Research On The Continuous Flow Synthesis Process Of Azo Dyes In Microchannels And The Treatment Technology Of Production Wastewater

Microchannel reactor is a continuous flow tubular reactor,which has the smaller piping size,very little liquid carrying capacity,and very large specific surface area volume ratio(up to 10,000-50,000 m²/m³),compared to conventional tubular reactors.Thus,the microchannel reactor has extremely high mixing efficiency(complete radial mixing in millisecond scale),extremely high heat transfer capacity(heat transfer coefficient up to 2500W/(m².K)),and a very narrow residence time distribution(almost non-returnable mixing,basically close to plug-flow).Compared with the traditional batch reaction process,microreactor can greatly enhance the mass transfer and heat transfer process,shorten the mixing and diffusion time,and realize uniform mixing and isothermal control of fluids.In addition,depending on the phase state of the reactants,microreactors are usually suitable for liquid-liquid and gas-liquid reactions,and the product cannot be solid,otherwise it is easy to block the reaction pipeline.With the upgrading of China's industrial adjustment,it is urgent for the chemical industry to develop towards the direction of greenness and sustainability.Using this new equipment and technology can significantly improve the essential safety of chemical process,realize precise control in fine chemical synthesis,develop efficient and environmentally friendly process,eliminate or reduce the generation of reactive by-products,and reduce waste discharge.This study focuses on the key steps of diazo dye synthesis(taking lemon yellow as an example).Under intermittent conditions,diazo reaction has safety risks,high temperature fluctuation,low mixing efficiency of raw materials,long residence time and many side reactions.It is suitable to select microchannel technology for optimization and improvement,so as to improve the yield of diazo reaction,optimize the refining process after the reaction and obtain qualified products,thus achieving the essential safety of the process and greatly reducing waste water production.Furthermore,for wastewater from azo dye production,a gel sphere containing manganese oxide-sodium alginate(MnO_x@MABs)was developed and an advanced oxidation technique was constructed to activate persulfate to remove azo dye wastewater(in the case of sunset yellow).The main conclusions of the paper are as follows:(1)Through the research on the synthesis process of lemon yellow,the synthesis raw materials of lemon yellow were adjusted to form a diazotization micro-channel process with sodium p-aminobenzene sulfonate solution,sodium nitrite,and hydrochloric acid as raw materials.The diazonium salt existed in the homogeneous solution through the control of residence time.The optimum reaction conditions were determined by studying the raw material concentration,residence time,hydrochloric acid addition,temperature,etc.A 97-98%final yield could be obtained under the optimum reaction conditions(5%sodium p-aminobenzene sulfonate,7 s residence time,n _HCl/n_??????was 2.2:1,and 5-25°C temperature).(2)Manganese oxide was synthesized by hydrothermal method.In combination with sodium alginate,MnO_x@MABs gel microspheres were successfully prepared,and SEM,XRD and FT-IR were used to analyze the morphology,structure and composition of the prepared gel microspheres.Then,these gel microspheres were used to activate persulfate to degrade sunset yellow,the representative pollutant of azo dye wastewater.The effects of the addition of MnO_x@MABs,p H value of wastewater,temperature,addition amount of PMS,and different initial concentration of azo dye wastewater on the degradation of sunset yellow were studied.The results show that the MnO_x@MABs/PMS system can degrade sunset yellow at a wide p H range.When 30 g/L of MnO_x@MABs and 0.5 m M of PMS were added to 100 m L of the wastewater with concentration of 200 mg/L,sunset yellow was completely degraded after stirred at40°C for 60 min.