Fischer-Tropsch synthesis (FTS), developed in the early 1900's, is defined as the catalytic conversion of H2 and CO to hydrocarbons and oxygenates with the production of H2O and CO2. Accurate microkinetic modeling can in principle provide insights into catalyst design and the role of promoters. This work focused on gaining an understanding of the chemistry of the kinetically relevant steps in FTS on Fe catalyst and developing a microkinetic model that describes FTS reaction kinetics. Stable Al2O3-supported/promoted (20% Fe, 1% K, 1% Pt) and unsupported Fe (99% Fe, 1% Al2O3) catalysts were prepared and characterized. Transient experiments including temperature programmed desorption (TPD), temperature programmed hydrogenation (TPH), and isothermal hydrogenation (ITH) provided insights into the chemistry and energetics of the early elementary reactions in FTS on Fe catalyst. Microkinetic models of CO TPD, ITH, and FTS were developed for Fe catalyst by combining transition state theory and UBI-QEP formalism. These models support the conclusion that hydrocarbon formation occurs on Fe via a dual mechanism involving surface carbide and formyl intermediates; nevertheless, hydrocarbon formation is more favorable via the carbide mechanism. Carbon hydrogenation was found to be the rate determining step in the carbide mechanism. CO heat of adsorption on polycrystalline Fe at zero coverage was estimated to be -91.6 kJ/mol and -64.8 kJ/mol from ITH and FTS models respectively, while a mean value of -50.0 kJ/mol was estimated from the TPD model. Statistically designed steady-state kinetic experiments at conditions similar to industrial operating conditions were used to obtain rate data. The rate data were used to develop a microkinetic model of FTS. FTS and ITH appear to follow similar reaction pathways, although the energetics are slightly different. In both cases, hydrocarbon formation via the carbide mechanism was more favorable than via a formyl intermediate while carbon hydrogenation was the rate determining step. Promotion of Fe with K does not alter Fischer-Tropsch synthesis reaction pathways but it does alter the energetics for the steps leading to the formation of CO2. This phenomenon accounts for the CO2 selectivity of 0.3 observed for K-promoted Fe against 0.17 observed for un-promoted Fe. A Langmuir Hinshelwood rate expression derived from the microkinetic model was put into a fixed bed FTS reactor design code; calculated reactor sizes, throughput, temperature profiles and conversion are similar to those of pilot and demonstration FTS reactors with similar feed rates and compositions.

I den här rapporten utvärderas det nya konceptet Power & Biomass to Liquid (PBtL). PBtL är ett alternativ till den tidigare och mer etablerade Biomass to Liquid (BtL) processen. Med PBtL förbättras utbytet av kol jämfört med BtL genom att elektricitet läggs till i processen. Elektriciteten används för att producera H2, som används för att höja H2/CO förhållandet istället för att använda WGS som i vanlig BtL process. Rapporten är en del i ett större PBtL projekt som bedrivits vid Institutt for kjemisk prosessteknologi vid NTNU och på SINTEF. Utvärderingen utfördes genom flera simuleringar av lågtemperaturs Fischer-Tropsch reaktorer i simuleringsprogrammet Aspen Plus. Omvandling och katalytiska reaktorer utvecklades och togs fram i programmet. Produktfördelningen i omvandlingsreaktorn modellerades med ASF distribution theory tillsammans med en metod för sammanslagning av högre kolväten. Fördelningen av paraffiner, olefiner och oxygenater baserades på experimentella resultat från Shafer et al. som studerade en slurryreaktor under liknande förhållanden. Den kinetiska reaktorn modellerades med en variant av ASF fördelningsteori kallad ”consorted vinylene mechanism” från Rytter och Holmen. Reaktorerna adderades till förgasningsprocess, som utvecklats tidigare av PBtL gruppen, I förgasningsprocessen förgasas biomassa till syntesgas, dvs H2 och CO. För att möjliggöra en utvärdering av det efterföljande steget med separering av vax, mellandestillat och lättare kolväten så antogs en väl fungerande separation av Fischer-Tropsch produkterna. En enklare separation av med flash förångning gjordes också, dels för fortsättningen av PBtL processen och för att kunna studera tailgasrecirkulering. Ett mindre bidrag var studier av en torkningsprocess för biomassa innan inloppet till förgasningsprocessen. PBtL konceptet diskuterades även ur ett praktiskt perspektiv.  