Abstract
Oxyalkylation with propylene carbonate (PC) is a safe process to convert lignin into a reactive liquid polyol to be used in polyurethane formulations. In this study, the effect of operating conditions of oxyalkylation (temperature, time and quantify of PC) on the quality of lignin-based polyol in terms hydroxyl number (IOH) and viscosity was studied. Full factorial modeling and response surface methodology (RSM) were applied to study the effect and interaction of process variables on the IOH and viscosity of lignin-based polyols. The results revealed that the IOH is highly affected by the reaction time, while the viscosity is affected by the amount of PC. Validation experiments confirmed the model is reliable. Furthermore, RSM optimization allowed to reduce the amount of PC by about 50% and to increase the lignin content in the polyol from 12.5% to 25% (w/w) depending on the temperature and time of the process and also on the purpose of the polyol produced (i.e., application in rigid foams or adhesives).
Highlights
In recent years, the production of bio-based polyols has attracted great attention since conventional polyols are produced from petrochemical derivatives, which make a significant contribution to the increase of greenhouse gas emissions
The application of design of experiment (DoE) using the full factorial and response surface methodology (RSM) methodology in this study enabled extracting information about how the conditions of the oxyalkylation process using propylene carbonate (PC) affect the quality of the lignin-based polyol
The response surface generated from second-order equations allowed to verify that the variables PC amount, temperature, and time have great impact on the responses
Summary
The production of bio-based polyols has attracted great attention since conventional polyols are produced from petrochemical derivatives, which make a significant contribution to the increase of greenhouse gas emissions. Bio-based polyols are currently available on the market and are supplied by companies such as BASF SE, Bayer, Dow Chemical, Huntsman, Covestro, Cargill, Dupont and Roquette. These companies are producing bio-based polyols mainly from vegetable oils and sugar platforms competing with food applications [1–3]. Another potential candidate for the production of bio-based polyols is kraft lignin, a by-product of the pulp and paper industry, and widely available from black liquor (about 55–90 million tons of kraft lignin/year), which is mainly burned for energy supply [4]. Chemical modifications to convert it into liquid polyols to produce polyurethanes (PUs) are necessary [5]
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