EFFICIENT MATERIALS UTILIZATION

Efficient Materials Utilization Assessment
Exploratory Studies on the Reuse of Gypsum and Recovery of Sulfur Products from Scrubber Residues from Utility Coal Combustion
Control of Mercury Emissions from Coal Fired Power Plants Using Fly-Ash-Derived Carbon
Clean Combustion of Manufacturing Residues in the Forest Products and Photographic Industries
Recycle of Lead and Base Metals from Metal Wastes of Brass Foundries
Pollution Prevention of an Electrodeposition Coating and Pre-treatment System
Amphophilic Solvents for Pollution Prevention
Means for Producing an Entirely New Generation of Lignin-Based Plastics
Oil Recovery From Cutting Fluids
Assessment of an In-Line Copper Recovery Technology as a Waste Reduction Strategy for the Metal Finishing Industry
The Mass Transfer Behavior of Unconfined Membranes
Membrane Module Design for the Pervaporation of Acetic Acid
Agglomeration of Granular and Fine Particulate Industrial Wastes

Goals: The goal of this ongoing project is the development of efficient materials utilization systems to assist selected industries to meet pollution prevention goals. They include the characterization of industrial residuals to be used for the development of efficient material utilization methods. These methods will ultimately be used to identify potential markets for the materials studied.

Rationale: Past industrial residual management practices, including the landfilling of solid residuals, is presently complicated by several environmental and economic issues. These issues have made this type of solid waste management option unattractive. The development of efficient material utilization methods for pollution prevention for industrial residuals will ultimately provide an alternative for handling solid wastes generated by specific industries. Only upon a complete characterization of these materials can efficient material utilization options be explored.

Several residuals, including municipal waste combustor (MWC) fly ash, are currently landfilled due to a lack of a better solid waste management option. MWC fly ash currently releases RCRA regulated metals above regulatory limits upon conduction of the EPA's Toxicity Characteristic Leaching Procedure (TCLP) making them difficult and expensive to manage. Only upon the identification of the sources of these metals can effective pollution prevention efforts be made. This information can then be used to modify industrial processes or input stream sources to minimize or eliminate the soluble forms of these metals from the solid residuals produced.

A large portion of the coal fly ash produced is currently landfilled due to the limited utilization of this material. This is a result of the lack of a reactivity-based classification system for coal fly ash which could be used to facilitate the use of this material in portland cement based concrete. Only upon a complete understanding of the mechanisms responsible for reactivity can the utilization of this material be increased.

Approach: The activities for this project include research efforts focusing on the chemical and physical characterization of MWC and coal fly ash using a variety of leaching analysis, particle separation, electron beam microscope, and X-ray diffraction analytical techniques. Research regarding MWC fly ash has included identification of lead bearing compounds since this toxic metal has been shown to leach out above EPA regulatory limits. Research regarding coal utility fly ash has focused on the characterization of glass bearing phases which contribute to pozzolanic activity in portland cement concrete.

Status:

MWC Fly Ash: Fly ash particles were extensively analyzed using a number electron beam and X-ray analysis techniques. Lead bearing phases within ash particles were found to be present in three primary forms: 1) well defined lead rich inclusions exhibiting no specific crystal habit, 2) in lower concentrations in sodium chloride and potassium chloride crystals exhibiting cubic and hopper shaped habits, and 3) in low concentrations in a porous chloride matrix. Lead phases were found to be reasonably well distributed in all particle size fractions. A small number of other elements were found to be frequently associated with the lead-bearing phases.

Using the temperature profile of the combustor, a thermodynamic approach was used to help explain the microscopic observations. Catalytic distillation is suggested as a reasonable mechanism for the transport of lead in the combustor. Results indicate that plastics are the most likely contributors of the lead in MWC fly ash.

Previously leached ash samples were analyzed in the electron microscope and compared to unleached samples. Results indicate that a large fraction of the lead phases within ash particles become mobile when exposed to a leaching medium. The lead phases appear to be redistributed within the particle matrix rather than remain entirely within solution. This confirms predictions made earlier in this project that adsorption-desorption mechanisms control the leaching of lead from MWC fly ash.

Powder X-ray diffraction was used to identify the major phases present. Recommendations were made for a preferred analytical procedure to be followed by other researchers so that a common inter-laboratory agreement could be made on the composition of MWC fly ash. Crystallographic evidence was also presented to support the observed lead speciation.

Consistent with the particle morphologies observed, a general particle formation mechanism was proposed based on the agglomeration of smaller particles into larger aggregates. A chloride rich paste serves as the binder in these agglomerates.

The results of this research provide an improved understanding of the behavior of lead in a municipal waste combustor. This understanding is important to pollution prevent ion efforts directed at modifying combustion conditions or input sources so that MWC fly ash satisfies environmental standards.

Coal Fly Ash: As a result of a detailed study of the mechanisms responsible for the pozzolanic reactivity of coal fly ash in portland cement concrete, recommendations were made for a selective phase dissolution procedure to determine fly ash reactivity. It is expected that this procedure could serve as the basis of a new reactivity-based fly ash classification system to replace the current ASTM procedure. A new classification system based on expected performance would likely lead to increased utilization of coal fly ash in concrete.

Exploratory Studies on the Reuse of Gypsum and Recovery of Sulfur Products from Scrubber Residues from Utility Coal Combustion:

Goals: Demonstrate by thermodynamic calculations and by bench-scale studies that the combination of two waste products, pyrite coal-spoil and electric utility scrubber wastes (gypsum sludge), can result in a valuable products; namely, sponge iron and lime.

