Ressource non renouvelable | EPFL Graph Search

Une ressource naturelle est qualifiée de non renouvelable ou épuisable lorsque sa vitesse de destruction dépasse, largement ou non, sa vitesse de création. Le sol se forme en quelques siècles à plusieurs millénaires suivant les conditions chimiques, physiques et biologiques et est actuellement détruit dans certaines régions en quelques dizaines d'années, voire quelques années. On peut aussi rapprocher l'actuelle destruction accélérée des espèces d'une ressource . On parle au contraire de ressource renouvelable lorsque leur production est possible sur un temps court (production animale, végétale…) et ne consomme pas elle-même une ressource non renouvelable, ou lorsque la ressource n'est pas détruite par l'usage (énergie hydroélectrique, énergie marémotrice, énergie éolienne, énergie solaire). Les projections actuelles montrent que le pétrole, qui a mis plusieurs dizaines de millions d'années à se former, sera épuisé au cours du . Cependant, le pétrole n'est pas la seule ressource no

Renewable Land: Planning the Evolution of Logistic Areas

Gloria Serra Coch

Land is the support of life and the generator of energy cycles in the planet, also being a finite resource. The first consequence of urban population growth and build environment expansion is land consumption. Present strategies reduce this expenditure, generally by attenuating dispersive growth, favouring compact city models and reusing built inventory. From current urban land, a noteworthy percentage is assigned for logistic use and this proportion is increasing as a consequence of delocalized economies. However, planning strategies seem to overlook these areas when addressing the mentioned issues. The common localization of these zones, well-connected and placed in the influence area of a city, gives them a high probability to be absorbed by the mixed-use urban tissue during the process of city growth. Planning urban logistic land considering its possible future conversion into mixed-use urban fabric becomes a pressing concern. The study analyses industrial areas that have been transformed into mixed-use urban tissue to, subsequently, stablishing a correlation between them and current logistic zones. In the case of logistic areas, special attention should be paid to transportation infrastructures, legislation and land-use organization, ecosystem preservation and mixed-use progressive introduction. The objective is to foster the planning of logistic land considering its potential future re-use and transformation into mixed-use urban tissue with low energy costs.

UNIV POLITECNICA CATALUNYA2021

Performance evolution and modeling of PEM fuel cell systems

Nicolas Roggo

In the context of climate change mitigation, different alternatives to reduce the atmospheric CO2 emissions are; increasing the efficiency, switching to renewable resource and reduce emissions from fossil resources by CO2 capture and storage (CCS) . Hydrogen is considered as potential alternative to cover the energy needs by using it as a fuel in internal combustion engines or fuel cells, or as chemical source. In proton exchange membrane (PEM) fuel cells, also known as polymer exchange membrane fuel cells, pure hydrogen fuelis combined with the oxygen from the atmosphere to produce water, heat and electricity. Many research has been done in recent years on fuel cell systems leading to higher efficiencies. The performance is influenced by the membrane properties, the catalysts, the number of cells and the operating conditions. For studying the performance of fuel cell systems process modeling is a well-known approach. Here the evolution of fuel cell efficiency, especially of PEMFC is studied within the aim of updating previously developed PEMFC process models to integrate them with different hydrogen production processes using fossil and renewable resources in order to assess the competitiveness on the energy market.

2012

Developing structure-oriented models for enzymatic hydrolysis of lignocellulosic biomass

Jessica Charlène Rohrbach

With the unsustainable use of fossil fuels increasing strains on human institutions and ecosystems, the development of a renewable energy alternative is of paramount importance. Second generation biorefineries, based on the production of fuels and chemicals from lignocellulosic biomass, appear as attractive alternative to their non-renewable counterparts. Within the multiplicity of existing valorisation routes, enzymatic hydrolysis of lignocellulosic biomass into its constituent sugars has generated considerable interest, notably in the context of biofuels production. However, major hurdles stemming from the intricate structure of the lignocellulosic feedstocks still impede large-scale deployment of this process. The multiplicity of highly intertwined spatiotemporal factors impacting the enzymatic hydrolysis of lignocellulosic biomass represents a challenge to rationally design efficient hydrolysis process. Here, we propose a theory-based modelling framework relying on pore-diffusion and surface reaction to explore the effects of recognised bottlenecks on the enzymatic hydrolysis of lignocellulosic substrates. The model is based on a set of partial differential equations describing the evolution of the substrate morphology to investigate the interplay between experimental conditions and the physical characteristics of biomass particles as the reaction proceeds. The overall quantity of cellulase present in the hydrolysis mixture is carefully considered to investigate its interplay with the available accessible cellulose surface. Also, non-uniformity in terms of cellulose accessibility and cellulose digestibility are introduced in the model to weight their influence on observed hydrolysis rates. Finally, deactivation mechanisms are considered through unproductive adsorption of cellulases on both cellulose and lignin fractions, with the existence of such phenomena alleged to be critical in the efficiency of the hydrolysis process. Based on predictions of our model, we were able to confirm the critical role of cellulose accessibility, as defined by the combination of particle size, porosity and accessible cellulose surface, in dictating early reaction rates for a range of pretreated beech wood substrates. While high biomass loading should be favoured to improve enzyme penetration in the substrates, high enzyme loadings going beyond the initial number of cellulose adsorption appeared beneficial in notably two cases: (i) to promote internal diffusion in large particles and (ii) counteract undesired enzyme adsorption on lignin. For the latter, a relatively low increase in enzyme loading was sufficient to offset the resulting slowdown. We also showed that the existence of structural heterogeneities, and in particular non-uniform pore volume distribution within the lignocellulosic samples, contribute to the rate slowdown observed at later stage of the hydrolysis, while not explaining it in its entirety. Unproductive adsorption to cellulose, coupled to decrease in the cellulase efficiency at the cellulose surface, appeared as major contributor to the rate slowdown. Overall, we show how the use of a theory-based model can help decouple and evaluate the effects of key factors in the enzymatic hydrolysis of lignocellulosic biomass. As such, our model can help pave the way towards efficient integrated rational design strategies for enzyme process engineering for biomass conversion.

EPFL2021

Developing structure-oriented models for enzymatic hydrolysis of lignocellulosic biomass

Jessica Charlène Rohrbach

EPFL2021