The challenges for chemical-intensive industries, including the producers of personal care products, in the 21st century are as great as those faced by almost any industry.1 The chemical industry, which has been effective in supplying a diverse range of intermediates and formulation components largely based on low-cost petroleum feedstock, is now under pressure to change the way it operates. The drivers for change affect all aspects of production, notably feedstock, manufacturing processes and the choice and key design features of products(Figure 1).
While the impact of increasing oil prices on the cost of transportation and heating fuels is frequently and often dramatically publicized, the effects on other oil-dependent industries and their downstream users receive less attention. Some 20% of the petroleum used in the European Union (EU) goes into chemical manufacturing such as feedstock and energy, and more than 90% of the organic chemicals used today are oil-derived.
To add to the problem of increasing costs, the industry also faces concerns over reliability of supply due to the demand from rapidly growing chemical industries in areas such as China. When the price of phenol, a major building block petrochemical, tripled in 2005, the price hike could be attributed to both oil price increases and demand from the growing industries of the East.
Chemical manufacturing has also had to face a climate of heightened legislation for the last 10 years and many companies have significantly “cleaned up their act” by reducing levels of pollution and improving workplace health and safety records. Pressures continue to mount, however, with rapidly increasing energy costs and restrictions over the storage of chemicals and disposal of hazardous waste, making competitiveness with the new industries in the East more difficult. While the 1990s can be seen as a period of improvement in “good housekeeping,” it is now apparent that step-change improvements such as the introduction of new, clean technologies are needed.
The early years of the 21st century have seen an unprecedented level of attention on the human and environmental safety of products. Perhaps inevitably, chemicals have come under the microscope from new legislation, notably REACH, but also from more sector-specific regulations such as Restriction of Hazardous Substances (RoHS), reflecting public concerns.2,3 One outcome of this is the increasing awareness by retailers of the range of chemicals they effectively sell that are disguised in the form of food, medicines, clothing, electronic goods, cleaning products and, of course, personal care products.
In the rush to be seen as “green,” retailers are competing over their green credentials, encouraged by frequently published reports from nongovernmental organizations (NGOs). Currently retailers are only aware of chemicals that can attract negative publicity; hence, the focus is almost entirely on avoidance of headline-grabbing substances such as phthalates and brominated flame-retardants. With a newly found inquisitiveness over supply chains using “green-tinted” spectacles, retailers and their customers are likely to ask more difficult questions relating to overall environmental footprints.
Personal care product producers are subject to these changing attitudes and need to respond early through their own lifecycle awareness. Future products need to be verifiably green and sustainable with well-understood and controlled supply chains.
Research for finding more environmentally friendly replacements for hazardous chemical processes dates back more than 20 years but the term green chemistry was suggested in the mid 1990s by the US Environmental Protection Agency (EPA). The term has become widely accepted—if sometimes interchanged with sustainable chemistry, which strictly speaking, is different—and has helped to provide focus to the movement towards more environmentally compatible chemical processes and products. The US EPA led the charge with grants to support green chemistry R&D, as well as an awards program.
Green chemistry centers, institutes and networks have been established in numerous countries including the United States, United Kingdom, Japan, Greece and Spain. A dedicated and high-impact factor journal, Green Chemistry, has been in business for almost 10 years and each year sees numerous national and international green chemistry conferences and other events.
Green chemistry can basically be considered a series of reductions (Figure 2).Greater resource efficiency and less waste will obviously benefit a company’s bottom line. Energy and water will be increasingly important resources in manufacturing, especially in many developing countries where numerous Western companies have outsourced all or part of their manufacturing. Reducing the number of process auxiliaries and, in particular, process steps, is also likely to provide financial savings as well as improved environmental performance—green chemistry is simple chemistry.
While most of the green chemistry research in the 1990s was process-focused, the last two years have seen growing interest in the other stages of the product lifecycle, notably raw materials and, with increasing user awareness, the product itselfincluding its fate, once released into the environment. Personal care chemists need to take measures to improve the green credentials of their products, to ensure the sustainability of their raw materials, and to minimize manufacturing costs through green chemistry reductions. By looking at the use of renewable resources as feedstock, cleaner synthesis methods in manufacturing, and greener products based on “benign by design” ideology, practical measures can be considered to achieve these goals.
