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- Hydroisomerization of n-decane over SAPO-11 catalysts synthesized with methylamine as co-templatePublication . Bertolo, Raquel; Fernandes, Auguste; Ribeiro, Filipa; Silva, João; Martins, Ângela; Ribeiro, Fernando RamoaThe present work deals with preliminary studies concerning a new synthesis approach to prepare SAPO materials with AEL structure and evaluate their catalytic behavior in the hydroisomerization of long paraffins. The new SAPO-11 catalysts were synthesized with the help of a small amine (methylamine, MA) added during the preparation of the initial gel. As MA incorporates into the structure of the final materials, it contributes, together with DPA (dipropylamine), to an increase in Si incorporation as isolated species, which results in Bronsted acid sites. Thus, this new and original synthesis strategy allows to obtain materials with enhanced Bronsted acidity when compared with free MA materials. The catalysts were tested in n-decane hydroisomerization (n-decane was used as a model molecule) and confirmed the effect of MA on the acidic properties of the catalysts. The samples synthesized with MA present a higher number of acid sites that increase the catalytic conversion but have a negative effect in the isomerization selectivity, i.e. a more significant amount of cracking products is formed.
- Sustainable product design education: engineering students’ perceptions and attitudesPublication . João, Isabel; Silva, JoãoMoving towards sustainable development is a global challenge requiring efforts from all the society, but governments and other stakeholders as well as researchers and academics have a central role to aid put in practice the knowledge and tools to enforce the vital changes. This work was developed to better understand the topic of sustainable product design among engineering students given the deficit of such kind of studies in the master courses of our engineering department. Survey data were collected from engineering students enrolled in master courses that have in its syllabus the product design curricular unit. The main objective of the work was to understand the students’ perceptions and attitudes in relation to sustainable product design to envisage actions to continually improve the course with the goal of developing students’ further knowledge and competencies with the focus on cradle to cradle design strategies.
- Industry energy optimization: A case study in a biodiesel production sitePublication . Palmeira, José; Silva, João; Matos, Henrique A. S.This paper presents a case study of heat exchanger network (HEN) retrofit with the objective to reduce the utilities consumption in a biodiesel production process. Pinch analysis studies allow determining the minimum duty utilities as well the maximum of heat recovery. The existence of heat exchangers for heat recovery already running in the process causes a serious restriction for the implementation of grassroot HEN design based on pinch studies. Maintaining the existing HEN, a set of alternatives with additional heat exchangers was created and analysed using some industrial advice and selection criteria. The final proposed solution allows to increase the actual 18 % of recovery heat of the all heating needs of the process to 23 %, with an estimated annual saving in hot utility of 35 k(sic)/y.
- Optimization studies through simulation of a methanol/water/glycerol distillation columnPublication . Palmeira, José; Silva, João; Matos, Henrique A.This paper presents an optimization study of a distillation column for methanol and aqueous glycerol separation in a biodiesel production plant. Considering the available physical data of the column configuration, a steady state model was built for the column using Aspen-HYSYS as process simulator. Several sensitivity analysis were performed in order to better understand the relation between the variables of the distillation process. With the information obtained by the simulator, it is possible to define the best range for some operational variables that maintain composition of the desired product under specifications and choose operational conditions to minimize energy consumptions.
- A thermogravimetric study of HDPE conversion under a reductive atmospherePublication . Costa, Cátia S.; MUÑOZ, MARTA; Ribeiro, M. Rosário; Silva, JoãoThe plastic waste has suffered a dramatic increase and has become one of the biggest environmental problems nowadays. The chemical transformation of plastics by catalytic cracking under hydrogen atmosphere (hydrocracking) is one of the viable solutions to this problem since it can convert plastic residues into petrochemicals and fuels. In this work a thermogravimetric study of high-density polyethylene (HDPE) conversion under hydrogen atmosphere and in the presence of catalysts with different textural and chemical features is presented. The effect of distinct micro (H-ZSM-5, H-FER and H-MOR) and mesoporous (SBA-15 and MCM-41) catalysts is studied, both in terms of energy requirements and products distribution. Moreover, the effects of sample preparation method, catalyst amount, Si/Al ratio and incorporation of a metallic function (Ni and Pt) are also analyzed. The results show that when MCM-41 and SBA-15 mesoporous silicas are added to HDPE no significant changes are observed in terms of the degradation profile. On the contrary, the use of microporous materials decreases significantly the onset of HDPE degradation temperature. The accessibility and acidic content of the materials proved to be the most important factors influencing the HDPE degradation profiles. Moreover, the introduction of a metal function results in a further shift to lower degradation temperatures and favors the liquid products distribution, promoting the formation of gasoline and diesel.
