Ind. Eng. Chem. Res. 1990,29, 432-436
432
L S M = liquid split manager MSA = mass separating agents (MSA processes include all PSE and SPA processes) SSAD = separation synthesis advisor SSH = separation synthesis hierarchy ZMS = zeotropic mixture selector PSE = physical solvents/entrainers (PSE processes include azeotropic/extractive distillation, liquid-liquid extraction, and stripping) SPA = solid-phase agents (SPA processes include adsorption and membrane permeation)
Literature Cited Buchanan, B. G.; Shortliffe, E. H. Rule-Based Expert Systems; Addison-Wesley: New York, 1984. Chandrasekaran, B. Generic Tasks in Knowledge-Based Reasoning: High-Level Building Blocks for Expert System Design. IEEE Expert 1986, Fall, 23. Cusher, N. A. UCC IsoSiv Process. In Handbook of Petroleum Refining Processes; Meyers. R. A,, Ed.; McGraw-Hill: New York. 1986. Davis, J. F.; Shum, S.K.; Chandrasekaran, B.; Punch, W. F., 111. A Task-Oriented Approach to Malfunction Diagnosis in Complex Processing Plants. Presented a t NSF-AAAI Workshop in AI in Process Engineering, Columbia University, New York, March 1987. Debreczeni, E. J. Future Supply and Demand for Basic Petrochemicals. Chem. Eng. 1977, 84 (June 6), 135. Egan, C. J.; Luthy, R. V. Separation of Xylenes: Selective Solid Compound Formation with Carbon Tetrachloride. Ind. Eng. Chem. 1955; 17, 250. Feigenbaum, E. A.; Ruchanan, B. G.; Lederberg, J. On Generality and Problem Solving: A Case Study Involving the DENDRAL Program. Mach. Intelligence 1971, 6, 165. Gandikota, M. S. Expert Systems for Selection Problem Solving Using Classification and Critique. Masters Thesis, The Ohio State University. Columbus, 1988.
Horsley, L. H. Azeotropic Data-HI; ACS Advances in Chemistry Series 116; American Chemical Society: Washington, DC, 1973. Kelley, R. M. General Process Considerations. In Handbook of Separation Process Technology; Rousseau, R. W., Ed.; John Wiley: New York, 1987; Chapter 4. King, C. -7. Separation Processes, 2nd ed.; McGraw-Hill: New I’ork, 1980. Martin, G. Q. Guide to Predicting Azeotropes. Hydrocarbon Process. 1975, 54 (111, 241. Mowry, J. R. UOP Sorbex Separations Technology. In Handbook of Petroleum Refining Processes; Meyers, R. A,, Ed.; McGrawHill: New York, 1986. Myers, D. R.; Davis, J. F.; Herman, D. J. Still: An Expert System for Distillation Design. Computers in Chemical Engineering The Ohio State University: Columbus, 1988; Vol. 12, Nos. 9 and 10, p 959. Nadgir, V. M.; Liu, Y. A. Studies in Chemical Process Design and Synthesis, Part 5. AIChE J . 1983, 29 (6), 926. Nath, R.; Motard, R. L. Evolutionary Synthesis of Separation Processes. AIChE J . 1981, 27 (41, 578. Nishida, N.; Stephanopoulos, G.; Westerbert, A. W. A Review of Process Synthesis. AIChE J . 1981, 27 (31, 321. Prengle, W. H.; Barona, N. Make Petrochemicals by Liquid Phase Oxidation. Hydrocarbon Process. 1970, 49 (31, 106. Ramesh, T. S.;Shum, S. K.; Davis, J. F. A Structured Framework for Efficient Problem Solving Diagnostic Expert Systems. Comput. Chem. Engl. 1988, 12, 891. Rudd, D.; Powers, G.; Sirola, J. J. Process Synthesis: Prentice Hall: Englewood Cliffs, NJ, 1973. Smith, B. D. Design of Equilibrium Stage Processes; McGraw-Hill: New York, 1963. Thompson, R. W.; King, C. J. Systematic Synthesis of Separation Schemes. AIChE J . 1972, 28 (5), 941. Walas, S. M. Phase Equilibria in Chemical Engineering; Butterworths: Stoneham, MA, 1985. Received f o r review June 2, 1989 Revised manuscript received October 17, 1989 Accepted November 20. 1989
Waste Lubricating Oil Rerefining by Extraction-Flocculation. 2. A Method To Formulate Efficient Composite Solvents M. Alves dos Reis* and M. Silva Jeronimo Faculdade de Engenharia, Departamento d e Engenharia Quimica, R u a dos Bragas, 4099 Porto Codex, Port uga I
A method to design efficient composite solvents is described. The method consists of selecting one of the components miscible with base oil as the “basic component”. The hydrocarbons and butanone are possible examples of basic components. The other component or solution of components is globally treated as the “polar addition”. This is, for example, an alcohol, a ketone, or a solution of two or more of these compounds. A ternary diagram of waste oil/basic component/polar addition, where the phase envelope and the curves of constant sludge removal are plotted, summarizes all information necessary to select the best solvent composition. In all cases studied, addition of 1-3 g/L KOH to the alcohols has increased the sludge and/or additive removal from waste and virgin oils. Using this method, we have concluded that solvents based on n-hexane and 2-propanol with 3 g/L KOH are very efficient. The weight composition 0.25 waste oil, 0.20 n-hexane, 0.55 2-propanol is proposed for industrial use. 1. Introduction Treatment of waste oils with polar solvents may be an interesting alternative to the classical sulfuric acid treatment. This process was named extraction-flocculation by Reis (1982) because the solvent dissolves the base oil and simultaneously promotes the fast flocculation of the undesirable impurities. Since the sludge produced in this
