Ind. Eng. Chem. Prod. Res. Dev. 1905, 2 4 , 630-635
630
(5) The number of required tank refills to dryness can be lowered by reducing the soluble water in the fresh fuel, particularly the water associated with the cosolvent. (6) Problems with water bottoms growth in a tank can be minimized by removing much of the original water bottoms from the tank before the first filling with alcohol/gasoline blend. Acknowledgment I appreciate the assistance provided by the technical staff at the Harvey Technical Center, ARCO Petroleum Products Co. I also thank Karen Meyers for help in the preparation of the manuscript and the management of the ARCO Chemical Co., for the encouragement and permission to publish this work. Nomenclature Ai = tank composition, vol % A[ = tank composition for previous refill, vol % A4 = water in tank, vol % A,,' = water in tank for previous refill, vol % Bi= material balances of components,vol % C = effectiveness rating of cosolvent E = refill number G, = size of fresh-fuel refill, vol % Ki = partition coefficients of components M = water bottoms at equilibrium, vol % M I = water bottoms, first previous refill, vol % M 2 = water bottoms, second previous refill, vol % M5 = water bottoms calculation for high cosolvent in fuel Ms = water bottoms calculation for low cosolvent in fuel Ni = fresh fuel composition, vol % N4 = water in fresh fuel, soluble, vol %
P = predicted number of refills V , = initial water bottoms size, vol % Xi = water bottoms composition at equilibrium, vol % Yi = gasoline-phase composition at equilibrium, vol % Yz= cosolvent in gasoline phase, vol % Y3 = methanol in gasoline phase, vol % Y4 = water tolerance of fuel, vol % i = component (gasoline, cosolvent, methanol, water, respectively) a, b, c, f, g, S = constants and slope for water-tolerance equations Registry No. HzO,7732-18-5;methanol, 67-56-1; ethyl alcohol, 64-17-5;isopropyl alcohol, 67-63-0;n-butyl alcohol, 71-36-3;isobutyl alcohol, 78-83-1; tert-butyl alcohol, 75-65-0.
Literature Cited Cox, F. W. "Component Relationships Within the Two-Phase Gasoline-Methanol-Water", Report 1979, BETC-R1-78/6. Haq, M. A. Hydrocarbon Process. May 1981, p 159. Hutchinson, D. A. ARCO Petroleum Products Co., Harvey, IL, private communication, 1982. Keller, J. L. "Methanol Fuel Modification for Highway Vehicle Use, Final Report", July 1978, NITS HCP/W3683-18. Roehm, P. German Patent 2826883, Dec 29, 1977. Ruiz-Bevia, F.; Prats-Rlco, D. Fluid Phase Equilib. 1983, IO, 77.
Received for review January 22, 1985 Accepted May 20, 1985 Supplementary Material Available: The experimental results of partition coefficients and water bottoms for gasoline, methanol, and water blended with each cosolvent, the regression equations, and the computer model with inserts (17 pages). Ordering information is given on any current masthead page.
Diethanolamine (DEA) Degradationt under Gas-Treating Conditions Chang S.
H s d and C. J. Kim'§
Exxon Research and Engineering Company, Clinton Township, Annandale, New Jersey 0880 1
The degradation of diethanolamine (DEA) under gas-treating conditions was studied by mass spectrometric analysis of the products. I n addition to the formation of 3-(2-hydroxyethyl)oxazolidone-2 (HEO), N,N'-bis(2-hydroxyethyl)piperazine (HEP), and N,N,N'-tfis(2-hydroxyethyi)ethyienediamine (THEED), as reported in the literature, DEA degradation leads to significant amounts of triamine derivatives that were identified as 3-(2-(bis(2-hydroxyethyl)amino)ethyl)-2-oxazolidone (HAO), N-(2-(N,N-bis(2-hydroxyethyl~mino)ethyl~N'~2-hydro~e~yl)piperazine (HAP), and N,N,N",N"-tetrakis(2-hydroxyethyJ~iethylenetriamine (THEDT). A comprehensive reaction mechanism that can account for all the products is proposed and discussed.
