Biorefineries

Techno-economical and environmental evaluation of lignocellulosic biorefineries

Second generation biofuels – the biorefinery concept

The use of biofuels to reduce greenhouse gas (GHG) emissions and fossil energy depletion is being increasingly contested due to overall sustainability concerns. Ethanol production from lignocellulosic wastes has the potential to significantly improve sustainability of biofuels for transport by avoiding land-use competition with food crops and reducing impacts related to agricultural inputs. However, high production costs remains the bottleneck for large-scale development of this pathway. In that sense, a huge potential exists in upgrading fuel and energy producing pathways into biorefineries in order to improve its financial performance and long-term sustainability.A biorefinery is a process, based in intensive fractionation scheme of fossil fuel refineries, in which biomass conversion leads to a multifunctional system producing fuels, value-added chemicals and power generation.Wet milling corn-to-ethanol production, with corn oil, corn gluten meal and feed as co-products is an example of a first-generation biorefinery. At BPE, ongoing research is devoted to second generation lignocellulosic biorefineries with special attention to pathways using agricultural residues such as sugarcane bagasse and rice straw as feedstock.

Different platforms are suitable to this end, including thermo-chemical and sugar-based biochemical pathways. BPE’s research is centered on Biochemical refineries with special attention to the influence of biomass pre-treatment in down-stream process stages and the potential for process integration and product diversification.

Sugar-lignin platform potential for value-added chemical production under the biorefinery concept

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             An overview of its potential

A promising general model for a lignocellulosic biorefinery is based on the sugar-lignin platform in which 5-carbon (C5) and 6-carbon (C6) sugars, issued from lignocellulosic matrix fractionation, are converted into fuels and building block chemicals by biotechnological or chemical pathways. Lignin output can be used as solid fuel for co-generation, with or without previous pelletization, or it can be upgraded into value-added chemicals.

Modular Platform for Integrated Assessment of Lignocellulosic Biochemical Refineries (LCBR-MPIA)

Boosting the development of large-scale lignocellulosic ethanol production is a complex and challenging task. First of all, capital and operation costs must be substantially reduced while minimizing environmental impacts from a life cycle perspective.Some strategies are envisioned as milestones leading to this end. First of all, we can think of the optimization of the pre-treatment step that improves the biomass accessibility to downstream enzymatic and fermentative process (alternatives include dilute acid pre-hydrolysis and hydrothermal methods). Secondly, advances in the development of recombinant microorganisms capable of using alternative energy sources and to survive in a broad range of reaction conditions can lead to increased process integration with consequent reduction in complexity and capital investment. Finally, upgrading the ethanol production pathway into a biorefinery producing chemical building blocks is a promising alternative regarding economic and environmental sustainability.In this context, innovative, flexible and dynamic modelling approaches are needed to solve a problem with multiple optimization criteria (economic and environmental), dealing with high levels of uncertainty and implying highly dynamic behaviour.

 

Process simulators and comprehensive databases of production processes can help to determine rigorous material and energy balances permitting robust scale-up and diminishing uncertainty in the evaluation and prospective of costs and environmental impacts in a dynamic context. However, modelling such a complex system requires both increased flexibility in applications and reduced computational burdens. This project aims at developing a modular platform for automated process synthesis aimed at the selection of optimal technically, economically and environmentally sound pathways for lignocellulosic biorefineries.

The platform, intended for multicriteria process synthesis of lignocellulosic biorefineries will consist of the following modules:

-Module 1 – Supply-side modelling:

This module deals with issues such as appropriate feedstock selection and valuation as well as optimal location and plant size, taking into account economical, environmental and geographical considerations.

 

-Module 2 – Process design and simulation:

This module includes the use of process simulators such as Aspen Plus © in order to establish rigorous material and energy balances for multiple technological variants of biochemical refineries from lignocellulosic feedstock. These variants will consist of different biomass pre-treatment alternatives, process integration schemes and multi-product scenarios.

 

-Module 3 – Process economics:

Discounted cash flow models and opportunity costs analysis will be used to rank process options according to its economical viability taking into account alternative uses of feedstock.

 

-Module 4 – Life Cycle Assessment:

LCA will be used to evaluate the environmental impact of biorefineries. In this case, dynamic and consequential variants of the methodology can be used to deal with the allocation of environmental burdens between co-products in the biorefinery concept.

 

-Module 5 – Multicriteria Optimization:

This module will integrate the preceding modules’ outputs configuring a decision-making tool for policy makers and academic and industrial agents.The whole idea is to develop a tool that can select an optimal pathway depending on feedstock characteristics and plant size and dynamically model its outputs from a life cycle perspective.

lignocellulosic ethanol pathway: upgrading into biorefinery and process integration alternatives

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