Abstract: Liquid-phase oxidation of toluene by air is an environment friendly technology to produce benzoic acid.In SNIA benzoic acid process, two heat exchangers are used to remove the reaction heat.However, severe scaling often occurs, especially on the tube surface of the exchangers.In the present study the scale was detected to be precipitates of CoC₂O₄&#8226;2H₂O, which was formed from the catalyst Co ion and the by-product oxalic acid.In the oxidation intermediate products of toluene, oxalic acid, maleic acid and hydroquinone were detected by HPLC.According to the research results,oxalic acid was formed through the deep oxidation of toluene or its derivates.Reaction temperature, pressure, air flow and the contents of benzene, water, benzoic acid, as well as the catalyst amount all affected scaling significantly.It was observed that the factors which inhibited the oxidation to benzoic acid enhanced scale formation.Aeration rate influenced the scaling reversely.Impurities, such as benzene or water, increased the scaling amount.Scale decreased with increasing Co content(<100 μg&#8226;g^-1).Less effect of reaction pressure was observed.

摘要： 甲苯液相空气氧化是环境友好的苯甲酸生产工艺.在SNIA苯甲酸生产过程中，CoC2O4&#8226;2H2O的生成导致甲苯氧化过程产生严重的结垢现象，严重影响生产的正常运行.通过液相色谱对反应中间产物进行检测，发现有痕量的对苯二酚、马来酸、草酸生成.对生成CoC₂O₄&#8226;2H₂O的可能途径进行了分析和研究，结果表明，通过苯、甲苯及其衍生物氧化生成草酸是导致结垢的主要原因.通过改变反应物组成及操作条件，对反应温度、操作压力、空速、催化剂用量、苯含量以及含水量等因素对结垢的影响进行了研究.结果表明，当生成苯甲酸的目标反应受到抑制时，结垢明显加剧.随着反应体系中的苯含量或含水量的增大，其结垢加剧.当催化剂浓度低于100 μg&#8226;g^-1时，随Co含量的增大，其结垢减轻.当反应体系中无苯甲酸时，反应受到抑制，结垢严重.当空气鼓气量低于4.0×10-3 m³&#8226;min^-1时，随空气鼓气量的增大，其结垢减轻.操作压力对结垢的影响较小.反应温度低于155 ℃时，反应受到抑制同时结垢加剧.