Synthesis Of 9-fluorenylmethanol And 9-fluorenone From Fluorene And Its Application For Extraction And Separation Of Phenanthrene From Anthracene Residue

Anthracene residue is a kind of solid waste produced in coal-tar-refining process,yielding nearly one million tons per year.It belongs to hazardous organic waste because it is rich in polycyclic aromatic hydrocarbons such as phenanthrene and fluorene.Currently,the accumulation and incineration of anthracene residue are causing a lot of environmental pressure.In contrast,phenanthrene and fluorene are also important and high value-added chemicals.Extraction of phenanthrene and fluorene from anthracene residue is an effective way for its resource utilization.Nevertheless,due to the similar properties of phenanthrene and fluorene,the separation of them by conventional separation methods is energy-intensive,long process and ineffective.9-fluorenylmethanol and 9-fluorenone,as the downstream products of fluorene,have higher value.This project adopts the reaction–separation coupling method to achieve the extraction and separation of phenanthrene from anthracene residue by following steps:the first was hydroxymethylation of fluorene to 9-fluorenylmethanol or oxidation of fluorene to 9-fluorenone,and then separated these two chemicals by taking advantage of the solubility difference between phenanthrene and 9-fluorenylmethanol or9-fluorenone.Among them,organic strong base as the conventional catalyst was used in the one-step hydroxymethylation of fluorene to 9-fluorenylmethanol.The selectivity of9-fluorenylmethanol was low,and dehydration as well as disubstitution product yielded easily,accompanied by which the alkaline waste liquid was produced.The synthesis of 9-fluorenone by air-liquid phase oxidation of fluorene showed high yield and selectivity,but the purity separation was limited due to the small polarity difference between phenanthrene and9-fluorenone.Therefore,the controllable synthesis of 9-fluorenylmethanol and the efficient separation of 9-fluorenone from phenanthrene were the key of this study.The primary contents and results of this paper are as follows.（1）One-step synthesis of 9-fluorenylmethanol from fluorene and its application for the extraction and separation of phenanthrene from anthracene residueA mixture of dimethyl sulfoxide（DMSO）or N,N-dimethylformamide（DMF）and ethanol was used as solvent,and carbonate was used as catalyst for the one-step hydroxymethylation synthesis of 9-fluorenylmethanol from fluorene.The effects of ethanol addition,carbonate type,reaction temperature,reaction time,material ratio and inorganic salt on the product distribution were investigated.With DMSO+10%ethanol or pure DMF as the solvent,n（fluorene）:n（formaldehyde）:n（potassium carbonate）=1:1:0.2,the yield of9-fluorenylmethanol was about 25%and the selectivity is higher than 82%at 13 ^oC for 15min.The addition of ethanol could promote the formation of dehydration product,and the inorganic salts Ca Cl₂ and Zn Cl₂ could inhibit the side reactions.Anthracene residue was pretreated with xylene at a liquid-to-solid ratio of 0.8:1 once,and the enriched phenanthrene and fluorene accounted for more than 70%.The mass ratio of phenanthrene and fluorene was nearly 4:1.So the mixture of phenanthrene and fluorene with mass ratio of 4:1 was used as raw material,by which 9-fluorenylmethanol yielded less in a single reaction,and phenanthrene did not participate in the reaction but increased the mass transfer resistance.After five cycles reaction,the yield and purity of phenanthrene can reach97.6%and 93.2%,respectively;the total yield of 9-fluorenylmethanol was 66.5%,and the average purity was 95.0%.With the pretreated anthracene residue as raw material,the yield of9-fluorenylmethanol after the primary reaction was 8.32%,and it was difficult to separate.（2）Synthesis of 9-fluorenone by air-liquid phase oxidation of fluorene and its application for the extraction and separation of phenanthrene from anthracene residueFluorene converted to 9-fluorenone by using aqueous KOH solution with 45%mass fraction as catalyst and air as oxidant.The reaction solvent,reaction temperature and catalyst dosage were investigated,and the optimum reaction conditions were determined as follows:DMSO as solvent,n（KOH）:n（fluorene）=0.06:1,and the reaction was carried out at 50 ^oC last for 30 min.The fluorene was completely converted,and the yield and selectivity of9-fluorenone were close to 100%.The liquid-solid mass ratio for separation was obtained by the phase diagram method and solubility calculation method according the model mixture of phenanthrene and 9-fluorenone with the mass ratio of 4:1.Using methanol and cyclohexane as first and second separation solvent,the optimum liquid-solid mass ratios were 1.6:1 and 2.8:1,respectively.By using the model mixture of phenanthrene and fluorene as the raw material,the fluorene converted completely after 50 min.The purity of phenanthrene and 9-fluorenone was greater than 98%after separation,and the yield was greater than 91%.Using the pretreated anthracene residue as raw material,the purity and yield of phenanthrene were 76.58%and 89.86%,respectively;the purity and yield of 9-fluorenone were 93.98%and 84.52%,respectively.