Resultaten visar att vid driftbetingelser på 210 °C, 25 bar och H2/CO = 1,95 så gav omvandlingsreaktorn en kolselektivitet för CH4 respektive C5+ på 14,77 respektive 75,40 mol% C. Högre temperatur, tryck och H2/CO förhållande i reaktorn resulterar i en högre kolselektivitet mot lägre kolväten. Vid samma driftbetingelser gav den katalysreaktorn en kolselektivitet för CH4 respektive C5+ på 7,612 respektive 86,00 mol% C. Resultaten visar att C8-C16 produktionen var högre än C17+ med avseende på molflöde men lägre beträffande massflöde för katalysreaktorn. Generellt så ökar kolselektiviteten med ökande kolnummer till ett maximum runt 13 för att sedan minska. / In this report, the new Power & Biomass to Liquid (PBtL) concept was evaluated. The PBtL concept is a new alternative to the more well-established Biomass to Liquid (BtL) concept where electricity is added to the process. The main purpose for developing the PBtL is that the BtL process exhibits poor carbon efficiency compared to the PBtL process. The electricity here is used to produce H2 in electrolysis. The report is part of a larger PBtL project pursued for several years at the Department of Chemical Engineering at NTNU and SINTEF. The evaluation was done by simulating different types of low temperature Fischer-Tropsch reactors in simulation software Aspen Plus. A conversion reactor and a kinetic reactor was developed. A conversion reactor based on the result from the kinetic reactor was also developed.  The conversion-based reactor was modeled with the ASF distribution theory which describes the distribution of products formed in Fischer-Tropsch synthesis along with a method of lumping higher hydrocarbons. The distribution between paraffins, olefins and oxygenates was based on experimental data from Shafer et al. with similar operating condition with a Slurry reactor. The kinetic-based reactor was modeled with ASF distribution theory with a consorted vinylene mechanism previously described in Rytter and Holmen. The reactors were added to a process for which the biomass gasification section had previously been developed by the PBtL group. The Fischer-Tropsch products were as well separated in order to evaluate the subsequent step of separation of waxes, middle distillate and lighter hydrocarbons. This enabled the option of recycling of tail gas to the Fischer-Tropsch reactor to be evaluated. A smaller contribution included addition of a biomass dryer prior the biomass gasification section. The PBtL concept is also shortly discussed from a practical point-of-view.  It was found that for the operating condition of 210 °C, 25 bar and H2/CO = 1.95 for the conversion-based reactor yielded a carbon selectivity towards CH4 and C5+ of 14.77 and 75.40 mol C% respectively. For the same operating condition, the kinetic-based reactor yield a carbon selectivity towards CH4 and C5+ of 7.612 and 86.00 mol C% respectively. It could be seen from the conversion-based reactor that elevating temperature, pressure and H2/CO (to a certain extent) results in higher carbon selectivity towards lower hydrocarbons. From the product separation with the kinetic reactor, it was observed that C8-C16 production was higher than the C17+ production in terms of mole flow but lower in terms of mass flow. For both models, carbon selectivity increases with carbon number and peaks around carbon number 13 and then starts to decrease.

