苯氧化法 苯氧化為順酐是在催化劑存在下進行的。

　　The oxidation of benzene to maleic anhydride by the benzene oxidation method is carried out in the presence of a catalyst.

　　常用催化劑的活性組分均為釩的氧化物（見金屬氧化物催化劑），為抑制苯被完全氧化，常加入鉬、磷、鈦、鎢、銀及堿金屬等元素的氧化物為添加劑，并采用低比表面的惰性物質為催化劑載體，如 α－氧化鋁、剛玉等。反應在常壓下進行，溫度350～400℃。工藝過程由苯的氧化，順酐的分離和提純兩大部分組成。

　　The active component of commonly used catalysts is vanadium oxide (see metal oxide catalysts). To suppress the complete oxidation of benzene, oxides of elements such as molybdenum, phosphorus, titanium, tungsten, silver, and alkali metals are often added as additives, and low specific surface area inert substances such as alpha alumina and corundum are used as catalyst carriers. The reaction is carried out under normal pressure at a temperature of 350-400 ℃. The process consists of two main parts: the oxidation of benzene, the separation and purification of maleic anhydride (see figure).

　　苯蒸氣和空氣能形成爆炸混合物，所以進入反應器的混合氣中，苯的濃度應在爆炸極限之外，一般為1%～1.4%(摩爾)。苯氧化為強放熱反應，工業上常采用列管式固定床反應器，有很大的傳熱面，管外為冷卻系統，反應熱可用于產生高壓蒸汽。

　　Benzene vapor and air can form explosive mixtures, so the concentration of benzene in the mixed gas entering the reactor should be outside the explosive limit, generally ranging from 1% to 1.4% (moles). The oxidation of benzene is a highly exothermic reaction, and a tubular fixed bed reactor is commonly used in industry, which has a large heat transfer surface and a cooling system outside the tube. The reaction heat can be used to generate high-pressure steam.

　　離開反應器的氣體中含順酐約1%（摩爾）,用冷卻的辦法可將其中所含一半左右的順酐冷凝為液體，其余部分則用吸收法回收。吸收劑用水或惰性有機溶劑，大多數工廠采用的是水。

　　The gas leaving the reactor contains about 1% (mole) of maleic anhydride. About half of the maleic anhydride can be condensed into liquid by cooling, and the remaining part can be recovered by absorption method. Absorbents use water or inert organic solvents, and most factories use water.

　　所得到的吸收液是順丁烯二酸的水溶液，濃度35%～40%(質量)，需用共沸溶劑（例如二甲苯、苯甲醚）進行脫水，把酸重新轉化成酸酐。脫水也可在膜式蒸發器中進行。粗酐經減壓精餾可得成品。

　　The obtained absorbent is an aqueous solution of maleic acid with a concentration of 35% to 40% by mass. It needs to be dehydrated using azeotropic solvents such as xylene and benzyl ether to convert the acid back into anhydride. Dehydration can also be carried out in a membrane evaporator. Crude anhydride can be distilled under reduced pressure to obtain the finished product.

　　以苯計算，整個過程的順酐收率為92%～96%（質量）。 C4烴氧化法 正丁烷與丁烯均含有與順酐相同的碳原子數，是順酐的理想原料。由于正丁烷較其他原料低廉，用正丁烷更為有利。其流程與苯氧化法基本相同，催化劑為釩-磷-氧體系，添加劑有鐵、鉛、鋅、銅、銻等元素的氧化物。

　　Calculated based on benzene, the yield of maleic anhydride in the entire process is 92% to 96% (by mass). Both n-butane and butene produced by C4 hydrocarbon oxidation method contain the same number of carbon atoms as maleic anhydride, making them ideal raw materials for producing maleic anhydride. Due to the lower price of n-butane compared to other raw materials, using n-butane is more advantageous. The process is basically the same as the benzene oxidation method, with a vanadium phosphorus oxygen system as the catalyst and oxides of iron, lead, zinc, copper, antimony and other elements as additives.

　　可用固定床反應器或用流化床反應器，反應溫度約400℃。

　　Fixed bed reactors or fluidized bed reactors can be used, with a reaction temperature of approximately 400 ℃.

　　正丁烷-空氣混合物中正丁烷濃度為1.0%～1.6%(摩爾)。整個過程的順酐收率按正丁烷計約為50%。由于C4烴氧化的選擇性較低,因此設備投資較以苯為原料時為高，且后加工不能采用部分冷凝，而必須將反應氣體中的順酐全部用吸收法回收，從而使能耗加大。但由于正丁烷比苯便宜，而且苯毒性大。因此，以正丁烷為原料是有吸引力的，對本法所用催化劑的改進工作，各國都在大力進行中。

　　The concentration of n-butane in n-butane air mixture is 1.0% to 1.6% (mol). The yield of maleic anhydride in the entire process is about 50% based on n-butane. Due to the low selectivity of C4 hydrocarbon oxidation, the equipment investment is higher than when benzene is used as the raw material, and partial condensation cannot be used for post-processing. Instead, all the maleic anhydride in the reaction gas must be recovered by absorption method, resulting in increased energy consumption. But due to the lower price of n-butane compared to benzene, and the high toxicity of benzene. Therefore, using n-butane as the raw material is attractive, and improvements to the catalyst used in this method are being vigorously carried out in various countries.

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