Alkali-metal-modified ZSM-5 zeolites for improvement of catalytic dehydration of lactic acid to acrylic acid

Abstract

Various ZSM-5 zeolites modified with alkali metals (Li, Na, K, Rb, and Cs) were prepared using ion exchange. The catalysts were used to enhance the catalytic dehydration of lactic acid (LA) to acrylic acid (AA). The effects of cationic species on the structures and surface acid-base distributions of the ZSM-5 zeolites were investigated. The important factors that affect the catalytic performance were also identified. The modified ZSM-5 catalysts were characterized using X-ray diffraction, temperature-programmed desorptions of NH3 and CO2, pyridine adsorption spectroscopy, and N2 adsorption to determine the crystal phase structures, surface acidities and basicities, nature of acid sites, specific surface areas, and pore volumes. The results show that the acid-base sites that are adjusted by alkali-metal species, particularly weak acid-base sites, are mainly responsible for the formation of AA. The KZSM-5 catalyst, in particular, significantly improved LA conversion and AA selectivity because of the synergistic effect of weak acid-base sites. The reaction was conducted at different reaction temperatures and liquid hourly space velocities (LHSVs) to understand the catalyst selectivity for AA and trends in byproduct formation. Approximately 98% LA conversion and 77% AA selectivity were achieved using the KZSM-5 catalyst under the optimum conditions (40 wt% LA aqueous solution, 365 °C, and LHSV 2 h −1).

Bio‐Acrylates Production: Recent Catalytic Advances and Perspectives of the Use of Lactic Acid and Their Derivates

“…ZSM‐5 (MFI framework) is a medium‐pore zeolite with two intersecting channels that recently attracted a lot of attention by several research groups. Similar to other zeolites, potassium was claimed to be the best counter ion compared to Li, Na, Cs and Rb, independently of the Si/Al ratio used ,,. Furthermore similar to Y and β, low Si/Al ratios seemed beneficial for a high catalytic performance, and a potassium exchange degree (expressed in fraction) of ca.…”

Lanthanum phosphate: an efficient catalyst for acrylic acid production through lactic acid dehydration

“…phosphates [22][23][24][25], rare earth metal phosphates [26][27], hydroxyapatites [28][29][30][31] and various types of alkali and alkaline earth metals modified zeolites [32][33][34][35][36][37]. Majority of these investigations reported that the dehydration of LA efficiently catalyzed over solid acid-base catalysts, which are typically with different acidity strength such as weak acidic and basic sites [26][27][28][29].…”

Concepts of modern technologies of obtaining valuable biomass-derived chemicals

“…Another way to modify ZSM-5 zeolites is by using ion exchange with alkali metals [86]. ZSM-5 zeolite (Si/Al molar ratio = 75) was preheated at 550 °C for 6 h and treated with an aqueous solution of MNO 3 (1 mol/L; M = NH 4 , Li, Na, K, Rb, or Cs; 14 g of ZSM-5 zeolite in 140 mL of MNO 3 ) at 80 °C for 6 h to obtain ion-exchanged ZSM-5.…”