Continental J. Environmental Sciences 4: 44-50, 2010 ISSN: Wilolud Journals, 2010

Transcription

1 Continental J. Environmental Sciences 4: 44-50, 2010 ISSN: Wilolud Journals, RECOVERY AND ANALYSIS OF SOLVENTS FROM WASTE IN PAINT INDUSTRY Onyeji, Lawrence Ibe Department of Chemical Engineering, Federal University of Technology, (FUT), Minna ABSTRACT Due to major problems generated in the paint industries by hazardous waste and its attendant effects, Solvent Recovery and Analysis as a means of waste minimization was investigated. The inputs in paints production, the sources of waste, the types and properties of solvents used in paint industries were also reviewed. The recovery of waste samples obtained from washing different gloss paints off production pots using MIBK and Toluene as washing solvents were carried out on laboratory scale by a combined filtration and distillation processes. These methods were chosen because they are the most efficient and cost effective from various recovery techniques reviewed. The results obtained showed that an average of % of wastes was recovered as both recyclable and reusable solvent. This is about N5, gain for every 200 litres filler washed after paint production. Analysis of the recovered solvent gave a sweet pungent odour and a light yellowish colour. Other physical properties of the recovered solvent are density g/m 3, boiling point 106 o C, and flash point 2.6 o C. These specifications are similar to those of fresh/new solvent and thus can be reused. KEY WORDS: Recovery, Analysis, Solvents, Waste, Paint Industry INTRODUCTION Hazardous waste and its environmental effects have become a major issue throughout the world. The types of waste generated by different industries vary and the principles of waste minimization are generic. The basic principle to avoid waste generation is far easier than to reprocess it later. (Cano-Ruiz and Mc-Rae, 1998). Potentially, the most difficult waste reduction strategy is to reproduce/recover the waste in such a way that it can be used in another related or unrelated process. This could however also prove to be simple solution to the problem of waste. It is clear that apart from difficulties arising from tackling the problem of waste generation; more energy, technology and cost are required, and hence the more difficult it becomes to strive towards a zero waste system (Hammer, 1977). The major driver for waste reduction is cost and health hazards. Pollution prevention can be defined as any practice which reduces or eliminates the amount of toxicity/pollutants entering the waste stream or the environment prior to recycling, treatment or disposal. Pollution Problems arise during wastes generation, transportation and disposal However, the preferred method of hazardous waste management is one that takes into account pollution prevention. Waste management is an aspect of pollution prevention which is an increasingly familiar terms in today s world due to urbanization and industrial growth. The reduction of toxic wastes generation can be done with focus on industrial wastes. Industrial wastes include sources of solids, liquids and gases which are frequently discharged into the environment i.e. onto lands, into streams and lakes and also to the atmosphere thereby causing hazards to human, animals and aquatic life (Arnold, 1984). Paints can be defined as clear or pigmented liquids that impart decorative as well as protective properties onto a surface it is applied. Paints generally consist of a mixture of the following components: pigments, binders, solvents and additives (Morgans, 1990). The focus of this is the solvents which are liquid agents used to dissolve other components in order to facilitate their application. Solvents are also used to clean the equipments for the production of subsequent batches of paint. It is this washing process that results in solvent wastage. The recovery and reusing of this washing solvent would reduce the amount of solvent disposed as waste. This will minimize environmental pollution with its attendant hazardous effects. To reduce the risks waste pose to human health and environment, both the government and industry adopted waste reduction policies. In order to reduce or eliminate the generation of waste at its source, some waste reduction techniques are listed below; 44

