苯氧化法 苯氧化为顺酐是在催化剂存在下进行的。

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

　　常用催化剂的活性组分均为钒的氧化物（见金属氧化物催化剂），为抑制苯被完全氧化，常加入钼、磷、钛、钨、银及碱金属等元素的氧化物为添加剂，并采用低比表面的惰性物质为催化剂载体，如 α－氧化铝、刚玉等。反应在常压下进行，温度350～400℃。工艺过程由苯的氧化，顺酐的分离和提纯两大部分组成。

　　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).

　　苯蒸气和空气能形成爆炸混合物，所以进入反应器的混合气中，苯的浓度应在爆炸极限之外，一般为1%～1.4%(摩尔)。苯氧化为强放热反应，工业上常采用列管式固定床反应器，有很大的传热面，管外为冷却系统，反应热可用于产生高压蒸汽。

　　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.

　　离开反应器的气体中含顺酐约1%（摩尔）,用冷却的办法可将其中所含一半左右的顺酐冷凝为液体，其余部分则用吸收法回收。吸收剂用水或惰性有机溶剂，大多数工厂采用的是水。

　　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.

　　所得到的吸收液是顺丁烯二酸的水溶液，浓度35%～40%(质量)，需用共沸溶剂（例如二甲苯、苯甲醚）进行脱水，把酸重新转化成酸酐。脱水也可在膜式蒸发器中进行。粗酐经减压精馏可得成品。

　　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.

　　以苯计算，整个过程的顺酐收率为92%～96%（质量）。 C4烃氧化法 正丁烷与丁烯均含有与顺酐相同的碳原子数，是顺酐的理想原料。由于正丁烷较其他原料低廉，用正丁烷更为有利。其流程与苯氧化法基本相同，催化剂为钒-磷-氧体系，添加剂有铁、铅、锌、铜、锑等元素的氧化物。

　　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.

　　可用固定床反应器或用流化床反应器，反应温度约400℃。

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

　　正丁烷-空气混合物中正丁烷浓度为1.0%～1.6%(摩尔)。整个过程的顺酐收率按正丁烷计约为50%。由于C4烃氧化的选择性较低,因此设备投资较以苯为原料时为高，且后加工不能采用部分冷凝，而必须将反应气体中的顺酐全部用吸收法回收，从而使能耗加大。但由于正丁烷比苯便宜，而且苯毒性大。因此，以正丁烷为原料是有吸引力的，对本法所用催化剂的改进工作，各国都在大力进行中。

　　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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