Renewable and high-purity hydrogen from lignocellulosic biomass in a biorefinery approach

Unprecedented efforts are being deployed to develop hydrogen production from bioresources in a circular economy approach, yet their implementation remains scarce. Today’s Challenges are associated with the shortage in the value chain, lack of large-scale production infrastructure, high costs, and low efficiency of current solutions. Herein, we report a hydrogen production route from cellulose pulp, integrating biomass fractionation and gasification in a biorefinery approach. Softwood sawdust undergoes formic acid organosolv treatment to extract cellulose, followed by steam gasification. High-purity hydrogen-rich syngas at a concentration of 56.3 vol% and a yield of 40 gH2/kgcellulose was produced. Char gasification offers the advantage of producing free-tar syngas reducing cleaning costs and mitigating downstream issues. A comprehensive assessment of mass and energy balance along the hydrogen value chain revealed an efficiency of 26.5% for hydrogen production, with an energy requirement of 111.1 kWh/kgH2. Optimizing solvent recovery and valorization of other constituents as added-value products in a biorefinery approach would further improve the process and entice its industrial takeoff.


Kappa number
The Kappa number (Kn) indicates the content of residual lignin in cellulose pulp.It is determined through a titrimetric analysis according to Tappi T236 standard method.It is calculated from the amount of potassium permanganate consumed by the lignin in 10 min at room temperature.Uncooked particles of raw biomass were eliminated to guarantee more precise measurements.The analysis was performed three times to ensure the repeatability of the measurements.
For the Kn determination, 1 g of dry cellulose pulp was added to 200 mL of distilled water.
First, the solution was mixed using a high-speed mixer and then transferred to an 800 mL beaker under moderate-speed stirring.Next, the residual cellulose pulp on the mixer was rinsed with 200 mL of distilled water; the mixture was then added to the 800 mL beaker.
Under stirring, 50 mL of 0.02 M potassium permanganate solution and 50 mL of 2 M sulfuric acid solution were added.The first reaction thus takes place between lignin, the permanganate, and the acid (Eq. 1) The reaction time was kept at 10 min.After that, 10 mL of KI solution (1N) was added, and the second reaction occurs (Eq.2).The solution changed from purple to brown color, and 4-5 drops of Starch solution was added which was used as a color indicator.Finally, the mixture was titrated with sodium thiosulphate of 0.2 M to the endpoint (Eq.3).A blank solution, without a sample, was carried out according to the same protocol.
Liq + MnO4 -+ 4H + Oxidized Lig + MnO4 -(Excess) + MnO2 + 2H2O (Eq. 1) The volume of consumed potassium permanganate solution by lignin is determined following: (Eq. 4) Where a and b are the equivalent volume of sodium thiosulphate solution (mL) used for the determination of the sample and the blank solution, respectively.M is the molarity of sodium thiosulphate solution.The Kappa number Kn is thus determined according to: (Eq. 5) where m is the weight of the pulp sample and d refers to the correction factor which depends on the quantity of consumed KMnO4.the values of d range from 0.958 to 1.044.The lignin content is calculated as follows: (Eq. 6) Aspen plus model development Biomass and its components as well as char and ash are defined as non-conventional solids in this process.Aspen Plus assumes that these components are heterogeneous solids and do not participate in phase equilibrium calculations.HCOALGEN and DGOALIGT library was used to determine the enthalpy and density based on their properties shown in Supplementary Table 1.The MIXCINC stream class was used since both conventional and non-conventional solids are present, but there is no particle size distribution.

Aspen flowsheet and model description
Supplementary figure 5 shows the Aspen Plus flowsheet process.Forty-five streams were -defined streams.The flowsheet comprises twentynine unit operation blocks, described in Supplementary Table 5.The flow rate of inlet streams in biomass pretreatment steps is determined by a Calculator based on the experimental results.
is carried out to ensure production of 90 g.h 1 a.Biomass drying is dried with forced air at 70 °C.In this model, drying is carried out in a block DRYER in which moisture is evaporated and controlled by a Calculator to reduce the moisture content to 2 % in the dried biomass.The evaporated moisture is separated from the solid by FLASH1.
Aspen plus considers that the molecular weight of a non-Therefore, the drying reaction of biomass is represented by the following equation: (Eq. 7) The extent of the reaction in the RStoic is defined by: b.Biomass drying stream SOLVPULP, consisting of a formic acid water mixture (85 wt.% FA), is added to the organosolv reactor at 5:1 w/w as a solvent-to-wood ratio.The reactor was pressurized to 1.5 bar at 85 °C.During this process, the biomass is fractionated following Eq.8 .Separated lignin and hemicellulose are not represented in the obtained solid since they are dissolved.
(Eq. 8) c. Solid washing Following that, the solid is cooled down and filtered by FILTER1 to separate dissolved lignin and hemicellulose.Next, the filtered solid is sent to an acid-washing stage to remove recipitated lignin.This step is represented by MIX1, in which 85 wt.% FA is mixed with the filtered solid at the liquid: solid ratio of 3.4.The mixture is then filtered in FILTER1.Acid washing is followed by water washing (MIX2) and filtration (FILTER2) to clean the solid and remove FA.The required water rate is determined using a Calculator with a water: dried biomass ratio of 12.

