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Ind. Eng. Chem. Prod. Res. Dev. 1981, 20,688-693
standard compression set formula. The value calculated was called an effective compression set for the sample. These data were plotted vs. the time in assembly (Figure 10).
Results The rate of load loss for both densities of condensation material was approximately the same. The projected load retention value for the higher density equilbrium material was approximately the same as for the lower density
equilibrium material. Currently, the predicted percent retention of load is between 57 and 66% of original load, with the condensation material having a higher load retention value. If a material has a high load retention, it usually will have a low compression set. Both densities of condensation-type materials seem to prove this point. Samples will continue to be monitored yearly over the 10-year study. Receiued for review July 6 , 1981 Accepted August 28, 1981
Useful Products from Piperazine. Methylpiperazines and an Amorphous Dibasic Acid/Piperazine Polymer W. Tyler Gelger, 111, and Howard F. Rase" Department of Chemical Engineering, The Universiry of Texas, Austin, Texas 78772
Piperazine, a byproduct in ethylenediamine production with declining commercial value, was considered as a raw material for more valuable products. A catalytic process was developed for producing 1-methylpiperazine and 1+dimethylpiperazine in good yield using hydrodesulfurizationcatalysts with piperazine and methanol as reactants at atmospheric pressure and 350 'C. Piperazine was also polymerized with mixed dibasic acids primarily in the C10-C,2 range to yield a unique amorphous product suitable for polymer blends.
Piperazine (NH-CH2-CH2-NH-CH2-CH,) is a cyclic ethyleneamine that is formed as a byproduct in ethylenediamine manufacture. Although it has a number of small-volume uses, its major application as an animal anthelmintic is destined to decline precipitously because of the development of new and more effective drugs. There is thus considerable incentive for converting piperazine to more useful forms either by ring opening reactions or by reacting with other compounds to produce useful products. The purpose of the present study was to suggest and investigate several possible reaction schemes that could yield useful products a t mild conditions and with low-cost reactants. Three areas of investigation were pursued (1) decyclization of piperazine, (2) reaction of piperazine with methanol, and (3) polymerization of piperazine with byproduct mixed dibasic acids. The later two studies yielded potentially valuable processes while the first produced additional insights on the nature of hydrodenitrogenation.
Experimental Equipment and Procedures Catalytic Reactor and Reaction Procedure. All catalytic runs were made using a microreactor previously described by Harrison et al. (1965). Prior to each run the reactor, containing a catalyst charge, was purged for 10-20 min with nitrogen and then calcined for 4 h at 315 "C. This treatment was followed by sulfiding when desired, using a 11.3% H2S-in-H2mixture flowing at 500 (vol/ h)/vol of reactor at 315 "C. Catalysts studied were American Cyanimid commercial hydrodeaulfurization catalysts HDS-2A (Co-Mo/A1203, with 2.34% Co and 9.9% Mo), HDS-3A (Ni-Mo/A1203, with 2.5% Ni and 10.44% Mo), and a blank A1203. All were in form of 1/16-in.extrudates with nominal surface areas of 270, 180, and 200 m2/g, respectively. After sulfiding and purging, the feed of piperazine in xylene or methanol was introduced along with hydrogen or nitrogen. Some carrier gas was essential in order to 0196-4321 /8 I f f220-0688$01.25/0
