Quaternary Ammonium Salt Loaded Lacunary Sodium Phosphotungstate Catalyzes The Selective Oxidation Of Fatty Alcohols By H₂O₂ With O₂

Fatty acids,as an important fine chemical,are widely used in biopharmaceuticals,fragrances and flavors,polymers,and surfactant production.The selective oxidation of fatty alcohols is one of the effective methods for the preparation of fatty acids.However,due to the poor activity of fatty alcohols,traditional oxidation methods usually use toxic and harmful oxidants or costly precious metal catalysts,which have the defects of environmental pollution and low economic efficiency and do not meet the requirements of sustainable development.Therefore,it is important to develop efficient and green methods to achieve selective oxidation of fatty alcohols for the preparation of fatty acids.In this thesis,a quaternary ammonium salt-loaded sodium phosphotungstate was developed as a recoverable catalyst with H₂O₂-coordinated O₂ oxidation system to achieve the selective oxidation of fatty alcohols for the preparation of fatty acids.The main research contents and results are as follows.（1）A series of quaternary ammonium-loaded phosphotungstic acid and lacunary sodium phosphotungstate catalysts were prepared based on Keggin-type phosphotungstic acid and different quaternary ammonium salts and applied to the H₂O₂ synergistic O₂ selective oxidation reaction with isooctanol as the template substrate.Screening experiments on a series of catalysts showed that the CTAC-loaded sodium phosphotungstate[（CH₃）₃NC₁₆H₃₃]Na₆PW₁₁O₃₉ had the best reactivity.In addition,it was shown that the addition of O₂ could effectively improve the conversion and selectivity of the reaction when H₂O₂ was used as the main oxidant.The optimum reaction conditions were optimized:O₂ pressure of 1atm,catalyst dosage of 3 wt%of isooctanol,n（H₂O₂）/n（isooctanol）of 2.5,response temperature of 90°C and response time of 12 h.Based on these conditions,the transformation rate of isooctanol was 94%and the selectivity of the target product isooctanoic acid was 88%.,and the yield of isooctanoic acid was increased compared with that when H₂O₂ oxidation alone was used 14%.The catalyst still had good catalytic effect after five times of repeated use and showed good catalytic activity for different chain lengths of aliphatic primary alcohols.（2）Sodium lignosulfonate quaternary ammonium salts were synthesized from sodium lignosulfonate,epichlorohydrin and tertiary amines with different carbon chain lengths,and a series of sodium lignosulfonate-quaternary ammonium salt-loaded sodium phosphotungstate catalysts were successfully prepared by combining them with sodium phosphotungstate by ion exchange method;the mechanism and behaviour of the catalysts were researched via FT-IR,XRD,TG,SEM and other characterization methods.The lacunary sodium phosphotungstate-sodium lignosulfonate quaternary ammonium salt Na PW₁₁-SL-QAS₁₆ with sixteen carbon chain length was screened as the best catalyst for the reaction by isooctanol template reaction.The optimal conditions for the reaction were determined by the single-factor optimization method:O₂ pressure of 1 atm,catalyst dosage of 5 wt%,n（H₂O₂）/n（isooctanol）of 2.5,response temperature of 90°C,and response time of 12 h.Based on these conditions,the transformation rate of isooctanol could reach 97%,the selectivity of isooctanoic acid was 95%,and the yield of isooctanoic acid was 10%higher than that when H₂O₂ oxidation alone was used.Based on the optimal conditions,the target fatty acids could be obtained in higher yields of 83-93%for different fatty alcohols,and the catalyst could be reused five times.In addition,XRF characterisation experiments showed that the Na PW₁₁-SL-QAS₁₆ catalyst exhibited better catalytic activity than the[（CH₃）₃NC₁₆H₃₃]Na₆PW₁₁O₃₉ catalyst due to the presence of more active components.This method has the value of applying sodium lignosulfonate,a paper by-product,as a carrier for fatty alcohol oxidation.（3）Controlled experiments such as radical trapping experiments,isotope experiments and hydrogen peroxide inhibition experiments were used to investigate the synergistic oxidation mechanism of H₂O₂ and O₂ in the reaction.It was shown that fatty alcohols are mainly oxidized by H₂O₂,while O₂ achieves synergistic oxidation with H₂O₂ by participating in the aldehyde-to-acid radical process catalyzed by the absence of sodium phosphotungstate quaternary ammonium salt.The synergistic and decomposition-inhibiting effect of O₂ can improve the utilisation of H₂O₂ in the reaction,thus increasing the yield of the reaction at the same amount of hydrogen peroxide.Based on the experimental results,a possible catalytic cycle mechanism of the quaternary ammonium-loaded Keggin-type lacunary sodium phosphotungstate catalyst in the selective oxidation of fatty alcohols by H₂O₂ with O₂ is proposed.