RRIM training manual on natural rubber processing

RRIM TRAINING MANUAL ON NATURAL RUBBER PROCESSING Rubber Research Institute of Malaysia eBook created (04/01/‘16): QuocSan SOME ASPECTS OF NATURAL RUBBER PROCESSING A Subramaniam Rubber Research Institute of Malaysia In this introductory lecture I shall touch on the scope and content of this refresher course on NR processing and comment on some areas where greater care needs to be exercised Although the SMR scheme was introduced 17 years age, it was only in the last year that the volume of SMR exported exceeded that of the conventional sheets Over 40% of Malaysian rubber is still sold as sheets and crepes It is therefore appropriate that this course covers the processing not only of SMR but also of conventional grades as well as latex concentrate Stapes In NR Processing In the processing of latex into dry rubber, the basic steps involved are: (i) preservation of latex, (ii) coagulation, (iii) conversion of coagulum into sheets, crepes or crumbs, and (iv) drying For field coagulum, processing involves cleaning and blending, size reduction into crumbs and drying These various steps are shown schematically in Figure The different techniques involved in the production of different grades of NR are considered in detail in this course FIGURE SCHEMATIC REPRESENTATION OF NR PROCESSING Those in charge of NR processing factories should also have a knowledge of the various types of machines used in processing, the care and maintenance of these machines, the packaging of rubber and quality and inventory control All these topics are covered in the lectures that follow Finally, there is the problem of effluent discharge from rubber factories, whether these be washings from the centrifuge bowl, serum from coagulation of field latex or skim or the discharge from remiller factories This important subject is discussed in the final part of this course SMR and New Processes The introduction of the SMR scheme in 1965 was a milestone in the development of the Malaysian rubber industry It marked the most significant changes in the processing and presentation of NR since the beginning of the rubber industry in the country The production of NR to technical specifications and the improved packaging and presentation helped to put NR in a more equitable position in its competition with SBR, the general purpose synthetic rubber The success of the SMR scheme was made possible by developments of new processes for converting latex and field coagulum into dry rubber The most notable of these were processes for converting rubber into crumbs and the drying of rubber at the higher temperature of 100°C The new processes require that the relevant factory personnel understand the characteristics of the raw materials and the effect of the different processing techniques and conditions on rubber properties It would be useful to highlight some of the differences between the conventional and new processes (i) Preservation SMR processing machinery are expensive and this requires that the processing factories are centralised for economies of scale Thus typically, SMR processing factories have production capacities of 10 to 50 tonnes per day compared to the one to two tonnes per day RSS factories Latex has therefore to be transported over a greater distance In order to prevent precoagulation, the tendency is therefore to add a relatively higher level of preservative, which is usually ammonia This in turn requires a higher level of formic acid to effect complete coagulation Higher ammoniation may also cause slower drying Two other preservative systems containing low levels of ammonia, viz ammonia-hydroxylamine and ammonia-boric acid, have been developed These have been used only with varying success and have not been widely used (ii) Coagulation In producing RSS or crepe rubber, the processing parameters are more uniform Formic acid is virtually the only acid used; the d.r.c of coagulation and the amount of acid used are standardised In SMR production the coagulation conditions tend to be more variable Although formic acid is the recommended acid, sulphuric acid is not always excluded The d.r.c of coagulation is not uniform; the amount of acid used can differ considerably from batch to batch Different chemicals are used to produce the different grades of SMR For example, SMR CV made by the Heveacrumb process uses hydroxylamine neutral sulphate, castor oil and emulsifier; SMR 20 may be dipped in phosphoric acid to improve its PRI The coagulation and processing conditions affect the rubber properties