Green Sustainable Process for Chemical and Environmental Engineering and Science

Supercritical Carbon Dioxide as Green Solvent

Inamuddin, Abdullah M. Asiri, Arun M. Isloor, Dr. Inamuddin

• Publisher: Elsevier
• Year: 2019
• Print ISBN: 9780128173886
• eBook ISBN: 9780128173893
• Topic: Technology & Engineering
• Subtopic: Chemical & Biochemical Engineering
• Index: Technology & Engineering

Green Sustainable Processes for Chemical and Environmental Engineering and Science: Supercritical Carbon Dioxide as Green Solvent provides an in-depth review on the area of green processes for the industry, focusing on the separation, purification and extraction of medicinal, biological and bioactive compounds utilizing supercritical carbon dioxide as a green solvent and their applications in pharmaceuticals, polymers, leather, paper, water filtration, textiles and more. Chapters explore polymerization, polymer composite production, polymer blending, particle production, microcellular foaming, polymer processing using supercritical carbon dioxide, and a method for the production of micro- and nano-scale particles using supercritical carbon dioxide that focuses on the pharmaceutical industry. A brief introduction and limitations to the practical use of supercritical carbon dioxide as a reaction medium are also discussed, as are the applications of supercritical carbon dioxide in the semiconductor processing industry for wafer processing and its advantages and obstacles. - Reviews available green solvents for extraction, separation, purification and synthesis - Outlines environmentally friendly chemical processes in many applications, i.e., organic reactions, metal recovery, etc. - Includes numerous, real industrial applications, such as polymers, pharmaceuticals, leather, paper, water filtration, textiles, food, oils and fats, and more - Gives detailed accounts of the application of supercritical CO2 in polymer production and processing - Provides a process for extraction, seperation and purification of compounds of biological medicinal importance - Gives methods for nanoparticle production using supercritical carbon dioxide - Provides a systematic discussion on the solubility of organic and organometallic compounds

Chapter 1

Polymer production and processing using supercritical carbon dioxide

Pooja Yadav^a; Mukta Agrawal^a; Amit Alexander^a; Ravish Patel^b; Sabahuddin Siddique^c; Shailendra Saraf^d; Ajazuddin^{a a} Rungta College of Pharmaceutical Sciences and Research, Bhilai, Chhattisgarh, India
^b Ramanbhai Patel College of Pharmacy, Charotar University of Science and Technology, CHARUSAT Campus, Changa, Ta-Petlad, Anand, Gujarat, India
^c Patel College of Pharmacy, Madhyanchal Professional University, Bhopal, Madhya Pradesh, India
^d University Institute of Pharmacy, Pt. Ravishankar Shukla University, Raipur, Chhattisgarh, India

Abstract

Carbon dioxide plays a vital role during the synthesis and processing (modification) of polymers. This chapter emphasizes recent advancements in polymer modification using SCO₂. The SCO₂ is a versatile solvent and finds application during polymer production as well as handling. Polymer production using SCO₂ includes various polymerization techniques such as homogeneous polymerization, heterogeneous polymerization, precipitation polymerization, suspension polymerization, and emulsion polymerization. Polymer processing using SCO₂ highlights different areas manipulating the property of polymers such as its viscosity, plasticization, tendency to form a microcellular foam, and polymer blends. The application of SCO₂ in polymer modification emphasize its purification, dyeing, impregnation, and particle production. Overall, SCO₂ can be considered as a good supporting medium for modification of polymers.

Keywords

Supercritical fluid; Carbon dioxide; Polymer processing; Polymer production; Polymerization

Contents

• 1. Introduction
• 2. Properties of supercritical CO₂
• 3. Applications of SCO₂ in polymer production and processing
  • 3.1 Purification of polymers
  • 3.2 Impregnation and supercritical dyeing
  • 3.3 Particle production
  • 3.4 Polymer modification
• 4. Polymer production
  • 4.1 Step-growth polymerization
  • 4.2 Chain growth polymerization
• 5. Polymer processing
  • 5.1 Plasticization of polymers
  • 5.2 Viscosity reduction
  • 5.3 Microcellular foam
  • 5.4 Polymer blending
• 6. Future prospects
• 7. Challenges ahead
• 8. Conclusion
• References

1 Introduction

In the past few decades, polymers have become an important part of daily life. Their feasible synthesis and processing are needed for various applications. Instead of using conventional solvents, now the research has been shifted to supercritical fluids. The supercritical fluids are described as a material maintained at a condition of temperature and pressure more than its critical values. It holds the unique combination of viscosity (like gas) and density (like liquid) which makes a supercritical fluid an excellent solvent [1, 2]. Supercritical carbon dioxide (SCO₂) is a non-toxic solvent, which is the best alternative for noxious organic solvents and chlorofluorocarbons. Owing to their immense physical properties such as non-flammability, chemically inertness, and cheapness, these find applications, not only in polymer synthesis, but also in polymer production. The supercritical conditions of carbon-dioxide (CO₂) can easily be achieved (Tc = 304 K and P_c = 7.38 MPa) (Fig. 1) and extracted out from the reaction by simply depressurizing the reactor. The high yield and increased product quality attract the usage of SCO₂[4].

