Continuous Production of Acrylonitrile-Starch Graft Copolymers by Ceric Ion Catalysis Zoila Reyes, Carroll F. Clark, Frederick Dreier,l and Russell C. Phillips2 Stanford Research Institute, Menlo Park, Calif. 94025
C. R. Russell and C. E. Rist A-orthern Regional Research Laboratory, A g r i d t u r a l ResearLh Service, U.S . Dspartment of Agriculiure, Peoria, Ill. 61604
The continuous production of graft copolymers of wheat starch with acrylonitrile (AN) was investigated in a semipilot-scale plant. Process variables were studied in runs of 10-20 Ib conducted with deoxygenated, aqueous AN-starch dispersions and an aqueous ceric ammonium nitrate solution. The reactants were fed simultaneously a t controlled rates a t the top of a stirred reactor column and, after a few minutes of retention in the column, the mixture was piped to a hold tank and periodically filtered. Large samples of AN-starch copolymers were prepared a t different grafting levels, and their properties were evaluated. On the basis of the data developed, preliminary cost estimates were made on the process. Estimated selling prices range from 26#/lb (for a 9% graft) to 32#/lb (for a 52% graft).
Research on the graft copolymerization of wheat starch with acrylonitrile (AX) on a laboratory scale a t Stanford Research Institute has been previously reported (Reyes et al., 1966). 111 this work ceric ion was used to initiate grafting. The kinetics and mechanism of the graftiiig process were investigated and the preferred conditions for preparation of grafts rrith well-defined properties were established (Reyes, unpublished work). The characteristics of the laboratory saniples indicated t h a t AS-grafted starch, or chemical niodifications thereof, may have applications as industrial adhesives, soil conditioners, aiid additives to paper, and as plast,ics. With this foundation established, the Sorthern Utilization Research and Development Division (NURDD) of the Xgricultural Research Service sponsored a pilot plant iiivestigation of ceric ion-initiated graft,ing.3 The purpose of the project ivas to provide large quantities of the product for evaluation aiid reliable engineering data for preliminary design and cost est'imatioii of a production facility. Experimental
Materials. T h e materials listed below were used without further purification in the pilot plant investigation: Material
Wheat starch, granular, 9.&lO.O% H20 Acrylonitrile (AN) Ceric ammonium nitrate
(CAN) K t r i c acid
Source
Hercules, Inc. ( S o . 120) Matheson, Coleniari and Bell Matheson, Coleman and Bell Baker Chemical
Present address, General Aniline & Filii1 Corp., Consumer Photo IXvision, 85% SW Hall Bv. Progress, Portland, Ore. 97027. * To whom correspondence should be addressed. 3 Presented at 16lst meeting, ACS, Los Angeles, California, March 28-.lpril 2, 1972. This research was conducted by Stanford Research Institute, Menlo Park, Calif., under contract with the USIIA and authorized by the Research and 1Iarketing Act of 1946. The contract was supervised by the Korthern Regional Research Laboratory, which is headquarters for the Northern llarketing and Nutrition Research Division, Agricultural Research Service, USDA! Peoria, Ill. JIention of firm nanies or commercial products does n o t constitute an endorsement by the USIIA over similar firms or products not mentioned. 62
Ind. Eng. Chem. Process Des. Develop., Vol. 12, No. 1, 1973
Analytical Methods. Catalyst Standardization. T h e ceric ion catalyst solutions, approximately 0.1N CAN in 1 S HNOs, were standardized with arsenic trioxide b y using osmium tetroxide as catalyst. X c i s t u r e Conteqt. The moisture content of the products of the large-scale pilot plant runs was determined b y t h e loss in weight observed when samples of the product's were dried in two ways: by vacuum drying t o constant weight in a vacuum oven a t 40-50°C and by azeot'ropic distillation with benzene followed by vacuum drying as in the first method. Equal values were obtained b y both methods; therefore, vacuum drying alone was used for all the samples. Homopolymer Content. The amount of homopolymer or ungrafted polyacryloiiit,rile (P-iX) in the products was determined by the weight of polynier extracted from samples of the dried graft with warm S,i1'-dimethylformamide ( D l I F ) . Usually the average amount of homopolymer extracted from the five samples was taken as the ungrafted P I S in the product. Grafted A S . The percentage of grafted XK in the copolymers was calculated from the nitrogen analysis of