Introduction Diethanolamine (DEA), or bis(2-hydroxyethyl)amine, is widely used for removing carbon dioxide, hydrogen sulfide, and other acidic components from gases. During use in plants, however, DEA loses its gas-treating activity as it degrades, causing considerable economic losses and operating problems. DEA degradation yields a complex mixture of polar, high-boiling organic materials that are difficult to isolate for analysis. In 1956, Polderman and Steele found that N,N'-bis(2-hydroxyethyl)piperazine (HEP) is one of the The term "degradation"refers to a decrease in gas-treating activity rather than to a breakdown of the compound. This usage is common in the gas-treating community. Corporate Research-Analytical Sciences Laboratory. f Corporate Research-Science Laboratories. f
0196-4321/85/1224-0630$01.50/0
DEA degradation products and suggested 3-(2-hydroxyethy1)oxazolidone-2 (HEO) as its probable precursor. Hakka et al. (1968) later isolated and identified another degradation product, N,N,N'-tris (2-hydrox yethyl)ethylenediamine (THEED). In addition to these compounds, the formation of high molecular weight compounds becomes important in the later stages of DEA degradation (Kim and Sartori, 1984). These high molecular weight products are very difficult to analyze by conventional GC using a packed metal column because of their high polarity. The study reported here was undertaken to characterize these unknown components with the goal of fully elucidating DEA degradation chemistry. Experimental Section Materials and Sample Preparation. DEA and HEP were purchased from Aldrich Chemical Co. H E 0 and 0 1985 American
Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24,
THEED were synthesized as described by Kim and Sartori (1984). An aged DEA solution was prepared from a mixture of 33.5% DEA, 6.2% COz,and 60.3% water (% w/w), which was sealed in a 10-mL stainless-steel bomb under nitrogen. The bomb was then immersed in a constant-temperature bath at 120 f 0.2 "C for 14 days. This temperature, higher than normal operating conditions, was chosen to accelerate degradation. At the end of 2 weeks, the bomb was immersed in cold water and opened; the reaction mixture was analyzed by a previously described procedure (Kim and Sartori, 1984). Of the original 33.5% DEA, it was found that 10.1% remained unchanged, 2.7% converted to HEO, 0.5% converted to HEP, and 14.7% converted to THEED. These compounds sum to 28%; the balance, 5.5% (DEA equivalent), was attributed to higher boiling compounds. This reaction mixture was then saturated with potassium carbonate and extracted with isopropyl alcohol. Following evaporation of the isopropyl alcohol, a light yellow oil was obtained. This sample was designated sample A. Another sample was collected from a slightly different experiment. A mixture of 33.2% DEA, 6.1% COz, 1.1% HzS, and 59.7% H20was sealed in several 10-mL stainless steel bombs that were kept at 140 "C for times ranging from 6 to 15 days. The products from these bombs were combined. The light fraction was stripped off at 190 "C under 5-mmHg vacuum, and the residue, a light-brown, syrupy liquid, was collected for direct-insertion probe mass spectrometric (P/MS) analysis. This sample was designated sample B. GC/MS Analysis. GC/MS analysis was carried out with a Finnigan 4000 GC/MS system using a 25 m X 0.25 mm i.d. OV-101 vitreous silica capillary column that was temperature-programmed from 75 to 275 "C at 6 "C/min. The injector and GC/MS interface were kept at 290 "C. Helium was used as a carrier gas at an average linear speed of 20 cm/s. Sample (0.5 pL) was injected into the column a t a split ratio of 40:l. The mass spectrometric analysis employed both electron-impact ionization (EX) and chemical ionization (CI). For CI, either methane or isobutane was used as a reagent gas at nominal source pressures of 0.25 and 0.1 torr, respectively; the ion source temperature was 150 "C. For EI, a 70-eV electron beam with an emission current of 0.4 mA was used; the ion source temperature was 260 "C. Silylation Procedure. Silylation of sample A was carried out for hydroxy number determinations using 1.0 mL of anhydrous pyridine, 0.2 mL of hexamethyldisilazane, and 0.1 mL of trimethylchlorosilane. The mixture was reacted in a screw-cap vial that was shaken vigorously for about 30 s and allowed to stand for more than 5 min at room temperature until derivatization was complete. P / M S Analysis. Direct-insertion probe mass spectrometric (P/MS) analysis was applied to the vacuum distillation residue of the DEA degradation products (sample B). The sample was deposited in a glass capillary tube that was inserted into the ion source of a Du Pont 21-491 mass spectrometer. Heat was applied to the sample through a heating coil around the capillary tube. Mass spectra were acquired as the probe temperature was increased until total ion current returned to the base line (-375 "C).
