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Chemical Processing in High-Pressure Aqueous Environments. 6. Demonstration of Catalytic Gasification for Chemical Manufacturing Wastewater Cleanup in Industrial Plants Douglas C. Elliott,* Gary G. Neuenschwander, Max R. Phelps, Todd R. Hart, Alan H. Zacher, and Laura J. Silva Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352
Catalytic gasification of organics has been demonstrated at the engineering development scale as an option for chemical manufacturing wastewater cleanup. A high-pressure (about 20 MPa) and high-temperature (about 350 °C) liquid water processing environment was used to treat wastewaters at two industrial sites. Organic byproducts from chemical manufacturing were converted primarily to methane and carbon dioxide in the presence of a fixed bed of nickel/ ruthenium catalyst. Test results with chemical manufacturing wastewater streams showed that this process could be effectively used with the appropriate catalyst to clean up wastewater and recover waste organics as useful fuel gas. Preliminary process economics were determined. Introduction Catalytic hydrothermal processing (250-350 °C, up to 22 MPa) can be used to treat chemical manufacturing process waters by converting the organic contaminants to gases. Known as the Thermochemical Environmental Energy System (TEES), this process can be utilized for both environmental cleanup and energy recovery. The system is operated as a liquid-phase, heterogeneously catalyzed process at nominally 350 °C and 20 MPa to produce a methane/carbon dioxide product gas from water solutions or slurries of organics. TEES is a registered trademark of Onsite*Ofsite, Inc., of Glendale, California, who holds the commercial license for operations in the U.S. and Canada. This technology is also available as Alligator 2000 under a separate license for parts of Asia. Earlier papers on the technology have addressed (1) the processing environment,1 (2) catalyst systems for this environment,2 (3) batch reactor tests with various organic chemical components and waste streams,3 and (4) continuous-flow reactor tests with fixed beds of catalyst in a tubular reactor.4 Here, we report the results of continuous-flow reactor studies in a mobile engineering development unit with chemical manufacturing wastewater streams at two industrial site tests. Background The use of hydrothermal processing (high-pressure, high-temperature liquid water) has received relatively limited study, but one application of this processing environment (TEES) has been demonstrated for catalytic gasification of organics. In this application, catalysts accelerate the reaction of organics with water and produce methane and carbon dioxide as the product gases. TEES has been reported both as a means of recovering useful energy from organic-in-water streams and as a water treatment system for dilute organic contaminants. Under the proper conditions, concentrated organics can be converted to useful fuel gas, or * Telephone: (509) 375-2248. Fax: (509) 372-4732. E-mail:
[email protected].
dilute hazardous organics can be destroyed. The offset of costs by energy recovery may make this waste treatment process economically attractive. Batch reactor test results have demonstrated process applicability to a wide range of organic components.2,5 Developing catalysts for this processing environment has also been an important factor in making this processing technology viable3, and two recent patents claim useful catalytic materials.6,7 Previous reports of continuous reactor tests of TEES include preliminary short-term processing results8,9 and later long-term and larger-scale processing results.4,10 This article provides additional results with two specific chemical manufacturing process streams: levulinic acid byproducts and a distillation bottoms stream. Preliminary cost estimates for the two applications are given based on the test results and industrial input. Experimental Section The equipment and procedures described below were used for the onsite testing of catalytic hydrothermal gasification of organics for wastewater cleanup in two chemical manufacturing plants. Equipment. Gasification tests were carried out in a fixed-bed catalytic tubular reactor. The mobile scaledup reactor system (MSRS) was based on the bench-scale design.4 It was a transportable system designed at a scale of 10 L/h of wastewater for obtaining engineering data for further scale-up of TEES. The MSRS, shown schematically in Figure 1, includes the reactor system mounted in a fifth-wheel trailer unit and also a small operations control and analytical room. Equipped with four fixed-bed tubular reactors, plumbed in series, and supporting equipment to achieve conversion, the test system’s actual flow rate ranged from 4 to 15 L/h. Design working conditions for the reactors were 350 °C at 24 MPa. The aqueous organic feedstock was loaded into the feed tank at the front end of the process. The 120-L tank had a centrifugal pump to fill it and an electrically driven paddle stirrer to agitate the contents. The feed stream was pumped from the feed tank through the tube
10.1021/ie980525o CCC: $18.00 © 1999 American Chemical Society Published on Web 01/23/1999
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Figure 1. Process schematic of mobile scaled-up reactor system and auxiliaries.