Rationale: Currently, the primary method for achieving environmental standards for flue gas cleanup is by contact with lime or limestone in wet scrubbers, and in developing technology by limestone and lime injection during coal combustion. Both approaches increase the volume of solid wastes in the form of un-reacted lime and gypsum, which must currently be land-filled. Also, in the process of mining high-rank Eastern coals, inorganic sulfur, in the form of the mineral pyrite, is physically removed and stockpiled. Physical removal of pyritic sulfur, however, presents a critical problem: the pyrite reject is a potentially hazardous waste. It cannot be allowed to be exposed to air oxidation and rainfall as this can result in release of soluble toxic elements to streams and groundwater. A general practice of pyrite removal from high sulfur coals would produce millions of tons of pyrite annually. For example, sulfur disposal from a 600 MW power plant, fed with the above coal at an assumed rate of 1.7 million tons per year, is estimated to yield 66,000 tons of rejected pyrite and 283,000 tons of refuse per year. Considering the 200 million tons of coal mined annually, removal of pyrite would result in about 7.5 million tons of pyrite containing 3.8 million tons of sulfur. In addition, the flue gas desulpherization (FGD) waste would be reduced from about 38 million tons to 18 million tons. Even with efficient pyrite removal from high sulfur coals, the problem of flue gas waste disposal remains. In the years since passage of the Ambient Clean Air Act of 1970, and its 1977 amendments, impoundment of FGD waste has involved hundreds of millions of tons of solids and the purchase of about 40 percent of its weight in lime, or 70 percent limestone. In addition to the costs of reagent and disposal, tens of thousands of acres of land have been removed from productive use to accommodate the wastes created. For example, earlier low solids sludge impoundments for a 2000 MW power plant required about 500 acres for disposal of combined FGD and fly ash solids for a 30-year plant life. Such impoundments impose the risk of continuous leaching of environmentally undesirable constituents into the groundwater and streams. The final report, which has been written on this program, indicates that the following potential benefits can result from implementation of this study: 1) Recycle lime and hence reduce its consumption (which also reduces the quantity of carbon dioxide produced in the production of lime from limestone), 2) Recover sulfur from gypsum wastes as a valuable by-product, 3) Produce iron from pyrite wastes, which would otherwise result in acid mine drainage, and 4) Prevent gypsum from contaminating utility fly ash which could otherwise be used in pozzolanic cement.

Approach: This study has explored the first three of a four-step combined-approach for incorporating pollution prevention at the mine and utility sites to combine wastes in a creative and innovative manner. The four steps consist of the following: 1) Physical beneficiation of high-sulfur coal to remove pyrite and reduce ash content, and separation of reaction products from step 2; 2) Pyrometallurgical co-processing of the pyrite and flue gas desulfurization waste to produce sponge iron or cast iron, sulfur and lime products; 3) Recycling of the lime to complete the process cycle; 4) Evaluation of coal mining and utility industries to determine whether market potential and acceptance of this approach can be implemented. The overall reactions which make up this process cycle are as follows:

Reactions in Overall Coal Processing and Desulfurization Cycle

1. FeS2 --> FeS + .5S2

2. FeS + C + CaO --> Fe (sponge) + CaS + CO

3. CaSO3 --> CaO + SO2

4. CaS + 3CaSO4 --> 4CaO + 4SO2

5. CO + .5O2 --> CO2 (for process heat)

6. Net reaction [(1) + (2) + (4) + (5)]:
FeS2 + C + .5O2 + 3CaSO4 --> Fe (sponge) + 3CaO + 4SO2 + .5S2 + CO2

Status: Work is essentially complete with the issuance in June of a final report. The reduction of FeS with carbon in the presence of lime has favorable kinetics above 950 degrees C. A stoichiometric excess of lime and carbon in the initial mixtures enhances the rate of iron production and increases the degree of reaction completion. A novel method of magnetic separation of iron-calcium sulfide mixtures produced a magnetic concentrate containing 77.8 wt% iron and 4.1 wt% sulfur. Further research is required to reduce the sulfur content in the iron to meet steelmaking standards. The reaction between calcium sulfide and gypsum occurs quantitatively above 950 degrees C.

Control of Mercury Emissions from Coal Fired Power Plants Using Fly-Ash-Derived Carbon:

Goals: Studies have shown that the mercury emissions from a typical 500 megawatt (MW) plant are about 500 pounds (227 kilograms) per year. Some of this is captured in electrostatic precipitators (ESP), or flue gas desulfurization (FGD) systems, but most finds its way to the environment. The goal of this project is to explore the possibility of using fly-ash-derived carbon as an adsorbent to remove mercury coal fired boiler effluent.

Rationale: Several techniques have been considered to control mercury from flue gases. These efforts can be classified into three groups: metal amalgamation, liquid scrubbing, and sorbent adsorption. Adsorption is the most promising technique.