prevent crystallization of piperazine in the small feed and product lines. Product Analysis. Gas chromatographic analysis of products was employed, using a Hewlett-Packard Model 5750 temperature-programmed gas chromatograph equipped with a thermal-conductivity detector. The column packing was 20% Carbowax 20M and 2% KOH on acid-washed 60/80 mesh Chromosorb W. Sampling was accomplished directly from the microreactor by means of a multiport Biotron sample value. Unknowns were identified by GC/MS analyses and comparison with knowns. Polymerization Techniques. Piperazine polymers were prepared via the salts of piperazine and dicarboxylic acids using the method of Coffman et al. (1947). In preparing the salt of dodecanedioic acid and piperazine, 7.494 g (0.0869 mol) of piperazine and 20.004 g (0.0869 mol) of acid were dissolved in 40 and 200 mL, respectively, of 95% ethanol. The acid solution was heated to completely dissolve the acid. Each solution was filtered, mixed together, and allowed to cool. A fine, white precipitate, which was formed very quickly as the solution cooled, was removed by filtration after 2 h of cooling. The precipitate was then dried and stored in a desiccator. Salts using a mixed acid were prepared in a similar manner using a mixed acid supplied by E. I. du Pont Company, called DBD. Polyamide was formed by placing the precipitated salt in a crucible in a laboratory oven supplied with a nitrogen purge. The oven temperature was held at 165 "C for 3.5 h, 200 "C for 1 h, and finally 230 "C for 35 min. Alternately, polyamide was formed by heating the salt in a vacuum oven at 170 "C and 30 in. HzO pressure for 60 h. The resulting polymers were analyzed by differential scanning calorimetry using a Perkin-Elmer Model DSC-2. Decyclization of Piperazine Ideally, decyclization of piperazine would combine splitting of the piperazine ring and addition of Hz or NH3 0 1981 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20,No. 4, 1981 689
to produce a straight-chain amine which would have a much larger market than piperazine itself. Unfortunately, the catalytic configuration required for decyclization is also favorable for denitrification, and there is a strong tendency for the intermediate nitrogen compound to rapidly decompose into NH3 and an alkane. This total process is an important aspect of petroleum refining called hydrodenitrogenation and is commonly practiced with either Co-Mo/A1203 or Ni-Mo/A120B. A number of studies on hydrodenitrogenation have been conducted using pyridine as a model for the nitrogen containing compounds in petroleum (McIlvried, 1971; Sonnemans et al., 1972; Sonnemans and Mars, 1974). Since pyridine, when hydrogenated, bears some resemblance to piperazine, its reaction sequence is of interest. Extensive studies by McIlvried (1971) at 315 "C and 750 psig have been reported and three steps described involving hydrogenation of pyridine to piperadine, ring cleavage to n-pentylamine, and finally deamination of the amine to form pentane and ammonia. This last step is very rapid and any attempt to inhibit it would require an unusual catalyst or selective poisoning of a standard hydrodenitrogenation catalyst. This later alternative was tested using the Ni-Mo/A1203 catalyst (HDS-SA) and ammonia as an inhibitor. Experimental Results on Decyclization. Although the solubility of piperazine in xylene is about one-seventh of that in water, xylene was selected as the solvent because it was nonreactive and did not interfere with the GC analysis. The screening tests conducted were confined to near atmospheric pressure. A solution of piperazine in p-xylene was fed at W / F values between 0.4 and 1.1 (g h)/cm3 of solution in the temperature range of 200 to 350 "C. At a value of W / F = 1,total conversion of piperazine was observed above 200 "C with a H2-to-piperazineratio of 0.12. Upon adding NH3 to the hydrogen while keeping the total gas flow rate constant, the piperazine conversion was reduced to 50-75%. When the NH3 flow was stopped, the conversion returned to loo%, indicating that the poisoning was temporary. In all tests the catalysts experienced massive coking and no significant amounts of vapor products other than unreacted reactants were detected. Results were similar with both sulfided and unsulfided catalysts. Higher H2 pressures obtained by high-pressure operation should prevent coking, but it is doubtful that the precursors formed would lead to useful compounds. The action of NH3 appears to be that of a temporary poison rather than a selectivity promoter. Clearly, the nitrogen atom in piperazine interacts with the active component of the catalyst and is in competition with the ammonia. Reaction of Piperazine with Methanol During the studies using piperazine dissolved in xylene some plugging problems, caused by the low solubility of piperazine in xylene, were encountered. Additional solvents were sought and methanol was found to be most