Hydrodeoxygenation of Phenolic Model Compounds over MoS 2 Catalysts with Different Structures

Chinese Journal of Chemical Engineering 16(5) 733mdash739 (2008)

Hydrodeoxygenation of Phenolic Model Compounds over MoS2

Catalysts with Different Structures

YANG Yunquan (杨运泉)1 LUO Hersquoan (罗和安)1 TONG Gangsheng (童刚生)1 Kevin J Smith2 and TYE Ching Thian2 1 Department of Chemical Engineering Xiangtan University Xiangtan 411105 China 2 Department of Chemical and Biological Engineering University of British Columbia Vancouver BC V6T 1Z3 Canada

Abstract Several MoS2 catalysts of different structure prepared by in situ decomposition of ammonium heptamolyb-date (AHM) and molybdenum naphthenate (MoNaph) and by MoS2 exfoliation (TDM) were characterized by BET X-ray diffraction (XRD) Energy Dispersive X-ray (EDX) and transmission electron microscopy (TEM) The analy-sis showed that MoS2 structure was dependant upon the preparation procedure The activity of the catalysts was de-termined by measuring the hydrodeoxygenation (HDO) of phenol 4-methylphenol and 4-methoxyphenol using a batch autoclave reactor operated at 28 MPa of hydrogen and temperatures ranging from 320-370degC By comparing the conversion the reactivity order of the catalysts was AHM＞TDM-D＞MoNaph＞thermal＞MoS2 powder＞TDM-W Also the effect of reaction temperature on the HDO conversion was explained in terms of equilibrium of reversible reaction kinetics The main products of the HDO for phenolic compounds were identified by gas chro-matographymass spectrometry (GCMS) The results showed that the product distribution and the HDO selectivity were correlated with the reaction temperature Two parallel reaction routes direct hydrogenolysis and combined hy-drogenation-hydrogenolysis were confirmed by the analysis of the product distribution High temperature favored hydrogenolysis over hydrogenation for HDO of phenol and 4-methoxyphenol whereas for 4-methylphenol the re-verse was true Keywords ammonium heptamolybdate derived MoS2 structure effect characterization hydrodeoxygenation re-activity product distribution

1 INTRODUCTION

Although hydrodeoxygenation (HDO) is an im-portant class of catalytic hydroprocessing reaction for oxygen removal from fuel oils derived from coal oil shale and especially from bio-mass with a high oxygen mass content (＞10) it has still received relatively little attention because of the negligible low concen-tration of the organo-oxygen compounds in petroleum or crude oil [1] Fuel instability associated with oxy-genated compounds present in these oils could lead to fuel quality deterioration during its storage and poor fuel performance [2] Bio-oils contain significant quantities of phenolic oxygen and removal of this kind of oxygen by HDO is of interest if these oils are to be used as alternative energy sources or green fuels

HDO occurs simultaneously with hydrodesulfu-rization (HDS) hydrodenitrogenation (HDN) and hy-drogenation (HYD) during the hydroprocessing of all kinds of feeds for the production of fuels So far MoS2 supported on γ-Al2O3SiO2 and promoted with Co or Ni has been widely used as a catalyst in these processes [3 4] but in some studies unsupported MoS2 was often reported as a model catalyst for hydroproc-essing to eliminate support and promoter effects [5-7] Unsupported MoS2 is also a significant catalyst for heavy oil hydrocracking in petroleum industry [8]

The catalyst morphology is one of the important factors to hydroprocessing The activity and selectiv-ity of MoS2 in the process mainly depends on the structure of the catalyst Many reports have been pub-lished on the structure-reactivity relationship for MoS2 catalyst [9 10] Good catalyst dispersion and hence high activity can be usually obtained by introducing

water- or oil-soluble catalyst precursors to the feed that decomposes to form the active MoS2 in situ Alonso et al claimed that MoS2 catalyst derived from in situ decomposition of ammonium thiometallates had much higher hydrogenation selectivity than that from ex situ during HDS of dibenzothiophene (DBT) [11] Tye and Smith studied the Cold Lake bitumen hydrocracking in a slurry reactor with MoS2 catalysts derived by different methods and showed how the structure of catalyst affected its activity conversion and coke yield [12] Del Valle et al [13] revealed a 35-fold increase in thiophene HDS activity of well-dispersed MoS2 compared to common crystalline MoS2

Since phenolic compounds constitute important part of bio-oils HDO of phenols is considered as a key and classical reaction in hydroprocessing for the feeds Laurent and Delmon [14] studied the influence of O- N- and S-containing compounds on HDO of phenols over CoMoγ-Al2O3 and NiMoγ-Al2O3 cata-lysts their results revealed that the hydrogenolysis path was more severely inhibited than the hydrogena-tion path in HDO of 4-methylphenol

The reaction network and the mechanism for HDO of phenolic compounds have been studied by many investigators [15-17] The major pathways for HDO of phenolic compounds were found to be via two parallel routines ie through hydrogenolysis and hydrogena-tion [2 18 19] regardless of which catalyst was used Usually a pseudo first-order reaction kinetic model was used to estimate the rate constant and the activation energy for HDO of phenolic compounds [16 20 21]

Several investigations showed that the distribu-tion of the products for HDO of phenolic compounds was very complicated [21-23] Generally benzene