* To whom correspondence should be addressed. 08S8-58S5/90/2629-0432$02.50/0
process is organic, it may be mixed with liquid fuels and burned or, better, find more noble applications. For example, it may be used as a component of offset inks (Reis and Jeronimo, 1982). This seems to overcome the major problem of the sulfuric acid treatment: the production of an acid sludge, which is a source of pollution and causes very difficult disposal problems. In our previous paper (Reis and Jeronimo, 1988) it was shown that the flocculating action and subsequent sludge removal promoted by the one-component solvents studied
0 1990 American Chemical Society
Ind. Eng. Chem. Res., Vol. 29, No. 3, 1990 433 Table I. Difference between the Solubility Parameters of Solvent, 8,, and Polyisobutylene, bZ solvent 1-butanol 1-propanol 2-propanol ethanol butanone
61-82, ( J / C ~ ~ ) ' / ~ solvent 7.0 propanone 8.2 n-hexane 7.4 cyclohexane 10.0 benzene
Polar compound 1
61-62, (J/cm3)'Iz
4.1 1.3 0.5 2.4
2.8 0.5
might be correlated with the difference in the solubility parameters of the solvent (6,) and of a typical polyolefin (6,) used in motor oil additive packages, polyisobutylene. When this difference is high, one should expect to obtain high sludge removal values. Table I shows that polar substances like alcohols and ketones have solubility parameters quite different from the solubility parameter of polyisobutylene. The capability of a polar solvent to segregate sludge from waste oils, as referred to above, is closely related to its solubility parameter. The polarity itself, as measured by the dipole moment, is not correlated with that capability. It was also shown that in some cases the polar solvent induces the formation of very stable dispersions, due to electrostatic repulsions. These dispersions can be destabilized by introducing in the solvent a small concentration of potassium hydrpxide, and this addition provides an effective way to increase the sludge removal from waste oils (Reis, 1982). In this paper, these principles are applied to find efficient and cheap solvents. 2. A Method To Formulate Composite Solvents In our previous paper (Reis and Jeronimo, 1988), the action of hydrocarbons, ketones, and alcohols on waste oils has been explained. Since an extraction-flocculation solvent must be soluble with the base oil at the operation temperature (generally room temperature, but not necessarily), alcohols and ketones having less than four carbon atoms had to be excluded from this study of one-component solvents. But it seems obvious that they may be used in the formulation of composite solvents for their established good antisolvency to the nonpolar or slightly polar macromolecules. In fact, data in Table I lend support to these concepts. This table suggests that 2-propanol would be a better flocculating agent than 1-butanol and ethanol even better than 2-propanol. Propanone would be more efficient than butanone, but none of these alcohols and ketone having less than four carbon atoms is miscible with base oil at room temperature. There is, in principle, a higher temperature where these one-component solvents may be extraction-flocculation solvents, e.g., where they have the compromised properties of being miscible with base oil and still being able to flocculate part of the undesirable components from waste oils. For example, to make n-hexane an extraction-flocculation solvent, one needs to cool it to a temperature where it is miscible with base oil and slightly miscible with the impurities to segregate; to make ethanol an extraction-flocculation solvent, one needs to heat it above room temperature. One process patented by the Institut FranGais du Petrole that has been industrially tested (Quang et al., 1973) is based on liquid propane, operating a t low temperatures. Butane and pentane are also claimed to be suitable. An increase of temperature increases the mutual solubility of oil/solvent but also decreases the capability to segregate sludge from waste oils because it also increases the mutual solubility of the solvent and the nonpolar or slightly polar macromolecules from the additive package.
