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Quantification of metal-acid balance in hydroisomerization catalysts: a step further toward catalyst design

Publication . Mendes, Pedro S. F.; Silva, João; Ribeiro, M. Filipa; Duchene, Pascal; Daudin, Antoine; Bouchy, Christophe

A methodology was developed to interpret the results of n-.paraffins hydroisomerization over bifunctional catalysts based on two simple kinetic models used consecutively. First, a macrokinetic model was used to obtain the corresponding turnover frequency over the acid sites and the maximum of C-16 isomer yield. Second, a dual-function model was used to correlate these catalytic descriptors to the ratio of metal to acid sites of the catalyst. To illustrate the methodology, Pt/HBEA and Pt/HUSY catalysts with different Pt loadings were evaluated. The impact of metal-acid balance on the catalytic turnover frequency and the maximal C-16 isomer yield were adequately captured for the bifunctional HUSY and HBEA catalysts. Moreover, the parameters of the dual-function model revealed to be intrinsic to the catalytic properties of the zeolite under the scope. This methodology is believed to be of interest for information-driven catalyst design for the hydroisomerization of n-paraffins.

2017-07Journal article

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Use of excess heat from ethylene recycling in a low-density polyethylene production plant

Publication . Matos, Rodolfo D. C.; João, Isabel; Silva, João

The 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.

2018-07Journal article

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Biocatalytic synthesis of 1,2-naphtoquinones derivatives mediated by CotA-laccase

Publication . Sousa, Ana Catarina; Santos, Iolanda; Martins, Lígia O.; Robalo, Maria Paula

Catalysis is one of the cornerstones of our present economy and society and the formation of value-added products is many times directly dependent on catalytic technologies. Nowadays, there is a growing need for development of green strategies involving clean organic reactions, which do not use harmful organic solvents and toxic reagents. Amongst the many options available for a synthetic organic chemist, biocatalysis has emerged as one approach with an excellent potential. Enzyme-catalyzed reactions offer a number of advantages compared to the traditional chemistry-catalyzed reactions and biocatalytic methods impart a “greener” character to the synthesis. Laccases (EC1.10.3.2, p-diphenol:dioxygen oxidoreductases) are multicopper oxidoreductive enzymes which have proven to be versatile and highly/efficient biocatalyst for the synthesis of different value-added chemicals and pharmaceuticals.1 A large number of 1,2-naphthoquinones derivatives have been reported to show antitumor activities by inhibit on of multiple enzymes.2 In addition to their anticancer properties, the naphthoquinone framework has significance in the development of new substances with promising biological activities in other diseases like neurodegenerative and viral diseases.3 The formation of naphthoquinone frameworks is quit-well documented and reported methods include various approaches using organic solvents and different chemical oxidants.4 In this context it is still a challenge to explore alternative and more sustainable synthetic routes for these compounds. As a part of our going research program for exploring the catalytic properties of CotA-laccase, a bacterial laccase isolated from the Bacillus subtilis, we describe in the present communication a practical and simple oxidative CotA-laccase mediated eco-friendly method to obtain 1,2-naphthoquinones derivatives using mild aqueous conditions and O2 as oxidant. All compounds were isolated in good yields and fully characterized by FTIR, NMR and ESI techniques.

2017-09Conference object

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Multi-scale modelling and simulation of Ca-looping cycle process for CO2 post-combustion capture

Publication . Pinheiro, Carla; Filipe, Rui; Torres, Miguel Abreu; Silva, João; Matos, Henrique A.

The present work focuses on one of the more promising new post-combustion technologies using calcium-based materials, known as the “Ca-looping cycle” process, which endeavors to scrub CO2 from flue gases and syngases by using natural lime-based sorbents and which appears to potentially offer limited CO2 capture costs. So, the major driving force is to improve overall efficiency, reduce the cost, and minimize adverse environmental impacts of post-combustion Ca-looping cycle CO2 capture, as compared to more conventional technologies (e.g., amine-based solvent scrubbing). There is a large energy penalty with amine scrubbing, the closest to market technology. The main objective of this work is to develop a first principles model to simulate different natural sorbents looping cycle performance in a fixed bed reactor laboratory scale system. A rigorous non-linear dynamic model of the looping cycle process was developed in gPROMS, based on the multiscale concept. The multiscale modeling is an emerging technique, where the characteristic length for each phenomena that occurs is taken into consideration, leading to a set of submodels with different scale lengths. These submodels when coupled together allow the simulation of a macrosystem (Hangos and Cameron, 2001). After the identification of the characteristic dimensions involved in the models, the first step is the development of a single particle model, which takes into account the energy and material transport, undergoing reactions (carbonation and calcination) and structural changes inside the particle. The material and heat transport inside the particle take into account the structural changes. Detailed models of single particle undergoing cycles of calcination and carbonation are developed. An improved decay approach is introduced in the model for those sorbents exhibiting carbonation decay with the number of cycles. The experimental characterization of the samples gave vital information on the physicochemical changes occurring during testing that need to be described in the model in the carbonation decay function. The conversion decay does not only depend on the number of cycles, but also on the conditions of the previous cycles, temperature, pressure, gas phase composition and characteristics of the material used for the carbonation. Model parameters are estimated from experimental results obtained for different sorbents tested (Santos et al., 2012)(Pinheiro et al., 2016). Several simulations for different sorbents and operating conditions were performed and the model was validated with experimental data obtained in a fixed bed reactor. It was also important to ensure that the model is numerically stable within a large range of values.

2018-07Journal article

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Waste polyolefins valorization to fuels by catalytic transformation under hydrogen pressure

Publication . Costa, Cátia S.; Ribeiro, M. Rosário; Silva, João

Waste plastics contribute to many environmental and social problems due to the loss of natural resources, environmental pollution, depletion of landfill space and demands of an environmentally oriented society. The amount of waste polymers increases by 6.6 to 12% each year, depending on the country and about 70% of waste are polyolefins, including polyethylene (PE), polypropylene (PP) and polystyrene (PS).

2017-11Conference object

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