Abstract Carbon nanotubes (CNTs) were grown catalytically by a chemical vapor deposition method and characterized by a range of techniques. Fe, Ru and Co catalysts supported on the carbon nanotubes were prepared and investigated for their performances in the Fischer-Tropsch synthesis. CNTs were synthesized in a quartz tubular reactor at atmospheric pressure and at temperatures of 700°C over iron supported on CaCO3 using C2H2 as carbon source. Prior to CNT synthesis, the iron catalyst was first reduced under the same conditions (700°C and atmospheric pressure) in a flow of 5% H2 balanced in Argon. The catalyst, for the preparation of the CNTs, was prepared by the incipient wetness impregnation. The purification of the CNTs was performed with 30 wt % HNO3. Characterization of the CNTs using TEM, SEM, HRTEM, BET and TPR revealed that the crude product contained solely CNTs, catalysts particles and support, while no amorphous carbon was observed. The purified product is comprised of an interwoven matrix of tubes that were shown to be multi-walled (MWCNTs). CNT supported FT based catalysts were also prepared by an incipient wetness impregnation method and tested in a plug flow reactor in Fischer-Tropsch synthesis. The TEM images of the different FT catalysts supported on CNTs revealed that the catalyst particles are well dispersed on the surface of the CNTs. The catalyst particles were very iii small, and some residual Fe catalyst material, not removed by the acid treatment, could clearly be seen on the surface of the CNTs. The reduction and metal dispersion properties of the catalysts were investigated through TPR and chemisorption techniques. A TPR study showed three reduction steps for Co catalysts, and addition of Ru to the catalyst decreased the reduction temperature of the catalysts. Gasification of the CNTs was noted to occur at temperatures higher than 600°C. The effect of metal catalyst loading and promoters on the activity and selectivity of CNT supported FT synthesis catalysts was studied under condition of 275°C, 8 bar, CO/H2 = 1/2 and different flow rates. The FT catalysts supported on carbon nanotubes displayed a high CO conversion and excellent stability with time on stream in the Fischer-Tropsch synthesis. Fe catalysts displayed the lowest methane selectivity compared to all other FT synthesis catalysts used in this study.

Due to the combined heavy dependence on crude oil and the unpredictable nature of the associated markets, an alternative means to produce the required hydrocarbon based products is much desired. The Fischer-Tropsch synthesis provides a route to the production of synthetic crude oil by a catalytic reaction between carbon monoxide and hydrogen (collectively referred to as syngas) at moderate temperatures and pressures. First discovered in the early 1900's, the process results in a multitude of products which can supply a range of transportation fuels and petrochemicals. However, knowledge of the reaction process is still not completely understood due to the complex product distribution which is obtained. In order to gain better control over the process outputs, enhancing the understanding of the mechanistic routes which govern the overall reaction is key. A novel route was developed to monitor the number and length of hydrocarbon species which accumulate and grow on the catalyst surface during the reaction by implementing in situ quantitative FTIR spectroscopy. Initially molar absorption coefficients, required in order to quantify the adsorbed hydrocarbon species, were determined utilising a custom made thermogravimetric infrared cell. The resulting absorption coefficients values were then applied to data which was derived from infrared spectra collected for various catalysts during multiple Fischer-Tropsch reactions. The quantitative analysis of the catalyst surface was then compared with reaction data collected using gas chromatography (GC), in order to investigate if a link exists between the surface species and reaction products. Results showed that while no direct link was detected, the observed surface species could be attributed to oxygenate products of the Fischer-Tropsch reaction which are not produced in a detectable amount by GC. The species were shown to reside on both the metal and support material, with the transportation mechanism to the support also investigated.

