Chemical Engineering Faculty, Federal University of Uberlândia, Av. João Naves de Ávila, 2121, Uberlândia, Minas Gerais, 38400-902, Brazil.
Laboratory of Lignocellulosic Materials, Federal University of São Carlos, Science and Technology Center for Sustainability, Rod. João Leme dos Santos, km 110, Sorocaba, 18052-780, Brazil.
Appl Biochem Biotechnol. 2021 Oct;193(10):3079-3097. doi: 10.1007/s12010-021-03580-2. Epub 2021 May 21.
Lignin recovery from black liquor is an important task for producing valuable chemical products. Acidification processes are currently applied by pulp and paper industries for black liquor treatment, in which two main streams are produced: the precipitated lignin fraction and a lignin-lean black liquor. Membrane filtration is a suitable alternative for lignin recovery from black liquor, but studies on lignin-lean black liquor filtration are scarce. Here, we evaluated the ultrafiltration process for lignin recovery from the both fractions of black liquor acidification. The lignin-lean black liquor presented 22 wt% of total solids with 4.6 wt% of lignin. Lignin retention from the lignin-lean black liquor by the 5 kDa ultrafiltration membrane was equal to 85%, with reduction in total solid concentration from 219.8 to 68.1 g L. Due to the relatively high solid concentration in the lignin-lean black liquor, cake formation was the main fouling mechanism during ultrafiltrations. The precipitated lignin solution presented 4.8 wt% of total solids with equivalent lignin concentration (4.7 wt%). The used membrane was able to retain almost 100% of solids and lignin from the solution prepared from the precipitated lignin. All fouling mechanisms were responsible for flux decay in ultrafiltration of the precipitated lignin solution. Steady state fluxes for lignin-lean black liquor and precipitated lignin solution were 0.9 and 15.9 L h m, respectively. According to TGA analyses up to 800 °C, precipitated lignin and lignin-lean black liquor presented total mass losses of 63.5% and 44.3%, respectively. Also, the permeate samples presented lower mass losses than their respective feed samples. The ultrafiltration process reduced the average weight molar mass (M) of the precipitated lignin solution and lignin-lean black liquor from 1817 to 486 g moland from 2876 to 1095 g mol, respectively. Thus, the 5 kDa ultrafiltration membrane was efficient for lignin recovery from the lignin-lean black liquor, while membranes with lower cut-off should be proposed for lignin purification from the precipitated fraction.
从黑液中回收木质素是生产有价值化学产品的重要任务。酸化过程目前被纸浆和造纸行业应用于黑液处理，其中产生了两个主要流股：沉淀木质素部分和木质素贫黑液。膜过滤是从黑液中回收木质素的一种合适的替代方法，但关于木质素贫黑液过滤的研究很少。在这里，我们评估了超滤过程从酸化黑液的两个部分中回收木质素。木质素贫黑液的总固体含量为 22wt%，木质素含量为 4.6wt%。5kDa 超滤膜对木质素贫黑液中的木质素的截留率为 85%，总固体浓度从 219.8g/L 降低到 68.1g/L。由于木质素贫黑液中相对较高的固体浓度，在超滤过程中，滤饼形成是主要的污染机制。沉淀木质素溶液的总固体含量为 4.8wt%，木质素浓度相等（4.7wt%）。所使用的膜能够从沉淀木质素制备的溶液中保留几乎 100%的固体和木质素。超滤沉淀木质素溶液时，所有的污染机制都导致通量衰减。木质素贫黑液和沉淀木质素溶液的稳定通量分别为 0.9L h m 和 15.9L h m。根据 TGA 分析，在高达 800°C 的温度下，沉淀木质素和木质素贫黑液的总质量损失分别为 63.5%和 44.3%。此外，与各自的进料样品相比，渗透样品的质量损失较小。超滤过程降低了沉淀木质素溶液和木质素贫黑液的平均重量摩尔质量（M），从 1817g mol 降低到 486g mol，从 2876g mol 降低到 1095g mol。因此，5kDa 超滤膜对木质素贫黑液中的木质素回收有效，而对于沉淀部分的木质素纯化，应提出更低截留分子量的膜。
