Ca-Mg-Al复合氧化物催化尿素与1,2-丙二醇制碳酸丙烯酯

doi:10.16085/j.issn.1000-6613.2019-1784

摘要/Abstract

摘要：

采用共沉淀法制备了系列Ca-Mg-Al复合氧化物催化剂，通过对沉淀剂配比、沉淀液pH值及焙烧温度等制备条件的考察，得到以Na₂CO₃为沉淀剂、pH=9.5、850℃下焙烧4h制备的Ca-Mg-Al催化活性最高。在 n(PG)∶n(urea)=1.5∶1、反应温度为145℃、绝压20kPa、反应时间4h、催化剂用量为尿素质量的5%时，碳酸丙烯酯收率达到84.6%。采用XRF、XRD、NH₃-TPD、SEM及BET对催化剂的组成、晶型及酸性进行了表征，发现随着沉淀剂中Na₂CO₃的含量增加，催化剂中CaO∶MgO的比例增大，碳酸丙烯酯的收率亦升高；经850℃焙烧后，催化剂中存在CaO和MgO两种活性中心，起协同催化作用；随着焙烧温度由700℃升高到850℃，NH₃-TPD脱附曲线向低温方向偏移，且强酸中心NH₃脱附峰面积比由81.14%明显下降为0，中强酸中心NH₃脱附峰面积比由0增加到78.07%，而碳酸丙烯酯收率由68%增加到84.6%，这表明催化剂强酸性位的减少是催化活性增加的主要原因。

关键词: 钙镁铝催化剂, 碳酸丙烯酯, 催化剂, 制备, 选择性

Abstract:

A series of Ca-Mg-Al mixed oxide catalysts were prepared by co-precipitation method. Through the investigation of the preparation conditions such as the ratio of precipitant, pH of precipitation solution and calcination temperature, it was found that the highest activity of Ca-Mg-Al catalyst was obtained when Na₂CO₃was used as precipitant, pH=9.5 and calcined at 850℃ for 4h. When the ratio of n(PG)∶n(urea) is 1.5∶1, the reaction temperature is 145℃, 20kPa (absolute pressure), the reaction time is 4h and the amount of catalyst is 5%, the yield of propylene carbonate is 84.6%. The composition, crystal form and acidity of the catalyst were characterized by XRF, XRD, NH₃-TPD, SEM and BET. It was found that with the increase of the content of Na₂CO₃ in the precipitant, the ratio of CaO to MgO in the catalyst increased, and the yield of propylene carbonate also increased. After calcination at 850℃, there were two active centers of CaO and MgO in the catalyst, which played a synergistic catalytic role. With the increase of calcination temperature from 700℃ to 850℃, the NH₃-TPD desorption shifted to low temperature, and the area ratio of NH₃ desorption peaks in strong acid center deceased significantly from 81.14% to 0. The area ratio of NH₃ desorption peaks in middle acid center increased from 0 to 78.07%, and the yield of propylene carbonate (PC) increased from 68% to 84.6%, which indicates that the decrease in the strong acid sites of the catalyst is the main reason for the increase in catalytic activity.

Key words: Ca-Mg-Al catalyst, propylene carbonate, catalyst, preparation, selectivity

中图分类号:

TQ225.52

柳鑫, 徐新, 王陇豫, 柴博, 周瑞梅, 于晶, 罗国华, 靳海波, 戴晓兵. Ca-Mg-Al复合氧化物催化尿素与1,2-丙二醇制碳酸丙烯酯[J]. 化工进展, 2020, 39(S1): 163-169.

Xin LIU, Xin XU, Longyu WANG, Bo CHAI, Ruimei ZHOU, Jing YU, Guohua LUO, Haibo JIN, Xiaobing DAI. Synthesis of propylene carbonate from urea and 1, 2-propanediol catalyzed by Ca-Mg-Al composite oxide[J]. Chemical Industry and Engineering Progress, 2020, 39(S1): 163-169.

图/表 15

表1 不同沉淀剂配比的催化剂的XRF表征数据

n(NaOH)∶n(Na₂CO₃)	Ca-Mg-Al催化剂各氧化物含量/%			n(CaO）∶n(MgO)
n(NaOH)∶n(Na₂CO₃)	CaO	MgO	Al₂O₃	n(CaO）∶n(MgO)
4∶1	35.5	43.7	16.9	0.81
1∶1	40.2	39.8	17.9	1.01
0（无NaOH）	55.2	29.2	15.6	1.89

图1 不同焙烧温度所制Ca-Mg-Al催化剂的XRD表征图a—500℃焙烧后；b—600℃焙烧后；c—700℃焙烧后；d—850℃焙烧后；e—900℃焙烧后

图2 不同焙烧温度所制Ca-Mg-Al催化剂的SEM图

表2 不同焙烧温度所制得的Ca-Mg-Al催化剂的BET表征结果

焙烧温度/℃	比表面积/m²·g^-1	平均孔径/nm	孔容/cm³·g^-1
800	85.94	7.95	0.17
850	132.09	9.10	0.31
900	83.28	14.04	0.36

图3 不同焙烧温度的催化剂的NH3-TPD表征

表3 Ca-Mg-Al催化剂的NH3-TPD结果

焙烧温度/℃	温度/℃			总面积	峰面积占总面积的百分比/%
焙烧温度/℃	Ⅰ	Ⅱ	Ⅲ	总面积	Ⅰ	Ⅱ	Ⅲ
700	142	—	350	547.71	18.86	—	81.14
800	150	—	378	418.11	24.85	—	75.15
850	143	285	—	274.64	21.93	78.07	—

图4 沉淀剂配比对催化性能的影响

图5 沉淀液pH对催化剂性能的影响

图6 焙烧温度对催化剂性能的影响

图7 反应时间对PC收率的影响

图8 催化剂用量对PC收率的影响

图9 尿素和1，2-丙二醇反应合成PC步骤及副反应

表4 催化剂反应前后对PC收率及选择性的影响

催化剂类型	收率/%	选择性/%
新鲜催化剂	84.6	98.7
回收的催化剂（未焙烧）	43.6	89.2
回收的催化剂（850℃焙烧）	82.5	95.2
MgO	78.4	97.6

表5 催化剂重复使用次数对PC收率及选择性的影响

催化剂使用次数	收率/%	选择性/%
1	84.6	98.7
2	82.5	95.2
3	81.4	94.8
4	77.6	93.3
5	50.2	90.5

图10 反应前后催化剂的XRD表征a—商品MgO；b—新鲜催化剂；c—回收的催化剂（未焙烧）；d—回收的催化剂（850℃焙烧再生后）

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