DlIF-extracted samples of the products. The molecular weight of the grafted P A i Sobtained by acid hydrolysis of the grafts ( D l I F extracted products) tvas determined viscometrically by the method of Cleland aiid Stockmayer (1955). The number of anhydroglucose units (AGU) per branch was calculated from the molecular weight of the grafted P+\S and percentage of An' in the graft. Solubility. The solubility of the large samples of AXstarch graft was evaluated in the following solvents: dimethylsulfoxide (DlISO), dimethylacetamide (DhLLi), formamide, D X F , cyclohexanone, butyrolactoiie, ethylene glycol, benzyl alcohol, chloroform, trichloroethaiie, ethylene chlorohydrin xylene, dimethyl hydrogen phosphite, 90% formic acid, water, aiid 1 s KOH. Paste Viscosity. The paste viscosity of the grafted products was determined in DlISO with a Brookfield Synchro-lectric Viscometer, 1Iodel RVF. h sample of the uiiextracted graft (45.0 grams) was dispersed in DAIS0 (405 grams) and the
dispersion was stirred and heated to 80°C in a constant temperature bath kept a t 90°C. It took 30 min of heating in the constant temperature bath t'o reach the desired teniperature. The viscosity of t'he resulting dispersion was measured at, 75OC, then, after cooling t o 25OC, and finally after t h e sample had been aged 24 h r a t 25°C. For comparison, the viscosity of a starch paste prepared under similar conditions was also determined. Modifications of Laboratory Procedure. Because conimercial AN contains polymerization inhibitors, a laboratory r u n was made with undistilled An' t o determine t h e effect of these inhibitors on the grafting reaction. Starch (0.05 ilGU), AX (0.1 mole), CA?; ( 5 ml of 0 . 1 5 in 1 N H?;03), and distilled water to make u p a volume of 100 nil mere used for this reaction, conducted a t 30°C for 30 min. T h e results are presented below with those froin ari identical reaction conducted with distilled AN :
NITROGEN SPAAGE TUBES
ACRlLONIT
CATALYST STORAGE
'r Figure 1. Pilot plant process flow sheet
Graft
yield, AN
9
111stilled received
12 59 12 49
AN in graft,
% 33 54 30 i 8
PAN,
Conversion,
g
%
0 33 0 38
85 73 79 75
There was little differeiice between the runs in total product coiiyield and amount of homopolymer produced. The tent of the graft obtained with -1s as received n-as 2.77, lower ' an thaii that of the graft obtained with distilled AS;thi: is acceptablj- m a l l peiialty for the process simplification. Consequently, AS was used without di,3tillation in the pilot plant irive st iga t ion, 111 addition, since the grafted starch contained only a small amount of homopol~-iiier,the IIAIF estractioii step was omitted i i i the large-scale experiments. Pilot Plant Studies. I n initial pilot plant studies, the grafting process included the follon-ing four steps : T h e starch was dispersed in water, the disperz' +ion pi-as deaerated, then previously deaerated acrylonitrile was added. This dispersion was added coiitinuously with the ceric catalyst solutioii t o the top of ail agitated reaction column. T h e reaction was terminated by esposure of the effluent f r o m the reactor t o air in a holding tank. T h e resulting graft polymer \vas filtered, washed with water, dried, ground, and screened. Tlie flow sheet of the pilot plant designed for these studies is preseiited in Figure 1. The pilot plant was designed with a nomiiial proceasing capacity of up t o 10 lb of dry starch per hour, equi\-aleiit to about 15 lb of product per hour. I he process as operated in this pilot plant is coiitinuous for the reactioii step but semicontinuous iii the preparation of reactants and recovery of the product. This niode of operatioii was selected because of the inaccuracies elitailed in coiitiiiuoudy feediiig small quant,itiesof solids in the pilot plant. Coiistruction materials for the pilot plant were selected that were resistaiit to the various solutions aiid would thua limit the contamination of the filial product. The major itenis of equipment, such as the mixing tank, agitators, and filters, were 302 staiiile teel. Hold tanks were constructed of polyethylene or steel, lined with a phenolic resin coatiiig. l h e reactor coluniri was made of tempered glass pipe 4 in. iii inside diameter by 36 in. long, n-ith Teflon end plates aiid a staiii1e.s steel agitator. Four 3-in. diameter tuibiiies were niouiited 011 the axial shaft. Tlie coniiecting piping was polyethyleiie !Tit11 nylon fittings. The valves were bronze, escept in the catalyst line to the reactor where a polyvinyl r .
