a new way to look at fischer−tropsch synthesis using flushing experiments

Published: March 10, 2011

r 2011 American Chemical Society 4359 dx.doi.org/10.1021/ie102095c | Ind. Eng. Chem. Res. 2011, 50, 4359–4365

ARTICLE

pubs.acs.org/IECR

A New Way to Look at Fischer�Tropsch Synthesis Using FlushingExperimentsXiaojun Lu, Xiaowei Zhu, Diane Hildebrandt,* Xinying Liu, and David Glasser

Center of Material and Process Synthesis, University of the Witwatersrand, Johannesburg, South Africa

ABSTRACT:When Fischer�Tropsch synthesis (FTS) reaction experiments were conducted in a gas�solid system with a TiO2-supported cobalt catalyst in a continuous stirred tank reactor (CSTR), we observed significant changes in the reaction rate andproduct selectivity at an early stage of time on stream (TOS) when all the reaction conditions were kept constant.1 We designedflushing experiments with an inert gas that started when the FTS reaction had reached steady state. After the completion of flushing,the FTS reaction was resumed with syngas. We then compared the results of the FTS reaction rate and product selectivity bothbefore and after flushing. The flushing experimental results suggested that the marked variations we observed were caused (eitherwholly or mainly) by liquid products deposited in the catalyst rather than by the change in the properties of the catalyst surface. Theconcentrations and the relative amount of the reactant in the flushed out stream were examined and the implications of the high H2/CO ratio for the reaction kinetics and product selectivity are discussed. On the basis of the dynamic concentrations of C1�C8 in theflushed outgas, we propose that reaction among the products takes place under moderate FTS reaction conditions.

1. INTRODUCTION

Our previous paper1 showed that when low-temperature FTSwas conducted on a TiO2-supported cobalt catalyst (10% Co/90% TiO2) in a CSTR, rapid and substantial changes occurred inthe FTS reaction rate and product selectivity at a certain time onstream (TOS). These changes can be clearly seen in Figures 1and 2. In these examples, changes were observed to start ataround 25 h of TOS. The time at which these changes occurredvaried with the reaction temperature.1 Two pseudosteady states(from around 8�25 h and after 85 h in Figures 1 and 2) wereobserved, and the secondary steady state was maintained withoutany further change for long TOS. The possible reasons wesuggested for these large and sudden changes were: alterationsin catalyst surface properties in a syngas environment or thedeposit of liquid phase products in the catalyst. The latter of thesecould affect the mass transfer of reactants and products, andconsequently alter the reaction rate and product selectivity.

These transient phenomena are believed by some to be partlythe result of the accumulation of the liquid in the catalyst.2,3

Anderson et al.4 first reported that intraparticle diffusion restric-tions on the rate of reactant arrival to hydrocarbon synthesis sitescontrolled the CO conversion rate of Fe-based catalysts. Postet al.5 report a simplified transport-reaction model that describesonly H2 transport limitations, although CO is the more probablediffusion-limited reactant in Fe and Co catalysts; they addressonly rate effectiveness factors for the primary CO hydrogenationreaction and do not discuss transport effects on synthesisselectivity or on secondary reactions. Iglesia et al.6 report atransport-reaction model of hydrocarbon synthesis selectivitythat describes intraparticle (diffusion) transport processes; theseprocesses control the rate of arrival of CO and H2 and the rate ofremoval of reactive products within catalyst pellets and reactors.The transport limitation enhanced the secondary reaction of theR-olefins. However there was no experimental evidence to provethe effect is from the liquid products in the catalyst directly, or to

explain the extent to which the performance of the FTS could beaffected.

On the other hand, a supported Co FT catalyst is believed byothers to reconstruct in a syngas atmosphere, and alter the surfaceproperties of the catalyst, which in turn will affect its performance,such as reaction rate and product selectivity. Schulz7,8 and his co-workers reported that the change in product selectivity and increaseof activity during reaction were caused by the “catalyst construction”.CO chemisorbs strongly on cobalt (as well as on Ni and Ru) and ithas been pointed out by Pichler9 that FT synthesis performs underconditions not so far from those which allow (thermodynamically)carbonyl formation from thesemetals. Thus the reaction of COwiththe metal surface can be assumed to induce surface restructuring.7

Images of a cobaltmetal surfacewhich had been used for FT synthesiswere obtained byWilson and deGroot10 through scanning tunnelingelectron microscopy. It is deduced from those pictures that segrega-tionproduces anordered surface structureunder a syngas atmosphere.