For example, the level of ammoniation, the pH of coagulation and the maturation time of the coagulation affect the viscosity, modulus and cure behaviour of rubber Varying the processing conditions even a little at random may affect the consistency in properties It is therefore of utmost importance that those involved in SMR production understand the influence of chemicals and processing conditions on the properties of rubber (iii) Conversion of coagulum into crumbs Conventional rubber processing machinery consists of crepers and sheeting batteries In SMR production, a wide range of machines may be used, differing in design, function and performance For example, size reduction of the coagulum may be carried out in a crumbier, granulator, creperhammermill, extruder, shredder or prebreaker Though the merits and defects of these machines have been known through experience over a number of years, there is still no general consensus on the best set of machines for SMR production The great diversity of machinery also means that the SMR factory must keep a larger number and variety of spares and use a core complicated maintenance schedule (iv) Drying Unlike the conventional grades, the conditions of drying of SMR vary greatly Though meet dryers used for SMR production use the same basic principle, i.e through-air circulation drying at 100°C, they differ in design, mechanical construction and efficiency While the recommended temperature of drying is 100°C, higher temperatures are used in many factories to speed up the drying process This may cause problems of overdrying or underdrying unless the conditions are strictly monitored It is also necessary to ensure that the dryers undergo cleaning and general maintenance at regular intervals in order to prevent contamination of the rubber by soot and rust Figure Latex concentrate processing showing different sources of wastewater Figure Block rubber processing showing sources of effluent Table shows the physical and chemical properties of effluent from typical rubber processing factories Generally the effluents are acidic in nature The pH variation from different types of factories is attributed mainly to different extent of acid usage Another feature is the high solids content, mainly in the dissolved form Exertion of oxygen demand is mainly contributed by these dissolved organic solids The BOD values (measure of the organic content) vary with different types of production ranging from about 740 mg/l in remilling concerns to about 2,580 mg/l in latex concentrate operations It has also been observed that even for similar type of operation, some degree of variation in BOD levels occur This is normally attributed to varying water consumption Another important characteristic of rubber factory effluent which merits consideration is the significant levels of nitrogen, mainly in the ammoniacal form Past studies have indicated that ammonia can give rise to environmental problems not only in relation to the oxygen demand it may exert but also of the toxicity and the potential to promote entroplication of rivers In rubber effluent, the ammonia is mainly derived from the preservative used This is the reason why latex concentrate effluent contains higher levels (395 mg/l) compared to others (10 - 55 mg/l) TABLE PHYSICAL AND CHEMICAL PROPERTIES OF EFFLUENT FROM DIFFERENT TYPES OF FACTORIES Types Factory of pH Suspended solids Total solids COD BOD NH3N Block rubber 6.3 230 995 1620 1140 55 RSS 4.9 140 3745 3300 2630 10 Remilling 6.2 350 480 900 740 15 4.2 190 6035 4590 2580 395 Latex concentrate AH values except pH expressed in mg/l It can therefore be said that in rubber factory effluent two potential pollutants are recognised, namely: a Organic carbon; and b Ammoniacal nitrogen In latex concentrate processing the main source of effluent is from the coagulation of skim latex Table indicates the levels of different components present in the skim serum Analysis shows that the serum contains significant levels of fertiliser elements (N, P, K, Mg) which has instigated evaluation on the possibility of utilising the wastewater as a source of fertiliser TABLE PROPERTIES OF SKIM SERUM Property pH Sample Sample Sample Average 4.10 5.40 4.82 4.77 Total solids 44 520 45 286 37 838 42 550 Volatile solids 38 340 38 646 32 248 36 410 624 348 584 850 C.O.D 32 445 37 617 27 997 32 690 B.O.U 15 675 13 425 11 900 13 670 Total nitrogen 664 190 997 620 Ammoniacal nitrogen 660 660 972 430 714 923 627 755 Nitrate nitrogen 3 Nitrite nitrogen 1 1 Total sugars 335 704 241 500 Reducing sugars 450 