(732c) Eco-Efficiency Analysis of Different Hydrolysis Processes for p-Xylene Production

The role of bio-based chemicals in supporting industrial sustainability has become increasingly important in view of the rigid environmental regulations being enforced at a global level[1, 2, 3]. More specifically, the renewable nature of biomass used as raw material, and the low life cycle carbon emissions render bio-based chemicals a promising alternative to conventional petroleum-based products[4]. However, the high production cost, mainly related to the feedstock price and employed biomass conversion technology, seems to limit the broader deployment of bio-based products in the energy and chemical market. Efforts are currently focused on the development of more energy-efficient, cost-competitive, and less carbon-intensive technologies for the conversion of selected biomass feedstocks to different bio-products[5, 6].

A novel synthesis route of p-Xylene has been proposed which employs molten salt hydrate (MSH) for the hydrolysis of biomass[7]. The overall process comprises four major steps:1) hydrolysis of biomass which commercially utilizes diluted acid (DA) and concentrated acid (CA) 2) dehydration of sugars 3) hydrodeoxygenation of 5-hydroxymethylfurfural and 4) cycloaddition of 2,5-Dimethylfuran. To evaluate the sustainability performance of the specific bio-based chemical which is assumed to be synthesized in a modular plant, an eco-efficiency analysis is carried out considering different supply chain logistics and lignocellulosic biomass feedstocks with respect to composition and crop production process. The employed eco-efficiency concept is based on the BASF methodology[8], which aggregates the relevant environmental impact category values of each selected process/product scenario into a single score through normalization and weighting – reflecting social preferences-, and combines that with the respective life cycle costs (LCC). Expanding on the previous studies of techno-economic and life cycle assessment of p-Xylene using hardwood/softwood biomass feedstock[7], the eco-efficiency scores of both novel and conventional hydrolysis techniques are estimated and presented in a two-dimensional portfolio matrix, enabling the identification of the best performing process design from both ecological and economic perspectives. The selected biomass feedstock is assumed to be delivered to the biorefinery plant by means of trucks at a distance of 100 km from the biomass conversion facility, while the production capacity is set at 400,000 metric ton of treated biomass feedstock per year[7].

In terms of the climate change impact category, the estimated CO₂-eq emissions of the MSH process are 75% lower and 9% higher than those of the DA and CA processes, respectively. In the case of water depletion impact category, the MSH process exhibits a lower value by 44% and 7% as compared to the aforementioned hydrolysis techniques. In terms of process economics, the minimum selling price of the p-Xylene produced by means of the MSH, DA and CA processes is estimated at $1,480, $2,320 and $1,900 per metric ton[7], correspondingly. Upon weighting and normalizing the life cycle impacts of each synthesis route, the eco-efficiency profile of the MSH process has proved to be better with respect to both overall environmental impact and LCC as compared to the other processes, rendering the novel technology the most eco-efficient process design option under the examined operating conditions and selected biomass feedstock. The outcomes of this eco-efficiency analysis, evaluating various supply chain designs, and biomass feedstocks besides hardwood/softwood, as well as different sets of weighting factors used in the eco-efficiency methodology, provide important insights into the major cost drivers and environmental hotspots determining the sustainability profile of p-Xylene production.

REFERENCES

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