Measurement and correlation of solubility of 9-fluorenone in 11 pure organic solvents from T=283.15 to 323.15 K

Huiqi Wang,Jianpo Ren,Shihao Zhang,Jiayu Dai,Yue Niu,Ketao Shi,Qiuxiang Yin,3,Ling Zhou,

1 School of Chemical Engineering and Technology,State Key Laboratory of Chemical Engineering,Tianjin University,Tianjin 300072,China

2 Sinochem Hebei Xinbao Chemical Technology Co.,Ltd,Handan 056500,China

3 The Co-Innovation Center of Chemistry and Chemical Engineering of Tianjin,Tianjin University,Tianjin 300072,China

Keywords:9-Fluorenone Solubility Correlation model Thermodynamic properties

ABSTRACT In this work,the solubility data of 9-fluorenone in 11 pure solvents (methanol,ethanol,n-propanol,isopropanol,n-butanol,iso-butanol,acetonitrile,ethyl formate,ethyl acetate,dimethyl sulfoxide,n-hexane)were measured by the gravimetric method from 278.15 K to 318.15 K under atmospheric pressure.The results showed that the solubility of 9-fluorenone in all tested solvents increased with the raised temperature.The solubility data were correlated by the modified Apelblat equation,λh model and NRTL (nonradom two fluid)model.The average relative deviation(ARD)correlated by three thermodynamic models indifferentsolvents wasallbelow 5%,whichindicatedthat the threethermodynamicmodelsfitthe solubility data well.Furthermore,the mixing thermodynamic properties of 9-fluorenone in pure solvent systems were calculated via NRTL model.The results indicated the dissolution process of 9-fluorenone is spontaneous and entropicallyfavorable.The solubilityand the mixingthermodynamicproperties providedinthispaperwould play an important role in industrial manufacture and follow-up operation of 9-fluorenone.

1.Introduction

As we know,the quality of product depends on the purity and crystal morphology.Solution crystallization plays an important role in the separation and purification process of product due to its better control of operation parameters.Thermodynamic data,especially solubility data,is of great importance in the design and optimization of crystallization operation.At present,it is still difficult to predict the solubility of chemicals directly.Classical solubility models are also based on experimentally measured solubility data.

9-Fluorenone (CAS registry No.486-25-9;Fig.1) also called dibenzopentacyclic ketone,is a common deep processing product of coal tar.As the raw material of important fine chemicals,9-fluorenone is widely used for preparing dye material,modifying properties of resin and additives of material fields [1,2].Zhangetal.[3] proposed a novel separation technology for the eutectic mixture of fluorene and fluorenone by solution crystallization on the basis of the determined fluorene-fluorenone-cyclohexane ternary solid-liquid equilibrium phase diagrams.At present,the solubility of 9-fluorenone only in pure solvents at room temperature has been tested,which is still not enough for industrial operation[4].Therefore,the solubility data of 9-fluorenone in common 11 solvents from 278.15 K to 318.15 K were provided in this paper,which supplemented more information about 9-fluorenone and provided the basis for industrial separation and purification process of 9-fluorenone.

Fig.1.Chemical and crystal structure of 9-fluorenone.

Fig 2.Power X-ray diffraction pattern of 9-fluorenone in different solvents.

Fig 3.The DSC and TG curve of 9-fluorenone in different solution (Black line represents TG curve and red line represents DSC curve).

Fig 4.The mole fraction solubility of 9-fluorenone in 11 pure solvents at the temperature ranging from 278.15 K to 318.15 K and pressure of 0.1 MPa: (a)alcohols,(b) esters and (c) others (acetonitrile,dimethyl sulfoxide,n-hexane).Experimental results are presented by scatter points and the modified Apelblat model fitting results are presented by lines.

In this work,the solubility data of 9-fluorenone in 11 common solvents,including methanol,ethanol,n-propanol,iso-propanol,n-butanol,iso-butanol,acetonitrile,ethyl formate,ethyl acetate,dimethyl sulfoxide,n-hexane,from 278.15 K to 318.15 K were measured by gravimetric method.The modified Apelblat equation,λ h equation,and the NRTL (non-radom two fluid) model were used to correlate the experimental solubility data[5].Furthermore,relevant mixing thermodynamic properties of dissolution process were calculatedviathe NRTL model [6].

2.Experimental

2.1.Materials

9-Fluorenone was purchased from Heowns Biochem LLC (mass fraction purity ≥0.98).Organic solvents (mass fraction purity≥0.995) were purchased from Tianjin Kermel Chemical Reagent Co.,Ltd.All the materials were used without further purification.

Detailed description of materials used in the paper are shown in Table 1.

Table 1 Detail of the materials specification

2.2.PXRD analysis

The crystal form of 9-fluorenone is characterized by powder Xray diffraction (PXRD) to confirm that there is no polymorphic transformation during the solubility measurement process.The PXRD patterns were collected by Rigaku D/MAX-2500 equipped with Cu Kα radiation (0.15406 nm) at 30 mA and 40 kV and the measurements were carried out from 2° to 50° at a scanning rate of 8 (°).min-1[6].