406 370 409 Suspended solids Albuminoid nitrogen Al 2.0 0.7 2.0 1.6 Ca 6.0 7.0 5.0 6.0 Cu 2.0 7.0 2.0 4.0 Fe 2.0 2.0 2.0 2.0 K 625 680 550 618 Mg 60.0 68.0 55.0 1.0 Mn 0.6 0.7 0.5 0.6 Na 6.0 7.0 20.0 11.0 P 60.0 63.0 55.0 61.0 Rb 2.0 2.0 5.0 3.0 Si 2.0 2.0 20.0 8.0 All values except pH are expressed in p.p.m Source: RUBBER RESEARCH INSTITUTE OF MALAYSIA 1974 TREATMENT METHODS Two treatment systems which have been evaluated on a big scale will be elaborated in this discussion They are: 1) Anaerobic-Facultative ponding system; and 2) Oxidation Ditch system Theoretical Considerations Both treatment systems employ two main concepts in biological breakdown: a) Anaerobic degradation b) Aerobic degradation In ponding system both anaerobic and aerobic breakdowns occur whereas in the oxidation ditch system, the treatment mechanism capitalises on the aerobic biological degradation Figures 4a and b show schematic representations of anaerobic and aerobic breakdowns respectively Figure 4a Schematic representation of anaerobic breakdown Figure 4b Aerobic breakdown The final methanogenesis stage of anaerobic breakdown is the rate determining stage This is because the methane bacteria are very slow growers and the corresponding reaction step is the slowest compared to the proceeding hydrolysis and acidification steps The success of methane formation depends to a significant extent on the survival of the obligative methane bacteria Among the environmental requirements are pH 6.5 - 7.5, absence of dissolved oxygen and acceptable levels of volatile acid and free ammonia which are known to be toxic to methane formers The aerobic breakdown, however, is dependant on adequate supply of oxygen In facultative ponds, supply of oxygen is obtained from the photosynthetic activities of algal cells which thrive symbiotically alongside the bacteria Figure depicts the biochemical processes occurring in facultative ponds Therefore, it is necessary to maintain conditions conducive to the growth and survival of algal and bacterial cells which include acceptable pH range, sunlight, and adequate presence of C, N and P In the oxidation ditch system, supply of oxygen is achieved by mechanical aeration Rotors in the form of paddles are normally employed It is critical that a proper design and selection of rotor is undertaken to meet the required degree of aeration Figure shows a schematic diagram of our oxidation ditch process Another important feature of the process is the sedimentation basin which is required to maintain high levels of bacterial concentration in the ditch for better performance Figure Biochemical process in facultative ponds Figure The oxidation ditch process-flowsheet Design Considerations Ponding system: Design criteria: As discussed earlier under theoretical requirements, the success of the ponding system depends on the following criteria: (i) Growth and survival of anaerobic methane bacteria in the anaerobic stage (ii) Adequate availability of oxygen for the aerobic breakdown in the facultative stage Studies have indicated that the methane bacteria is susceptible to pH conditions They are known to be slow growers and therefore requires high retention time to discourage possible washout Retention times less than days have been found to be unacceptable Using the ponding system for treatment of latex concentrate effluent, commercial scale studies1 have shown that the following design criteria are applicable to achieve final discharge BOD less than 100 mg/l a) An optimum organic loading of 120g BOD/m³/day, and b) A BOD removal constant, k = 0.061 day-1 in the facultative treatment assuming plug flow conditions Nitrogen removal, however, has not been very encouraging Studies are currently being undertaken to accommodate acceptable nitrogen removal In the treatment of block rubber effluent, pilot plant studies2 have suggested the following design criteria: a) An optimum loading of 150g BOD/m³ day and b) k = 0.117 day-1 General Considerations The following items have to be considered in pond construction: Anaerobic pond: The operating depth can vary from 1.8 m and more, depending on soil stability and level of the water table Controlled scum formation to minimise malodour, characteristic of emission from anaerobic breakdown, is allowed Excessive scum formation is not encouraged as this may lead to a reduction, in effective treatment volumes as well as possible blockage of pipes etc Facultative pond: The depth should vary only between 0.9 - 1.5 m Scum formation should be constantly removed to enable complete exposure of surface