Material cost

An indication of the cost of some commonly used metals is given in Table 7.5. The actual cost of metals and alloys will fluctuate quite widely, depending on movements in the world metal exchanges. 

The quantity of a material used will depend on the material density and strength (design stress) and these must be taken into account when comparing material costs. Moore (1970) compares costs by calculating a cost rating factor defined by the equation  

His calculated cost ratings, relative to the rating for mild steel (low carbon), are shown in Table 7.6. Materials with a relatively high design stress, such as stainless and low alloy steels, can be used more efficiently than carbon steel. 

The relative cost of equipment made from different materials will depend on the cost of fabrication, as well as the basic cost of the material. Unless a particular material requires special fabrication techniques, the relative cost of the finished equipment will be lower than the relative bare material cost. For example the purchased cost of a stainless-steel storage tank will be 2 to 3 times the cost of the same tank in carbon steel, whereas the relative cost of the metals is between 5 to 8. 

If the corrosion rate is uniform, then the optimum material can be selected by calculating the annual costs for the possible candidate materials. The annual cost will depend on the predicted life, calculated from the corrosion rate, and the purchased cost of the equipment. In a given situation, it may prove more economic to install a cheaper material with a high corrosion rate and replace it frequently rather than select a more resistant but more expensive material. This strategy would only be considered for relatively simple 

---

Unwanted byproducts usually cannot be converted back to useful products or raw materials. The reaction to unwanted byproducts creates both raw materials costs due to the raw materials which are wasted in their formation and environmental costs for their disposal. Thus maximum selectivity is wanted for the chosen reactor conversion. The objectives at this stage can be summarized as follows ... 

Raw materials efficiency. In choosing the reactor, the overriding consideration is usually raw materials efficiency (bearing in mind materials of construction, safety, etc.). Raw material costs are usually the most important costs in the whole process. Also, any inefficiency in raw materials use is likely to create waste streams that become an environmental problem. The reactor creates inefficiency in the use of raw materials in the following ways ... 

Considering raw materials costs only, the economic potential (EP) of the process is defined as... 

Raw materials costs dominate the operating costs of most processes (see App. A). Also, if raw materials are not used efficiently, this creates waste, which then becomes an environmental problem. It is therefore important to have a measure of the efficiency of raw materials use. The process yield is defined as... 

EP = value of products - raw materials costs - annualized capital cost - energy cost... 

The value of PRODUCT formation and the raw materials cost of FEED that reacts to PRODUCT are constant. Alternatively, if the byproduct has no value, the cost of disposal should be included as... 

By considering only those raw materials which undergo reaction to undesired byproduct, only the raw materials costs which are in principle avoidable are considered. Those raw materials costs which are inevitable (i.e., the stoichiometric requirements for FEED which converts into the desired PRODUCT) are not included. Raw materials costs which are in principle avoidable are distinguished from those which are inevitable from the stoichiometric requirements of the reaction. ... 

Figure 8.4 shows the cost tradeoffs for the present case. At high conversions, the raw materials costs due to byproduct formation are dominant. This is so because the reaction to the undesired... 

The whole problem is best dealt with by not making the waste in the first place, i.e., waste minimization. If waste can be minimized at the source, this brings the dual benefit of reducing waste treatment costs and reducing raw materials costs. 

Figure 10.7 shows the basic tradeoff to be considered as additional feed and product materials are recovered from waste streams and recycled. As the fractional recovery increases, the cost of the separation and recycle increases. On the dther hand, the cost of the lost materials decreases. It should be noted that the raw materials cost is a net cost, which means that the cost of lost materials should be adjusted to either... 

Figure 10.7 shows that the tradeoff between separation and net raw materials cost gives an economically optimal recovery. It is possible that significant changes in the degree of recovery can have a significant effect on costs other than those shown in Fig. 10.7 (e.g., reactor costs). If this is the case, then these also must be included in the tradeoffs. 

Figure 10.7 Effluent treatment costs should be included with raw materials costs when traded off against separation costs to obtain the optimal recovery. (From Smith and Petela, Chem. Eng., 513 24, 1991 reproduced by permission of the Institution of Chemical Engineers.)...

In most processes, the largest individual cost is raw materials. Raw materials costs and product prices tend to have the largest influence on the economic performance of the process. The value of raw materials and products depends on whether the materials in question are being bought and sold under a contractual arrangement (either within or outside the company) or on the open market (the spot price). Open-market prices can fluctuate considerably with time. Products are normally sold at below open-market price when under a contractual arrangement. 