Received 2007-10-15 accepted 2008-04-16

To whom correspondence should be addressed E-mail hluoxtueducn

Chin J Chem Eng Vol 16 No 5 October 2008 734

toluene phenol xylenol andor cyclohexylbenzene are present in the products for HDO of phenol and substi-tuted phenolic compounds A recent investigation [24] indicated that during the HDO of phenols these dis-tributions can be changed greatly by changing MoS2 catalyst morphology and structure hydrogenolysis of C OH bonds of 4-methylphenol was favored over MoS2 with a lower degree of stacking whereas aromatic ring hydrogenation of phenol was favored over MoS2 with a higher degree of stacking However the effect of reaction temperature on the distribution and the selec-tivity of the HDO of phenols is still worth of study

In the present work the effects of reaction tem-perature catalyst morphology and structure on HDO of phenol 4-methylphenol and 4-methoxyphenol were examined Unsupported MoS2 catalyst was prepared by different methods and used as a model hydroproc-essing catalyst to eliminate support and promoter ef-fects and the activity and selectivity of the catalysts for HDO of the chosen model compounds were described

2 EXPERIMENTAL

21 Materials

All the materials are presented in mass concen-tration until specified otherwise MoS2 (＜2 μm pow-der 990) n-butyllithium (AR 990)hexane (AR 990) used for exfoliation ammonium heptmolybdate tetrahydrate (AHM AR 990) used for in situ decomposition phenolic model compounds (reactants AR ge980) n-hexadecane (solvent AR 990) and carbon disulfide (AR 990) used for reaction were obtained from Sigma-Aldrich Mo-lybdenum napthenate (MoNaph 60 Mo) was sup-plied by ICN Biomedicals Inc Hydrogen (995) was supplied by Paraxair Inc

22 Catalyst preparation

MoS2 catalysts with 5 different structures were prepared according to the method described as follows

The first two catalysts were prepared by in situ decomposition of soluble Mo precursors molybde-num naphthenate (MoNaph) and ammonium hepta-molybdate tetrahydrate (NH4)6Mo7O24middot4H2O (AHM) The MoNaph or AHM was mixed with the reactant carbon disulfide and n-hexadecane solvent and then placed into the reactor described below The reactor was heated up to 320-370degC and hydrogen was introduced into the reactor During this heating period MoS2 was produced by the in situ decomposition of the MoNaph or AHM and by the reaction with H2S [4 11] The re-action equation for AHM or MoNaph derived MoS2 catalyst was as follows [4]

35H2+AHM+7CS2 ⎯⎯rarr

7MoS2+28H2O+7CH4+6NH3 (1) or

H2+MoNaph+CS2 ⎯⎯rarrMoS2+H2O+CH4 (2)

The third catalyst was commercially available crystalline MoS2 powder (99) from Sigma-Aldrich

and used without further treatment The last two catalysts were the laboratory pre-

pared exfoliated MoS2 which was dispersed in water (TDM-W) or in decalin (TDM-D) respectively Exfo-liation was carried out under argon atmosphere in a glove box using a slightly modified method of Joen-sen et al [25] MoS2 powder was soaked in hexane containing 25 molmiddotL－1 of n-butyllithium at room temperature with LiMo ratio = 1 The suspension was sealed in a sample bottle and left to stand for at least 72 h so that all Li was intercalated into MoS2 The intercalated MoS2 settled to the bottom and the top layer of solution was decanted The Li-intercalated MoS2 was subsequently exposed to water (TDM-W) or to decalin (TDM-D) and sonicated for 30 min fol-lowed by 30 min of stirring Excess n-butyllithium was removed by a series of washing steps in which the exfoliated MoS2 was separated by centrifuge and re-dispersed in water The washing process was re-peated until the solution pH reached 7 Finally the washing process was repeated three more times re-placing water with isopropanol and then isopropanol with decalin The exfoliated MoS2 dispersion was ad-justed to 2 of MoS2 dispersed in water or decalin

23 Catalyst characterization

The X-ray diffraction (XRD) patterns of MoS2 were recorded with a Siemens D5000 powder diffrac-tometer with power settings of 40 kV and 30 mA us-ing CuKα radiation (λ＝01541 nm) The step-scan (001ordm) was taken over the range 2θ from 5ordm to 70ordm Samples were prepared by diluting the exfoliated MoS2 suspension in ethanol followed by drying a few drops of the suspension on a glass slide

Bulk compositions of the catalysts were esti-mated using energy dispersive X-ray analysis (EDX) with a Hitachi S300N scanning electron microscope operated at 20 kV

BET surface areas were measured by N2 adsorp-tion at －196degC using a FlowSorb II 2300 Micromer-itics Analyzer Samples were degassed at 150degC for 2 h prior to measurement The precision of the meas-urements was within plusmn5

Transmission electron microscopy (TEM) was performed under high-resolution mode on a Hitachi H7600 electron microscope operated at 200 kV After grinding with pestle and mortar each catalyst sample was dispersed in ethanol and deposited on a car-bon-coated copper grid The specimen was dried in air prior to analysis

24 Catalyst reactivity test

Reactions were carried out in a 300 ml stirred batch reactor (Autoclave Engineers USA) loaded with 100 ml of n-hexadecane and 600times10－6 (mass concen-tration) Mo equivalent of the MoS2 catalyst 8 to 12 g of the single phenolic model reactant was mixed with 100 ml of n-hexadecane solvent for each reaction The reactor was first flushed by nitrogen and then con-stantly pressurized at 28 MPa of H2 (995) during


the reaction and stirred at 1000 rmiddotmin－1 the heating rate was controlled at 10degCmin－1 from room tem-perature to the desired value The reaction proceeded at the set temperature for 4-6 h