to sunlight penetration This would ensure a higher activities of the photosynthesis algae which supply most of the oxygen required in the breakdown Other Considerations The embankments of the ponds should have a slope of at least 1:1.5 to avoid any erosion The growth of terresterial vegetation along the banks of the ponds should be prevented to minimise the possibility of mosquito breeding The possibility of fluid short circuiting in ponds should be minimised by allowing the liquor to enter each pond about 20 to 30 mm above floor level and to leave the pond at a diagonally opposite point on or just below the surface of the pond In addition it is recommended that the length to breadth ratio should be at least 2:1 Figure depicts a typical arrangement for pond construction Figure Side view of effluent treatment plant Oxidation Ditch The oxidation ditch performs best if the following design requirements are met: a) Aeration capacity of rotors should be acceptable to the BOD loading b) The BOD loading should be at a level that will produce a mixed liquor that will have acceptable settling characteristic The oxidation ditch has been used only for treatment of latex concentrate effluent Earlier laboratory studies3 have indicated that hydraulic retention time should not be less than days to effect acceptable removal Latest studies have indicated that organic loading rate of between 0.108 - 0.158g BOD/g VSS day gave good removal Commercial plant studies4 have also indicated that at a loading of 0.092g BOD/g MLSS day would produce an effluent containing BOD averaging about 47 mg/l Research are still going on to optimise the loading UTILISATION An alternative approach to treatment is to scrutinise possible useful constituents of the wastewater which may be utilised beneficially without creating a secondary environmental problem Analysis of rubber factory effluent, discussed earlier, indicates substantial presence of N, P, K, Mg, Ca which are essential ingredients in fertilising compounds The other constituent of course, is water itself Studies5 have shown that extensive benefits may be derived by application of effluent on to land, especially latex concentrate effluent It has been observed that a significant increase in yield (11-18% for rubber, 19% for oil palm) result Long term monitoring of the exercise (3-5 years) has also indicated negligible maleffects on soil properties Further studies are currently being undertaken to evaluate any possible contamination of ground water through leaching and also possible buildup of nitrogen in the soil However, it is expected that with proper optimisation of application rate, the above will be negligible The water content of the effluent may be exploited for irrigational purposes in water stress areas In fact, evaluation is currently underway CONCLUSION In conclusion it should be said that significant progress has been achieved in handling rubber factory effluent The lecture has demonstrated two possible outlets for the effluent i.e treatment and utilisation As far as treatment gives two processes which have been evaluated in significant detail show good promise The utilisation aspects have also suggested attractive possibilities in terms of cost savings in fertiliser and increase in crop yield REFERENCES AHMAD IBRAHIM, MOHD ZIN KARIM, ZAID ISA and SETHU, S (1979) Anaerobic/Facultative ponding system for treatment of latex concentrate effluent RPRIM Planters’ Conference, 1979 AHMAD IBRAHIM Unpublished PONNIAH, C D (1975) Treatment of acidified skim serum by a laboratory scale oxidation ditch Proc Agro-Industrial Wastes Symposium, p.94 AHMAD IBRAHIM (1979) Treatment of latex concentrate effluent using an oxidation ditch process Symposium on recent developments in effluent treatment, Penang MOHD TAYEB DOLNAT, MOHD ZIN KARIM, ZAID ISA and K R PILLAI Land disposal of rubber factory effluent Its effect on soil properties and performance of rubber and oil palm RRIM Planters’ Conference 1979 .. .RRIM TRAINING MANUAL ON NATURAL RUBBER PROCESSING Rubber Research Institute of Malaysia eBook created (04/01/‘16): QuocSan SOME ASPECTS OF NATURAL RUBBER PROCESSING A Subramaniam Rubber. .. the influence of chemicals and processing conditions on the properties of rubber (iii) Conversion of coagulum into crumbs Conventional rubber processing machinery consists of crepers and sheeting... PRI The coagulation and processing conditions affect the rubber properties For example, the level of ammoniation, the pH of coagulation and the maturation time of the coagulation affect the viscosity,