The effect of ageing step elimination on the memory effect presented by Mg0.75Al0.25 hydrotalcites (HT) and their catalytic activity for cyanoethylation reaction

The absence of ageing step in the coprecipitation method leads to modification of textural and structural properties of Mg_0.75Al_0.25 hydrotalcites which are reflected in the “memory effect” and in the catalytic activity of these samples for cyanoethylation reaction between ethanol and acrylonitrile where the beta-ethoxypropionitrile is the prevailing reaction product. The solids were characterised by XRD, DRIFT, TEM and base sites determination by adsorption of molecules with different pK_a aiming to establish a correlation between structural characteristics and the catalytic activity.     

Dielectric properties of cyanoethylated bagasse composites

Bagasse was converted into a thermo-moldable material by cyanoethylation. The effect of reaction conditions employed during the preparation of cyanoethylated bagasse (CE-B) fibers on dielectric properties of hot-pressed composites was studied. Increase in the nitrogen content of the cyanoethylated fiber, i.e., the nitrile groups resulted in an increase in the dielectric constant and a decrease in the dissipation factor (tan δ) peak of the composites. Increase in the reaction temperature and the alkali concentration resulted in a decrease in the dielectric constant and tan δof the composites. Thickness swelling (TS) and equilibrium moisture content of composites conditioned at different relative humidities (RHs) were studied and the extent of the effect of the absorbed moisture on the dielectric properties was also studied. Increase in the nitrogen content, the alkali concentration, and the reaction temperature during the preparation of cyanoethylated fibers resulted in a decrease in TS and moisture absorption of the composites formed. The dielectric properties of the composites conditioned at 60 or 90% RH deteriorated severely. The effect of temperature on the dielectric constant and tan δof a selected CE-B composite was studied. The dielectric constant and tan δincreased as the temperature increased.     

2-氰基乙基戊胺的合成

以甲苯和正丁醇的混合溶液作溶剂,正戊胺与丙烯腈反应合成2-氰基乙基戊胺;验证了溶剂种类和用量,原料配比,反应温度及时间对正戊胺转化率、2-氰基乙基戊胺选择性、单程总收率的影响;最佳工艺条件为:溶剂为混合溶剂[m(甲苯):m(正丁醇)=2:1],m(溶剂):m(正戊胺)=3.0~4.0,n(丙烯腈):n(正戊胺)=1.0,反应温度为50~60℃,丙烯腈滴加时间50min,保温反应时间100min;单程总收率可达83.6%,产品纯度可达98.0%以上。     

Impact of the memory effect on the catalytic activity of Li-Al hydrotalcite-like compounds for the cyanoethylation reaction

The target of this work is to investigate structural and textural modifications of Li-Al hydrotalcite-like compounds by memory effect and their impact on the catalytic activity of these solids for the cyanoethylation reaction. The samples have been characterized by XRD, FT-IR, TG-DTG, surface area and porous structure. The catalytic test results showed that the reconstruction of the hydrotalcite leads to a decrease of the catalytic activity compared to the parent hydrotalcite. This fact may be related either to the smaller specific surface area of the reconstructed form or to the leaching of Li⁺ during reconstruction. It has been also noticed that the calcination of Li-Al hydrotalcite leads to the formation of a α-LiAlO₂ stable phase.     

Cyanoethylation of Tamarind Kernel Powder

Tamarind Kernel Powder (TKP) is derived from the seeds of Tamarindus indica Linn., a common tree of India and South East Asia with high economic importance. TKP is used in cotton sizing, as a wet‐end additive in the paper industry as well as a thickening, stabilizing and gelling agent in the food industry. Cyanoethylation of TKP was carried out with acrylonitrile (AN) in presence of sodium hydroxide under different reaction conditions. Variables studied were concentration of sodium hydroxide and AN, gum‐liquor ratio as well as reaction temperature and time. The degree of substitution (DS), reaction efficiency (RE) and total extent of etherification were determined. The optimum conditions for preparing cyanoethyl‐TKP (DS 0.49) comprised 0.088 mol (1.3 equiv./OH group) of sodium hydroxide, and 0.050 mol (0.7 equiv./OH group) of AN at 30°C for 45 min using 0.026 mol TKP (0.07 mol OH groups) in 100 mL water. Rheological studies of cyanoethyl‐TKP solution exhibited non‐Newtonian pseudoplastic behavior, relatively high viscosity, cold‐water solubility, solution stability and clarity as compared with unmodified TKP.     

Cyanoethylation of alcohols over solid base catalysts

Cyanoethylation of alcohols with acrylonitrile to form 3-alkoxypropanenitriles proceeds effectively over solid base catalysts such as alkaline metal oxides and hydroxides, lanthanum oxide, and alumina supported potassium fluoride and hydroxide at a reaction temperature below 323 K. The order of the reactivity of alcohols varied with the types of catalyst. With magnesium hydroxide and calcium hydroxide, the reactivity of alcohol decreased: methanol>ethanol>2-propanol, while with the alkaline earth oxides, lanthanum oxide, and alumina supported KOH and KF, the reactivity order was opposite. The reactivity orders are interpreted by the acidity of alcohol combined with the basic strength of the catalysts. The catalytic activity of solid base catalysts were scarcely affected by exposure of the catalyst to air before use for the reaction.     

Cyanoethylation of Cassia tora Gum

Cyanoethylation of Cassia tora gum was carried out with acrylonitrile in presence of sodium hydroxide under different reaction conditions. Variables studied were concentrations of sodium hydroxide and acrylonitrile, reaction temperature and time. The degree of substitution, reaction efficiency and total extent of etherification were determined. The optimum conditions for preparing cyanoethyl Cassia tora gum (DS 0.44) were 0.608 mol acrylonitrile and 0.625 mol sodium hydroxide at 30 °C for 4 h. Rheological properties of cyanoethyl Cassia tora gum solutions showed non‐Newtonian pseudoplastic behavior regardless of the degree of substitution (DS). At a constant rate of shear the apparent viscosity of cyanoethyl Cassia tora gum solutions increased with the increase in %N of the product.