side of the heat exchanger by a positive displacement, reciprocating plunger pump. The heat exchanger was a double-tube heat exchanger that was constructed of 316SS tubing. With a total length of 17 m, the heat exchanger could bring the feedstock to within 60 °C of the final operating temperature. The final heating of the feed was accomplished in the coiled tubular preheater, which was enclosed in a cabinet fitted with ceramic furnaces. Once heated, the feed was routed to the four reactor vessels. The reactors were of a tubular fixed-bed design with volumes of 1.1 L each. After leaving the reactor(s), the product stream was routed through the outer tube of the double-tube heat exchanger to provide heat for preliminary heating of the feed stream. Downstream of the exchanger, the process pressure was reduced to ambient over a spring-loaded back-pressure regulator. The product stream then entered a liquid/gas separator tank, where process water was reclaimed and combustible gases were vented. Procedures. Actual startup of the experiment usually required 3-4 h to bring operating conditions to the desired levels. Operating data were recorded, and data windows were defined based on steady-state (or near steady-state) operating conditions. (a) Gas Analysis. Gas samples were withdrawn manually every 30-60 min. The gaseous stream was mainly composed of CO2, CH4, H2, and C2+ hydrocarbons, as well as water vapor. Gas analysis was performed by gas chromatography (GC) using a Carle AGC. A 1-mL gas sample loop was used for injecting gas into the chromatograph. The AGC used a set of three columns (80% Porapak N/20% Porapak Q, 50/80 mesh; Molecular Sieve 13X, 80/100 mesh; and 8% OV-101 on Chromosorb W AWDMCS, 80/100 mesh) with automatic switching controls to separate hydrogen, carbon dioxide, carbon monoxide, methane, ethane, ethylene, oxygen, and nitrogen. Propane and butane were detected in the backflush from the columns. A thermal conductivity detector was used in the AGC. Hydrogen was determined through the use of the Carle hydrogen transfer system, a metallic membrane for hydrogen separation by diffusion. The GC signal was processed in a SpectraPhysics 4290 integrator, which plotted the signal, integrated peaks, and determined retention times; it then printed a table of data that included peak identifications and gas composition based on previously analyzed standard gas mixtures.
(b) Calculation of Carbon Conversion to Gas. Once the gas samples from the experiments were analyzed, calculations were made to determine the conversion of the organic feedstock to gases. Carbon conversion to gas was then calculated on a mass basis for the carbon in the product gases as a percent of the carbon in the feedstock. (c) Analysis of Liquid Effluent. The liquid effluent was analyzed for chemical oxygen demand (COD) and pH, with spot checks for ammonia, sulfate, chloride, and trace metals, if needed. The COD method used was the dichromate closed-reflux colorimetric method, no. 5220D.11 The pH was measured by an electrode calibrated against buffered pH 4.0, 7.0, or 10.0 solutions. The ammonia analytical procedure involved the use of an ammonia-specific gas-sensing electrode (ORION 9512). The electrode was calibrated in 10 M NaOH. Sulfate analysis was based on the U.S. Environmental Protection Agency approved colorimetric method using the HACH SulfaVer reagent pillows. Ion chromatography (IC) was performed on some samples to verify the colorimetric method. Chloride was