There is a false assumption by many individuals that green equals natural, and that when the industry refers to green(er) chemicals, it means natural or plant extracts. The first stage of developing a truly green and sustainable chemical product should be based on a renewable resource; in the case of an organic chemical, this means biological materials including trees, grasses and agricultural residues. However, it is likely that the majority of these future products will require green chemical modification of that resource to give it the necessary properties for effective use. The best examples of this are the so-called bio platform molecules—relatively simple compounds that can be obtained in simple one or two-stage processes from biomass(see Figure 3).7
Some of the key platform molecules that are expected to become widely available from bioresources via the fermentation route are shown in Figure 4.
These are all oxygenated and hydrophilic. Nonetheless, their high degree of functionality makes them good candidates for chemical transformations as shown, for example, by succinic acid (see Figure 5).8
It is important to note that these molecules are produced in fermentation broths—aqueous, high dilution (< 10% w/w) and mixed with other products plus nutrients, enzymes, etc. Energy-demanding and wasteful separation and purification processes will massively reduce the economic and environmental credibility of such chemicals, and green chemistry needs to be chemistry that is effective under such conditions.
Some heterogeneous catalysts including those based on carbonized polysaccharides can achieve this, and when combined with membrane technology, provide future routes to the continuous conversion of dilute aqueous feedstock to nonaqueous chemical products.9 Other renewable molecules to be considered for future feedstock in green and sustainable supply chains include vanillin, a rare aromatic example, and fatty acids and esters that are now produced in ever larger quantities from biodiesel manufacture.
Clean synthesis and clean chemical production are where the green chemistry movement began and remain in the heart of the area. The starting point for developing a clean synthesis strategy is to set metrics to measure reaction efficiency by means other than the traditional value of yield alone.10 Atom economy, or the percentage of atoms in the substrates that go into the desired product, and the E factor or the ratio of waste to product weights, are the best established of these, although both have limitations. Atom economy ignores any reagents, catalysts and solvent, whereas with an E factor, one has to decide on the system boundaries and whether to include the process auxiliaries, such as the solvent and quench or wash water. In a typical documented synthetic procedure for an organic reaction, apart from the substrates, the reaction mixture contains solvent and frequently other auxiliaries such as acid, base or catalyst, and the work up can involve large amounts of water and organic solvent.
In a way it does not, within reason, matter what one includes—e.g., it is often prudent to ignore solvents that are clearly and practically recyclable—as long as like-for-like comparisons can be made with alternative procedures. One increasingly serious omission from all of the major green chemistry metrics that currently exists is energy; given the increasing cost of energy it would be foolish to ignore this in route selection.
The major and most widely applicable solutions to inefficient, wasteful or otherwise dangerous synthetic routes are:
1. Alternative routes, carefully evaluated by green chemistry metrics and other critical parameters, including energy and the use of hazardous chemicals;
2. Catalysis and especially heterogeneous catalysis such as supported AlCl3 and other solid acids and bases;
3. Solvent avoidance or substitution with a nonvolatile solvent such as an ionic liquid or an easily recyclable and benign solvent such as supercritical CO2. Given the immaturity or limitations of alternative solvents, the industry can also use a series of parameters to thoroughly compare the credentials of different VOC solvents such as solvent power, toxicity, safety, recoverability and even a mini-lifecycle assessment to allow the inclusion of sustainability as a factor.
4. Avoiding auxiliaries—including protecting and deprotecting agents but also extending to avoiding solvents altogether wherever possible.
It should also be remembered that the bulk of process chemistry waste tends to come after the actual reaction. Separations or reaction quenches are often achieved by drowning the reaction in a large volume of water; organic solvents can be used to wash out products; and other process auxiliaries can be used to clean up and purify the product.
Through the use of the right reagents and catalysts, as in heterogenized forms or permanently separated by a membrane reaction, much of this can be avoided. It may also be possible through the use of a membrane or other flow reactor such as a spinning disc reactor to continually remove product from the reaction zone. Even in a static reactor the use of supercritical CO2 as a reaction solvent or simply as an extraction medium has the advantage of easy separation simply through a reduction in pressure.11
There will be an increasing number of occasions where substitution of a process reagent or more significantly of a final product will become important. This may be driven by availability and cost issues, difficulty in manufacture, legislation, expedient application of greener product guidelines, as in assessing the probable need for substitution on the basis of known or extrapolated persistence, bioaccumulation and toxicity data, or customer or NGO and media pressure. A good strategy for substitution is to consider both existing “green” chemicals and biomass-derived products likely to emerge in the near future (see Figure 6). The acceptability criteria may set limits to change, such as “no more than 20% greater cost;” or “no more than two process steps from the raw material;” or “commercially available feedstock.”