Fischer-Tropsch synthesis is a commercial technology that allows converting synthesis gas, a mixture of CO and H2, into fuels and chemicals. This process could be one of the actors in the reduction of oil dependency of the transportation sector. In fact, it has great potential for producing synthetic fuels also from renewable sources, such as biomass, after its thermochemical conversion (gasification) into synthesis gas. Concerning the quality of a diesel fuel produced with this technology, it has a lower local environmental impact than conventional diesel, since it is practically free of sulphur and nitrogen compounds and yields lower exhaust emissions of hydrocarbons, CO and particulates. The present study focuses on the use of cobalt-based catalysts for the production of diesel. In particular, it looks upon correlation between product selectivities when varying the catalyst properties and the effect of process parameters, such as a low H2/CO ratio, typical of a biomass-derived synthesis gas, and the water partial pressure. Different cobalt-based catalysts, with different properties, such as conventional 3-dimensional porous network supports (γ-Al2O3, α-Al2O3, TiO2, SiO2), Co-loading, preparation technique, etc., were investigated in the Fischer–Tropsch reaction at industrially relevant process conditions. For a set of process conditions, a linear relationship seems to exist between the selectivity to methane (and other light products) and higher hydrocarbons (identified by the industrially relevant parameter SC5+, selectivity to hydrocarbons with more than 4 carbon atoms) indicating a common precursor. Ordered mesoporous materials (SBA-15), characterized by a 1-dimensional mesoporous network, were tested as model supports and showed the possibility of occurrence of CO-diffusion limitations at diffusion distances much shorter than those required for conventional 3-dimensional porous network supports. The linear relationship mentioned above, derived for conventional supports, was shown to be an efficient tool for indicating whether measured selectivities are affected by CO-diffusion limitations. Some of the catalysts were exposed to H2-poor syngas and to external water addition and the effects on the selectivity relationships were investigated. Furthermore, the possibility of internal water-gas shift of a H2-poor syngas with mixtures of Co/γ-Al2O3 and a Cu/ZnO/Al2O3 catalyst was investigated both as a technical solution for direct use of a model bio-syngas in the Fischer-Tropsch synthesis, and as a means to study the effect of indigenous water removal on the reaction rate to hydrocarbons. It was found that removal of indigenously produced water slows down the reaction rate significantly. Lastly, the effect of water partial pressure on the Fischer–Tropsch rate of the Co catalyst supported on narrow-pore γ-Al2O3, on its own, was studied. Inlet water partial pressure was varied by external water vapor addition at different H2/CO molar ratios ranging from 1 to 3. The effect of water showed to be positive on the rate for all the H2/CO ratios, but more significantly at H2-poor conditions. The nature of this positive effect on the rate seems to be unrelated to changes in amounts of amorphous polymeric carbon detectable by temperature-programmed hydrogenation of the spent catalyst. / <p>QC 20120914</p>

Thesis--Leyden. / In Periodical Room.

Submitted by Eduarda Figueiredo (eduarda.ffigueiredo@ufpe.br) on 2015-03-11T14:35:25Z No. of bitstreams: 2 Dissertação Completa_Rodrigo.pdf: 2042384 bytes, checksum: adeaba5f9e93bef7dcc818744781565e (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) / Made available in DSpace on 2015-03-11T14:35:25Z (GMT). No. of bitstreams: 2 Dissertação Completa_Rodrigo.pdf: 2042384 bytes, checksum: adeaba5f9e93bef7dcc818744781565e (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Previous issue date: 2012-05-31 / A tecnologia de produção de combustíveis sintéticos iniciou seu desenvolvimento a partir de 1919, na Alemanha, tendo o carvão mineral como insumo para a gaseificação. Com o passar dos anos novos insumos foram utilizados, como a biomassa e o gás natural, cada um com rotas tecnológicas próprias. Com o uso do gás natural esta rota tecnológica é conhecida como Gas-To- Liquids (GTL) sendo uma transformação química que gera faixas de hidrocarbonetos líquidos e estáveis à temperatura e pressão ambientes. Este processo tem como etapa principal etapa à reação de Fischer Tropsch (FT), pois transforma gás síntese resultante da reforma do gás natural em hidrocarbonetos líquidos que ao serem refinados tornamse importantes produtos para indústria petroquímica, de transporte e áreas afins. Essa transformação pode ser realizada no próprio local de produção do gás, evitando investimentos e problemas ambientais na construção de gasodutos. No Brasil, o gás natural apresenta crescente incremento da sua produção, e forte aumento das suas reservas, como por exemplo, a descoberta do pré-sal e o gás natural presente pode estar tanto associado quanto não-associado ao petróleo. Devido às estruturas de plataformas normalmente se localizarem em áreas remotas, torna-se custoso o aproveitamento desse gás que é liberado pela produção do óleo, sendo o mesmo queimado ou ventado. Devido às restrições estabelecidas pela legislação ambiental, a queima do gás natural nas plataformas de produção passa a ser problemática e crítica. Este trabalho teve como objetivo desenvolver e avaliar por meio de simulação computacional uma planta de GTL na produção de hidrocarbonetos líquidos via a reação de FT e utilizá-lo na otimização do processo, na busca por um processo com maior capacidade produtiva e com menores gastos energéticos, gerando um melhor aproveitamento do gás natural, produzindo materiais com maior valor agregado. Foram utilizados os softwares de simulação MATLAB® e HYSYS®, que permitiram a analise de resultados satisfatórios para a conversão e distribuição de hidrocarbonetos gerados em comparação com o descrito pela literatura. A qualidade dos hidrocarbonetos gerados foi analisada pela avaliação do diesel obtido.

