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APPLICABILITY OF WIPED-FILM EVAPORATION TECHNOLOGY m7-R3 2C79.5r-3 pap-
FOR WASTE MINIMIZATION PURPOSES WITH
William J. Keller, Jr.
A feasibility study was done to determine if a wiped- film evaporator could be successfully used to reduce the volume of five nitro-organic still bottoms streams. The 3 . 8 million pounds per year of waste are currently incinerated.
The wiped-film evaporator was successfully employed in the recovery of n-ethylmetatoluidine, metaphenylenediamine, n,n-diethylmetatoluidine, aniline, n,n-diethylanilhe, and n-ethylaniline. of material currently wasted by 41% to 2.2 million pounds a year. The recovered products represent an annual net increase of 1.6 million dollars. A byproduct discovered in the waste, o-aminophenol, represents an additional $617,000 annual increase in revenue.
A production WFE would reduce the amount
The protection of the environment has become a major priority for the people of the United States. and state governments have responded to public pressure by passing legislative acts that not only establish lower acceptable discharge concentrations for pollutants, but also provide tougher penalties for those failing to abide by these regulations. A s a result, waste treatment and handling has become an increasing financial burden and a legal concern for many industries.
A chemical company that is currently losing significant amounts of marketable products in process waste streams has been targeted for a waste minimization study. The purpose of this study was to determine the feasibility of wiped-film evaporation as a waste minimization tool in the recovery of product materials from several of their waste streams.
The waste streams studied are generated from processes used to manufacture a variety of nitro-organic compounds. All of the streams have general characteristics of high viscosity, high boiling points, and toxic decomposition products. existing plant facilities are tar-like byproducts that form during the production cycle. studied and their approximate compositions are listed in Table 1.
The major obstacles to further refining in
The waste streams that were
The vertical wiped-film evaporator (WFE) used in this study was a two inch diameter unit manufactured by Pope Scientific Inc ( 3 1 . The basic still components are composed of borosilicate glass, with the wiper drive system and blades made of 316 stainless steel and teflon,
Table 1. Approximate composition of waste streams targeted for waste minimization.
2 ,408 ,064 lb/yr Composition
Aniline (AN). Toluidine (TOL) Heavies**
737,976 lb/yr Composition
Metaphenylenediamine' (MPD) 4 0 % Heavies" 60%
326 ,318 lb/yr Composition
Ani 1 ine' 5 0 % Orthophenylenediamine. (OPD) 4 0 % Paraphenylenediamine' (PPD) 8% Metaphenylenediamine' (MPD) 2%
176,978 lb/yr Composition
N-Ethylmetatoluidine' (NEM) 14 % #1 Heavies". 13%
#2 Heavies" 40% N,N-Diethylmetatoluidine' (DEM) 3 3 %
153,677 lb/yr Composition
N-Ethylaniline' (NEIA) N,N-Diethylaniline (DEA) Heavies"
9% 4 0 % 51%
. Desired product .. Heavies are unidentified relatively non-volatile
materials of asphalt-like consistency. 0.. #1 heavies are heavies that elute on the gas
chromatograph between NEM and DEM.
Figure 1. evaporator.
Basic still configuration for wiped-film
respectively. illustrated in Figure 1.
The basic system configuration is
Waste stream material was charged into the feed tank of the WFE, mercury (mm HG) absolute pressure, and heated to the desired experimental temperature. maintained at a 1-3 drops per second feed rate. All experimental conditions were then recorded, and the collected WFE product cuts weighed and analyzed.
and product purity percentages were plotted against WFE wall temperature. temperature for optimum recovery and purity percentages.
The WFE was evacuated to 5 millimeters of
Feed material flow was
After several experimental runs, the product recovery
These plots were used to determine the
The experimental results of the five streams studied are individually presented and discussed below.
As illustrated in Figure 2, the recovery of aniline from Stream 1 material was successful. The optimum
. . . . . . . . . . . ............................................................. . . . . . . . . . . 1 , , 1 , , 1 1 1 , I . . . . . . . . . . . * # , , , . . , I I . . . . . . . . . . . , , , , . . , .
. . , . 0 " " " " " . . . . . . . . 0 8 IQ Q cp ,e ,\Q ,+ ,* ,@ ,@ ,@ ,+ ,@
TEMPERATURE (dag C)
Figure 2. Stream 1 experimental recovery and recoverec product purity.
temperature range for recovery is 13O-14O0C, which corresponds to the concurrent maximums of 85% for both product recovery and purity. of 95% occurred at 160C, the exiting bottoms were extremely viscous and determined to be unpumpable with existing equipment.
Although a maximum recovery
The MPD recovery percentages of greater than 95%, as shown in Figure 3, represent another successful recovery attempt. Practical application of this method, however, may be difficult. Localized hot and cold spots within the still resulted in the freezing of WFE bottoms material. In a production facility, this could result in the plugging of pipes and other equipment.
Although the product purity percentages for these experiments, as illustrated in Figure 4, were promising, recovery percentages could only be calculated for two experimental runs. on every localized cold spot, which resulted in several clogs.
