Study On Catalytic Performance Of Cr₂O₃/Al₂O₃ For Hydrogenation Of Alkylphenols

Medium-low temperature coal tar has a high oxygen content,which is mainly phenols.During hydrocracking,phenols are prone to generate water to inactivate the catalyst,and also cause waste of phenols,a valuable chemical.By separating and transforming the phenols in medium-low temperature coal tar,the utilization value can be improved.phenols can be divided into lower phenols and higher phenols according to the difference in boiling point.The lower phenols can be separated and recovered by solvent extraction and elution methods,etc.However,there are few studies on the high-value utilization technology of high-grade phenol,which accounts for 40% of the total phenol in low-temperature coal tar.Higher phenols are mainly monocyclic alkylphenols in medium-low temperature coal tar,it can be converted into light aromatic hydrocarbons or lower phenols through catalytic hydrogenation reaction,and then use a mature process for centralized recovery,which can achieve the purpose of higher value of higher phenols.Based on the conversion of alkylphenols to light aromatic hydrocarbons or lower phenols all involve the breaking of side chain alkyl groups,qnd the reaction needs to be carried out at a higher temperature.In this study,a series of Cr₂O₃/Al₂O₃ catalysts with high dealkylation activity and good thermal stability was prepared.and part of them were modified by phosphorus.X-ray diffraction?XRD?),Chemical adsorption?NH₃-TPD?,nitrogen adsorption?BET?,X-ray photoelectron spectroscopy?XPS?,scanning electron microscopy?SEM?and other means were used to characterize the catalyst.The catalytic dealkylation was studied using4-ethylphenol as a model compound.The activity of the catalyst was evaluated on a fixed-bed reactor,and the product composition was analyzed using gas chromatography.The main work and conclusions are as follows:?1?The effect of Cr₂O₃/Al₂O₃ catalysts with different structure ?-Al₂O₃ supports on the performance of alkylphenol hydrodealkylation was studied.The results show that the Cr₂O₃/Al₂O₃ catalyst with 1#?-Al₂O₃ support has the best reaction effect.When the reactants are almost completely converted,the dealkylation rate is 67.36% and the selectivity of aromatics is 83.98%.Based on this catalyst,the main reaction conditions were investigated,and the optimal reaction conditions were as follows: LHSV 6 h^-1,H₂/Oil 500:1,reaction pressure 3.5 MPa,and reaction temperature 450?.?2?The effects of different Cr₂O₃ loadings?Cr₂O₃ loadings:5wt%,10wt%,15wt%,20wt%,25wt%?on the reaction performance of the catalyst were investigated.The results show that the conversion rates of the series of catalysts are all above 99%.With the increase of Cr₂O₃ loading,the dealkylation rate and aromatic selectivity both increase first and then decrease,and reach the highest when the loading is 15wt%.?3?The influence of different phosphoric acid content modification?phosphoric acid content of 4wt%,6wt%,8wt%,10wt%,12wt%?on the reaction performance of the catalyst was studied.The results showed that the introduction of phosphoric acid significantly improved the dealkylation performance of 4-ethylphenol.When the content of phosphoric acid was 8%by weight,the effect of dealkylation of 4-ethylphenol was the best,dealkylation rate is74.40%.?4?Catalysts with different chromium sources and different loadings were prepared,and their effects on the products were investigated,which provided a solution for the further development of highly efficient catalysts.