As a precise explanation for these phenomena could not begiven on the basis of the experiments and the subsequent analysiswe performed, we concluded further experiments need to bedesigned and carried out.1 A group of flushing experiments withinert gas (argon) at various temperatures, plus FTS runs withsyngas after flushing, were designed and conducted. The reac-tants and hydrocarbons from the reactor system during and afterflushing were analyzed. The results are discussed below.

2. EXPERIMENTAL SECTION

2.1. Standard FTS Experiments. The FT experiments werecarried out in a 100 mL continuous stirred tank reactor (CSTR)

Received: October 15, 2010Accepted: February 28, 2011Revised: February 21, 2011

4360 dx.doi.org/10.1021/ie102095c |Ind. Eng. Chem. Res. 2011, 50, 4359–4365

Industrial & Engineering Chemistry Research ARTICLE

(Autoclave Engineers) in a gas�solid system without adding anysolvent. A supported cobalt catalyst with 10% Co/90% TiO2

(BET area 28.6 m2/g, average pore diameter 35.8 nm) was used.Approximately 3 g of prepared cobalt catalyst was loaded into acatalyst basket (provided with the reactor). The experimental setup, reduction of the catalyst and analysis method for the CSTRoperation have been described in our previous work.1 Thereaction conditions are set as follows: the feed gas was switchedfromH2,whichwas used for reduction, to syngas (10%N2/30%CO/60%H2). The pressure of the reactor was stabilized at 2.0MPa(g).The space velocity of the reactants was controlled at 1.2lh�1-(gcat)�1 by a mass flow controller. The temperature used forreaction in the experiments was 190 �C. The applied stirring speed(SS) was varied according to the requirements of different experi-ments, but kept above 100 rpm in all cases to ensure that idealmixing could be achieved.2.2. Reactor System Flushing Experiments. When the

reaction reached steady state (that is, the reaction rate andproduction of product were stable) the pressure of the reactorsystemwas reduced to 0.3MPa(g), and the feed gas was switchedfrom syngas to argon (Afrox, UHP, 99.999% in purity) at thereaction temperature. The gaseous products and unreactedreactants were replaced rapidly by argon at a relatively high flowrate, 400 mL/min, for around 3 min, and thereafter continuousflushing was carried out with argon at a lower flow rate of around4 mL/min. That the gas replacement had taken place wasconfirmed by the analysis of the gas stream from the reactor at

the end of the replacement phase that showed no detectable FTreactants and products. Once the argon gas flow rate was reducedthe temperature of the reactor was set to the desired flushtemperature (a sequence of 190 �C, 230 and 210 �C) with aramping rate of 10 �C/min. During the flushing, a 300 rpm SSwas applied. The product traps were bypassed so that all thematerial carried out of the reactor by the argon gas could be sentdirectly to the online gas chromatograph (GC) (Agilent 6890A,equipped with a TCD and an FID) for analysis. All the tail gaslines were maintained at 180 �C to prevent condensation of thelight hydrocarbons.As the flushing proceeded, the components eventually became

undetectable in the flushed-out stream after which the flushingexperiment was considered complete. In the experiments weperformed, the length of time required was around 30 h.2.3. FTS Experiments after the Flushing. Once the flushing

was completed, the feed for the reactor was switched back tosyngas to allow the FT reaction to resume. The conditions for theFT reaction after flushing were the same as they had been beforethe flushing. Further flushing at different temperatures could beperformed once the reaction had reached steady state again.

3. RESULTS AND DISCUSSION

3.1. FTS Behavior after Flushing. The CO conversion, CH4

selectivity, and olefin to paraffin (O/P) ratios for light hydro-carbons during the reaction before and after flushing are plottedwith TOS in Figures 3�5. The flushing temperature sequence,190, 230, and 210 �C is also shown on these diagrams.In Figure 3 it can be seen that the CO conversion decreased

from around 17.5% when the catalyst was fresh, to around 10%when the secondary steady state had been achieved. The COconversion increased after each flushing, but to different extents.The 190 �C flushing lifted the CO conversion only very slightly;230 �C flushing made the CO conversion increase from around10% to approximately 14%; and 210 �C flushing increased theCO conversion to about 12%, which is intermediate between theCO conversion increments that the 190 �C flushing and the230 �C flushing achieved.The CH4 selectivity increased significantly, from around 5%