During the reaction liquid samples (～1 ml) were withdrawn at 20-30 min intervals for the first 2 h then at 40-60 min intervals for the remaining time After reaction the solids (catalyst) present in the re-actor were recovered by filtration washed with pen-tane vacuum dried for 3 h at 100degC and dried further at 160degC for 2 h before characterization

Some reaction runs were carried out by pyrolysis or thermal decomposition under the above conditions except that none of the catalysts was added into the reactor during the processes for the purpose of the comparison of thermal and catalytic effects on HDO

The reactivity for each experiment was calculated based on product gas chromatograph (GC) analysis using the above definitions [Eqs (3) (4)] with the assumed a 100 mole balance

The carbon mole balance for all experiments was within plusmn5

25 GC analysis and GCmass spectrometry (MS) identification

Liquid samples were analyzed with a Shimadzu gas chromatograph (model GC-14A) using a flame ionization detector (FID) fitted with a capillary col-umn (AT-5 30 mtimes032 mmtimes025 μm) operating at an initial temperature of 60degC for 6 min then ramping to 170degC at 20degC min－1 and kept for 7 min then ramp-ing again at 20degCmin－1 to 280degC The identities of the products were determined by comparison with pure reference samples and by Agilent 68905973N GCMS analysis of selected liquid samples

3 RESULTS AND DISCUSSION


The MoS2 prepared by different methods were characterized by recovering the solid MoS2 after reac-tion from microporous membrane filtration The XRD and TEM micrographs of the AHM derived MoS2 cata-lyst was shown in Figs 1 and 2 respectively EDX analyses of the recovered solid confirmed the presence of Mo and S only with an average SMo atom ratio of 25plusmn02 The measured properties of the recovered MoS2 are summarized in Table 1 [24] BET surface area analysis showed that the AHM and MoNaph de-rived MoS2 had significantly higher BET areas as com-pared to that of the crystalline MoS2 and exfoliated MoS2 which had comparable areas The average stack height of the MoS2 particles estimated from the XRD

line-broadening of the peak (002) as shown in Fig 1

32 Reactivity of different structure catalysts

For the pseudo 1st-order HDO reaction the rela-tionship between the conversion (x) and the rate con-stant Kprime in the unit of s－1m3mol－1 can be described as follows [26]

catln(1 )x KC tminus minus = (5)

where Ccat is the concentration of the catalyst in the reactor at the HDO reaction time t

residual concentration of phenolic compoundConversion () 1 100initial concentration of phenolic compound

⎛ ⎞= minus times⎜ ⎟⎝ ⎠

(3)

moles of hydrodeoxygenated phenolic compoundSelectivity () = 100moles of reacted phenolic compound

times (4)

Figure 1 XRD diffractograms of MoS2 catalysts (a) untreated commercial crystalline MoS2 (b) MoS2 recovered after HDO using AHM precursor

Figure 2 TEM of AHM derived MoS2 recovered after HDO(mass concentration 600times10－6 1000 rmiddotmin－1 28 MPa H2 5 h 350degC)

Table 1 Properties of different MoS2 catalysts [24]

Catalyst BET area

m2g－1

Slab length nm

Stack height nm

Numberof layers

crystalline MoS2 42 560 358 57

exfoliated MoS2 78 400 55 9

MoNaph derived MoS2 253 10 18 (08①) 28(13①)

AHM derived MoS2 261 93 21 (11①) 33 (18①)

① As determined from TEM micrographs


A typical kinetic plot about the relationship between the conversion and the reaction time of the HDO of phenolic model compounds at 350degC 28 MPa H2 and 600times10－6 (mass concentration) Mo was shown as in Fig 3 The slopes of the linear plots yield the pseudo 1st-order rate constants and Fig 3 con-firms that the assumption of 1st-order kinetics of each reactant is reasonable

Figure 3 The first-order kinetic curves for HDO of pheno-lic model compounds at 350degC 28 MPa H2 1000 rmiddotmin－1 and 600times10－6 (mass concentration) Mo 4-methylphenol 4-methoxyphenol phenol

Figures 4 and 5 showed respectively the rela-tionship of the pseudo 1st-order rate constants Kprime ver-sus reaction time t by different structure catalysts for HDO of phenol and 4-methylphenol at the reaction temperature ranging from 320degC to 370degC In the whole range of the reaction temperature the activity order of the catalysts for HDO of phenol and 4-methylphenol was established as follows

AHM＞TDM-D＞MoNaph＞thermal＞ powder＞TDM-W

Figure 4 Relationship of Kprime vs T for HDO of phenol by different structure catalysts (mass concentration 600times10－6 Mo 1000 rmiddotmin－1 28 MPa H2 5 h) powder MoS2 TDM-D AHM TDM-W MoNaph thermal

Based on the above conclusion the further inves-tigation on the reactivity of the catalysts for the HDO of 4-methoxyphenol was focused on AHM derived

MoS2 The relationship of Kprime vs T for the HDO of 4-methoxyphenol by AHM derived catalyst was shown in Fig 6

Figure 6 Relationship of Kprime vs T for HDO of 4-methoxyphenol by AHM derived MoS2 catalyst (mass concentration 600times10－6 Mo 1000 rmiddotmin－1 28 MPa H2 5 h) Kh－1 Kprimemlmiddot(mol MoS2middots)－1

