Gore膜在高纯磷酸制备中的应用及性能研究
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摘要
磷酸按生产方法可分为热法磷酸和湿法磷酸,按用途可分为农业级、工业级、食品级和半导体级磷酸。高纯磷酸是指食品级磷酸和半导体级磷酸等高纯度、高浓度的磷酸。从热法磷酸出发来制取高纯磷酸是目前磷酸生产发展的一大趋势。热法磷酸中含有少量重金属杂质,主要是铅以及微量的锌、铜、镍、锰、铬和镉等。通过在热法磷酸中加入重金属的脱除剂使之生成沉淀过滤除去,从而实现磷酸的净化。
     本研究中,以五硫化二磷为重金属脱除剂与工业级热法磷酸在水浴中加热并搅拌的条件下进行反应和沉降,首次采用Gore膜对磷酸进行过滤,代替通常使用的化纤滤布进行过滤,通过正交试验分析了各因素对除铅率影响的大小;通过单因素实验,研究了反应温度、反应压强、反应时间、除铅剂用量、沉降时间和Gore膜过滤次数等因素对除铅率的影响规律;进而测定了Gore膜过滤磷酸时的截留率、过滤常数、滤饼的压缩性指数、过滤阻力等性能,并与传统使用的滤布进行了对比。
     通过实验,得到如下结论:
     (1)在高纯磷酸生产中用Gore膜代替传统的滤布过滤,经实验证明是可行的。该法大大地提高了磷酸的净化效率,除铅效果远优于传统的
    
     Gore膜在商纯磷酸制备中的应用及性能月开究刘伟升
    方法,一次过滤即可使除铅率达到86.9%,最优条件下除铅率可达95.5
    %。可以一次滤掉绝大部分固相杂质,净化后磷酸澄清透明,效果很好。
     (2)综合考虑生产实际,以Gore膜为过滤介质,得到净化工业磷酸
    的较佳工艺条件为:反应温度80℃,反应压力Zxl05Pa,反应时间60min,
    PZSS用量0.2%,沉降时间48h,Gore膜过滤2次。在此条件下,重金属
    的一次脱除率达95.5%,重金属含量可降至2.6ppm。
     (3)在16.38KPa,24.66KP,32.goKPa下,Gore膜对磷酸的过滤常数
    尤分别为0.252 lmz/s,o.3719mZ/s,o.4sgzmZ/s,磷酸试样的特性常数
    卜l.25oZx一。一,m4/(N .5),滤饼的压缩指数:=0.05,Gore膜的介质常数分别
    为e。=10105,。。一o.14s3m,/m,。滤饼可视为不可压缩物质。
     俨)Gore膜的总阻力主要以滤饼阻力R。为主,说明该膜本身的阻力
    占分率较小。对于过滤微细悬浮物的操作,用Gore膜较为适宜。
     (5)在16.376KPa下,过滤时间275秒时,Gore膜截留率高达93.3%,
    明显优于747”滤膜和758”滤膜,可见其对磷酸中杂质的截留效果很好。
Phosphoric acid is grouped as four kinds by its production method, that is agricultural grade, technical grade, food grade and semiconductor grade. High purity phosphoric acid means food grade, semiconductor grade and other high purity and high concentration phosphoric acid. At present the production of high purity phosphoric acid is one big developmental tendency from the beginning of hot-process phosphoric acid. Hot-process phosphoric acid contains a little impurities which are mainly Pb and very little Zn, Cu, Ni, Mn, Cr and Cd. Phosphoric acid can be purified through adding heavy metal removal reagent to form sedimentations and then filtrate to get rid of them.
    In this study, P2S5 was used as heavy metal removal reagent to react with technical grade phosphoric acid heated by water bath, beat up, filtrated by Gore membrane at the first time instead of the normally used filtration cloth.
    
    
    
    
    Through orthorhombic experiment, the effect abilities of six factors were studied; through single factor experiment, the effect laws of react time, react temperature, react pressure, dosage of P2S5, filtration times by Gore membrane and sedimentation time were determined; then Gore membrane's interception rate, filtration constant, condensation exponent of filtration cake, filtration resistance, etc. were determined and compared with 747# and 758# filtration cloths.
    These following conclusions were drawn on the basis of the experiments:
    (1) It is feasible to use Gore membrane instead of filtration cloth to purify phosphoric acid in the production of high purity phosphoric acid. This method can greatly improve the filtration efficiency and the filtration effect is much better than the traditional method, the Pb removal rate can reaches 86.9 % filtrating once by Gore membrane and the rate is 95.5% at the best technical conditions. Gore membrane can successfully filtrate most of the impurities by once, the filtration effect is good and the phosphoric acid is clear and transparent after filtration.
    (2) Considering the practical production , the best technical conditions are : reaction time 60min, reaction pressure 2 105Pa ,reaction temperature 80 C, dosage of P2S5 0.2%, sedimentation time48h , filtration times 2 by Gore
    
    
    
    
    membrane . At the conditions, the Pb removal rate can reach 95.5% and the quantity of heavy metals decline to 2.6ppm.
    (3) At the pressure of 16.38Kpa, 24.66KP, 32.90KPa, the filtration constants when filtrating phosphoric acid by Gore membrane are K=0.2521m2/s, 0.3719m2/s, 0.489Im2/s respectively . The characteristic constant of phosphoric acid is k=1.2502 10-5m4/(N.s), the condensation exponent of filtration cake is s=0.05. Gore membrane's medium constants are :
    e=1010s, qe= 0.1483 m3/m2. The filtration cake can be regarded as impressible cake.
    (4) The general resistance of gore membrane are mainly the filtration cake resistance RC, it means the resistance of gore membrane itself is small. So it is more suitable to use Gore membrane when filtrating some fine suspending.
    (5) The interception rate of Gore membrane is 93.3% at 16.38Kpa and filtrating for 275 seconds. This rate is much better than those of 747# and 758 # filtration cloths. This demonstrates Gore membrane has good interception effect to the impurities in the phosphoric acid
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