for separation (e.g., (4) crystallization) are present, these steps increase the capital and operating costs of the AA purification process by requiring additional (4) 3 201231451 and utility equipment to achieve the desired separation. Therefore, it can be protected in such a way that the formation of the wind corpse is reduced: the AA method makes it extravagant and desirable to reduce the cost and purity. SUMMARY OF THE INVENTION In one embodiment of the invention, the propylene oxidation process uses reduced steam to reduce the amount of PA in the process. The method for oxidizing propylene to acrylic acid typically comprises the step of contacting @烧, oxygen, steam and, optionally, a diluent gas (e.g., nitrogen) with a propane oxidation catalyst under oxidizing conditions. Since steam is necessary for the economic conversion of propane to AA, it cannot be intuitively apparent that it can be advantageous to significantly reduce the amount of steam in the process. However, surprisingly, when the vapor feed concentration is lowered, it is quite high. The PA content of the content will reduce the economic benefits of the method, although the loss of some corresponding AA production, but the capital and operating costs of the process required to separate the PA from the final product can compensate for the loss of production. This process can also be used to reduce the PA content of the products of conventional propylene or propane-containing propylene streams. In one embodiment, the invention is a process for the direct oxidation of propane to acrylic acid, the process comprising the steps of: containing 5-10% propane, 5-15% oxygen, 1-20% under oxidizing conditions (preferably 10-15%) a gas mixture of steam and the remaining diluent gas (expressed as a weight percent (wt%) based on the weight of the mixture) is contacted with a propane oxidation catalyst. The amount of PA produced is typically less than 1, 〇〇〇pprn or less than 750 ppm or less than 500 ppm. [Embodiment] 4 201231451 Definitions Unless otherwise stated, the context implies or is customary in the art, all parts are And percentages are by weight and all test methods are prior art methods up to the application period of the present invention. For the purposes of U.S. patent practice, the contents of any cited patent, patent application, or publication are hereby incorporated by reference in its entirety in its entirety herein in Definitions in the art (to the extent that they are inconsistent with any definition specifically provided in the present invention) and the disclosure of common sense. Numerical ranges in the present invention are approximate unless otherwise indicated, and thus may include values outside the range. The range of values includes all values from and including the lower and upper limits and incremented in __ units, with the proviso that there are at least two units of spacing between any lower limit and any upper limit. For example, if the compositional properties, physical properties, or other properties (such as, for example, molecular weight, etc.) are from 100 to 00, all individual values (such as 100, 101, 102, etc.) and subintervals (such as 1 明确 are explicitly enumerated). 