The pseudo first-order rate constants for HDO of the three phenolic model compounds by AHM derived MoS2 catalyst at the reaction temperature ranging from 320degC to 370degC were summarized in Fig 7 For phenol and 4-methoxyphenol the maximum value of Kprime was 631 mlmiddot(mol MoS2middots)

－1 and 1092 mlmiddot(mol MoS2middots)－1

at 350degC respectively whereas for 4-methylphenol the maximum value of Kprime was 2124 mlmiddot(mol MoS2middots)－1 at 360degC

Figure 7 Relationship of rate constants Kprime vs reaction tem-perature T for HDO of phenols by AHM derived catalyst (mass concentration 600times10－6 Mo 1000 rmiddotmin－1 28 MPa H2 5 h) phenol 4-methylphenol 4-methoxyphenol

Figure 5 Relationship of Kprime vs T for HDO of 4-methylphenolby different structure catalysts (mass concentration 600times10－6 Mo 1000 rmiddotmin－1 28 MPa H2 5 h) AHM thermal powder TDM-D


Figure 8 revealed the pseudo first-order rate con-stants for HDO of phenolic model compounds by dif-ferent structure catalysts at 350degC It was observed that at 350degC the AHM derived MoS2 catalyst showed much higher activity to HDO of all the phenolic compounds than the other catalysts with an only ex-ception of the exfoliated catalyst TDM-D to HDO of 4-methoxyphenol Under the same conditions the catalyst TDM-W showed very little catalysis to HDO of phenol

As described in Section 31 the results from BET XRD and TEM revealed that MoS2 catalyst derived from AHM by in situ decomposition had a much lar-ger BET area and a smaller particle size (in terms of the average stack height the slab length and the num-ber of stack layers) These results indicated that the AHM derived MoS2 catalyst was highly dispersed in the solution and a huge number of activity sites were available during the HDO reaction The rate constants of reaction kinetics for different structure catalysts shown in Fig 8 confirmed the correctness of the facts The differences of the rate constants between the AHM and the MoNaph derived MoS2 catalysts in the HDO

of phenol were likely due to the incomplete decompo-sition of the MoNaph as being a complex mixture of multiple saturated fatty acid salts during its prepara-tion or pre-sulfuration whereas for the TDM-W and the TDM-D catalysts these differences might be caused by the clustering or conglomeration of the TDM-W catalyst particles during their transferring from the polar solvent of water into the non-polar solvent of n-hexadecane at the beginning of the HDO reaction

33 The product distribution and the reaction mechanism for HDO of phenolic compounds

The product distribution and the selectivity for HDO of phenol 4-methylphenol and 4-methoxyphenol were shown in Tables 2 to 4 From these tables it can be concluded that the main products for HDO of phenol are benzene cyclohexylbenzene and 4-cyclohexylphenol and for the HDO of 4-methylphenol the main prod-ucts are toluene phenol and 24-xylenol whereas benzene phenol anisol methylphenol cyclohexylben-zene and 4-cyclohexylphenol are the main products

Figure 8 Relationship of rate constants Kprime vs different structure catalysts for HDO of phenols [Mo 600times10－6 (mass concentration) 1000 rmiddotmin－1 28 MPa H2 5 h 350degC) phenol 4-methylphenol 4-methoxyphenol

Table 2 Product distribution (in mol percentage) for the HDO of phenol by AHM derived MoS2 catalyst [600times10－6 (mass concentration) Mo 1000 rmiddotmin－1 28 MPa H2 5 h]

Product distribution (selectivity) Temperature degC

Conversion by mol Benzene

Methylcyclohexane

Toluene

m-cresol

(m-methylphenol)Cyclohexylbenzene

4-cyclohexylphenol

330 302 2429 437 ＜443 477 ＜389 3955

350 5144 3609 606 ＜430 430 ＜378 4325

370 2383 4963 ＜320 ＜341 919 2595 863

Table 3 Products distribution for HDO of 4-methylphenol by AHM derived MoS2 catalyst [600times10－6 (mass concentration) Mo 1000 rmiddotmin－1 28 MPa H2 5 h]

Product (selectivity) Tem degC

Mole concn

Benzene

Methylcy-clohexane

4-methyl- cyclohex-

ene

Ethylidene-cyclopen-

tane

Toluene

1-methyl-cyclohexene

m-xylenem-dimethyl-benzene

Phenol

o-methylphenol

m-methylphenol

24-xylenol 24-dimethyl-

phenol

330 2699 ＜048 129 5896 ＜035 222 441 3229

350 5224 ＜052 ＜041 ＜042 ＜042 4978 ＜042 064 678 094 ＜039 3927

370 5878 ＜42 ＜334 ＜356 ＜309 3227 663 ＜312 4377


for HDO of 4-methoxyphenol The results shown in Tables 2 to 4 suggested that

with the increasing of substitution degree by the func-tional groups in phenolic model compounds and the complexity of the substituted phenolic molecules structure the HDO products by AHM derived MoS2 catalyst included more species and the production dis-tribution became much wider

The fact that the main products for HDO of phe-nolic compounds were benzene toluene phenol cyclohexylbenzene cyclohexylphenol and 24-xylenol etc supported strongly the hypothesis presented by Wandas et al [16] Laurent and Delmon [14] Massoth et al [17] and Kirby et al [27] that the major pathways for HDO of phenolic molecules were through the di-rect hydrogenolysis route of the C O bond and the combination route of hydrogenation-hydrogenolysis which first occurred by the cracking of CAR CAR bond and then followed by the rupturing of CAR O bond (CAR representing the carbon atom in aromatic ring group)

