(597d) Using Deep Eutectic Solvents (DESs) to Extract Lignin from Black Liquor | AIChE

(597d) Using Deep Eutectic Solvents (DESs) to Extract Lignin from Black Liquor

Keywords: Lignin, Black liquor, Deep Eutectic Solvents, Extraction

Corresponding author: J.A. Lalman, Telephone: +1 519 253 3000 ext 2519; Fax: +1 519 971 3686, lalman@uwindsor.ca

Abstract

Recent developments in renewable technologies to convert low-value agriculture residues into value-added products is rapidly emerging in Canada, the United States, the European Union and other nations (Stigsson, 2017; Arkell et al., 2014; Humpert et al., 2016). The global annual lignin production is estimated at 50 million tonnes with 1.1 million tonnes being used to produce lignosulphonates and the remaining used for energy production in pulping mills (Edgar, 2015). However, this data excludes lignin production from corn and wheat biorefineries. The demand for products produced from lignin and other renewable energy feedstocks such as cellulose and hemicellulose is expected to increase with depleting fossil fuel supplies (Edwards, 2000; Orr, 2006).

Utilizing cellulose and hemi-cellulose to produce products such as methane, ethanol, diesel and hydrogen has focused mainly on using non-woody and woody biomass (Lalman et al., 2017). In biorefineries such as in the pulp and paper industry, cellulose is used to manufacture paper products while in other similar industries such as sugar cane, the sugar component, a disaccharide, is extracted and converted into value-added materials such as consumer sugar products and ethanol. In the pulp and paper industry, the feedstock is mainly composed of cellulose, a glucose polymer, hemicellulose, a polymer consisting of xylose, mannose, glucose, galactose and lower levels of arabinose and rhamnose, plus lignin. In the sugar cane industry, the feedstock composition used to produce sugar products and ethanol is lignin plus sucrose, a disaccharide. The lignin component, designated as black liquor, is an aqueous soluble fraction produced in pulp and paper mills while in the sugar cane industry, the lignin component is a solid and labelled as bagasse. A common process employed by these industries is to add value by converting lignin into heat and energy by employing combustion as the terminal process (Lalman et al., 2017).

Black liquor, a waste stream from the pulp and paper industry, has a lignin content ranging between 29 – 54% (Humpert et al., 2016). The high calorific energy value of black liquor (Demirbas, 2003), based on the dry solid content, is a driving factor for considering it as an excellent candidate for upgrading into value-added chemicals. In the pulp and paper industry, approximately 66% of electricity and heat required to remove water from wood pulps is derived from black liquor combustion (Humpert et al., 2016). A few reports have examined converting lignin model compounds and black liquor photocatalytic by-products into value-added chemicals and electricity (Lalman and Ray, 2009; Shewa and Lalman, 2014). These researchers employed TiO2 photocatalysis to produce short chain biodegradable carbon chemicals.

Lignin in black liquor can be recovered by employing precipitation under acid or alkaline conditions as well as membrane separation (Keyoumu et al., 2004; Jonsson and Wallberg, 2009). Membrane processes such as ultrafiltration is primarily used to recover lignosulphonates from sulphite pulp mill spent liquors while Kraft lignin is mainly recovered by precipitation. Major disadvantages during lignin precipitation include operating under elevated temperatures and pressures, using hazardous chemicals and plugging of the filter with a subsequent reduction in process efficiency (Tomani, 2010; Lake, 2011).

Recently, solvent extraction has been examined to recover lignin from a variety of renewable pretreated feedstocks. Deep eutectic solvents (DESs) are recognized as an alternative to traditional solvents and ionic liquids (Hou et al., 2008). DESs are generally composed of two or three components which are capable of associating with each other, through hydrogen bonding, to produce a eutectic mixture (Abbott et al., 2003). The resulting eutectic mixture has a melting point lower than that of each individual component. Desirable characteristics of DESs include low cost, high solute solubility, wide potential window, able to operate under low temperature conditions, and having negligible impact on the environment (Abbott et al, 2003). DESs are produced by mixing an organic salt plus a HBD (Yu et al., 2008).

Over the past few years, a number of studies have focused on using DESs to recover lignin from lignocellulosic biomass (Jablonsky et al., 2015; Kumar et al., 2016). These researchers reported delignification of rice straw and wheat straw using choline chloride (ChCl):Lactic acid (LA) (1:5) and ChCl:oxalic acid (OXA) (1:1) DESs and concluded they were able to recover approximately 60% of the lignin fraction. With recent developments in utilizing DESs to recover lignin from lignocellulosics, expanding and developing the technology to include black liquor is expected to add-value to lignin waste streams from pulping mills and other biorefineries. Hence, the objective of the current study is to extract lignin from black liquor using DESs.

Black liquor was provided by a pulp and paper mill located in Ontario, Canada. The study examined the impact of varying the black liquor to DES ratio, operating temperature, and the salt:HBD ratio on lignin recovery. The eutectic mixtures were prepared using methods reported by Ghareh Bagh et al. (2013, 2014, and 2015). The organic salt plus HBD were placed in a jacketed vessel and vigorously mixed at a specific temperature and atmospheric pressure to produce a homogenous colorless liquid. The list of DESs is presented in Table 1. ChCl was used as the salt and the selected HBDs included LA, OXA, malic acid (MA) and urea.