The challenge of mercury control lies in the characteristics of the gaseous streams. A successful candidate technique should be the one that is able to capture various forms of mercury (e.g. mercury vapor, mercuric chlorides, organic mercury, etc.) of very low concentrations (0.1 - 200 mg/NM3) from an extremely large flow rate (up to 1,300 NM3/S). Activated carbon has been used to enhance mercury control in incinerators in Europe and the United States for almost a decade. Utility-generated mercury is more difficult to control, because it occurs in the elemental form. Mercury from incinerators is usually in the more easily adsorbed form. Tests have shown carbon injection has potential for removing mercury from flue gases in the utility industry. The removal efficiency has been reported to be from 90% - 95%. However, the commercialization of adsorption processes depends mainly on the understanding of the adsorption mechanisms and the availability and cost of the adsorbents.

A potential base material for the production of adsorbents may be the carbon derived from fly ashes of coal-burning power plants. The potential is based on the following: 1) The carbon derived from fly ash, even without activation, already has a certain capacity to adsorb mercury vapor from flue gas. The preliminary test conducted at the MTU Institute for Material Processing (IMP) shows 90% mercury removal can be achieved using the carbon derived from fly ash. 2) Use of fly-ash-derived carbon may reduce the cost to produce activated carbon (AC). Since the volatile matter in coals have been driven off during the combustion process, it is likely that only activation is required to activate the residual carbon. Conventional AC production typically involves raw materials preparation (crushing and sizing), carbonization and activation. If fly ash carbon is used, the cost for raw material preparation and carbonization can be saved. 3) The technology to recover the carbon from fly ash has been developed. An IMP patented process can separate a high grade carbon from fly ash. The LOI of the recovered carbon can be as high as nearly 90%, and 90% of the carbon can be recovered.

The annual output of fly ash was 68 million tons in 1994. This is sufficient to insure an adequate supply of carbon. It is expected to reach 120 million tons in the year 2000. The average carbon content in coal-burning fly ash is currently 6 percent. The implementation of low NOx combustion technologies (CAAA requirement) will further increase the carbon content significantly. After removal/recovery of the carbon from the fly ash, the cleaned ash is a valuable material with wide applications (e.g. concrete, plastic fillers, refractories, etc.). The uncertainty of using fly ash recovered carbon to manufacture ACs is the trace metal content in the carbon. This will be addressed at the completion of this study.

Approach: The complete study will consist of three phases: I) characterization of the fly-ash-derived carbon, II) preparation of AC, and III) determination of process parameters for adsorption processes. In Phase I, emphasis will be on the evaluation of physical properties, chemical composition and adsorption capacity of the fly-ash-derived carbon, to include density, particle size and pore distribution, specific area, and the ability to adsorb mercury. The activation, including doping, of fly-ash-derived carbon will be conducted in Phase II. The recovered carbon will be activated or chemically impregnated to enhance mercury capture from flue gas. Comparison will be made between the fabricated carbon and the commercial carbons based on adsorption tests. In Phase III, a systematic study will be conducted to determine the process configurations and parameters for maximizing mercury adsorption at least cost. This includes the choice of using adsorption columns, or direct injection of carbon into flue gas, location of injection, the method to recover and regenerate the mercury-loaded carbons, and process economies.

Status: Phases I and II were started simultaneously. A lab simulation system is ready for the Phase III study. Measurement of specific area shows the source carbon, without any treatment, has an area of about 20 m2/g. Adsorption tests conducted on a fixed bed and isotherm studies indicated this carbon has an adsorption capacity of greater than 30mg mercury per gram and removal efficiency of 90% mercury has been observed in the fixed bed tests. The fabrication of a fluidized bed for activation of the carbons is in progress.

Clean Combustion of Manufacturing Residues in the Forest Products and Photographic Industries:

Goals: 1) Determine conditions for clean combustion of plywood and particleboard in laboratory-scale fixed bed combustor and compare to State guidelines; 2) develop emission factors for benzene, formaldehyde and other organic emissions due to combustion of plywood and particleboard; 3) determine conditions for clean combustion of photofinishing effluent in a laboratory-scale rotary kiln combustor; 4) collect and analyze inorganic products from 1) and 3).

Rationale: The wood products industries generate $180 billion in sales annually in the United States. Adhesives and other non-wood products added during manufacture may cause disposal problems. During primary and secondary manufacturing, waste trimmings are often burned to power the manufacturing process, and the final disposal of the product is often at an industrial power plant. Industrial boiler and incinerator facilities are having difficulty getting permits, and boiler companies are having difficulty meeting performance guarantees. This is due to emissions of volatile organics, and damage to the boiler due to slagging and corrosion when using manufactured wood products. Similarly, photofinishing is a large industry typically involving relatively small sites. Photofinishing plant effluents contain various organic and inorganic compounds, making disposal via municipal wastewater treatment inadequate. Combustion appears to be the only other low cost solution. The approach here is to concentrate the effluent by evaporation and incinerate it in a rotary kiln, thereby destroying the organics and binding the inorganics to the cement materials.

Approach: During the 1994-95 period testing continued using 11 mm pine plywood cubes in the 120 mm i.d. by 5 m long fixed bed combustor previously described. The cube feeder was improved so that the feed rate was accurately controlled and measured. The sensitivity of the gas sampling technique and the measurements with the gas chromatograph/mass spectrometer was improved. Similarly, tests continued with photofinishing effluent and other common materials (for comparison) in the 200 mm i.d. by 400 mm long rotary kiln combustor with a 130 mm i.d. by 3.6 m long plug flow reactor attached, and using the same gc/ms setup for emissions measurements.