determined with an ion-specific electrode and was verified with IC. Trace metals were determined in an inductively coupled plasma, atomic emission spectrometer (ICP-AES). Aqueous samples were analyzed directly or with dilution with deionized water. Solid samples were digested with aqua regia acid prior to analysis. Results and Discussion The onsite tests yielded information on the effectiveness of the TEES process with the two chemical manufacturing process streams and validated the engineering design and mechanical integrity of the MSRS. These tests were the first with this process at an industrial site. Furthermore, they were the first process tests at this large scale using the two industrial wastewater streams discussed below as the feedstocks. Levulinic Acid Byproduct Cleanup. The levulinic acid byproduct tests were completed at the Biofine, Inc., Levulinic Acid Production Demonstration Plant at South Glens Falls, New York. The tests occurred over a 2 week period at the end of January and the beginning of February 1998. The MSRS was operated for 192 h, including 115 h using the levulinic acid byproduct as the feedstock. Levulinic acid is produced in the Biofine plant from waste cellulosic streams by a controlled acid hydrolysis of a heated, pressurized water slurry.12 The chemistry is primarily
[C6H10O5]n f HCOOH + formic acid cellulose H3C(CdO)CH2CH2COOH (1) levulinic acid (4-oxo-pentanoic acid) but there are also pathways that lead to minor byproducts, primarily from hemicellulosic contaminants in the cellulosic waste. The formic acid and mixed furfural byproducts are separated from the levulinic acid product as a dilute aqueous stream in a flashing step following the main reactor. Biofine proposes to dispose of this stream by anaerobic digestion, and TEES was evaluated as an alternative treatment and energy-recovery technology. The testing was conducted in two portions: (i) an initial operating phase of 44 h with byproduct feedstock
Ind. Eng. Chem. Res., Vol. 38, No. 3, 1999 881 Table 1. Biofine Test Results: First Processing Period time, hours feed COD, ppm LHSV, L/L/hr temperature, °C feed sulfate, ppm COD conversion, % gas yield, L/L higher heating value of gas, MJ/m3 gas composition, % methane carbon dioxide hydrogen ethane hydrocarbon gases a
organic solvent
19-22
23-26
29-35
36-44
acetone
acetone
acetone/MEK
acetone/MEK
11 780 2.70 352 598 99.4 7.0 22.3
10 110 2.62 355 598 99.3 7.2 22.8
8040 2.33 358 598 99.98 4.4 22.1
7200 2.24 360 598 99.9 4.3 22.5
53 400 1.66 352 NDa 99.9 28.9 26.2
53 400 3.19 342 ND 99.7 22.8 28.0
81 000 1.94 350 ND 99.99 36.0 28.7
81 000 3.09 345 ND 99.89 36.5 30.1
51 43 4 0.5 0.9
51 43 4 0.6 1.3
50 40 9 0.4 0.8
50 38 11 0.3 0.8
59 33 5 1.1 1.1
61 32 3 2 2
56 33 4 5 7
55 33 3 6 3
ND ) not detected, below level of detectability.
Table 2. Biofine Test Results: Second Processing Period time, hours feed COD, ppm LHSV, L/L/hr temperature, °C feed sulfate, ppm COD conversion, % gas yield, L/L higher heating value of gas, MJ/m3 gas composition, % methane carbon dioxide hydrogen ethane hydrocarbon gases a
2-4
6-13
18-22
31-35
37-42
48-54
60-62
64-69
6460 2.06 360 50 99.5 4.6 NA
5250 2.28 359 86 97.7 4.4 22.9
6620 2.63 356 166 96.5 2.2 21.8
7360 2.69 356 131 89.8 5.0 25.5
8000 1.94 357 131 95.6 3.6 25.2
9130 1.99 357 NAa 89.9 4.8 29.8
7700 1.38 358 NA 96.4 3.1 24.1
7700 1.38 360 NA 91.3 2.8 24.6
29 40 22 4 4
24 49 17 5 6
20 49 16 5 9
21 50 16 5 9
20 48 14 5 13
21 50 16 5 8
22 49 16 5 8
NA NA NA NA NA
NA ) not analyzed.