with fresh catalyst to about 25% when the secondary steady state(TOS = 140�180 h) was achieved, as can be seen in Figure 4.The 190 �C flushing reduced the CH4 selectivity by a smallmargin; 230 �C flushing made the CH4 selectivity drop drama-tically to around 7%, which was very close to the level at which ithad been when the catalyst was fresh; and 210 �C flushingdecreased the CH4 selectivity to around 19%, which was in-between the CH4 selectivity reduction that the 190 �C flushingand the 230 �C flushing brought about.Figure 5 gives the changes of the O/P ratios of light hydro-

carbons (C2�C4) during the reaction periods before and afterthe flushing experiments were conducted. The results displayedshow substantial reduction in O/P ratio when the FTS wascarried on for around 80 h. These low O/P ratios were increasedafter flushing, with the extent of the change dependent on theflushing temperature. Higher temperatures produced higherincreases. Flushing at 230 �C could raise these ratios close totheir original values at the beginning of the experiment, as isshown in the plot during the first 80 h TOS.When we look at these three figures, some common phenomena

can be observed. First, the values for CO conversion, CH4 selec-tivity, and O/P ratios of C2�C4 changed after each flushing when

Figure 1. CO conversion and CH4 selectivity at 210 �C during theentire TOS when stirring speed (SS) remained constant (P = 20 bar (g),FR = 1.2l h�1(gcat)�1 SS = 100 rpm).

Figure 2. O/P ratio at 210 �C during the entire TOSwhen SS remainedconstant (P = 20 bar (g), FR = 1.2l h�1(g cat)�1 SS = 100 rpm).



compared with their values at the end part of the reaction (beforeflushing). Second, the values for those parameters at the tails ofreactions after flushing returned to the levels just before flushing,regardless of the flushing temperature that had been applied.As argon was used for flushing, there is no reason to suggest

that chemical or structural changes took place on the catalyst andsubsequently affected the performance of the FTS after eachflushing. The changes in the parameters after each flushing wereprobably attributable to physical alterations in either the catalystor the catalyst regime rather than on the catalyst surface. In agas�solid FTS system, liquid could be formed as a result of thereaction conditions and the low volatility of long chain hydro-carbons. Certainly liquid-phase product has been found in thereactor under conditions similar to those in the experimentalruns here. During flushing, the inert gas flow would drive off theliquid on and in the catalyst, which could bring about analteration in the catalyst regime. The higher flushing temperaturewould increase the volatility of the liquid and drive off moreliquid from the catalyst, which in turn wouldmean that less liquidwould remain when the FTS reaction was resumed. Both theamount and the composition of the liquid in the catalyst wouldbe changed by the various flushing temperatures, and these

would affect the conversion and product selectivity. Therefore,we believe the liquid deposit in the catalyst is responsible for thechanges of conversion and product selectivity before and afterflushing and it is probably a key factor in FTS performance.One would expect the liquid in the catalyst to have an

inhibiting effect on the transportation of reactants to the activesites of the catalyst, and obstruct themass transfer of the productsout of the catalyst. This is consistent with the reaction rateslowing down, as seen in Figures 1 and 3. The O/P ratiosincreased, as illustrated in Figures 2 and 5, probably owing to thesecondary reaction of olefins, as the slower rate of mass transferprovides greater opportunities for their readsorption. Although itis proposed the liquid in the catalyst affects both the reaction rateand the product selectivity, the extent of these effects differs.When we compare Figures 3�5, we can see that productselectivity (Figures 4 and 5) changes more than the reactionrate (Figure 3).3.2. Reactants and Products in the Flushed-Out Gas

during Flushing. The online GC detected the reactants andshort chain hydrocarbon products (C1�C8) in the flushed-outgas. Their contents in the flushed-out stream are illustratedin Figures 7�12.

Figure 3. CO conversion during FT reaction before and after flushing with different flushing temperatures.

Figure 4. Methane selectivity during reaction before and after flushing with different flushing temperatures.



