摘要
负载液相催化剂(SLPC)兼具均相催化剂和非均相催化剂的优点。为此,本文针对甲醇气相氧化羰基化合成碳酸二甲酯反应,进行了负载液相催化剂制备、表征及反应性能的研究,并优化了反应条件。
在固定床反应器上考察了液膜相溶剂种类和负载量、活性组分负载量、浸渍方式及载体等对SLPC催化合成碳酸二甲酯反应性能的影响。结果表明:由CuCl_2, PdCl_2及KOAc构成的活性组分具有催化活性;以二甘醇作为液膜相溶剂的SLPC上碳酸二甲酯的空时收率高于以四甘醇作为液膜相溶剂的SLPC,当二甘醇的负载量为37.1%时,碳酸二甲酯的空时收率可达1040g/L-cat·h。在活性炭、SiO_2、γ-Al_2O_3等载体中,只有活性炭载体具有催化活性,且不同种类活性炭载体的催化活性有较大差别。
采用BET、XRD、XPS及SEM等表征方法对SLPC的表面性质和结构进行了研究。二甘醇溶剂相的存在使活性组分的分布更为均匀,从而提高了催化合成碳酸二甲酯的活性。活性炭表面存在的含氧官能团促使Cu2+还原,进而使之具有催化活性。SLPC的比表面较载体大幅度下降而初期活性大幅度提高,这一现象也说明了液膜相的存在。催化剂活性随运转时间下降的原因是液膜相溶剂的流失。
考察了操作条件对催化剂反应性能的影响,适宜的反应条件为:压力0.3MPa、反应温度160℃、原料气空速7168 h~(-1)、进料组成MeOH/CO/O_2=3.6/2.3/1。比较了负载液相催化剂与固相催化剂的催化性能,负载液相催化剂的活性要明显高于固相催化剂。经XRD表征,固相催化剂上出现的KCl晶相在负载液相催化剂上消失。
SLPC has effectively combined the features of homogeneous and heterogeneous catalyst. Selecting PdCl_2、CuCl_2 and KOAc as active components of SLPC, and gas-phase oxidative carbonylation of methanol to DMC on it were studied. Multiple technique including BET、XRD、XPS and SEM were used to characterize the morphological and electronic structure of the catalysts.
SLPC were prepared using DEG and TetraEG as liquid-phase solvent respectively. The catalytic activity of DEG-PdCl_2-CuCl_2-KOAc/AC is better than it of TetraEG-PdCl_2-CuCl_2 -KOAc /AC. When the loading of DEG is 37.1%(wt%), STY of DMC reached to 1040g·(L-cat·h)~(-1); SEM testified that DEG can make distribution of active component on surface of catalyst better, but remarkably decline of the surface area of catalyst with the increase of loading of DEG is verified by BET. The catalysts have no catalytic activity , whose supports are SiO_2 andγ-Al_2O_3, and coal activated carbon is better than coconut shell activated carbon as the supports. The main reason for this result is their chemical properties, XPS show that Cu~+ appear on PdCl_2-CuCl_2-KOAc/AC, and the active site is Pd~(2+) and Cu~+ in this reaction, but there is not Cu~+ on PdCl_2- CuCl_2- KOAc /SiO_2. There are many functional groups containing oxide on the surface of activated carbon, such as carboxyl, carbonyl and quinonyl. these groups are thought the reduction site in the surface of activated carbon, however, SiO_2 andγ-Al_2O_3 don’t possess this function.
The effects reaction conditions on catalytic performance were studied, the optimal reaction conditions were obtained through experiment: 0.3Mpa, 160℃, 7168h~(-1), molar ratio of MeOH, CO and O_2 is 3.6:2.3:1. The catalytic activity of SLPC is higher than the supported solid catalyst. The XRD pattern show that there is crystal phase of KCl on the surface of supported solid catalyst PdCl_2-CuCl_2-KOAc/AC and PdCl_2- CuCl_2- KOAc /SiO_2, but it don’t appear on the surface of DEG-PdCl_2-CuCl_2-KOAc/AC, The DEG added result in this situation.
引文
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