Pretreatment of lignocellulosic biomass with sulfur dioxide and/or sulfurous acid

A process for pretreating lignocellulosic biomass comprising:

• a) feeding acid and lignocellulosic biomass into a pretreatment reactor, said acid comprising at least one of sulfur dioxide and sulfurous acid, said acid added to the pretreatment reactor with the lignocellulosic biomass, separate from the lignocellulosic biomass, or a combination thereof;
• b) adding heat to the pretreatment reactor such that said lignocellulosic biomass and acid are heated for a time and at a temperature sufficient to provide a slurry comprising pretreated lignocellulosic biomass, said slurry disposed within the pretreatment reactor adjacent a headspace, said headspace comprising sulfur dioxide;
• c) removing the slurry from the pretreatment reactor;
• d) reserving at least a portion of the sulfur dioxide in the headspace within at least one of the pretreatment reactor and a reservoir connected to the pretreatment reactor as the slurry is removed from the pretreatment reactor;
• and
• e) pretreating additional lignocellulosic biomass in the presence of e reserved sulfur dioxide.

A process for hydrolyzing lignocellulosic biomass comprising the steps of:

• a) feeding lignocellulosic biomass into a pretreatment reactor through a loading valve, said pretreatment reactor connected to a vapour reservoir through a reservoir valve;
• b) closing the loading valve;
• c) feeding at least one of steam, sulfur dioxide, and sulfurous acid into the pretreatment reactor with the loading valve closed, thereby increasing a pressure in the pretreatment reactor;
• d) heating the lignocellulosic biomass disposed in the pretreatment reactor for a time and at a temperature sufficient to provide a slurry comprising pretreated lignocellulosic biomass, said heating conducted with the reservoir valve open;
• e) closing the reservoir valve such that sulfur dioxide gas is confined to the vapour reservoir;
• f) opening a discharge valve such that the slurry is discharged from the pretreatment reactor while the sulfur dioxide in the vapour reservoir remains in the vapour reservoir;
• g) closing the discharge valve and loading another batch of lignocellulosic biomass into the reactor through the loading valve;
• h) closing the loading valve;
• i) opening the reservoir valve;
• j) feeding at least one of steam, sulfur dioxide, and sulfurous acid into the pretreatment reactor;
• and
• k) hydrolyzing cellulose from the discharged slurry in the presence of cellulase to produce glucose.

A process for hydrolyzing lignocellulosic biomass comprising:

• a) feeding lignocellulosic biomass and acid into a pretreatment reactor, said acid comprising at least one of sulfur dioxide and sulfurous acid;
• b) heating said lignocellulosic biomass in the pretreatment reactor for a time and at a temperature sufficient to provide a slurry comprising pretreated lignocellulosic biomass, said slurry adjacent a headspace comprising sulfur dioxide;
• c) removing at least a portion of said slurry from the pretreatment reactor;
• d) preventing at least a portion of the sulfur dioxide in the headspace from exiting the pretreatment reactor as the at least a portion of the slurry is removed such that a concentration of sulfur dioxide in at least a region of the headspace of the pretreatment reactor is substantially maintained while the slurry is removed;
• e) hydrolyzing cellulose in the removed slurry in the presence of cellulase to produce glucose;
• and
• f) selecting an amount of make-up sulfur dioxide to be added to the pretreatment reactor in dependence upon an amount of sulfur dioxide prevented from exiting the pretreatment reactor.