7 ,
chloride valve vias used. The filter was of 316 stainless steel construction, and a spun polyethylene twill weighing 9.25 oz 'yd2 was used as t h e filter cloth. The polymerization was moderately exothermic, and cooling ivas provided in the reactor column by flowing cooliiig m t e r through six vertical ,-in. o.d. glass tubes arranged around the inside periphery of the glass pipe. These tubes also served as mixing baffles t o reduce the swirl in the column. The heat of polymerization tvas equivalent to about a 10°C rise in the reaction mixture temiperature; hoTvever, the temperature n-as easily controlled to less than 3OoC by runhirig cold water slowly through the tubes inside the reactor. Because of the potential hazard of handliiig quantities of -\S,a number of precautions were taken i n the design and operation of the pilot plant. AS is highly flammable aiid also toxic (both by inhalation and iii contact with the skin). The flammability hazard was partly reduced ill this process because it was necessary to blanket all equipment with iiitrogeii before the polymerization step to exclude oxygen from the reaction. The hazards weie also reduced because the -1s was dissolved in water throughout the process. However, for niaximuni safety air motors were used 011 all agitators and a n air pump was used to transport the -1S-starcli dispersion. In additioii, the equipment was set up in front of a hood with a high air flow to remove any voiatiles. I n i f i a l Runs. Two small batches (about 15 lb. each) of -1s-starch copolyrner were prepared by the following method. Aleasured amounts of tal) water (90.5 lb) and starch (10 Ib) were poured into the 30-gal mixing tank, agitated, aiid deosygeiiated by spargiiig with about 10 it3 mill of nitrogen gas for 15 min. The -1s\vas eparged with nitrogen aiid a neighed quantity (5.85 lb) was pumped into the starch-ivater dispersion. The reuultiiig mixture was then pumped t o an elerated 15-gal agitated hold tank from n-hich it coiitiiiuously flowed by gravity (through a regulating valve and a flow meter) to the t o p of the reaction column a t a n approximate rate of 1.8 lb niiii. The catalyst, a 0.0991S solution of C A S in 1 S nitric acid, !vas held in an elevated 15-gal storage tank and flowed to the top of the column through a valve and flow meter a t a ratio of 0.090 Ib min. -1catalybt to starch-water1S n-eight ratio of 1: 19.6 was used for both ruiis. The colicentrations of XS,starch, aiid C h S iii the reaction medium were 1-11, 0.5 A G P ,I.; and 0.005?1,respectively. Tlie reactor columii gave a nominal 10-miii retention time with the flow equivalent to 14 lb,hr of product. There appeared to Ind. Eng. Chem. Process Des. Develop., Vol. 12, No. 1, 1973
63
Table I Pilot plant no. 1
laboratory
Homopolymer, % A4Nin main product (includes homopolymer), % Conversion, %, based on AN Viscosity av mol wt, mV AGU/branch
Pilot plant no. 2
2
6
6
32.8
31.5
30.5
74.5
70.7
67.5
126,000 15,000
...
58,000 929
...
