Thesis Proposal
The Petroleum and Petrochemical College
Chulalongkorn University
Thesis title : Adsorption of surfactants on ink and on paper fibers related to paper recycling
Thesis for Master Degree in Petrochemical Technology
Name of student : Ms. Sureerat Jairakdee
Student I.D. no : 4271023063
Name of advisor : Prof. J. F. Scamehorn
Name of co-advisor : Assoc. Prof. Kunchana Bunyakiat
: Dr. Kitipat Siemanond
Acadamic year : 1996
Date of preparation : 31 March 2000
Student signature :
Approved by :
Introduction
Consumption of paper continues to grow in both the developed countries and countries with emerging economies in globalized and open market such as Southeast Asia. With continually growing demand for paper products, recovery and recycling of secondary fibers have become increasingly important.
The objective of paper recycling is to recover paper fibers from wastepaper, such as paper use in photocopying, which may contain ash, various chemicals, printed or copied inks (offset ink, copying toner particles, etc.) and/or other contaminants. Improved deinking technology has allowed more recycled fiber used in papermaking process while maintaining or improving quality of the final product.
“Deinking” is the process of removing ink and other contaminants from waste paper and there are two main techniques in current use : wash deinking and flotation deinking. “Wash deinking” is particularly useful for the ink and other particles being removed smaller than about 5 .mu.m. The process requires adding dispersants so that when a dilute waste paper pulp slurry is thickened, the very fine particles, including the hydrophilic flexographic type inks, will tend to stay with the water being removed to thereby produce a relatively clean pulp.
“Flotation deinking” entails forming an aqueous suspension of waste paper pulp fibers, inks, and other non-cellulosic contaminants and then mixing air into the suspension. In the presence of various additives, air bubbles selectively attach to ink particles and carry those particles to the surface of the aqueous suspension, thereby forming ink rich froth. The froth is then removed leaving behind a relatively ink-free fiber slurry. Flotation deinking process has heretofore been especially useful in removing hydrophobic inks with particle size larger than about 10 .mu.m. The additives used in such processes are generally specialty surfactants or fatty acids ,which are intended to agglomerate the relatively large hydrophobic ink particles to increase removal efficiency in flotation cell, and combined with calcium which acts as an activator. The exact mechanism of the interaction of surfactant with calcium, ink, and fiber is not well understood. This thesis will investigate the adsorptive mechanism of surfactant and co-adsorption of calcium on the ink.
Objectives
Scope of Research Work
This thesis research work studies on the adsorption characteristics of surfactant and co-adsorption of calcium on inks and on paper fibers at equilibrium. The effect of pH and calcium concentration to the adsorption surfactants on inks and on paper fibers will be investigated. The data from experiment will be plotted to analyze the adsorption isotherms of surfactants on inks and on paper fibers. The zeta potentials were determined at 30° C
Sodium octanoate, which represents medium chain length carboxylates will be used as surfactant, which adsorbs on the model ink (carbon black) and on paper fibers. Ca2+ from calcium chloride is used as co-adsorption. The pH condition in the experimental will be varied by sodium hydroxide (NaOH).
The experiments will work on the test tubes. In all the adsorption experimentation, the concentration of the calcium and surfactant will be remained below the solubility product equilibrium constant (Ksp) value so that no precipitation of surfactant occurred. The surfactant concentration will be remained below the CMC (critical micelle concentration) for all experiments.
Literature Survey
G.M. Dorris and N. Ngugen (1995) had studied flotation of model inks (flexographic inks) without fibers. Flexographic inks, which were composed of a pigment, usually carbon black that dispersed in water with the use of water soluble carboxylic derivatives, which also performed as binder. The results showed that, in basic condition, the floatability of flexographic inks at alkaline condition improved with the addition with calcium ions and much more so with the addition of both sodium oleate and calcium ions, under turbulent agitation. The results suggested that conventional calcium soaps of fatty acids were effective flotation collectors for flexographic inks. Contrary results obtained in flotation deinking mills suggest that the problem of deinkability of flexo inks may not be due only to poor floatability, but also to other phenomena such as ink redeposition on fibres.
Achille E.Riviello, Jr. (1997) had studied ink removal from secondary fiber by flotation deinking. The underlying mechanism of “ collector chemistry ” are elucidated and found to be complex combinations of the ink particle interactions stemming from the nature of the surfactant/calcium relationship. This study focuses on two medium chain-length fatty acids (sodium octanoate and sodium dodecanoate) and a comparable chain-length sulfate (sodium dodecyl sulfate) so as to be able to observe the system behavior below the Ksp of the surfactant/calcium complex. By investigating the adsorption isotherms of the surfactants on both model inks and fibers, the associated zeta potentials, the aggregation characteristics of the model ink, and the flotation of the ink and fibers, the fundamental mechanisms were found to be adsorptive rather than precipitative. This mechanistic understanding could translate into more efficient surfactant formulations for the flotation deinking process.