Thesis (MScEng)--Stellenbosch University, 2012 / ENGLISH ABSTRACT: Through many years of research, a number of production schemes have been developed for converting lignocellulosic biomass into transport fuels. These technologies have been assessed through a number of techno-economic studies for application in a particular context in terms of the technical and economic feasibility. However, previous studies using these methods have tended to lack vigour in various aspects. Either the energy efficiency of the processes were not maximised through adequate heat integration, or a competing technology which existed was not considered. From an economic perspective, the financial models would often lack the vigour to account for the risk and uncertainty that is inherent in the market prices of the commodities. This phenomenon is especially relevant for the biofuel industry that faces the full fledge of uncertainties experienced by the agricultural sector and the energy sector. Furthermore, from an environmental perspective, the techno-economic studies had often ignored the environmental impacts that are associated with biofuel production. Thus, a comparative study could have favoured an option due to its economic feasibility, while it could have had serious environmental consequences. The aim of this study was to address these issues in a South African context, where biofuels could be produced from sugarcane bagasse. The first step would be to modify an existing simulation model for a bioethanol scenario that operates with a Separate Hydrolysis and Fermentation (SHF process) configuration into a second processing scenario that operates with a Simultaneous Saccharification and Fermentation (SSF process) configuration using reliable experimental data. The second step was to ensure that the maximum energy efficiency of each scenario was realised by carrying out pinch point analysis as a heat integration step. In contrast to these biological models is the thermochemical model that converts bagasse to gasoline and diesel via gasification, Fischer-Tropsch synthesis and refining (GFT process). While there were no significant advances in technology concerning this type of process, the energy efficiency was to be maximised with pinch point analysis. The GFT process obtained the highest energy efficiency of 50.6%. Without the affects of pinch point technology, the efficiency dropped to 46%, which thus emphasises the importance of heat integration. The SSF had an efficiency of 42.8%, which was superior to that of the SHF at 39.3%. This resulted from a higher conversion of biomass to ethanol in the SSF scenario. Comparing the SHF model to an identical model found in literature that did not have pinch point retrofits, this study showed lower efficiency. This arose because the previous study did not account for the energy demands of the cold utility systems such as the cooling tower operation, which has been shown in this study to account for 40% of the electrical energy needs. The economic viability of all three processes was assessed with Monte Carlo Simulations to account for the risks that the fluctuations in commodity prices and financial indices pose. This was accomplished by projecting the fluctuations of these parameters from samples of a historical database that has been transformed into a probability distribution function. The consequences were measured in terms of the Net Present Value (NPV) and Internal Rate of Return (IRR) for a large number of simulations. The results of these variables were aggregated and were then assessed by testing the probability that the NPV<0, and that the IRR recedes below the interest rate of 12.64%. The investment was thus deemed unfeasible if these probabilities were greater than 20%. Both biological models were deemed profitable in terms of this standard. The probabilities were 13% for the SSF and 14% for the SHF. The GFT process however was deemed completely unfeasible because the probability that the NPV<0 was 78%. Given that the GFT process had the highest energy efficiency, this result arises mainly because the capital investment of 140,000USD/MWHHV of biomass energy input is to enormous for any payback to be expected. The environmental footprint of each process was measured using Life Cycle Assessments (LCAs). LCAs are a scientifically intricate way of quantifying and qualifying the effects of a product or process within a specified boundary. The impacts are assessed on a range of environmental issues, such as Global Warming, Acidification, Eutrophication and Human toxicity. Furthermore, if the project under concern has multiple output products, then the impacts are distributed between the output products in proportion to the revenue that each generates. The impacts were either relative to the flow of feedstock, which was 600MW of bagasse, or to the functional unit, which was the amount of fuel required to power a standard vehicle for a distance of 1 kilometre. In either case, the GFT scenario was the least burdening on the environmental. This was expected because the GFT process had the highest energy efficiency and the process itself lacked the use of processing chemicals. Relative to the feedstock flow, the SSF was the most environmentally burdening scenario due to the intensive use of processing chemicals. Relative to the functional unit, the SHF was the most severe due to its low energy efficiency. Thus, the following conclusions were drawn from the study:  The GFT is the most energy and environmentally efficient process, but it showed no sign of economic feasibility. iv  There is no significant difference in the economic and environmental evaluation of the SSF