Table II Statistical reaction time, min
3 6 9 18
Vol of Homopolymer in dry reactants AN in dry retained, product, product, ml % %
2,471 4,942 7,413 7,413
24 29 29 31
5 0 4 0
3 4 4 5
0 3 5 7
AN in graft,
Conversion,
%
%
22 25 26 26
2 8 1 8
55 69 71 77
be a slight tendency for solids to collect on t'he walls a t the top of the column. The aqueous AN-starch-CAN reaction mixture flowed from the column to a n open 50-gal hold tank and was periodically filtered in the filter press. Exposure of the mixture to the air in the hold tank terminated the reaction. The reaction product filtered easily, forming a porous cake that could be washed with water while in the press. Air was blown through the filtered cake to remove excess wash watei-, and the press was opened to withdraw the cake. This material contained a n average of 60y0 water, which was removed by drying to a constant weight in a forced convection oven for a period of about 10 hr a t 75°C. The cake tended to shrink and crack on drying, which cont)ributed to easy drying. The dry product was readily ground in a hammer mill aiid then was screened to - 120 mesh through a continuous rotary screen. The oversize fraction (about 20%) was returned to the grinder for a second pass. For comparison, the results obtained in these two pilot plant' runs are presented in Table I with results from a similar laboratory run. Although slightly higher amounts of homopolymer were produced in t,he pilot plant runs, the initial products were very similar to the materials obtained iii the laboratory. Total product yield was not determined accurately for the first pilot plant run; 15.5 lb were obtained iii the second. Conversion and yield compared satisfactorily with those of large laboratory runs. The graft prepared in the continuous column reactor had shorter branches and therefore a higher grafting frequency (greater number of chains) than graft obtained in the laboratory run. It was not clear why there should be this difference between the products of the laboratory and pilot plant procedures. Grafts with comparable grafting frequency and chain size as those made in the pilot plant had previously been produced on a laboratory scale by alternate addition of A?; and CAT to the aqueous starch dispersion. To gain a better understanding of the reaction, this alternate addition of reactants was evaluated 011 a larger scale. The following procedure was used: Water (103 lb) and granular starch (11.2 lb) were weighed into a 40-gal tank, agitated, and deoxygenated with iiitiogen 64 Ind. Eng. Chem. Process Des. Develop., Vol. 12, No. 1 , 1973
gas (10 ft3/min) for 10 min. One twelfth (0.55 lb) of the total amount of AN to be grafted was added to the tank, and this was followed in 1 min by one twelfth (0.48 lb) of the total amount of 0 . l l N CAN solution required for the reaction. The mixture was allowed to react for 4 min, and the alternate additions were continued in the same manner for 1 hr, when the total amounts of both reactants had been added. The products of these runs had properties similar to those of the preceding pilot plant runs or to those obtained in laboratory reactions by the alternate addition procedure. The molecular weight of the grafted PAN ranged from 58,000 t,o 60,000 and the number of XGU/braiich ranged from 880 t o 930. This type of product seemed to characterize large-scale grafting of starch in the SRI process, regardless of reaction procedure (continuous or discontinuous addition of reagents), Before large quantities of grafts were made, several variables were investigated in the pilot plant'. Eflect of Reaction Time. The grafting of -1sto starch by ceric ion catalysis was studied as a function of time in the continuous column reactor. Water (206 Ib), starch (22.4 lb), hS (13.2 lb), and CAX (10.8 Ib of 0.0991N solution) were used for this run. The time of reaction was varied by changing the rate of flow of the reactants into the column and the volume of reactants retained in the column. After a given amount of material had reacted in the column for a specified period of time, the product was filtered, washed with water, aiid dried. Samples of these products were further drieJ to constant weight in a vacuum oven a t 40°C and characterized. Results are presented in Table 11. The percent conversion was calculated from the AN content of the product and t h e amount of AN fed to the reactor. Both the homopolymer content of the product and the amount of grafted AN increased with time of reaction; however, the latter leveled off within 9-10 min when grafting was essentially complete, whereas the amount of homopolymer continued to increase slowly after t'his time. Eflect of ;IN and C A N Concentrations. Several