The reaction temperature also played a very im-portant role to the products distribution and the selec-tivity of the HDO reactions For HDO of phenol and 4-methoxyphenol the selectivity for benzene me-thylcyclohexane and cyclohexylbenzene increased with the rising of the temperature whereas it decreased for 4-cyclohexylphenol and phenol respectively High reaction temperature was to be more favorable to hy-drogenolysis route and low temperature benefited to hydrogenation route

However the products distribution and the selec-tivity for the HDO of 4-metylphenol shown in Table 3 revealed a slightly different result from that of the HDO of phenol or 4-methoxyphenol In the HDO of 4-metylphenol a large amount of 24-xylenol was presented in the products beside toluene and phenol which directly confirmed the correctness about the formation mechanism of 24-xylenol proposed by Wandas et al [16] Contrarily to the HDO of phenol or 4-methoxyphenol for the HDO of 4-methylphenol the selectivity decreased for the generation of toluene and increased for the generation of phenol and 24-xylenol with the rising of the temperature This re-sult indicated that at high temperature hydrogenation mechanism could occur more easily than hydrogenoly-sis mechanism during the HDO of 4-methylphenol

Finally it should be emphasized that the conver-sion defined in the present study mainly concerned about the disappearance of the model phenolic reac-tants As shown in Table 2 to 4 a huge amount of

oxygen-containing compounds were present in the products by the reaction and their contents covered nearly more than 50 of the products Therefore a followed treatment with a more rigorous operation condition or a more effective catalysts would be nec-essary to the fully completion of a high conversion for the HDO of phenolic compounds

34 The effects of reaction temperature on HDO reactivity

The effects of reaction temperature on the HDO of the three phenolic model compounds were similar to each other by AHM derived MoS2 catalyst which were shown as in Figs 4 to 7 From these figures a very notable rule was observed that under 350degC for phenol and 4-methylphenol whereas 360degC for 4-methylphenol the pseudo first-order rate constants for the HDO of all the phenolic compounds increased with the rising of reaction temperature However they decreased with a further rising of the temperature after these points From Fig 4 it also was found that even if the HDO reactions were carried out just by a simple thermal method or pyrolysis the changing trend of the HDO rate constants of phenol with the temperature was almost the same as that of the three phenolic model compounds by the AHM derived MoS2 catalyst

A typical thermodynamic calculation revealed that during HDO of phenol the enthalpy change ΔH0 of the reaction is 783 kJmiddotmol－1 at 25degC and 4234 kJmiddotmol－1 at 350degC respectively [28] These results implied that an exothermic reversible reaction equilib-rium effect might exist in the reaction networks for the HDO of phenolic compounds The reversed influences by the reaction temperature on HDO reactions ther-modynamically and kinetically led to the appearance of an optimal reaction temperature to make the reac-tion rate constant to be at its greatest value [29]

4 CONCLUSIONS

Several MoS2 catalysts with different structure were prepared by in situ decompositions of ammonium heptamolybdate (AHM) and molybdenum naphthenate (MoNaph) and by MoS2 exfoliations (TDM) for the HDO of the three phenolic model compounds The activity of the catalysts was determined by measuring the conversion and the selectivity in the HDO of phe-nol 4-methylphenol and 4-methoxyphenol using a

Table 4 Products distribution (in mol percentage) for HDO of 4-methoxyphenol by AHM derived MoS2 catalyst [600times10－6 (mass concentration) Mo 1000 rmiddotmin－1 28 MPa H2 5 h 330degC]

Product (selectivity) Mole concn

Ben-zene

Cyclo-hexane

Methylcy-clohexane

Toluene

Anisol

Phenol

o-methyl-phenol

p-methyl-phenol

m-methyl-phenol

Cyclohexyl- benzene

3-phenyl-3-methyl -1-pentyne

2-cyclohexyl-phenol

3517 1342 ＜129 ＜108 ＜115 ＜098 4282 232 229 242 488 556 1563

3517 1313 400 ＜329 676 2182 ＜289 ＜289 507 893 470 952

3517 241 275 086 ＜062 387 3891 423 483 1368 1096 320 053


batch autoclave reactor operated at 28 MPa hydrogen and temperatures ranging from 320-370degC By com-paring their conversions the HDO reactivity order of the catalysts was built as follows


The AHM derived MoS2 catalyst showed the highest activity for the HDO of phenolic compounds because of its best structure The effect of reaction temperature on the HDO conversion was explained in terms of equilibrium effects and reversible reaction kinetics

The characterization of the catalysts by BET XRD EDX and TEM revealed that the MoS2 structure was dependant upon the preparation procedure and the AHM derived MoS2 catalyst exhibited a much finer structure than the other catalysts

The main products for the HDO of phenolic compounds identified by GCMS were benzene tolu-ene phenol cyclohexylbenzene 4-cyclohexylphenol and 24-xylenol etc The results showed that the product distribution and HDO selectivity correlated with the reaction temperature Two parallel reaction routesmdashdirect hydrogenolysis and combined hydrogenation- hydrogenolysis were confirmed by GCMS analysis of the product distributions High reaction temperature was to be favorable to hydrogenolysis route and low temperature benefited to hydrogenation route during the HDO of phenol and 4-methoxyphenol whereas for the HDO of 4-methylphenol the reverse was true