attractive. A solution of 35 g of piperazine in 100 mL of methanol is below saturation conditions, yet 15 times more concentrated than saturated solutions in xylene. Pure methanol did not react when fed at 350 "C to a reactor charged with the Ni-Mo/A1203 catalysts. Piperazine in methanol was then fed at a W / F of 0.5 g/(cm3 of solution/h) at 350 "C. Hydrogen or nitrogen rates of 450-1500 standard volumes per liquid volume of feed were used as carrier gases largely to prevent piperazine crystallization in the product lines. Three distinct chromatographic peaks were observed in the effluent samples. One was clearly H20, and the other two were identified
by GC/MS and confirmed with pure compound samples as 1-methylpiperazine (MPP) and 1,4-dimethylpiperazine (DMPP). Both of these compounds are used in the polymer and specialty chemicals industry. MPP has been used as a catalyst in the production of urethane polymer foam (Maxey and Harrington, 19701, sulfur-containingpolyesters (Borg-Warner, 1966), and poly(epoxy-tetrafluoroethane) (Maxey and Harrington, 1970). The dimethyl compound, DMPP, has found much wider application, mainly as a catalyst for the cross-linking of epoxy-based polyurethanes (Seki, 1976). I t has also recently been used as a catalyst in dimerization of acrylonitrile (Onsager, 1976), polyester production (Gentry, 1975), and polymerization of epoxy resins with polyisocyanates (Monin, 1976). Piperazine and some alkyl-substituted piperazines have been used in patented corrosion inhibitors for water or alcohol solutions (Grayson, 1978). Thus, MPP should find application in this area. It is a liquid at room temperature and is more soluble in water than piperazine. The methyl group may also make it more soluble in hydrocarbons than piperazine. Piperazine and any monosubstituted piperazine would bond to the metal surface at the nitrogen atom, so DMNP will probably have less corrosion inhibiting properties. Both compounds have been produced by several methods using piperazine, monoethanolamine, or diethanolamine as a starting material. Piperazine can be reacted with formaldehyde over Ni/Si02 hydrogenation catalyst (Moss, 1976) to give MPP and DMPP. They can also be obtained from monoethanolamine and methanol with phosphoric acid as a catalyst at 1600 psi and 300 "C (Schulze, 1978) or from diethanol-methylamine and ammonia with phosphoric acid at 162 atm and 300 "C (Brennan et al., 1976). One German patent claims the use of methanol and piperazine at atmospheric pressure over 90.10, Si0-H3PO4 catalyst (Dockner et al., 1973). However, all of the other patented processes use straight chain amines as starting materials and require high pressures. No patents exist for a Ni-Mo or Co-Mo catalyzed process with methanol and piperazine feed at atmospheric pressure. Based on the appearance of H 2 0 in the product, the reaction of piperazine with methanol to form MPP and DMPP must be a simple dehydration reaction.
n ,N +
N,
- N,ApCH,
CH,OH
I
piperazine
methanol
+
H20
U
MPP
-
n n + HO, CH30H H3CNuNCHJ NuNCH3 + methanol MPP
DMPP
Using methanol and piperazine as starting materials has several advantages over alternate patented processes for producing these two methylpiperazines: (1)Methanol is a more economical feedstock than formaldehyde, since formaldehyde is manufactured from methanol. (2) Piperazine is also a much more economical feedstock than MEA or any other straight chain amine, since demand for it is decreasing. (3) Ni-Mo and Co-Mo on alumina are much easier to handle than the Si02-H3P04used in the one patented atmospheric-pressure process. (4) Using piperazine, methanol and Ni-MO or Co-Mo requires lower reaction pressures than needed in most of the patented processes. For these reasons a more detailed study of this unique catalytic route to MPP and DMPP was undertaken.
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 4, 1981 I00
0
I
Y
'
350°C
0
100
50
300'
I50
325'
350'
375'
T E M P E R A T U R E , 'c
TIME IMIN)
Figure 1. Typical catalyst deactivation patterns for unsulfided catalyst ( W / F = 0.7 g of cat./(cm3 of solution/h) for Ni-Mo and 0.6 for the others. H,/feed ratio = 1500 std volumes per liquid solution volume; pressure = 1 atm.
Figure 3. Piperazine conversions for various catalysts at time 100-175 min (see Figure 1 for conditions).