Reactants in the Flushed-Out GasResult. The concentrations of H2 and CO in the flushed-

outgas during one continuous flushing are shown in Figure 6.The mean residence time for argon gas under fast flushing was0.9 min and under slow flushing conditions was about 90 min,yet significant amounts of both CO and H2 were found in theflushed-outgas even after 20 h, which indicated that both camefrom liquid. In Figure 6, we can clearly see that the concentra-tion of H2 is much higher than that of CO throughout theflushing period, and the ratio of H2/CO is even higher than2 (the ratio in the feed gas) implying its solubility in the liquidis higher.The amounts of H2 and CO in the flushed-out stream during

the entire flushing period were calculated and H2 was around 4times that of the flushed-out CO. This result shows that the ratioof H2 to CO in the liquid-covered catalyst is far higher than inboth the feed gas and the gas in the reactor.Implications for the Kinetics. Some researchers have inves-

tigated the solubility of H2 and CO in the liquid products.11�13

For example, Chou et al.14 carried out experiments to measurethe solubility of hydrogen, carbon monoxide, methane, carbondioxide, ethane, and ethylene in FTSASOLwax, which is primarily amixture of n-paraffins, at pressures from 10�50 atm and at

temperatures from 200�300 �C. The results showed that at200 �C and 20 atm, which is very similar to the reactionconditions in our experiments, the solubility of CO is around1.46 times that of H2. Various other scientists have publishedfindings on the diffusion of the synthesis gas and products inthe liquid produced.15,16 The experimental results reported byErkey et al.16 showed that the diffusion coefficient of H2 isaround 2.4 times that of CO in FT wax at 220 �C and 14 bar.Generally speaking in Sasol wax under FTS conditions, CO

has a better solubility but poorer diffusivity than H2. However,the composition of the material in the catalyst is likely to consistof more than a mixture of n-paraffins. (What is the role of water?)The information obtainable from the literature deals with thediffusion properties and solubility of H2 and CO separately, butthe situation where H2 and CO are both present inside liquid-filled pores may be better described as a combination of theirdiffusion and solubility characteristics. This raises further ques-tions. For example, one of themmay dominate. Another questionis to what degree these two factors decide the real H2/CO ratioaround the catalyst active sites. The results derived from flushingexperiments show an entirely different H2/CO ratio from whatwould normally be expected, and as these reactants (CO andH2)are crucial to the performance of FTS, both for the reaction rateand the product distribution, this result may help us to under-stand FTS better.Products in the Flushed-Outgas. The short chain hydrocar-

bon products (C1�C8) can be detected in the flushed-outgasalmost throughout the flushing period. For convenience ofinterpretation, the hydrocarbons in the flushed-outgas can begrouped into three: CH4, C2�C4, and C4�C8. Their contents inthe flushed-outgas at different time of flushing are given inFigures 7�11. As C4 was the common thread for groupC2�C4 andC4�C8, it appeared in Figures 8 and 9 and 10 and 11.As is illustrated in Figure 7, the general trend for CH4 content

in the flushed-outgas was to decrease as the flushing progressed.It started at a relatively high concentration when compared withthe other hydrocarbons detected in the flushed-outgas, anddiminished rapidly until about 15 h of flushing had been com-pleted. From that point it remained at a very low but still detectableconcentration until the end of the flushing experiment.

Figure 5. O/P ratios for C2�C4 during reaction before and after flushing with different flushing temperatures.

Figure 6. Molar fraction of reactants in the flushed-out stream duringthe flushing period.



Both olefins and paraffins for C2�C4 were found in theflushed-outgas, and their concentrations over the time of flushingare plotted in Figures 8 and 9. The general trend of theirconcentration in the flushed-outgas was similar to that of CH4.In a normal stripping process for a group of hydrocarbons, thelightest component will bemost easily and hence be the first to bestripped off, and the disappearance rate of the hydrocarbons inthe solution decreases as the molecular weight increases becauseof the volatility properties of the hydrocarbons.In both the olefin (Figure 8) and paraffin (Figure 9) groups,

we can clearly see that although C4 was initially present in thehighest concentration, followed by C3 and then C2, it had thefastest disappearance rate during the flushing period. As theduration of flushing continued, C4H8 and C4H10 were the first intheir own groups to become undetectable by the online GC,while C2H4 and C2H6 were found to change the least in com-parison with the other hydrocarbons. All of these results are inconflict with those expected in a normal stripping procedure.This indicates that these phenomena cannot be explained bystripping alone.Furthermore, if we compare Figures 8 and 9 based on the same

carbon number, we can see that the disappearance rate of thealkanes is much more rapid than that of alkenes as can be judgedby the slopes of the curves. The flushing experiment was initiated

