Scope: Escobar - Deep Eutectic Solvent Pulping Technology to Reduce Carbon Emission in Pulp and Paper Industry

We propose to advance the high-kappa (high-lignin) softwood containerboard pulping process to reduce greenhouse gas (GHG) emissions by replacing the traditional kraft process using a low-GHG emission Deep Eutectic Solvent (DES) pulping process, Figure 1. The process contains (1) low-severity DES solvent pulping, (2) low-energy pulp mechanical refining, (3) lignin recovery for aviation fuel production, and (4) solvent recovery by new anti-solvents, membrane ultrafiltration, and/or process steam with mechanical vapor recompression. By applying the DES system in pulping, we will reduce CO2 emissions by eliminating the recovery boiler and lime kiln, which are energy intensive processes in the current kraft process. DES will also produce lignin product, which can be converted to aviation fuel and biobased polymer for further CO2 reduction. DES is typically prepared by mixing two constitutive precursors, a hydrogen bond donor and a hydrogen bond acceptor, to form a homogenous liquid that has a melting point lower than its constituents. Compared to expensive ionic liquids, DES have many advantages: (1) DES are bio-based renewable solvents that are composed of amides, sugars, alcohols, amino acids, and/or lignin derived aromatic compounds, which are biodegradable and (2) DES are also non-toxic, and safe to handle due to low vapor pressure, non-volatility, and low flammability [4-7]. DES have been tailored for many industrial applications, mainly in organic reactions and separations. We will find the best hydrogen donor and acceptor combination in terms of pulping performance and solvent recovery. Disk refining is widely used in the pulping industry to improve the bonding of fibers and ultimately improve the strength of a paper sheet. We have a unique refining equipment called the Szego mill, which has shown equivalent refining ability with only 1/3 of the energy needed with a disk refiner [8]. A key for carbon emission reduction is solvent and lignin recovery. We propose three different approaches to simplify the separation process and reduce energy demand. (a) New anti-solvent system: Commonly ethanol:water mixture is used as anti-solvent to precipitate lignin from DES lignin solution. We will evaluate different anti-solvents (e.g., 2- methyl tetrahydrofuran, dimethyl ether, or methyl acetate), which requires much less anti-solvent loading and distillation energy. (b) Membrane ultrafiltration: Membrane system will be used to recover dissolved lignin from DES system combined with the new anti-solvent system. We will work on membrane properties and configuration of this ultrafiltration-based diafiltration system to facilitate lignin separation. (c) Mechanical vapor recompression: Solvent recycle is energy intensive process and requires large amount of steam, if distillation/evaporation is used. Mechanical vapor recompression and thermal vapor recompression can be used to recycle waste vapor into quality steam. This system is not common in the US pulp and paper industry due to the relatively cheap natural gas, but it has been widely used in other countries. We will evaluate the potential of using this system through rigorous process simulation.