1
O' 0 -0
0
+ 300'
I
I
325'
350'
1
3750
1
TEMPERATURE, 'C
Figure 2. Effect of temperature of conversion and selectivity for unsulfided HDS 3A, Ni-Mo/Al,03 (see Figure 1 for conditions).
Detailed Experimental Observations. Based on the favorable preliminary observations, more detailed tests were conducted in the flow microreactor with a 2.3~1 methanol-piperazine feed solution. The effects of temperature, catalyst pretreatment, reactant feed rate, and ammonia concentration on conversion and selectivity were studied. Both the Ni-Mo/Alz03 (HDS-3A) and the CoMo/A1203 (HDS-2A) were tested. The HDS-SA catalyst was studied in the sulfided and unsulfided states, as well as in pellets and powder. Al,03 support was also tested. In all runs, l-methylpiperazine (MPP), 1,Cdimethylpiperazine (DMPP), and water were the major reaction products. Two minor byproducts were seen, one being pyrazine. The other was not positively identified, but was probably another substituted piperazine or pyrazine. The HDS-2A catalyst gave the highest conversion of piperazine, but produced a large amount of minor byproducts. Untreated HDS-SA gave a slightly smaller conversion of piperazine, but produced virtually no byproducts. Catalyst Deactivation. Catalyst deactivation was observed in all the experimental runs. Deactivation for all the catalysts was rapid at first, as shown in Figure 1,but leveled off after about 40 min. Selectivelywas not affected. The lined-out period was used for all comparisons. While catalyst fouling did occur, it was not as severe as in the decyclization studies as evidenced by appearance of the discharged samples. The spent Ni-Mo and Co-Mo catalysts were light to medium gray, and the blank alumina showed virtually no color change from its original white. In contrast, the spent catalyst in the decyclization studies appeared dark black with a noticeable surface deposit. Effect of Temperature. The general effect of temperature on piperazine conversion and selectivity for MPP and DMPP is shown in Figure 2 for Ni-Mo/AlzO,. Similar trends were observed for the other catalysts (Figures 3-5). At low temperatures, the piperazine conversion was low
360'
325'
350'
375'
TEMPERLTURE, 'C
Figure 4. Selectivity to l-methylpiperazine (see Figure 1 for conditions). >oo l
80
>
E
2
C o - M o A1203 N I - M o A1203
T E M P E R A T U R E , 'C
Figure 5. Selectivity to 1,4-dimethylpiperazine (see Figure 1 for conditions).
and MPP was the sole product. As the reaction temperature was increased, conversion increased and DMPP appeared as a major product. This behavior is expected for series reactions and was observed in all of the tests. Homogeneous Reaction and Wall Effects. A test was run with inert boiling chips in place of the catalyst to determine if the reaction proceeds uncatalyzed. The inert packing was selected to give the same reactor velocity and holdup and to assure complete heating of the reactants. No reaction was observed at 350 "C, and any ammonia added to the feed had no effect. Therefore, the walls of the reactor had no catalytic effects and homogeneous reactions were negligible. Effect of Catalyst Type on Conversion. Piperazine conversions for the four catalysts are shown in Figure 3 for run times in the range of 100-175 min where the activity decline was not as precipitous. These data suggest that the unsulifided Co-Mo catalyst is the most active, followed by unsulfided Ni-Mo, sulfided Ni-Mo, and blank A1203 Periodic checks of catalyst activity at a standard temperature of 350 "C makes it possible to list more accurate conversions at a standard condition and activity equivalent to 30 min run time. On this basis conversions are 100% for unsulfided Co-Mo, 96% for unsulfided Ni-
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 4, 1981 691 loo80
I
I
I
I
-
SO c
5 ? 60l-
0
i 420 0i
Co.Mo AI203
NI-MD A1203 a N I - M AI203,SUlfided ~ Blank A1203
AI >
Conversion c '.
