Materials Science Forum Vol. 965

Abstract: The possibility of using renewable feedstocks for biodiesel production and reducing gas emissions makes it an attractive large-scale substitute to traditional fossil diesel. Although renewability is one of the main driving forces in biodiesel use, traditional production routes employ methanol as the transesterification agent, a chemical generated from fossil carbon. Aiming at further improving biodiesel’s sustainable performance, the replacement of methanol by ethanol has been proposed. Use of the ethylic production route could further reduce CO₂ emissions, energy consumption and generate more jobs. The objective of this study is to unveil whether substituting methanol for ethanol does indeed result in a less carbon and energy intensive production chain while also increasing job generation and decreasing social strife. To assess production chain performance a lifecycle approach was used composed by: (i) Data assemblage from literature to represent the ethylic/methylic biodiesel systems; (ii) Construction of quantitative indicators to compare material and energetic flows; and (iii) Principal Component Analysis (PCA) for data interpretation and relevance ranking of calculated social/environmental indicators. Focus was given to CO₂ emissions, energy consumption and social aspects of sustainability. Results show that use of ethanol does indeed reduce CO₂ emissions, due to extra agricultural carbon sinks in the production chain but increases energy consumption and energy loss. Methanol also resulted in a chain with higher average wages, more jobs generated and less forced labor cases but with a higher accident rate and a high salary disparity. PCA showed that carbon intensity is one of the most important environmental metrics while energy consumption was considered secondary, but the high correlation between these aspects highly impact chain sustainability. PCA also greatly differentiated agricultural and industrial links of respective production chains, with industrial links being governed by CO₂ emissions and process safety and agricultural links by water consumption, land use and energy loss. A distinct tradeoff was seen between environmental and social considerations of sustainability and between carbon intensity and energy consumption reductions. As a result, substitution is only justified in scenarios in which CO₂ emissions outweigh energy intensity and social aspects.

Abstract: CO₂ is the most important greenhouse gas in terms of emitted quantities and its emission has increased significantly due to the action of anthropogenic sources. Among the alternatives for mitigation of this gas is the direct synthesis of propylene carbonate (PC), which requires efficient and selective catalysts. In this scenario the titanate nanotubes (TNT) are promising catalysts because they can be modified to become selective for the PC synthesis. The present work has the objective to develop titanate nanotubes with different metals (Na, Sn and Zn) as well as protonated titanate nanotubes (HTNT) and to test their efficiency in the direct synthesis of PC. The synthesized nanostructures were characterized by TEM, EDS, XRD and N₂ adsorption-desorption. The results showed that the synthesized TNT have a specific surface area of 155, 232, 56 and 140 m2/g (NaTNT, HTNT, SnTNT and ZnTNT, respectively). Besides, the ion exchange of [Na⁺] by [Sn⁺²] and [Zn⁺²] decreased the crystallinity of nanostructure. On the catalytic tests, the system NaTNT/ZnBr₂ showed the best results with a yield of 61% and a selectivity of 81% in PC. The catalytic system SnTNT/DMF and ZnTNT/DMF are promising to this reaction showing interesting yields and catalytic activity (59 and 53%; 295 and 265 mmol/g) for PC synthesis.

Abstract: Offshore oil production in deep waters challenges CO₂ removal technologies since, for extracting the oil, a huge flow rate of CO₂-rich gas must be processed. Currently, amine absorption and membrane permeation are widely used for CO₂ abatement in offshore rigs although they present some drawbacks such as high heat demand for CO₂ stripping and high-power requirement to meet trans-membrane partial pressure difference, respectively. In this context, due to their low vapor pressure, high thermal stability and low energy consumption, ionic liquids have been considered a promising alternative to conventional CO₂ capture technologies. The aim of this work is to define the most economically suitable operating condition for CO₂ capture from Brazilian Pre-Salt natural gas using ionic liquid [Bmim][NTf₂]. According to a process condition screening methodology, based on CO₂ and CH₄ Recoveries, Specific Energy Consumption and Life Cycle Cost, alternative with a two-stage solvent regeneration at 15 and 4 bar configures the most suitable one.