REFERENCES

1 Speight J Chemistry and Technology of Petroleum Marcel Dekker New York (1991)

2 Furimsky E ldquoCatalytic hydrodeoxygenationrdquo Appl Catal A 199 147-190 (2000)

3 Viljava TR Komulainen RS Krause AOI ldquoEffect of H2S on the stability of CoMoAl2O3 catalysts during hydrodeoxygenationrdquo Catal Today 60 83-92 (2000)

4 Li CL Xu Z Gates BC Petrakis L ldquoCatalytic hydroprocess-ing of SRC-I I heavy distillate fractions (4) Hydrodeoxygmation of phenolic compounds in the acidic fractionsrdquo Ind Eng Chem Proc Des Dev 24 92-97 (1985)

5 Daage M Chianelli RR ldquoStructure-function relations in molyb-denum sulfide catalysts The rim-edge modelrdquo J Catal 149 414-427 (1994)

6 Farag H Sakanishi K Kouzu M Matsumura A Sugimoto Y Saito I ldquoDibenzothiophene hydrodesulfurization over synthesized MoS2 catalystsrdquo J Mol Catal A 206 399-408 (2003)

7 Devers E Afanasiev P Jouguet B Vrinat M ldquoHydrothermal syntheses and catalytic properties of dispersed molybdenum sul-fidesrdquo Catalysis Letters 82 (12) 13-17 (2002)

8 Del Bianco A Panariti N Marchionna M ldquoUpgrading heavy oil using slurry processesrdquo Chemtech 25 35-43 (1995)

9 Tye CT Smith KJ ldquoHydrodesulfurization of dibenzothiophene over exfoliated MoS2 catalystrdquo Catalysis Today 116 461-468 (2006)

10 Hall AG Chan AD Smith KJ ldquoCharacterization of dispersed hydroprocessing catalysts prepared in reversed micellesrdquo Can J Chem Eng 76 (4) 744-752 (1998)

11 Alonso G Valle MD Cruz J Licea-Claverie A Petranovskii V Fuentes S ldquoPreparation of MoS2 and WS2 catalysts by in situ de-composition of ammonium thiosaltsrdquo Catal Lett 52 55-61 (1998)

12 Tye CT Smith KJ ldquoCold Lake bitumen upgrading using exfloli-ated MoS2rdquo Catal Lett 95 203-209 (2004)

13 Del Valle M Avalos-Borja MJ Cruz SF ldquoExfoliation of MoS2 catalysts structural and catalytic changesrdquo Mater Res Soc Symp Proc 351 287-292 (1994)

14 Laurent E Delmon B ldquoInfluence of oxygen- nitrogen- and sul-fur-containing compounds on the hydrodeoxygenation of phenols over sulfided CoMoγ-A12O3 and NiMoγ-A12O3 Catalystsrdquo Ind Eng Chem Res 32 2516-2524 (1993)

15 Girgis MJ Gates BC ldquoReactivities reaction networks and ki-netics in high pressure catalytic hydroprocessingrdquo Ind Eng Chem Res 30 2021-2058 (1991)

16 Wandas R Surygala J Sliwka E ldquoConversion of cresols and naphthalene in the hydroprocessing of three-component model mix-tures simulating fast pyrolysis tarsrdquo Fuel 75 687-694 (1996)

17 Massoth FE Politzer P Concha MC ldquoCatalytic hydrodeoxy-genation of methyl-substituted phenols Correlations of kinetic pa-rameters with molecular propertiesrdquo J Phys Chem B 110 14283-14291 (2006)

18 Odebunmi EO Ollis DF ldquoCatalytic hydrodeoxygenation (I) Conversion of o- p- and m-cresolsrdquo J Catal 80 56-64 (1983)

19 Furimsky E Massoth FE ldquoHydrodenitrogenation of petroleumrdquo Catal Rev 47 297-489 (2005)

20 Chon S Allen DT ldquoCatalytic hydroprocessing of chlorophenolsrdquo AIChE J 37 (11) 1730-1732 (1991)

21 Li CL Xu ZR Cao ZA Gates BC ldquoHydrodeoxygenation of 1-naphthol catalyzed by sulfided Ni-Moγ-A12O3 Reaction net-workrdquo AIChE J 31 170-174 (1985)

22 Bredenberg JB Huuska M Raumlty J Korpio M ldquoHydrogenolysis and hydrocracking of the carbon-oxygen bond (I) Hydrocracking of some simple aromatic O-compoundsrdquo J Catal 77 242-247 (1982)

23 Grange P Laurent E Maggi R Centeno A Delmon B ldquoHy-drotreatment of pyrolysis oils from biomass reactivity of the various categories of oxygenated compounds and preliminary techno-economical studyrdquo Catal Today 29 (1-4) 297-301 (1996)

24 Yang YQ Tye CT Smith KJ ldquoInflenece of MoS2 catalyst morphology on the hydrodeoxygenation of phenolsrdquo Catal Comm 9 1364-1368 (2008)

25 Joensen P Frindt RF Morrison SR ldquoSingle-layer MoS2rdquo Mater Res Bull 21 457-461 (1986)

26 Iwata Y Sato K Yoneda T Miki Y Sugimoto Y Nishijima A Shimada H ldquoCatalytic functionality of unsupported molybdenum sulfide catalysts prepared with different methodsrdquo Catal Today 45 (1-4) 353-359 (1998)

