While existing methodologies assess process performance in terms of cost, operational risk, energy consumption, technology readiness level, and environmental impact, there is a significant gap in integrating these diverse parameters into a unified performance index explicitly linked to the Sustainable Development Goals (SDGs).
The evaluation of a chemical process is crucial for ensuring its efficiency, the quality of the products, safety, innovation and sustainability. Innovation in a chemical process can be related to the use of disruptive technologies and methods that leads to a safer operation with less intensive use of resources. This is known as Process Intensification (PI) and can be considered as an enabler for sustainable development in chemical and biochemical processes.
Even though, there are different methodologies that evaluates their performance compared to conventional processes, there is a need for multifactorial assessment based on the evolving global policies in terms of sustainable development. Therefore, this work presents and analyzes various methodologies to evaluate the performance of intensified alternatives for chemical processes emphasizing their alignment with the sustainability dimensions. In particular, this work proposes a novel index based on the Sustainable Development Goals (SDG), proposed by the United Nations, in order to: i) assess the performance of a chemical process within a sustainable framework, ii) determine the opportunity areas of the assessed technological alternatives, iii) aid in the decision-making process by facilitating a comparison between technological alternatives and, iv) reassess selected technologies based on technological advancements and environmental regulations and policies. The proposed index is called Sustainable Intensification Index (SII).
The SII-based methodology is as a robust framework that considers specific criteria for selecting process variables needed for the evaluation, while reducing the arbitrariness intrinsic to the selection of weighting criteria or bias from the process designer.
SII-based methods
Regarding, SII methodologies these were developed to evaluate several technological configurations of chemical processes (intensified and conventional), which have different focus: a) graphical, b) importance level and c) sustainability level. All these methods rely on process variables (PVs) that are selected through specific criteria. For instance, the process variables must be explicitly or implicitly present in all the assessed technologies and must be directly related to the overall performance of the process. Moreover, PVs must be related to the SDGs and it should be easy to determine numerically. The chosen PVs for the assessment were: total annual cost (TAC, economic performance of the chemical process), eco-indicator99 (Eco99, environmental effects of a chemical process), index of risk (IR, chemical process safety), process duty (PD, total energy used in a chemical process), condition number (CD, technology controllability), technology readiness level (TRL, technology maturity and applicability). These PVs were normalized in order to apply the different methodologies while enabling a fair comparison between each PV.
The graphical method consist of using the normalized PVs to create a spider chart, whereas a PV with a value of 1 corresponds to the most favorable scenario for that specific variable. This methods allows a quick interpretation of the process performance by estimating the area for each polygon. The SII for this method is defined as the ratio of the formed polygon area and the total hexagon area. This avoids any subjectiveness inherited of a visual representation.
Importance level method was developed different weighting techniques of the PVs based on the SDGs. Weighting Technique 1 (WT1) is a summative system in which each PV is assigned a point if it directly comply with a SDG. The weight of each PV is obtained by the ratio of the individual point and the total points obtained by all PVs. Similar to WT1, Weighting Technique 2 (WT2) considers the relationship between SDG and PVs; however, the points are assigned based on the "number of coincidences" in which each SDG is related to a PV. For instance, three points are assigned to Eco99 related to the SDG 13 (climate action) if it considers emmissions of greenhouse gases, resource depletion and climate change. For this methodology, the SII is obtained as a weighting function (sum of the product of the normalized PV and the assigned weight).
In addition, the sustainability level methodology is based on the categorization of each normalized PV into different levels of performance (low, medium and high). Subsequently, the SII for this methodology is obtained by a weighted sum considering the upper and lower limits for each level of performance.
Based on results for the three methodologies to obtain the SII, it is possible to obtain an overall index to try to avoid the inherent bias of each of them, which is defined as Overall Sustainable Intensification Index (OSII). Results show that SII and OSII can be used to a fair comparison between different technologies (intensified or conventional) considering sustainability, controllability and technical feasibility criteria which is a powerful tool for the assessment. Also, the three discussed SII methodologies allow the identification opportunity areas for future developments for process technologies in order to satisfy environmental, controllability and technical requirements.