Results GC/MS Analysis. Analysis of sample A by GC/MS showed six major components. The first four components were DEA, HEO, HEP, and THEED; the remaining two, which appeared at higher retention times, were tentatively
No. 4, 1985 631
lesi
Figure 1. Isobutane chemical ionization mass spectrum of compound X.
designated X and Y. They were identified as follows. Molecular Weight by CI. Molecular ions were generally not present in the E1 spectra of the compounds analyzed. Therefore, CI was used for obtaining molecular weight information. With CI, pseudomolecular ions are generated by an ion-molecule reaction between reagent gas ions (reactant ions) and sample molecules. Pseudomolecular ions can be protonated or hydride-abstracted molecular ions, depending on the relative basicity between the reactant ions and the sample molecules (Harrison, 1983). For most oxygen- and nitrogen-containing compounds, protonated molecular ions are generated by CI using methane or isobutane as a reagent gas. Unlike the molecular ions generated under E1 conditions, only a small amount of internal energy is deposited into the pseudomolecular ions, which leads to less fragmentation. From the m/z (mass-to-charge ratio) values of the protonated molecular ions observed in the CI spectra, the molecular weights of the components can be determined. The chemical ionization mass spectra of compounds X and Y, with isobutane as a reagent gas, are shown in Figures 1and 2. From the m/z values of the protonated molecular ions, the molecular weights of X and Y were found to be 218 and 261, respectively. Hydroxy Number Determination. The number of hydroxy groups was determined from the CI spectra of the compound before and after silylation, which was selective for hydroxy groups but left amino groups largely unreacted (Hsu, 1985). A typical comparison of isobutane CI spectra before and after selective silylation is shown in Figure 3 for THEED. The number of hydroxy groups can be calculated from the difference in m/z values of pseudomolecular ions of the compound before and after silylation. number of OH groups = m/z(MH+, silylated) - m/z(MH+, unsilylated) 72 The results of measurements for the number of hydroxy groups in each compound are listed in Table I. The validity of the method is demonstrated from the results for known compounds-DEA, HEO, HEP and THEED. The numbers of hydroxy groups in X and Y were found to be two and three, respectively. Structure Elucidation by EL Under E1 conditions, extensive fragmentation of the molecular ions can furnish valuable information about molecular structure. The
632
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 4, 1985
'* '1
"/
3
RSS
Figure 2. Isobutane chemical ionization mass spectrum of compound Y.
Figure 4. 70-eV electron-impact ionization mass spectrum of N,N'-bis(2-hydroxyethyl)piperazine. r
t
1 1
5
vis.
Figure 3. Comparison of isobutane chemical ionization spectra of N&,"-tris(2-hydroxyethyl)ethylenediamine (THEED) and-silylated THEED.
Figure 5. 70-eV electron-impact ionization mass spectrum of 3-(2hydroxyethy1)oxazolidone-2.
