Lignin can be precipitated from kraft black liquor (BL) through the addition of an acidifying agent such as carbon dioxide or sulfuric acid. In most of the existing lignin precipitation processes that are using acid addition, sufficient acid is added to drop the pH of the black liquor from about 13−14 to about 9−10, followed by lignin particle coagulation, lignin slurry filtration, and lignin cake washing with sulfuric acid and water. At pH values of less than 11, the potential exists for the generation of significant quantities of totally reduced sulfur (TRS) compounds and other volatile sulfur species. Such compounds which include hydrogen sulfide, methyl mercaptan, dimethyl sulfide, and dimethyl disulfide are strongly odorous compounds with well-known negative effects on human health and other forms of life. To address this problem, as well as other problems associated with existing lignin recovery processes, FPInnovations and Noram recently developed a new process called the LignoForce System. This process employs a black liquor oxidation step to convert TRS compounds present in kraft black liquor to nonvolatile species. This paper discusses the applicability of the LignoForce System to several feedstock black liquors (e.g., softwood, hardwood, and eucalyptus) as well as the sulfur compound outgassing potential from various stages of this process compared to a reference case in which the black liquor was not oxidized. In addition, the emission of volatile sulfur and organic compounds from the two lignin products at different temperatures is discussed and compared.

Hydrolysis lignin (HL) refers to a lignin‐rich residue obtained after the enzymatic hydrolysis of biomass. It is recalcitrant, heterogeneous, insoluble in most common solvents, and less reactive than other lignins. To enhance the reactivity of HL, a novel environmentally friendly depolymerization approach was demonstrated to produce depolymerized hydrolysis lignin (DHL) using Kraft cooking liquor, white liquor (WL) – recoverable by the Kraft recovery cycle. The effects of various process parameters such as reaction time, WL/HL ratio, and reaction temperature on lignin depolymerization were investigated using a 2 L Parr reactor under N2. The DHLs obtained were then characterized by Gel permeation chromatography (GPC)‐Ultraviolet Detector (GPC‐UV), 31P Nuclear Magnetic Resonance (NMR) spectroscopy, and ultraviolet visible (UV–visible) spectroscopy, while the filtrates were characterized by high‐performance liquid chromatography (HPLC) for saccharinic acids. The DHL yield reached 45–70% from the treatments at 150–190 °C for 1 h at a WL/HL mass ratio of 1:4 ~ 2:1. The weight‐average molecular weight (Mw) value of the DHL obtained at 190 °C after treatment for 1 h at a WL/HL ratio of 2:1 (w/w) was 2600 Da. Moreover, a significant increase in non‐condensed phenolic hydroxyl and carboxylic acid group content was observed with decreasing Mw. Compared with various existing lignin modification approaches, the approach reported here is less expensive and more environmentally friendly if integrated into Kraft pulp mill operations with the residual WL from the lignin depolymerization process being recycled to the mill chemical recovery cycle. Process scale‐up was also demonstrated using a 20 L circulating reactor. In this case, the Mw of the DHL produced after treatment at 170 °C for 2 h was 2400 Da. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd.

The mountain pine beetle epidemic in British Columbia is leaving behind vast stands of dead pine trees to be harvested. Several years after death, when the needles have fallen off, the trees are referred to as gray-stage. The trees’ natural defense system when attacked is to pitch out the beetles by producing large amounts of canal resin to flood the beetles’ bore holes; hence, changes in wood resin (extractives) will accompany beetle attack. Increased extractives concentration has been shown in the final bleached pulp in a kraft mill pulping a large proportion of gray-stage pine wood killed by the mountain pine beetle. Similar to the wood extractives content in gray-stage pine chips, pulp extractives in gray-stage mill pulps are variable and can occasionally be high (e.g., > 0.05%), likely because of the composition of the extractives in the incoming chips. Although this usually does not cause pitch problems in the pulp mill and its customer paper mills, kraft mills that sell gray-stage pulp to extractives-sensitive customers should check extractives content before shipment to make sure it is not unacceptably high.