초임계수에서 유사화학작용제(DMMP)의 산화반응 연구

이병민, 이윤우, 임종성, 김재덕, 김성현*

한국과학기술연구원 초임계유체연구실, 고려대학교 화학공학과*

Supercritical water oxidation of chemical agent simulant

(dimethyl methyl phosphonate)

Byoung-Min Lee, Youn-Woo Lee, Jong-Sung Lim, Jae-Duck Kim and Seung-Hyun Kim*

Supercritical Fluid Rearch Lab, KIST

Chemical Engineering Department, Korea University*

Theories and Applications of Chem. Eng., 2002, Vol. 8, No. 1

Introduction

Among a lot of causes threatening environment, ecosystem destruction and the bad influence to human body by the chemical weapon has been continuously discussed from The First World War (1915) until now. As a part of these endeavors, CWC (Chemical Weapons Convention), to destroy all chemical weapons in the world forever, was effective in April 29, 1997 and 169 nations signed and 121 nations ratified except some nations including North Korea nations now dated on Nov.,1998. This treaty about developing, producing, reserving, forbidding use and discharging chemical weapons regulates to discharge chemical weapons by 2007, within 10 years since after it was effective.[1]

Now, The processing of military chemical weapon treatment are Biological method, Incineration, Wet Air Oxidation, Chemical Oxidation and etc.[1,2] However, as the recognition of environment problem is raised, the technology for higher treatment effectiveness is being requested. Supercritical Water Oxidation (SCWO) is an emerging technology capable of essentially complete destruction of toxic and hazardous organic waste. When reaction temperature and pressure is over 374℃ and 220bar, oxidant and organic material exist in homogeneous phase, then, the mass transfer problem is idealistically solved and so the reaction rate becomes fast. The chemical weapons in the supercritical condition can be converted to environmental friendly material like H2O and CO2.[3,4]

In this study, supercritical water oxidation of chemical agent simulant (DMMP) has been studied. DMMP is similar to the nerve agent GB, Sarin in structure , miscible in water and relatively non-toxic in comparison to the actual chemical agents.[5] It will be confirmed that supercritical water oxidation technology is applicable for military chemical weapons.

화학공학의 이론과 응용 제8권 제1호 2002년

Experiment

Fig.1 shows a schematic diagram of SCWO experimental apparatus. This experiment system consists of two feeding pumps, DMMP/hydrogen peroxide storage, preheater, reactor, heat exchanger, filter, back pressure regulator and so on.

Each of the DMMP and the hydrogen peroxide  solution was preheated in 1/16-in O.D. x 2m length and 1/16-in. O.D. x 4m length of SS 316 tube. The length of DMMP line was  designed shorter than that of oxidant line to minimize destruction by pyrolysis during preheating. The reactor was made of a SS316 (15cm length x 3/8-in O.D.). The effluent was cooled rapidly in a counter current heat exchanger of 12cm length and then, the system pressure was reduced by using back- pressure regulator (Tescom co. 26-1721-24). The depressurized reactor effluent was separated into gas and liquid phase. The concentration of DMMP in the liquid effluent was analyzed by a Hewlett-Packard 4890 GC (Gas Chromatography) with a 0.32mm  ID×30m length, 5 □m film thickness capillary column AT-1. The gas samples were analyzed using a Hewlett-Packard 5890 GC with a thermal conductivity detector.  A Rheodyne  injection valve was used for on-line sample injection into a 10-ft length x 1/8-in OD Supelco Carboseive S-II permanent gas column.

화학공학의 이론과 응용 제8권 제1호 2002년

Theories and Applications of Chem. Eng., 2002, Vol. 8, No. 1

To begin the experiment, both DMMP and oxidant pump was started using distilled and deionized water as a feed. After volumetric flow rate, reaction temperature and pressure were reached at steady state, feed solutions are provided by feeding pumps. The reactor system becomes stable for 15-20 min. Total flow rate for the oxidant and DMMP feed streams ranged from 7 to 15ml/min (flow rate ratio =1:1, respectively).  The flow rates were measured repeatedly using graduated vessels and a stopwatch until a steady-state condition was reached. The accuracy of the volumetric flow measurement was within ±5%. Upon finishing reaction system, products in the inner wall of reactor and preheating line was removed by distilled deionized water and methanol.