produced principally during unsteady operation and, therefore, not particularly representative of the expected byproduct stream, and (ii) a second period of 71 h when the byproduct was produced in a more consistent and representative quality. Between the two periods, organic solvents were processed for 19 h to verify catalyst activity. The results of the processing tests in the first period are given in Table 1. During this processing period, the levulinic acid byproduct contained a high level of sulfate carryover from the acid hydrolysis process. On the basis of bench-scale tests performed before the onsite test, this sulfate can deactivate the catalyst via a sulfiding mechanism. The amount of sulfate fed to the reactor system was sufficient to sulfide about 12% of the catalyst metal; however, analysis of the catalyst after the test gave no evidence of the Ni3S2 seen in the benchscale test. The test results from the first period show very high activity for the catalytic process. Through the period, several concentrations and flow rates were tested with high conversion of COD throughout. There does appear to be a very slight loss of activity shown by decreases in COD conversion with the Biofine feedstock even at slower processing rates and higher temperatures. The increase in the relative amount of hydrogen in the product gas may also suggest a loss of catalyst activity but is more likely attributable to the slightly higher processing temperatures used later in the period (also note this effect in the solvent processing tests made for comparison). As shown in Table 1, the solvent processing tests verify the high activity of the catalytic system for
gasification of these simple organic components. Even at concentrations of 5-10 times the levulinic acid byproduct streams, similar conversions were achieved. This implies a global reaction of near first order with no mass transfer limitations evident. The second period of processing followed a process shutdown to a cold state and restart after 65 h in coordination with the Biofine restart. Early in the second operating period, a pump failure required a shutdown for maintenance, which involved a system pressure letdown and temperature cooldown. This outage marked the beginning of a period of lower activity in the catalytic system. As shown in Table 2, the gas yields were reduced, the COD conversion was reduced, and the gas composition shifted dramatically away from methane toward hydrogen production. The explanations of the catalyst deactivation are derived from the several feedstock contaminants. As mentioned above, sulfate contamination could lead to metal sulfide formation in the catalyst. In fact, no nickel sulfide was detected by X-ray diffraction (XRD) in spent catalyst samples, whereas ICP-AES analysis showed sulfur levels of 5928 ppm and 142 534 ppm in two of the same catalyst samples. These same analyses showed minor deposition of iron (2371-27 310 ppm), phosphorus (299-1859 ppm), zinc (3023-3948 ppm), and copper (339-485 ppm). Physical degradation (softening) of the catalyst pellets also occurred in the first reactor tube. In addition, a mass of primarily calcium sulfate powder was found at the inlet to the first reactor tube. The composition of the material was verified by an XRD finding of approximately 80% CaSO4 and by ICP-AES analyses showing that Ca and S levels were consistent
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Table 3. Analyses of the Process Streams Used in the Onsite Test of DuPont Chemical Wastewater
COD, ppm sulfate, ppm chloride, ppm pH ammonia, ppm a
raw wastewater
ion-exchanged wastewater
TEES liquid effluent
18 280-24 290 500-700 63 5.3-5.8 NA
11 020-14 820 2-8 227-461 11.26-11.53 361
650 NAc 140 7.5 2500
NA ) not analyzed.
with 50% CaSO4 in the powder. Other major components were iron, copper, potassium, and phosphorus with catalyst fines representing 15% or less. Nickel metal sintering occurred to a degree expected for this catalyst and these conditions and would not be sufficient to explain the loss of catalyst activity. This test showed that operational controls will be needed to limit the carryover into the TEES system of unwanted components during upsets in the Biofine process. However, the processing results showed that the catalysis can be accomplished for gasifying the byproducts and that the engineered systems can be made to work at larger scale. Chemical Manufacturing Wastewater Cleanup. These wastewater tests were completed at an E. I. duPont de Nemours & Co., Inc., manufacturing plant in Texas over a 2 week period in April 1998. The MSRS was operated for 227 h, including 219 h using the chemical manufacturing wastewater as the feedstock. The wastewater was a distillation bottoms stream that contained about 1% organics