when the liquid build-up was complete, so that the amount ofalkene was supposed to be far lower than that of alkane. This canbe confirmed by the first data points in Figures 8 and 9. Thus thealkenes of the same carbon number should become undetectablesooner than the alkanes owing to their slightly higher volatilityand smaller amount when compared to alkanes. But it was notthe case in our experimental results. This leads to the conclusionthat reactions might have occurred during the flushing.CO and H2 were found in the liquid in the catalyst, and the

flushing conditions were at typical reaction temperature andmoderate pressure for FTS, so we might assume that an FTSreaction occurred. As can be seen from Figure 5 the liquid insidethe catalyst would favor the formation of alkanes instead ofalkenes. It is therefore believed that the disappearance rate foralkanes should be slower than that of alkenes. But our resultsshowed an opposite trend. It is therefore quite possible that theFT reaction assumption alone is not adequate to explain thisresult. The experimental results show clearly that more alkeneswere present than might be thought possible. If we compare theO/P ratios during flushing with them in the reaction afterflushing, we can see the ratios at the second half of the flushingperiod (taking C3H6/C3H8 for an example derived from the

Figure 7. Molar percentage of CH4 in the flushed-outgas during theentire flushing period at two flushing temperatures.

Figure 8. Molar percentage of C2�C4 alkenes in the flushed-outgasduring the entire flushing period with TFlushing = 210 �C.

Figure 9. Molar percentage of C2�C4 alkanes in the flushed-outgasduring the entire flushing period with TFlushing = 210 �C.

Figure 10. Molar percentage of C4�C8 alkanes in the flushed-outgas inthe entire flushing period with TFlushing = 210 �C.



result in Figures 8 and 9, the ratios are larger than 1) are higherthan those at the initial stage of the reaction when it is resumedfrom the flushing at 210 �C (see Figure 5, C3H6/C3H8 was onlyaround 0.6). Therefore it would appear that some of the olefinsare not from the reaction of reactants. This provides a clue thatleads us to propose that reaction between the products mayhappen inside the catalyst under flushing conditions.At FTS reaction conditions, secondary reactions of primary

olefins include hydrogenation, chain growth, isomerization,hydrogenolysis, and cracking. The first three are widely acceptedby the researchers while the last two remain contentious. Nocracking or hydrogenolysis reactions of cofed olefins (ethene,1-butene, 1-hexene, 1-decene) was observed by Hanlon andSatterfield.17 Also Dwyer and Somorjai18 did not observe anycracking products from added ethene or propene. However,cracking of added olefins was observed by Jordan and Bell19�21

on a ruthenium catalyst at low total pressure. Cracking ispromoted by high hydrogen pressures and high temperatures(T > 300 �C) and is strongly inhibited by CO pressure22,23 andH2O pressures.24

The results shown here in our work suggest that reactionsmight take place under conditions similar to FTS (typicaltemperature but lower total pressure and especially far lowerpartial pressure of reactants). The results in Figures 8 and 9

suggest that the reaction took place during flushing and thediscussion above concluded that other than FT the reactionsinclude reactions between products especially olefins. A possiblereaction we suggest is not necessarily cracking but a reaction suchas eq 1 below.

Cn � 1H2ðn � 1Þ þ Cn þ 1H2ðn þ 1Þ ¼ 2CnH2n ð1ÞThe molar percentages of flushed-out C4�C8 paraffins in the

outlet stream are shown with flush time at 210 �C in Figure 10and 230 �C in Figure 11. The concentrations of C4�C8 in theflushed outgas at the beginning of the flush were similar, as can beseen from the data points at a flushing time of 2.35 h. At the endof the flushing experiment, the concentrations of C4�C8 weremarkedly different. This tells that the disappearance rate forlighter hydrocarbons is far more rapid than for heavier hydro-carbons. This is the kind of result one might expect if stripping ofliquid alone was happening. This also suggests that if a reactionother than FT was taking place it was only significant for thelower hydrocarbons.The amount of C1�C8 hydrocarbons flushed out from the

catalyst during the entire flushing period could be calculated byintegrating the measured results. As the inlet argon flow rate wasconstant, the outlet flow rate can be assumed to be constant andequal to the inlet argon flow rate, since the amount of materialstripped from the catalyst was small when compared withthe amount of argon. The total flushed- out amounts of C1�C8

hydrocarbons at two flushing temperatures are given in Figure 12.In Figure 12, we can see that throughout the flushing periods at

two different temperatures, the amounts of hydrocarbons flushedout are comparable for each carbon number.The distribution of the products from the catalyst shows a