2 Modification or redesigning processes Reformation or redesign of product Recovery and recycling of solvents Raw materials substitution with environmentally friendly ones Improved maintenance, housekeeping and operating practices. The incineration of used solvents. (USEPA, March,1991) For pollution control measures, recovery is becoming increasingly favoured and preferred over other waste reduction techniques. Recovery and reuse of organic solvents is a generally desired practice because of the high cost of the solvents, potential shortages and anti-pollution regulation governing the disposal of such solvents. In paint industry, classification of paints depends on the type of solvents they contain. Solvents used vary from water (for emulsion i.e. water based paints) to organic solvents such as toluene, methyl isobutyl ketone (MIBK) etc (for gloss i.e. oil / solvent based paints). Solvent-based paint manufacturing plants produce significant quantities of hazardous waste, which must be properly treated before it can be disposed. Since the cost for treating this waste is high, reducing the quantity of waste has become a crucial issue in this industry (Derya et al., 2005). Wastes in paint industry are found to occur in two basic forms; Liquid and Semi- solid wastes Solvents are also known as DILUENTS or CARRIERS. Generally, solvents are liquids that are used to dissolve other components. In the paint industry, solvents are liquid or mixtures of liquids that dissolves pigment, resins and other paint components. Paint industries consumed large quantities of solvent produced. There are three major uses of solvent in paint industry; 1. As a cleaning agent; i.e. used to remove oily deposits from a substrate in preparation for painting, and to clean up equipment, paint splatter and spillages after paint application. 2. As an integral part of a paint formulation i.e. the purpose of solvent is to carry the paint to the substrate in a form that allows the paint to be sprayed, brushed, rolled or towered uniformly. It also assists in achieving the gloss level and dry film thickness required. 3. As paint thinner; i.e. To adjust application properties such as viscosity, flow out, drying time, spreading rate and wet edge (Dulux, 2007) Solvents are generally divided into; Inorganic and Organic solvents. The inorganic solvents are soluble in polar solvents e.g. Water, while Organic solvent are soluble in non-polar solvent and are mostly organic in nature. E.g. Xylene, toluene, MIBK e.t.c. Generally, organic solvents are classified as hydrocarbon solvents, oxygenated solvents and others (Connolly, 1981). The production of paints is a complex process involving dispersion of pigments and additives into a solution of resin and solvent. This is followed by simple mixing operations. The most important step is the initial pigment dispersion operation, sometimes termed grinding. (Derya and Fusun, 1973). Most paint manufacturers produce many different types/colour of paint, including both organic solvent-borne and water-borne paints. Each type/colour of paint is manufactured in a separate batch, and all manufacturing equipment are generally cleaned between batches of different types or colour of paint to prevent contamination. Generally,an organic solvent is required to clean equipment after manufacturing an organic solvent-borne paint while water are used after manufacturing of water borne paints. Since the manufacturing process involves the use of pigments (different colour) and binders, it is necessary to clean the equipments before another batch of paint is made. This process is called washing. Washing is done to: Keep the equipments clean for subsequent use, Prevent clogging of pipes and Prevent contamination. Due to the nature of the chemicals used in paint manufacturing, solvents are used for this washing process, thus, resulting in solvent wastage. At EAGLE PAINTS NIG. LTD, LAGOS STATE which is the case study for this work; it was discovered that approximately; 25 Litres of solvent is required to wash a 200 Litres filler. (Company s formulation handbook). 45

3 Solvent Recovery Methods; There are many ways of recovering solvents in paint industries. However, most solvent recovery processes involve one, or a combination of the following unit operations: Decantation, filtration. Cooling, distillation, condensation, adsorption, drying, extraction.e.t.c. The best combination depends primarily upon the nature of the solvents, the manner of emission, and the quality and specifications of the recovered solvent. The best process would usually be that which produces the highest recovery of quality solvent, at lowest equipment and operating costs taken pollution control measure and safety into consideration. To choose a separation method for a given solvent, there are factors to be considered, these include; Nature of waste, Properties of desired solvent and the expected use of recovered solvent In paint industries, the wastes encountered (from which solvents are to be recovered) are in the liquid or semi-solid state. The liquid wastes are as a result of the washing process, after the paint has been manufactured via a batch process. Also the washing of milling equipment, produce solvent wastes containing both resins and inorganic pigments. A solvent s physical and chemical properties provide the basis for its recovery method. It s boiling and melting points, relative volatility, solubility, chemical reactivity e.t.c determine the separation technique(s) to be used. This is because each recovery method takes advantages of one property or the other. For example, distillation takes advantage of relative volatility; extraction utilizes its solubility e.t.c. This work is aimed at analysing the various solvent recovery methods in paint industries and choosing the most suitable process in terms of effectiveness and cost efficiency. This will reduce the cost of paint production as waste solvents will be recovered and reused thus reducing the cost paint in our local market. EXPERIMENTAL PROCEDURE Two different solvent wastes; Methyl Isobutyl Ketone (MIBK) and Toluene used for washing white and blue gloss paints off the production pots were respectively collected from Eagle Paint Nig. Ltd. Lagos. The recovery of MIBK was done using distillation process only. On the other hand, because of its semi-solid composition, the Toluene was recovered by both filtration and distillation processes. 120ml and 300ml of MIBK were measured and poured into two different distillation flasks and the distillation equipment set. The flasks were heated and the temperatures at which the first drop of distillate occurred and that of the last drop were noted and recorded. The same volumes of Toluene were also measured out but were filtered first to remove the solid particle in the solvent waste before distillation. Also the temperatures at which the first drop of distillate dropped and that at which the last drop occurred were noted and recorded. In order to ascertain the quality and specifications of the solvent recovered, some physical property tests were carried out. These include; Colour check, Density, Boiling point, Flash point and Odour. 46

