"Green technology" is by no means a new buzzword. It has been around for at least a couple of decades. But not many are aware of what it takes to actualise green technology, beyond the secure knowledge that a non-polluting and energy-saving approach underpins it. This review is intended to give readers a flavour of green technology from a chemist's perspective, as materials and their transformations lie at the core of all industrial processes. In this sense, "green technology" is effectively a deployment of "green chemistry".

Green chemistry is an inclusive concept that covers catalysis, green solvents, streamlining of complicated processes, optimisation of the use of energy, materials and water, recycling, waste reduction, and even real-time analysis for pollution prevention. For the industry at large, the real challenge is how green chemistry principles can be applied to the way we design chemicals, manufacturing processes and commercial products that will minimally impact the environment.

In this two-part review, we shall briefly examine some of the key features of green chemistry by providing recent examples of products and processes which have already been achieved or awaiting commercialisation. Part One covers the fields of Plastics, Paints & Coatings, and Green Synthetic Pathways while Part Two deals with Renewable Energy, Green Buildings and Green Nanotechnology in Environmental Sustainability.

Plastics

Plastics, which are derived mainly from petroleum-based raw materials, present a vexing global problem in terms of pollution. Biodegradable plastics with significantly lower carbon footprint hold much promise of mitigating this.

1. BASF has developed a versatile compostable bioplastic (Ecovio) with variable polylactic acid (PLA) content sourced from corn. It has already found application as plastic films for food packaging and as dual-use bags.
2. Recycling of PET bottles has been effectively achieved using a category of metal-free green catalysts known as organocatalysts. The catalysts speedily depolymerise PET to yield 91 per cent of the highly pure monomer.
3. Green solutions for tackling the considerable waste plastic that goes to landfills or incinerators present an attractive 'waste to wealth' opportunity and the fulfilment of a vision for circular plastics economy. Two standout innovations in this regard are:
   • the already commercialised use of waste plastic for the modification and extension of bituminous binder in an asphalt mix, resulting in improved stiffness and deformation resistance of the asphalt used in road surfaces; and
   • the development of plastic lumber as a durable, rot and termite-resistant alternative to timber.

Paints & Coatings

1. The paints & coatings industry has made great strides in recent years in using green solvents and producing products with low or zero volatile organic content (VOC). Ethyl lactate, derived from processing corn, is one such example of green solvent with high solvency power that dissolves a wide range of polyurethane resins with ease.
2. Recycled PET, acrylics, and soybean oil have been used to create a water-based acrylic alkyd paint. The paint combines the performance benefits of alkyds and low VOC content acrylics.
3. A green two-step silica-based pre-treatment to prepare metal surfaces before application of a protective paint coating has been developed, which avoids the traditional use of heavy metal phosphates and organic solvents.

Green synthetic pathways

The computer chip

A statistic not widely known about the computer chip is that its manufacture consumes large amounts of hazardous chemicals, energy and ultrapure water. The energy-intensive process, along with reliance on dangerous materials and continuing miniaturisation, has made the process an environmental and technical challenge. The solution to these challenges is supercritical carbon dioxide, which is liquid CO2 hovering just below the supercritical state. Besides water, it is one of nature's best-known green solvents. It has already found use in decaffeinating coffee beans, micronising pharmaceutical compounds, and in dry-cleaning. Supercritical CO2, with its extremely low viscosity and surface tension, dispenses altogether the need for copious amounts of water to wash away the photoresist, and it does so without affecting the delicate miniature silicon structures.

Specialty Chemicals & Pharmaceuticals

1. The synthesis of sitagliptin, the active ingredient in Januvia™ (a treatment for Type 2 diabetes) has been significantly enhanced using an engineered enzyme catalyst. The catalyst reduces the number of reaction steps from eight to three and eliminates aqueous waste.
2. Vegetable oils containing unsaturated fatty acids are a valuable source of renewable and cheaper feedstocks for generating a sustainable chemical industry. It benefits the industry through the selective functionalisation of their olefinic bonds via transition-metal catalysed metathesis reactions. The selective functionalisation has enabled the synthesis of a variety of speciality chemicals in cosmetic, agricultural and pharmaceutical fields.
3. Kraft lignin (KL) has been shown to form nanocapsules by self-assembly induced by adding water to an ethanol solution of KL. The capsules have potential applications in many fields.
4. Propylene oxide (PO), one of the most common industrial chemicals in the world, is traditionally produced using chlorohydrin, which leads to substantial amounts of co-products. An innovative, cost-effective green process has been found based on a zeolite-catalysed reaction of hydrogen peroxide and propylene that produces only water as a co-product.
5. A new class of green solvent systems called gas-expanded liquids (GXLs) has caught the attention of industrial chemists in recent years. GXLs are liquid mixtures consisting of an organic solvent combined with a high-fluidity gas, such as CO2, in the near-critical regime. GXLs are well suited for a wide variety of applications. An essential industrial example is the oxidation of p-xylene to terephthalic acid in CO2-expanded acetic acid which proceeds in high yield.

--BERNAMA

Academician Professor Emeritus Datuk Dr V G Kumar Das has offered his views solely in his private capacity and they do not in any way represent the views of the Academy of Sciences Malaysia.