Table I
compd DEA HE0 HEP THEED compd X compd Y
MHt (unsilylated) 106 132 175 193 219 262
MHt (silylated) 250 204 319 409 363 478
no. of OH groups 2 1 2 3 2 3
structure of an unknown compound can be deduced from the observed fragment ions characteristic of the molecule if we know the fragmentation patterns of structurally similar compounds. However, there are no reference spectra for HEO, HEP, and THEED in the literature. The E1 spectra we obtained are shown in Figures 4-6 to enable recognition of the characteristic fragmentation patterns. In the E1 spectrum of HEP (Figure 4), the ions corresponding to losses of water and a hydroxymethyl radical (CH,OH) from its molecular ion are present at m / z 156 and 143, respectively. The two major fragment ions with m/z values of 100 and 70 appear to be derived from piperazine-ring c-C cleavage, as commonly observed in the E1 spectra of other piperazine derivatives (Shetty et al., 1983). (See Scheme I.)
7l 'P
I IM
171
Figure 6. 70-eV electron-impact ionization mass spectrum of THEED.
The most characteristic ions in the E1 spectrum of H E 0 (Figure 5) are the m/z 113,101, and 100 ions, which correspond to water, CH20, and CH20H losses, respectively, from the molecular ion.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 4, 1985 633 Scheme I /
HO CH2Ch - N ~
\
CH4CH2 \
? N - CHICH“ - O H / CHpCH,
-
HO CH,CHI ~
~
N
in‘ CH~CH,-OH
,‘ CH, ‘c-0
+
HzO (5)
//
0
HA0
HA0
+
DEA
-
HOCH,CH,
\NCH CH NCH,CH,N /CHZCHZOH + / \CH,CH,OH HOCH,CH, H
co,
THEDT (6)
HE0
+
THEED
-
HOCHzCHz
\NCH CH NCH,CHJ’4HCHzCH,0H /
HOCHzCH2
+
CO,
CH,CH,OH
i- T H E DT (71
THEDT or
i-THEDT
-
HOCH2CHz
\
p c H 2
/NCHZCHZN \
HOCH,CHz
CH,CH,
\NCH,CH,OH /
+
HO ,
(8)
HAP
An intriguing aspect of this proposed reaction sequence is that a set of simple condensation and displacement reactions can explain all observed products. Extension of this chemistry suggests that HEP and HAP are the end products of DEA degradation and that only i-THEDT can undergo further polymerization to tetrameric compounds. Since under the conditions of our study we found no evidence of tetramer formation, the structure of the tetrakis hydroxyethyl derivative may then be THEDT. However, it is also possible that a significant amount of LTHEDT is formed (eq 7) that subsequently undergoes preferential cyclization to HAP rather than polymerization to tetramers.
If reactions 4-8 are the secondary degradation paths, then, in the strictest sense, the rate law defined in eq 3 must be modified. However, the contribution of secondary paths to the rate of DEA degradation is expected to be very small compared with that of primary paths (eq 1 and 21, a t least in the initial stages of the reaction. Support for this reasoning lies in the observation that eq 3 is valid for a range that covers the reaction to at least the point at which 70% of the DEA has been degraded (Kim and Sartori, 1984). At this point of 70% DEA degradation, the upper limit value of the amounts of triamine derivatives formed corresponds to 5.5% of the original 33.5% DEA; i.e., a maximum of 24% of the degraded DEA is converted to triamine derivatives. As the proposed secondary degradation route involves conversion of diamine to triamine derivatives, the maximum contribution of the secondary route to the overall DEA degradation is 8% (one third of 24%), while the remaining 92% is controlled by the primary route defined in eq 1and 2. This analysis shows that the DEA degradation is controlled mainly by the primary route, while the contribution by the secondary route becomes significant only when the concentration of DEA becomes much smaller relative to those of THEED and HAO. It is nevertheless noted that a new set of kinetic data to determine the rates of reactions 5-7 would be needed for a complete characterization of the DEA degradation.