MPP Selectivity
211 z u
0,o 049 a, 0.79
~
By.Products
1
0
a". '325
350 375 T E M P E R A T U R E , "C
400
Figure 8. Effect of W / F on conversion and selectivity.
ammonia partial pressure at 50 cm3/min is several orders of magnitude greater than the piperazine pressure. If ammonia blocked sites normally used by piperazine, then the piperazine conversion should drop drastically. Since the piperazine conversion is only slightly affected, methanol must be the reactant interacting with the catalyst. Carrier Gas Rate. Hydrogen or nitrogen were used throughout the tests to dilute the entering feed and prevent piperazine crystallization in the lines. Both gases gave identical results and, therefore, had no part in the reaction. As experience with the reactor operation grew, the carrier gas rate was decreased. This increased the experimental accuracy by increasing the product concentrations. To ensure that the results from the beginning and last of the testing program could be meaningfully compared, the effect of the carrier gas rate on conversion and selectivity was investigated and found to have negligible effect on conversion and no effect on selectivity over a flow-rate range of 60 to 200 standard cm3/min. Since the carrier gas flow rate is a small fraction of the total flow, this observation is reasonable. Catalyst-to-Feed Ratio. The effect of increasing the catalyst to feed ratio was observed at 350 and 375 "C, as shown in Figure 8. When the ratio was increased by about 60%, the piperazine conversion increased by 10%. Selectivity for DMPP also increased by nearly lo%, while the amount of byproducts stayed constant. Therefore, the production of MPP and DMPP is probably not an equilibrium reaction, or at least equilibrium is not approached at the conditions studied. Summary of Results with Methanol. (1)Although alumina effectively catalyzes the production of MPP and DMPP from methanol and piperazine at atmospheric pressure, the combination of Ni-Mo and Co-Mo with alumina increases the piperazine conversion by up to 20%. Co-Mo gives the highest piperazine conversions, but also produces a large amount of minor byproducts. (2) Ni-Mo and Co-Mo also enhance the catalyst selectivity for DMPP. Unsulfided Co-Mo gives higher piperazine conversions, lower selectivities for DMPP, and more bypro-
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 4, 1981
ducts than unsulfided Ni-Mo. (3) Unsulfded Ni-Mo gives higher piperazine conversions, higher selectivities for DMPP, and less byproducts than sulfided Ni-Mo. (4) The effectiveness factor for the cylindrical catalyst is about 1.0. No mass transfer limitations were observed at these conditions of temperature and pressure. (5) The catalytic sites probably interact with the methanol during the reaction rather than the piperazine. This was shown by the small effect ammonia had on piperazine conversion. (6) Piperazine conversion and DMPP selectivity can be increased by increasing the catalyst-to-feed ratio. The DMPP and MPP do not approach equilibrium at the temperatures and pressures used. A Low-Cost Piperazine Polymer Piperazine is considered a low-grade or waste product by many ethyleneamine producers. High-molecular-weight dibasic acid mixtures are marketed as low-cost byproducts of other processes. Since piperazine has been used with dibasic acids in several polyamide applications, a useful polymer produced from these two waste products could be valuable. This possibility was examined by preparing a polymer from piperazine and a commercial dibasic acid mixture using melt polymerization. The polymer was amorphous, unlike most polyamides, and therefore may be useful in polymer blends. For comparison with the mixed-acid/ piperazine polymer, a polymer was also made from piperazine and pure dodecanedioic acid, one of the main constituents of the acid mixture. Unlike the mixed-acid polymer, it was crystalline. Gentry (1975) has prepared and characterized a number of pure dibasic acid/ piperazine polyamides by solution, interfacial, and thermal condensation. Polyamide Polymerization. Piperazine and dibasic acid conveniently polymerize in a condensation reaction in which water is removed and an amide bond is formed as shown below. Since the reaction is reversible, the water formed must be driven off to produce a high-molecularweight polymer. /7 i I l ol
