生物柴油氧化機(jī)理及其潤滑性演變分析

周大平　魏海軍　王忠誠　吳剛　丘燁

摘要：由于生物柴油的氧化安定性較差，導(dǎo)致其無法大規(guī)模應(yīng)用。為找出生物柴油氧化后成分變化及其對油液潤滑性的影響，對體積分?jǐn)?shù)為5%、10%、20%、50%和100%的B5、B10、B20、B50、B100生物柴油進(jìn)行氧化，并通過傅里葉變換紅外光譜分析和四球機(jī)摩擦磨損實(shí)驗(yàn)對生物柴油的氧化產(chǎn)物及氧化后油液的潤滑性進(jìn)行檢測。實(shí)驗(yàn)結(jié)果顯示，在生物柴油氧化過程中CC不飽和鍵和酯基中的CO羰基含量下降，但是氫過氧化物以及羧酸、醛、酮類含氧化物含量增加。隨著氧化實(shí)驗(yàn)的進(jìn)行，生物柴油的氧化促進(jìn)了油液潤滑性的提高，且在氧化8 h時(shí)測試出的磨斑直徑最小即潤滑性最好;超過8 h后，生物柴油的酸值對油膜的破壞導(dǎo)致其潤滑性能下降。因此，生物柴油短時(shí)間內(nèi)氧化有助于提高油液的潤滑性，但長時(shí)間氧化會(huì)導(dǎo)致酸值過高降低其潤滑性。

關(guān)鍵詞：生物柴油; 氧化; 官能團(tuán); 潤滑分析

中圖分類號(hào)：? U677;TQ517.4

文獻(xiàn)標(biāo)志碼：A

Analysis on oxidation mechanism and lubricity evolution of biodiesel

ZHOU Daping， WEI Haijun， WANG Zhongcheng， WU Gang， QIU Ye

（Merchant Marine College， Shanghai Maritime University， Shanghai 201306， China）

Abstract：

Because of the poor oxidation stability of biodiesel， it can not be used on a large scale. In order to find out the composition change after oxidation of biodiesel and its effect on the lubricity， the oxidation of B5， B10， B20， B50， B100 biodiesel with volume fraction of 5%， 10%， 20%， 50% and 100% is carried out， and the oxidation products of biodiesel and the lubricity of oxidized biodiesel are tested by Fourier transform infrared spectroscopy analysis and the four-ball friction tester. Experimental results show that during the oxidation process of biodiesel， the CC unsaturated bond content and the CO carbonyl content decrease， but the content of hydroperoxide and carboxylic acid， aldehyde and ketone oxides increases. With the progress of oxidation， the oxidation of biodiesel promotes the lubricity， and through 8 h oxidation， the wear spot diameter measured is smallest， which shows that the oxidized biodiesel is of the best lubricity. After 8 h， the lubricity decreases because of the destruction of the oil film by the acid value of biodiesel. Therefore， the oxidation of biodiesel in a short period of time helps to improve the lubricity， but a long period of oxidation leads to excessively high acid value to reduce its lubricity.

Key words：

biodiesel; oxidation; function group; lubrication analysis

0 引 言

石化柴油中除硫化物外，含有氮和氧元素的極性官能團(tuán)也是保持柴油自潤滑性的重要成分[1]。然而，隨著環(huán)保要求的日趨嚴(yán)格，在通過深度加氫工藝去除柴油中硫化物的同時(shí)也會(huì)將氮氧化合物去除，從而導(dǎo)致油液的潤滑性下降，造成發(fā)動(dòng)機(jī)柱塞偶件和噴油器針閥等部件磨損過快[2]。生物柴油與石化柴油完全相溶，二者可以任意比例混合。生物柴油本身具有良好的潤滑性，其潤滑效果與脂肪酸甲酯（fatty acid methyl ester， FAME）的不飽和度、碳鏈長度等因素有關(guān)[3]。……