Effects of Catalysts and pH on Lignin in Partial Wet Oxidation of Wood and Straw Black Liquors

Abstract

Partial wet oxidation (PWO) of kraft black liquor (KBL) and wheat straw black liquor (WSBL) was carried out at 170−230°C. PWO was conducted under oxygen gas only or in the presence of iron catalysts or hydrogen peroxide as an additional oxidant. Unlike the catalysts, increasing temperature enhanced the PWO process in general. Lignin concentration decreased 57−64% and weight-average molar mass of lignin from 2.7−3.3 kDa of original black liquors to 1.5−1.8 kDa after PWO at 210−230°C. Unlike in KBL, presence of hemicellulose in WSBL was responsible for increasing total acid concentration from 16 g/L to 30 g/L in PWO at 230°C. A two-stage process comprising lignin precipitation before subsequent PWO decreased chemical oxygen demand of the liquid fraction by 38−41%. Lignin was fractionated into a solid fraction and a watersoluble fraction which showed 21−26% lower polydispersity compared to lignin in the original black liquors.

Calcium Chelation of Lignin from Pulping Spent Liquor for Water-Resistant Slow-Release Urea Fertilizer Systems

“…Industrially, carbon dioxide supplementation to kraft black liquor is used to reduce the pH to about 10 and precipitate lignin for subsequent washing with water containing sulfuric acid. − In the Lignoboost process, the operation costs are mainly related to the consumption of chemicals . Alkaline oxidation is known to convert carbohydrates partially into organic acids and reduce the pH and molar mass of lignin . Consequently, fewer acidification chemicals are needed.…”

“…Alkaline oxidation is known to convert carbohydrates partially into organic acids and reduce pH and molar mass of lignin. 42 Consequently, less acidification chemicals are needed. LignoForce System subjects concentrated black liquor to such initial oxidative treatment that avoids formation of reduced sulfur compounds in the successive lignin precipitation with carbon dioxide.…”

Reductive or oxidative catalytic lignin depolymerization: An overview of recent advances

“…In this section, we aim at describing alternative approaches towa rd oxidative lignin depolymerization. One of them wa s reported by Muddassar et al who compared lignin depolymerization within two types of black liquor: a "native" black liquor (ie non-treated); and a black liquor treated by acidification with CO 2 with the aim of increasing the production of organic acids [49]. Black liquors of two lignins were considered in this work, a Kraf t and a soda lignin (the latter being produced from wheat straw).…”

Hydrothermal Liquefaction of Softwood: Selective Chemical Production Under Oxidative Conditions

“…In the case of oxidative treatments, oxygen was supplied into the reactor 5 °C before reaching the set temperature. The reactor configuration was the same as previously described . A total of 28 HTL treatments in the presence or absence of 5 bar partial pressure of oxygen (AGA, Finland 99.99% purity) and 1.6 g/L of sodium carbonate (Merck, 99% purity) were conducted (Table ).…”

“…Moreover, in contrast to alkaline reductive conditions, HTL in the presence of oxygen can be beneficial for the production of intermediate products since hydrothermal treatment releases more liquid products than pyrolysis does . It is also known that alkaline oxidative treatments are effective in depolymerization of pulping black liquors in the partial wet oxidation process …”