Fig. 1 Schematic representation of temperature–pressure phase diagram of the pure component, surrounded by triple point (T) and critical point (C). (Adapted from S.P. Nalawade, F. Picchioni, L.P.B.M. Janssen, Supercritical carbon dioxide as a green solvent for processing polymer melts: processing aspects and applications, Prog. Polym. Sci. 31(1) (2006) 19–43.)

Moreover, CO₂ is a gas in ambient conditions, which makes it easy to remove from the polymeric product instead of using costly methods of solvent evaporation or drying. Mixtures of solvents are used to enhance the strength of chemical reaction during the synthesis and processing of polymers [5]. However, by incorporating SCO₂ into the response gives advantages over conventional solvents, such as:

• • it possesses environmentally benign characteristics such as being non-toxic, non-flammable, and low cost;
• • easy removal of the solvent after the reaction;
• • faster rate of reaction at mild conditions; and
• • higher selectivity and higher yield in chemical reactions (obtained due to temperature and pressure above critical values).

2 Properties of supercritical CO₂

SCO₂ has widely gained importance in recent years because of its assured diffusivity and density. These can change the glass transition temperature (Tg) of the polymers leading to their reduced viscosity [6]. Undeniably, even though CO₂, due to its distinct symmetrical structure, has no dipole moment, it can show inviolable quadruple moment (acting at a smaller distance than dipolar interaction), hence increasing the solubility [7, 8]. The CO₂ itself shows excellent solubilizing power and is therefore used as a solvent and antisolvent. CO₂ is preferred as a polymerization medium because:

• • these are cost-effective, non-flammable, non-toxic, and are readily obtainable in pure form;
• • solvent recovery becomes easy due to the use of CO₂;
• • the high solubility of various polymers within CO₂ finds its application for their synthesis;
• • for porous polymers to be synthesized, the supercritical fluid having CO₂ facilitates as non-solvating power and acts as an organic diluent; and
• • carbon dioxide usually doesn’t interact with the strong nucleophiles (e.g., alkoxides, primary amines, etc.), and hence it can be suggested polymerization in CO₂ is generally through the anionic mechanism.

The nonpolar molecules, having low molecular weight, can be readily solubilized in supercritical CO₂ rather than water and ionic compounds because supercritical CO₂ has a relatively small dielectric constant (ɛ = 2). SCO₂, owing to its tremendous physiochemical properties, is also cheap, non-toxic, and non-flammable, hence finding applications in the production and refinement of polymers. Owing to...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributors
• Chapter 1: Polymer production and processing using supercritical carbon dioxide
• Chapter 2: Extraction of lipids from algae using supercritical carbon dioxide
• Chapter 3: Extraction of catechins from green tea using supercritical carbon dioxide
• Chapter 4: Application of supercritical CO2 for enhanced oil recovery
• Chapter 5: Metal recovery using supercritical carbon dioxide
• Chapter 6: Use of supercritical carbon dioxide in alkylation reactions
• Chapter 7: Extraction of phytochemicals from saffron by supercritical carbon dioxide
• Chapter 8: Extraction of bioactive compounds
• Chapter 9: Extraction of propolis using supercritical carbon dioxide
• Chapter 10: Solubility of pharmaceutical compounds in supercritical carbon dioxide: Application, experimental, and mathematical modeling
• Chapter 11: Decaffeination using supercritical carbon dioxide
• Chapter 12: Supercritical fluids for the extraction of oleoresins and plant phenolics
• Chapter 13: Applications of supercritical carbon dioxide in textile industry
• Chapter 14: Hydrogenation of fats and oils using supercritical carbon dioxide
• Chapter 15: Extraction of bioactives from citrus
• Chapter 16: Solubility of organic compounds in scCO2
• Chapter 17: Supercritical fluid based extraction of marigold principles
• Chapter 18: Industrial polymer synthesis using supercritical carbon dioxide
• Chapter 19: Organometallic compounds solubility in supercritical carbon dioxide (SCCO2): Measurement techniques, variables affecting solubility, recent developments, and thermodynamic modeling
• Index