[Gq
HN
NH
piperazine
t I-CCR
CH
e
Y
h
N RC
OF
t
W.$
dibasic acid polyamide
To attain the high extent of reaction needed to produce high-molecular-weight polymers, stoichiometric equivalence of the reactants must be provided. This is most easily obtained by producing and purifying a 1:l salt of the diacid and diamine (Kaufman and Falcetta, 1977). Side reactions, impurities, and byproducts must be eliminated to achieve a high degree of polymerization, and reduced pressure aids in this goal. All impurities with a single functional group must be removed before polymerization, since they react with the growing polymer chain and effectively stop the chain growth. Only a small amount of impurity will severely decrease the degree of polymerization obtainable. Experimental Results Several polymer samples of piperazine and dibasic acid were made and analyzed. The mixture of dibasic acids gave a polymer with different properties from the pure dodecanedioic acid polymer, as summarized in Table I. Dibasic Acid Mixture Polymer. The composition of the dibasic mixture, which consisted primarily of highmolecular-weight acids, is given in Table 11. A piperazine acid salt was precipitated from methanol solution, using the method of Coffman et al. (1947) for pure
Table I. Properties of Piperazine-Dibasic Acid Salts and Polymers product and method of polymerization T g ,K T,, K structure poly( dibasic acid-piperazine) 300 365 amorphous 69 h at 160 "C initially under vacuum 60 h at 1 atm dibasic acid-piperazine salt 43 2 poly( dodecanedioicpiperazine) 69 h at 170 "C 41 5 crystalline 30 in. of H,O, vacuum (405)a 3.5 h at 165 "C 360 crystalline 1.0 h at 200 "C (315) 0.6 h at 230 "C N, purge, 1 atm dodecanedioic acid450 piperazine salt a Two melting points were observed. See text for discussion.
Table 11. Dibasic Acid Mixture Composition wt % component 34 dodecanedioic acid, C , , 40 undecanedioic acid, C,, 7 decanedioic acid, C,, 8.5 dibasic acids, C,-C, 1 monobasic acids 0.5 water 0.9 dinitrolauric 7.2 nitro-dibasic acids (NO,-DBA's) inorganic nitrogen compounds 0.9 100.0 total
acids. Since the monobasic acids and other impurities were present in very small concentrations, they probably remained in solution allowing formation of a very pure salt. The salt was placed in a 4-in. glass crucible and heated in an oven at 160 "C for 69 h. Initially, the heating was conducted under vacuum. The resulting polymer was dark black, very hard, and bonded to the glass crucible. The black color was probably due to excessive oxidation and could have been largely avoided by polymerizing the sample under nitrogen or vacuum during the entire heating period. The polymer was not crystalline as most nylons are, but was amorphous in appearance and behavior. This was probably caused by the presence of a mixture of dibasic acid chain lengths. Nylons crystallize due to hydrogen bonding between the amide and carbonyl groups. The different acid chain lengths in this polymer may prevent the formation of these bonds, since successive amide and carbonyl groups will not line up. This use of an acid mixture to produce amorphous polymers has been used before with other more common nylons. The glass transition temperature was at 300 K, as shown in Figure 9. Since the polymer was amorphous, it would not be expected to have a melting point. However, upon heating, some crystallization occurred near 330 K followed by melting. The areas under the curves that fall above and below the dotted horizontal line in Figure 9 are approximately equal, which indicated that all of the crystallinity occurred upon heating and did not exist in the polymer below 310 K. Since this polyamide is not capable of self-hydrogen bonding to the extent as those with more regular structures, it may be useful as a component in polymer blends. It has been suggested that miscible binary blends, those with a single amorphous phase containing both polymer
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 4, 1981 693 5.0
I
Scan R a t e : 20.0 d e g l m l n
Sample W t : 12.10mg
A
Scan R a t e : 2 0 . 0 d e g l m l n
“ t
1 I
P o l y m e r i z e d under vacuum S a m p l e W t : 10.0 mg
0.0 2;o 0 0 ’ 2;o
290
330 370 T E M P E R AT URE , K
410
Figure 9. DSC analysis of mixed-acid/piperazine polymer.