Abstract: This work aimed to fulfill a technical evaluation of the applicability of gas-liquid membrane contactors (GLMC) to remove CO₂ from CO₂ rich natural gas in offshore rigs. For this purpose, a simulation case in HYSYS 8.8 (AspenTech) was performed to remove CO₂ from a natural gas stream with concentration of 40% mol CO₂ using an aqueous solution of monoethanolamine (MEA) 30% w/w. GLMC unit operation is not available in HYSYS, though. Hence, it was necessary to develop a mathematical model based on log-mean of differences of CO₂ fugacities in both phases. Moreover, a GLMC Unit Operation Extension (UOE) was created for GLMC units to run in the process simulator HYSYS 8.8 using its thermodynamic infrastructure. The developed GLMC unit operation extension performed accordingly to the expected behavior. For a gas feed flow rate of 5 MMNm³/d (typical from FPSO's), the calculated total GLMC mass transfer area was 1,986 m², which requires 14 GLMC modules. Consequently, this operation showed to be a feasible option for CO₂ removal in natural gas conditioning on offshore rigs. The heat ratio in the reboilers of CO₂ stripping columns was found to be 167 kJ/mol, compatible with data found in the literature of CO₂-MEA-H₂O systems.

Abstract: Every day huge amounts of CO₂ are released into the atmosphere by enterprises such as biorefineries. In this context, the present work proposes a plausible scenario where a large-scale sugarcane-based biorefinery capture over 92% of its CO₂ emissions to be used as enhanced oil recovery (EOR) agent. The study is based on the integration of sugarcane crop–large-scale ethanol biorefinery–post-combustion capture–CO₂ pipeline to EOR. As results, the plant obtained a CO₂ recover of 91.3% from post-combustion capture, allowing export 5.29 MM tCO₂/y. Basic revenues of this project came from ethanol production, electricity sales, and EOR. In addition, four scenarios were investigated considering incomes from the handling of the captured CO₂. All scenarios were evaluated in terms of the use of 1 and 2 bbl/tCO₂ for EOR, leading to the conclusion that long-term economic sustainability can be assured only for some scenarios and mainly above 2 bbl/tCO2.

Abstract: The use of CO₂-rich natural gas (%CO₂ ≈ 20%mol) for power generation in offshore hubs results in simpler upgrade process, while imposes an extra challenge to mitigate emissions. Power generation via combined cycle configurations and post-combustion capture with CO₂ reinjection are investigated for carbon-footprint reduction, while increasing gas export and oil production, respectively. The processes are simulated using Aspen HYSYS software and compared to currently installed simple cycle configuration in terms of footprint, weight, power, efficiency and CO₂ emissions. The combined cycle including two gas turbines and one single-pressure steam cycle (CC 2:1:1) results in the most favorable power system, having 53% efficiency, 476.8 gCO₂/kWh emissions and similar dimensions compared to the simple cycle. The integration of a post-combustion capture sending the CO₂ for enhanced oil recovery results in 241 gCO₂/kWh for the CC 2:1:1 and 251 gCO₂/kWh for the simple cycle, without great impacts in total efficiency. The CC 2:1:1 with post-combustion capture presents higher net efficiency, lower dimensions and greater economic advantages, enabling emissions reduction without having significant impacts on the power generation.

