金属离子改性NaY分子筛催化乳酸脱水制丙烯酸

Catalytic Dehydration of Lactic Acid to Acrylic Acid over NaY Zeolites Modified with Metallic Ions

对乳酸脱水制取丙烯酸的热力学进行了计算,并以NaY分子筛为催化剂对乳酸脱水反应参数进行了优化;采用K+,Ba2+,La3+对NaY分子筛进行改性,并用N2物理吸附,NH3-TPD,CO2-TPD等手段对催化剂进行了表征。实验结果表明,优化的工艺条件为乳酸质量分数38%、载气N2流量30 mL/min;金属离子改性的分子筛改变了分子筛表面酸碱位点分布进而影响了催化剂的乳酸脱水性能,其中,La/NaY分子筛具有适度的酸量及最高的碱量从而呈现出优异的催化性能,在325℃时丙烯酸收率达56.3%,而NaY分子筛上丙烯酸收率只有21.6%。适当降低酸强度及酸量可提高丙烯酸收率,并可削弱乙醛的形成;而提高碱量及适度减弱碱强度可有效提高丙烯酸收率。

The catalytic dehydration of bio-based lactic acid to acrylic acid over the unmodified and the modified NaY zeolite catalysts with K＋ , Ba2＋ and La3＋ was investigated and the thermodynamic analysis for the dehydration reaction was performed. The effects of the input concentration of lactic acid and the flow rate of nitrogen on the dehydration were studied. To improve the catalytic performance of the NaY catalyst, the NaY zeolite catalysts modified with K＋, Ba2＋ and La3＋ were prepared and characterized by means of N2 adsorption, NH3-TPD and CO2-TPD. The results showed that the optimized concentration of lactic acid and the flow rate of nitrogen were 38% （w） and 30 mL/ min, respectively. The modification could change the surface acid/base distributions and affect the catalytic performance. La/NaY exhibited the highest acrylic acid yield 56.3 % at 325 ℃, which could be attributed to the appropriate acidic amount and high basic amount on the catalyst, while NaY only indicated 21.6% acrylic acid yield under the same conditions. The research showed that the suitable declines of both acidic sites and acid strength of the catalysts were beneficial to the formation of acrylic acid and could reduce the generation of acetaldehyde. And suitable decrease of the base strength and increase of the basic sites could improve the yield acrylic acid in the dehydration.