〇 to 144, 155 to 170, 197 to 2, etc. h For a range containing values less than i or containing a number greater than i (eg, 1 · 1, 1.5, etc.), as the case may be, one unit It is considered to be 0.0001, 0.001, 0 01 or 〇丨. For a range containing a single digit number less than ι〇 (for example, to 5), one unit is typically considered. These ranges are only All possible combinations of the specified values and the numerical values between the lowest value and the highest value recited are considered to be explicitly stated in the present invention. In the present invention, a PA is specifically provided for the oxidation conditions of the party, the AA stream. The range of values for the content and its analogs. Method reactant 201231451 The starting material is usually a propane gas "at least one oxygen-containing gas, vapor and diluent gas. Propane does not have to meet any particularly high purity standards, and = may contain propylene or other Hydrocarbon or Hydrocarbons having heteroatoms as impurities. In a specific example, 'propane does not contain any appreciable amount of propylene, such as less than 丨wt%, or less than 〇5 wt%, or less than U by weight of propane. Propylene. In one embodiment, propane contains a relatively large amount (e.g., wt% or more) of propylene, such as found in lower grade propylene feeds such as lower propane feeds from a flow catalytic cracker. L Oxygen • The oxygen-containing gas used in the practice of the present invention may be pure oxygen, such as oxygen gas, oxygen gas or two or more such gases: the diluent gas is typically an inert gas such as (but not limited to nitrogen, wind, helium, and carbon dioxide. Diluted gases can be used to dilute substances and/or adjust space velocity, oxygen partial pressure, and vapor partial pressure. These can be used alone or with one or more other A gas combination is added to the party: In a specific example, 'Chenxuan can be supplemented or replaced with another alkane suitable for gas phase oxyaldehyde or carboxylic acid. 匕口堂蛊η - t spear, propane, the alkane pass Burning tobacco Typically, it is an Isomity or a Dingxuan. Other alkanes with Propylene do not have to meet any particularly high purity standards. They may contain one or more ~ dilute hydrocarbons as impurities. Typical dilute hydrocarbons include C: isobutylene, positive Butene, pentene and the like. Propylene, in a specific example, 'c3-8-tobacco feedstock replacement C-burning, can contain a large amount of hydrocarbons, for example up to 49 weights of two seats - a specific example Yin, The feed is isobutylene. /0). The suitable molar ratio of propane/oxygen/diluent gas/water and the feed ratio of propane/air/steam in the starting material gas mixture in 201231451 are known in the art. For example, the appropriate range is disclosed in USP 5,380,933. Typical ranges include propane. Oxygen: water·dilution gas is 1: (〇11〇): (〇_5〇): (〇_5〇), more typically 1. (0.5-5): (1- 30): (0-30). In one embodiment, the starting gas inoculant comprises from 5 weight percent (wt%) to 1% by weight or from 6% to 8% by weight of propane, l〇wt/i> to 20% by weight of oxygen; 1 wt% to wt% of steam; and the balance of nitrogen. Process Conditions The starting gas mixture is oxidized using an oxidation catalyst. The reaction is usually carried out under atmospheric pressure, but it can be carried out under elevated pressure or reduced pressure. The reaction pressure is typically in pounds per square inch (psig) to 100 psig, more typically from 〇psig to 5 〇 Psig (0 to 0.70 megapascals (MPa), more typically 〇Μρ & to 〇35 MPa) . The reaction temperature is usually (^ to woe, more typically 2 Torr (rc to 5 〇〇 ° C, even more typically 3001: to 48 (rc and even more typically 350 ° C to 440 ° C. gas). The space velocity is usually from 1 hrl to 1 Torr, more typically from 3 hr-i to M00W and even more typically from 300 hr·丨 to 3, hr·丨. Reactor _ starting gas The (iv) time of the mixture is typically from 0.1 second to 10 seconds, more typically from 1 second to 4 and. The oxidation catalyst is not poorly pleasing... The composition of the η genus emulsion catalyst can vary widely, and the 妯+ can be used. Any catalyst known to be used in the art for the oxidation of alkanes to unsaturated aldehydes and/or carboxylic acids is represented by a catalyst of formula I. Such catalysts 201231451 M〇iybMlcM2c〇n (1), wherein M1 is Te and/or Sb, M2 is selected from the group consisting of Nb ' Ta, W, Ti, A · 1, &, ^, _, Ga, Fe, ^, Co, Rh, Ni, pd ' pt, La,
