Green Chemistry

In 1996, Mark Holtzapple of Texas A&M University received the Academic Award for the Green Chemistry challenge. This award was given to him for the development of a family of technologies that converts waste biomass into animal feed and industrial chemicals and fuels by adding lime to a fermentation process. This waste biomass includes municipal solid waste, sewage sludge, manure, and agricultural residues. As we all know all of these wastes are a serious threat to our environment as our population is increasing exponentially. Currently 209 tons of municipal solid waste is produced each year in the United States alone-EPA. All of these types of waste have little value or even a negative value, which means there is a very high cost asso

ciated with their disposal. The research that Mark Holtzapple has done in this field of study has the potential to significantly improve the condition of our environment and help solve our waste disposal problem. The conversion of waste biomass described in Dr. Holtzapple’s paper falls under focus area one of the Green Chemistry Awards, the use of alternative synthetic pathways, natural processes, and alternative feedstocks. The fermentation of the waste is an alternative pathway because it is used as a fuel and energy instead of being completely worthless and put in a landfill. The biomass is used as alternative feedstocks for cattle and various other ruminants. The entire process being used is a natural process because microorganisms are used to digest the waste. The entire process is also inherently safer for the environment because it reduces the chances of leaks at landfills and helps reduce methane gas from being produced at landfills. It also reduces the carbon dioxide emissions because its own emissions are balanced by photosynthesis.

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President Clinton announced the Presidential Green Chemistry Awards Challenge on March 16, 1995. It is designed to promote pollution prevention and industrial ecology through a new Environmental Protection Agency (EPA) design for the environment partnership with the chemical industry. This award recognizes accomplishments and promotes the research, development, and implementation of innovative green chemical technologies that have been or can be utilized by industry in achieving their pollution prevention goals. This program invites nominations that describe the technical benefits of a green chemistry technology as well as human health and environmental benefits. This program does not exclude anyone. An independent panel, chosen by the American Chemical Society, judges nominations for the awards. The award recipients receive national and public recognition for their accomplishments in their research, development, and implementation of green chemistry technologies. There are award amounts that range from $50,000 to $150,000 per award per year, but these are provided by EPA/NSF partnership for environmental research not the presidential awards program -EPA.

There has been research done for many years now on the conversion of waste biomass into fuels, but there have been drawbacks. Almost all commercialized processes are based on cornstarch. The starch is hydrolyzed with enzymes to make sugar, which is then converted into desirable products like citric acid and ethanol. Lignocellulosic feedstock has been used using the same process except sugar is produced instead of amylase. The problem is that cellulose is very difficult to hydrolyze, so much larger amounts of enzymes are required. The cost of cellulose is very expensive and economically unrealistic. The process that Mark Holtzapple has created does not use an extra enzyme. Instead the microorganisms make their own enzymes; this lowers the cost significantly. The very first step in Mark Holtzaples’ process of converting the waste biomass into more useful products is to treat it with lime to make the waste more “digestible”. Lime removes almost 1/3 of the indigestible lignin from lignocellulosic waste. When the lime is added to manure and sludge, lime saponifies the fats making them more digestible.

Agricultural residues treated with lime can be fed directly to ruminant animals like goats, sheep, and cows. Ruminant animals have microorganisms in their digestive tract that anaerobically converts biomass into carboxylic acids like acetic, propoinic, and butyric acids. The acids provide metabolic energy when they are absorbed into their blood stream. The lime treatment doubles the digestibility of their agricultural residues. Grains, the current digestible feeds of choice for the ruminant animals have devastating effects on the environment. Grain farming to produce feed causes soil erosion as well as leaching of fertilizers, pesticides, and herbicides into the groundwater. As an alternative, Mr. Holtzapple points out that the microorganisms in cattle can be utilized by industries to digest waste biomass in a fermentor , which in a sense is an artificial rumen. The acids produced during the digestion are neutralized by calcium carbonate to form the same salts the ruminant do.

These salts are concentrated and may be converted thermally into ketones like acetone, methyl ethyl ketone, and diethyl ketone. The acids can also be converted back into salts again with the reverse process. All the chemicals that are produced from this biomass process are oxygenates, which are hard to produce from petroleum because petroleum has no oxygen. The problem is that he oxygen has to be introduced, which brings a risk of explosion when the oxygen makes contact with petroleum. The oxygenates produced from biomass on the other hand, are very cost competitive when compared to petroleum derived oxygenates. Figure one shows the biomass conversion technologies. Another, alternative is for the biomass already treated with lime to be fermented where it is converted salts like calcium acetate, propionate, and butyrate. Then the salts are concentrated with a liquid sponge consisting of triethyl amine and methyl diethyl amine, which selectively absorb water from the fermentation process leaving the salts in a concentrated form.