4 RESULTS Table 1; Results of the recovery parameters Using MIBK and Toluene as Washing Solvent. S/No DESCRIPTION MIBK TOLUENE 1ST TEST 2ND TEST 1ST TEST 2ND TEST 1 Volume of Waste (feed) (ml) Temperature at which first drop of distillate occurred ( o C) Temperature at which last drop of distillate occurred ( o C) Volume of distillate recovered (ml) Duration of experiment (min) Percentage recovery (%) Table 2: Comparison of Physical Properties of Pure Solvent with Recovered Solvent (MIBK and Toluene) S/No PHYSICAL PROPERTIES PURE SOLVENT MIBK RECOVERED SOLVENT PURE SOLVENT TOLUENE RECOVERED SOLVENT Odour Slight camphor Slight Camphor Sweet Pungent Sweet Pungent Colour Colourless Colourless Colourless Light Yellow Density (g/ml) Boiling Point ( o C) Flash Point ( o C)

5 Table 3. Financial Benefits of the laboratory test. S/No PARTICULARS COST UNIT REMARK 1 1 Drum (205 Litres) of Solvent 65, Naira From MKT 2 Cost per litre Naira 3 Solvent required to wash 200 litres filler 25 litre Eagle Paint Log Book 4 Average volume of solvent waste charged 210 ml 5 Average solvent recovered 150 ml 6 Average % solvent recovered % 7 Average volume of solvent from washing 200 litre filler litres 8 Savings from the recovered solvent after washing Naira DISCUSSION Table 1 shows that the percent solvent recovered for both solvents ranges from 70 to 75% with an average percent recovery of 71.43%. Table 1 also shows that it took a longer temperature range (48 o C to 52 o C) for distillation to be completed for MIBK than Toluene (25 o C to 28 o C). This is because waste toluene was first filtered which removed most of the semi-solid that would have affected the distillation temperature. Also MIBK has a higher boiling point and thus is expected to distil at higher and longer temperature range. From the percentage recovery, it can be observed that filtration before distillation has no effect on the volume of solvent recovered as depicted in Table 1. The addition of filtration process in experiment 2 has no effect on the volume of solvent recovered. Since volume is one of the major variables, it was needless to perform the same combine filtration and distillation with MIBK. It is however very useful and important in separating solids and semi-solids (such as thick lumps of paint) that are sometimes encountered in the waste for recovery. However the residue of the unfiltered waste was more viscous than the residue from the filtered sample. This is because some of the semi solids that would have increased the volume and viscosity of the residue were removed during filtration. Table 2 shows that the density of the recovered solvents, for both MIBK and Toluene is slightly less than that of the unused/new solvents. This is as a result of the distillation process which gave the recovered solvents purer properties. This slight difference in density is more in toluene which can be the effect of the initial filtration. Although there are these slight differences, it can generally be concluded that the physical properties of the recovered solvents are within the standard purity range/specification. Hence the recovered solvents are reusable for both paint production and as washing agents. Above all the process choice is indeed effective in terms of equipment, and savings. Table 3 shows that the financial benefit of recovering the solvent used to wash 200 litres filler is about N This when projected to industrial scale will be worthwhile. Also the equipments required are available and affordable. 48