0 0 Oil
0.5
1 n - Hexane
Figure 1. Phase envelopes for some systems of SAE-20 oilln-hexane/polar compound, 20 'C. Compositions in weight fractions. Me = methanol; E t = ethanol; 2-P = 2-propanol; Pr = propanone.
In this paper, we shall explore the use of composite so!vents at room temperature. We think this is a better alternative than using hot single solvents like propanone or 2-propanol or cooled hydrocarbons. The main reason for this choice is the belief that, by the proper selection of components and compositions, one can find formulations having a more favorable balance of the above-mentioned compromised properties. Solvents Based on a Hydrocarbon and a Polar Compound. Solvents based on hydrocarbons are generally cheap and easily available. Many hydrocarbons, e.g., nhexane, are also easy to recover by distillation and have low toxicity. These facts make hydrocarbons very promising components of extraction-flocculation solvents for industrial use. Since hydrocarbons are miscible with base oils and with the macromoleculesto be separated, one needs to introduce a polar compound along with the solvent. It seems obvious that, to increase the flocculation of these macromolecules and, consequently, to increase the sludge removal from waste oils, one must include in the solvent the minimum quantity of hydrocarbon or, equivalently, the maximum quantity of polar compound compatible with the necessary miscibility with base oils. So the first experimental study to make is the determination of the monophasic and biphasic regions in the ternary diagrams base oil/hydrocarbon/polar compound. To accomplish this task, one determines the lines that separate these two zones, named phase envelopes. The base oil used in this study has been SAE-20. In fact, it is the average oil that one finds in rerefined stocks. Nevertheless, considering several hydrocarbon/polar compound combinations, it was observed that, when SAE-20 is changed to SAE-10 or SAE-30, consequent changes in the phase envelopes are unimportant. Figure 1 shows the phase envelopes obtained for some SAE-2O/n-hexane/polar compound systems. If one substitutes rz-hexane by another hydrocarbon, for example, benzene, toluene, or cyclohexane, the corresponding changes in the phase envelope are very small. The next step is the determination of sludge removal from waste oils, in the monophasic region. The compositions that must be studied are represented by points at the right side of the phase envelope lines. The experimental method to determine the percent sludge removal has been described (Reis and Jeronimo, 1988).
434
Ind. Eng. Chem. Res., Vol. 29, No. 3, 1990 2 - Propanol
'n
6
\~
\
0 1 O
011
I
0.5
,
\
\
\
\
\
\.
\
\
1
n -Hexane
Figure 2. Phase envelope for the system SAE-20 oil/n-hexane/2propanol, 20 "C. Compositions in weight fractions. Dotted lines are lines of constant solvent-to-oil ratio.