and SHF process, even though the SSF is considered to be a newer and more efficient process. The major cause of this is because the setup of the SSF model was not optimised. / AFRIKAANSE OPSOMMING: Deur baie jare van navorsing is ‘n aantal produksie-skemas vir die omskakeling van lignosellulose biomassa na vloeibarebrandstof ontwikkel. Hierdie tegnologië is geassesseer ten opsigte van die tegniese en ekonomiese haalbaarheid deur middel van tegno-ekonomiese studies in bepaalde tekste. Tog het hierdie vorige studies besliste beperkings gehad. Of die energie-doeltreffendheid van die proses is nie gemaksimeer deur voldoende hitte-integrasie nie, of 'n mededingende tegnologie wat bestaan is nie oorweeg nie. Vanuit 'n ekonomiese perspektief, was die finansiële modelle dikwels nie die omvattend genoeg om rekening te hou met die risiko en onsekerheid wat inherent is in die markpryse van die kommoditeite nie. Hierdie verskynsel is veral relevant vir die biobrandstof bedryf wat die volle omvang van onsekerhede ervaar waaraan die landbousektor en die energiesektoronderhewig is. Verder het die tegno-ekonomiese studies dikwels die omgewingsimpakte wat verband hou met biobrandstofproduksie geïgnoreer. Dus kon ‘n opsie deur die ekonomiese haalbaarheid bevoordeel word, ten spyte van die ernstige omgewingsimpakte wat dit kon inhou. Die doel van hierdie studie was om hierdie kwessies aan te spreek in 'n Suid-Afrikaanse konteks, waar biobrandstof uit suikerriet bagasse geproduseer kan word. Die eerste stap was om 'n bestaande simulasiemodel vir 'n bio-scenario wat met Afsonderlike Hidroliese en Fermentasie (SHF proses) stappe werk, te modifiseer vir 'n tweede verwerking scenario wat met 'n gelyktydige Versuikering en Fermentasie (SSF proses) konfigurasie werk. Die verandering is gedoen deur die gebruik van betroubare eksperimentele data. Die tweede stap was om te verseker dat elke scenario die maksimum energie-doeltreffendheid het, deur 'n hitte-integrasie stap, wat gebruik maak van “pinch-point” analise. In teenstelling met hierdie biologiese modelle, is daar die thermochemiese roete waar petrol en diesel van bagasse vervaardig word via vergassing, Fischer-Tropsch-sintese en rafinering (GFT proses). Daar was geen betekenisvolle vooruitgang in tegnologie vir hierdie proses nie, maar die energie-doeltreffendheid is gemaksimeer word deur energie-integrasie. Die GFT proses toon die hoogste energie-doeltreffendheid van 50,6%. Sonder die invloed van energie-integrasie het die doeltreffendheid gedaal tot 46%, wat dus die belangrikheid van hitte-integrasie beklemtoon. Die SSF het 'n effektiwiteit van 42,8% gehad, wat beter was as dié 39,3% van die SHF opsie. Hierdie hoër effektiwiteit wasas gevolg van die hoër omskakeling van biomassa na etanol in die SSF scenario. Die energie doeltreffendheid vir die SHF-model was laer as met 'n identiese model (sonder energie-integrasie) wat in die literatuur gevind wat is. Dit het ontstaan omdat die vorige studie nie 'n volledig voorsiening gemaak het met die energie-eise van die verkillingstelselsnie, wat tot 40% van die elektriese energie behoeftes kan uitmaak. Die ekonomiese lewensvatbaarheid van al drie prosesse is bepaal met Monte Carlo simulasies om die risiko's wat die fluktuasies in kommoditeitspryse en finansiële indekse inhou, in berekening te bring. Hierdie is bereik deur die projeksie van die fluktuasies van hierdie parameters aan die hand van 'n historiese databasis wat omskep is in 'n waarskynlikheid verspreiding funksie. Die gevolge is gemeet in terme van die netto huidige waarde (NHW) en Interne Opbrengskoers (IOK) vir 'n groot aantal simulasies. Die resultate van hierdie veranderlikes is saamgevoeg en daarna, deur die toets van die waarskynlikheid dat die NPV <0, en dat die IRR laer as die rentekoers van 12,64% daal, beoordeel. Die belegging is dus nie realiseerbaar geag as die waarskynlikhede meer as 20% was nie. Beide biologieseprosesse kan as winsgewend beskou word in terme van bostaande norme. Die waarskynlikhede was 13% vir die SSF en 14% vir die SHF. Aangesien die NHW van die GFT-proses onder 0 met ‘n waarskynlikheid van 78% is, is die opsie as nie-winsgewend beskou. Gegewe dat die GFT-proses die hoogste energie-doeltreffendheid het, is die resultaat hoofsaaklik omdat die kapitale belegging van 140,000 USD / MWHHV-biomassa energie-inset te groot is, om enige terugbetaling te verwag. Die omgewingsvoetspoor van elke proses is bepaal deur die gebruik van Lewens Siklus Analises (“Life Cycle Assessments”) (LCAS). LCAS is 'n wetenskaplike metodeom die effek van ‘n produk of proses binne bepaalde grense beide kwalitatief en kwantitatief te bepaal. Die impakte word beoordeel vir 'n verskeidenheid van omgewingskwessies, soos aardverwarming, versuring, eutrofikasie en menslike toksisiteit. Voorts, indien die projek onder die saak verskeie afvoer produkte het, word die impakte tussen die afvoer produkte verdeel, in verhouding tot die inkomste wat elkeen genereer. Die impak was met of relatief tot die vloei van roumateriaal (600MW van bagasse), of tot die funksionele eenheid, wat die hoeveelheid van brandstof is om 'n standaard voertuig aan te dryf oor 'n afstand van 1 kilometer. In al die gevalle het die GFT scenario die laagste belading op die omgewing geplaas. Hierdie is te verwagte omdat die GFT proses die hoogste energie-doeltreffendheid het en die proses self nie enige addisionele chemikalieë vereis nie. Relatief tot die roumateriaal vloei, het die SSF die grootse belading op die omgewing geplaas as gevolg van die intensiewe gebruik van verwerkte chemikalieë. Relatief tot die funksionele eenheid, was die SHF die swakste as gevolg van sy lae energie-doeltreffendheid.

