Basic Research On Complex Extraction Of Caproic Acid From Its Dilute Aqueous Solution

Caproic acid is a kind of basic chemical raw materials,widely used in organic synthesis,spices,plastics,adhesives and pharmaceutical industry.In recent years,the downstream product especially the rapid expansion of spices such as ethyl hexanoate,allyl caproate hexanoate,is rapidly expanding,so the demand for caproic acid is also gradually increasing.Caproic acid is the tight prospects of fine products.The purification of caproic acid from dilute solution is an important step in the production of caprolactam.Complex extraction is an important method for the separation and purification of organic carboxylic acids.In this paper,caproic acid from dilute solution was as the separation object.Tributyl phosphate(TBP)and trioctylamine(TOA)were selected as complexing agent,n-octanol and kerosene were selected as diluents.The preliminary exploration and system screening of caproic acid separation experiment were carried out.On the basis of discussed experiment,the influence factors of caproic acid concentration,extraction temperature,phase ratio,complexing agent concentration on the extraction equilibrium distribution coefficient were discussed.Furthermore,the orthogonal test of the caproic acid concentration,complexing agent content,octanol content and temperature for four variables was designed.The optimum operating conditions and the best ratio to extract caproic acid were analyzed by extreme analysis.With UNIFAC group contribution method,the distribution coefficient of caproic acid in n-octanol-water and kerosene-water system was calculated.On the basis of discussed above,considering both the physical extraction and chemical extraction,the mathematical model of caproic acid complexation extraction was established.The conclusions of this paper included:(1)after comprehensive consideration,trioctylamine,kerosene and n-octanol ternary mixed extractant was successfully selected.(2)With the increase of caproic acid concentration,extraction temperature,phase ratio of W/O,the distribution coefficient of extraction equilibrium gradually decreased.However,with the increase of tri-octylamine and octanol content within a certain range,extraction equilibrium distribution coefficient gradually increased.(3)The optimum conditions for the extraction of caproic acid were obtained by orthogonal test: initial concentration of caproic acid: 0.018mmol/L,the volume fraction of trioctylamine: 30%,the volume fraction of n-octanol: 50%,extraction temperature: 25°C.Under this condition,extraction equilibrium distribution coefficient of caproic acid was as high as 503.48.(4)With the UNIFAC group contribution method and the calculation principle of distribution coefficients,a C language program was designed to calculate the activity coefficients and the distribution coefficients of caproic acid in n-octanol-water and kerosene-water system respectively.The results were in good agreement with the literature values,which proved the feasibility of this method.(5)Considering both the physical extraction and chemical extraction,the mathematical model of caproic acid complexation extraction was established,and the relative error between the calculated and experimental values was almost within ±30%.The model provides a thermodynamic basis for the purification of caproic acid from dilute solution by complex extraction method.