Derek Perry 1 , Ken B. Anderson 1,2* , John C. Crelling 1,2 , William W. Huggett 2 .
1.
Thermaquatica Inc., 1740 Innovation Drive, Ste. 212, Carbondale, IL 62903
2.
Department of Geology, Southern Illinois University Carbondale, Carbondale, IL 62901
Abstract:
Oxidative Hydrothermal Dissolution (OHD) is a novel, environmentally friendly technology for the conversion of coal (and other solid organic materials) into low molecular weight, water soluble products. Solublization takes place when coal reacts with dissolved molecular oxygen, in hightemperature, high-pressure subcritical water. The OHD product is an aqueous solution consisting of a mixture of low-to-medium molecular weight aromatic and aliphatic acids and related derivatives that could potentially supplement or replace some petroleum–derived products as chemical feed stocks. No exotic catalysts or additional solvents or reagents are required to readily achieve complete conversion. The process has been studied for a number of years, being first demonstrated at the micro-scale through semi-batch and semi-continuous reactors.
The current work has developed a well-engineered pilot-scale (up to 10kg/hr) system for demonstration of first stage scale up and also for the production of raw OHD product (“liquor”) in sufficient quantities for evaluation of potential refining and end use strategies. The system was designed to control system variables, including pressure, temperature, flow rate, concentration of product stream (with water recycle) over a specified range of operating conditions.
This presentation will discuss experience with operation of OHD on this (pilot) scale, and will describe the results obtained to date from a variety of coals including bituminous (Illinois) coal and lignite.

 Author to whom correspondence should be directed, kanderson@thermaquatica.com

Introduction:
Over at least the last half century, recognition of our strong dependence on petroleum for the production of both liquid fuels and chemicals, including precursors for polymers, has driven sustained interest in development of alternative means to produce functionally equivalent products, from alternative feed stocks, including coal. Much of this effort has focused on technologies such as gasification, liquefaction, and pyrolysis, all of which ultimately depend on reductive bond cleave to break up the macromolecular structure of the coal, and all of which focus on producing a raw product (some form of syncrude) that can be refined using conventional technology. Oxidative Hydrothermal Dissolution (OHD) is the result of rethinking this strategy. The
OHD process, which has been developed with support from the Illinois Clean Coal Institute, uses oxidative bond cleavage to disrupt coal’s macromolecular network, directly producing functionalized low molecular weight, water-soluble products, many of which are comparable to products currently derived from petroleum-derived precursors.
The molecular structure of coal is poorly defined but can be reasonably described as clusters of aromatic rings of various sizes and configurations that are interconnected by either aliphatic or ether functional groups. OHD uses oxidative bond scission to break apart these macromolecular structures, using subcritical liquid water as the reaction medium (and solvent), and dissolved O
2
as the oxidizing agent. The process does not require exotic solvents, catalysts, or complex reactors, and is, therefore, inherently simple and environmentally-friendly. Most inorganic materials that are present, (for example as discrete mineral phases), are not affected under OHD conditions and simply pass through the process unaltered
1
. (An exception to this generalization is pyrite which oxidizes to sulfate and iron oxides analogous to the processes by which pyrite weathers when exposed to the environment). No gaseous nitrous or sulfur oxides are produced. Previous efforts have demonstrated that for coal, water works as an excellent solvent for the products, and OHD is able to achieve complete conversion, with 70 to greater than 90% carbon recovery (as functionalized low molecular weight products), with very little CO
2
production.
Prior work:
Both semi-continuous and continuous laboratory-scale proof-of-concept testing has been successfully completed at Southern Illinois University Carbondale (SIUC), and U.S. and international intellectual property (IP) protection is now in place
2,3,4
. Experimental studies have been completed, to-date, using two bench-scale reactor systems. The first of which is a semi-continuous micro-scale reactor, where a fixed charge (up to 200mg of +60 mesh coal) is exposed to a hydrothermal fluid stream with a precisely controlled flowrate, temperature, and pressure (typically 220-350 ° C, and
1500-2500psi). On the bench scale, oxidant (dissolved O
2
) is produced by in-situ thermal decomposition of hydrogen peroxide (H
2
O
2
), as an experimental convenience. Identical experimental results have been obtained when dissolving gaseous O
2
to generate the saturated

liquid solution. The OHD product (aqueous solution, aka “liquor”) is then collected for offline analysis. This initial reactor system is illustrated schematically in Figure 1.
Figure 1: Semi-continuous reactor design for bench-scale studies (<0.2 g/hr)
The fully-continuous lab scale system is represented in Figure 2. This system is capable of a processing rate of up to about 200g of pulverized (and/or micronized) coal, per hour. Coal slurry is preheated as it is delivered into the reactor, where it is brought into contact with the dissolved oxygen. Contact time is a variable, based on the length of the reactor and the flow rate, but contact times of less than 30 seconds are typical.
The specific qualities of the OHD product distribution are primarily dependent on the nature of the starting material, and to a lesser degree on the process conditions. Coal conversion (reaction rate) typically increases with temperature, and to some extent the product distribution from a feed may be altered and optimized, based on the choice of reaction temperature and other relevant parameters such as pressure, residence time, O
2
concentration, etc. Coal-derived products are generally mixtures of functionalized and poly-functionalized low molecular weight aliphatic and aromatic compounds, dominated by aromatic mono-acids, aromatic poly-acids, aliphatic monoacids, and aliphatic poly-acids. Phenolic products may also be generated, especially from low rank raw materials.
5