and high levels of sulfate. The TEES catalyst is active for reforming most organic chemical functional types (except those containing sulfur), but it can become fouled with inorganic precipitates or poisoned by certain other inorganic components. Previous bench-scale tests with this feedstock had shown that sulfate removal by ion exchange was possible and was needed to maintain catalyst activity for more than 50 h. Accordingly, the MSRS was operated in conjunction with an ion-exchange pilot plant. The pilot plant included three 8 ft tall, 8 in. diameter columns that each contained 2 ft3 of resin. The strong anion-exchange resin was used according to the manufacturer’s suggested methods. It was received in the chloride form, and the desired hydroxide form was attained by washing with 1 M NaOH. On the basis of the analyses of the process streams given in Table 3, it is apparent that not all of the chloride was removed in the caustic wash. Although effective sulfate removal was achieved with the ion exchange, significant levels of
organic material also adhered to the resin, which in turn removed potential feedstock from the gasification system and complicated regeneration and disposal of the resin. Regeneration of the resin was tested (per manufacturer’s suggested methods), but reuse at the initial levels of exchange could not be verified. Ion-exchange pretreatment for this chemical wastewater, although adding a step, is indicative of pretreatment measures that must be considered when implementing TEES to maximize its effectiveness. The MSRS was operated continuously for the first 213 h of the test with only four short outages (from 8 to 45 min) for maintenance. The results of several processing windows are summarized in Table 4. Initial results exceeded expectations that were based on earlier benchscale testing, which indicated a 99.5% COD conversion could be achieved at 1.7 L/L/h liquid hourly space velocity (LHSV). The initial high activity began to degrade within the first 24 h of operation, and after 4 days of operation, the feed rate was reduced. After this initial break-in period of 5 days for the catalyst, consistent operations were maintained for the balance of the test. The steady operation correlates with reduced chloride in the feedstock following removal of chloride from the ion-exchange resin bed. Bench-scale testing (without the chloride contamination problem) have shown high, stable catalytic activity throughout a 17 day period.13 Pressure variations in the reactor system resulting from control valve instability also may have contributed to the higher effluent levels and the higherthan-expected hydrogen level in the product gas. On the last day of the test, the system was shut down, cooled, and restarted to evaluate the robustness of the operating system and the catalyst. After the shutdown, the conditions attained in the operations during the last half-day were nearly equivalent to conditions before the shutdown. This test showed that operational controls will be needed to limit the carryover into the TEES system of unwanted components from the ion exchange pretreatment system. However, similar to the results seen for the levulinic acid byproduct stream, the processing results show that the catalysis can be accomplished for gasifying the wastewater organics and that the engineered systems can be made to work at larger scale. Processing Cost Estimates. Preliminary cost estimates were developed for these two applications based on the processing results obtained in these tests and considering bench-scale processing results as well. The conceptualized plants were based on industrial input for actual applications of the technology. Table 5 pro-
Table 4. Processing Results with DuPont Chemical Wastewater time on stream, hours feed COD, ppm LHSV, L/L/hr temperature, °C feed sulfate, ppm COD conversion, % effluent COD, ppm gas yield, L/L higher heating value of gas, MJ/m3 gas composition, % methane carbon dioxide hydrogen ethane hydrocarbon gases
7-13
80-91
132-156
189-204
208-218
7840 2.04 350 3 99.7 21 3.6 28.4
13 000 1.90 353 8 95.4 650 4.1 31.0
11 020 1.11 352 4 94.3 650 3.8 37.7
11 040 1.14 350 8 94.6 630 3.0 37.7
11 740 1.14 351 2 93.1 850 3.2 34.2
57 19 15 2 1
52 16 24 5 3
62 10 15 7 5
62 10 15 7 5
58 9 23 8 2
Ind. Eng. Chem. Res., Vol. 38, No. 3, 1999 883 Table 5. Preliminary Process Cost Estimates
capacity, m3/h feedstock concentration ppm COD effluent concentration, ppm COD capital cost, $ (million), installed operating cost, $/m3 gas production value, $/yr
levulinic acid byproduct
chemical manufacturing wastewater
13.8 50 000 250 4.8 5.8 100 000
9.1 44 000 300 4.1 7.1 99 000