Reaction conditions

The oxidation of DMMP in supercritical water was performed in temperature 300∼400℃, pressure 240bar and residence time 10∼40sec. The concentration of  DMMP    was 6000∼12000ppm (50∼100mM) and concentration of hydrogen peroxide used as oxidant was 34000∼68000ppm (excess 100%H2O2).

Result and discussion

The description of the reaction would be :

C3H9O3P + 10H2O2 → 3CO2 + H3PO4 + 13H2O

Fig 2 shows the results of DMMP quantitative analysis. When the concentration was increased from 1200ppm to 12000ppm,  the absorbance peak area of GC-FID was increased linearly.

Theories and Applications of Chem. Eng., 2002, Vol. 8, No. 1

화학공학의 이론과 응용 제8권 제1호 2002년

Experiments were performed in the range of subcritical region (Fig 3), near-critical region (Fig 4) and supercritical region (Fig 5). The concentration of H2O2 (excess 100%) and reaction pressure(240bar) were fixed while the initial concentration, temperature and residence time were changed.  The concentration of pure water was changed from 0.7417g/□ to 0.1484g/□. Figures 3∼5 show to high conversion in short residence times. It shows high conversion over 95%  within  40sec at subcritical region and within 10sec at supercritical region. Conversion was not high at 300oC  but remarkably high at 400oC. Destruction effectiveness of supercritical region was four times in comparison to that of subcritical region.  It was caused by very fast reaction rate due to homogenious phase in supercritical water. However, high conversion doesn't absolutely mean that DMMP is perfectly divided into H2O and CO2. The following table 1 is listed probale intermediates produced in the SCWO of DMMP(turner, 1993).[5]

화학공학의 이론과 응용 제8권 제1호 2002년

Table 1. Intermediates produced in the SCWO of DMMP

	name	molecular weight	density	boiling point
		(g/mol)	(g/□)	(℃)
CO2	carbon dioxide	44.01
CO	carbon monoxide	28.01	0.791	-191.5
HCOOH	formic acid	46.03	1.210	100.7
CH3OH	methanol	32.04	0.791	64.6
CH3CHO	acetic aldehyde	44.05	0.788	20.0
HOCH2CH2OH	ethylene glycol	62.07	1.116	195.0
CH3COOH	acetic acid	60.05	1.049	117.9
CH3CH2OH	ethyl alcohol	40.07	0.789	78.3
HCOH	formaldehyde	30.03	1.090	-19.5
H3PO4	phosphoric acid	98.00	1.685	260.0
(CH3)2P(O)H	dimethyl phosphonicacid	94.05
(CH3O)2P(O)H	dimethyl phosphite	110.05
CH3P(O)(OH)2	methyl phosphonicacid	96.02
(HO)2P(O)CH2CO2H	phosphono aceticacid
(CH3O)3P(O)	trimethyl phosphate	140.08	1.179	197.2
(CH3)2P(O)CO2CH3	trimethylphosphono formate
(CH3O)2P(O)CH2CO2CH3	trimethylphosphono acetate

As result of this preliminary experiment, we confirmed that SCWO is suitable for destruction of military chemical weapons. Further study is on going to investigate in details.

Theories and Applications of Chem. Eng., 2002, Vol. 8, No. 1

Reference

[1] Jong-Chol Lee:J. Korea Solid Waste Engineering Society Vol.16, No.3, 205∼           216(1999).

화학공학의 이론과 응용 제8권 제1호 2002년

[2] Jong-Chol Lee:J. Korea Solid Waste Engineering Society Vol.16, No.3, 217∼           231(1999).

[3] P.E. Savage, S. Gopalan, T.I.Mizan, C.J.Martino, E.E.Brock, AIChE J.41(1995)1723.

[4] P.E. Savage, Chem. Rev.99 (1999) 603.

[5] M.D. Turner, Supercritical water oxidation of dimethyl methylphosphonate and

thiodiglycol, Ph.D. thesis, University of Texas at Austin, Austin, TX, 1993.