Status: The work has been completed. The following conclusions have been drawn. For lean combustion of plywood the benzene emission factor was 7+15 g/g wood and the toluene emission factor was 3+5 g/g wood for furnace exit temperatures of 650C to 950 and residence times of 0.5 s to 1.5 s. For exit temperatures below 650C the benzene and toluene emissions increased rapidly. When the residence time was 2 s to 3 s, the critical temperature for increased benzene and toluene emissions was 450C. Emissions of formaldehyde were 205 g/g for lean combustion of plywood with exit temperatures above 500C and residence times of 1 s. For exit temperatures below 500C and for shorter residence times the formaldehyde emissions increased rapidly and emission factors over 1000 g/g. were obtained. There was little difference between wood, plywood, and particleboard for lean combustion. Benzene, toluene and formaldehyde emissions correlated with CO concentration, and emissions remained low provided the CO was below 4000 ppmv. This CO limit was five times higher than the CO limit of 800 ppmv suggested by the Wisconsin Department of Natural Resources for good combustion practice.

A laboratory scale rotary kiln incinerator was designed, built and made operational for solid, liquid and slurry feeds. Exploratory tests have been made. Emissions from wood, particleboard, polyvinyl chloride (PVC) and C-41 photofinishing effluent have been tested in more detail. The total ion chromatograms for the wood, particleboard and PVC show numerous aromatic compounds when the carbon monoxide level is high. The C-41 effluent has been tested at several conditions to date. No compounds are identified when the CO is low, but when the CO is high several organic compounds were identified above the 50 ppm level.

Recycle of Lead and Base Metals from Metal Wastes of Brass Foundries:

Goals: The primary objective is to develop and optimize a process by which brass wastes containing copper, zinc and lead can be recycled in-process or beneficiated into a valuable commodity for resale. The secondary goal is to investigate the feasibility of producing litharge (PbO) through a hydrometallurgical process, low temperature calcination, in which base metals are recovered from insoluble lead residues. As funding was acquired in the area of low temperature volatilization of mercury (Great Lakes Protection Fund--State of Michigan Department of Natural Resources) the project scope grew to include the removal of mercury from copper concentrates.

Rationale: Although this project dealt with a specific type of waste, namely lead-bearing wastes of brass foundries, the research was aimed at a more broad type of waste. The success of the project is measured by the amount of lead recovered from the waste and the amount subsequently converted to a more useful form. Currently, several thousand tons of this type of waste are generated and landfilled annually. The lead in brass wastes is in the metal form, but the approach of the process development would allow for other forms of waste to be treated. It is believed that a larger impact will be felt as the process is applied to other wastes, such as the recycle of lead storage batteries or the spent cupelas of fire assay laboratories. Currently these wastes are significantly larger in quantity.

Mercury is one of the most studied metal contaminants. The cycling of mercury is documented and quite well understood. The mercury recovery portion of the project would gain ground in the area of direct treatment processes to facilitate collection while not impacting a manufacturing process. Mercury appears in ores as elemental mercury and cinnibar (HgS). Each of these minerals often concentrate with the minerals of value. As these concentrates are processed to form metal, the mercury minerals are volatilized and emitted to the atmosphere. The process will be usable for any metal concentrate and will be generic enough to help lower the emission of mercury. Although the exact number is not known, some estimates place the amount of mercury lost during mineral processing to be as large as 3-4,000 lbs annually in the U.S. alone.

Approach: Initially, the optimal leachant had to be determined based on dissolution rate, separability, removal % and ability to reuse the leachants after processing. Sulfuric acid, ammonia hydroxide, hydrochloric acid, chlorine, and cyanide leachants are effective media used to dissolve Cu and Zn; selective leaching of lead by acetic acid may also be an effective process. Thermodynamics of lead in water suggested that lead sulfate, lead carbonate and lead hydroxide are the most stable precipitates which may be formed in solution. Reagent grade lead salts were purchased for experiments to produce PbO by low temperature conversion.

Concentrates from the Copper Range Company were acquired to test the low temperature removal of mercury. Elemental Hg and pulverized cinnibar mineral samples were blended with samples of the concentrate. These samples were then heated to various temperatures in a sealed chamber. Air was flowed through the oven and subsequently sparged through a concentrated nitric acid solution to collect any volatile mercury. The solution was analyzed for mercury so that a mass balance could be closed. Recovery of mercury was determined as a function of source type (Hg or HgS), temperature (350-550oC), air flowrate, and duration of heating.

Status: Sulfuric acid with air and small amounts of copper ions produced the best results in which the leaching of copper and zinc was accomplished. Full recovery of the copper and zinc is accomplished using a two-step electrowinning process on the leach solutions. Nearly pure copper (99.9%) is plated initially, followed by a plating of the zinc from solution. In addition, less than 0.6% of the lead is lost and 100% of the residue was lead sulfate. Sodium carbonate mixed with lead sulfate resulted in complete conversion of the sulfate to lead carbonate. Results of roasting studies conducted on lead carbonate found that at low temperatures (400-450oC) complete conversion to PbO (both litharge and massicot) could be accomplished in less than 1 hour. The significance of these results is a novel, low cost process to produce PbO from virtually any lead source (waste or raw material). Current economic estimates of the process show that PbO could be made for as low as $0.26 per pound. Given the current rate of PbO varies from as low as $0.20/lb to as high as $1.00/lb, this may be significant savings for the company. The process is being applied to the waste crucibles of gold mining operations which contain large amounts of lead. The wastes will be stripped of the lead, and the lead will be processed to recover litharge for reuse in the assay process. In addition, funding is being sought from the International Lead Zinc Research Organization for the application of the process to recycle lead storage batteries, as well.

