Choice of Feedstock

3-Alkylated pyridines such as 3-picoline, 3(5)-ethylpyridine and 2-methyl-5-ethyl-pyridine (MEP) are the natural choice as starting materials for the nicotinates. The choice of alkyl pyridine is governed by their availability and the process being used. 

Pyridine bases such as 3-picoline and MEP are predominantly manufactured by the Chichibabin reaction, where a mixture of aldehydes or ketones is reacted with ammonia. Thus, formaldehyde, acetaldehyde and ammonia react in the gas phase to produce a mixture of pyridine and 3-picoline. By choosing the appropriate aldehyde or ketone, catalyst and phase (liquid or gas phase), the composition of the mixture can be varied at will, depending on the desired end-product. In the gas phase, silica alumina catalysts are often used, while in the liquid phase acid catalysts based on phosphoric or acetic acid are employed. In the 1990s, Reilly patented MET and BEA-based zeolite catalyst compositions for ammonia-aldehyde conversions to pyridine, picolines and alkyl pyridines. 

Chemically, 3-picoline is the ideal starting-material for nicotinic acid or amide the methyl group can be selectively and readily oxidized to the carboxyl derivative with few by-products or pollutants. High selectivity coupled with the low molecular weight ratio (1 1.3) compared to the end-products make picoline an attractive industrial starting-material for the production of nicotinic derivatives. 

3-Picoline is obtained, typically in a 1 2 ratio along with the main product pyridine, by the gas-phase reaction of acetaldehyde, formaldehyde and ammonia. The lack of selectivity of this reaction to either pyridine or picoline has hitherto meant that the economy of the major product (pyridine) has determined the price and availability of picoline. Consequently, producers of pyridine have been able to control the quantity and prices of picoline on the market. This has led to the search for alternative feedstock and manufacturing processes for picoline. 

As mentioned above, the bulk of picoline is produced today by condensation of acetaldehyde, formaldehyde and ammonia in the gas phase, which simultaneously produces large quantities of pyridine. A selective and suitable alternative method starting from these or similar simple molecules has yet to be developed. Given the thermodynamic properties of the molecules and reactions involved it does not seem likely to expect a selective process for 3-picoline in the near future following this strategy, although shape-selective catalysts may hold a key. 

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Olefin Sources. The choice of feedstock depends on the alcohol product properties desired, availabiUty of the olefin, and economics. A given producer may either process different olefins for different products or change feedstock for the same appHcation. Feedstocks beheved to be currentiy available are as follows. 

ElexibiHty allows the operator to pick and choose the most attractive feedstock available at a given point in time. The steam-cracking process produces not only ethylene, but other products as weU, such as propylene, butadiene, butylenes (a mixture of monounsaturated C-4 hydrocarbons), aromatics, etc. With ethane feedstock, only minimal quantities of other products ate produced. As the feedstocks become heavier (ie, as measured by higher molecular weights and boiling points), increasing quantities of other products are produced. The values of these other coproduced products affect the economic attractiveness and hence the choice of feedstock. 

Proper choice of feedstocks and use of relatively severe operating conditions ia the reformers produce streams high enough ia toluene to be directiy usable for hydrodemethylation to benzene without the need for extraction. 

Catalytic crackings operations have been simulated by mathematical models, with the aid of computers. The computer programs are the end result of a very extensive research effort in pilot and bench scale units. Many sets of calculations are carried out to optimize design of new units, operation of existing plants, choice of feedstocks, and other variables subject to control. A background knowledge of the correlations used in the "black box" helps to make such studies more effective. 

Table 14.8 summarises the specific features of hydrogen production for each of the ten countries. It must be mentioned that the different price levels are not only derived from the choice of feedstock for hydrogen production but also from regional differences in distribution costs. 

Cracking large hydrocarbons usually results in olefins, molecules with double bonds. Thats why the refinery cat crackers and thermal crackers are sources of ethylene and propylene. But the largest source is olefin plants where ethylene and propylene are the primary products of cracking one or more of the following ethane, propane, butane, naphtha, or gas oil. The choice of feedstock depends both on the olefins plant design and the market price of the feeds. 

The source of hydrogen for coal liquids production could be, as in the case of shale oil production, either the gas or the bottoms product from the liquids plant. Again, the choice of feedstock for hydrogen production will be dictated by economic, market, and environmental considerations. 

Today, the choice of feedstock for chemicals production depends on complex technical, economic, environmental, and political factors. Clearly, not all chemicals are suitable for production from coal with current technology. Some factors to be considered in the evaluation of the appropriate feedstock for a particular chemical product are (1) the relationship between the carbon/hydrogen ratio in the chemical product and the feedstock, (2) the delivered cost of alternative raw materials, (3) capital costs, (4) environmental protection, and (5) the reliability of supply. Recently, except for special situations, such as that for Sasol in South Africa, the manufacture of chemicals from coal at coal prices relative to the prices of petroleum and natural gas has not been attractive economically. 

Song and co-workers developed a set of exercises that allows students the opportunity to analyze a series of reactions and judge them based on choice of feedstock, atom economy, reaction conditions, environmental exposure, and resource conservation (77). One example asks the students to consider the following two series of reactions and then decide how to synthesize eight moles of aluminum hydroxide (Figure 1). 

Choice of feedstock (costs are relevant of course, but also total resources, energy, waste, etc. in the manufacture of the given feedstock are important factors). 

Hydrocarbons heavier than naphtha can be used as -ieedsteeks-for-ammonia-produclion by partial oxidation processes. Natural gas and naphtha also can be used, but since the plant cost for the partial oxidation process is considerably higher than that for steam reformir, the lighter feedstocks are seldom used. However, the partial oxidation process does offer the advantage of wider choice of feedstock with greater tolerance for impurities. 

Anionic surfactants comprise the bulk of the surfactants used in laundry detergents today. The anionic surfactants are derived from both oleochanical and petrochemical sources. The choice of feedstock depends on availability and cost... 

The production of the desired cut can be increased by the proper choice of feedstock and processing conditions. 

A number of other chemicals have been converted to MA. There is no account of any of them being utilized commercially thus far. Among these are furfural, " mixed olefins, cyclopentadiene, toluene, " ter-penes, etc. So far, these have been of academic interest due to unfavorable economics and/or low selectivity to MA. Raw material supply and demand pictures are known to change rapidly and particularly so in the recent past. For the present, however, given the present economics and state-of-the-art technology, benzene and C4 hydrocarbons (n-butane in the United States) are the choice of feedstocks. In addition, there is by-product MA produced during phthalic anhydride manufacture. 

For many years into the future there will be a continuing requirement for the large-scale production of ammonia, principally for fertilizer use. The main objectives for commercially sized plants are high efficiency, low capital cost, and high reliability. The trends in plant design to achieve these objectives can be considered on a number of different levels, ranging from broad issues such as choice of feedstock to details of the ammonia converter design. 

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