2.3.Differential thermal analysis

The melting properties of 9-fluorenone are measured by the differential scanning calorimeter (DSC,MettlerToledo,Switzerland).The pre-weighted samples (5-10 mg) were heated at a rate of 10 K.min-1from 303.15 K to 473.15 K under nitrogen atmosphere[7,8].

2.4.Solubility measurement

The solubility data of 9-fluorenone in 11 pure solvents are measured by gravimetric method.The experiments were performed in a jacketed glass vessel (20 ml) equipped with a magnetic stirrer.The temperature of solution was controlled by the circulating water from thermostat (CF41,Julabo,German,uncertainty ＜0.01 K).Excess amount of 9-fluorenone was added into the preheated/-cooled solvents in sealed brown glass vials.These vials were placed into the jacketed glass vessel with temperature controlling.The mixture was continuously agitated for 12 h by a magnetic stirrer to reach the solid-liquid equilibrium completely,and then kept static for 4 h to make solids settled[9,10].About 2 ml of upper saturated clear solution was withdrawn by the preheated/cooled syringes (with polytetrafluoroethylene 0.22 μm filter) and weighted in a pre-weighted breaker immediately by an electric balance(type AL204,Mettler-Toledo,Switzerland)with an accuracy of±0.0001 g.Then the filtrate was dried in a vacuum oven at 313.15 K for around 4 h to make solvents evaporated completely.The residue was weighted and analyzed by PXRD.The solubility of 9-fluorenone was obtained by calculating the sample mass change before and after drying.For each temperature point,the experiments were performed for three times and the arithmetic average value was used as the final result [11,12].

The mole fraction solubility of 9-fluorenone in pure solvents was calculated by Eq.(1) [13],

wherem1andm2represent the mass of 9-fluorenone and solvent in saturated solution;M1andM2represent the molar weight of 9-fluorenone and solvent,respectively [14].

2.5.Solubility correlation

The measured solubility was correlated by the Modified Apelblat model,λhmodel and the NRTL model.

2.5.1.ThemodifiedApelblatmodel

The modified Apelblat model was a semi-empirical equation,which was proposed on the basic of the Clausius-Clapeyron equation.It is widely used in solubility correlation.The relationship between molar fraction solubility and temperature was linked by three thermodynamic parameters [15].The equation can be expressed as following:

whereA,BandCrefer to model constants;xis the mole fraction solubility of fluorenone andTpresents the absolute temperature.

2.5.2.λhmodel

On the basis of the generalized relation equation,λh equation was proposed by Buchowski-Ksiazaczak.Two parameters were used to relate the experimental solubility [16].It is expressed as Eq.(3):

where λ andhrefer to model parameters;Tis the experimental temperature andTmis the standard melting temperature.

2.5.3.NRTLmodel

NRTL equation was proposed on basis of the concept of local composition.A non-random parameter was introduced into the Boltzmann-type equation to link the local composition and the total composition,which can reflect the characteristics of the system.The activity coefficient was considered to determine the thermodynamic properties.And the model is widely used to describe solid-liquid equilibrium properties for many non-ideal solutions,which is presented as follows [17]:

wherexiis the mole fraction of 9-fluorenone,ΔfusHandTmare the melting enthalpy and melting point of 9-fluorenone,respectively,and γiis the activity coefficient of componentiin the mixed solution [18].For the solution with pure solvents:

whereGij,Gji,τijand τjiare parameters of this model,which can be expressed as following:

where τ is a constant which was assumed for the non-randomness of the solution;grepresents the Gibbs energy of intermolecular interaction;α is an adjustable empirical constant.

3.Results and Discussion

3.1.Solid characterization

PXRD patterns of 9-fluorenone in the process of solubility experiment was verified and the results were shown in Fig.2.The PXRD patterns of 9-fluorenone of all solid used have the same characteristic peaks in this work.This means that no polymorphic transformations occurred during the process [5].

Fig.3 shows the DSC and TG curve of 9-fluorenone in different solvents,which has a strong endothermic peak indicating its melt point is 356.54 K [u(Tm)=0.5 K],the determined fusion entropy(ΔfusH)=16.297 kJ.mol-1[ur(ΔfusH)=0.05] [15].The mass loss of 9-fluorenone after 356.54 K can ascribe to the decomposition.And the experimental results are in good agreement with those in Ref.[19].

3.2.Solubility results

3.2.1.Solubilityof9-fluorenonein11puresolvents

The experimental and calculated mole fraction solubility of 9-fluorenone in 11 pure solvents,as a function of temperature,is listed in Table 2,and the solubility curves are presented in Figs.4[17].