Fischer-Tropsch synthesis is the technology for converting fuel feedstocks such as natural gas and coal into transportation fuels and heavy hydrocarbons. There is scope for research and development into integrated processes utilising synthesis gas for the production of a wide range of hydrocarbons. For this purpose there should be strategies for the development of Fischer-Tropsch processes, which consider both economic and technological feasibilities. The aim of this study was to optimize Fischer Tropsch Plants in order to produce gasoline and gas oil by investigating the benefits of recycling & co-feeding of unconverted gas, undesired compounds, and lighter hydrocarbons over iron-based catalysts in order to save on capital and operating costs. This involved development of FT models for both two-phase and three-phase reactors. The kinetic parameters for these models were estimated using optimization with MATLAB fitting to experimental data and these models were then applied to ASPEN HYSYS flowsheets in order to simulate nine different Fischer-Tropsch plant designs. The methodology employed involved qualitative modelling using Driving Force Analysis (DFA) which indicates the necessity of each compound for the Fischer-Tropsch reactions and mechanism. This also predicts each compounds influence on the selectivity of different products for both two-phase and three-phase reactors and for both pure feeding and co-feeding arrangements. In addition, the kinetic models for both two-phase and three-phase reactor were modified to account for parameters such as the size of catalyst particles, reactor diameter and the type of active sites used on the catalyst in order to understand and quantify their effects. The kinetic models developed can describe the hydrocarbon distributions consistently and accurately over large ranges of reaction conditions (480-710K, 0.5-2.5MPa, and H2/CO ratio: 0.5-2.5) over an iron-based catalyst for once-through processes. The effect of recycling and co-feeding on the iron-based catalyst was also investigated in the two reactor types. It was found that co-feeding unwanted compounds to synthesis gas increases the production of hydrocarbons. This recycling and co-feeding led to an increase in H2/CO feed ratio and increased selectivity towards C5+ products in addition to a slightly increased production of light hydrocarbons (C1-C4). Finally, the qualitative model is compared with the quantitative models for both two-phase and three-phase reactors and using both pure feeding and co-feeding with the same reactor conditions. According to the detailed quantitative models developed, in order to maximize hydrocarbon production pressures of 2MPa, temperatures of 450K and a H2/CO feed ratio of 2:1 are required. The ten different Fischer-Tropsch plant cases were based on Fischer-Tropsch process. FT reactor models were built in ASPEN HYSYS and validated with real FT plant data. The results of the simulation and optimization supported the proposed process plant changes suggested by qualitative analysis of the different components influence. The plants involving recycling and co-feeding were found to produce higher quantities of gasoline and gas oil. The proposed heuristic regarding the economic scale of the optimized model was also evaluated and the capital cost of the optimized FT plant reduced comparison with the real FT plant proposed by Gerard. Therefore, the recycling and co-feeding to FT reactor plant was the best efficiency to produce both gasoline and gas oil.