small batches (15-25 lb) mere made in the coritinuous column reactor to study the effect of variations in the coiicent'rations of AN and C . U . A summary of t,he operating conditions and results is presented in Table 111. It is clear that as the ratio of AN to starch is decreased, the add-on levels of AN in the product also decrease. However, the grafting levels at,taiiied in the last two batches were significantly lolver than expected. This was probably due to the lower coiicentrations of CALXused for these batches, yet iii laboratory-scale reactions a comparable decrease in the CALXconcentration had little effect. From these results aiid other pilot plant data, it appears that with a C A N concentration of 0.005 mol/'l,, different degrees of grafting can be obtained by varying the t o starch mole ratio. Thus, products containing 50,30, 15, aiid 10% -1scan be prepared by using .G-starch mole ratios of 4: 1, 2: 1, 1: 1, and 1:2, respectively. Preparation and Characterization of Large Samples of AN-Starch Graft. Three types of AX-starch graft were 1)rodnced in 115-120-lb lots in the cont'inuous column reactor. The general procedure used was similar to t h a t described above for tmheinitial runs, except t h a t for each run several batches of AY-starch-water misture were [irepared a i d continuously processed ill the reactor. Results were as shown in Table IV. T h e properties of these large samples are shown in Table V. Chemical 3lodijication of the .-I S-Starch Grafts.The solubility of the AN--starch grafts can be improved through
Table Ill Dry product
Flow rates to reactor, Ib/hr Water
Starch
107.3 106.7 99 94 102
11.2 11.21 22.5 22.4 22.5
AN
3.3 3.3 3.3 2.64 3.3
0.1 07N CAN
AN-starch mole ratio
6.42 6,42 6.41 3.3 2.56
1:l 1:l 1:2 1:2.5 1:2
Homopolymer,
Grafted AN, %
%
3.7 4 2 2.7 5.0 2 6
14.3 14 9 9.9 4.3 2.8
Table IV
-fa P
Sample no.
water, Ib
Starch, Ib
-\
103 106 7 99
11 2 11 21 22 5
B C
Statistical reaction
Reactants AN, Ib
6 6 3 3 3 3
chemical reactions of the nitrile or hydroxyl groups. The follomiiig three esamples of such reactions were briefly evaluated: Hydrolysis of the nitrile group by aqueous alkali yielded light' yellow, water-soluble product's. (A large portion of the P 1 N in the grafts was converted t'o sodium polyacrylate.)
CAN, Ib
time, min
5 4 of 0 0 9 9 1 s 6 4 of 0 1 0 4 5 s 6 57 of 0 1045s
10 8 8
AN,
no.
Starch, Ib
D
100
8.3
9.8
Ib
'
React,ioii of the nitrile group with hydroxylamine-introduced amidoxine groups improved solubility of the grafts iii water (Schouteden, 1957). Treatment of the grafts with 40y0aqueous formaldehyde in t h e presence of 1% ammonium chloride yielded products soluble in DNF. (Both the nitrile aiid hydroxyl groups can react with formaldehyde.) *Aqueous alkaline hydrolysis of samples of AQ-starch grafts from laboratory reactions yielded clear viscous solutions from which light yellow, water-soluble products were obtained. For this hydrolysis a 5-gram sample of the graft was refluxed with 100 ml of 1-V NaOH for l1I2hr. K h e n samples of products A, I3, arid C were subjected t o aqueous alkaline h\-drolysis viscous, dark brown, almost black, solutions were obtained. These products yielded light-colored solutions only when the hydrolysis was carried out in the presence of metal chelatiiig agents such as ethylenediaminetetraacetic acid (EDT;1). I t was inferred that traces of metal ions (possibly Fe"') preseiit in the grafts prepared in the pilot plant caused the discolorat'ioii observed during alkaline hydrolysis. Semiquantitative spectrographic analyses were made of the original starch, a graft from a laboratory react'ioii, and pilot plant product -1.As suspected, the latter contained the highest amount of iron, 40 ppm; starch contained 14 ppm, aiid the laboratory grat't contained 6 ppm. The pilot plaiit grafts adsorbed the iron salts possibly from the tap water used for their preparation and washing or from the stainless steel equipmelit. AN-Starch Grafts with Minimum Traces of Metallic Contaminants. Production of .lS-Starch Grafts in Plastic Equipment. To produce grafts a s free as possible from metallic coiitamiiiants, the stainless steel equipment in the pilot
%
2:l 1:l 1:2
Statistical reaction
Deionized water, Ib
Conversion,
87 3 77 97 7
plant was replaced by similar components made of glass fiber or polyethyleiie. TKOsmall runs made in the modified plant assembly with deionized water yielded products with little discoloratioii o n alkaline hydrolysis. h large-scale run (115 lb) was then prepared in a s?ries of batches, each of which was made with the following materials:
Reactants Sample
Dry product AN-starch, mole ratio
0.099N CAN, I b
5.44
Dry products
time, min
AN-starch mole ratio
Conversion.
