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The energy needs of the world continue to grow, as does the resulting environmental impact. Policy makers continue to call for alternative energies to replace today's petroleum-based liquid fuels. However, liquid fuels have significant advantages, and it is probably unwise to abandon the existing infrastructure without appropriately exploring alternatives to lessen the environmental burden of producing liquid fuels. Biomass and coal are often proposed as alternatives to petroleum-based carbon sources, but those processes lose a significant amount of their potential product to unwanted carbon dioxide emissions. However, combining biomass and coal with cleaner natural gas yields processes with less environmental impact to produce liquid fuels with small, zero, or even negative carbon dioxide emissions. Our process synthesis approach is applied to commonly encountered liquid fuel production methods to identify promising routes and to establish feasibility limits on those less promising alternatives. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2062-2078, 2013 [ABSTRACT FROM AUTHOR]

The effect of co-feeding nitrogen in Fischer–Tropsch synthesis (FTS) in a fixed bed reactor over a Co/TiO 2 catalyst was investigated. The partial pressure of reactants (CO and H 2 ) in the feed to the reactor was kept constant, while the partial pressure of N 2 was switched between a low and high value. The low value corresponded to a syngas feed while the high value corresponded to a feed of syngas enriched with N 2 . A comparison of the results obtained from more than four switches between syngas and syngas enriched with N 2 are reported. The results indicate that there was almost no effect on the overall reaction rate, but that there was a significant, positive effect on the product selectivity. A lower selectivity to the undesired light hydrocarbons (especially methane) was observed when co-feeding N 2 . Such results cannot be explained by classic kinetics alone as the partial pressures of CO and H 2 were held constant during the experiment. The laboratory data indicates that the selectivity to the (C 5 –C 19 ) fraction is particularly enhanced by co-feeding N 2 in FTS. [ABSTRACT FROM AUTHOR]

The olefin (O) to paraffin (P) ratio is important in Fischer-Tropsch synthesis (FTS) and there is some disagreement as to how important diffusion, re-adsorption of olefins or other rate based phenomena are in determining this. We measured the performance of a cobalt catalyst for nearly 3000 h time on stream. During this period there was first the initial unsteady state behaviour as the catalyst settled in, then we changed the temperature, the catalyst deactivated and finally we flushed the reactor with N 2 and then resumed reaction to see if this would disturb the performance of the catalyst. We plotted the data in the standard formats typically used, but we also plotted the data in two other ways. The first way, which we refer to as the Yao plot, is a plot of P n+1 /O n+1 versus P n /O n where for us n is a carbon number from n = 2–5 as we only measure the lower hydrocarbons. We find that the data lies on two straight lines, one for n = 2 and the other for n > 2. What is important is that these straight lines hold during the settling in period, the change in temperature, the deactivation of the catalyst and even after the catalyst had been flushed with nitrogen. The olefin and paraffin distributions are thus dependent and cannot be changed independently. This result could imply that the product distribution might be determined by some sort of reaction equilibrium among some species (we refer to this as quasi-reaction equilibrium) or vapour–liquid equilibrium (VLE), or a combination of the two factors. The second plot, which we refer to as the Lu plot, is a plot of the relationship between normalised mole fractions of O n , O n+1 and P n. These plots have previously been used in distillation and reactive distillation and the behaviour that is seen for the FT system indicates that there is a stable equilibrium point and perturbations to the reactor cause the measured data to make a step change away from this point and that over time the points move back to the stable point. This behaviour is strongly suggestive of a reactive distillation map with a stable point. This is found in for example systems with reversible reactions. Our findings suggest that equilibrium processes, such as VLE and reversible reactions, may be contributing to the observed behaviour in FT and that we perhaps should not rely solely on rate based processes, such as kinetics and diffusion, in trying to understand the behaviour of FT. [ABSTRACT FROM AUTHOR]

