Fernando Israel Gómez-Castro

Simulation study on biodiesel production by reactive distillation with methanol at high pressure and temperature: Impact on costs and pollutant emissions

a b s t r a c t Recently, a two-step biodiesel production process which uses short-chain alcohols at supercritical con- ditions has been proposed. In addition, literature reports suggest that the COSMO-SAC thermodynamic model is a suitable alternative for the prediction of VLE for supercritical methanol/methyl esters mix- tures. Thus, in this work a simulation study of the two-step supercritical method for the production of biodiesel is performed by using the COSMO-SAC model. Further, alternative system configurations for biodiesel production based on reactive distillation are proposed and their total emissions are compared to those corresponding to the conventional catalytic method. The study demonstrates the benefits of using reactive distillation for the esterification step and discusses the environmental impact of the supercritical production process. It has been found that the intensified alternatives reduce the emissions considerably and, through the reuse of the excess methanol, the emissions level of the supercritical process can be compared to those of the catalytic method.

Simulation and optimization of a biojet fuel production process

Abstract Aviation sector contributes with 2% of the total CO 2 emissions due to human activities. Moreover, predictions estimate that air traffic will duplicate in the next 20 years, with the corresponding increasing in CO 2 emissions. The International Air Transport Association (IATA) has established four strategies to reduce CO 2 emissions; one strategy is the development of aviation fuel from renewable feedstocks, known as biojet fuel. In 2009 UOP Honeywell received a patent for its process to produce aviation fuel from renewable feedstocks. The process considers the transformation of vegetable oil through hydrogenating, deoxygenating, isomerizing and selective hydrocracking to generate propane and hydrocarbons fuels. The resulting aviation fuel is very similar to the fossil one, with the only difference that the first one does not contain aromatic compounds. Due to this, the ASTM standard established the use of biojet fuel in mixtures with fossil jet fuel with up to 50% of the bio-fuel. Also, it is important to remark that in this moment the process of UOP Honeywell is the only one certified for the production of aviation fuel from renewable feedstocks. In this work we propose a model for the production of biojet fuel, obtaining an estimation of the conversion of the reactions of the process of UOP Honeywell. Also, the optimization of the purification stage is performed using a multiobjective genetic algorithm with constraints, which is coupled to Aspen Plus process simulator, in order to generate results considering the complete models of the process. Results show a high conversion of the vegetable oil (castor oil) to biofuels (biojet fuel and green diesel); also, energy can be generated in the process as result of the conditioning of the stream that is fed to the distillation train.

Optimization of a reactive distillation process with intermediate condensers for silane production

Abstract This work presents a reactive distillation column for the catalytic disproportionation of trichlorosilane to silane which includes three consecutive reversible reactions. This reaction system is however characterized by a large distinction in the boiling points of the components, which make the reactive distillation extremely favored. Nevertheless, the normal reactive distillation column possesses the shortage of high refrigeration requirement. By removing heat at temperature higher than that at the condenser a superstructure representation, rigorous simulations, and optimization problems were combined to derive optimal reactive distillation columns which can realize heat integration between stages and utilities at several refrigeration conditions. An iterative simulation-optimization procedure was proposed to consider temperature changes in stages due to heat integration. The results showed that the installation of two inter-condensers results in the best option with economic savings up to 56%.

A comparative simulation study of power generation plants involving chemical looping combustion systems

Abstract This work presents a simulation study on both energy and economics of power generation plants with inherent CO 2 capture based on chemical looping combustion technologies. Combustion systems considered include a conventional chemical looping system and two extended three-reactor alternatives (exCLC and CLC3) for simultaneous hydrogen production. The power generation cycles include a combined cycle with steam injected gas turbines, a humid air turbine cycle and a simple steam cycle. Two oxygen carriers are considered in our study, iron and nickel. We further analyze the effect of the pressure reaction and the turbine inlet temperature on the plant efficiency. Results show that plant efficiencies as high as 54% are achieved by the chemical looping based systems with competitive costs. That value is well above the efficiency of 46% obtained by a conventional natural gas combined cycle system under the same conditions and simulation assumptions.