clear trend. The amount of CH4 is the largest when comparedwith that of the carbon number hydrocarbons which follow. Adescending distribution can be observed for C2 to C4, but thedecrease is slight, and possibly attributable to reaction during theflushing. For the carbon number range above C4, the amount ofhydrocarbons started to increase with the increase of carbonnumber. The product distribution in the catalyst derived fromthe experiment except for the component CH4 is comparablewith the prediction that Zhan et al.25 made on the basis of asimulation. In their simulation, CH4 is the smallest component inthe liquid in the catalyst, while here in our experimental result it isthe largest one. The distribution of flushed-out hydrocarbonswith carbon numbers is very different from the normal ASFdistribution.

4. CONCLUSION

Flushing experiments in a stirred basket reactor were per-formed after the FTS reaction had reached steady state at 190 �C,and the FTS reaction was resumed once the flushing experimenthad been completed. We compared the results of the reactionrate and product selectivity from FTS before and after flushing.We pointed out at the beginning that there were two apparentsteady-states for the FT reaction, an initial one which sponta-neously turned into a later one.Three different flushing tempera-tures (190, 210, and 230 �C) appeared to return the conversionand product selectivity in the reactor after flushing back to theinitial levels before flushing to different extents. We surmised theflushing treatment by argon changed the amount and composi-tion of a liquid phase that had formed during the reaction. Thistherefore suggested that the considerable changes in reaction rate

Figure 11. Molar percentage of C4�C8 alkanes in the flushed-outgasduring the entire flushing period with TFlushing = 230 �C.

Figure 12. Total flushed-out amounts of C1�C8 hydrocarbons.



and product selectivity we observed during the early stage of FTreactionwere caused (either wholly ormainly) by liquid productsdeposited in the catalyst. We further surmised that the depositedliquid in the catalyst provided diffusional restrictions for thereactants and products so that the reaction rate was slowed downand the olefin/paraffin ratios were decreased because of theenhancement of the secondary reaction of olefins.

The data for reactants and products in the flushed out streamduring flushing were also collected and the results providedfurther interesting insights into FTS. The amount of H2 drivenout from the catalyst was around 4 times that of CO instead of 2times, which was the ratio in the feed gas. We suggest that this isthe reason that the selectivity toward CH4 and paraffins increasedramatically when liquid is formed. The high H2/CO ratioaround the active sites of the catalyst also probably made CObecome the limiting reactant for reaction. The dynamic behaviorof the concentration of hydrocarbons in the flushed out streamsuggested that stripping of the liquid by the flushing gas alonecould not explain the slow rate of decrease of the lowerhydrocarbons relative to the higher ones. This suggested thatreactions among the products might take place under themoderate FT reaction conditions (such as the temperature andpressure applied for flushing) in the vessel.

The flushing experiments provided a new and unique way toexamine the FTS reaction and enabled us to draw novel andinteresting conclusions about the nature of the reaction and theliquid that was in the reactor.

’AUTHOR INFORMATION

Corresponding Author*E-mail: [email protected].

’ACKNOWLEDGMENT

The authors would like to acknowledge financial support fromNational Research Foundation (NRF), South African ResearchChairs Initiative (SARChI), Technology and Human Resourcesfor Industry Programme (THRIP), University of the Witwaters-rand, Johannesburg, South African National Energy ResearchInstitute (SANERI), and Golden Nest International (GNI).

’REFERENCES

(1) Lu, X.; Hildebrandt, D.; Liu, X.; Glasser, D. Making Sense of theFischer�Tropsch Synthesis Reaction: Start-up. Ind. Eng. Chem. Res.2010, 49, 9753.(2) Madon, R. J.; Iglesia, E. Hydrogen and CO Intrapellet Diffusion

Effects in Ruthenium-Catalyzed Hydrocarbon Synthesis. J. Catal. 1994,149, 428.(3) Iglesia, E.; Reyes, S. C.; Soled, S. L. Reaction-Transport Selec-

tivity Models and the Design of Fischer�Tropsch Catalysts. In Com-puter-Aided Design of Catalysts; Becker, E.R., Pereira, C.J., Eds.; MarcelDekker: New York, 1993.(4) Anderson, R. B.; Seligman, B.; Schultz, J. F.; Kelly, R. E.; Elliot,

M. A. Fischer�Tropsch Synthesis: Some Important Variables of theSynthesis on Iron Catalyst. Ind. Eng. Chem. 1952, 44, 391.(5) Post, M. F. M.; van’t Hoog, A. C.; Minderhoud, J. K.; Sie, S. T.