About 8 tons of dry undigested solid waste is generated by the MixAlco process for every 40 tons of food residue waste fed into the process. This MixAlco process produces liquid fuels and the sludge generated can be further converted into synthesis gas using the process of pyrolysis. The hydrogen component of the product synthesis gas may be separated by pressure swing adsorption and used in the hydrogenation of ketones into fuels and chemicals. The synthesis gas may also be catalytically converted into liquid fuels via the Fischer-Tropsch synthesis process. The auger-type pyrolyzer was operated at a temperature between 630-770 degrees C and at feed rates in the range of 280-374 g/minute. The response surface statistical method was used to obtain the highest syngas composition of 43.9 +/- 3.36 v % H2/33.3 +/- 3.29 v % CO at 740 degrees C. The CH4 concentration was 20.3 +/- 2.99 v %. For every ton of sludge pyrolyzed, 5,990 g H2 (719.3 MJ), 65,000 g CO (660 MJ) and 21,170 g CH4 (1055.4 MJ) were projected to be produced at optimum condition. At all temperatures, the sum of the energies of the products was greater than the electrical energy needed to sustain the process, making it energy neutral. To generate internal H2 for the MixAlco process, a method was developed to efficiently separate H2 using pressure swing adsorption (PSA) from the synthesis gas, with activated carbon and molecular sieve 5A as adsorbents. The H2 can be used to hydrogenate ketones generated from the MixAlco process to more liquid fuels. Breakthrough curves, cycle mass balances and cycle bed productivities (CBP) were used to determine the maximum hydrogen CBP using different adsorbent amounts at a synthesis gas feed rate of 10 standard lpm and pressure of 118 atm. A 99.9 % H2 purity was obtained. After a maximum CBP of 66 % was obtained further increases in % recovery led to a decrease in CBP. The synthesis gas can also be catalytically converted into liquid fuels by the Fischer-Tropsch synthesis (FTS) process. A Co-SiO2/Mo-Pd-Pt-ZSM-5 catalyst with a metal-metal-acid functionality was synthesized with the aim of increasing the selectivity of JP-8 (C10-C17) fuel range. The specific surface areas of the two catalysts were characterized using the BET technique. The electron probe microanalyzer (with WDS and EDS capabilities) was then used to confirm the presence of the applied metals Co, Mo, Pd and Pt on the respective supports. In addition to the gasoline (C4-C12) also produced, the synthesis gas H2:CO ratio was also adjusted to 1.90 for optimum cobalt performance in an enhanced FTS process. At 10 atm (150 psig) and 250 degrees C, the conventional FTS catalyst Co-SiO2 produced fuels rich in hydrocarbons within the gasoline carbon number range. At the same conditions the Co-SiO2-Mo-Pd-Pt/HZSM-5 catalyst increased the selectivity of JP-8. When Co-SiO2/Mo-Pd-Pt-HZSM-5 was used at 13.6 atm (200 psig) and 250 degrees C, a further increase in the selectivity of JP-8 and to some extent diesel was observed. The relative amounts of olefins and n-paraffins decreased with the products distribution shifting more towards the production of isomers.