Bl B Ce、Sn、Zn、Si及In組成之群之元素中之至少一 者—為0.01至l’c為>〇至1>d為至丄且订為由⑴ 甲除氧以外之元素的原子價及頻率所確定之數目。在一個 具體實例中’Μ’為Te且M、Nb。催化劑可經支撐或未經 支撐’且其可使用已知及市售設備藉由許多已知程序中之 任:者來製備（參見例如USP6，18M25)。典型支撐物包括 -氧化妙、氧化！ g、二氧化#、紹石夕酸鹽、石夕藻土及錯。 催化劑典型地呈粒子形心例如顆粒、粉末、丸粒、珠粒 等。催化劑形狀及催化劑粒徑可為了方便而變化。 反應器 、本發明之方法可在任意設計之固定床或流化床反應器 中進行。在—個具體實例中，該方法於流化床反應器中進 行。在一個具體實例十，該方法於固定床反應器中進行。 在一個具體實例中，該反應器為任意组態之管式反應 益，例如直線形、曲線形、螺旋形等。雖然管截面典型地 =圓形，但其可具有任何幾何形狀，例如卵形、多邊形等。 管截面沿著其長度典型地為均一的。若管截面並非圓形， 則跨越截面之最寬長度對應於具有圓截面之管的外徑。 官可由在高溫及高壓反應條件下保留其完整性且在反 應條件下對於反應起始物質、催化劑及反應產物為惰性的 何材料製成。例示性材料包括金屬（例如不鏽鋼）、陶免 8 201231451 及玻璃。管壁厚度亦可為了方便且在至少一個位準上變 化，其隨管的構建材料而變。 氧化催化劑典型地裝填於管中且在管的各端處或附近 由多孔塞或塞子固定。對於氧化反應之起始氣體混合物及/ 或氣體產物，塞為多孔的。催化劑以使得起始氣體混合物 在氧化條件下流經且圍繞催化劑粒子之方式裝填以便將丙 烷轉化為丙烯酸。工業化方法典型地每次採用一個以上管 式反應器，且此等反應器典型地捆於單個外殼中，經由外 殼使熱傳送流體在管之間及周圍通過以維持整個外殼及各 管中的均勻溫度。反應為放熱反應且因此釋放熱量。熱傳 送流體用於移除熱量且避免形成可能不利地影響催化劑之 熱點。合適的熱傳送介質包括無機鹽及d〇wthermtm產 品。反應器可由單個反應器級數、多個反應器級數於獨立 反應器財或多個反應器級數於單個反應胃殼中組成。選 擇反應器級數之最佳數目以使AA產率最大，同時維持經濟 的資本及操作成本。 藉由以下實施例進一步描述本發明。除非相反地指 出，否則所有份數及百分比皆以重量計。 特定具體實例 、此等實施例中所用之催化劑為根據USP 7,304,〇 14中所 述之料製備之高效能仏/㈣腸混合金屬氧化物。以下 霄包例在相似條件下試驗且在惶定氧轉化率下比較。 實施例1 將未經稀釋之催化劑裝料（4〇cc)裝入由卜于直徑黃 9 201231451 銅夾套包覆之0 25吋〇D 316不鏽鋼（SS)管中。夾套有 助於該方法之溫度控制及其等溫操作。以重量百分比計之 進料組成為6.0%丙烷、11.3%氧氣、40%蒸汽及餘量氮氣。 滞留時間為在大氣壓下3.0秒。調節反應器溫度得到所需轉 化率。藉由氣相層析（GC )分析氣體及液體產物。 實施例2 除進料組成為6.0 wt%丙烷、11.3 wt%氧氣、20 wt%蒸 汽及餘量氮氣以外，重複實施例1。 實施例3 除進料組成為6·0 wt%丙烧、11.3 wt%氧氣、1 〇 wt%蒸 Ά及餘量氮氣以外，重複實施例i。 貫施例4 除進料組成為6.0 wt%丙烷、11·3 wt%氧氣' 5 wt%蒸 飞及餘量氮氣以外，重複實施例1。 四個試驗結果記錄於下表中。資料清楚展示蒸汽減少 至小於20 wt%導致PA產量減少，其他一切相同。 表 ---- 實 施例1 -4之反應條件及結3 蒸汽含量，％ 溫度，°C C3轉化率，。/〇 〇2轉化率，％ AA產率，。/。 PA > ppm 2 40 350 59.0 73.4 41.0 1700 20 355 60.0 77.0 42.4 950 [列 3 10 360 62.5 80.0 42.4 470 4 5 360 59.9 77.8 41.1 330 雖然本發明已經由較佳具體實例之先前描述而在一定 筇上被描述，但此細節主要目的為說明。在不悖離如以 10 201231451 下申請專利範圍令所述之本發明之精神及範疇的情況下， 可由熟習此項技術者進行許多變化及修改。 【圖式簡單說明】 無 【主要元件符號說明】 無At least one of the elements of the group consisting of Bl B Ce, Sn, Zn, Si, and In—from 0.01 to 1'c is > 〇 to 1> d is 丄 and is ordered by (1) an element other than oxygen. The number determined by the valence and frequency. In a specific example, 'Μ' is Te and M, Nb. The catalyst can be supported or unsupported' and can be prepared by any of a number of known procedures using known and commercially available equipment (see, e.g., USP 6, 18M25). Typical supports include - oxidation, oxidation! g, dioxide #, Shao Shi Xi acid, Shi Xizao soil and wrong. The catalyst is typically in the form of a particle heart such as granules, powder, pellets, beads, and the like. The shape of the catalyst and the particle size of the catalyst can be varied for convenience. The reactor, the process of the invention can be carried out in a fixed bed or fluidized bed reactor of any design. In a specific example, the process is carried out in a fluidized bed reactor. In a specific example 10, the process is carried out in a fixed bed reactor. In one embodiment, the reactor is of any configuration tubular reaction, such as linear, curved, spiral, and the like. Although the tube section is typically = circular, it can have any geometric shape, such as oval, polygonal, and the like. The tube section is typically uniform along its length. If the tube section is not circular, the widest length across the section corresponds to the outer diameter of the tube having a circular cross section. The granule can be made of any material which retains its integrity under high temperature and high pressure reaction conditions and which is inert to the reaction starting materials, catalysts and reaction products under the reaction conditions. Exemplary