Some examples of classes of compounds and substances where either substitution is becoming important and/or where renewable, i.e., biomass-derived, sources are becoming available, are briefly discussed below.
Future sources of aromatic compounds are particularly uncertain. Among the most promising bio-platform molecules for future chemical manufacturing, the only aromatic compound is vanillin, which can be obtained from lignin in low, 2–3% yields. Some other natural materials also contain aromatic compounds, although their yields by extraction or even reactive (e.g., oxidation) extraction are similarly low. One different approach is to start from glucose, which is widely and easily available from numerous biomass materials, and to use a combined biochemical process to produce simple benzenoid aromatics (see Figure 7).
The para-substitution pattern of one of these products is consistent with that used in some sunscreen agents in personal care products. Some emollients contain ortho-substitution patterns, commonly ortho-substitutional phenols, that may be accessible from vanillin.
There is concern over the apparent poor biodegradability of some chelants including EDTA, although this has been contested. Nonetheless, there has been a great effort directed towards more environmentally friendly substitutes for EDTA. One example of this is EDDS (see Figure 8).
Unfortunately the activity of EDDS is not as effective as EDTA. Phosphonates have also been proposed but its biodegradability may not be much better than that of EDTA.12
Plant waxes can be extracted using environmentally benign supercritical carbon dioxide. One of the most interesting sources is wheat straw, which is abundant, widely available in Europe and of low value.13 The benign extraction technology has the additional advantage of being tunable so that different fractions of the complex mixture of chemicals called waxes can be collected. These have different properties and different application values including cosmetics as well as nutraceuticals and insect semiochemicals. All UK waxes are imported. Furthermore, there is a growing desire to avoid animal-derived waxes in products such as cosmetics.
In other current research at the Green Chemistry Centre at York, natural polysaccharides such as starches are being used to stabilize nanoparticles. This could have value in applications such as sunscreens where titanium dioxide nanoparticles are known to be more efficient UV light reflectors than larger particle aggregates, but where there are concerns over the particles’ ability to trigger damaging electron-transfer processes if they can migrate through the skin.
By using “neutral” materials such as starch in more imaginative ways, and by building up new products using bio-derived platform molecules, new formulations of sustainable chemical products can be created. And by using clean synthesis methods and green chemical technologies to carry out the chemical conversions en route, the industry can ensure green and sustainable chemical products.
1 JH Clark, Green chemistry today (and tomorrow), Green Chem, 8 17 (2006)
2 DJ Knight, Regulation of Chemicals, RAPRA Review Report, 16 181 (2006)
3 J Garrod, The current regulation of environmental chemicals, RE Harrison and RE Hester, eds, in Chemicals in the Environment, RSC: Cambridge 1–20 (2006)
4 JH Clark, Green Chemistry for the second generation biorefinery, J Chem Technol Biotechnol 82 803 (2007)
5 L E Manzer, Biomass derivatives: A sustainable source of chemicals, J Bozell and K Patel, eds, in Feedstock for the Future, ACS: New York 40–51 (2006)
6 AJ Ragouskas et al, The path forward for biofuels and biomaterials, Science 311 484 (2006)
7 T Werpy and G Petersen, Top Value Added Chemicals from Biomass, technical report No. DOE/GO-102004-1992, National Renewable Energy Lab, Golden, CO USA (2004) available at: www.osti.gov/bridge
8 V Budarin, JH Clark, R Luque and DJ Macquarrie, Versatile mesoporous carbonaceous materials as acid catalysts, Chem Commun 634 (2007)
9 V Budarin, R Luque, D J Macquarrie and J H Clark, Chem European J, 13 6914 (2007)
10 DJ Constable et al, Green chemistry measures for process research and development, Green Chem, 3 7 (2001)
11 N Tanchaix and W Leitner, Supercritical carbon dioxide as an environmentally benign reaction medium for chemical synthesis, JH Clark and DJ Macquarrie, eds, in Handbook of Green Chemistry & Technology, Blackwell: Oxford 482-501 (2002)
12 B Nowack, Environmental chemistry of phosphonates, Water Research 37 2533 (2003)
13 FEI Deswarte, JH Clark, JJE Hardy and PM Rae, The fractionation of valuable wax products from wheatstraw using CO2, Green Chem 8 39 (2006)