Table 3 Parameters of the modified Apelblat model and ARD values for 9-fluorenone in 11 pure solvents

Table 4 Parameters of λh model and ARD values for 9-fluorenone in 11 pure solvents

Table 6 The mixing thermodynamic properties of fluorenone in 11 pure solvents

It can be found that the solubility of 9-fluorenone shows a strong temperature dependency,which increases significantly with the raise of temperature.It has the largest solubility in ethyl formate and the lowest solubility inn-hexane among 11 solvents.The solubility of 9-fluorenone in methanol andn-hexane is close below 288.15 K.With the increase of temperature,the solubility of 9-fluorenone in methanol is significantly higher than that innhexane.When the temperature is lower than 303.15 K,the solubility of 9-fluorenone iniso-propanol and ethanol is similar.Above 303.15 K,the solubility of 9-fluorenone iniso-propanol is significantly higher than that in ethanol.The solubility order at temperatures below 303.15 K in all solvents as ethyl acetate ＞ethyl formate ＞ dimethyl sulfoxide ＞ acetonitrile ＞iso-butanol ＞n-propanol ＞n-butanol ＞iso-propanol ≈ethanol ＞methanol ＞n-hexane.The solubility order in all solvents above 303.15 K as:ethyl formate ＞ethyl acetate ＞acetonitrile ＞dimethyl sulfoxide ＞n-propanol ＞n-butanol ＞iso-butanol ＞iso-propanol ＞ethanol ＞methanol ＞n-hexane.

The solubility of 9-fluorenone in all solvents is not strictly in consistent with the order of polarity of solvents.The dissolution ability in organic solvents of solutes not only depends on the polarity(π*)of solutes and solvents,but also the interactions of solutesolvent and solvent-solvent,which are influenced by the ability of hydrogen bond,steric hindrance and the extent of self-association within solvent molecules(cohesive energy density).Therefore,this phenomenon can ascribe to the interactions between the solutesolvent and solvent-solvent.

3.2.2.Evaluationoffittingmodels

Tables 3-5 show the fitting parameters of three models in 11 pure solvents.And the value of average relative deviation (ARD)is used for evaluating the quality of results and the ARD is calculated as follow equation [20].

whereNrefers to the number of experimental pointsrepresent the measured solubility and calculated solubility,respectively [21].

Results shows that the largest ARD value for all models is below 5%,indicating all models used in this paper gave satisfactory correlation results.Compared with the other two models,NRTL model stands out to be the most accurate model with the lowest average ARD value (3.18%) in pure solvents.

3.2.3.Thermodynamicparametersofthedissolutionprocess

The ideal solution mixing thermodynamic properties can be presented as followed Eqs.(9)-(11):

wherexiis the mole fraction of 9-fluorenone and solvents,ΔmixGid,ΔmixHidand ΔmixSidrepresent the mixed Gibbs energy,the mixing enthalpy,and the mixing entropy in ideal solution,respectively[22].

In real condition,the activity coefficient is calculated by the NRTL model to calculate the mixed thermodynamic properties.

where ΔGE,ΔHEand ΔSErefer to the excess properties which are calculated by Eqs.(15)-(17) and ΔmixG,ΔmixHand ΔmixSare the mixing properties of real situation [23,24].

γi,the activity coefficient of the compositioniin real solution,is calculated by the NRTL model,andxiis the molar fraction of the compositioni.

The calculated mixing thermodynamic properties in 11 pure solvents are listed in Tables 6.The value of ΔmixGin 11 pure solvents is all negative and decreases as the temperature increases.It indicates the mixing process of fluorenone in selected solvents is spontaneous and more likely to occur as the temperature increases[25].The value of ΔmixHis positive,which indicates that dissolution process is endothermic[26].Besides,the positive value of ΔmixSrepresents that the mixing process confirms to principle of entropy increasing and is entropy-driven [17,27,28].

4.Conclusions

In this work,the solubility order at temperatures below 303.15 K in all solvents is ethyl acetate ＞ ethyl formate ＞dimethyl sulfoxide ＞acetonitrile ＞iso-butanol ＞npropanol ＞n-butanol ＞iso-propanol ≈ethanol ＞methanol ＞nhexane.The solubility order in all solvents above 303.15 K is:ethyl formate ＞ethyl acetate ＞acetonitrile ＞dimethyl sulfoxide ＞npropanol ＞n-butanol ＞iso-butanol ＞iso-propanol ＞ethanol ＞meth anol ＞n-hexane.As the temperature rises,the solubility of 9-fluorenone increases,too.The three models,including the modified Apelblat equation,λhequation and the NRTL model,have great correlation performance,with ARD in three models below 5%.NRTL model stands out to be the most accurate model.The thermodynamic parameters obtained by NRTL model suggest that the dissolution behavior of 9-fluorenone is spontaneous,endothermal and entropy-driven in 11 organic solvents used here.The solubility data obtained here could provide significant value in industrial manufacture and the follow-up research on 9-fluorenone.

Data Availability

Data will be made available on request.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The work is supported by Tianjin Municipal Natural Science Foundation (21JCYBJC00600).