The mercury volatilization experiments lead to similar successes. Not only could 100% of the elemental mercury be recovered at temperatures of less than 400oC, but the cinnibar was broken down as well. Optimization of the process found that 5N HNO3 was required to effectively strip the mercury from the gas. Treatment of the solution with zinc powder recovered all of the mercury in a reduced state. Further work is being conducted to automate the recovery process.

Pollution Prevention Assessment of an Electrodeposition Coating and Pre-treatment System:

Goals: The goals of this project are to: 1) assess the net environmental benefits of using a water-borne electrodeposition (E-Coat) paint process, instead of conventional organic solvent-based spray painting for metal products in manufacturing plants; and 2) identify refinements in operating procedures, process control, and treatment technology to enhance pollution prevention and waste minimization in E-Coat systems.

Rationale: The potential for major reductions in air emissions has made electrodeposition paint coating (E-Coat) technology a leading alternative to conventional solvent-borne spray painting for metal parts in manufacturing. Additional pollution prevention opportunities exist, however, especially with regard to wastewater and solid waste pollution problems. Contaminant loading of certain organic compounds, phosphorus, heavy metals, and dissolved and suspended solids in wastewater may be increased as a result of discharges from the water-borne E-Coat system and associated processes. Significant volumes of solid waste also are generated as process residuals and wastewater treatment sludge. This project is identifying methods to minimize the overall environmental impacts of an existing, state-of-the-art E-Coat paint and pre-treatment system, while maintaining coating quality and process efficiency.

Approach: Environmental impacts and pollution prevention opportunities are being evaluated and quantified in a four-phase study for an E-Coat system at Onan Corporation, a manufacturer of electric generators. The first phase involves assessing the impacts of the change from spray painting to the E-Coat process on air emissions. Air emissions inventory data for 1993 are being used for the spray painting baseline. A materials balance approach will be used to estimate E-Coat air emissions based on a combination of vendor-supplied data, measured material usage rates, and measured VOCs in wastewater discharges. In the second phase, baseline information will be developed to characterize and quantify wastewater discharges and solid waste production from the E-Coat system under its existing mode of operation. This involves a variety of in-plant and laboratory measurements, flow monitoring activities, and tracking material and chemical usage rates. Data will be gathered to characterize the variability of discharge characteristics on both short-term (hours) and longer-term (weeks to months) bases. Generated data will be evaluated to identify and prioritize target areas for additional pollution prevention and waste minimization. Phase three will develop simulation models of the E-Coat system or portions of the system to identify and evaluate potential pollution prevention and waste minimization measures. The modeling will use existing software (such as Stella), or new models will be developed as needed. In the fourth phase, waste discharge and production data will be gathered to evaluate the actual effectiveness of operational changes installed in the E-Coat system as a result of the findings from phases two and three.

Status: Work began on this project in late FY1995. A detailed work plan and a time table for the work have been established. Inspections of the E-Coat facility were made by all project participants to familiarize them with the E-Coat system. Sampling and monitoring equipment has been ordered. Library research has been done to find analytical methods for organic acids and glycol ethers -- chemicals used in the E-Coat system that are of concern as contaminants of the waste stream. Data on plant operating conditions have been assembled by Mr. Dhennin.

Amphophilic Solvents for Pollution Prevention:

Goal: This research will develop new solvents which prevent pollution. These new solvents are non-volatile, and can be made soluble in water by varying process conditions, like pH or temperature. These new solvents can be easily recycled.

Rationale: Solvents are used in a variety of industries. They are used to apply paints and inks, to separate and purify products, to effect chemical reactions, and to clean equipment. At one time, industrial solvents were largely discarded after use. This is now too costly, in both financial and environmental items. While most solvents are now partially recycled, much is still lost. For example, one medium-sized drug plant buys 10 million kilograms of new solvent per year at an average cost of $2.00 per kilogram. The techniques that are used to recycle solvent, such as distillation, extraction, and adsorption are often expensive and can create secondary environmental hazards themselves.

Approach: The new solvents will be modeled on a new, commercially-used ink developed by the Deluxe Corporation. While most commercial inks require organic solvents for cleanup, this new ink may be washed with water. The ink consists of an oil, a resin, and other species including pigments. The key to the new ink is the resin and its interaction with the other components at different pH levels. The resin is an amphophilic molecule. This means that it has both hydrophobic (water-hating) and hydrophilic (water-loving) regions. The resin's hydrophilic region consists of carboxylic acid groups which are not sufficiently hydrophilic to make the molecule water soluble. This is good, since the ink must not be water soluble while printing. With the addition of a basic wash, the resin becomes a water-soluble soap that can emulsify the oil in the same way that a dish-washing detergent emulsifies grease to clean pots and pans. The resin/soap molecules surround droplets of oil; their hydrophobic groups, which are compatible with the oil, point toward the oil, and their hydrophilic groups are oriented toward the water. These droplets of oil, surrounded by resin, are suspended in the water solution. The ink is thus washed from the printing press with a water wash.

The planned research will develop a scientific basis for the ink's action, and will expand this concept to design solvents for other industries. The research focuses on two areas: thermodynamics and kinetics. Thermodynamics concerns itself with the stability of the system; can the system form a stable emulsion or solution in water? Kinetics concerns itself with the rate of the process; how fast will the system solubilize? In order for a solvent system to be effective, it must work quickly. It does no good to have a stable system whose formation time exceeds the typical time required to prepare conventional inking systems. Both thermodynamic and kinetic considerations must be examined in order to design the best solvent systems.