4: 1
82.7
8
%
PROPERTIP OF PRODUCT D. Moisture coiltent, 4.1%. Melting point: There n a s no melting point: the starch grafts decomposed a t 285'C and charred a t 340°C. Total -1sin a
~
Table V. Properties of l a r g e Samples of AN-Starch Graft Sample no. B
A
Paste viscosity, cP; 10% in DMSO -it 75'C At 25OC .Aged a t 25' for 24 hr Melting point, "C Decomposed Charred Moisture content, yG Homopolymer 111 d r y l)roduct, 7 0 Grafted AS in dry DNF-extracted qample, 70 Molecular weight of grafter PAIX, .lGU/ branch Solubility
180 434 512
25 62 62
230 280 6
230 265 8
C
Starch
25 2400 71 8860 66 7440 230 270 9.5
7.5
7 5
4 9
290
149
9 3
62.000 36,000 36.000 1,270 2.170 937 The three samples dissolved in hot DMSO, and were partly +oluble in 11Xk1, formamide, DNF, but? rolactone, water, and l.\- KO13
Ind. Eng. Chem. Process Des. Develop., Vol. 12, No. 1, 1973
65
WATER AND UNREACTED A N 6100 l b l h r ACRYLONITRILE STORAGE
STARCH
7 2 0 go1 I h r I% A N
ACID M A K E U P
' o ~ oN
STORAGE
EXCESS WATER .DISCARD
CATALYST AND
CERIC AMMON-?
FILTRATE
320 lb/hr 4 8 g o I l hr
WEIGH FEEDER
COLUMN REACTOR CONTROL
DEOXYGENATOR MIXER
HOLD TANK
TO 85' F
c
I L
T U N N E L DRYER
ROTARY FILTER
MIXER I
_ _ _ _ _ LI __________________-_____________________------------J 185'F
HAMMER MILL
b F b F b F b
1000 I b PRODUCT 30 */a A N STARCH GRAFT
-
Figure 2. Commercial process flow sheet
dry, unextracted sample was 52YG. Homopolymer content: Because of the high AN content of the graft, it mas not possible to extract the homopolymer aithout removing a fraction of the graft. When 10-gram samples of the dry material were extracted four times n i t h 100 ml of warm D M F , the average weight of the DNF-soluble fraction n a s 30% of the weight of the sample. Infrared analysis, hone\ er, shoned this product to contain both starch and P A N , from its nitrogen analysis, the AS in the extract was 62.2YG. In a n effort to determine the composition of the D1IFsoluble product, a sample of the original material (10 gramb) n a s extracted five times u i t h 100 ml of warm D N F . The solids conteiit of the evtractioiis decreased from approximately 1y0for the first extractioii t o 0.1% for the fifth one Hoaever, infrared a n a l y w shoaed that both starch aiid PAN neie present iii all the fractions. I n addition, 110 change in the infrared spectrum of the pioduct in the first extraction was obsewed h\ extracting it mith 5Yc KaOH, thus iiidicatiiig that the starch present in this fraction mas grafted. The hS conteiit oi the DlIF-soluble product iii the fifth extraction lfas 66% aiid that of the main product obtained after the fifth extraction n a s 49.3%. This amount of &1Sis probablj grafted because little change in the nitrogen content of the main product n as observed on further extraction n i t h D N F . Fractionation of the product as described bj Fanta et al. (1966) yielded 38.6% of DlISO-H,O soluble product and 61.4% of DMF soluble; both contained starch and P-IX;. hsauming, then, that the graft contains 49.3% -4X and that no ungrafted staich is present, the initial unextracted is a mixture of 5.3% P A I S product that contains 52y0 -1s and 94.7% AN-starch graft. Ungrafted starch a a s not deteimiried M O L E C U LWLIGHT. ~R The molecular neight of the grafted PAK obtained b j hydrolysis of the DNF-evtracted sample was 158,000. (This PAS contained appreciable amounts of starch not removed b) hjdrollsis n i t h 0 . 