Table 1. DESs used in this study

DESs

Salt

HBD

Ratio

ChCl:LA

ChCl

LA

1:9

1:10

ChCl:OXA.2H2O

OXA·2H2O

1:2

1:3

ChCl:MA

MA

1:1

1:2

ChCl:Urea

Urea

1:1

1:2

Notes: LA = lactic acid; OXA = Oxalic acid; MA = Malic acid

The DESs were synthesized at temperatures less than 100°C under atmospheric pressure. Black liquor plus DESs were mixed in a jacketed vessel at 300 rpm for 6 hours using a specified DES/black liquor ratio at 25, 60, 75, 90oC, respectively. Milli-Q (MQ) water was added to precipitate the lignin fraction. The MQ plus lignin mixtures were filtered and the recovered solids was analysed spectrophotometrically to determine the acid soluble lignin [TAPPI UM 250]. The insoluble lignin (Klason lignin) was determined gravimetrically using TAPPI T 222 om-02.

The temperature, black liquor:DES ratio, and DES utilized for extraction were optimized based on the mass fraction (percent) of lignin recovered. The optimization design was based on a one-factor approach. The lignin recovered and purity was a function of the temperature, type of DES and DES:black liquor ratio. The optimum was observed at 90oC for a 1:3 OXA:DES ratio and a 1:3 black liquor:DES ratio. An approximately 850 mg lignin/g of solid extracted and the recovery was approximately 80%. For the MA-DES and LA-DES combinations under same temperature and black liquor:DES ratio, the optimum recovery range was approximately 73% and 78% with 770 and 800 mg lignin/g solid extracted, respectively. However, at ambient, a 1:3 black liquor:DES ratio, the lignin recovery for ChCl:LA (1:9) was 60% and approximately 380 mg lignin/g solid extracted.

References

Abbott, A.P., Capper, G., Davies, D.L., Rasheed, R.K., Tambyrajah, V. (2003) Chemical Communications. 70–71.

Arkell, A., Olsson, J., Wallberg, O. (2014) Chemical Engineering Research and Design. 92, 1792-1800.

Demirbas, A. (2003) Energy Sources. 25(7), 629-635.

Edgar, C. 2015. Global Lignin Products Market-Segmented By Product Type, Source, Application, and Geography-Trends and Forecasts (2015-2020)-Reportlinker Review. http://www.prnewswire.com/news-releases/global-lignin-products-market-segmented-by-product-type-source-application-and-geography-trends-and-forecasts-2015-2020-reportlinker-review-300145371.html

Edwards, J. D. (2000) Part II conference, petroleum provinces of the 21st century, San Diego, CA.

Ghareh Bagh, F.S., Mjalli, F. S., Hashim, M. A., Hadj-Kali, M.K.O., AlNashef, I.M. (2013) Journal of Chemical and Engineering Data. 58, 2154-2162.

Ghareh Bagh, F.S., Hadj-Kali, M.K.O., Mjalli, F. S., Hashim, M. A., AlNashef, I.M. (2014) Journal of Molecular Liquids. 199, 344-351.

Ghareh Bagh, F. S., Shahbaz, K., Mjalli, F. S., Hashim, M. A., AlNashef, I.M. (2015) Journal of Molecular Liquids. 204, 76-83.

Hou, Y., Gu, Y., Zhang, S., Yang, F., Ding, H., Shan, Y. (2008) Journal of Molecular Liquids. 143, 154–159.

Humpert, D., Ebrahimi, M., Czermak, P., (2016) Membranes 6, 42-54.

Jablonskey, M., Skulcova, A., Kamenska, L., Vrska, M., Sima, J. (2015) BioResources. 10, 8039-8047.

Jönsson, A.S., Wallberg, O., (2009) Desalination. 237, 254–267.

Keyoumu, A., Sjödahl, R., Henriksson, G., Ek, M., Gellerstedt, G., Lindström, M. E. (2004) Industrial Crops and Products. 20, 143–150.

Kumar, A.K., Pharik, B. S., Pravakar, M. (2016) Environmental Science and Pollution Research. 23, 9265–9275.

Lake, M.A., Blackburn, J.C. (2011) International Patent Application. PCT/US2010/049773.

Lalman, J.A., Ray, S. (2009) Provisional Patent Application Serial Number 61/272,567.

Lalman, J.A., Shewa, W.A., Gallagher, J., Ravella, S. (2017) Biomass and Bioenergy In Quality living through chemurgy and green chemistry, Lau, P.C.K. (editor), Springer, New York, NY.

Orr, L. (2006) Global and Energy Project. Stanford University. (after John Edwards, American Association of Petroleum Geologists).

Shewa, W.A., Lalman, J.A. (2014) Proceedings of the Water Environment Federation. 20, 2484-2503.

Stigsson, L., Arkell, A., Olsson, J. (2017) EP3004455 A4.

TAPPI UM 250. (1991) TAPPI Useful Methods. Atlanta, GA, USA.

TAPPI T 222 om-02. (2002) TAPPI Test Methods. Atlanta, GA, USA.

Tomani, P. (2010) Cellulose Chemical Technology. 44 , 53-58.;

Yu, Y. H., Lu, X. M., Zhou, Q., Dong, K., Yao, H. W., Zhang. S. J. (2008) Chemistry - A European Journal. 14, 11174-11182.