Energy integration of a hydrotreating process for the production of biojet fuel

Biojet fuel has been identified as the most promissory alternative to reduce CO2 emissions in the aviation sector, which contributes about 2% of the total emissions of carbon dioxide. There are several processes available for the production of biojet fuel; nevertheless, the hydrotreating process is one of the most promising, since it can be adapted to the existing refinery infrastructure and it is also certified by ASTM. Biojet fuel, nevertheless, is still not economically competitive with the conventional, petroleum-based jet fuel. Thereby, in this work we propose the energy integration of the hydrotreating process considering Jatropha Curcas as renewable raw material. We present a kinetic model for the reactive section, in order to estimate the energy released by the process, which is used to partially satisfy the energy requirements of the purification section. Finally, the effect of the energy integration on the price of biojet fuel is analyzed. Results show that the cost per liter of biojet fuel is very close to the cost of the fossil one, when the energy generated in the process is used. Thus, through a proper energy integration on the production process, the cost of biojet fuel can be competitive with that of the fossil jet fuel.

Analysis of alternative non-catalytic processes for the production of biodiesel fuel

One of the most common supercritical processes for the production of biodiesel fuel involves the use of methanol as reactant. Besides obtaining biodiesel fuel, glycerol is also produced. To avoid the production of glycerol as by-product, alternative reactants for the production of the biofuel have been proposed in recent years. As expected, the use of different reactants may have an impact on the separation processes required to obtain biodiesel fuel complying with international standards. Thus, in this work flowsheets for the different supercritical processes for the production of biodiesel are proposed and analyzed in a simulation environment. The analyzed processes are then compared in terms of energy requirements, total annual costs, and environmental impact. It has been found that the two-step processes show advantages in terms of CO2 emissions, but in terms of total annual cost the one-step processes are better, showing potential for low CO2 emissions. Nevertheless, the processes in one-step (with methanol or methyl acetate) result in lower CO2 emissions and TAC if they are operated at lower temperature. Acetic acid process is the more energy-intensive and expensive of the four processes.

Optimization of Alternative Distillation Sequences for Natural Gas Sweetening

The separation of CO2 and/or H2S from the natural gas processing is focused on preventing some undesired effects, as decreasing the heat capacity in the natural gas, and so on. Moreover, the carbon dioxide removal has an extensive interest in other application fields, like mitigating CO2 emissions, being an entrainer in EOR (Enhanced Oil Recovery), among others. One novelty alternative to deal with CO2 separation consists in the use of cryogenic extractive distillation by utilizing as entrainer the liquid hydrocarbon fraction obtained in the process. This process has some advantages, such as that the entrainer is CO2 selective, noncorrosive, and waterless by-product, effective for high CO2 concentration feedstock. In this work, the Aspen Plus One 7.0 process simulator was used to model the CO2 - ethane azeotrope for different extractive distillation sequences and distinct entrainers, considering a rate based model. The study included the formal design and optimization (minimizing the Total Annual Cost (TAC) and maximizing the acid gas removal) to finally compare the alternative configurations with the conventional chemical absorption system used in the industrial field. Complementary studies regarding the controllability, thermodynamic efficiency and greenhouse gases generation were conducted. The proposed cryogenic extractive distillation sequences showed, in terms of costs and CO2 emissions, better performance than the conventional chemical absorption configuration. Even more, the extractive thermally coupled distillation structures reached the best energy savings with appropriate dynamic behavior, making these alternatives competitive and environmentally friendly.

