Used solvent disposal

Organic solvents are in the main derived from petroleum. The exceptions are small amounts formed as by-products in agriculture and coke ovens. They can be produced by relatively simple distillation (e.g. mineral spirits) or by processes involving several stages of synthesis (e.g. THF, NMP). Their manufacturing costs can, therefore, be very sensitive to the cost of the naphtha fraction of crude oil from which they are derived. Alternatively, because of the value added through various stages, the cost maybe almost divorced from the petroleum market. 

A breakdown of the types of solvent consumed in Western Europe (Table 8.1) shows approximately the ciurent division into chemical types. 

The market trend, strongly influenced by environmental pressures, is likely to be away from aromatic hydrocarbons in formulations for domestic use. This win probably also apply to chlorinated hydrocarbons. This is not necessarily true of their industrial use, but further improvements in recapturing and recycling will reduce their production and sales. 

A trend towards aliphatic hydrocarbons—low in toxicity, photochemical activity and price and easy 

The value of used aliphatic hydrocarbons before recovery may be little different to that of purchased fuel oil or gas, and it is possible that in some circumstances it win be more economic to burn the used solvent for its heat value than to try to recover it to a high standard. The possibility exists that an oil company supplying a hydrocarbon solvent and having the expertise in burning difficult fuels may be able to offer a service and an attractive price for such a disposal. 

---

There are five components to the cost of using a Grignard reagent (/) magnesium metal, (2) the haUde, (J) the solvent, (4) the substrate, and (5) disposal of the by-products. The price of magnesium in mid-1992 was 3.20/kg, having risen from 1.20/kg in 1966 to 1.36/kg in 1970 and 2.90/kg in 1979. Prices for tetrahydrofuran and diethyl ether, the two most commonly used solvents, have also increased (Table 3) in the same period. The cost of the hahde depends on its stmcture, but as a general rule the order of cost is chloride < bromide < iodide. 

The amount of gas employed in a GC analysis is not usually important, particularly where open tubular columns are used. In LC, however, solvent use presupposes a solvent disposal difficulty if not a toxicity problem and, thus, solvent consumption can be extremely important. 

Generally, size exclusion chromatography is carried out using columns with an internal diameter of 7.8 mm. However, some SEC applications require the use of expensive solvents. For this purpose, size exclusion columns with a smaller internal diameter (4.6 mm) have been developed. Of course one should use proportionally lower flow rates with narrow-bore columns. If the standard column size uses a flow rate of 1 ml/min, then the smaller 4.6-mm columns should be used at a flow rate of 0.35 ml/min. This provides the same linear velocity as 1 ml/min on 7.8-mm columns. The decreased flow rate reduces solvent consumption and solvent disposal cost. The performance of the smaller diameter columns is not compromised if properly optimized instrumentation is used. 

The mobile phase is interesting in that the water is buffered appropriately to complement the dissociation constants of the solutes. A mixture of methanol and acetonitrile is employed, the acetonitrile being used to increase the dispersive interactions in the mobile phase. The reason for the particular solvent mixture is not clear and it would appear that the separation might be achieved equally well by using a stronger solution of methanol alone or a more dilute solution acetonitrile alone. There is no particular advantage to one solvent mixture over another except for the fact that waste acetonitrile produces greater solvent disposal problems than methanol. 

SafeChem, a subsidiary of Dow, has developed a handling system for chlorinated solvents that allows them to be used in closed-loop degreasing systems. The Safe-Tainer system uses two dedicated double wall containers one to hold fresh solvent and the other used solvent. The containers are connected to the cleaning equipment with zero dead volume, leak-free connections that prevent spills, leaks or vapour emissions during use. Used solvent is collected for recycling and professional disposal of any residues. The system minimises solvent use and release to the environment. A study carried out by Dow during a trial in... 