components, result only when the heat of mixing is exothermic (Barlow and Paul, 1981). ConsequentIy, if the pure components interact weakly in the pure state, they are more apt to form miscible blends of the lower endothermic energy required to dissociate the self-interactions, Therefore, the mixed-acid/piperazine polymer with its lower tendency to hydrogen bond may provide a way for incorporating nylon properties in blends with other polymers. Pure Dibasic Acid Polymer. A polymer was made from pure dodecanedioicacid and piperazine to see if its properties differed from the mixed-acid polymer discussed above. About haIf of the mixed acid was dodecanedioic accd, so the polymers might be expected to have similar properties. However, they exhibited several major differences. Polymer samples were prepared by two methods, one under vacuum and the other under a nitrogen purge. Both polymers were crystalline at ambient temperature and were a brown color. Again, the discoloration was probably due to oxidation, which is common with amine compounds. The polymer formed under vacuum was a lighter brown, indicating less oxidation. When the polymers were cooled quickly after differential-scanning colorimetry, they showed two crystalline forms upon remelting, as seen in Figure 10. The equal polymer segment lengths from the pure acid probably allowed for these two crystalline forms, which was not possible with the mixed-acid polymer. The polymer formed under vacuum showed a higher melting temperature than that made at atmospheric pressure. The longer reaction time and lowered pressure gave a higher degree of polymerization, and therefore a higher melting point. Conclusions. (1)Piperazine and DBD, a mixture of high molecular weight dibasic acids, will form an amorphous polyamide. The polymer has a glass transition temperature slightly above 25 OC. (2) The mixed-acid/
290
330 370 TEMPERATURE, O K
410
0
Figure IO. Melting endotherms for piperazine-dodecanedioic acid polymers.
piperazine polymer is amorphous due to the different chain lengths present in the acid mixture that prevent effective hydrogen bonding between polymer chains. (3) The mixed-acid/piperazinepolymer crystalIizes slightly when heated over 320 K. It then melts again at about 360 K. (4) Piperazine and dodecanedioic acid form a crystalline polymer that shows two crystal forms after rapid cooling from melt. General Conclusions It is apparent from these preliminary studies that several useful products can be produced using piperazine. The reactions over Co-Mo/A1208 or Ni-Mo/A1203 catalysts with methanol deserve further investigation of catalyst life characteristics,which in the brief tests in this study appear promising. Various polymer blends should be studied using the amorphous polymer produced in this study in order to establish its intrinsic value as a blending material. Literature Cited Barlow, J. W.; Paul, D. R. Ann. Rev. Meter. Sci. 1981, 1 1 , 299-319. Borg-Warner Cop. Neth. Patent 6 517 157, 1966. Brennan, M. E.; Yeakey, E. L.; Schulre, H. German Patent 2 624 042, 1976. Coffman, D. D.; Berchet, G. J.; Petemon, W. R.; Spangel, E. W. J . polLm. Scl. 1947, 2(3), 306. Dockner, T.; Toussaint, H.; Qedter, M. atKmen Patent 2 205 597, 1973. Gentry, D. R. Ph.D. Dlssertatbn, Clarkson College of Technology, Potsdam, N.Y., 1975. Harrlson, D. P.; Hall, J. W.; Rase, H. F. Ind. Eng. C b m . 1965, 57(1), 18. Kaufman, H. S.; Falcetta, J. J. “IntrPductlon to Polymer Science and Technology: An S E Textbook”; Wlley: New York, 1977; p 34. “Kirk-Othmb Encyclopedia of Chemical Technology“, 3rd ed.; Gayson, M., Ed.; Intersclence: New York, 1978 Vol. 11, pp 295-308. Maxey, E. M.; Harrlngton, J. T. German Patent 2019768, 1970. Mclhnied, H. G. I d . Eng. Chem. Process Des. Dev. 1971, 10, 125. Monln, Y. German Patent 2551 631, 1976. Moss, P. German Patent 2531 060, 1976. Onsager, 0. T. US. Patent 3950320, 1976. Schulre, H. U.S. Patent 4066649, 1978. Sekl, M. Japan Patent 100 193, 1976. Sonnemans, J., (kudrlaan, F., Mars, P. Roc. Int. Congr. &tal. 5th f a h Beach, 1972, 76, 1085. Sonnemans, J.; Mars, P. J . Catal. 1974. 34, 215. Received for review June 22, 1981 Accepted July 17, 1981