D.C. Schmidt and J.C. Berg (1997) had studied the selective removal of toner particles from repulped slurries by flotation. The role of particle shape on toner flotation was investigated. Model toner disks and spheres were created. Interactions of model particles with a fixed air bubble in a flow-tube were observed with high-speed cinematography. Motion analysis of the resulting pictures shows that disks differed from spheres in two ways: first, disks had a much higher probability of collision with the bubble than spheres; and second, after collision, disks were much less likely to attach to the bubble. Disks that collide with bubbles edge-on bounce off because contact time is too short. Disks that turn to their side before collision seldom attach because the drainage area is too large.
M. Rutland and R.J. Pugh (1997) had studied mechanism of surfactant and calcium in adsorption by surface force and coagulation technique. The surface force technique concerned the invention of fatty acid flotation collectors and calcium activator with a negatively charged mica substrate at high pH. Since the surface of ink particles under deinking conditions are enriched by negatively charged groups, these experiments enabled some details of the fundamental mechanisms involved in deinking flotation to be clarified. The results (carried out at relatively low calcium and fatty acid concentrations) summarized as follows: (a) At pH >10, the negatively charged surface generated a long range DLVO double-layer repulsion and the potential at the mica/electrolyte interface could be estimated. However, at short distances, a repulsive non - DLVO hydration barrier was detected due to adsorbed Na+. (b) On addition of CaCl2 ,the Na+ was replaced by the specific adsorption of the less strongly hydrated Ca(OH)+ solution species or more strongly hydrolyzable calcium species. This resulted in the elimination of the hydration forces and mica-mica contact. On addition of fatty acid, no change in the force profile was detected suggesting no calcium was removed from the surface and there was no evidence of calcium soap formation in the surface region. This result implies that under alkali conditions, the calcium does not induce a bridging mechanism in the presence of fatty acid (below the calcium soap precipitation level). In fact, the calcium could only operate as bridging agents if they can specifically bind to the surface, as well as to the carboxylated fatty acid. The “calcium dehydration/destabilization mechanism” was verified by coagulation studies with quartz suspension. At higher fatty acid and calcium concentrations, calcium soap was precipitated in bulk solution. It was suggested that microencapsulation of the ink particles with hydrophobic species occurs through heterocoagulation with the bulk precipitated calcium soap particles.
R.N. Rao and P.Stenius (1998) had studied the mechanisms of ink and the influence of several nonionic surfactants on release of ink from cellophane, a polyamide sheet and photocopy paper, were used as model substrates. A simple assumed model of the dry ink structure consisting of a primary layer which is directly bound to the substrate as well as a secondary and tertiary layers, was used to explain qualitatively how ink detachment took place during deinking of news-offset ink. While the addition of surfactant is important because it softens the ink and affects the ink/fiber interactions. For complete detachment of ink generally required mechanical force, however mechanical action alone could not successfully remove ink in direct contact with the fibers. Moreover, they indicated the structural difference in surfactants might affect kinetics rather than actual detachment mechanism.
M.A.D. Azevedo, J. Drelich and J.D. Miller (1999) had studied the effect of pH on pulping and flotation of mixed office wastepaper. The effect of pulping reagents on the deinking flotation of laser-printed wastepaper was investigated with regard to the removal efficiency of toner and mineral filler particles at different pH values. The results show that caustic pulping reduces the abrasive action and/or causes the fibre swelling, both of which result in the toner to be released from the fibres as larger particles and a poor flotation response is obtained. On the other hand, neutral pulping not only causes the toner to be released as smaller particles but also increases the simultaneous flotation removal of toner and mineral filler particles. On the basis of the flotation results and atomic force microscopy force experiments confirmed that the remarkable removal of mineral fillers, and the good flotation of both toner and mineral fillers from mixed office wastepaper can be achieved under the same conditions at pH values between 5.0-7.0 for both neutral and alkaline pulping conditions.
Felix Carrasco, Maria Angles Pelach and Pere Mutje (1999) had studied flotation deinking of high-quality off-set printed papers using a laboratory cell with a nominal capacity of 50 litres. Disintegration condition prior to flotation were held constant to facilitate study of operating conditions during the flotation stage. The analyzed process variables were pulp consistency (0.75%, 1%, 1.25%), air flow rate (500, 750, 1000 L/h), and agitation speed (850, 1150, 1450 rpm). A deinkability factor-based on handsheet brightness after flotation-was used to evaluate process efficiency and establish the optimum flotation conditions, increasing any of the process variables (pulp consistency, agitation speed, air flow rate) helped increase the deinking efficiency. The change in deinkability factor with operating conditions is explained by applying probability theory to predict the frequency of collisions between air bubbles and ink particles. Thus the highest efficiency was obtained when the process variables were at their maximum level (pulp consistency of 1.25 %, agitation speed of 1450 rpm, and air flow rate of 1000 L/h). A deinkability factor of 88% was obtained under these condition. Analysis of the results showed excellent correlation between deinkability factor and flotation operation conditions, and the proposed empirical equation had a regression coefficient r2 of 0.90. Statistical analysis showed that consistency and agitation speed had a significant effect on the deinkability factor, while the influence of the air flow rate was far less significant.