Orientador: Mario de Jesus Mendes / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Campinas / Made available in DSpace on 2018-07-17T00:50:54Z (GMT). No. of bitstreams: 1 Santos_OneliaAparecidaAndreodos_M.pdf: 5044753 bytes, checksum: 4d24d41e569f872f9de1eb02687ec8d3 (MD5) Previous issue date: 1986 / Resumo: A reação de síntese de Fischer - Tropsch tem merecido uma grande atenção pelo seu interesse tecnológico e científico. Naturalmente este interesse está, em grande parte, associado ao problema da escassez do petróleo, na medida em que a síntese de Fischer - Tropsch oferece uma rota adequada para a transformação de combustíveis sólidos em combustíveis líquidos e gasosos e em insumos básicos da industrIa petroquímica. Dada a estrutura do mercado brasileiro, este interesse está essencialmente dirigido para a substituição do óleo diesel e do óleo combustível. A experiência mostra que, através de uma seleção adequada do catalisador e das condições operatórias,é possível alterar, dentro de certos limites, a distribuição dos produtos obtidos na reação de síntese. Neste trabalho é apresentada uma discussão sobre a natureza dos catalisadores usados na síntese de Fischer-Tropsch, assim como o mecanismo da reação, com ênfase nos catalisadores à base de ferro. Pretende-se com esta discussão, identificar algumas possíveis vias para o desenvolvimento de catalisadores otimizados, mais ativos e mais seletivos, para determinadas frações de produtos (gasolina, diesel, olefinas, etc). É ainda apresentada uma descrição da instalação desenvolvida para a coleta de dados cinéticos na síntese de Fischer - Tropsch, e discutidas, com base em resultados preliminares, as dificuldades encontradas, em particular no que respeita à análise das misturas complexas obtidas como produto da reação. / Abstract: The Fischer-Tropsch synthesis reaction has received great attention due to its scientific and technological interest. This interest arises mostly in association with the dwindling of petroleum reserves, and because the Fischer - Tropsch synthesis offers an appropriate route for the transformation of solid fuels into liquid or gaseous fuels, as well as basic chemicals for the petrochemical industry. Considering the structure of the Brazilian market, this interest is essencially directed for the substitution of diesel and fuel oil. Accumulated experience with the synthesis reaction shows that it is possible to alter, within certain limits, the distribution of the products obtained. In this work a discussion is presented on the nature of the catalysts used in the Fischer - Tropsch synthesis, as well as on the reaction mechanism, with emphasis on catalysts based on iron. The aim of this discussion is to establish possible schemes for the development of optimized catalysts, with better activity and selectivity for desired product fractions(gasoline, diesel, olefins,etc). It is also presented the description of an experimental equipment developed for collecting kinetic data on the Fischer - Tropsch synthesis, and discussed the difficulties that were met in the preliminary tests, particularly with reference to chemical analysis of the products of reaction. / Mestrado / Mestre em Engenharia Química

This research forms part of a programme of work at the University of Canterbury investigating the production of liquid fuels from biomass. The drivers for this research are the plentiful supply of woody biomass in New Zealand as well as the necessity for a reduction in the use of fossil fuels. Fischer-Tropsch synthesis has been chosen as the base conversion method for syngas to liquid fuels. While Fischer-Tropsch plants are traditionally very large, the low geographical density of the biomass feedstock necessitates a shift from a traditional economies of scale approach. In this research a sawmill integrated polygeneration scenario is proposed that recognises the synergy between the heat and electrical requirements of a mill and the Fischer-Tropsch process that can supply both as well as liquid fuels. Techno-economic modelling of variations to this polygeneration arrangement were performed using a traditional Fischer-Tropsch slurry reactor as the basis. The breakeven price of syncrude produced in the process based on a 30 year plant life and 10% discount factor was as low as $US 167 per barrel. This arrangement is coupled with development of and experimentation with a microchannel reactor in a further attempt to overcome economies of scale disadvantages. The lab scale microchannel reactor consisted of a shim with 50 channels of 37mm length with 0.2mm height and 0.3mm width. The microchannel reactor was tested with shorter run periods to compare different catalyst washcoats consisting of neat cobalt, cobalt on titania and a combustion synthesis method over a temperature range of 210-240°C at 20 bar. Comparison was also made to a lab scale fixed bed reactor with a powdered cobalt on titania catalyst. The neat cobalt washcoat proved to have the best performance per unit mass of catalyst of the three washcoats. The performance of the microchannel reactor was 32-40 times better per unit catalyst mass than the fixed bed reactor. From data based on the shorter runs the neat cobalt washcoat and the cobalt on titania washcoat were selected for further analysis over longer runs at a range of pressures from 2-20 bar and temperatures from 210-240°C. These runs were each approximately 70 hours long and provided a better analysis of the narrowed catalyst choice. The productivity results of the catalysts were fitted to established kinetic equations from literature with an excellent correlation. More accurate Anderson-Schultz-Flory selectivity values were also obtained ranging between 0.72 to 0.82. This is certainly an area that would warrant further attention as a higher selectivity has a very positive affect on plant economics. Establishment of the kinetic equations for the catalyst performance allowed modelling of reactors with greater volume along with investigation of mass transfer limitations to assist in scale up of the technology. It was found that under 4-5mm hydraulic diameter channel dimensions the mass transfer limitation from the bulk gas phase to the catalyst interface is negligible. A scaled up microchannel reactor concept design is proposed utilising stainless steel mesh folded into 2mm channels to increase catalyst surface area compared to straight shim. A costing correlation was produced per unit of reactor volume to allow a full scale cost of the microchannel reactor to be estimated for inclusion into the techno-economic model. The revised techno-economic model was optimised through pressure variation to give a breakeven syncrude value of $US118 per barrel at Fischer-Tropsch reaction conditions of 10 bar and 240°C. This brings the value well within historical crude price trends.