This paper will discuss the conversion of gas produced from biomass into liquid fuel through the combination of naturally occurring processes, which occur in landfills and anaerobic digesters, and a gas-to-liquids (GTL) facility. Landfills and anaerobic digesters produce gases (LFG) that can be converted into syngas via a Tri-reforming process and then synthesized into man-made hydrocarbon mixtures using Fischer-Tropsch synthesis. Further processing allows for the separation into liquid hydrocarbon fuels such as diesel and gasoline, as well as other middle distillate fuels. Conversion of landfill gas into liquid fuels increases their energy density, ease of storage, and open market potential as a common “drop in” fuel. These steps not only allow for profitable avenues for landfill operators but potential methods to decrease greenhouse gas emissions. The objective of this paper is to present a preliminary design of an innovative facility which processes contaminated biogases and produces a valuable product. An economic analysis is performed to show feasibility for a facility under base case scenario. A sensitivity analysis is performed to show the effect of different cost scenarios on the breakeven price of fuel produced. Market scenarios are also presented in order to further analyze situations where certain product portions cannot be sold or facility downtime is increased. This facility is then compared to traditional mitigation options, such as flaring and electricity generation, to assess the effect each option has on cost, energy efficiency, and emissions reduction.

Nano-scaled carbons were produced by thermal treatment of pine wood chips and bio-char. The influence of temperature, heating rate, pyrolysis time, and type and flow rate of purge gas on the production of nano-carbons was investigated. Using TEM and SEM, different carbon-based nanomaterials were observed in the prepared samples. The effect of metal ion doping on the bio-char was also investigated. Highly functionalized nano carbonaceous materials were synthesized by low temperature hydrothermal carbonization (HTC) using glucose, sucrose, xylose, and cellulose. Carbon-encapsulated iron (Fe@C) core-shell particles were also synthesized by the HTC method and used as catalyst for Fischer-Tropsch synthesis to produce liquid hydrocarbons from syngas; it showed excellent activity. Nano-structured Co-Mo carbides over several nano-sized carbon materials were prepared using the carbothermal reduction and carbothermal hydrogen reduction methods. Nano-structured Co-Mo carbides derived from Vulcan® XC-72 were used as the catalyst to produce higher alcohols.

Fischer-Tropsch Synthesis (FTS) is a promising technology for the production of ultra-clean fuels and chemical feedstocks from biomass, coal, or natural gas. Iron catalysts are ideal for conversion of coal and biomass. However, precipitated iron catalysts used in slurry-bubble column reactors suffer from high attrition resulting in difficulty separating catalysts from product and increased slurry viscosity. Thus, development of an active and selective-supported iron catalyst to manage attrition is needed. This thesis focuses on the development of a supported iron catalyst and kinetic models of FTS on the catalyst using advanced statistical methods for experimental design and analysis. A high surface area alumina, modified by the addition of approximately 2 wt% lanthanum, was impregnated with approximately 20 wt% Fe and 1% Pt in a two step procedure. Approximately 10 wt% Fe and 0.5 wt% Pt was added in each step. The catalyst had a CO uptake of 702 μmol/g, extent of reduction of 69%, and was reduced at 450°C. The catalyst was stable over H2 partial pressures of 4-10 atm, CO partial pressures of 1-4 atm, and temperatures of 220-260°C. Weisz modulus values were less than 0.15. A Langmuir-Hinshelwood type rate expression, derived from a proposed FTS mechanism, was used with D-optimal criterion to develop experiments sequentially at 220°C and 239°C. Joint likelihood confidence regions for the rate expression parameters with respect to run number indicate rapid convergence to precise-parameter estimates. Difficulty controlling the process at the designed conditions and steep gradients around the D-optimal criterion resulted in consecutive runs having the same optimal condition. In these situations another process condition was chosen to avoid consecutive replication of the same process condition. A kinetic model which incorporated temperature effects was also regressed. Likelihood and bootstrap confidence intervals suggested that the model parameters were precise. Histograms and skewness statistics calculated from Bootstrap resampling show parameter-effect nonlinearities were small.