Deviation of C 2 (including olefin and paraffin) in the Anderson–Schulz–Flory (ASF) distribution in Fischer–Tropsch synthesis (FTS) has been observed consistently but relatively few studies have focused on this. Explanations for C 2 deviation have been proposed by previous researchers in the literature and secondary reactions of ethene are believed as the cause for the deviation. However, the ratio particularly between C 2 and C 3 olefins and other neighbouring olefins has not yet been thoroughly investigated and this might lead eventually to insights in the mechanism of Fischer–Tropsch synthesis. FTS experimental runs were conducted in a tubular fixed bed reactor on a TiO 2 -supported cobalt catalyst. The reaction conditions were varied including the H 2 /CO ratio in the feed, the reaction temperature, and the space velocity (SV) of the feed gas. The decrease of the reaction rate caused by a lack of H 2 when the H 2 /CO ratio was low is discussed. The olefin/paraffin (O/P) ratios obtained at different temperatures and SVs are presented as they relate to the three H 2 /CO ratios. We then focus on the distribution of C 2 and C 3 under varied reaction conditions, including temperature, SV, and H 2 /CO ratio, and characterize the relationship between C 2 and C 3 in terms of both the olefins and the total amounts of them. Experimental data derived from other reactor types, continuous stirred tank reactor (CSTR) and batch reactor with the same catalysts, have also been included in the investigation of C 2 and C 3 distribution. The ratio between C 2 and C 3 olefins is a linear function of CO conversion only in spite of the fact that the data is for different feed flowrates and compositions, operating temperatures and different reactors. However the ratio for the total C 2 to total C 3 was different for different H 2 /CO feed ratios, but for a fixed H 2 /CO ratio was a linear function of temperature only. [ABSTRACT FROM AUTHOR]

Low pressure Fischer-Tropsch synthesis was tested using iron catalysts reduced by three different reducing gases. In this regards, three reactors were set up in parallel and each of them loaded with the same quantity of the iron catalyst (FeCuKSiO 2 ). After loading, the catalysis in the first reactor was reduced with synthesis gas (a combination of carbon monoxide and hydrogen). The catalyst in the second reactor was reduced using hydrogen (H 2 ) gas, and while that in the third reactor was reduced with carbon monoxide (CO) gas. In this study only the gas-phase products leaving the reactors were analysed and compared under the same operating conditions such as flow rate, pressure and temperature for 1000 h TOS. The results obtained indicate that the initial use of different reducing agents does not have a large impact on the long term catalyst activity but does have an impact on long term selectivity. The three reactors stabilize to about the same overall CO conversion of 14.5% which corresponds to a consumption rate of 2.64 × 10 −4 mol/min.gcat (reactivity) after about 150 h while the selectivities in the three reactors are not the same. Methane selectivity showed the trend: Carbon monoxide reduced > Syngas reduced > Hydrogen reduced. Furthermore, reducing with CO gives much more olefins than reducing with syngas and H 2 . The paraffin production rates did not follow a consistent trend. [ABSTRACT FROM AUTHOR]

Highlights: [•] Heat transfer experiments were carried out with three supported cobalt catalysts. [•] Experiments were conducted under FT reaction and non-reaction conditions. [•] keff under reaction conditions is 2–3 fold of the values recorded with no reaction. [•] Presence of liquid under FT reaction is the main reason for the big change in keff . [•] keff under reaction could be correlated with change of FT chain growth probability. [Copyright &y& Elsevier]

Abstract: Fischer–Tropsch synthesis (FTS) using H2/CO/CO2 syngas mixtures over cobalt and iron based catalysts was carried out in a fixed-bed reactor. CO2 rich feeds produce products that are mostly light hydrocarbons with higher molar paraffin to olefin (P/O) ratio, whereas CO rich feeds shift the product composition to an FT type product with higher olefin product selectivity over both iron and cobalt based catalysts. Although the P/O ratio for FTS is strongly dependent on the operating conditions, the experimental evidence shows that the linear relationship between P (n+1)/O (n+1) and P (n)/O (n) holds for a large number of experiments. It is also shown to be independent of the type of the reactor, the composition of the syngas, reaction conditions and the kind of catalyst. Two features about the ratio of ξ =[P (n+1)/O (n+1)]/[P (n)/O (n)] for the FT products have been identified: (1) with n >2, the experimental values of ξ n>2 are higher than 1, fairly constant and independent of chain length n; (2) with chain length n =2, the ratio of P 3/O 3 to P 2/O 2 (ξ n=2) is significantly different, and shows that ξ n=2 ≪ ξ n>2. An equilibrium hypothesis is considered in an attempt to explain this experimental phenomenon. A simple vapor–liquid equilibrium (VLE) model indicates that the ratio of P (n+1)/O (n+1) to P (n)/O (n) changes in a range of (1, 1/β), where β is the variation of the vapor pressure coefficient, which is related to the incremental energy of vaporization per CH2 unit of the hydrocarbon chain. Our experimental results support the expression when the chain length n >2. But with chain length n =2, this expression is unable to explain the relationship between P 3/O 3 and P 2/O 2. Another model, based on quasi reaction equilibrium, is developed to explain the linear relationship between P (n+1)/O (n+1) and P (n)/O (n). We assume that the reaction of C n+1H2n+2 +C n H2n+2 =C n+1H2n+4 +C n H2n reaches quasi-equilibrium. Because the experimental results are quite close to the equilibrium calculations, we postulate that the product distribution might be determined by considering reaction equilibrium. [Copyright &y& Elsevier]