Fischer-Tropsch (FT) synthesis is a reaction which entails the conversion of synthesis gas, also known as syngas (a mixture of H2 and CO gases), to liquid hydrocarbon fuels, oxygenated hydrocarbons, chemicals and water. This syngas mixture is obtained from natural gas, coal, petroleum, biomass or even from organic wastes. In this study cobalt catalysts supported on novel carbon spheretitania (CS-TiO2) composite materials were synthesized and tested for their performance in the FT process. Initially carbon spheres (d = 80-120 nm) were prepared in a vertical swirled floating chemical vapour deposition reactor without the use of a catalyst. The rate of production was controlled and the highest production rate of about 195 mg/min was obtained at an acetylene (C2H2) flow rate of 545 mL/min at 1000 °C. The produced carbon spheres (CSs) had a narrow size distribution with a uniform diameter size. Purification and functionalisation of the CSs improved the total surface area, due to the removal of PAHs which blocked the CS pores. The introduction of functional groups to the CSs was achieved and these changed the wetting properties of the CSs. Functionalising the CSs for longer than 17 h in HNO3 destroyed the morphology of the CSs. After successful preparation of functionalised CSs, the interactions between CSs and TiO2 were studied by in the TiO2 composite using two different sol-gel methods, namely the conventional sol-gel and the surfactant wrapping sol-gel method. The surfactant wrapping sol-gel method entailed the modification of the CSs by dispersing them in a surfactant, in this case hexadecyltrimethylammonium bromide or CTAB [(CH3(CH2)15N(CH3)3Br]. This introduced alkyl “tails” which eased the dispersability of the CSs before coating them with Ti[O(CH2)3CH3]4 (a source of TiO2) to produce a homogeneously coated CS-TiO2 composite material (defined as ASW3). It should be mentioned that many, many experiments were performed to develop an efficient and reliable method to make homogeneously coated CS-TiO2 composites since it was found to be very difficult to achieve an interaction between carbonaceous materials and TiO2 especially by sol-gel procedures. The traditional sol-gel method was used to prepare CS-TiO2 composites with different ratios viz. 1CS-1SG, 1CS-2.5SG, 1CS-5SG, 1CS-10SG, 1CS-25SG and 1CS-50SG. These composites showed weak interactions between CSs and TiO2 even at high TiO2 loading ratio. Interestingly the surface area of these composites showed high values of 80 and 85 m2/g for 1CS-5SG and 1CS-10SG, respectively. At lower TiO2 ratios the measured surface area was similar to that of CSs, i.e 10 m2/g for 1CS-1TiO2. At high TiO2 ratios the measured surface area was similar to that of TiO2, i.e 49 m2/g for 1CS-50TiO2. The TEM images of CS-TiO2 (ASW3) composites prepared by surfactant wrapping methods showed a successful TiO2 coating of CSs. The TiO2 grain size was 8.0 nm with both anatase and rutile phases. High surface areas (up to 98 m2/g) of composite materials were achieved by employing this procedure. The high surface areas achieved suggest that the interaction between CSs and TiO2 was homogeneous and the increase was due to the “bridge” formed between CSs and TiO2. A series of cobalt catalysts (10% by weight) supported on these materials was carried out by the deposition precipitation method using Co(NO3)2·6H2O as the metal precursor. After appropriate drying and calcination the catalysts were characterized using traditional characterisation techniques and tested in the FT reaction using a fixed bed reactor. The the 10%Co/CS catalyst produced a CO conversion of 15.2% while the catalyst had a low total BET surface area (6 m2/g) compared to non-carbonaceous catalysts with higher BET surface areas. This observation suggests that the surface area did not necessarily play a role in the CO conversion, but that other properties (reducibility and dispersion) of CSs influenced the catalyst activity. After coating CSs with TiO2 and loading cobalt to produce 10%Co/ASW3 both the BET surface area of the catalyst and the CO conversion increased to 83 m2/g and 20.1%, respectively. CO-TPD of 10%Co/ASW3 showed a large amount of strongly adsorbed CO. This increased CO was due to the interaction between CSs and TiO2 which developed CO adsorptive sites.

