Polycardanol with different molar mass and sulfonated polystyrene with various degrees of sulfonation were prepared by cationic polymerization of cardanol and sulfonation of polystyrene in ethyl sulfate solution, respectively. The molar masses, solution behavior, and effect of these polymers on the stability of asphaltene dispersion were studied as a function of the concentration. The results indicate that, at low concentrations, both sets of polymers behave as flocculants and dispersants at higher concentrations. The flocculation efficiency correlates, within certain limits, with the polymer molar mass and polar groups content.
Some fundamental and practical aspects of a Hf-Zn catalyst, with a nominal composition of 3.0 wt% Hf and 9.3 wt% Zn and prepared as a physical mixture of Hf/SiO2 (85 wt%) and the zincsilicate hemimorphite (15 wt%), have been studied for the one-step conversion of ethanol to 1,3butadiene. The elucidation of the main reactions leading to 1,3-butadiene and by-products was made by means of kinetic curves and catalytic tests where intermediates were individually fed. In addition, the convenience of by-product separation from unreacted ethanol in an industrial process was studied by performing experiments where ethanol was co-fed with intermediates.The causes of catalyst deactivation and the impact on catalyst structure and performance of regeneration by calcination were also investigated. According to our results, the pathway to 1,3butadiene over the Hf-Zn catalyst includes ethanol dehydrogenation, acetaldehyde aldol condensation, crotonaldehyde reduction with ethanol, and crotyl alcohol dehydration. The recycling of the by-products butanal, acetone and 1-butanol into the reactor should be avoided, as the first two are converted to heavy compounds by aldol condensation reactions, while 1-butanol dehydration leads to butenes, which are difficult to separate from 1,3-butadiene. The suppression of diethyl ether formation from ethanol by recycling to extinction is possible. It has been found that catalyst deactivation is mainly caused by the retention of oxygenated aromatic-type coke species, preferentially formed on the dehydrogenating Zn 2+ sites associated with the hemimorphite component of the catalyst, and probably also by a loss in Zn 2+ sites due to the reduction to Zn 0 during catalysis. This reduction induces an imbalance between Hf 4+ and Zn 2+ sites, which changes catalyst selectivity. Regeneration by calcination with air removes coke and re-oxidizes a fraction of Zn 0 back to Zn 2+ , but it does not fully re-establish the original Zn 2+ /Hf 4+ balance.
The electrophoretic mobility of asphaltene particles formed by precipitation induced by the addition of n-heptane to asphaltene solutions in toluene was measured in water and in nonpolar media. Dispersed in water, the particles presented a negative electrophoretic mobility, whereas in toluene their mobility was positive and around 2.0 × 10 -9 m 2 /V s. When resins were present in the precipitating medium, a coprecipitation of these fractions occurred, indicating an adsorption or binding process of the resins on the nascent asphaltene particles. This interaction, however, did not significantly change the electrophoretic mobility of the asphaltene particles. In contrast with commercial dispersants, resins fail to stabilize asphaltene dispersions. This result indicate that the descriptions representing asphaltenes as a solid phase intrinsically insoluble in hydrocarbon media dispersed by adsorbed resins molecules does not accurately represent the structure of these fractions
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