Status: Research on thermodynamics has focused on model compounds, and developing fits for the experimental data for these compounds. In order for a mixture to be stable as one phase, the Gibbs' free energy of mixing for the mixture must be negative, and its second derivative, with respect to composition of each of the components, must be positive. That is, the free energy surface of the mixture must be concave in the upward direction in order to ensure mixing. The free energy is modeled with two contributions: an entropic contribution which favors mixing, since a mixture is more 'disordered' than the pure components; and an enthalpic contribution, or heat of mixing, which often inhibits mixing. When two components are dissimilar, they tend not to mix; the result is a positive heat of mixing. By calculating these entropic and enthalpic contributions, and determining which compositions will produce solutions (one phase), and those which will not (two or more phases), we can begin to design new solvent systems.

Research on kinetics recognizes that the Deluxe ink in the basic wash is not a thermodynamically stable system, but a metastable macroemulsion. The kinetic experiments focus on the rate of emulsification of the ink, and its response to several factors:

1. Initial pH of solution
2. Concentrations of resin and oil
3. Stirring rate
4. Resin composition

The preliminary experiments yielded the following results:

1. When the initial pH is increased, the neutralization rate also increases.
2. When the initial concentration of resin in the oil is increased, the rate first increases and then decreases.
3. When the stirring is increased, the emulsification rate increases to a maximum value.

Means for Producing an Entirely New Generation of Lignin-Based Plastics:

Goal: The goal is to develop the basic technology necessary for establishing a plant where the first biodegradable plastics that are truly lignin-based can be manufactured. The industrial byproduct, lignin, for producing these plastics, will be isolated from kraft black liquor generated by a pulp mill in International Falls, Minnesota.

Rationale: The conversion of wood chips to pulp for manufacturing paper generates huge quantities of byproduct, lignin, annually in the United States. The kraft process is still the method that is primarily employed for the purpose by the pulping industry. The best estimates indicate that more than 26 million tons of kraft lignin are generated as byproducts of pulping operations every year. As steps have been taken to maximize production, the recovery furnaces, in an ever increasing number of mills, have become overloaded; the result is that all the byproduct lignin can no longer be used in its traditional role as a fuel. Unfortunately, the necessary capital investment usually precludes construction of a new recovery furnace, so that there is little prospect of rectifying the situation in the majority of recovery-loaded mills. Even though untreated black liquor cannot be discharged directly into rivers, an exacerbation of pollution originating from pulp mills is likely to occur. It is difficult to envisage a more compelling way of responding to the problem than by creating biodegradable plastics from the kraft lignin in surplus black liquor.

Intensive efforts devoted to incorporating lignin preparations into useful polymeric materials have been under way for almost twenty years in a number of laboratories. Generally the most encouraging formulations have resulted from chemical modification and covalent linking into polyurethanes, phenol-formaldehyde resins, epoxies, acrylics, etc. In other cases, promising blends, involving the lignin derivatives themselves, have been created. Despite the judicious schemes devised for fractionating and derivatizing the lignin preparations employed, the optimum lignin contents in these polymeric materials have typically fallen in a range of 25 to 40%.

An approach has now been developed at UM for formulating blends containing 85% underivatized industrial kraft lignin that possess Young's moduli around 1 GPa. Nothing like it has ever before been achieved. The strength properties of these new plastics vary monotonically with the degree of intermolecular association between the constituent kraft lignin components. Thus this marks the birth of the first generation of polymeric materials that are truly lignin-based.

Approach: The successful formulation developed at UM for fabricating 85% industrial kraft lignin based plastics involves solvent casting (in aqueous 82% pyrrolidine) of blends with polyvinyl acetate and two plasticizers (diethyleneglycol dibenzoate and indene). Polyvinyl acetate is a commonly used polymer that, for example, provides the basic material in the familiar white glues where it is present in emulsion form. Solvent casting does not represent a suitable method for producing plastics in an industrial context, but a promising alternative approach is provided by spray-drying aqueous (water-based) kraft lignin solutions into which the polyvinyl acetate has been introduced as an emulsion. Thus, two commercially available polyvinyl acetate based emulsion products have been selected for blending with kraft lignin, "Elmer's Glue-All" (Borden) and "Advantage 1" (Franklin International); the latter contains formaldehyde as a crosslinking agent for greater durability.

The present feasibility study will be completed by employing the spray-dried powders in compression- or injection-molding trials dedicated to fabricating components for tensile testing. Here the impact of degree of association and crosslinking between the molecular constituents in the kraft lignin preparation will be explored upon the mechanical properties of the new biodegradable plastics produced.

Status: The compositions of the commercially available polyvinyl acetate based emulsion products, chosen as blend components in the spray-dried powders sought for the present work, differ from the pure polymer and two plasticizers that yielded the first successful formulation for the 85% kraft lignin based plastics. Accordingly, for the purposes of mechanical testing, 85% kraft lignin containing materials were fabricated in the forms of blends with both the Borden and Franklin International polyvinyl acetate based emulsions. The plastics cast in aqueous pyrrolidine exhibited Young's moduli that were unexpectedly 40% to 85% lower in magnitude than those cast in water solution, but the tensile properties of the latter are suitable for spray-drying trials since they were quite similar to the materials blended with polyvinyl acetate, diethyleneglycol dibenzoate and indene.

