Phase behaviour of fischer-tropsch wax fractions under high pressure

The phase behaviour of five distillation fractions of a Fischer-Tropsch wax were investigated at pressures up to 40 kbar by means of differential thermal analysis. The approximate constancy in the number of significant components (i.e. greater than 5% by wt.) in each wax fraction is probably responsible for them appearing to behave as a series. Similarity of the phase diagrams of the individual wax fractions gave rise to the construction of a ‘master’ phase diagram. A possible new high-pressure phase was detected in the heaviest fraction, but the possibility of phase separation cannot be excluded.     

Deactivated iron catalyst in the fischer-tropsch synthesis

The selectivity for higher hydrocarbons (C₁₁–C₁₇) has been studied in the Fischer-Tropsch synthesis using fresh and used fused iron catalysts under different reaction conditions. On increasing the temperature higher hydrocarbon products were formed in the C₁₁–C₁₇ range. The deactivated fused iron catalyst is less active but selective to heavier hydrocarbon chain molecules. The product distribution is shifted towards heavier hydrocarbons due to the effects of the pore volume, presence of potassium and site densities at the surface.     

Self-Tuning control of fischer-tropsch synthesis in a tube-wall reactor

This paper describes the implementation of a self-tuning controller (STC) on a bench-scale tube-wall reactor for the Fischer-Tropsch synthesis using a plasma-sprayed iron catalyst. The concentration of the hydrocarbons in the C₁₀ range in the reactor effluent was controlled by manipulating the H₂/CO ratio of the inlet synthesis gas. The output of the self-tuner was cascaded to two PI-controllers which maintained a constant total inlet gas flow rate as well as ensuring the desired H₂/CO ratio. The concentration measurement was performed by an on-line gas chromatograph with an analysis time of approximately 30 s. The performance of the STC in set-point tracking, rejection of randomly occurring deterministic disturbances, and estimation and adaptation to the unknown process dead time was investigated. The STC was able to reduce the variance of the process output and of the manipulated variable when compared to the variances obtained with a PI-controller.     

An oxygenated C1 intermediate in the fischer-tropsch synthesis on cobalt

The active surface carbon in the Fischer-Tropsch synthesis over a cobalt catalyst spends most of its time on the surface as an intermediate which is common to both methanol and hydrocarbon products. This intermediate is distinct from CO_ads but contains the original C-O bond.     

The catalytic cracking of a fischer-tropsch synthesis product

The use of a feed mostly composed of linear alkanes ranging from C₅ to C₃₀ has made it clear that initiation of catalytic cracking does not proceed on very strong Bronsted sites with the liberation of hydrogen. It has also shown that cracking of the linear molecules probably occurs on the first active site inside a zeolite pore with the result that the products formed lie almost totally in the C₄ to C₁₀ range and are highly isomerized.     

Dynamics of the fischer-tropsch synthesis over a supported cobalt catalyst

Step-change experiments between H₂, CO, and syngas mixtures with time resolution of ca. 0.3 s were undertaken to critically test mechanisms proposed in the literature for the Fischer-Tropsch synthesis. A silica-supported cobalt catalyst was used. Results suggest C₂₊ olefins and branched paraffins form from a carbon deposit on the catalyst surface. Two pathways appear to exist for methane formation. The first of these is from the carbon deposit through direct hydrogenation and through hydrogenolysis of the long-chain materials formed. The second pathway is hydrogenation of strongly adsorbed CO.     

The effects of catalyst surface heterogeneity on the fischer-tropsch synthesis

We find that the surface energetic heterogeneity of Fischer-Tropsch catalysts is either not important kinetically or may be masked by the effect of increasing molecular size, so that the classical Anderson-Schulz-Flory distribution is routinely observed in product distributions. The anomalous yields of C₁ and C₂ observed in many cases may also be due to surface heterogeneity but can in practice be readily, and more conveniently, accounted for by assigning individual rate constants to their formation. The “break” sometimes observed in ASF distributions cannot be explained by surface heterogeneity and is best explained by the presence of two distinct modes of product formation.     

