Study Of Oxidized Wax From Coal-Based Fischer-Tropsch Wax

Fischer-tropsch wax is an indirect coal liquefaction product with high melting point,low penetration and high hardness.In recent years,with the maturing of Coal-to-liquids technology,the production capacity of F-T wax increases and the market is close to saturation.The primary F-T wax products are far from meeting the needs of industrial development.The oxidation-modified F-T wax has good emulsification and lubricity,and is widely used in biodegradation,ink,PVC processing and other industries,which improves the added value of products and is widely valued by enterprises.At present,the domestic oxidation modification of F-T wax mainly adopts catalytic oxidation process,which is complicated and the product was brown and had a pungent smell.The non-catalytic oxidation process is still in the laboratory stage,and there is no mass production and lack of pilot production experience.Therefore,This paper studies the scale-up process of F-T wax non-catalytic oxidation process and produces excellent oxidized wax,combining stirring scale-up with CFD to solve the problems of dissolved oxygen and mass transfer.The effect of different operating conditions and agitator internals on gas-liquid dispersion in a multiple impeller(HEDT-WH_d-WH_d)stirred tank was studied.The results showed that increasing stirring speed and superficial velocity can increase total gas holdup and dissolved oxygen.Reducing gas velocity and increasing stirring speed can reduce the bubble size and increase gas-liquid exposed surface.The total gas holdup of tube distributor was 15%to 20%higher than that of aerator;The dissolved oxygen of the aeration was about 0.5 mg/L higher than that of the tube distributor.According to the Euler-Euler multiphase flow model and the standard k-εturbulence model,the CFD simulation of the three-layer combined impeller stirred tank was carried out.The simulation results showed that increasing stirring speed can raise local gas holdup and enhance mass transfer near the middle and bottom impellers.Increasing superficial gas velocity,the diffusion range became wider and local gas holdup increased.Structure of gas distributor had a great impact on phase dispersion.The large structure of tube distributor affectted circulation of the bottom flow field and the local gas holdup at the reactor wall is higher;Aerator had more uniform gas phase dispersion and better mass transfer.The relative error of simulation results of two distributors was around 8%,similar to cold experiment.On basis of cold experiments and simulation,F-T wax was used to conduct catalytic oxidation reaction with air in stirred reactor.Results showed that the optimal process conditions were as follows:temperature 150℃,gas flow rate 110 L/min,reaction time 6 h,and aerator was more suitable.The oxidized wax products with acid value of 26.83 mg KOH/g,saponification value of 56.80 mg KOH/g,dripping melting point of 96.3℃and insertion degree of 25℃≤12 mm can be prepared under the technological conditions.Compared with oxidized wax on the market,the experimental samples in this paper had the advantages of high saponification value,white color and light ester flavor.