Group). This published information can be used to assess at what price a new product will sell or to assess the minimum allowable selling price for given raw materials costs. 

Manufacture Various methods for the manufacture of acrylates are summarized in Figure 1, showing thek dependence on specific raw materials. For a route to be commercially attractive, the raw material costs and utilization must be low, plant investment and operating costs not excessive, and waste disposal charges minimal. 

After development of a new process scheme at laboratory scale, constmction and operation of pilot-plant faciUties to confirm scale-up information often require two or three years. An additional two to three years is commonly required for final design, fabrication of special equipment, and constmction of the plant. Thus, projections of raw material costs and availabiUty five to ten years into the future become important in adopting any new process significantly different from the current technology. 

Important side reactions are the formation of ether and addition of alcohol to the acrylate to give 3-alkoxypropionates. In addition to high raw material costs, this route is unattractive because of large amounts of sulfuric acid—ammonium sulfate wastes. 

Dehydrogenation of Propionates. Oxidative dehydrogenation of propionates to acrylates employing vapor-phase reactions at high temperatures (400—700°C) and short contact times is possible. Although selective catalysts for the oxidative dehydrogenation of isobutyric acid to methacrylic acid have been developed in recent years (see Methacrylic ACID AND DERIVATIVES) and a route to methacrylic acid from propylene to isobutyric acid is under pilot-plant development in Europe, this route to acrylates is not presentiy of commercial interest because of the combination of low selectivity, high raw material costs, and purification difficulties. 

The propylene-based process developed by Sohio was able to displace all other commercial production technologies because of its substantial advantage in overall production costs, primarily due to lower raw material costs. Raw material costs less by-product credits account for about 60% of the total acrylonitrile production cost for a world-scale plant. The process has remained economically advantaged over other process technologies since the first commercial plant in 1960 because of the higher acrylonitrile yields resulting from the introduction of improved commercial catalysts. Reported per-pass conversions of propylene to acrylonitrile have increased from about 65% to over 80% (28,68—70). 

In all appHcations involving zirconia, the thermal instabiHty of the tetragonal phase presents limitations especially for prolonged use at temperatures greater than - 1000° C or uses involving thermal cycling. Additionally, the sensitivity of Y—TZP ceramics to aqueous environments at low temperatures has to be taken into account. High raw material costs have precluded some appHcations particularly in the automotive industry. 

Expanded polystyrene bead mol ding products account for the largest portion of the drinking cup market and are used in fabricating a variety of other products including packaging materials, iasulation board, and ice chests. The iasulation value, the moisture resistance, and physical properties are inferior to extmded boardstock, but the material cost is much less. 

One possible route is to make formaldehyde direcdy from methane by partial oxidation. This process has been extensively studied (106—108). The incentive for such a process is reduction of raw material costs by avoiding the capital and expense of producing the methanol from methane. 

Ethers, such as MTBE and methyl / fZ-amyl ether (TAME) are made by a catalytic process from methanol (qv) and the corresponding isomeric olefin. These ethers have excellent octane values and compete on an economic basis with alkylation for inclusion in gasoline. Another ether, ethyl tert-huty ether (ETBE) is made from ethanol (qv) and isobutylene (see Butylenes). The cost and economic driving forces to use ETBE vs MTBE or TAME ate a function of the raw material costs and any tax incentives that may be provided because of the ethanol that is used to produce it. 

Usually at least five times the cost of the rough because cutting recovery is only 25% or even less. The cutting cost may become more important than the materials cost in small faceted stones. 

Phospha.tes. Many phosphates cl aim unique material advantages over siUcates that make them worth the higher material costs for certain apphcations. Glass-ceramics containing the calcium orthophosphate apatite, for example, have demonstrated good biocompatibiUty and, in some cases even bioactivity (the abiUty to bond with bone) (25). Recent combinations of fluorapatite with phlogopite mica provide bioactivity as well as machinability and show promise as surgical implants (26). 

Plant investment and maintenance costs are relatively high for a new iodine plant in the United States or in Japan because of the deep weUs required for brine production and disposal as weU as the corrosive nature of the plant streams. The principal materials cost is for chlorine and for sulfur dioxide, although in the United States the additives used for the brines, such as scale inhibitors and bactericides, also have a considerable influence on costs. 

The principal material cost for the Chilean iodine producers is sulfur used for the manufacture of sulfur dioxide, the reducing agent for the iodates contained in the leach solutions. Also, the use of sodium carbonate for the neutralization of the depleted solutions is an important cost factor. 

---