Composition modulation of the fischer-tropsch synthesis over a supported cobalt catalyst

Different cycling strategies are explored to see if carbon chain growth can be enhanced and methane formation suppressed. Of the strategies considered, bang-bang cycling between H₂ and CO feeds substantially increased the consumption of CO and H₂, but the formation of higher hydrocarbons and olefins was reduced. The best strategy for longer chain hydrocarbons suitable for jet or diesel fuels was found to be cycling between syngas mixtures. None of the cycling strategies was able to produce C₈₊ or low-molar mass olefin yields that matched yields found in steady-state operation.     

Studies of the fischer-tropsch synthesis on a colbalt catalyst. III. mechanistic formulation of the kinetics of selectivity for higher hydrocarbon formation

Mechanistic models are derived to quantify selectivity in the Fischer-Tropsch synthesis. The models are fitted to experimental selectivity data obtained on a cobalt catalyst and are found to give a satisfactory fit. Results show that branching reactions can be explained by assuming a rate limiting 1-2 hydrogen shift. For small molecules the 1-2 shift takes place on one site, whereas larger molecules need an adjacent sit for the shift to take place. The “break” arises from the sum of two Anderson-Schulz-Flory distributions arising on two different locations.     

Integral method of analysis of fischer-tropsch synthesis reactions in a catalyst pellet

A generalized integral method is developed to analyze complex reactions in a catalyst pellet. This method is valid for any kinetics and takes into account both internal and external heat and mass transfer effects. The integral equations are solved for a Fischer-Tropsch kinetic model to obtain effectiveness factors. Isothermal multiplicities are observed for low values of the surface coverage parameter α(α = 1/K₁p_co,0), and low values of the parameter σ₂₁ (ratio of Thiele moduli for H₂ and CO). The effectiveness factor is mildly sensitive to the external resistances.     

The role of paraffin wax in the formation of minor products in the catalytic cracking of petroleum distillates over La-Y

An investigation of the role of paraffin wax in the catalytic cracking of wax-bearing petroleum distillates has been carried out in a fixed-bed reactor containing La-Y catalyst over a temperature range from 482° to 524°C. By using the concept of initial product selectivity derived from the time-on-stream theory of catalyst decay, it was found that increasing the wax content of the feedstocks resulted in an increase in the yield of C₅⁺ gasoline and a decrease in the yields of most of the gaseous products and of coke. Ethane and propylene and the olefin content of the gasoline increased in yield with the addition of wax. The mixing of cracking feedstocks has only a linear effect on the reactivity and no synergistic effects in any of the observed properties of the reaction are in fact observed.     

The role of paraffin wax in the formation of minor products in the catalytic cracking of petroleum distillates over la-y

An investigation of the role of paraffin wax in the catalytic cracking of wax-bearing petroleum distillates has been carried out in a fixed-bed reactor containing La-Y catalyst over a temperature range from 482° to 524°C. By using the concept of initial product selectivity derived from the time-on-stream theory of catalyst decay, it was found that increasing the wax content of the feedstocks resulted in an increase in the yield of C₅⁺ gasoline and a decrease in the yields of most of the gaseous products and of coke. Ethane and propylene and the olefin content of the gasoline increased in yield with the addition of wax. The mixing of cracking feedstocks has only a linear effect on the reactivity and no synergistic effects in any of the observed properties of the reaction are in fact observed.     