5 s HC1 ) The .\GU branch n a s 1002. SOLUBILITY. The pioduct i oluble in DXSO, D l I F , and partly soluble in n ater, butyrolactone, dimethylacrylamine (DM 1i),formamide, benzyl alcohol, and 1S KOH. P a s ~ c~ I ~ C O S I TIN I DlISO. .kt 7s0C, the paste viscosity in DMSO n a s 887 5 cP, a t 25"C, 3,240 cP, and after aging a t 25°C for 24 hr. 3200 cP. 66 Ind.
Eng. Chem. Process Des. Develop., Vol. 1 2 , No. 1 ,
1973
ai^^^^^^ ALKALINE HYDROLYSIS. A 2-gram sample of product D suspended in 100 ml of I S S a O H was refluxed with stirring for approximately 90 min; a t the end of t h a t time a light yellow viscous solution was obtained. This product, prepared under conditions that avoided metallic contamination, more closely approximated the products of earlier laboratory runs than did the preceding pilot plant products. This seems to indicate that the grafting reaction is highly sensitive to low concentrations of iron. Estimated Costs for Production of AN-Starch Grafts b y Ceric Ion Catalysis
Plant Flow Sheet. A flow sheet for the commercial production of AX-starch grafts by ceric ion catalysis is shon n in Figure 2. The process shown is basically t h e same as t h a t used in the pilot plant to produce the four 100-lb samples of AX-starch grafts n i t h varying AS levels. T h e plant flon sheet is designed for completely contiiiuous operation, including recycle of the unreacted AX and recovery of the catalyst. N o s t of the equipment and operations shoan on the flow sheet were selected from the experience and data developed in the pilot plant, and thus the scale-up uncertainty is relatively low. On the other hand, there are possibly some alternative operatioiis and equipment that should be investigated to ensure optimum design of the full-scale plant. This applies primarily t o the filtration and catalyst recovery steps. -1continuous centrifugal separator is a n alternatir e to the iotarl filter, and the catalyst recovery might be better accomplished n i t h a precipitation or ion exchange process rather than evaporation of the filtrate. Iiicreasing the starch-towater iatio is another possible improvement in the process. However, as will be seen in the ensuiiig discussion of process economics, it is doubtful that any of these changes would reduce the production costs by more than 5%. Estimation Plant and Operating Costs. .\ plant capable of producing 5 million lb/yr of AS-starch grafts was estimated to cost $1,077,200. The plant investment is based on 1971 costs and a Marshall-Stevens Equipment Inde.; of 315 The annual operating costs nere estimated for a plant producing 5 million lb/yr of starch grafts with AS add-on
levels of 52, 30, 15, and 9%. These results are given in the following table with the resulting starch graft cost per pound : AN-starch
Annual operating costs, $1000’s AS-starch graft cost, %/lb
grafts
52%AN
30%AN
15%AN
9%AN
1600
1450
1350
1300
0 32
0 29
0 27
0 26
literature Cited
Cleland, It. L., Stockmayer, W. H., J . Poiymer S a . , 17, 473 (1955).