materials include metals (eg, stainless steel), Taobao 8 201231451, and glass. The wall thickness can also be varied for convenience and at least one level, which varies with the material of the tube construction. The oxidation catalyst is typically packed in a tube and secured by a porous plug or plug at or near each end of the tube. For the starting gas mixture and/or gaseous product of the oxidation reaction, the plug is porous. The catalyst is charged in such a manner that the starting gas mixture flows under oxidizing conditions and around the catalyst particles to convert the propane to acrylic acid. Industrialization methods typically employ more than one tubular reactor at a time, and such reactors are typically bundled in a single outer casing through which the heat transfer fluid passes between and around the tubes to maintain uniformity throughout the outer casing and tubes. temperature. The reaction is an exothermic reaction and thus releases heat. The heat transfer fluid is used to remove heat and to avoid the formation of hot spots that may adversely affect the catalyst. Suitable heat transfer media include inorganic salts and d〇wthermtm products. The reactor may consist of a single reactor stage, multiple reactor stages in a separate reactor or multiple reactor stages in a single reaction stomach shell. The optimum number of reactor stages is chosen to maximize AA yield while maintaining economic capital and operating costs. The invention is further described by the following examples. All parts and percentages are by weight unless otherwise indicated. Specific Examples The catalysts used in these examples are high performance cerium/(iv) enteric mixed metal oxides prepared according to the materials described in U.S. Patent No. 7,304, filed on. The following examples of bags are tested under similar conditions and compared at a reduced oxygen conversion. Example 1 An undiluted catalyst charge (4 cc) was charged into a 0 25 吋〇D 316 stainless steel (SS) tube covered with a diameter yellow 9 201231451 copper jacket. The jacket contributes to the temperature control of the method and its isothermal operation. The feed composition in percent by weight is 6.0% propane, 11.3% oxygen, 40% steam and the balance nitrogen. The residence time is 3.0 seconds at atmospheric pressure. The reactor temperature was adjusted to obtain the desired conversion rate. Gas and liquid products were analyzed by gas chromatography (GC). Example 2 Example 1 was repeated except that the feed composition was 6.0 wt% propane, 11.3 wt% oxygen, 20 wt% steam, and the balance nitrogen. Example 3 Example i was repeated except that the feed composition was 6.00 wt% propane, 11.3 wt% oxygen, 1 wt% steam and the balance nitrogen. Example 4 Example 1 was repeated except that the feed composition was 6.0 wt% propane, 11.3 wt% oxygen '5 wt% evaporated and the balance nitrogen. The four test results are recorded in the table below. The data clearly shows that steam reduction to less than 20 wt% results in a decrease in PA production, everything else is the same. Table ---- Reaction conditions of Example 1-4 and knot 3 Steam content, % temperature, °C C3 conversion. /〇 〇2 conversion rate, % AA yield,. /. PA > ppm 2 40 350 59.0 73.4 41.0 1700 20 355 60.0 77.0 42.4 950 [Column 3 10 360 62.5 80.0 42.4 470 4 5 360 59.9 77.8 41.1 330 Although the invention has been described above by a preferred embodiment It is described, but the main purpose of this detail is to illustrate. Many variations and modifications can be made by those skilled in the art without departing from the spirit and scope of the invention as set forth in the appended claims. [Simple diagram description] None [Main component symbol description] None