Conclusion DEA degradation has previously been considered to yield only dimeric compounds, HEP and THEED. Our study found significant amounts of polar, higher boiling trimeric compounds, which were identified for the first time as HAO, HAP, and THEDT or i-THEDT. We also found that reaction paths leading to these products can be easily explained by extending a previously proposed mechanism (Kim and Sartori, 1984) that concluded that the DEA degradation is controlled by the chemistry represented by eq 1,2, and 4. Our findings provide a nearly complete characterization of DEA degradation paths. From the point of view of gas processing, the acid gasremoving capabilities of the degradation products become subjects of interest. Hakka and co-workers (1968) observed that only one of the two amino groups of the dimeric compounds HEP and THEED is effectively utilized in acid gas absorption-desorption cycles. The formation of trimeric degradation products would thus be expected to reduce further the acid gas-removal capacity. It is interesting to note that DEA degradation ultimately leads to substituted piperazine derivatives that contain only tertiary amino groups. Accordingly, the overall concentration of secondary amino groups relative to tertiary amino groups would steadily decrease, and this, according to the known chemical kinetics of COz reaction with secondary and tertiary amines (Danckwerts, 1979), would result in a slower rate of C 0 2 absorption. Registry No. DEA, 111-42-2;HEO, 3356-88-5; HEP, 122-96-3; THEED, 60487-26-5; HAO, 98800-40-9; HAP, 86377-11-9; THEDT, 60487-25-4;i-THEDT, 98800-41-0;COP,124-38-9;bis[ 2- [ (trimethylsilyl)oxy]ethyl]amine, 20836-40-2; 3-[ 2-[ (trimethylsilyl)oxy]ethyl]-2-oxazolidinone,98800-42-1;N,N’-bis[2[ (trimethylsilyl)oxy]ethyl]piperazine,98820-71-4; N,N,N’-tris[ 2- [ (trimethylsilyl) oxy]ethyl]ethylenediamine, 98800-43-2; 3[2 4 bis[2- [(trimethylsilyl)oxy]ethyl]amino]ethyl]-2-oxazolidinone, 98800-44-3; N - [2- [ bis[ 2- [ (trimethylsily1)oxyl ethyllamino] ethyl]-N’- [2-[ (trimethylsilyl)oxy]ethyl]piperazine, 98800-45-4.
Literature Cited Danckwerts, P. V. Chem. Eng. Sci. 1979, 3 4 , 443-446. Hakka. L. E. et at. Gas R o c . Can. 1966, 67. 32.
Ind. Eng. Chem. Prod. Res. Dev. 1985, 2 4 , 635-641 Harrison, A. G. "Chemical Ionization Mass Spectrometry"; CRC Press: Boca Raton, FL, 1983. Hsu, C. S. "33rd Annual Conference on Mass Spectrometry and Allied Topics", San Diego, CA, May 26-31, 1985; The American Society for Mass Spectrometry: East Lansing, M I 1985; FOC16. Kim, C. J.; Sartori, G. Int. J. Chem. Kinet. 1984, 16, 1257-1266.
635
Polderman, L. D.; Steele, A. B. 011 Gas J. 1958, 54, 206-214. Shetty, H. U. et al. Blomed. Mass Specfrom. 1983, 10, 601-607.
Received for review April 8, 1985 Accepted July 27, 1985
Chemical Modeling Analysis of the Yields of Single-Ring Phenolics from Lignin Liquefaction Francls P. Petrocelll and Mlchael T. Kleln" Department of Chemical Engineering, Universiv of Delaware, Newark, Delaware 79776
Insights into the products obtained from the catalytic liquefaction of lignin were gained through the experimental hydroprocessingreactions of the model compounds 4-methylguaiacol, 4-methylcatechol, eugenol, vanillin, o ,o'biphenol, o -hydroxydiphenylmethane,and phenyl ether over a sulfided CoOMo03/y-A1,03 catalyst. Compounds with aromatic methoxyl groups (4methylguaiaco1, eugenol, vanillin) underwent prlmary demethylation as their major reaction. Hydroxyl groups were removed readily at temperatures well below those required for thermal dehydroxylation. Catalytic cleavage of the interaromatic unit linkages of o-hydroxydiphenylmethane and phenyl ether was facile, while o ,o'-biphenol was converted to single-ring products through a 2-phenylphenol intermediate: dibenzofuran was also a primary product from the reaction of o ,o'-biphenol. Product yields' temporal variations were used in the analysis of lignin liquefaction. This chemical modeling suggests that catalytic lignin liquefaction should permit the recovery of 10 wt % single-ring phenols and hydrocarbons at conditions where 2 wt % would be realized through thermal fragmentation alone.