- Investigation of cooperative effects between Pt/zeolite hydroisomerization catalysts through kinetic simulationsPublication . Mendes, Pedro; Silva, João; Ribeiro, M Filipa; Daudin, Antoine; Bouchy, ChristopheA kinetic dual-function model was employed to simulate the performance of binary mixtures of Pt/zeolite catalysts (so-called hybrid catalysts) in the hydroconversion of n-paraffins. The catalytic activity and the maximal yield in feed isomers were simulated for mixtures of catalysts with distinct characteristics to investigate the conditions in which cooperative effects based on metal-acid balance may arise. Superior performances of the hybrids compared to both individual catalysts could be achieved in most of the simulated systems, particularly when mixing Pt-catalysts containing zeolites with dissimilar characteristics. A careful choice of the proportion and metal-acid balance of individual catalysts is, nevertheless, necessary. Moreover, the cooperation in the hybrid catalysts was rationalized based on the performance of the individual catalysts being mixed. The more alike the individual catalysts, to a certain extent, the broader the range of metal to acid sites ratio over which hybrids perform better than both individuals. On the other hand, the relative gain in performance arising from the cooperative effect would decrease. This study unveils hence the influence of each one of the preparation parameters of hybrid catalysts on its behaviour shedding light into the complexity of such catalytic systems.
- Incorporation of niobium in SAPO-11 materials: Synthesis and characterizationPublication . Bertolo, Raquel; Martins, Angela; Silva, João; Ribeiro, Filipa; Ribeiro, Fernando Ramoa; Fernandes, AugusteThe present work concerns a new synthesis approach to prepare niobium based SAPO materials with AEL structure and the characterization ofNb species incorporated within the inorganic matrixes. The SAPO-11 materials were synthesized with or without the help of a small amine, methylamine (MA) as co-template, while Nb was added directly during the preparation of the initial gel. Structural, textural and acidic properties of the different supports were evaluated by XRD, TPR, UV-Vis spectroscopy, pyridine adsorption followed by IR spectroscopy and thermal analyses. Pure and well crystalline Nb based SAPO-11 materials were obtained, either with or without MA, using in the initial gel a low Si content of about 0.6. Increasing the Si content of the gel up to 0.9 led to an important decrease of the samples crystallinity. Niobium was found to incorporate the AEL pores support as small Nb2O5 oxide particles and also as extra framework cationic species (Nb5+), compensating the negative charges from the matrix and generating new Lewis acid sites. (C) 2011 Elsevier Inc. All rights reserved.
- Use of excess heat from ethylene recycling in a low-density polyethylene production plantPublication . Matos, Rodolfo D. C.; João, Isabel; Silva, JoãoThe recovery of the wasted heat is an effective way of improving the energy efficiency of industry sites and can contribute to the reduction of the operating costs and the CO2 emissions. In the production of low density polyethylene, the polymerisation reaction is carried out with a large excess of ethylene at very high pressure. The excess ethylene is separated at an intermediate pressure (around 280 bar and 310 °C) and then it is recycled. In this recycle, the stream is cooled in several steps to temperatures close to 35 °C before being recompressed. In some units, the first cooling is carried out with air coolers up to temperatures around 130 °C. In a unit with a recycle of 33 t/h, this cooling corresponds to releasing to the atmosphere about 4.6 MW of thermal power. We present a study of different alternatives for the use of this excess heat. We studied the implementation of a refrigeration cycle by absorption with LiBr/H2O, the production of steam and the electricity generation by Rankine and Kalina cycles. The Aspen HYSYS process simulator was used to study the different alternatives. The capital cost was estimated for each of the evaluated options as well as the benefits expected to be obtained. In the study conditions, the absorption refrigeration cycle is the best solution presenting a return period of 3 years.
- Exploring students entrepreneurial mindset. Insights to foster entrepreneurship in engineering educationPublication . João, Isabel; Silva, JoãoHigher education graduates have a huge potential forinnovative processes and sustainable economic development. The higher education institutions must play an important role in engaging students for entrepreneurial careers, enhancing their skills in entrepreneurship. Students capable of identifying opportunities and turning ideas into business, who have good communication and leadership skills as well as strong technical competencies are likely to be highly valued in the marketplace. This paper presents the results of a survey to investigate students’ entrepreneurial mindset. The main concern is to understand the interest of the students in entrepreneurship and reasons to start or not start a business, the engineering students’ perceptions of their entrepreneurial related abilities, as well as their perception about the extent by which entrepreneurship is addressed in their engineering programs. The students were selected among two engineering master courses in a Portuguese Engineering School of a Polytechnic Institute. The curricular unit of entrepreneurship is part of the curriculum in one of the master course, while in the other course the students do not have such subject in their study program. The data were collected to investigate differences within and across engineering students who are and who are not participating in entrepreneurship courses as well as diferences concerning some demographic characteristics.
- Excess‐heat recovery and promotion through organic chemical heat pumpsPublication . Silva, Luís António Pinela da; João, Isabel; Silva, JoãoHeat recovery and promotion is essential to decarbonization, and chemical heat pumps based on reversible organic reactions can aid to fulfil this. This paper stud ied the isopropanol/acetone/hydrogen (IAH) and the tert-butanol/isobutene/water (tB/iB) systems regarding their performance and economic competitiveness through simulation and found that the IAH presents satisfactory performance and has the potential to be a very promising solution in increasing the overall energy efficiency while also preventing the emission of massive amounts of CO2 and other greenhouse gases released during energy production and transforma tion. This system presents enough arguments to become a very successful solution if proper politico-economic support and incentives are established and put into practice.