Recycling Process Research And Development Of BDO From BDO Distillation Waste

In the Reppe refining process, wiped film evaporator was used to purify BDO by distillation,thus the bottom would remain BDO distillery waste. According to statistics, about100kg of the waste was produced along with a production of one ton BDO, which wasdark and sticky residue with high salt content, mainly containing BDO, high boilingalcohol impurities，ethers oligomers，sodium hydroxide，sodium formate，a littlepolymers and solid residues. Therefore， the recovery of the BDO and othercomponents from the waste can not only reduce environmental pollution, but alsoconsiderably benefit economy. Direct recovery of BDO from the waste by distillationmethods was conducted in some enterprises，but the result was not satisfactory, and theremaining distillation residues was difficult in recycling.This topic proposed a simple recycling process. Salts and impurities were firstremoved by salting-extraction pretreatment, then reduced pressure bath distillation wasconducted to separate and depolymerize the distillation waste, thus the BDO, DHF,3-tetrahydrofuran methanol and other products could be fully recovered.Firstly, the salting-extraction mechanism and the optimum condition wereinvestigated. The optimal salting extraction condition was determined by changingtemperature condition and the amount of salting-out agent, extraction agent andsulfuric acid. The optimal mass ratio of waste: extraction agent: salting-out agent:sulfuric acid is1:1:0.3:0.09. After salting-extraction pretreatment, the lower waterphase was a mixture of sodium sulfate and solid residues, the upper oil phase wascomplex with BDO, ether oligomer, mixed alcohols, polymers and a small amount ofwater.Secondly, the oil phase was pumped into the distillation apparatus, followed withthe recovery of BDO and other components under different boiling points and thecollection the remaining distillation substrate. For the crude BDO, infraredspectroscopy was used to characterize its structure, and gas chromatography-massspectrometry was used for qualitative and quantitative analysis. In addition, theformation mechanism of the by-product3-tetrahydrofuran methanol was brieflyintroduced.Then，using the distillation substrate as materials collected from the previous step, sulfuric acid was used as catalyst for the hydrolysis of the materials, and the hydrolysiscondition was optimized. On the basis of a single factor, regarding the totaldepolymerization recovery of BDO and DHF as an index，the optimum hydrolysisconditions was determined by orthogonal experiments. The depolymerizationtemperature is165℃, and the solid-liquid ratio is1:1.5with the sulfuric acidconcentration of8%and the reaction time of4h. Under the optimal conditions, thedepolymerization recovery can reach38.3%.Finally, in order to shorten waste recovery time and reduce cost，the wasterecovery process was optimized in this work, and the material accountancy of theoptimized process was conducted. After optimization, the recovery rate of BDO，DHF,3-tetrahydrofuran alcohol, and sodium sulfate is23.9%,8.5%,3.7%,20.7%,respectively, with a residues emissions load of18%，which indicates obviously goodwaste recycling effect.