27 Kirby SR Song C Schobert HH ldquoHydrodeoxygenation of O-containing polycyclic model compounds using a novel or-ganometallic catalyst precursorrdquo Catal Today 31 121-135 (1996)

28 Perry R Chilton CH Chemical Engineersrsquo Handbook McGrew-Hill New York (1973)

29 Levenspiel O Chemical Reaction Engineering 3rd ed John Wiley New York (2002)


toluene phenol xylenol andor cyclohexylbenzene are present in the products for HDO of phenol and substi-tuted phenolic compounds A recent investigation [24] indicated that during the HDO of phenols these dis-tributions can be changed greatly by changing MoS2 catalyst morphology and structure hydrogenolysis of C OH bonds of 4-methylphenol was favored over MoS2 with a lower degree of stacking whereas aromatic ring hydrogenation of phenol was favored over MoS2 with a higher degree of stacking However the effect of reaction temperature on the distribution and the selec-tivity of the HDO of phenols is still worth of study

In the present work the effects of reaction tem-perature catalyst morphology and structure on HDO of phenol 4-methylphenol and 4-methoxyphenol were examined Unsupported MoS2 catalyst was prepared by different methods and used as a model hydroproc-essing catalyst to eliminate support and promoter ef-fects and the activity and selectivity of the catalysts for HDO of the chosen model compounds were described

2 EXPERIMENTAL

21 Materials

All the materials are presented in mass concen-tration until specified otherwise MoS2 (＜2 μm pow-der 990) n-butyllithium (AR 990)hexane (AR 990) used for exfoliation ammonium heptmolybdate tetrahydrate (AHM AR 990) used for in situ decomposition phenolic model compounds (reactants AR ge980) n-hexadecane (solvent AR 990) and carbon disulfide (AR 990) used for reaction were obtained from Sigma-Aldrich Mo-lybdenum napthenate (MoNaph 60 Mo) was sup-plied by ICN Biomedicals Inc Hydrogen (995) was supplied by Paraxair Inc

22 Catalyst preparation

MoS2 catalysts with 5 different structures were prepared according to the method described as follows

The first two catalysts were prepared by in situ decomposition of soluble Mo precursors molybde-num naphthenate (MoNaph) and ammonium hepta-molybdate tetrahydrate (NH4)6Mo7O24middot4H2O (AHM) The MoNaph or AHM was mixed with the reactant carbon disulfide and n-hexadecane solvent and then placed into the reactor described below The reactor was heated up to 320-370degC and hydrogen was introduced into the reactor During this heating period MoS2 was produced by the in situ decomposition of the MoNaph or AHM and by the reaction with H2S [4 11] The re-action equation for AHM or MoNaph derived MoS2 catalyst was as follows [4]

35H2+AHM+7CS2 ⎯⎯rarr

7MoS2+28H2O+7CH4+6NH3 (1) or

H2+MoNaph+CS2 ⎯⎯rarrMoS2+H2O+CH4 (2)

The third catalyst was commercially available crystalline MoS2 powder (99) from Sigma-Aldrich

and used without further treatment The last two catalysts were the laboratory pre-

pared exfoliated MoS2 which was dispersed in water (TDM-W) or in decalin (TDM-D) respectively Exfo-liation was carried out under argon atmosphere in a glove box using a slightly modified method of Joen-sen et al [25] MoS2 powder was soaked in hexane containing 25 molmiddotL－1 of n-butyllithium at room temperature with LiMo ratio = 1 The suspension was sealed in a sample bottle and left to stand for at least 72 h so that all Li was intercalated into MoS2 The intercalated MoS2 settled to the bottom and the top layer of solution was decanted The Li-intercalated MoS2 was subsequently exposed to water (TDM-W) or to decalin (TDM-D) and sonicated for 30 min fol-lowed by 30 min of stirring Excess n-butyllithium was removed by a series of washing steps in which the exfoliated MoS2 was separated by centrifuge and re-dispersed in water The washing process was re-peated until the solution pH reached 7 Finally the washing process was repeated three more times re-placing water with isopropanol and then isopropanol with decalin The exfoliated MoS2 dispersion was ad-justed to 2 of MoS2 dispersed in water or decalin


The X-ray diffraction (XRD) patterns of MoS2 were recorded with a Siemens D5000 powder diffrac-tometer with power settings of 40 kV and 30 mA us-ing CuKα radiation (λ＝01541 nm) The step-scan (001ordm) was taken over the range 2θ from 5ordm to 70ordm Samples were prepared by diluting the exfoliated MoS2 suspension in ethanol followed by drying a few drops of the suspension on a glass slide

Bulk compositions of the catalysts were esti-mated using energy dispersive X-ray analysis (EDX) with a Hitachi S300N scanning electron microscope operated at 20 kV

BET surface areas were measured by N2 adsorp-tion at －196degC using a FlowSorb II 2300 Micromer-itics Analyzer Samples were degassed at 150degC for 2 h prior to measurement The precision of the meas-urements was within plusmn5

Transmission electron microscopy (TEM) was performed under high-resolution mode on a Hitachi H7600 electron microscope operated at 200 kV After grinding with pestle and mortar each catalyst sample was dispersed in ethanol and deposited on a car-bon-coated copper grid The specimen was dried in air prior to analysis

