Sustainable Production of Acrylic Acid: Catalytic Performance of Hydroxyapatites for Gas-Phase Dehydration of Lactic Acid

Abstract

Hydroxyapatites (HAP m -T) of varying molar Ca/P ratios m (1.58−1.69) and calcination temperatures T (360−700 °C) were prepared and comprehensively characterized by nitrogen adsorption, TG, XPS, XRD, CO 2 -TPD, and NH 3 -TPD and were employed to catalyze the gas-phase dehydration of lactic acid (LA) to produce acrylic acid (AA). While the texture and crystallinity of the HAP m -T sample were affected little by variation of m, its surface acidity decreased but basicity increased with the increase in m. The HAP m -T sample with a higher T showed a higher crystallinity but lower surface area, acidity, and basicity. The conversion of LA decreased with increasing either m or T of the HAP m -T catalyst; the selectivity for AA maximized at m = 1.62 but decreased steadily with the T increase. The HAP 1.62 -360 sample (m = 1.62, T = 360 °C) was identified as the most efficient catalyst, offering an AA yield as high as 50−62% for longer than 8 h (AA selectivity: 71− 74 mol %) under optimized reaction conditions (360 °C, WHSV LA = 1.4−2.1 h −1 ). Correlating the catalyst performance with its surface acidity and basicity disclosed that the LA consumption rate increased linearly with the acidity/basicity ratio, but volcanotype dependence appeared between the AA production rate and the acidity/basicity ratio, which reveals a kind of cooperative acid−base catalysis for selective AA production. The HAP m -T catalysts became more or less deactivated after reaction, but the reacted ones could be fully regenerated by in situ treatment with flowing air.

Highly efficient and robust Mg0.388Al2.408O4 catalyst for gas-phase decarbonylation of lactic acid to acetaldehyde

“…Similarly, AD formation rate also increased with increasing surface acid density but decreased with surface base density. The observations on the increase with surface acid density and decrease with base density of the area-specific catalytic rates for LA consumption and AD formation agreed well with the previous reports [33,50,51].…”

“…It has been known that the catalytic decarbonylation rate of LA into acetaldehyde over the calcium hydroxyapatite would be dependent on the catalyst surface acid-base property [50,59]. Indeed, from the results shown in Fig.…”

“…Area-specific catalytic rate is defined as previous references reported [50,51], and is determined with Eqs. (4) and (5 [18,[52][53][54].…”

Dehydration of ethyl lactate over alkaline earth phosphates: Performances, effect of water on reaction pathways and active sites

“…Other efficient catalysts for LA dehydration are sulphates [17], alkaline earth phosphates [18][19][20][21] and hydroxyapatites [22][23][24]. Recently, we have shown that selective alkaline earth phosphates contained mostly acidic and basic sites with similar weak strength.…”

Vapor-phase catalytic dehydration of lactic acid to acrylic acid over nano-crystalline cerium phosphate catalysts

“…Several authors reported in the literature recently on the dehydration of LA to AA over hydroxyapatite (HAp) catalysts [16][17][18][19] and Na-Y zeolites [20][21][22][23]. Ghantani et al prepared various HAp catalysts by changing Ca/P molar ratio at different pHs and reported a maximum of 60 % selectivity towards AA [17].…”