Abstract: Thermal power plants with oxy-combustion CO₂ capture are featured by large scale oxygen demand, where cryogenic air separation is most suitable. In such context, a Pre-Purification Unit (PPU) is required, prior to air fractionation, to remove hazardous air contaminants – H₂O, CO₂ and several trace-species – preventing ingress into the Cold Box. The conventional PPU – named FULL-TSA – remove those contaminants by means of Temperature Swing Adsorption (TSA), ordinarily using double-layered bed with activated alumina for adsorbing H₂O and zeolitic molecular sieve for adsorbing CO₂ and further trace-species, which implicates in relatively high demand of low-pressure steam for impurities desorption. A novel pre-purification concept (SS-TSA) embraces a Supersonic Separator (SS) performing the bulk of separation service, abating nearly 98.5% of H₂O, followed by a finishing single-bed molecular sieve (MS) TSA step, which is featured by its relatively small size, for removing CO₂ and remaining impurities. This work presents the energy analysis, as well as the related indirect CO₂ emissions, of such a novel concept (SS-TSA) comprising air compression, cooling, SS dehydration and finishing MS-TSA against the conventional method fully based in TSA purification (FULL-TSA). Process simulation in HYSYS 8.8 assisted technical evaluation and comparison of alternatives, which included the use of two Hysys Unit Operation Extensions – SS-UOE and PEC-UOE – for rigorous thermodynamic SS modeling with phase equilibrium sound speed. SS was designed to impose only 1.4% of head loss, while shrinking TSA service to about 10% of FULL-TSA counterpart, also recovering super-cooled aqueous condensate that reduces water make-up and N₂ consumption for cooling. Changing from FULL-TSA to SS-TSA the average demand of low-pressure steam reduced from 1.37 to 0.16 MW. In terms of electricity demand the difference was quite small, referring to a tiny increase of 0.07 MW in SS-TSA comparatively to total power demand of 14.97 MW in FULL-TSA. Assuming a natural gas combined cycle cogeneration plant matching requirements to air compression and pre-purification process, equivalent reduction in CO₂ indirect emission was 20 kg/h for SS-TSA. These results point superiority of SS-TSA.

Abstract: Carbon dioxide (CO₂) is considered one of the main gases that cause global warming. In this perspective, its injection in aquifers and oil and gas reservoirs has been a possible alternative to reduce its emission in the atmosphere. An alternative strategy in which CO₂ is used efficiently in the Oil Industry is the Carbonated Water Injection (CWI), where the carbon dioxide is injected through the reservoir dissolved in the brine, eliminating problems of gravitational segregation and low sweeping efficiency present in other gas injection methods. Once injected, the fluid may react with the carbonate rock and inducing their dissolution, causing changes in the petrophysical properties of the rock. This work investigated changes in the average porosity of carbonate samples from Brazilian reservoir through a dynamic flow test with enriched brine with 100% CO₂ injection under high pressure and high temperature conditions and simulating a region around the face of the injector well, with an injection pressure of 8,500 psi, a temperature of 70 °C and a flow rate of 2cm3/min. The core-flooding experimental setup includes two coreholders arranged in series with samples confined in its interior, which are swept by X-ray Computed Tomography (CT), taking measurements of average porosity data. The results showed that there was dissolution in the sample assembled in the first coreholder since the porosity had increased, while in the second, no significant alterations of the porosity were observed (around 8.5% of its initial value). This observation can still be confirmed by the analysis of the dissolved moles, which exhibit behavior similar to the porosity, indicating that some minerals actually suffered dissolution from the injection of carbonated brine.

Abstract: Supersonic separator is investigated via process simulation for treating CO₂ rich (>40%) natural gas in terms of dew-points adjustment and CO₂ removal for enhanced oil recovery. These applications are compared in terms of technical and energetic performances with conventional technologies, also comparing CO₂ emissions by power generation. The context is that of an offshore platform to treat raw gas with 45%mol of CO₂, producing a lean gas stream with maximum CO₂ composition of ≈20%mol, suitable for use as fuel gas, and a CO₂ rich stream that is compressed and injected to the oil and gas fields. The conventional process comprises dehydration by chemical absorption in TEG, Joule-Thomson expansion for C3+ removal, and membrane permeation for CO₂ capture. The other alternatives use supersonic separation for dew-points adjustment, and membranes or another supersonic separation unit for CO₂ capture. Simulations are carried out in HYSYS 8.8, where membranes and supersonic separation are modeled via unit operation extensions developed in a previous work: MP-UOE and SS-UOE. A full technical and power consumption analysis is performed for comparison of the three cases. The results show that the replacement of conventional dehydration technology by supersonic separators decreases power demand by 8.5%, consequently reducing 69.66 t/d of CO₂ emitted to the atmosphere. The use of supersonic separation for CO₂ capture is also superior than membranes, mainly due to the production of a high-pressure CO₂ stream, that requires much less power for injection compression than the low-pressure permeate stream from membranes. Therefore, the case with two supersonic separator units in series presents the best results: lowest power demand (-23.9% than conventional case), directly impacting on CO₂ emissions, which are reduced by 2598 t/d (-27.82%).