Increasing the temperatures can regenerate these amines , which forces the water to leave the amine. This water can then be recycled back into the fermentation process. The concentrated salts are then chemically converted into fuels like carboxylic acids, ketones, and alcohol. The ketones produced from thermal conversion of the salts are not suitable as an automobile fuel even though they have high octane ratings. They would dissolve the polymers in the fuel of current automobile engines, but there is a way around this problem by hydrogenating the ketones to their corresponding alcohols. This hydrogen could be generated from natural gas or other renewable resources. Another significant advantage of fuels derived from waste biomass is that they are a way to control global warming caused by the combustion of fossil fuels. The carbon dioxide released from the combustion of biomass is balanced through photosynthesis because the waste would not be put into landfills where it always has the potential to leak into ground water and release methane, a greenhouse gas.

There are twelve principals the Green Chemistry Awards follow and each award given has fallen into these twelve principals in some way or another. The first principal is prevention, which states that it is far better to prevent waste then to clean it up after its created. The conversion of waste biomass into fuels and energy prevents waste from being put into landfills where there is a risk of leaking and methane being produced. It also prevents the mass production of carbon dioxide because the process produces an amount that can be reused by our environment through photosynthesis. Second, the atom economy states that synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product and Mark Holtzapple’s process is very efficient with no unusable byproducts. Third, the less hazardous chemical synthesis principal says that wherever practicable synthetic methods should be designed to use and generate substances that posses little or no toxicity to human health and the environment.

The process uses biological fermentation so that the process’ inputs and outputs are very safe to both human health and the environment. Fourth, designing safer chemicals says that chemicals should be deigned to effect their desired function and while minimizing their toxicity. Alcohol, one of the products of the process, is a safer fuel than traditional fuels made from oil and petroleum. Fifth, solvents and auxiliaries should be made unnecessary whenever possible. There are no toxic solvents or auxiliaries put into this process. The energy requirements of chemical processes should be recognized for their environmental and economic impacts and should be minimized. Sixth, if at all possible, synthetic methods should be conducted at ambient room temperature and under normal atmospheric conditions. The fermentation process is conducted under normal atmospheric conditions at room temperature. Seventh, the use of feedstocks or a raw material should be renewable rather than depleting whenever economically and technically feasible.

The use of waste biomass as the primary feedstock in this process allows us to avoid using nonrenewable petrochemical feedstocks. Eighth, derivatization is the use of blocking groups, protection /deprotection, and temporary modification of physical and chemical processes. Unnecessary derivativization should be minimized or avoided if possible because these steps require additional reagents and can generate waste. The process of normal fermentation requires minimum derivative. Ninth, catalytic reagents are superior to stoichiometric reagents. The use of lime in this process, although not a catalyst in the traditional sense, makes the biomass more digestible and therefore improves the efficiency and effectiveness of the process. Tenth, chemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist in the environment. There are no toxic or non-biodegradable byproducts in this process so that nothing will persist in the environment. Eleventh, Real-Time Analysis for Pollution Prevention are analytical methodologies that need to be further developed for real-time, in-process monitoring and control prior to the formation of hazardous substances.

This is the only principal that does not apply to Mark Holtzapple’s process because no hazardous substances are produced. Twelfth, substances used in a chemical process should be chosen to minimize the potential for chemical accidents, including release into the environment, explosions, and fires. The reaction here involves a naturally safe process: all of the inputs and byproducts are safe and nontoxic preventing and hazardous fires, explosions, etc. to occur. In summary, this is very “green” process. This technology displaces the traditional petrochemical distillation process that has very negative environmental impacts. By comparison, the old refinery process to produce fuel included three processes, separating the types of hydrocarbons present in crude oils into fractions of more closely related properties, chemically converting the separated hydrocarbons into more desirable fraction compounds, and purifying the products of unwanted elements and compounds.

The primary process for doing all this is distillation. Very large quantities of water are required in order to support the refinery operations. The water must be treated to remove harmful chemicals before it can be disposed of back into waterways. Each unit must be closely monitored because they vent out hydrocarbons, flue gases, and particulate matter that are all detrimental to the environment. As you can see the traditional method for producing fuel does not have any benefit to the environment and it always pose a threat to society and the workers because there is risk for explosion and the pollutants it emits to our environment. This process Mark Holtzapple has designed is a win-win situation for a number of reasons. First off, there are no harmful byproducts put into the environment unlike today’s traditional distillation process to produce fuel.

Also, the matter being used to produce the fuel would have otherwise been put into a landfill where it produces methane gas, takes up space, and can leak into the ground water. This new process uses no harmful chemicals and therefore poses as no threat to any workers or people involved in the process. You lose less environmentally friendly fuel and you are using discarded waste to produce a useable environmentally friendly fuel, alcohol. Fifty percent of United States petroleum is imported form foreign countries this new process will also help reduce the trade deficit. There is a considerable difference in the cost of the two methods, and lastly the fermentation process is considerable cheaper than the refinery process. This is a very Eco-efficient process.

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