Continuous production of cellulose mixed esters via homogeneous reactive twin-screw extrusion catalyzed by ionic liquid

Abstract

Cellulose mixed esters (CMEs) substituted with two different types of acyl groups are promising polymeric materials with various tunable properties but are arduous to produce. This is because of the insolubility of cellulose in common solvents, and thus, the industrial production of CMEs with desired degrees of substitution (DSs) requires a costly multistep process. To accomplish their facile production, homogeneous reactions have been performed using ionic liquids (ILs) as solvents for cellulose. However, the high viscosity of the cellulose-IL solutions causes insufficient mixing in batch reactors; thereby, favoring low cellulose concentrations with long reaction times (typically hours). Herein, we demonstrate a rapid and scalable production of CMEs by exploiting the excellent shear mixing of a twin-screw extruder as a flow reactor. A co-solvent system comprising an IL, 1-ethyl-3-methylimidazolium acetate, and dimethyl sulfoxide was applied to dissolve cellulose at a high concentration (15 wt.%) via twin-screw extrusion. During continuous extrusion at 80 °C, cellulose reacted with two acyl reagents, isopropenyl acetate (IPAc) and vinyl propionate (VPr) (2.5:0.5, mol/mol), to yield cellulose acetate propionate (CAP) within minutes. The CAP was stably produced during the operation time of 50 min with an average isolated yield of 71%. The DSs of the acetyl and propionyl groups of CAP were 1.77 and 0.50, respectively, corresponding to sufficiently high conversion rates of 70% for IPAc and 100% for VPr.

Investigation of cellulose dissolution in morpholinium-based solvents: impact of solvent structural features on cellulose dissolution

“…6,7 But this solvent is prone to exothermic and oxidative reactions since it is a strong oxidant and is sensitive to alkylating and acylating agents and redox-active transition metal ions. 8 Development of ionic liquids capable of dissolving cellulose [9][10][11] should also be mentioned in this context as it has opened new avenues for shaping and modifying cellulose, 12,13 with the recycling of the solvent remaining as one of the main challenges. N,N-dimethylacetamide (DMAc)/LiCl is another well-studied solvent mainly used in gel permeation chromatography (GPC) for evaluating molecular weight distribution of cellulose 14 as well as for its homogeneous functionalization.…”

Cellulose processing in ionic liquids from a materials science perspective: turning a versatile biopolymer into the cornerstone of our sustainable future

“…Moreover, the combination of homogeneous dissolution of cellulose in ionic liquids with efficient mixing in an extruder can yield a desired product within minutes of reaction time. 316,317…”

“…Moreover, the combination of homogeneous dissolution of cellulose in ionic liquids with efficient mixing in an extruder can yield a desired product within minutes of reaction time. 316,317 Regarding the choice and structure of the ionic liquid, the most popular ones for material fabrication are first generation ionic liquids based on dialkylimidazolium cations, such as [Emim][Ac], [Amim][Cl] and [Bmim][Cl]. While in many cases an ionic liquid with good dissolution power proved sufficient to fulfill the target purpose (e.g., for thin film and coating applications), there are cases where the structure of ionic liquid could substantially influence the performance for the application.…”

Ionic Liquids as Organocatalysts and Solvents for Lignocellulose Reactions

“…The resulting CAP exhibited DSs of 1.8 and 0.5 for the acetyl and propionyl groups, respectively, thereby corresponding to high conversion rates of IPAc and VPr (70 and 100 %, respectively). [42] Furthermore, CAP production via REX can outpace standard batch production owing to its continuous flow and a higher initial concentration of cellulose (15 wt.%), ultimately achieving an excellent production rate of ~1 kg d À 1 , whereas the batch reaction achieves only gram scale production.…”