Methanol and Ethanol. These alcohols have no technical utility in combination with n-hexane for extraction-flocculation of macromolecules from base oil because of immiscibility. In fact, the monophasic region is very narrow, and in the case of methanol, if one substitutes SAE-20 base oil by a waste oil, compositions inside the monophasic region generate two phases, a fact explained by the existence of other solutes in the base oil contained in the waste oil. For this reason, the phase envelope curves in Figure 1 do not apply when SAE-20 is replaced by a waste oil. This simply means that compositions with technological interest are located a t some distances to the right side of the phase envelope line. In fact, the formation of two phases is not acceptable because it implies loss of oil with the sludge. When the polar compound is ethanol, miscibility problems are not so serious, but as shown by Reis (1982), it is not possible to obtain a binary solvent n-hexanelethanol giving better sludge removal than the better one-component solvent (1-butanol). 2-Propanol. Figure 2 shows the phase envelope for the system SAE-20/n-hexane/2-propanol. The dotted lines are the geometric sites of compositions corresponding to constant solvent-to-oil weight ratios. By substituting SAE-20 base oil by a waste oil, one can study the sludge removal for any composition on the monophasic region. When the solvent to waste oil ratio, R, is below 1.5, sludge removal values are small, and due to a high viscosity of the solution, the settling of flocculated particles is slow. If the solvent to waste oil ratio is high, extraction-flocculation and solvent recovery equipment and operation will be expensive. Having in mind these reasons, the compositions studied are located between the lines defined by R = 1.5 and R = 9. If in Figure 2 one follows one of the dotted lines from the abcissas axis in the direction of the phase envelope line, the fraction of 2-propanol increases by the same amount the fraction of n-hexane decreases, because the oil fraction is constant. The sludge removal is expected to increase in this direction unless some critical polarity is reached where part of the segregated matter forms a dispersed phase, stabilized by electrostatic repulsions (Reis, 1982; Reis and Jeronimo, 1988). It was observed, without exceptions, that the addition of 3 g/L KOH to any alcohol used as a component of extraction-flocculation solvents significantly improves the
3 0
10
20
KOH Concentration in 2 - p r o p a n o l , g / L
Figure 3. Sludge removal for the system waste oil (0.25)ln-hexane (0.20)/2-propanol (0.55) versus KOH concentration in 2-propanol, 20 "C. This composition is represeilted by point P in Figure 2.
sludge removal obtained for any composition outside the phase envelope. If this addition is made, one may be sure that following a dotted line in Figure 2 in the direction of the phase envelope line always increases the sludge removal from waste oil. The optimal KOH concentration in the alcohol may be determined for a selected composition point in Figure 2, by plotting the sludge removal versus KOH concentration in the alcohol. Figure 3 shows one of these plots, obtained for the composition represented in Figure 2 by point P: oil = 0.25, n-hexane = 0.20, 2-propanol = 0.55. In all other cases studied, the optimal concentration is between 1 and 3 g/L. The existence of a KOH optimal concentration may be confirmed by comparing the settling curves obtained for a fixed waste oil/n-hexane/2-propanol composition and several KOH concentrations. Figure 4 quite sharply shows the existence of an optimal concentration somewhere between 3 and 4 g/L, possibly very near 3 g/L. The method to obtain these settling curves was previously described (Reis and Jeronimo, 1988). The sludge removal results obtained for the range of compositions between lines R = 1.5 and R = 9 in Figure 2 may be plotted as curves of constant percent sludge removal. These are drawn as follows. By selecting a few composition points in each line of constant solvent-to-oil ratio, the percent sludge removal is determined and plotted as a function of the weight of 2-propanol per unit weight of oil + n-hexane. When these abcissas are chosen, the sludge removal lines are initially linear like the sludge removal curves obtained for single solvents (Figure 5 ) . The points of intersection of an horizontal line with these curves are points of constant sludge removal. These points were plotted in Figure 6. The waste oil used in these determinations is the average waste oil referred as MWO in our previous paper (Reis and Jeronimo, 1988). Other Binary and Multicomponent Solvents. As shown previously (Reis and Jeronimo, 1988), 1-butanol is the best single solvent. This suggests its selection to
Ind. Eng. Chem. Res., Vol. 29, No. 3, 1990 435 2 -Propanol
'n 10 0.5
5 c
c
e
L
m
-5 c
al al
5
0
5
L
011
c
L
0.5
1
n - Hexane
Figure 6. Curves of constant sludge removal for the system waste oil/n-hexane/2-propanol with 3 g/L KOH, 20 "C. Curves plotted are geometric sites of compositions giving sludge removals of 0, 1,2, 3, 4, 5, and 6 g/100 g of waste oil.
cn
I
0
12.5
25
37.5
50
Time, min
Figure 4. Settling curves for waste oil (0.25)ln-hexane (0.20)/2propanol (0.55) considering several KOH concentrations in 2propanol, 20 "C.