24 Catalyst reactivity test

Reactions were carried out in a 300 ml stirred batch reactor (Autoclave Engineers USA) loaded with 100 ml of n-hexadecane and 600times10－6 (mass concen-tration) Mo equivalent of the MoS2 catalyst 8 to 12 g of the single phenolic model reactant was mixed with 100 ml of n-hexadecane solvent for each reaction The reactor was first flushed by nitrogen and then con-stantly pressurized at 28 MPa of H2 (995) during



















(3)


times (4)




Catalyst BET area

m2g－1

Slab length nm

Stack height nm

Numberof layers




AHM derived MoS2 261 93 21 (11①) 33 (18①)


























Methylcyclohexane

Toluene

m-cresol


4-cyclohexylphenol

330 302 2429 437 ＜443 477 ＜389 3955

350 5144 3609 606 ＜430 430 ＜378 4325

370 2383 4963 ＜320 ＜341 919 2595 863



Mole concn

Benzene

Methylcy-clohexane

4-methyl- cyclohex-

ene


tane

Toluene



Phenol

o-methylphenol

m-methylphenol


phenol

330 2699 ＜048 129 5896 ＜035 222 441 3229

350 5224 ＜052 ＜041 ＜042 ＜042 4978 ＜042 064 678 094 ＜039 3927

370 5878 ＜42 ＜334 ＜356 ＜309 3227 663 ＜312 4377












4 CONCLUSIONS




Ben-zene

Cyclo-hexane

Methylcy-clohexane

Toluene

Anisol

Phenol

o-methyl-phenol

p-methyl-phenol

m-methyl-phenol

Cyclohexyl- benzene


2-cyclohexyl-phenol

3517 1342 ＜129 ＜108 ＜115 ＜098 4282 232 229 242 488 556 1563

3517 1313 400 ＜329 676 2182 ＜289 ＜289 507 893 470 952

3517 241 275 086 ＜062 387 3891 423 483 1368 1096 320 053







REFERENCES
















































(3)


times (4)




Catalyst BET area

m2g－1

Slab length nm

Stack height nm

Numberof layers




AHM derived MoS2 261 93 21 (11①) 33 (18①)


























Methylcyclohexane

Toluene

m-cresol


4-cyclohexylphenol

330 302 2429 437 ＜443 477 ＜389 3955

350 5144 3609 606 ＜430 430 ＜378 4325

370 2383 4963 ＜320 ＜341 919 2595 863



Mole concn

Benzene

Methylcy-clohexane

4-methyl- cyclohex-

ene


tane

Toluene



Phenol

o-methylphenol

m-methylphenol


phenol

330 2699 ＜048 129 5896 ＜035 222 441 3229

350 5224 ＜052 ＜041 ＜042 ＜042 4978 ＜042 064 678 094 ＜039 3927

370 5878 ＜42 ＜334 ＜356 ＜309 3227 663 ＜312 4377












4 CONCLUSIONS




Ben-zene

Cyclo-hexane

Methylcy-clohexane

Toluene

Anisol

Phenol

o-methyl-phenol

p-methyl-phenol

m-methyl-phenol

Cyclohexyl- benzene


2-cyclohexyl-phenol

3517 1342 ＜129 ＜108 ＜115 ＜098 4282 232 229 242 488 556 1563

3517 1313 400 ＜329 676 2182 ＜289 ＜289 507 893 470 952

3517 241 275 086 ＜062 387 3891 423 483 1368 1096 320 053







REFERENCES






















































Methylcyclohexane

Toluene

m-cresol


4-cyclohexylphenol

330 302 2429 437 ＜443 477 ＜389 3955

350 5144 3609 606 ＜430 430 ＜378 4325

370 2383 4963 ＜320 ＜341 919 2595 863



Mole concn

Benzene

Methylcy-clohexane

4-methyl- cyclohex-

ene


tane

Toluene



Phenol

o-methylphenol

m-methylphenol


phenol

330 2699 ＜048 129 5896 ＜035 222 441 3229

350 5224 ＜052 ＜041 ＜042 ＜042 4978 ＜042 064 678 094 ＜039 3927

370 5878 ＜42 ＜334 ＜356 ＜309 3227 663 ＜312 4377












4 CONCLUSIONS




Ben-zene

Cyclo-hexane

Methylcy-clohexane

Toluene

Anisol

Phenol

o-methyl-phenol

p-methyl-phenol

m-methyl-phenol

Cyclohexyl- benzene


2-cyclohexyl-phenol

3517 1342 ＜129 ＜108 ＜115 ＜098 4282 232 229 242 488 556 1563

3517 1313 400 ＜329 676 2182 ＜289 ＜289 507 893 470 952

3517 241 275 086 ＜062 387 3891 423 483 1368 1096 320 053







REFERENCES









































4 CONCLUSIONS




Ben-zene

Cyclo-hexane

Methylcy-clohexane

Toluene

Anisol

Phenol

o-methyl-phenol

p-methyl-phenol

m-methyl-phenol

Cyclohexyl- benzene


2-cyclohexyl-phenol

3517 1342 ＜129 ＜108 ＜115 ＜098 4282 232 229 242 488 556 1563

3517 1313 400 ＜329 676 2182 ＜289 ＜289 507 893 470 952

3517 241 275 086 ＜062 387 3891 423 483 1368 1096 320 053







REFERENCES




































REFERENCES






























Hydrodeoxygenation of Phenolic Model Compounds over MoS 2 Catalysts with Different Structures

Documents

Transcript of Hydrodeoxygenation of Phenolic Model Compounds over MoS 2 Catalysts with Different Structures