The current interest in porous crystalline metal-organic frameworks (MOFs) [1] is largely due to their wide range of compositions and structure types with low framework densities, their tunability, and the possibility of accessible, coordinatively unsaturated metal sites (CUS). The existence of CUS can strongly modify interactions with gases [2] or liquid adsorbates, [3] and is thus of particular importance gas storage and separations.The redox properties of transition-metal-substituted zeolites and mesoporous materials have been extensively studied and used for selective catalysis in liquid-phase oxidation, [4] removal of nitrogen oxides, [5] and photocatalytic reactions.[6]These features are very rare for MOFs containing 3d metals, in particular with respect to the reducibility of the framework metal ions. [7] For this reason, we examine herein both the conditions of generation of iron CUS with mixed valence Fe II

The adsorption capacities of carbon dioxide on six commercial hydrotalcite-like compounds and the main factors (aluminum content, anion type, water content, and heat treatment temperature) influencing their adsorption capacity at high temperatures have been investigated using a gravimetric technique. There is an optimum aluminum content and heat treatment temperature for the adsorption capacity. The carbonate anion favors adsorption of carbon dioxide compared to OH-, and a low content of water also improves the adsorption capacity. The carbon dioxide adsorption capacity is mainly dependent on the microporous volume, interlayer spacing, and layer charge density of the hydrotalcite-like compounds.

Vanillin production from chemical oxidation of Pinus spp. Kraft lignin is investigated. At a temperature of 130 °C, an oxygen partial pressure of 3 bar, a total pressure of 9 bar, and a lignin concentration of 60 g/L in an alkaline medium of 2 N NaOH, a maximum vanillin yield of 10% is obtained. On the basis of experimental results in a batch reactor operated under various conditions of temperature, oxygen partial pressure, total pressure, initial lignin concentration and pH, a kinetic model is proposed to simulate vanillin production from oxidation of Kraft lignin. The reaction rate of vanillin production is, for pH > 11.5, r C = k NC[O2]1.75[L] − k CI[O2][C] and, for pH < 11.5, r C = k NC[O2]1.75[L] − Af(pH)[C]2. An attempt to predict pH variation during the reaction is also made. The overall flowsheet of the process is briefly addressed, and the recovery of vanillin by adsorption is discussed.

Propylene and propane single-adsorption equilibrium isotherms and mass-transfer kinetics over 13X and 4A zeolite pellets have been investigated using gravimetry and zero length column techniques, respectively. The 13X zeolite shows a higher loading capacity and lower mass-transfer resistance while 4A zeolite shows the highest selectivity for propylene. The experimental adsorption equilibrium isotherms were adjusted with the Toth isotherm. Kinetic studies indicate that macropore diffusion controls the mass transfer inside 13X zeolite pellets while micropore diffusion controls the propylene adsorption on 4A zeolite pellets.

No abstract

Lignin is one of the main components of the pulping liquors and a potential source of high-added-value chemicals. The aim of this work is to evaluate the potential of industrial Eucalyptus globulus sulfite liquor and kraft liquors (collected at different stages of processing before the recovery boiler) for the production of syringaldehyde (Sy) and vanillin (V) by oxidation with O 2 in alkaline medium. Oxidations were performed in a jacketed reactor with controlled temperature and pressure by (1) direct reaction of pulping liquors and (2) reaction of kraft lignins isolated from liquors. Lignins produced by LignoBoost technology were also evaluated. The products profiles were established, as well as the yields, temperature and O 2 uptake during the reaction. Sulfite liquor is the best raw material leading to the highest yield by direct oxidation (33 kg of Sy and 15 kg of V per lignin ton), followed by thin kraft liquor (KL) which, compared to evaporated and heat treated liquors, also led to lower proportion of byproducts such as syringic and vanillic acids. Lignin isolation benefits yields and selectivity but just in the case of KL, leading to 28 kg of Sy and 12 kg of V per ton of lignin. The performance of the materials studied is primarily affected by the lignin characteristics but also by the inorganic content of the pulping liquors, whereas no effect of the carbohydrates was noticed.

No abstract

In this paper, the influence of some lignin features on its oxidative conversion to high-added-value phenolic aldehydes is discussed. Four softwood and three hardwood lignins are considered due to their different origins regarding the wood species, pulping process, and lignin isolation process. The lignins were characterized based on nitrobenzene oxidation (NO), frequency of phenolic hydroxyl (OHph) groups, and molecular weight determination, attempting to evaluate their potential to produce vanillin (V) and/or syringaldehyde (Sy) through the alkaline oxidation with oxygen. The raw-materials, Pinus spp. kraft lignin (LWest), Lignoboost kraft lignin (LBoostS), and Organosolv beech lignin (LOrgs) were selected to perform bench-scale oxidations with O2. These lignins contain lower content of nonlignin material and show higher yields of NO and high OHph groups content. In the oxidation with O2, LWest provide the highest production of V, 4.4% w/w (corresponding to 36% of NO yield). Considering the characteristics of LOrgs, an unexpected low Sy yield (2.5% w/w) was obtained (19% of the NO yield). The high reactivity of syringyl nuclei may be pointed out as the main reason for the faster production and degradation of Sy in oxidation. The concentration profile of products, the variation of pH in the reactive medium, and the variation of temperature with the reaction time of oxidation with O2 are shown and discussed with reference to the investigated lignins features.