活性炭擔(dān)載的鉑催化劑在堿性條件下選擇性氧化甘油制備乳酸（英文）
發(fā)布時間：2018-09-08 12:26
【摘要】：生物柴油是一種環(huán)境友好的燃料,隨著其生產(chǎn)及應(yīng)用的快速增長,其生產(chǎn)過程中重要的副產(chǎn)物甘油將會大量過剩.因此,將甘油轉(zhuǎn)化為高附加值的化學(xué)品對于提高生物柴油整體競爭力具有重大意義.乳酸是重要的化工原料,可用于制備生物兼容和可降解的聚乳酸塑料,廣泛應(yīng)用于食品和醫(yī)藥等領(lǐng)域.近年來,由甘油制乳酸的研究受到格外關(guān)注,相對于水熱反應(yīng)和氫解反應(yīng)等,催化選擇氧化反應(yīng)因溫和的反應(yīng)條件而更具競爭力.目前,甘油催化選擇氧化制乳酸一般需加入較高比例的NaOH,而堿的類型對反應(yīng)性能的影響鮮有報道.另外,催化劑常采用TiO_2和CeO_2等氧化物載體,而炭載體具有比表面積較大、在酸堿溶液中穩(wěn)定及貴金屬易于回收等優(yōu)點,在催化領(lǐng)域有著廣泛應(yīng)用.因此,本文研究了活性炭(AC)擔(dān)載的Pt催化劑在甘油催化選擇氧化制乳酸反應(yīng)中的催化性能.首先研究了Pt/AC催化劑和堿在甘油催化選擇氧化制乳酸過程中的催化作用.實驗發(fā)現(xiàn),Pt/AC和堿協(xié)同作用才能得到乳酸.Pt/AC催化劑在甘油脫氫生成中間產(chǎn)物(甘油醛和二羥基丙酮)的過程中起主導(dǎo)作用,堿的存在能夠促進甘油羥基脫氫;中間產(chǎn)物實驗證實,中間產(chǎn)物生成乳酸過程中堿起主導(dǎo)作用,它促進甘油醛和二羥基丙酮脫水反應(yīng)和坎尼扎羅重排反應(yīng)獲得乳酸.進一步研究發(fā)現(xiàn),中間產(chǎn)物二羥基丙酮比甘油醛更有利于乳酸生成,而Pt/AC催化劑有利于中間產(chǎn)物氧化為甘油酸.進一步研究了不同類型的堿對反應(yīng)性能的影響.結(jié)果表明,堿金屬氫氧化物(LiOH,NaOH,KOH)比堿土金屬氫氧化物(Ba(OH)_2)更有利于提高甘油轉(zhuǎn)化率和乳酸選擇性.在加入堿金屬氫氧化物條件下,甘油轉(zhuǎn)化率與其離子半徑呈正相關(guān),而乳酸選擇性則呈相反趨勢.在LiOH存在下,乳酸選擇性明顯高于NaOH和KOH條件.當(dāng)LiOH:甘油摩爾比為1.5時,甘油轉(zhuǎn)化率和乳酸選擇性均最高.在較低的LiOH與甘油摩爾比時,隨著反應(yīng)的消耗,溶液中的OH 減少,其促進甘油脫氫的作用變?nèi)?并且不利于中間產(chǎn)物進行坎尼扎羅反應(yīng),故反應(yīng)活性和乳酸選擇性較差;而當(dāng)LiOH比例過高時,會導(dǎo)致溶解氧濃度迅速降低,從而使甘油轉(zhuǎn)化率和乳酸選擇性下降,同時副產(chǎn)物甘油酸的選擇性有所提高.這可能是因為較高比例的堿會促進中間產(chǎn)物甘油醛生成,該中間產(chǎn)物在Pt/AC催化作用下發(fā)生進一步氧化反應(yīng)生成甘油酸.研究了反應(yīng)時間對催化性能的影響.結(jié)果表明,反應(yīng)6 h后,甘油已經(jīng)完全轉(zhuǎn)化,乳酸選擇性最高,達到69.3%;進一步延長反應(yīng)時間,乳酸選擇性有所下降,而副產(chǎn)物乙酸選擇性略有增加,這可能是部分乳酸分解所致.Pt/AC催化劑經(jīng)5次循環(huán)使用后仍保持了較高的甘油轉(zhuǎn)化率和乳酸選擇性
[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.
【作者單位】： 中國科學(xué)院大連化學(xué)物理研究所潔凈能源國家實驗室(籌);中國科學(xué)院大學(xué);中國科學(xué)院大連化學(xué)物理研究所催化基礎(chǔ)國家重點實驗室;
【基金】：supported by the National Natural Science Foundation of China(21176236)~~
【分類號】：O643.36;TQ225.4
本文編號：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.
【作者單位】： 中國科學(xué)院大連化學(xué)物理研究所潔凈能源國家實驗室(籌);中國科學(xué)院大學(xué);中國科學(xué)院大連化學(xué)物理研究所催化基礎(chǔ)國家重點實驗室;
【基金】：supported by the National Natural Science Foundation of China(21176236)~~
【分類號】：O643.36;TQ225.4
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