d. Drying
Next, washed solid is dried to obtain a final moisture of 2.2%.The step is carried out in HEATER1 to evaporate water and FLASH2 to separate water vapor from the solid.

e. Pyrolysis
The pyrolysis step is simulated using REA-PYRO reactor.Ext-Cell is converted to gases, bio-oil, and biochar.The product distribution information is derived from experimental data.The following assumptions are made on volatile products: Gaseous products includes H2, CO, CO2, CH4, and C2H4 Bio-oil consists on water and tars which includes C6H6, C7H8, C6H6O and C8H10O2 The reactor is operated at 700 °C and at atmospheric pressure; the yield distribution is determined through: (Eq. 9) where the is the molecular weight of a single product; the conversion of each reaction is the yield of .From the REA-PYRO the product stream, PROD-PYR, enters FLASH3 for separating char in the stream SOLID and volatile products in the stream VAPORS.

f. Volatiles combustion
Volatiles obtained from pyrolysis are burned to provide heat for the endothermic steps.As mentioned in the manuscript, this approach is used in the multi-stage gasification process, ID: RGibbs).The heat of combustion fumes is recovered to achieve energy integration of the global process (COOLER3).
g. Char gasification conventional components (Cs, H2 and O2) and ash.The yield of the reactor is calculated according to the elemental composition of char given in Supplementary Table 1.The outlet stream CHAR is then mixed with steam provided by the superheated stream WATER-2.The total input enters the gasifier REA-GASI (Aspen ID: RPlug).In this study, the reactions included in the char gasification process are listed in Supplementary Table 6 and initiated in pre-exponential factor of forward WGSR is adjusted.This can be explained by the rapid kinetics of the reaction and the configuration of the lab-scale reactor used in the experimental study.Indeed, the temperature decreases gradually along the reactor which can promote the forward WGSR.
The reactor is about 6 cm in diameter and 60 cm in length and operates at different temperatures, 850 and 950 °C.The outlet gas steam of the gasifier enters CYCLONE for separating ash and residual carbon from the gas stream.
h. Water-gas shift Afterward, the gas stream is then cooled down to 300 °C and separated from water through TRAP1.Before entering the water-gas shift, pressure the syngas (SYNGAS) to 5 bar.The compression is achieved by a multistage compressor COMP1.The steam input is supplied by The syngas and steam streams are fed the water-gas shift conditioning section which consists of two reactors, a hightemperature shift (HTS) and a low-temperature shift (LTS) reactor.The WGSR is exothermic and hence a lower temperature enhances CO conversion.At the industrial scale, the HTS generally operates at temperatures between 290 and 440 °C, and the LTS often operates between 160 and 210 °C.Syngas leaving the HTS and LTS shift reactors still contain 2 to 5 % and 0.6 to 1 % CO 1 .
Both shift reactors are simulated as stoichiometric reactors (Aspen ID: RStoic) and the indirectly.
vol of CO at the leaving stream of each reactor.CO concentration in the outlet steam of HTS and LTS is fixed at 4 and 0.8 vol.%, respectively.The CO conversion from the global water-gas-shift system is thus around 80 %.The syngas and steam mixture is cooled down to 35 °C to separate water (TRAP2).
i. Pressure Swing adsorption (PSA) The target of this stage is to obtain a high-quality hydrogen gas that can be used in subsequent applications.Gas cleaning is achieved by separating hydrogen from other gaseous species present in the syngas.The simulation of the PSA system is simplified by employing ideal separators representing two separation units.The system efficiency and conditions are adopted from literature 2 -gas-shift is compressed at 30 bar and cooled down to 35 °C by a multistage compressor COMP2 to feed the PSA system.Within the first unit (PSA1), high-quality hydrogen (99.99 % purity) is bottom stream at the same pressure of the inlet stream.The depressurization and pressurization of the tail gas streams are simulated by VALVE1,2,3 (1 bar) and COMP3,4,5 (30 bar).In the second PSA unit, CO is adsorbed and separated while CO2 and CH4 exit from the top stream for their subsequent sequestration.(Eq.10) where the weight of carbon in biochar (g) is mbiochar (1-Xash) %C.The weight of carbon in syngas was determined according to: (Eq. 11) The data are presented in Supplementary Table 2.
Steam flow rate (g.h - Process simulation was simplified, and the following assumptions were made: All units are operated at steady-state, isothermal, and isobaric conditions.Pyrolysis and gasification units are operated at 1 bar Drying and devolatilization occur instantly Ash are inert; catalytic and inhibiting effects are neglected Ideal gas considered Heat loss and pressure drops are neglected, temperature and pressure distribution within the units are uniform b.Definition of physical property method and operations units

Table 3 |
Influence of steam flow rate on gasification of softwood sawdust (SS) biochar at 950 °C.Supplementary Table 4 | Theoretical yield of hydrogen from biomass steam gasification (full conversion of CO).Supplementary Table7| Data of energy-consuming units and hot streams (hydrogen production basis 1 Kg.h -1 ).