Bjorn Johansson and Goran Strom (1999) had studied on the flotability of model offet ink suspension (without fibres) that have been performed using a Hallimond tube and a standard calcium chloride-sodium oleate collector system. The average ink particle size was 1 m m indicating poor floatability of untreated primary ink particles. This suspension was mixed with deinking particles, coating components and dissolved paper chemicals to evaluate their effects on flotation performance. The results were combined with data on agglomeration kinetics to determine important factors in the flotation deinking process. Parameters such as electrolyte and collector concentration will increase the agglomeration rate, help increase the flotation efficiency while surface-active chemicals that stabilize the ink particles cause flotation efficiency decrease. The importance of agglomeration was confirmed. The particles remaining after flotation were discrete primary ink particles. An interesting result was that no upper particle size limit for flotation was observed when ink particles were flotated without fibers, although particles longer than 200 m m were present indicating the role of a fiber network for the retention of large particles.
References
Methodology
Experimental Set-up
The carbon black (type 400R) will be used as model ink. Due to a relatively high concentration of ionic salts originally present, it will be necessary to remove the salts by washing the carbon. Carbon black will be mixed with distilled or deionized water in the ratio of 1:4, agitated thoroughly, centrifuged, and water decanted off. This procedure will be repeated 3 times, which will be sufficient to reduce the calcium concentration below 0.1 ppm.
The fiber will be prepared by pulping common office paper (Xerox 4200 DP 20 lb.) at 5% consistency for 20,000 beats at 3000 rpm. Then pulp slurry will be washed over a 140 mesh screen to remove all fillers and extraneous ions until the calcium concentration was less than 0.1 ppm. After that the fiber will be pressed to remove excess water and will be oven dried at 50° c. The surface area of the dry fiber will be approximately 1.51 m2/g.
The surfactant employed for the investigation will be sodium octanoate (purity of greater than 99%) .
Calcium chloride will be oven dried for 12 hours at 90° c just prior to making the stock solution, the standard Ca2+ solution must be standardized, due to the chemical hygroscopic nature.
Sodium hydroxide and hydrochloric acid will be used as pH adjustment.
Water used for experimentation will be distilled or deionized.
The adsorption isotherms will be obtained at 30° c using the solution depleting; 1.0 g of carbon will be mixed with 10 mL of solution, allowing to equilibrate for 3 days with occasional agitation, and centrifuged. The surfactant and calcium concentrations in the supernatant liquid will be analyzed for the residual concentrations of surfactant and calcium.
Zeta potentials will be determined using a Zeta Meter. The potential across the cell will be adjusted as a function of the ionic strength (specific conductance) of the sample so as to avoid thermal overturn associated with overpotentials. The measurements will be taken at a constant temperature of 30° C
The adsorption isotherms will be obtained at 30° C using the solution depleting; 1.8 g of dried fiber will be mixed with 10 mL of solution, allowing to equilibrate for 3 days with occasional agitation, and centrifuged. The surfactant and calcium concentrations in the supernatant liquid will be analyzed for the residual concentrations of surfactant and calcium.
Experimental procedures
Controlled parameters
For adsorption isotherm experiment, the volume of suspension, quantity of ink, the surface area of paper, and operating temperature will be kept constant. Type of paper must be the same.
And the initial concentration of calcium from paper or ink must be less than 0.1 ppm.
Variable parameters
The variable parameters, pH value, surfactant and calcium concentrations will be varied
Methods of chemical analysis and measurement
The concentrations of surfactant adsorb on ink or on fiber are detected by total organic carbon analyzer (TOC). Calcium concentration will be measured by atomic adsorption spectroscopy (AAS).
Data calculation and analysis
G = (Ci - Cf) V / m -----------------------------(1)
For this thesis, Equation (1) will be used to calculate the amount of surfactant adsorbed onto the surface of ink.
Where
Schedule of Research Activities and Time table
Sequence of Research Activities
Time table
Year : 2000
| Activity | Month |
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| Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Jan | Feb | Mar | |
| 1 | ***** | ***** | |||||||||||
| 2 | ***** | ||||||||||||
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| 4 | ***** | ***** | ***** | ***** | **** | ***** | ***** | ||||||
| 5 | **** | ***** | ***** | **** | **** | ||||||||
| 6 | **** | ***** | ***** | ||||||||||
| 7 | **** | ***** | ***** | ||||||||||
Budget
Chemicals
Carbon black -------------------------------- 5,000
Sodium Octanoate -------------------------- 9,000
Office Paper (Xerox 4200 DP 20 lb) ---- 2,000
Calcium chloride --------------------------- 1,500
NaOH ---------------------------------------- 1,500
HCl ------------------------------------------- 1,500
KCl ------------------------------------------- 1,500
DI water ------------------------------------- 3,000
Buffer solution pH 7------------------------ 1,000
Paraffin film --------------------------------- 1,000
Analysis costs ----------------------------- 12,000
Utilities -------------------------------------- 4,000
Total -----------------------------------------43,000 Bahts