还原参数对铁基催化剂F—T合成性能的影响

在浆态床反应器中详细考察了还原参数对工业铁基催化剂在F—T合成反应中的影响。研究结果表明：提高还原气体中CO／H2的比值有助于提高烯烃的选择性;提高还原气体的空速可以提高催化剂的活性,但是烯烃的选择性有所降低;升高还原温度在一定程度上可以提高催化剂的活性,但是温度过高容易造成催化剂积炭活性下降,适宜的还原温度范围为210～260℃。     

沉淀剂对氧化铝及其负载钴费托合成性能的影响

分别使用(NH4)2CO3、NH4HCO3和饱和NH4HCO3与Al(NO3)3·9H2O进行共沉淀,制得碳酸铝氨、勃姆石以及碳酸铝氨与勃姆石的混合物,焙烧后得到具有不同性质和孔径分布的氧化铝。通过XRD、FTIR、TGA等表征技术,研究了不同沉淀剂对氧化铝前驱体物相组成和结构的影响。通过XRD、BET等技术研究了焙烧后氧化铝的性质和结构,并研究了前驱体和焙烧后氧化铝之间的关联关系。最后,研究了不同氧化铝负载钴制备催化剂的费托合成催化性能。     

Effects of mass transfer on the performance of slurry reactors used for fischer-tropsch synthesis

The influence of mass transfer on the H₂/CO ratio in the liquid phase of a slurry reactor used for Fischer-Tropsch synthesis has been analyzed theoretically. It is determined that even under circumstances where the gas-liquid mass-transfer resistance is a small fraction of the overall resistance, differences in the solubilities and diffusivities of H₂ and CO can give rise to liquid-phase H₂/CO ratios which differ substantially from that of the gas fed to the reactor. The direction and magnitude of the change in the liquid-phase H₂/CO ratio is dependent on the H₂-CO consumption ratio, the interfacial area for mass transfer from the bubble phase, the Damkohler number, and the space velocity of the feed gas.     

Thermodynamics of solid formation in cottonseed oil

The aim of this study is to establish thermodynamic relations which govern the equilibrium of solid formation during the cooling of cottonseed oil either when tripalmitin is added to it or when the oil is cooled in the presence of solvent with consequent enrichment of the solid phase in certain triacylglycerols. We have established analytical expressions of the functions and variables of state that can describe the experimental results obtained. The effect of the addition of tripalmitin to refined cottonseed oil is well represented by simple expressions.     

Effect of water on the solubilities and mass transfer coefficients of gases in a heavy fraction of fischer-tropsch products

The effects of water on the solubilities, C^*, and volumetric mass transfer coefficients, k_La, for CO, H₂, CH₄ and CO₂ in a heavy fraction of Fischer-Tropsch liquid were examined at elevated pressures and temperatures at different mixing power inputs. For these gases, higher solubilities were measured in the hydrocarbon mixture saturated with water than those obtained in the hydrocarbon free of water. The k_La values for the four gases were slightly affected by the presence of dissolved water in the hydrocarbon mixture; and they were strongly dependent on the power input per unit liquid volume. Two empirical correlations for k_La as a function of turbine speed and pressure are proposed.     

F-T合成非均匀型Co／ZrO2／SiO2催化剂的研究

采用无定形SiO2为载体,制备出蛋壳型F—T合成催化剂。利用SEM、EDS等技术考察了钴基催化剂的结构和还原性能。结果表明,催化剂的反应活性在很大程度上取决于可利用的氧化钴的量。助剂ZrO2的添加有利于提高催化剂的分散程度、催化活性及C5^＋选择性。     

The pressure effect on the wax formation in diesel fuel☆

The prevention of wax formation under high pressure on new diesel engine requires a good understanding of the behaviour of the paraffin molecules crystallization. In this work a diesel from a Petrogal refinery was investigated under pressure. In particular the melting curve was measured from atmospheric pressure to 100 MPa by an optical technique. The behaviour of the solid phase with the pressure was also investigated up to 50 MPa by filtration. The results obtained show an increase in the diesel cloud point of about 25 °C at the operating pressure of a common rail engine. It is clear from our results that the increase of the diesel cloud point must be taken into account in the development of new diesel engines where the diesel is injected under high pressure.All the results obtained were successfully predicted with a thermodynamic model able to describe multiphase equilibrium.