Sustainable Production of Acrylic Acid: Alkali‐Ion Exchanged Beta Zeolite for Gas‐Phase Dehydration of Lactic Acid

Abstract

Gas-phase dehydration of lactic acid (LA) to acrylic acid (AA) was investigated over alkali-exchanged β zeolite (M(x)Na(1-x)β, M=Li(+), K(+), Rb(+), or Cs(+)) of different exchange degrees (x). The reaction was conducted under varying conditions to understand the catalyst selectivity for AA production and trends of byproduct formation. The nature and exchange degree of M(+) were found to be critical for the acid-base properties and catalytic performance of the exchanged zeolite. K(x)Na(1-x)β of x=0.94 appeared to be the best performing catalyst whereas Li(x)Na(1-x)β and Naβ were the poorest in terms of AA selectivity and yield. The AA yield as high as 61 mol % (selectivity: 64 mol %) could be obtained under optimized reaction conditions for up to 8 h over the best performing K0.94Na0.06β. The acid and base properties of the catalysts were probed, respectively by temperature-programmed desorption (TPD) of adsorbed NH3 and CO2, and were related to the electrostatic potentials of the alkali ions in the zeolite, which provided a basis for the discussion of the acid-base catalysis for sustainable AA formation from LA.

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].…”

“…Unlike the mechanism on dehydration of LA into acrylic acid which has been discussed by many previous reports [50,51,59], the mechanism for decarbonylation of LA to acetaldehyde is rarely investigated so far. Recently, Ghantani et al [59] have proposed the decarbonylation reaction mechanism of LA to form acetaldehyde over the calcium hydroxyapatite.…”

“…As mentioned above, for Mg 0.388 Al 2.408 O 4 catalyst predominant weak-medium acidity as well as an excellent acid-base balance plays an important role in durability and acetaldehyde selectivity. It is known that strong acidic sites have a strong catalysis for decomposition of C-C bond, resulting in deposition of carbon or formation of coke on the catalyst surface [51,60,63]. Thus the catalyst with more strong acidic sites rapidly deactivates in the process of the catalytic decarbonylation reaction of LA due to covering the active sites of the catalyst surface by the formed carbon or cokes.…”

“…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

“…However, AA is rarely obtained selectively from LA because of easy decarbonylation/decarboxylation leading to acetaldehyde (A) and CO x [8][9][10]. High yields of acrylic acid were obtained using modified zeolites [11][12][13][14][15][16] but they suffered from coking and probable hydrothermal instability.…”