Experimental Study On The Separating Synthetic Liquid In The Production Of 4-tert-Butylbenzaldehyde And 4-tert-Butylbenzoic Acid

In this study, synthetic liquid separation of 4-tert-Butylbenzaldehyde and 4-tert-Butylbenzoic acid formate production process was improved, the salt containing wastewater and waste gas containing toluene. Synthetic liquid separation processes used in this study including washing separation, stripping separation and ultrasound enhanced crystallinity. Firstly, recovered all the catalyst and most of the acetate in the synthesis liquid by the method of washing liquid separation; Then stripping separation method is used to respectively separate and recycle the organics exists in the organic phase of secondary washing; finally, make use of acetic acid as the solvent instead of toluene, using ultrasound enhanced recrystallization method to purify the tertiary butyl benzoic acid.The best way to separate synthetic liquid is washed twice:"the first washing" is to recycled acetate, cobalt acetate, sodium bromide; and "the second washing" is aim at remove most of the acetic acid in the organic phase and separate portions of tert-butyl benzoic acid; moreover, "the second washing" can be repeated. For the first washing, the best ratio is 1:5; while the second washing is 1:1; in addition, for every washing, the amount of acetate and tert-butyl benzoic acid in the organic phase and used water levels are in line with the relation y=axb. Take acetic acid and catalyst as the research object, the process of acetic acid and catalyst separated from the solution system can be think of as a solvent extraction process, and the distribution coefficient and the extraction rate of acetic acid were increased with the increase of water consumption, when the catalyst ratio remain 1:10, the distribution coefficient D goes to infinity, an extraction rate E tends to 1. Take PTBA as research object, the process of PTBA from saturate in the solution system to precipitated as crystals, can be seen as a solvent separation process, the main factor to influence the washing separating is the changes of solubility in the solution system and the solubility of PTBA increased while the acetic acid concentration increased; From the crystallization thermodynamics analysis, the relationship between PTBA in pure acetic acid solubility with temperature accord logX= A+(B/T)+Clog T, higher the temperature, the greater solubility, and there is also dynamic process exists in the two stage of PTBA crystallization nuclei formation and crystal grew up.By comparative analysis, I found that the stripping using nitrogen gas as a carrier gas is more suitable to separated organic phase in ’the second washing’. And the optimum nitrogen flow rate is 100L/h, the best stripping temperature is 95℃. Higher the stripping temperature, the amount separated from organic phase greater, namely higher the stripping efficiency, but, the prevent the t-butyl benzaldehyde in the organic phase easily oxidized, selected 95℃ as the right temperature.In the optimum conditions of 95℃,100L/h, stripping time is 180min, the total separation of the organic phase was 35%, the separation rate of acetic acid, p-tert-butyl toluene, p-tert-butylbenzene formaldehyde respectively is, 96.73%,50.89%,5.41%; Acetate is the easiest to separate, in the prior 90min can be completely separate, followed by tert-butyl toluene, p-tert-butyl-benzaldehyde is most difficult to separate.Ultrasonic enhancement of PTBA optimal conditions was:with acetic acid as solvent, at low frequency (25kHz), power 240W. In the PTBA-acetic acid solution system, Acetic acid as the solvent, in OW-300W ultrasonic power range, the greater the power, the shorter the crystallization induction period, the greater the rate of crystallization; Contrast of 25kHz and 40kHz ultrasonic frequency, low frequency smaller induction, low frequencies the greater rate of crystallization; the more uniform and better particle size of crystalline product obtained by ultrasound, the more regular crystal form obtained by stirred; in the range of 180W-240W for ultrasonic power, the crystalline product is more uniform, out of this power range, the obtained crystalline product is be effected.sBy the study of series of processes, the optimum condition of clean production process to separate PTBA synthetic liquid is the following:washed twice the synthetic (the first washing ratio is 1:5 and the second washing ratio is 1:1); using nitrogen gas as a carrier gas to separated organic phase in ’the second washing’(the nitrogen flow rate is 100L/h, the stripping temperature is 95℃); Enhanced ultrasound crystallization with acetic acid as the solvent (ultrasonic power 240W, frequency 25kHz). Under the optimum condition, took 1000ml synthetic liquid as the research object, the removal of acetic acid by the first washing and the second washing were respective 90.70% and 96.44%, the majority of acetic acid is separated and the catalyst can be separated completely, the tert-butyl benzoic acid crystals crude product was 49.20g; By stripping gas separation of the organic phase, the separation of tertiary butyl benzoic acid was 95.36%, acid completely separated, tert-butyl group toluene separation was 79.04%, the separation of tert-butylbenzene formaldehyde was 18.17%; with the acetic acid as the sovent, the crude product of tert-butyl benzoate was recrystallized and introducing ultrasound enhanced crystallinity, then drying the resulting crystals, finally analysis the crystals by SEM, chromatography XRD and IR, found the result that the resulting crystal is tert-butyl benzoic acid, and the crystal structure and composition were not changed at all.