活性炭担载的铂催化剂在碱性条件下选择性氧化甘油制备乳酸（英文）
发布时间：2018-09-08 12:26
【摘要】：生物柴油是一种环境友好的燃料,随着其生产及应用的快速增长,其生产过程中重要的副产物甘油将会大量过剩.因此,将甘油转化为高附加值的化学品对于提高生物柴油整体竞争力具有重大意义.乳酸是重要的化工原料,可用于制备生物兼容和可降解的聚乳酸塑料,广泛应用于食品和医药等领域.近年来,由甘油制乳酸的研究受到格外关注,相对于水热反应和氢解反应等,催化选择氧化反应因温和的反应条件而更具竞争力.目前,甘油催化选择氧化制乳酸一般需加入较高比例的NaOH,而碱的类型对反应性能的影响鲜有报道.另外,催化剂常采用TiO_2和CeO_2等氧化物载体,而炭载体具有比表面积较大、在酸碱溶液中稳定及贵金属易于回收等优点,在催化领域有着广泛应用.因此,本文研究了活性炭(AC)担载的Pt催化剂在甘油催化选择氧化制乳酸反应中的催化性能.首先研究了Pt/AC催化剂和碱在甘油催化选择氧化制乳酸过程中的催化作用.实验发现,Pt/AC和碱协同作用才能得到乳酸.Pt/AC催化剂在甘油脱氢生成中间产物(甘油醛和二羟基丙酮)的过程中起主导作用,碱的存在能够促进甘油羟基脱氢;中间产物实验证实,中间产物生成乳酸过程中碱起主导作用,它促进甘油醛和二羟基丙酮脱水反应和坎尼扎罗重排反应获得乳酸.进一步研究发现,中间产物二羟基丙酮比甘油醛更有利于乳酸生成,而Pt/AC催化剂有利于中间产物氧化为甘油酸.进一步研究了不同类型的碱对反应性能的影响.结果表明,碱金属氢氧化物(LiOH,NaOH,KOH)比碱土金属氢氧化物(Ba(OH)_2)更有利于提高甘油转化率和乳酸选择性.在加入碱金属氢氧化物条件下,甘油转化率与其离子半径呈正相关,而乳酸选择性则呈相反趋势.在LiOH存在下,乳酸选择性明显高于NaOH和KOH条件.当LiOH:甘油摩尔比为1.5时,甘油转化率和乳酸选择性均最高.在较低的LiOH与甘油摩尔比时,随着反应的消耗,溶液中的OH 减少,其促进甘油脱氢的作用变弱,并且不利于中间产物进行坎尼扎罗反应,故反应活性和乳酸选择性较差;而当LiOH比例过高时,会导致溶解氧浓度迅速降低,从而使甘油转化率和乳酸选择性下降,同时副产物甘油酸的选择性有所提高.这可能是因为较高比例的碱会促进中间产物甘油醛生成,该中间产物在Pt/AC催化作用下发生进一步氧化反应生成甘油酸.研究了反应时间对催化性能的影响.结果表明,反应6 h后,甘油已经完全转化,乳酸选择性最高,达到69.3%;进一步延长反应时间,乳酸选择性有所下降,而副产物乙酸选择性略有增加,这可能是部分乳酸分解所致.Pt/AC催化剂经5次循环使用后仍保持了较高的甘油转化率和乳酸选择性
[Abstract]:Biodiesel is a kind of environment-friendly fuel. With the rapid growth of its production and application, glycerin, an important by-product in the production process, will be surplus. Therefore, the conversion of glycerol to high added-value chemicals is of great significance for improving the overall competitiveness of biodiesel. Lactic acid is an important chemical material, which can be used to prepare biocompatible and degradable poly (lactic acid) plastics. It is widely used in food and medicine. In recent years, the research on the preparation of lactic acid from glycerol has attracted special attention. Compared with hydrothermal reactions and hydrogenolysis reactions, the catalytic selective oxidation reaction is more competitive due to mild reaction conditions. At present, the catalytic selective oxidation of glycerol to lactic acid usually requires the addition of a high proportion of NaOH, and the effect of the type of base on the reaction performance is rarely reported. In addition, TiO_2 and CeO_2 are often used in the catalysts, while the carbon supports have the advantages of large specific surface area, stable in acid-base solutions and easy recovery of precious metals, so they are widely used in the field of catalysis. Therefore, the catalytic performance of activated carbon (AC) supported Pt catalyst in the selective oxidation of glycerol to lactic acid was studied. The catalytic effect of Pt/AC catalyst and alkali on the selective oxidation of glycerol to lactic acid was studied. It was found that lactic acid. PT / AC catalyst played a leading role in the process of dehydrogenation of glycerol (glyceraldehyde and dihydroxy acetone), and the presence of base could promote the dehydrogenation of glycerol hydroxyl. The intermediate product plays a leading role in the formation of lactic acid, which promotes the dehydration of glyceraldehyde and dihydroxyacetone and the rearrangement of cannizaro to obtain lactic acid. It was found that the intermediate product, dihydroxyacetone, was more favourable to the formation of lactic acid than glyceraldehyde, while the Pt/AC catalyst was advantageous to the oxidation of the intermediate product to glyceric acid. The effect of different types of alkali on the reaction performance was further studied. The results showed that alkali metal hydroxides (LiOH,NaOH,KOH) were more favorable than alkaline earth metal hydroxides (Ba (OH) St 2) in increasing glycerol conversion and lactic acid selectivity. When alkali metal hydroxide was added, glycerol conversion was positively correlated with its ion radius, while lactic acid selectivity showed a reverse trend. In the presence of LiOH, the selectivity of lactic acid was significantly higher than that of NaOH and KOH. When the molar ratio of LiOH: to glycerol was 1.5, the conversion of glycerol and the selectivity of lactic acid were the highest. When the molar ratio of LiOH to glycerol is low, with the consumption of the reaction, the amount of OH in the solution decreases, and the effect of promoting dehydrogenation of glycerol becomes weaker, which is not conducive to the Cannitzaro reaction of the intermediate product, so the reaction activity and the selectivity of lactic acid are poor. When the ratio of LiOH is too high, the concentration of dissolved oxygen decreases rapidly, which leads to the decrease of glycerol conversion and the selectivity of lactic acid, and the selectivity of glyceric acid, the by-product. This may be due to the fact that a higher proportion of alkali can promote the formation of glyceraldehyde, which is further oxidized to glyceric acid under the catalysis of Pt/AC. The effect of reaction time on the catalytic performance was studied. The results showed that after 6 h reaction, glycerol was completely transformed, the selectivity of lactic acid was the highest, and the selectivity of lactic acid decreased with the further prolongation of reaction time, while the selectivity of acetic acid, a by-product, increased slightly. This may be due to the partial decomposition of lactic acid. PT / AC catalyst has maintained high glycerol conversion and lactic acid selectivity after 5 cycles.