Figure 2: Fully-continuous reactor design for bench-scale studies (50-200 g/hr)
GC-MS analysis of the OHD product distributions for various ranks are shown in Figure 3.
Representative OHD product distributions from lignite, bituminous coal (Illinois #6 seam), and anthracite are shown. Products generated from lower rank materials are predominantly methoxysubstituted benzoic acids (mono-carboxylic acids). With an increase in rank, the distributions shift towards dicarboxylic acids, and then tricarboxylic acids.
The product distribution from (North Dakota) lignite typically contains less than ten major products, with the predominant product being vanillic acid (mono-carboxylic) reflecting the nature of the original lignin from which the bulk of the coal is derived. The distribution for Illinois #6 seam coal becomes more complex, with multiple analogues of methoxylated compounds becoming more common, reflecting increasing alteration and condensation of the original bio-derived structures with increasing rank. Maturation results in further condensation of the coal structure and increasing preponderance of tri- (and tetra-) substituted aromatic carboxylates (various isomers) in the liquor. In all cases, no high-molecular weight products are observed.

Figure 3: Multiple ion Chromatogram (m/z 135 + 163 + 196 + 210 + 221 + 224), illustrating the effect of rank on OHD product distribution.
Process Development:
Further development of the OHD process requires demonstration of the technology at increasingly larger scales. To this end, we are currently developing an OHD process demonstration unit (PDU) designed to process on the order of 1-10 kg/hr of coal. The basic design concept used for development of the PDU closely follows the configuration illustrated in Figure 2. The initial goals of this effort are:
1.
Demonstration of the process at a small engineering scale and development of relevant engineering experience for future further scale up, and
2.
Implementation of the capability to produce OHD liquors in quantities sufficient for development of down-stream processing strategies.

Development of the PDU has focused on development of a semi-modular system capable of testing
OHD on a range of feeds over a wide range of flow rates, O
2
concentrations, and hydrothermal pressures/temperatures. The unit was designed to be compact in size, well-ventilated, and enclosed for safety purposes, with all major system components and control loops fully automated.
It was also equipped to allow remote operator control and detailed monitoring of key process variables.
The most significant change from the small-scale design is the addition of the flash tank to allow initial product dewatering and steam/heat recycling. This allows the concentration of the raw liquor to be modified and controlled. A control loop is in place, allowing the operator to control the extent of dewatering (in principle, up to 99%) by removal of water as steam. The recovered steam can be recondensed with heat recovery and water recycle.
The fabricated pilot-scale unit, in final stages of pre-acceptance testing is illustrated in Figures 4 & 5.
Even in construction and testing this unit has proven that OHD processing can be accomplished at scales greater than laboratory scale and has provided value experience transferable to larger scale.
No fundamental scalability issues have been encountered, although engineering issues (primarily associated with wear and material selection in high velocity regions) have been encountered and are being addressed.
Figure 4: Fully-continuous reactor for pilot-scale studies (1-10 kg/hr)

Figure 5: Fully-continuous reactor for pilot-scale studies (1-10 kg/hr)
Conclusions:
A 1-10 kg/our PDU for preliminary scale-up of oxidative hydrothermal dissolution (OHD) has been designed and fabricated, and is expected to be in operation in the near future. No fundamental impediments to process scalability have been identified. Even in construction and preliminary testing the unit has provided valuable information and experience in the design and operation of
OHD reaction systems beyond the laboratory scale, and is expected to continue to do so after final commissioning.
Acknowledgement:
The authors gratefully acknowledge the Illinois Clean Coal Institute (ICCI) for their support of the work described herein.
References:
1.
Ken B. Anderson, John C. Crelling, William W. Huggett, Derek Perry, Tom Fullinghim, Patrick
McGill and Paul Kaelin; Oxidative Hydrothermal Dissolution (OHD) of Coal and Biomass; ACS
Fuel Division, Denver 2011.

2.
International (PCT) Patent Application Serial No. PCT/US2010/23866 filed February 11, 2010 based on US provisional application No. 61/151,677 filed February 11, 2009 entitled PROCESS FOR THE
DISSOLUTION OF COAL, BIOMASS, AND OTHER ORGANIC SOLIDS IN SUPERHEATED WATER.
3.
International (PCT) Patent Application Serial No. PCT/US12/40746 filed June 4, 2012 based on US provisional Patent Application No. 61/492,910 filed June 3, 2011, entitled PRODUCTION OF
ORGANIC MATERIALS USING AN OXIDATIVE HYDROTHERMAL DISSOLUTION METHOD.
4.
US Patent Application Serial No. 13/488,092 filed June 4, 2012, entitled PRODUCTION OF ORGANIC
MATERIALS USING AN OXIDATIVE HYDROTHERMAL DISSOLUTION METHOD.
5.
Ken B. Anderson, John C. Crelling, William W. Huggett, Derek Perry, Tom Fullinghim, Patrick
McGill and Paul Kaelin; Oxidative Hydrothermal Dissolution (OHD): An efficient, environmentally friendly process for the dissolution of coal and biomass in aqueous media, for the production of fuels and chemicals Proceedings of the 36 th
International Technical
Conference on Clean Coal and Fuel Systems, Sheraton Sand Key, Clearwater, Florida, USA, June
5-9, 2011, p27-35.