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In a previous paper, conceptual process design, simulation, and mass and energy balances were presented for an organosolv process with a hardwood feed of 2350 metric tons (MT) per day and ethanol, lignin, furfural, and acetic acid production rates of 459, 310, 6.6, and 30.3 MT/day, respectively. In this paper, the investment and operating costs of the process and the minimum ethanol selling price (MESP) to make the process economically feasible were estimated. The total capital investment of the plant was approximately 720 million USD. Lignin price was found to affect the MESP considerably. With a base case lignin price of 450 USD/MT, the MESP was approximately 3.1 USD per gallon (gal). Higher lignin price of 1000 USD/MT was required to equal the MESP with the December 2013 ethanol market price (2.0 USD/gal). In addition to lignin price, the MESP was found to be strongly affected by feedstock, enzyme, and investment costs. Variations in feedstock and investment costs affected the MESP by approximately 0.2 and 0.5 USD/gal, respectively. Changing the enzyme dosage and price from base case estimate of 5270 USD/MT and 0.02 g/g cellulose to more conservative 3700 USD/MT and 0.06 g/g cellulose, respectively, increased the MESP by 0.59 USD/gal.

The implementation of wood extraction prior to pulping (pre-hydrolysis), with subsequent recovery of hemicellulose, is expected to affect the operation of a conventional kraft pulp mill. The magnitude of impacts will depend especially on the extraction conditions. In this specific work, the consequences of integrating the auto-hydrolysis process are studied using a detailed mill balance. A softwood pulp mill in Finland was used as a reference. With 14.1% of wood extracted, the wood demand increased by 15.5% and the steam generation in the recovery boiler by 13.5%. The removal of approximately 17% of lignin from black liquor would put the flue gas side of the boiler back to the original required capacity. In turn, this would enable the simultaneous recovery of lignin and hemicellulose. To make this process economically feasible, the extra revenue from the sales of lignin and hemicellulose products would need to compensate for the additional operating costs in the pulp mill.

Organosolv pulping can be used as a pretreatment step in bioethanol production. In addition to ethanol, organosolv pulping allows for the production of a pure lignin product and other co-products. Based on publicly available information, conceptual process design and simulation model were developed for an organosolv process. The simulation model was used to calculate the mass and energy balances and approximate fossil-based carbon dioxide (CO2) emissions for the process. With a hardwood feed of 2,350 dry metric tons (MT) per day, 459 MT/day (53.9 million gallons per year) of ethanol was produced. This corresponded to a carbohydrate to ethanol conversion of 64 %. The production rates of lignin, furfural, and acetic acid were 310, 6.6, and 30.3 MT/day, respectively. The energy balance indicated that the process was not energy self-sufficient. In addition to bark and organic residues combusted to produce energy, external fuel (natural gas) was needed to cover the steam demand. This was largely due to the energy consumed in recovering the solvent. Compared to a dilute acid bioethanol process, the organosolv process was estimated to consume 34 % more energy. Allocating all emissions from natural gas combustion to the produced ethanol led to fossil CO2 emissions of 13.5 g per megajoule (MJ) of ethanol. The total fossil CO2 emissions of the process, including also feedstock transportation and other less significant emission sources, would almost certainly not exceed the US Renewable Fuel Standard threshold limit (36.5 g CO2/MJ ethanol).

To clarify the influence of prehydrolysis on fiber characteristics, Scots pine (Pinus sylvestris L.) wood chips were subjected to pressurized hot-water and dilute-acid prehydrolysis (0.5% H2SO4) prior to kraft pulping to partially remove hemicelluloses as hydrolyzate. After the prehydrolysis, the wood chips were submitted to kraft pulping and the pulp was fully bleached in oxygen (O), chlorine dioxide (D), alkaline extraction (E) and chlorine dioxide (D)-sequence. Measurements with an automated optical fiber analyzer showed that prehydrolysis prior to kraft pulping caused significant changes in the fiber dimensions and morphology of the final bleached pulp. Especially, a decrease in fiber width and an increase in fiber deformations were observed compared to a reference kraft pulp. The scanning electron microscopy of handsheets supported the morphology analyses and revealed alterations also in the fiber ultrastructure. The changes in both chemical and physical fiber characteristics require attention when considering the correct processing and end-use of prehydrolysis-kraft pulp fibers.

The integration of an ethanol production process based on prehydrolysis of softwood chips to a kraft pulp mill is discussed. A simulation model of this biorefinery has been created with WinGEMS simulation software to calculate the mass and energy balances of the biorefinery and to examine the effects of the integration on the operation of the pulp mill. Integrating the prehydrolysis process to the modeled pulp mill producing 1000 Adt/day of pine pulp would increase the wood consumption by 16%. With the increased wood consumption, 40 t/day of ethanol could be produced, and the excess power production could be increased by 460 MWh/day. The integration of the ethanol production process to a pulp mill would have considerable effects on the operation of the pulp mill. The coupling of hydrolyzate evaporation with black liquor evaporation would require major modifications in the evaporation plant. Due to the burning of organic residue from the ethanol process and to the increase in the heating value of black liquor, the load on the recovery boiler would increase by 31%.