Diffusion Limitations in Fischer�Tropsch Catalysts. AIChE J. 1989,35, 1107.(6) Iglesia, E.; Reyes, S. C.; Madont, R. J. Transport-Enhanced

R-Olefin Readsorption Pathways in Ru-Catalyzed Hydrocarbon Synth-esis. J. Catal. 1991, 129, 238.

(7) Schulz, H.; Nie, Z.; Ousmanov, F. Construction of the Fischer�Tropsch Regime with Cobalt Catalysts. Catal. Today 2002, 71, 351.

(8) Schulz, H. Major and Minor Reactions in Fischer�TropschSynthesis on Cobalt Catalysts. Top. Catal. 2003, 26, 73.

(9) Pichler, H.; Frankenburg, W. Advances in Catalysis; AcademicPress: New York, 1952; Vol. IV

(10) Wilson, J.; de Groot, C. Atomic-Scale Restructuring in High-pressure Catalysis. The Journal of Physical Chemistry 1995, 99, 7860.

(11) Albal, R. S.; Shah, Y. T.; Carr, N. L.; Bell, A. T. Mass TransferCoefficient and Solubilities for Hydrogen and Carbon Monoxide underFischer�Tropsch Conditions. Chem. Eng. Sci. 1984, 39, 905.

(12) Masumoto, D. K.; Satterfield, C. N. Solubility of Hydrogen andCarbon Monoxide in Selected Non-aqueous Liquids. Ind. Eng. Chem.Process Des. Dev. 1985, 24, 1297.

(13) Huang, S. H.; Lin, H. M.; Tsai, F. N.; Chao, K. C. Solubility ofSynthesis Gases in Heavy n-Paraffins and Fischer�Tropsch wax. Ind.Eng. Chem. Res. 1988, 27, 162.

(14) Chou, J. S.; Chao, K. Solubility of Synthesis and Product Gasesin a Fischer�Tropsch SASOL Wax. Ind. Eng. Chem. Res. 1992, 31, 621.

(15) Satterfield, C. N.; Huff, G. A. Effects of Mass Transfer onFischer�Tropsch Synthesis in Slurry Reactors. Chem. Eng. Sci. 1980,35, 195.

(16) Erkey, C.; Rodden, J. B.; Akgerman, A. Diffusivities of SynthesisGas and n-Alkanes in Fischer�Tropsch Wax. Energy & Fuels. 1990,4, 275.

(17) Hanlon, R. T.; Satterfield, C. N. Reactions of Selected 1-Olefinsand Ethanol Added during the Fischer�Tropsch Synthesis. Energy Fuels1988, 2, 196.

(18) Dwyer, D. J.; Somorjai, G. A. The Role of Readsorption inDetermining the Product Distribution during CO Hydrogenation overFe Single Crystals. J. Catal. 1979, 56, 249.

(19) Jordan, D. S.; Bell, A. T. Influence of Ethene on the Hydro-genation of CO over Ruthenium. J. Phys. Chem. 1986, 90, 4797.

(20) Jordan, D. S.; Bell, A. T. The Influence of Butene on COHydrogenation over Ruthenium. J. Catal. 1987, 108, 63.

(21) Jordan, D. S.; Bell, A. T. The Influence of Propylene on COHydrogenation over Silica-Supported Ruthenium. J. Catal. 1987,107, 338.

(22) Dry, M. E. The Fischer�Tropsch Synthesis. InCatalysis-Scienceand Technology, Vol. 1; Anderson, J.R.; Boudart, M., Eds.; Springer-Verlag, New York, 1981.

(23) Dalla Betta, R. A.; Piken, A. G.; Shelef, M. HeterogeneousMethanation: Initial Rate of CO Hydrogenation on Supported Ruthe-nium and Nickel. J. Catal. 1974, 35, 54.

(24) Madon, R. J.; Reyes, S. C.; Iglesia, E. Primary and SecondaryReaction Pathways in Ruthenium-Catalyzed Hydrocarbon Synthesis. J.Phys. Chem. 1991, 95, 7795.

(25) Zhan, X.; Davis, B. H. Assessment of Internal DiffusionLimitation on Fischer�Tropsch Product Distribution. Appl. Catal.2002, 236, 149.

a new way to look at fischer−tropsch synthesis using flushing experiments

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