In this study the synthesis and use of carbon nanofibers (CNFs) as catalysts supports for Fischer Tropsch synthesis is reported. The synthesis of carbon nanofibers with two distinct morphologies was optimized based on the reports in the literature that the straight (SCNF) and helical (CCNF) carbon nanofibers grow on Cu catalysts with different particle sizes. To selectively grow CNFs with a single morphology Cu catalysts were designed using different synthesis procedures (by using unsupported, coated and silica supported catalysts). The prepared copper oxide (CuO) nanoparticles were characterized by techniques such as TEM, XRD and nitrous oxide chemisorption. These techniques showed that the unsupported and coated CuO catalyst precursors has large particle sizes (range 100-300 nm) and thus had low Cu atomic surface area, while the supported CuO catalysts displayed low particles sizes in the nanoscale regime (<20 nm) and hence had high atomic surface area. Preparation of CNFs was carried out 300 using acetylene (C2H2) gas as the carbon source. Cu catalysts with large particle sizes resulted in straight CNFs and the small supported Cu nanoparticles grew helical CNFs because of the change in the nanoparticle surface energy during adsorption of the acetylene gas and the silica (SiO2) support effects that limited Cu nanoparticles from sintering (i.e. final particles size 60 nm). Soxhlet extraction proved to be an invaluable step in removing adsorbed polycyclic aromatic hydrocarbons. Because of the low thermal stability of these CNFs the materials were then annealed at higher temperatures ranging from 500-1400 in an inert environment (passing N2 gas). The helical CNFs snapped under high temperature annealing ( 900 ) resulting in shorter lengths in comparison to the straight CNFs. BET analysis of the annealed CNFs indicated that the CNFs annealed at 500 and 900 have increased surface area and have a mesoporous pore structure with the surface area ranging from 200-350 m2/g. Raman and Fourier transform IR spectroscopy indicated that the CNFs annealed at 500 and 900 , (which were the main material of interest because of their high surface area and thermal stability) had different hybridized carbon content. CNFs annealed at 500 contained both sp2 and sp3 hybridized carbon while annealing the CNFs at 900 resulted in a complete rehybridization of the carbon content to sp2. The carbon sp3 content in the CNFs annealed at 500 therefore implied that CNFs annealed at this temperature are more defective in comparison to the CNFs annealed at 900 . Since it is well known that material functionalities are affected by the amount of defects present inside the different CNFs were then applied as catalyst supports for Fischer Tropsch synthesis (FTS) to compare the support effects on cobalt active sites. The CNF surfaces were first modified by functionalization using concentrated HNO3 solution. The preparation of the catalyst systems was performed by a simple HDP method using urea. The CNFs and the FT catalysts were characterized using different techniques such as XRD, TEM, BET, TPR and Raman spectroscopy. Reactor studies performed at 220 (P = 8 bar, GHSV= 1200 mL.h-1. ) showed the catalysts had activities with CO conversion ranging from 25-45%. It was observed that catalysts supported on CNFs annealed at 500 displayed higher average activities of about 15% (based on the CO conversions) in relation to the catalysts supported on CNFs annealed at 900 . Catalysts showed minimal water gas shift reaction and high methane selectivity (i.e. 20-30%) which can be attributed to the small Co crystallite sizes and low pressure reaction conditions.