0
0
1
2
3
Mass of 2-propanol/( mass of oil+ mass of n-hexane)
Figure 5. Sludge removal for the system waste oil/n-hexane/2propanol versus the mass of 2-propanol per unit of mass of waste oil plus n-hexane, 20 "C.
formulate composite solvents. Whisman et al. (1978),after methodic study, including pilot-scale testing (Corlew and Sluski, 1976),have proposed an efficient ternary solvent where the major component is 1-butanol. The other components are butanone and 2-propanol.
Ternary solvents may be studied by an experimental method similar to the method explained to obtain Figure 6 for the binary solvent n-hexane/2-propanol. Consider, for example, the ternary solvent butanone/propanone/ ethanol. Butanone must be taken as the basic component, because it is the only component miscible with base oil. A solution of propanone and ethanol is taken as the polar component, and a diagram similar to Figure 6 is obtained. The process is repeated for other propanone/ethanol solutions, leading to a set of diagrams summarizing the information to select the most efficient solvent. 3. Discussion It was observed that the formulation of binary solvents can be adequately made by first choosing a basic component, which must be miscible with base oil. For example, among the organic substances in Table I, the possible basic components are the hydrocarbons butanone or 1-butanol. The best choice may require other criteria, namely, price, ease of recovery, and safety. n-Hexane is a good choice by all these criteria, except for safety concerns, since it forms explosive mixtures with air. Nevertheless, there is large experience in its use in edible oil extraction, in plants very similar to waste oil rerefineries based on extractionflocculation. Since the sludge removal from waste oils is related to the segregation by antisolvency of nonpolar or slightly polar polymers, like polyisobutylene (Reis and Jeronimo, 1988),the next step in the development of a binary solvent is the addition of a polar compound in order to segregate these polymers, keeping the base oil completely soluble in the composite solvent. A figure like Figure 6, where the phase envelope and curves of constant sludge removal are plotted, summarizes the necessary information about the solvent performance. For example, following Figure 6, the authors propose for industrial use the weight composition represented by point P: waste oil = 0.25, n-hexane = 0.20, 2-propanol with 3 g/L KOH = 0.55. This composition is a good compromise of the necessary solvent properties: (i) high sludge removal; (ii) low solvent/waste oil ratio ( R = 3) to minimize the costs of equipment and operation of extraction-flocculation and solvent recovery by distillation; (iii) safe distance to the phase envelope to prevent the formation of two phases and loss of oil with the sludge. This design method based on the determination of the diagram exemplified in Figure 6 is easy to apply to other
436
I n d . E n g . Chem. Res. 1990,29, 436-439
binary solvents. For example, to study the binary solvent 1-butanol/ethanol, 1-butanol should replace n-hexane and ethanol should replace 2-propanol in Figure 6. Ternary and multicomponent solvents also can be studied by this method, but experimental work will increase as the variance of the system increases. For example, if one intends to study the action of solvents composed of butanone/propanone/ethanol,one must select butanone as the basic compound (replacing n-hexane in Figure 6) and a solution of propanone and ethanol as the polar component (replacing 2-propanol in Figure 6). A diagram similar to Figure 6 is obtained for this particular propanonelethano1 solution. Considering other propanone/ ethanol solutions, ranging from 0% to 100% propanone, a set of diagrams will summarize the necessary information to select the best solvent, having in mind the necessary technical and economic compromises. Generally, six of these diagrams are enough to design a ternary solvent. In all binary and ternary solvents studied by us, the addition of 1-3 g/L KOH has proved to increase the sludge and/or additive removal from waste and virgin oils. This action has been theoretically explained (Reis and Jeronimo, 1988). 4. Conclusions
The formulation of composite solvents for extractionflocculation can be made by selecting a compound miscible with the base oil as the “basic component”. This component may, like butanone and 1-butanol, have some some flocculating action on waste oil, or, like hydrocarbons, may not have this capability. In the case of hydrocarbons, a polar compound is necessary to promote the sludge segregation and flocculation. When the basic component has some flocculating action, the “polar component” is added to improve the solvent flocculating capability, increasing the sludge removal. This polar addition may be an alcohol, a ketone, or a solution of two or more of these compounds. The study of binary solvents is reported in the form of a ternary diagram, including information about solvent and
oil miscibility and the complete data about sludge removal. The method may be extended to ternary and multicomponent solvents, by selecting a basic component miscible with base oil and solutions of the other components as the polar component. In all solvents studied by us, including one-component solvents like 1-butanol, the addition of 1-3 g/L KOH to the alcohols in the solvents has proved to significantly increase sludge and/or additive removal from waste and virgin oils. Acknowledgment This work has been supporJed by a grant from Junta Nacional de InvestigaGgo Cientifica e Tecnoldgica and from PETROGAL, for which we express our gratitude. Registry No. KOH, 1310-58-3;1-butanol, 71-36-3; 1-propanol, 71-23-8; 2-propanol, 67-63-0; ethanol, 64-17-5; butanone, 78-93-3; propanone, 67-64-1; n-hexane, 110-54-3; cyclohexane, 110-82-7; benzene, 71-43-2.