6 It was discovered that as the solvent distilled out, the waste solution became supersaturated as polymers or salts (that make up the pigments, additives, and binder e.t.c) began to deposit. Also more concentrated solution starts immediately adjacent to the heating surface as the vapour is being generated and solids tend to build up on the equipment near the heating surface. This eventually forms residue high in viscosity. Similar problem to that of washing equipments in the paint industry were also encountered in cleaning up equipments after the solvent recovery process. CONCLUSION This work has shown that about 71% of waste solvents in a paint industry can be recovered for reuse in both productions of new paint and as washing agent for paint production equipment. This work is most favoured because of the process choice, combination of filtration and distillation, which is very simple, available and affordable. The process used is/are physical process(es) and so has/have no effect on the chemical composition of the solvents. Thus the properties of the recovered solvent fall within the set standard specifications for this solvent. The addition of filtration process in experiment 2 has no effect on the volume of solvent recovered. Since volume is one of the major variables, it was needless to perform the same combine filtration and distillation with MIBK. The slightly lower density achieved in the recovered solvent is a proof of the efficiency of the process of distillation in terms of purity. RECOMMENDATIONS In the recovery of solvents using a combined filtration and distillation recovery method, it is suggested that the washing solvent recovered can be reused by manufacturers of solvent-borne paint to reduce the volume of solvent wastes without affecting the quality of product, as well as impacting positively on the environment. Also sound experience and knowledge of chemistry of the paint formulations is needed to plan a reuse. This technology system can produce cost savings with little Capital outlay for implementation. Hence, it is recommended that cost estimation for setting up of solvent recovery unit in an already existing plant should be carried out. This technology, poses three main problems. Recommendations are then made to tackle these problems; High risk of fire and explosion: This is as a result of high volatility of the solvent and the temperatures involved in distillation. Also sometimes, exothermic reactions are triggered and thus resulting in explosions. Thus; Every recovery process should be carried out on a laboratory scale to test it for exothermic nature and to note temperature ranges. (these temperature ranges must be strictly adhered to on a large-scale basis) Adequate ventilation should be provided. Smoking should be prohibited and electrical equipment should be designed to a recognized, explosion-proof standard. After conducting a recovery operation, equipment should be cleaned of residue before another waste feed of another composition is charged into it, to avoid exotherms resulting in explosions Vapour pressure reduction: non-volatile materials present in the waste for recovery causes difficulties by reducing the vapour pressure of solvents. The distillation column should be airtight The evaporating surface and condensing surface should be place as close to each other as practicable Odour: Though most solvent have a distinct smell/odour, unacceptable smell occur as a result of decomposition of the solvent itself. The storage tank should be well sealed to prevent decomposition by evaporation. Storage and transportation: This is another factor that poses problem in waste management and recovery of solvent process. Drums should be stored in a well-ventilated area away from sources of ignition and heat. The storage temperature should not exceed 40 C. Comply with national and international requirements regarding the transport of hazardous 49

7 material. Containers should be in good condition and properly labelled. Keep containers in a well-ventilated place, away from sources of ignition. REFERENCES Arnold H. Hof1fman, (1984), Solvent Paint Waste Minimization and Recycling (A case study Major Paint Co ;) Los Angeles, CA P P 1-12 Cano-Ruiz, J.A and Mc-Rae G.J (1998) environmentally conscious chemical process design. Annu. Rev. Energy Environ. 23 P P Characteristics of the paint and allied coating products industry. ( Connoly E.M... (February, 1981). An overview of the U.S Paint and Coatings; Chemical Economics Handbook. P P 592 Derya Dursun and Fusun sengel (2005), Recourses, conservation and Recycling Waste minimization. P P 4 Dulux Protective Coatings Technical Information and Advice ( October,2007) P P 1-2 Gardon J.L and Plane J.W, (1973) Non-Polluting coatings and coating processes New York Hammer JM (1977) Water and Waste-Water Technology., New York. 37 pp. Morgans W.M. (1990). Outlines of paint Technologies P P U.S. Environmental Protection Agency (USEPA), March,1991 Pollution Prevention Fact Washington, DC: Office of Pollution Prevention Received for Publication: 18/04/2010 Accepted for Publication: 20/07/