| Pyridine and picolines,as main pyridine bases,have found versatile applications in pesticide,medicine and daily-use chemical intermediate.The production of pyridine bases couldn't satisfy the need of applications in new environment-friendly insecticide,perfume and feed additives.Currently,the pyridine and picolines are mainly produced from formaldehyde,acetaldehyde and ammonia by a fluidized-bed reactor through a vapor phase reaction.The 2-picoline and 4-picoline could be produced when acetaldehyde and ammonia are fed,while pyridine and 3-picoline are the main products when formaldehyde are added.However,the existence of 4-picoline makes it difficult to separate from 3-picoline.And also,the fluidized-bed catalytic process has high requirements for catalyst and operation.Further more,formaldehyde and acetaldehyde are restricted to oil resource market,easy to polymerize and difficult to get stored.However,there are good economic and social benefit to produce pyridine bases from renewable biomass resources,such as biomass ethanol and acrolein from biomass glycerol.Ethanol could be greatly and easily produced from biomass fermentation.Plenty of glycerol byproducts,which appear during the production process of biodiesel,are difficult to get used.It is meaningful and attractive for producing pyridine bases from acrolein since the techniques and technologies of producing acrolein from selective dehydration of glycerol are being mature.This process has many advantages,such as no 4-picoline,high 3-picoline yield and smart reaction mode.It is a communication bridge between biomass resources and pyridine base industries to produce pyridine bases with ethanol and acrolein,both of which could come from biomass resources.The engineering and technology of producing pyridine and picolines from ethanol and acrolein with a fixed-bed reactor through a vapor phase method were studied in this paper.And that,3-picoline was also produced from acrolein in a kettle-type reactor through a liquid phase reaction.At last,the catalytic mechanism and reaction process were discussed.Followings are the main contents:(1)Ion exchange,impregnation and alkaline treatment methods were used to modify HZSM-5 zeolite to improve the catalytic performances.The crystal structure,surface properties,morphology and pore structure of the catalysts had been characterized by means of modern techniques.Pyridine and picolines were prepared from ethanol and ammonia on a fixed-bed reactor with modified HZSM-5 catalysts.Over a NaOH and Zn modified HZSM-5(Si/Al=75)catalyst,a 50%yield of pyridine bases,which contained 84%of pyridine,was obtained.And also,a small amount of picoline,acetonitrile,ethylene and other products had been produced.The optimazed reaction conditions were as followings:the reaction temperature of 410 ?,the alcohol liquid hourly space velocity of 2.1 h-1,ethanol/methanol/ammonia/oxygen ratio of 2/1/3/0.8(mol).(2)The 3-picoline was synthesized with acrolein and ammonium salt using propionic acid,ethylene glycol butyl ether and acetic acid as solvent,respectively.The influences of reaction conditions to the 3-picoline yield were studied in detail,such as the kind and weight of solvent,ammonium salt,diluent and catalyst,temperature,the feeding flowrate,time,etc.The yield of 3-picoline reached up to 60%over the SO42-/ZrO2-FeZSM-5 catalyst,with no other pyridine products and only acrolein polymer by-products.The optimized reaction conditions are as followings:acrolein/ammonium acetate/acetic acid of 0.025/0.125/1.8(mol),acrolein feed concentration of 8%,a flow rate of 12 mL·h-1,feeding time of 1.5 h,reaction temperature of 130 ?.(3)The pyridine and 3-picoline were produced from acrolein and ammonia with a fixed-bed reactor in a vapor phase reaction.The influences of process parameters,such as temperature,catalyst,space velocity and raw material ratio to the yield of pyridine bases were studied.The yield of pyridine bases had reached up to 68%over a HF/MgZSM-5 catalyst,with a 3-picoline yield of 35%and pyridine yield of more than 29%.The optimized reaction conditions were as followings:acrolein gas hourly space velocity of 160 h-1,reaction temperature of 425 ?,acrolein/water/ammonia ratio of 1/2/1(mol),time of 4 h.The best catalyst had been produced when the load of MgF2 was 3%,silica/alumina ratio was 25 and the calcination temperature was 700 ?.(4)According to the research of aldehyde/ammonia,ethylene/ammonia and ethanol/ammonia reactions,it was proposed that pyridine bases could be produced through acetaldehyde,ethylene and ethylamine during the ethanol/ammonia reaction process,with acetaldehyde and ethylamine routes as the main ones.The product distribution was determined by the reactions of ethyleneimine and/or ethylene amine,which were considered to be the active intermediates.The operation conditions and catalyst had great effect on the product distribution and mechanism route,which might undergo oxidation,dehydrogenation,dehydration,addition,elimination and decomposition procedure.(5)According to the charge distribution,electrostatic interaction and frontier molecular orbital of acrolein and propylene imine,a mechanism of preparing 3-picoline from acrolein and ammonia was summarized.It was confirmed through analyzing the distribution of pyridine base products using acrolein,formaldehyde and acetaldehyde to react with ammonium acetate.The similiar formation mechanism of pyridine bases from aldehyde and ammonia was also proposed.The ?,?-unsaturated alkenyl imine and dihydropyridine were regarded as the key intermediates.(6)The reaction of acrolein with ammonia on HF/MgZSM-5 catalyst was studied through FT-IR spectrometer equipped with an in-situ transmission cell.The variation frequency of IR spectrum was investigated to confirm the adsorption form of acrolein on catalyst surface,making sure propylene imine as the active intermediate.The reaction order and active energy of acrolein were calculated,as well as the catalytic procedures of pyridine and 3-picoline from acrolein and ammonia were proposed. |
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