摘要
将二氧化碳进行化学利用是减少大气中二氧化碳浓度的有效方法,在众多将二氧化碳转化为有机物的研究中,目前实现产业化的只有二氧化碳基生物降解塑料和尿素。尿素的工业化生产主要有氰氨化钙法和CO_2法,其中氰氨化钙法没有实现大规模工业化应用,目前世界上广泛采用氨和二氧化碳直接制备尿素法。以二氧化碳为原料制备尿素工艺又可分为水溶液全循环法、二氧化碳汽提法和氨汽提法。三种工艺各有优缺点,总体来看,水溶液全循环法成本较高;二氧化碳汽提法与前者相比,设备减少,流程简化,能耗降低;二氧化碳汽提法与氨汽提法相比,汽提压力降低,汽提效率提高,因此该工艺仅需低压分解而无需中压分解,对于新建尿素装置来说,二氧化碳汽提工艺投资较少,因此近年来新建尿素装置及大型尿素装置改造大都采用该工艺。目前对尿素制备反应的认识始终围绕着与甲铵相关的两个反应——生成甲铵的反应及甲铵脱水生成尿素的反应而展开。尽管工业上以二氧化碳和氨制备尿素有三种不同的工艺,但工艺条件均为高温高压,主要原因是没有找到合适的催化剂,因而研究者们一直在致力于常温常压条件下制备尿素的研究,不断在新型催化反应、光催化反应和电还原反应等方面进行探索。
Chemical utilization of CO2 is an effective way to reduce the CO2 concentration in the atmosphere.Among many studies on the conversion of CO2 into organics,only CO2-based biodegradable plastics and urea have been industrialized.The industrial production of urea mainly adopts calcium cyanamide process and CO2 process.Large-scale industrialized application of calcium cyanamide process has not been achieved,and ammonia and CO2 are widely used for urea production in the world.The urea production processes using CO2 can be divided into aqueous solution total recycle process,CO2 stripping process and ammonia stripping process,each has its own advantages and disadvantages.In general,the aqueous solution total recycle process has a relatively high cost.Compared with the aqueous solution total recycle process,the CO2 stripping process has fewer equipment,simpler process flow and lower energy consumption.Compared with the ammonia stripping pro-cess,the CO2 stripping process has lower stripping pressure and higher stripping efficiency,so it only requires low pressure decomposition instead of medium pressure decomposition.For grassroots urea plant,CO2 stripping process requires less investment,therefore,it has been used in most of the grassroots urea plant and large-scale revamped urea plant in recent years.At present,the understanding of urea production reaction focuses on two reactions related to carbamate,i.e.the reaction of carbamate formation and the dehydration reaction of carbamate to urea.Although there are three different processes for urea production using CO2 and ammonia in the industry,high temperature and high pressure are required because no suitable catalyst has been found.Therefore,researchers have been committed to the study on urea production at normal temperature and pressure and continuously explored in the fields of new catalytic reaction,photocatalytic reaction and electroreduction reaction.
作者
史建公
刘志坚
刘春生
Shi Jiangong;Liu Zhijian;Liu Chunsheng(Engineering Technology Research Institute of SINOPEC Catalyst Co.,Ltd.,Beijing 101111;SINOPEC Catalyst Co.,Ltd.,Beijing 100029;Sino-Global Energy,Beijing 100011)
出处
《中外能源》
CAS
2019年第1期68-79,共12页
Sino-Global Energy
关键词
二氧化碳
尿素
氨
二氧化碳汽提法
甲铵脱水
高温高压
carbon dioxide
urea
ammonia
carbon dioxide stripping
carbamate dehydration
high temperature and high pressure