Literature Cited Corlew, J. S.; Sluski, R. J. Treatment of Waste Lubricating Oil Using BERC/ERDA solvent. Report RI-76/11; Bartlesville Energy Energy Research Center: Bartlesville, OK, 1976. Quang, D. V.; Audibert, F.; De Ville, H. Process for Regenerating Used Lubricating Oils. U.S. Patent 3,773,658, Nov 1973. Reis, M. A. RegeneraGao de Oleos Lubrificantes Usados por ExtracGao-FloculaGao. Ph.D. Dissertation, Oporto University, Faculty of Engineering, Oporto, Portugal, 1982. Reis, M. A.; Jeronimo, M. S. Fabrico de Tinta de Base para Fabrico de Tinta de Impressa0 a Partir de Oleos Usados. Portuguese Patent 75 702, Oct 1982. Reis, M. A.; Jeronimo, M. S. Waste Lubricating Oil Rerefining by Extraction-Flocculation. 1. A Scientific Basis to Design Efficient Solvents. Ind. Eng. Chem. Res. 1988,27 (7), 1222-1228 Whisman, M. L.; Reynolds, J. W.; Goetzinger, J. W.; Cotton, F. 0. Process for Preparing Lubricating Oil from Used Waste Lubricating Oil. US.Patent 4,073,720, Feb 1978. Received f o r revieu! July 25, 1989 Accepted November 29, 1989
Absorption Method To Clean Solvent-Contaminated Process Air B j o r n L. A r m a n d , Helena B. Uddholm,* and Par T. Vikstrom Environmental Department, K-Konsult, S-117 80 Stockholm, Sweden
An absorption system t o purify process air and recover solvents has been developed. T h e system makes use of a new kind of absorber and evaporator, which are rotary-driven and designed to optimize the contact surface between the gas and the absorbent. A silicone oil was used as the absorbent. A test rig has been evaluated a t a pharmaceutical industry in Sweden. The tests have shown that the devices function very well mechanically and that the silicone oil is a suitable absorbent for many non-water-soluble solvents such as, for instance, methylene chloride, toluene, trichloroethylene, butyl acetate, and ethyl acetate. Considerable quantities of solvents escape with exhaust air from industrial processes. These not only have an adverse impact on the environment but also cause large financial losses for the industries. Existing methods to eliminate the gases are expensive; consequently, small- and medium-sized industries cannot afford the expense of installing a cleaning system. Appropriate methods to eliminate gaseous pollutants are adsorption on a solid, absorption in a liquid, or chemical reaction to form a harmless substance. The latter method usually entails the combustion of an organic substance and cannot be used
because of the possibility of the formation of chlorinated solvents such as dioxin. The high costs of installing absorption systems have led to the increasing use of adsorption systems, despite the advantages offered by the former technique. In order to find a satisfactory procedure to capture and recover solvents from processes with small air flows at low concentrations, we have developed a system that makes use of a new kind of absorber and evaporator. Many solvents are not very soluble in water, and therefore, the devices have been developed to also suit absorbents other 1990 American Chemical Society