【作者单位】： 中国科学院大连化学物理研究所洁净能源国家实验室(筹);中国科学院大学;中国科学院大连化学物理研究所催化基础国家重点实验室;
【基金】：supported by the National Natural Science Foundation of China(21176236)~~
【分类号】：O643.36;TQ225.4
本文编号：2230514
[Abstract]:Biodiesel is a kind of environment-friendly fuel. With the rapid growth of its production and application, glycerin, an important by-product in the production process, will be surplus. Therefore, the conversion of glycerol to high added-value chemicals is of great significance for improving the overall competitiveness of biodiesel. Lactic acid is an important chemical material, which can be used to prepare biocompatible and degradable poly (lactic acid) plastics. It is widely used in food and medicine. In recent years, the research on the preparation of lactic acid from glycerol has attracted special attention. Compared with hydrothermal reactions and hydrogenolysis reactions, the catalytic selective oxidation reaction is more competitive due to mild reaction conditions. At present, the catalytic selective oxidation of glycerol to lactic acid usually requires the addition of a high proportion of NaOH, and the effect of the type of base on the reaction performance is rarely reported. In addition, TiO_2 and CeO_2 are often used in the catalysts, while the carbon supports have the advantages of large specific surface area, stable in acid-base solutions and easy recovery of precious metals, so they are widely used in the field of catalysis. Therefore, the catalytic performance of activated carbon (AC) supported Pt catalyst in the selective oxidation of glycerol to lactic acid was studied. The catalytic effect of Pt/AC catalyst and alkali on the selective oxidation of glycerol to lactic acid was studied. It was found that lactic acid. PT / AC catalyst played a leading role in the process of dehydrogenation of glycerol (glyceraldehyde and dihydroxy acetone), and the presence of base could promote the dehydrogenation of glycerol hydroxyl. The intermediate product plays a leading role in the formation of lactic acid, which promotes the dehydration of glyceraldehyde and dihydroxyacetone and the rearrangement of cannizaro to obtain lactic acid. It was found that the intermediate product, dihydroxyacetone, was more favourable to the formation of lactic acid than glyceraldehyde, while the Pt/AC catalyst was advantageous to the oxidation of the intermediate product to glyceric acid. The effect of different types of alkali on the reaction performance was further studied. The results showed that alkali metal hydroxides (LiOH,NaOH,KOH) were more favorable than alkaline earth metal hydroxides (Ba (OH) St 2) in increasing glycerol conversion and lactic acid selectivity. When alkali metal hydroxide was added, glycerol conversion was positively correlated with its ion radius, while lactic acid selectivity showed a reverse trend. In the presence of LiOH, the selectivity of lactic acid was significantly higher than that of NaOH and KOH. When the molar ratio of LiOH: to glycerol was 1.5, the conversion of glycerol and the selectivity of lactic acid were the highest. When the molar ratio of LiOH to glycerol is low, with the consumption of the reaction, the amount of OH in the solution decreases, and the effect of promoting dehydrogenation of glycerol becomes weaker, which is not conducive to the Cannitzaro reaction of the intermediate product, so the reaction activity and the selectivity of lactic acid are poor. When the ratio of LiOH is too high, the concentration of dissolved oxygen decreases rapidly, which leads to the decrease of glycerol conversion and the selectivity of lactic acid, and the selectivity of glyceric acid, the by-product. This may be due to the fact that a higher proportion of alkali can promote the formation of glyceraldehyde, which is further oxidized to glyceric acid under the catalysis of Pt/AC. The effect of reaction time on the catalytic performance was studied. The results showed that after 6 h reaction, glycerol was completely transformed, the selectivity of lactic acid was the highest, and the selectivity of lactic acid decreased with the further prolongation of reaction time, while the selectivity of acetic acid, a by-product, increased slightly. This may be due to the partial decomposition of lactic acid. PT / AC catalyst has maintained high glycerol conversion and lactic acid selectivity after 5 cycles.
【作者单位】： 中国科学院大连化学物理研究所洁净能源国家实验室(筹);中国科学院大学;中国科学院大连化学物理研究所催化基础国家重点实验室;
【基金】：supported by the National Natural Science Foundation of China(21176236)~~
【分类号】：O643.36;TQ225.4
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