Extraction. Centrifuging the soil extract in the screw-capped vial can easily break the solvent emulsions that often form during extraction. The vial can survive up to 6000 centrifugation if rubber stoppers are inserted into the centrifuge cup to provide a flat base to protect the vials. The desired phase (usually the upper) can be easily removed with a pipet or, if it is to be discarded, it can be removed using a disposable pipet connected by tubing to a suction flask and a vacuum line. 

The following provides cost information (expressed in fourth-quarter 1993 dollars) for retrofitting an existing scrubber system with a condensation scrubber under typical operating conditions, adapted from EPA cost-estimating spreadsheets (EPA, 1996) and referenced to the volumetric flow rate of the waste stream treated. For purposes of calculating the example cost effectiveness, the pollutant is PM at a loading of approximately 7 g/sm3 or 3 gr/scf. The costs do not include costs for post-treatment or disposal of used solvent or waste. 

To operate the evaporator, we place the reaction solution in a round-bottomed flask while the pressure inside the evaporator is decreased to about x p. The flask is then rotated. The solvent evaporates more easily at this low pressure than at p. The solvent removed under vacuum is trapped by a condenser and collected for easy re-use, or disposal in an environmentally sensitive way. 

Caution These operations involve reagents and solvents with potentially harmful vapors (Brg, NH3) and therefore should be conducted in an efficient hood. The use of disposable gloves is highly recommended. 

Although organic solvents are commonplace in industry, they are highly volatile and dangerous in the large quantities that manufacturing processes require. Disposing of used solvents is a major environmental concern. 

General Electric Company, under an EPA permit, incinerated nearly 6,000 L (1,500 gal.) of 20% liquid DDT formulations in a liquid injection incinerator near Pittsfield, Massachusetts, in September 1974 (4). The facility utilized a vortex combustor of the type normally used for disposal of oils and solvents. Operating temperatures ranged from 870 to 980°C with retention times of 3 to 4 s and 120 to 160% excess air. Overall destruction efficiency exceeded 99.99%. Concentrations of DDT, DDE, and DDD in the stack gas and scrubber water were below analytical detection limits. 

The second variant of LPME uses a disposable, porous, hollow microfibre. In this case, the sample solution is placed in a vial equipped with a modified lid. A loop of microfibre passes in and out of the lid, such that the loop dips into the sample solution in the vial. The extraction solvent is injected into the capillary fibre from the outside. Again, stirring may be used. After an equilibration period, where solutes are able to traverse the fibre wall into the extraction solvent, the contents of the capillary are withdrawn and injected onto the chromatographic system. The two forms of this technique are illustrated in Figure 4.9. 

The use of solvents in the chemical industry and in the chemical-related industries is ubiquitous. Beyond chemical industries, solvent use has become an integral part of life in the twenty-first century. In 1991, the production of the 25 most commonly used solvents was more than 26 million tons per year. According to EPCRA section 313 data, of the chemicals and chemical categories tracked by the program in 1994, five of the top 10 chemicals released or disposed of were solvents, and included methanol, toluene, xylene, methyl ethyl ketone, and dichloromethane. The total quantity of these chemicals released or disposed of was over 687 million pounds, which accounts for 27% of the total quantity of TRl-listed chemicals released and disposed of in that year (Sullivan, 1997). 

The following drawing shows that about 29% of the solvent are carried into the waste water (which is fed into an internal waste water recycling). The remaining 71% can be found in the used solvent or in the filter cake and were so far disposed of as dangerous waste (Fig. 1). 

Figure 3.1 identifies the major stages in a solvents life cycle production, transport, use, and disposal. Although there are many opportunities to recycle and reuse solvents they will eventually need to be disposed of as waste. As an example, consider a process which uses tetrahydrofuran (THF). A 1 kg reduction in the amount ofTHF would reduce the CO2 emissions from THF production by about 16kg [3], This reduction in CO2 emissions does not account for the savings in transportation or disposal of excess THF in a process. Therefore, reductions in solvent use by the pharmaceutical industry not only reduce the waste it produces as part of its processes but also the waste that would be generated from the manufacture of additional solvent. 

---