The OPD component of the stream froze
Due to the lack of valid recovery data, this cannot
PURlTY .. .- ........... .................
ieo IIM im in im 11y) im 1s m TUIPERATURE (d.a C)
igure 3. Stream 2 experimental recovery and recoverec product purity. -3
i i i i f v .... .:. ..... -:. ..... .:. ..... .:. ..... .: ....
. . . . 6
.................. ~ ANILINE PURITY
OPD WRm * ANIUNE RECOVERY . om RECOMRY .....................
m, 1 ; ............ . . 0
95 loo m n a o s so TEMPERAWE (dog C)
igure 4. Stream 3 experimental recovery and recoverec product purity.
be considered a successful recovery attempt. Furthermore, until OPD freezing can be prevented, this is not a viable recovery method.
As Figure 5 demonstrates, the recovered product purity remained relatively constant throughout the experimental runs. The recovery percentages, however, increased with progressively higher WFE wall temperatures. The 95% recovery level achieved with a WFE wall temperature of 190" allowed this to be designated a successful recovery.
The two distinct recovery percentage groupings in Figure 6 represent two different internal condenser operating temperatures. The low recovery percentages occurred at high (75-85OC) internal condenser temperatures, while the higher percentages occurred with low (25-30'C) internal condenser temperatures.
1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
....... e ............. . . . . . . . ......
9 * .................................................... i ! : : : ! : 8 NEM RECOVERY
'I DEM RECOVERY
' NEM PURITY DEM PURITY
120 130 140 15D 180 170 180 190
WALL TEMP (deg C)
Figure 5. Stream 4 experimental recovery and recovered product purity.
. . . . . . . . . . . . .
-.- NEA PURITY NEA RECOVERY
DEA RECOVERY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
, . .
I S . , ,
, , I * . . . . . . . . ' i : : : : : : : 0 : : : : : :
. . . . . . . .
90 95 100 10511011s1201~ 1 ~ 1 3 6 1 4 0 1 ~ 1m1561m
TEMPERATURE (dag C)
igure 6. Stream 5 experimental recovery and recoverec product purity.
The low internal condenser runs resulted in recovery percentages of up to 80%. When combined with the relatively constant product purities, it was determined that another successful recovery had been achieved.
An added benefit to this study involved Stream 1 material. The solids were analyzed, and found to be o-aminophenol (OAP), an extremely valuable material.
Crystalline solids were present in this stream.
Since the production method is a cyclic process, Stream i composition will change during the course of a process cycle. The possibility of OAP recovery made it desirable to know the changes in Stream 1 OAP and aniline concentrations throughout a production cycle.
Aniline concentration, as illustrated in Figure 7 , remained within the 40-60% range throughout cycle life. OAP concentration, however, increased from less than 1% to approximately 16% by the end of the cycle. that OAP production could be maximized, representing a new and significant source of revenue.
. . . . . . . . . . . . . . . . . . . . . . .
I 1 I 1 I . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . .
- q Y r ! ! t... . . . .
ELAPSED TIME (hm) I
Figure 7. Aniline and OAP concentrations in Stream 1 during a production process cycle.
Even though successful recoveries have been declared for four of the five targeted streams, process economics ultimately govern the applicability of a treatment system. The economic feasibility presents the potential increase in revenue based upon current market value of the recovered products.
respective finishing processes, and this expenditure was not considered in this analysis. WFE operational expenses and the expected decreases in waste disposal costs were also ignored.
All recovered products are to be reintroduced to their
Expected annual increase in revenue from WFE recovery operations was evaluated by calculating the quantity of material recovered at market values. That is:
Revenue = (Mass Flow)(Recovery Fraction) (Market Value)
For example, the aniline recovered from Stream 1 at the optimum recovery of 85% was calculated as
(1,336,957-) lb (0.852) ( = $517,068 /yr Yr lb lb
Anticipated revenues calculated for each stream (Table 10.1) were summed to yield a total potential revenue increase of $1.6 million annually.
Cooling and filtering Stream 1 material would be a means of reclaiming the 16,956 lbs of OAP lost every process cycle. This wasted OAP represents, at current market prices, an annual loss of $671,000.
Table 10.1. The calculation of expected gross revenues resulting from the recovery of products in the WFE.
CURRENT WFE STREAM COMPONENT MARKET RECOVERY REVENUE NUMBER COMPONENT MASS VALUE PERCENT RECOVERED
1 ANILINE 1,336,957 0.455 85 517 , 068
2 MPD 292 , 755 2.63 95 731,449
3 ANILINE 163,159 0.455 0 MPD 130,527 2.63 0 OPD 26,105 3.77 0 PPD 6,526 5.80 0
0 0 0 0
4 NEM 25,449 2.60 95 62 860 DEM 58 , 686 2.60 95 144 , 954
5 NEA 13 , 308 1.80 80 19 , 164 DEA 61,563 2.00 80 98 , 501
Total 1,573 , 996
The WFE was successfully used for recovery of products from Streams 1, 2, 4, and 5. This represents a current annual loss of $1.6 million.
Filtering or centrifuging room temperature Stream 1 material would recover $671,000 of lost o-Aminophenol.
A better temperature control system for exposed glass surfaces of the WFE is needed for the processing of high boiling, quick freezing materials.
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