4.5. Green chemistry examples

Since chemical products are present in virtually any sphere of technology, we can find numerous examples of studies and innovations that illustrate the application of green chemistry principles. Some of them are given below. In the end of this lesson, you will be asked to research one of these cases (of your choice) in more detail and to provide a brief evaluation of its promise.

A. Innovative propylene oxide process

Companies DOW and BASF jointly developed a technology of conversion of hydrogen peroxide into propylene oxide (HPPO) that has significant "green" advantages over competing technologies:

It uses hydrogen peroxide and propylene as raw materials, producing only propylene oxide and water.
It reduces waste water by 70-80%.
It uses 35% less energy.
Its capital cost is 25% less.
It avoids need for co-product infrastructure and markets.

Source: www.epa.gov

B. Advanced amine technology for carbon capture

Alstom-DOW pilot plant captures CO2 from new or existing industrial facilities with an improved sustainability profile:

Pilot plant in West Virginia is designed to capture 1,800 tons CO2 per year.
Advanced Amine process leads the industry in carbon capture efficiency.
Capture rate ~90% with 99.5% purity of CO2.
Process significantly reduces parasitic energy requirements.

Source: Pump Industry Analyst, 2009

C. Metathesis catalysis for making high-performing, green specialty chemicals at advantageous costs

Elevance employs Nobel-prize-winning catalyst technology to break down natural oils and recombine the fragments into novel, high performance green chemicals. These chemicals combine the benefits of both petrochemicals and biobased chemicals. Elevance produces specialty chemicals for many uses, e.g., concentrated cold-water detergents that provide better cleaning with reduced energy costs.

Significant energy savings
Reduction of greenhouse gas emissions by 50% (compared to petrochemical technologies)

Source: ACS

D. An efficient biocatalytic process to manufacture simvastatin

Simvastatin, a leading drug for treating high cholesterol, is manufactured from a natural product. The traditional multistep synthesis was wasteful and used large amounts of hazardous reagents. Professor Y. Tang (UCLA) conceived a synthesis using an engineered enzyme and a practical low-cost feedstock. Codexis optimized both the enzyme and the chemical process.

great reduction of hazard
less amount of waste
cost-effective approach
better meets needs of customers

Some manufacturers in Europe and India use this process to make Simvastatin.

Source: ACS

E. Enzymes save energy and wood fiber for manufacturing high-quality paper and paperboard

Traditionally, making strong paper required costly wood pulp, energy-intensive treatment, or chemical additives. But that may change. Buckman’s Maximyze®enzymes modify the cellulose in wood to increase the number of "fibrils" that bind the wood fibers to each other, thus making paper with improved strength and quality − without additional chemicals or energy. Buckman's process also allows papermaking with less wood fiber and higher percentages of recycled paper, enabling a single plant to save $1 million per year.

Source: ACS

F. Gas-expanded liquids for sustainable catalysis

Gas-expanded liquid (GXL) is a substance generated by dissolving a compressible gas (for example, CO₂ or a light olefin) in a regular liquid substance at mild pressures (tens of bar). When CO₂ is used as the expansion gas, this process produces CO₂-expanded liquid (CXL). An attractive feature of GXLs is that they combine the advantages of compressed gases and of traditional solvents. GXLs retain the beneficial attributes of the conventional solvent (polarity, catalyst/reactant solubility) but provide higher miscibility of permanent gases (O₂, H₂, CO, etc.), as compared to organic solvents at ambient conditions. GXLs also results in enhanced transport rates compared to regular liquid solvents. The enhanced gas solubility in GXLs have been exploited to alleviate gas starvation (often encountered in homogeneous catalysis with conventional solvents). Environmental advantages of GXL include:

replacement of harmful organic solvents with environmentally benign CO₂;
reduced flammability due to CO₂ presence in the vapor phase;
lower process pressures (tens of bar) compared to supercritical CO₂ (hundreds of bar) which is linked to energy savings.

GXLs thus have many characteristics of an ideal alternative solvent.

Source: Anastas and Zimmerman, 2013, pp. 5-36. (This book is available online through the Penn State Library system.)

G. Synthesis of magnetite (Fe₃O₄) nanoparticles "green" way

Shape-controlling studies of magnetite nanomaterials are pursued actively since their magnetic and electrochemical properties, as well as their catalytic activities, greatly depend on their nanostructures. As catalysts, Fe₃O₄ nanoparticles possess some advantages over natural enzymes (e.g., horseradish peroxidase, HRP) because (i) they can maintain relatively high catalytic activities under a wide range of environmental changes, even in severe conditions (pH = 2–7, 70 °C) and (ii) their preparation and purification procedures are reproducible and cheaper than those of natural enzymes. The robustness, repeatability, and low price of Fe₃O₄ nanoparticles make them suitable as catalysts for H₂O₂ oxidation for a broad range of applications in biotechnology and environmental chemistry.

However, the synthesis of Fe₃O₄ nanoparticles with controlled morphology is still a challenge. Current approaches, such as a hydrothermal process, solvothermal process, and thermal decomposition, involve toxic sources (e.g., organic solvents and surfactants), rigorous conditions (high temperature, high pressure), and tedious synthetic procedures, which prevent the large-scale production and widespread practical applications of Fe₃O₄ nanoparticles. Additionally, the recovery of Fe₃O₄ nanoparticles for repeated use is still difficult. Therefore, nontoxic, water-based approaches for the fabrication of morphology controllable Fe₃O₄ nanoparticles, which can be produced on a large-scale and effectively recovered, are urgently needed.

This article introduces a new straightforward approach developed for fabricating Fe₃O₄ nanoparticles/hydrogel magnetic nanocomposites, in which the morphology of the nanoparticles can be controlled under nontoxic and water-based conditions. The 3D hydrogel networks, which contain a liquid-like microenvironment facilitating small molecule diffusion and transport, can act as an ideal nano/micro-reactor but also as a great carrier for the synthesis and immobilization of nanoparticles. This study was inspired by magnetotactic bacteria, which are capable of producing bacterial magnetic particles (BacMPs) with a highly controlled morphology (e.g., nanocube, nanooctahedron, and nanododecahedron) due to their nanoscaled magnetosome vesicles acting as nanoreactors, and negatively charged proteins playing the role of iron ion-binding sites. With a higher catalytic activity, the magnetic nanocomposite loaded with Fe₃O₄ nanooctahedra has a sensitive response towards H₂O₂ detection with a limit of 5 × 10⁻⁶ mol L⁻¹.

An additional benefit of this work is that the magnetic nanocomposite can be recovered more effectively and easily using the hydrogel as a carrier. "Based on the facile, economical fabrication strategy, large-scale production of this magnetic nanocomposite with a tunable peroxidase-like activity can be expected to revolutionize catalysis applications in biotechnology and environmental chemistry."

Source: Geo et al., 2013

Assignment Details

At the end of this lesson, you will be asked to choose one of the above cases or any other you may find on the Internet for more detailed evaluation. More information can be found on the Lesson 4 Activity Sheet on Canvas.

4.5. Green chemistry examples