vides the highlights of these estimates of capital and operating costs. TEES has significant cost advantages in the area of recovered energy product, minimal energy requirements, and small land requirements compared to biotreatment and incineration processes. The primary cost for the process is capital (although typically less than other thermal oxidation systems); catalyst costs are the major component of the operating costs. On the basis of these results and earlier laboratory results, the catalyst lifetime was assumed to be 12 months. The capital cost estimates were made using literature values for major equipment items and a factor method to complete the installed cost. Estimates are believed to be in the range of (30%. The operating costs listed in Table 5 include the gas product credit and a credit for recovery of the spent catalyst but do not include capital charges. Conclusions The TEES process has now been demonstrated in continuous-feed, fixed-bed catalytic reactor systems in onsite tests at chemical manufacturing plants. The systems have been operated with consistency at conditions of 350 °C and 21 MPa at processing rates from 4 to 15 L/h, despite complications related to the inorganic components in the wastewater feedstocks. Aqueous effluents with low residual COD (as low as 100 ppm) and a product gas of medium- to high-BTU quality have been produced from industrial wastewaters with organic chemical contamination. These results have shown that careful monitoring and control of feedstock trace components (e.g., calcium, sulfate, and chloride) are critical for maintaining long-term catalyst activity. Acknowledgment The authors acknowledge the support for this research provided by the U.S. Department of Energy through its Office of Industrial Technologies and the program manager, Mr. Charles Russomanno. Pacific Northwest National Laboratory is operated for the U.S. Department of Energy by Battelle under Contract DE-
AC06-76RLO 1830. We gratefully acknowledge the industrial participation of E. I. duPont de Nemours & Co., Inc., and Biofine Inc., who worked with us to facilitate the tests and allowed us to operate our mobile scaled-up reactor system at their processing sites. Literature Cited (1) Sealock, L. J., Jr.; Elliott, D. C.; Baker, E. G.; Butner, R. S. Chemical Processing in High-Pressure Aqueous Environments. 1. Historical Perspective and Continuing Developments. Ind. Eng. Chem. Res. 1993, 32, 1535. (2) Elliott, D. C.; Sealock, L. J., Jr.; Baker, E. G. Chemical Processing in High-Pressure Aqueous Environments. 2. Development of Catalysts for Gasification. Ind. Eng. Chem. Res. 1993, 32, 1542. (3) Elliott, D. C.; Sealock, L. J., Jr.; Baker, E. G. Chemical Processing in High-Pressure Aqueous Environments. 3. Evaluation of Feedstock Effects. Ind. Eng. Chem. Res. 1994, 33, 558. (4) Elliott, D. C.; Phelps, M. R.; Sealock, L. J., Jr.; Baker, E. G. Chemical Processing in High-Pressure Aqueous Environments. 4. Continuous-Flow Reactor Process Development Experiments for Organics Destruction. Ind. Eng. Chem. Res. 1994, 33, 566. (5) Baker, E. G.; Sealock, L. J., Jr. Catalytic Destruction of Hazardous Organics in Aqueous Solutions; PNL-6491-2; Pacific Northwest National Laboratory: Richland, WA, 1988. (6) Sealock, L. J., Jr.; Baker, E. G.; Elliott, D. C. Method for Catalytic Destruction of Organic Materials. U.S. Patent 5,630,854, 1997. (7) Elliott, D. C.; Sealock, L. J., Jr.; Baker, E. G. Method for the Catalytic Conversion of Organic Materials into a Product Gas. U.S. Patent 5,616,154, 1997. (8) Baker, E. G.; Sealock, L. J., Jr.; Butner, R. S.; Elliott, D. C.; Neuenschwander, G. G.; Banns, N. G. Catalytic Destruction of Hazardous Organics in Aqueous Wastes: Continuous Reactor System Experiments. Hazard. Waste Hazard Mater. 1989, 6(1), 87. (9) Elliott, D. C.; Neuenschwander, G. G.; Baker, E. G.; Sealock, L. J., Jr.; Butner, R. S. Low-Temperature Catalytic Gasification of Wet Industrial Wastes; FY 1989-1990 Interim Report, PNL7671; Pacific Northwest National Laboratory: Richland, WA, 1991. (10) Elliott, D. C.; Sealock, L. J., Jr. Chemical Processing in High-Pressure Aqueous Environments: Low-Temperature Catalytic Gasification. Trans. 1nst. Chem. Eng. 1996, 74A, 563. (11) American Public Health Association. Standard Methods for the Examination of Water and Wastewater, 18th ed.; APHA Publishing: Washington, D. C., 1992. (12) Fitzpatrick, S. W. Lignocellulosic Degradation to Furfural and Levulinic Acid. U.S. Patent 4,897,497, 1990. (13) Elliott, D. C.; Hart, T. R.; Neuenschwander, G. G.; Deverman, G. S.; Werpy, T. A.; Phelps, M. R.; Baker, E. G.; Sealock, L. J., Jr. Low-Temperature Catalytic Gasification of Wet Industrial Wastes; FY 1993-1994 Interim Report, PNL-10513; Pacific Northwest National Laboratory: Richland, WA, 1995.
Received for review August 10, 1998 Revised manuscript received November 6, 1998 Accepted November 30, 1998 IE980525O
