Section X  

Thermo-Depolymerization

Imagine being able to turn some of our biggest problem wastes cleanly and efficiently into products our advanced society needs anyway: pure water, clean-burning natural gas, refined oil, and purified minerals. Think of what a big difference it could make if all our old tires, outdated computers, plastic bottles, household garbage, agricultural and industrial waste, and even oil-refinery sludge could be recycled instead of piling up in a landfill. A process that could do all that could really make a difference in saving the planet—but such a process only exists in science fiction, right?

Maybe not. A company called Changing World Technologies recently made headlines by announcing the development of a process called thermo-depolymerization, or TDP for short. The company claims the process will handle just about any carbon-containing waste and yield minerals, gas, and oil, all with no toxic by-products and only a modest input of energy. And, as they are demonstrating at their pilot plant in Philadelphia, Pennsylvania, TDP does not rely on exotic machinery, complicated chemistry, or magic wands. Indeed, TDP is decidedly lo-tech, but the results at the pilot facility are amazing.

Churn vs. Burn: A New Approach to Processing Waste

The secret of TDP's success, claims Brian Appel, CEO of Changing World Technologies, is in the water. Other waste-processing technologies use high temperatures that boil off water and then melt or burn the waste material in order to break it down. Such processes are costly, because a lot of energy is needed to convert water to steam. They also tend to result in highly toxic by-products (see box). TDP, on the other hand, exploits water's ability to retain heat, and uses it to churn the offending waste into a kind of hot sludgy soup. This process is not much different than the geologic processes that produced our oil deposits in the first place, except that a batch of TDP oil can be cooked up in a few hours, instead of the millions of years needed by Mother Earth.

TDP begins when the waste (anything from turkey guts to old computers) is fed into a large grinder that pulverizes the incoming material. In the first-stage reactor, the material is mixed with water and cooked at about 500 degrees Fahrenheit, usually for about 15 minutes. To keep the water from boiling off at those temperatures, the reaction vessel is kept under pressure. The superheated soup is then released from the pressurized tank into a low-pressure environment, where the sudden drop in pressure causes the water to boil off. This steam is captured and its heat energy is used to heat more incoming waste, a recycling process that saves energy and thus makes the process more cost-effective. The water itself is pure and can enter municipal sewer systems without further treatment.

The remaining material, which consists of mineral and metal wastes as well as carbon-containing compounds (such as plastics, oils, and gases) is then ready to move on to a second-stage reactor. The solids (minerals and metals) settle out, and are collected for sale to various industries. What solids are collected depend on the incoming waste, so animal bones from a meat-processing plant might produce a calcium-rich waste, while ground-up appliances would yield metal solids. After minerals and metals are removed, the remaining carbon-rich compounds are funneled into a second reactor, which heats the mixture to about 900 degrees Fahrenheit to further break down complex molecules into simple hydrocarbon chains. The second-stage effluent is then separated by a distillation apparatus into gases, various oils, some residual water, and a pile of carbon powder. Methane gas (identical to natural gas that is pumped out of the ground) is captured and used to heat the water needed for the stage one reactor. As with the minerals, the oils collected depend on the nature of the waste being processed. The distillation apparatus is capable of separating gasolines, light oils, heavy dark oils, the water, and the carbon powder, storing each in individual storage tanks. Best of all, TDP does all this without generating any toxic emissions or other hazardous by-products.

The TDP process is not identical for every kind of waste. Scientists at CWT's demonstration plant have spent the last few years devising recipes for different waste samples. Waste with high water content, such as animal offal or plant waste from agriculture, is mostly broken down in the initial water-rich pressure-cooking stage. On the other hand, drier wastes such as plastics are processed mostly in the second-stage reactor. The waste treatment protocol therefore has to be experimentally optimized for each different kind of waste to maximize its efficiency. Time in each reactor, as well as optimal processing temperatures, need to be discovered by trial-and-error for each new waste sample.

The Carbon Cycle

Changing World Technologies claims that TDP will help slow global warming by keeping carbon out of the atmosphere. Most scientists believe that global warming is being caused in large part by carbon dioxide (CO₂) gas that is released into the atmosphere by the burning of fossil fuels. Slowing down or reversing this increase in global temperature will thus mean reducing CO₂ emissions from our cars and factories. But can TDP really help with such a monumental task? To answer this question we first need to understand how carbon functions in our ecosystem.

The carbon cycle is the accounting of how the element carbon, in various forms such as atmospheric CO₂ gas, aqueous carbonic acid in our oceans, and as a major component of living tissue, circulates through our global ecosystem. Carbon dioxide gas from the atmosphere is taken in by plants, which convert the CO₂ to solid biomass through photosynthesis. Carbon dioxide is released back to the atmosphere by respiration (animals breathing out), as well as through the chemical reactions of decay. Carbon dioxide is also exchanged between the ocean and the atmosphere through a reaction where CO₂ combines with sea water to create carbonic acid, a component of ocean water that keeps the oceans at a constant pH.