A previous error in characterizing the molecular weight distributions of the kraft lignin preparations incorporated into the new plastics has been rectified. It has hereby become evident that both the Young's modulus and stress at yield point are approximately linearly dependent upon the weight-average, rather than number-average, molecular weight. Such structure-function relationships will be very important in predicting the mechanical properties of new series of formulations for kraft lignin based plastics.

Oil Recovery From Cutting Fluids:

Goal: To determine whether membranes can be used effectively for the recovery of the oil content of spent cutting fluids. To characterize the factors that affect oil separation, and provide the information needed to determine whether membrane technology can be an effective pollution prevention and source reduction technology for the metal machining industry.

Rationale: The recovery and reuse of the oil content of the cutting fluids generated in machining shops will have several benefits: 1) the lifecycle of the oil used in the machining processes will be extended, 2) the amount of waste generated by a machining facility will be reduced, and 3) the oil content of wastewaters will be reduced.

Approach: Cutting fluids are designed to be very stable. High concentrations of surfactants are added to the oil and water so that a stable emulsion is formed. This fluid is used to lubricate and cool the parts being machined. Spent cutting fluids can be treated with acids and coagulants to crack the emulsion and separate the oil and water phases. Most oily wastewaters contain only a small concentration of oil (typically less than 5%), so this treatment results in an oily sludge and a large volume of strongly acidic water, both of which require further treatment before they can be disposed of safely. This conventional approach does not lend itself to oil recovery.

Recently, the use of ultrafiltration has been used to remove trap oil and solids from cutting fluids, however, they are prone to fouling by the free oils. In addition, the oil concentrate still needs to be disposed of and a large volume of water must be treated to separate a small (<5%) amount of oil.

In this study, we use a different approach. The hollow fiber membranes are treated to make them selectively transport oil and reject water. They are then used to separate the small concentration of oil from the spent cutting fluid. The approach is based on earlier work, conducted at UM, that showed oil saturated membranes reject water, but transport oil.

Status: Work was initiated at the end of FY1995 on this project.

Assessment of an In-Line Copper Recovery Technology as a Waste Reduction Strategy for the Metal Finishing Industry:

Goal: To investigate the ability of Continuous De-Ionization (CDI) to recover copper sulfate and purified water from acidic copper-rich electroplating rinsewaters for reuse with in the same process.

Rationale: By recovering and reusing copper sulfate and purified water from the rinsewaters generated in plating shops, the discharge of pollutants from acidic copper electroplating rinses can be eliminated. This novel approach would also eliminate the need to purchase, handle, and eventually dispose of treatment chemicals presently used in conventional and ion exchange treatment of these rinsewaters.

Approach: Electrodeionization (also known as continuous deionization or CDI) produces water using a combination of ion exchange resins and ion exchange membranes. Alternating cation and anion membranes are configured in a stack arrangement. Mixed cation and anion exchange resin is placed in selected compartments to which the feed solution is introduced. Cations and anions are removed by the resin, and direct current placed across the membrane stack results in the movement of the ions through their selective membranes into adjacent compartments, where the ions become concentrated. The effluent from the compartment containing the ion exchange resin is the product.

The process can produce extremely high purity water (18 MW-cm), but its biggest advantage is that it can dramatically reduce the amount of waste generation. Conventional lime precipitation can generate large volumes of hydroxide sludge that is difficult to handle and expensive to dispose of. In addition, the metal content of the rinsewater is lost. With CDI, both the water and copper are recovered and recycled directly by installing the system directly into the plating line. No waste is generated.

Status: Work was initiated at the end of FY1995 on this project.

The Mass Transfer Behavior of Unconfined Membranes:

Goal: To collect the information required to develop a more efficient membrane contactor in which the membranes are not constrained by a modular housing. To characterize the mass transfer behavior for hollow fiber membranes when they are not housed in a shell.

Rationale: In order to obtain very high mass transfer rates in membrane modules, it is necessary to use a large amount of membrane area per unit volume, and to create fluid flow conditions that encourage high shear rates at the membrane-water interface. As a result, membrane modules typically have high pressure drops across them and the energy input required for mass transfer is high. If the membranes are not confined within a housing, the energy requirements can be reduced dramatically and, although the mass transfer kinetics may drop somewhat, the overall cost of separation should be reduced.

Approach: To optimize the design of a membrane contactor, it is necessary to have detailed information about the factors that influence the mass transfer rates of the membrane, and while this information is available for all kinds of membrane contactors, none is available for membranes that are not housed within a shell. This study examined the mass transfer behavior of unconfined membranes as a function of different operating conditions and fluid flow regimes. Sealed hollow fiber membranes were placed in the vicinity of a submerged jet so that the turbulent flow generated by the jet fluidized the fibers and good contact between the fibers and water was encouraged. The mass transfer behavior of the fibers was measured for different operating conditions (e.g. flow rate, temperature, etc.) and design configurations (e.g. jet diameter, fiber length, etc.). These data were reduced to a single, dimensionless correlation that can be used for design purposes. The energy losses associated with the unconfined membrane configuration were measured and compared with the energy losses in tubular membrane modules.

Status: The research for this project is complete, and the results are being prepared for publication. The study examined the behavior of membranes used for gas transfer and for solvent recovery but the results of these studies are presented in non-dimensional form, so that they are generally applicable.

