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Thermochemical conversion of lignocellulosic biomass and downstream processing represents an attractive alternative in biomass-to-liquid fuels (BtL) production. There are several thermochemical conversion routes that not only can produce fossil-like fuels, but also can simultaneously produce a wider range of fuels in terms of gasoline and diesel profiles. In this work, synthesis, evaluation and integration of conversion of softwood biomass to liquid transportation fuels is investigated within a systematic framework. Five BtL conversion processes were presented by combining promising thermochemical conversion, upgrading and separation technologies. Process flowsheet setups and simulations are performed with Aspen Plus® V8.8. The total production processes are evaluated with both products profiles and costs indicators for capital, energy and total annual costs. Finally, opportunities for process integration to improve the process performance are explored for four integration scenarios. The base case processes with and without integrations were compared to quantify the effect of the integrations on the total annual cost (TAC) and emissions. It was obtained that energy and mass integration could reduce the TAC of the Gasification-LTFT-Fractional Upgrading-Fractionation process by 25% and liquid and gas emissions by 97% (wt) and 43% (wt), respectively.

Thermochemical process routes are promising technological routes to convert lignocellulosic biomass into biofuels with similar properties as fossil fuels. In a previous work (Ind. Eng. Chem. Res. 57, 9925-9942, 2018), we have studied five base case processes for biofuels production with fixed process structures. This work presents an integrated methodology to consider new process structures for optimal synthesis of lignocellulosic biomass-to-liquid fuels production processes. Given that the five base cases showed not only significant difference of production costs among the process sections, but also distinct biofuel product profiles in terms of gasoline and diesel productivity, the current methodology is developed in two parts: Part 1 presents the superstructure synthesis through the stepby-step definition of unit operations' possible interconnections to include all possible new process alternatives than base cases. The superstructure is developed based on the data collected from unit operations' rigorous simulation of the base cases. Part 2 presents the superstructure algorithm set-up and optimization for optimal synthesis of BtL process flowsheets with specified product profiles of gasoline and diesel productivity. Rigorous simulation results for process units and process sections are used in the superstructure formulation and its algorithm development. Three case studies have showed that the integrated methodology can generate new production process with specified product profiles while having lower total manufacturing costs than base cases.

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A critical review of separation methods and technologies for lignocellulosic biomass conversion through thermochemical processes to liquid fuels is presented. The multistep processing of biomass includes thermochemical conversion, product upgrading and final fuels separation. Chemicals and biofuels are produced from intermediate streams in each processing section. In the thermochemical conversion, product streams from gasification, liquefaction and pyrolysis require separation technologies for conditioning of main products and removal of impurities. In the upgrading the separation technologies play an important role in the definition of different process configurations for conversion of unstable hydrocarbon fractions into specific biofuel types and chemicals via upgrading reactions. In the final fuels' separation section, separation technologies must be implemented to separate desired biofuels from gases, chemicals, wastewater and solid products. Hence, for total BtL processes, separation technologies are important to improve the interface between the sections and to determine the substructures and subsequent processing methods and techniques. It is observed that separation is more demanding in such biorefinery processes for BtL productions. On the other hand, the widely used separation methods in refineries are also mostly employed in BtL