Abstract: The effect of Au addition on the structure of Co/Al2O3 and Co/SiO2 systems and their performance in the Fischer–Tropsch synthesis (FT) reaction has been investigated. In particular, the effect of the addition of Au (0–5%) to 10% Co/Al2O3 and 10% Co/SiO2 catalysts has been evaluated. An improvement in Co reduction was observed by adding Au to the supported Co/Al2O3 and Co/SiO2 catalysts. For both the silica and alumina-supported catalysts the catalyst activity increased significantly after the addition of Au up to 1.5wt.%. Further increases in Au led to small increases in catalyst activity. The effect of adding Au to the supported Co catalysts was found to be similar to the effect of adding noble metals (Ru, Re and Pt); the Au also improved the catalyst reducibility and activity in the FT reaction. The most significant effect of Au addition on the catalyst activity was found for 5%Au/10%Co/Al2O3 where the maximum conversion was more than six times higher when compared to the activity of the undoped catalyst (10%Co/Al2O3). [Copyright &y& Elsevier]

Abstract: The effect of the cobalt carboxylate chain length (C2, C5 and C9) on the preparation of alumina supported cobalt catalysts has been studied by TPR, XRD and hydrogen chemisorption techniques. The activity and selectivity of the prepared catalysts have been evaluated for Fischer-Tröpsch (FT) activity in a stirred basket reactor. It is shown that for catalysts with Co content of 10wt.% the activity increases as the carboxylate chain length increases while the selectivity towards methane and light hydrocarbons decreases with the carboxylate chain length. This change relates to the effect of the chain length on the catalyst particle size. The catalyst prepared using cobalt acetate was found to present the highest metal–support interaction and the poorest performance for the Fischer-Tröpsch reaction. When the metal content was increased to 15 and 20wt.% Co, respectively, the metal–support interaction for the catalyst particles prepared from cobalt acetate significantly decreased making it a better catalyst for the FT reaction compared to the catalyst particles prepared from C5 and C9 cobalt carboxylates. [Copyright &y& Elsevier]

Abstract: The effect of the addition of ethanol (2% and 6%) during Fischer–Tröpsch (FT) synthesis has been investigated using a 10% Co/TiO2 catalyst in a stirred basket reactor (T =220°C, P =8bar, H2/CO=2). The transformation of ethanol vapour (2% and 6% in nitrogen) over the Co/TiO2 catalyst was also studied in the absence of the synthesis gas under FT reaction conditions. Ethanol was observed to be incorporated in the growing chain and was found to (i) increase the selectivity to light products, (ii) increase the olefin to paraffin ratio and (iii) significantly decrease the catalyst activity. These effects were almost completely reversed when the ethanol in the feed was removed. Thermodynamic predictions, TPR and XRD analysis have shown that cobalt metal particles were oxidised to CoO by ethanol but that re-reduction to Co metal was possible when ethanol was removed from the feed stream allowing the catalyst to recover most of its initial performance, in particular when high flow rates were used. [Copyright &y& Elsevier]

• Activation with syngas led to better performance than activation with H 2. • P/O ratios became similar and did not depend on the activation agent after 2200 h. • A linear relationship between P (n+1) /O (n+1) and P n /O n was obtained. • This shows a dependence between the olefin and paraffin product distributions. The effect of activating atmosphere, reaction conditions and time on stream (TOS) on the catalytic performance and especially on the paraffin to olefin ratios (P/O) over an iron catalyst during Fischer-Tropsch synthesis was investigated. Activation with syngas led to better catalyst performance. For the long-term FT runs, although a higher catalytic activity and P/O ratio have been measured for the catalyst reduced by syngas, similar CO conversions, P/O ratios and product selectivity were achieved for the catalysts reduced by either syngas or H 2 after 2200 h TOS, which indicates that no matter which kind of reducing agent is used to reduce the catalyst, the catalyst performance tends to be similar after a long TOS. Despite the P/O variations with different reaction conditions, a graphical approach (Yao plot) gave a linear relationship between P (n+1)/ O (n+1) and P n /O n indicating the inner constraints between the olefin and the paraffin product distribution. [ABSTRACT FROM AUTHOR]