Fanta, G. F., Burr, R. C., Russell, C. R., Rist, C. E., J . A p p l . Polymer Scz., 10,929 (1966). Reyes, Zoila, unpublished work. Reyes, Zoila, Rist, C. E., Russell, C. It., J . Polymer S a . , Part A-1, 4, 1031-43 (1966). Schouteden, F. L. M., Xakromol. Chem., 2 4 , 2 5 (1957). RECEIIEDfor review 3Iarch 6, 1972 ACCLPTEDOctober 2, 1972 Presented at the Division of Carbohydrate Chemistry, 161st Meeting, rlCS, Los Angeles, Calif., Xarch 1971.
Effective local Compositions in Phase Equilibrium Correlations Jose M. Marina’ and Dimitrios P. Tassios Newark College of Engineering, nTewark, N . J . 0’7102
The ambiguity in choosing the proper value of cy in the NRTL equation is eliminated by replacing alpha by - 1 . For miscible systems, no loss in accuracy is observed when correlating binary vapor-liquid equilibrium (VLE) or predicting ternary behavior. For binary immiscible systems, better accuracies are obtained.
F o r a quantitative treatment of separation techniques, such as distillation and extraction, we must’ rely heavily on the phase equilibria relationships. There arises, therefore, the necessity of a functional expression between activity coefficient, temperature, and composition. Throughout the years several such expressions have been proposed. Among these, the equations of Van Laar (1913), lllargules (1895), and Wohl (1946) are probably the best known. More recently Wilson (1964), by introducing the concept of local mole fractions, developed a n expression which provides a very good represent,ation of miscible systems but fails to describe immiscible behavior. Later Renon and Prausnitz (1968) based on the concept of local mole fractions and Scott’s (1956) two-liquid theory, developed the nonrandom two-liquid ( S R T L ) equation, which describes with good accuracy miscible and immiscible systems. Both of these expressions seem to represent the data with a greater degree of accuracy than the previously proposed expressions. Since the Wilson equation contains only two parameters per binary system, it lends itself to the study of equilibrium from a pair of data points, such as in the case of azeotropic data. The XRTL equation, on the other hand, contains three parameters, thus requiring a minimum of three data points for their evaluation. Renon had some success in trying to overcome this problem by proposing rules for evaluation of the parameter CY from qualitative coilaiderations on the nature of the system and its components. However, a t times, these rules are ambiguous and difficult to apply. Our purpose in this work is to fill the gap between these two equatioiis, that is, to develop a true two-constant expres-
sion for miscible and immiscible systems. Such an expression would combine bhe advantages of both t’heWilson and S R T L expressions thus allowing not only prediction of vapor-liquid equilibrium from azeotropic data but also prediction of vaporliquid equilibrium (T’LE) from mutual solubility data and vice versa. The expression presented here is the result of an extensive study of the parameter a in the S R T L equation, indicating that the substitution a = - 1, not only yields the same degree of accuracy previously obtained for miscible systems, but improves data prediction for immiscible systems. NRTL Equation
Renon and Prausnitz (1968) modified Wilson’s equation for local mole fractions by introducing the constant CY to account for the nonrandom~iessof liquid solutions:
where S,j
=
local mole fraction of component i around a central molecule of j
gij
=
residual Gibbs energies
X1 and S2= mole fractioiis of components 1 and 2 LIaking use of this expression arid Scott’s (1956) two-liquid theory, they dereloped the N R T L equation, a three-parameter equation capable of describing VLE of miscible and immiscible systems with remarkable accuracy:
Present address, Merck & Co., Rahway, K.J. To whom correspondence should be addressed. Ind. Eng. Chem. Process Des. Develop., Vol. 1 2 , No. 1 , 1 9 7 3
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