Carbon dioxide concentration in our atmosphere is very low, making up only about 0.04% of the air that we breathe. However, starting in about the year 1800, industrial processes started spewing carbon dioxide gas into the atmosphere. The carbon that had for millions of years been bound up in oil deep underground, suddenly started to be converted back to CO₂ at rates much faster than photosynthesizing plants could take it back out of the atmosphere again. Oil burning increased even more dramatically in the 20th century, with a concomitant increase in the concentration of atmospheric CO₂. Carbon dioxide is often referred to as a "greenhouse gas" because of its ability to trap heat. Compare temperatures on Earth with that of Venus, where the atmosphere is 96% CO₂ and temperatures reach a blistering 450 degrees Celcius (850 degrees Fahrenheit). Scientists worry that if much more carbon dioxide is pumped into our air, our planet could suffer a greenhouse effect as well, and become uninhabitable.

TDP proponents note that since the thermo-depolymerization process recycles carbon-containing materials that are already in use by our civilization, it can slow global warming. TDP, if widely implemented, has the potential to drastically reduce our need to pump oil, or carbon biomass, out of the ground. Instead of burning more crude oil, we use the carbon we already have (plant and animal biomass, and products that came from oil in the first place such as plastics—things which would eventually re-enter the carbon cycle as CO₂ anyway), and generate oil from that. Less carbon, less global warming. By this argument, implementation of TDP would have an added bonus: it would reduce or eliminate our dependency on foreign oil.

Waste Not, Want Not

Changing World Technologies promises that TDP can solve our municipal garbage problem. Americans are very good at making garbage. Each day each person in the country generates an average of over four pounds of the nasty stuff. We throw away 18 billion diapers each year; diapers that won't degrade in a landfill for 300 years. We also trash enough aluminum to rebuild our commercial airline fleet in three months, and enough plastic utensils every year to circle the globe 300 times—and old computers are getting to be a real problem. With machines becoming obsolete every few years or so, the pile of potentially toxic techno-garbage is growing higher all the time. We are running out of places to put the stuff, and transporting garbage thousands of miles to remote dump sites seems like a terrible waste of time, money, and energy. Few would argue that something needs to be done. This is one reason TDP is generating so much excitement. Currently, less than 10% of our garbage gets recycled. But clean, efficient TDP plants churning out useful compounds would be much better than unsightly landfills piled high with the detritus of human civilization—especially if those billions of tons of garbage could significantly reduce our $100 billion dollar yearly foreign oil habit.

The Future of Thermo-Depolymerization

Thermo-depolymerization appears to have a lot of promise, but is as of yet an unproven technology. Although CWT promises that TDP can handle about any kind of material except nuclear or radioactive waste, not everyone is convinced the process will perform as well as promised. And it won't instantaneously solve our garbage problems, either.

Even if the process works as efficiently as promised, full implementation of this technology will require time, and a large investment of capital. Thousands of TDP plants, large and small, would need to be built. And although CWT publicizes that TDP is at least 85% efficient (so that for every 100 units of potential energy bound up in your waste, at least 85 units emerge on the other side as useful oil or gas), there is no data that all of that energy could be extracted from different kinds of waste, and no independent verification of the efficiency figures provided by this small private company. Is the process really as wonderful as claimed?

Another recent claim of clean, readily available and limitless energy, cold fusion, has made the scientific community, as well as the public, extremely leery of energy-producing processes that sound too good to be true. With cold fusion, the scientists Pons and Fleishmann's 1989 promise of a room-temperature nuclear reaction set off a worldwide flurry of activity as scientists tried to validate the claims. In the end, the process, whatever it had been, proved irreproducible by even the best chemists and physicists, and grandiose claims of the cheap, limitless energy proved, as expected, too good to be true. Like cold fusion, it will take some real data to convince others that thermo-depolymerization is real.

The company's claim of slowing global warming also appears problematic. Their argument is based on the principle that leaving carbon (fossil fuels) in the ground will slow the emission of carbon into the air. However, even if TDP-generated oil is burned instead of its crude-oil counterpart, carbon is still being released from a solid state into gaseous CO₂, increasing the greenhouse gas's concentration in the atmosphere. It is not so much the total amount of carbon that is "above ground" that matters in global warming, but it is the amount present as CO₂ in the atmosphere. This point appears to be missing in CWT's accounting of the carbon cycle.

Meanwhile, CWT promises to have its first full-scale plant in Missouri, which will turn leftover turkey parts from ConAgra's Butterball plant into heating oil, up and running by late 2003. The U.S. government is also watching closely, and has awarded over $12 million in grants to aid TDP research. If the technology proves itself at test facilities and in small-scale trials like the ConAgra plant, and if the process is as efficient as claimed, conversion to TDP technologies seems inevitable, especially as concerns over foreign oil use and environmental concerns about garbage continue to escalate. The world is now watching, but only time will tell if this new "carbohydrate economy" will truly turn out to be the answer to saving our little blue globe from our own technology.

Copyright 2006, John Wiley & Sons Publishers, Inc.