Membrane Module Design for the Pervaporation of Acetic Acid:

Goal: The aim of this project is to construct the best membrane module for the separation of acetic acid from water by pervaporation. Pervaporation is the process where a liquid mixture is evaporated across a selective membrane, giving a combined selectivity from the difference in volatilities and from the membrane. This membrane is held in a membrane module which keeps the liquid mixture on one side while the vapor is removed from the other. The module can take a variety of configurations.

Rationale: Acetic acid is one of the top 20 organic intermediaries in the chemical industry and is commonly found in small concentrations in aqueous waste streams. Distillation, the current separation method, is expensive, especially for small concentrations, so the streams are commonly dumped into the environment. If a more economical separation method could be found for removing the acetic acid, then it would become cost effective for companies to separate the acetic acid, because they could then sell it for other uses. Thus, such a process would be economically and environmentally advantageous.

Approach: The first part of the research is to find a membrane that will preferentially pass acetic acid over water in a pervaporation system. Such a membrane would have to exploit the differences between water and acetic acid. For this reason some obvious choices are basic membranes, ion-exchange membranes and organic membranes. The three dimensional Hansen solubility parameters can also be used as a guide to tell what materials would be more compatible with acetic acid than with water. Once a suitable membrane has been found, experiments will be done with it in a hollow fiber membrane module, because this geometry offers the greatest promise for high flux per membrane area and hence, cost efficiency. A hollow fiber module is made up of very small membrane tubes with one phase on the inside and the other on the outside. After the mass transfer is better understood for that system, experiments can be done trying to maximize performance. These could include installing baffles for directing flow, using an inert sweep stream for removing the vapor, trying different vacuum locations, and installing turbulence generators.

Status: The experiments in this project were to find an acetic acid selective membrane. Basic membranes and ion-exchange membranes were explored and were unsuccessful. Later work was in the area of organic membranes and polymers chosen by the Hansen parameters, such as polyethylacrylate. These experiments failed to turn up anything positive either. We also looked into polymerizing solvents used for acetic acid liquid-liquid extraction, but found this to be impossible. The only membrane material that we came across which is selective for acetic acid is polydimethylsiloxane. This material only has a selectivity of around two, which is too low for any kind of serious application. At this point, May 1994, the funding which we had been receiving from CenCITT expired. This, combined with the lack of success, caused us to abandon the acetic acid research. Since this time, we have continued the module design research under other funding, looking instead at removing VOCs from water; an area which has been much more successful.

Agglomeration of Granular and Fine Particulate Industrial Wastes:

Goals: The project has three main objectives: 1) To improve the removal of inorganic fine particulates from waste streams; 2) To control the composition of the particulate wastes by physical separation, which will simplify utilization while reducing the amount of hazardous waste produced, and; 3) To improve the handling characteristics of the particulates by pelletizing them into a coarser, more easily handled and utilized form.

Rationale: Many industries produce wastes that consist of fine particulates, for example, coal-fired power plants (fly-ash, and flue-gas scrubber sludge), foundries (bag-house dusts), and chemical plants (wastes from the manufacture of emulsions, pigments, and other colloidal dispersions). It is important not only to remove these particulates from air or water to prevent pollution, but also to recover them in a form that can be utilized easily, so that it will not be necessary to dispose of them in landfills. Recovery and re-use of these particulates is complicated both by their small size (which makes removal and handling difficult), and by their highly variable quality. Recovery of these wastes in a purified form will make their utilization much more attractive to industry. These wastes also have properties that make them useful as binders for making pellets from other particulates. This application can provide a significant means of utilizing these wastes. For example, the pelletization of iron ore for blast-furnace feed consumed 558,000 tons of inorganic pellet binder in 1994, so there is a definite market for such binders if they can be produced at a low cost from fine particulate wastes.

Approach: Methods are being developed in this research to agglomerate fines from suspension, using selective oil agglomeration and electroflocculation to collect the ultrafines into loose floccules. The flocculated material is then formed into pellets, which are hardened both by chemical reaction and by sintering so that they can be handled and utilized. This project is also investigating the use of these ultrafine wastes as binders for manufacture of iron ore pellets.

Status: Electroflocculation was investigated for agglomerating silicone emulsions from wastewater. This process was found to be capable of recovering silicones from dilute suspensions with a high enough concentration that they could be recycled directly. Coal fly-ash was treated by a combined oil-agglomeration/froth flotation process to remove carbon, which is a troublesome contaminant which prevents many fly-ashes from being utilized. By using the proper reagents at a dosage of less than 0.5 kilograms/metric ton, the carbon content was reduced from an unacceptable 7% by weight to only 1.8% by weight, which is much less than the 2-4% by weight considered tolerable in most of the existing uses for fly-ash. The de-carbonized fly-ash has also been found to be suitable for formation of high-strength, light-weight sintered pellets, and shows promise for use as a binder component for formation of pellets of other inorganic materials. In particular, iron-ore pelletization experiments were carried out using equipment and materials contributed by industry, which closely replicates the performance of the full-scale pelletizing plant. Pellets were made from magnetite concentrate, using as binder the de-carbonized fly-ash produced previously. These pellets had dry-crushing strengths of 5.4 pounds force per pellet, which met the industrial specification of 5 pounds force or greater. This was a significant breakthrough, as iron-ore pellets of sufficient strength had never before been produced with fly-ash-based binders.

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