Introduction Native lignin is a copolymer of single-ring phenolic units (Freudenberg and Neish, 1968; Glasser et al., 1981) that comprises carbon, hydrogen, and oxygen in proportions of approximately 65%, 6%, and 29%, respectively. The oxygen hinders the thermal conversion of lignin to useful low molecular weight products, and its removal by selective catalysis seems desirable. The utility of standard heterogeneous hydroprocessing catalysts in the removal of nitrogen and sulfur heteroatoms from aromatic constituents in petroleum and coal liquids (Gates et al., 1979) thus motivated the present interest in catalytic hydrodeoxygenation during lignin liquefaction. The complexities of both lignin and its reaction-product spectra render liquefaction pathways obscure. This motivated our use of simple model compounds whose chemical structures resemble structural residues of the macromolecule. The comparatively simple product spectra obtained from model compound reactions allow inference of operative reaction pathways and kinetics. The present report explores lignin liquefaction and hydrodeoxygenation in terms of the model compounds 4-methylguaiacol, 4methylcatechol, eugenol, vanillin, o,o'-biphenol, ohydroxydiphenylmethane,and phenyl ether, the structures of which are illustrated in Table I. Previous lignin pyrolyses and hydropyrolyses (Jegers, 1982; Domburg et al., 1971; Iatridis and Gavalas, 1979; Connors et al., 1980) suggest that phenolics can be obtained in yields of up to 30 w t %. However, these complex mixtures of at least 32 different guaiacols, catechols, and phenols would more likely contain each in 1% yield than any one in a large yield. Additionally, yields of guaiacols and catechols from batch pyrolysis pass through a maximum before decreasing at longer reaction times (Jegers, 1982; Connors et al., 1980), and char rather than phenols is their selectively favored decomposition product. Finally, 0196-432118511224-0635$01.50/0
because of the presence of thermally stable biphenyl, diphenylmethane, and phenyl ether bonds in lignin, its pyrolysis produces a significant yield of phenolic dimers and trimers (Iatridis and Gavalas, 1979). The foregoing suggests that catalytic lignin liquefaction and hydrodeoxygenation would be useful for two reasons. First, the catalyst can redirect the reactions of guaiacols and catechols away from the formation of char and toward the formation of thermally stable, noncoking phenols (Jegers and Klein, 1983). Second, hydrocracking of the thermally stable intermit links just noted should fragment dimers and trimers to single-ring products. An additional incentive is that the single-ring product fraction resulting from the catalytic hydrodeoxygenation of lignin should also be less complicated than its purely thermal analogue because of the removal of oxygen-containing substituents. Previous analyses of the hydrodeoxygenation of simple oxygen-containing compounds over hydroprocessing catalysts provided a framework for the present study. The hydrodeoxygenation of dibenzofuran (Krishnamurthy et al., 1981), cresols (Odebunmi and Ollis, 1983) anisole and guaiacol (Hurff and Klein, 1983; Bredenberg et al., 1982), and 4-propylguaiacol (Vuori and Bredenberg, 1984) demonstrates the feasibility of oxygen removal at conditions far less severe than required for thermal fragmentation and deoxygenation. In summary of what follows, the first of the remaining sections delineates experimental and analytical methods. Experimental results follow. Next is our discussion of the present results both in relation to previous hydrodeoxygenation studies and also in terms of their implications to the liquefaction of actual lignins.
Experimental Methods Table I lists the structures of the reactants and also the experimental conditions of initial reactant and catalyst 0 1985 American Chemical Society