Modelling of the hydrotreating process to produce renewable aviation fuel from micro-algae oil

Abstract Renewable jet fuel has been identified as the most promissory alternative to reduce CO2 emissions in the aviation sector, allowing its sustainable development. This renewable fuel, also known as biojet fuel, can be obtained from different types of biomass, which include lignocellulosic biomass, sugar, starchy and triglyceride feedstock. In particular, the conversion of triglyceride feedstock to biojet fuel is realized through the hydrotreating process, where hydrodeoxygenation, hydroisomerization and hydrocracking reactions are carried out; after that, the purification of the renewable hydrocarbons is realized through distillation columns. The modelling and intensification of the hydrotreating processes have been previously analyzed for castor oil and jatropha curcas oil, which are the non-edible crops with highest productive potential in Mexico. However, another raw material with high productive potential is micro-algae oil, since it can be cultivated in non-fertile lands, avoiding the competition with food crops for ground use. Therefore, in this work we propose the modelling of the hydrotreating process to produce biojet fuel, considering micro-algae oil as raw material. The reactive section is modelled with a multifunctional catalyst; thus, all the hydrotreating reactions are carried out in one vessel. The produced renewable hydrocarbons are purified by conventional distillation sequences: direct, indirect and combined. Thus, three conventional hydrotreating processes are defined and evaluated in terms of total annual costs, CO2 emissions and price of biojet fuel. It has been found that the hydrotreating process that includes the direct conventional sequence presents the lowest total annual costs. Also, in all scenarios the biojet fuel price is competitive with the fossil one. Considering the high productivity per hectare, microalgae oil is a very promissory raw material for sustainable production of renewable jet fuel with a competitive price.

Process integration for the supercritical production of biodiesel and the production of lignocellulosic bioethanol

Abstract Biodiesel and bioethanol are among the most studied biofuels. For the production of biodiesel, the use of supercritical alcohols has been reported as an alternative with some advantages over the traditional base-catalyzed processes. Nevertheless, due to the high pressure and temperature conditions under which the supercritical process operates, the energy demand can be considerably high. On the other hand, production of bioethanol through lignocellulosic biomass is a topic of interest, because it avoids the competence with food industry derived of using first-generation biomass. In such processes, several reaction steps are required, with water as one of the main resources. Therefore, the integration of both production processes could be advantageous in terms of energy costs and environmental impact. In this work, the feasibility of mass and energy integration between the supercritical biodiesel production process and a lignocellulosic bioethanol process is evaluated, as a strategy to reduce external energy requirements and mass agents. By this approach, reductions on the utilities costs are expected if compared with the individual processes.

Optimal design and control of trains of dividing wall columns for the separation of petrochemical mixtures

The purification of most of the fluid mixtures of industrial relevance is performed in distillation columns trains. In spite of its low energetic efficiency, distillation remains as the most used separation process, due to its great flexibility to obtain products with high purity. Nevertheless, actual concerns about the energy use and the reduction of CO2 emissions encourage the efforts in the increasing of the energetic efficiency of these schemes. Among these schemes with major energetic efficiency, the dividing wall column allows a reduction of energy consumption along with a reduction in capital investment and space requirements. The dividing wall columns have been recently used in different applications; however, to our knowledge, they have not been used in the separation of petroleum mixtures. In this work, we study the use of trains of dividing wall columns for the separation of a typical mixture of refinery cuts. The proposed train is compared with conventional distillation sequences in terms of energy consumption and control properties. Both conventional and thermally coupled trains are designed with a multiobjective genetic algorithm, with constraints handling, coupled to Aspen Plus. As a result, Pareto front of both sequences are obtained, and some of these designs are selected to perform control studies. We also analyze the dynamic behavior of the structures under different operating points, including the one with minimum energy consumption. The basic idea is that if one changes the operation point, the control properties might change as well. The control analysis properties are analyzed with the application of the singular value decomposition technique. Results show interesting trends in the optimal designs that integrated the trains in energy consumption and that the controllability properties of integrated distillation sequences may change significantly depending on the selected operation point control properties.