Furfural extraction plant

Several cases of spontaneous ignition after exposure to air of fine coke particles removed from filter strainers on a petroleum refinery furfural extraction unit have been noted. This has been associated with the use of sodium hydrogen carbonate (bicarbonate) injected into the plant for pH control, which produced a pH of 10.5 locally. This would tend to resinify the aldehyde, but there is also the possibility of a Cannizzaro reaction causing conversion of the aldehyde to furfuryl alcohol and furoic acid. The latter, together with other acidic products of autoxidation of the aldehyde, would tend to resinily the furfuryl alcohol. Pyrolysis GLC showed the presence of a significant proportion of furfuryl alcohol-derived resins in the coke. The latter is now discarded into drums of water, immediately after discharge from the strainers, to prevent further incidents. 

In 1992, a rather unusual furfural plant was built. With a front end according to the AGRIFURANE process described in chapter 10.2, the back end was designed as shown in Figure 112. The filtered reactor condensate containing 5 % furfural, 1.7 % acetic acid, 0.17 % formic acid, and various low boilers was introduced into an extraction tower 1 fed with chloroform at the top. On the way downwards, the heavy chloroform (density 1.498 g/cc at room temperature) picked up the furfural, and in view of the poor solubility of chloroform in water, it formed a chloroform/furfural extract at the bottom. This extract entered a distillation column 2 removing the chloroform as the head fraction. From a buffer tank 3, this chloroform was recycled to the extraction tower 1. The sump fraction of the distillation column 2 consisted of furfural, polymers, waxes, and some low boilers. This fraction was introduced into a distillation column 4, which yielded a head fraction of low boilers, a side stream of furfural, and a sump fraction of polymers and waxes. 

One of Sun s objectives for the new plant was that the base stocks be at least of the same quality as those from solvent refining, therefore this hurdle had to be overcome. Their solution was to give the total dewaxed hydrocrackate product a light furfural extraction (about 97% raffinate) to remove the tri+ aromatics which appeared to be at the root of the problem.1516 Thus their process involved two solvent extraction steps, one before the hydrocracker and one afterwards. This route gave stable base stocks, but with some residual color. An example of the improvement obtained can be seen in Table 7.10, where 100, 200, and 500 SUS base stocks ( 1, 2, and 3 in Table 7.10) of approximately 110 VI from hydrocracking a distillate/DAO blend were tested for stability before and after furfural extraction. The results show that the extraction improves color relative to unextracted samples for the immediate hydrocracker products and that their performance in the stability test was improved as well by extraction. 

A number of solvents were studied as candidates for replacing furfural in existing butadiene extraction plants. The significant data from that study have been reported (3), and the most promising solvents are compared in Table I. 

A commercial plant for these processes follows the general scheme of Fig. 11.23 (95). For 200,000 lb./day of degummed soybean oil and a solvent ratio of 8.3 1, two extraction columns each 5.5 ft. in diameter, 87 ft. tall (75 ft. of packing), operate in parallel for the furfural extraction at 120°F. The interface is held between the oil and solvent inlets, so that both phases are dispersed in one section of the tower or the other. The naphtha extraction is carried out in a single packed tower 4.5 ft. in diameter, containing a 50-ft. depth of Raschig rings, at 70 F. Furfural and... 

Figure 8.12 Furfural/acetic acid extraction plant to treat the condensate from Lenzing s sulfite pulping process (extraction efficiency -80-90%). ...

Aromatic and Nonaromatic Hydrocarbon Separation. Aromatics are partially removed from kerosines and jet fuels to improve smoke point and burning characteristics. This removal is commonly accompHshed by hydroprocessing, but can also be achieved by Hquid-Hquid extraction with solvents, such as furfural, or by adsorptive separation. Table 7 shows the results of a simulated moving-bed pilot-plant test using siHca gel adsorbent and feedstock components mainly in the C q—range. The extent of extraction does not vary gready for each of the various species of aromatics present. SiHca gel tends to extract all aromatics from nonaromatics (89). 

Lubricating Oil Extraction. Aromatics are removed from lubricating oils to improve viscosity and chemical stabihty (see Lubrication and lubricants). The solvents used are furfural, phenol, and Hquid sulfur dioxide. The latter two solvents are undesirable owing to concerns over toxicity and the environment and most newer plants are adopting furfural processes (see Furan derivatives). A useful comparison of the various processes is available (219). 

Pure xylan is not employed in industry. but crude xylan or pentosans are of industrial importance. Xylan has been proposed as a textile size but is not employed as yet for this purpose.130 Perhaps the largest use of pentosans is in their conversion to furfural, which has many applications and serves as the source of other furan derivatives. At the present time, large quantities of furfural are used in the extractive purification of petroleum products, and recently a large plant has been constructed to convert furfural by a series of reactions to adipic acid and hexamethylene-diamine, basic ingredients in the synthesis of nylon. In commercial furfural manufacture, rough ground corn cobs are subjected to steam distillation in the presence of hydrochloric acid. As mentioned above, direct preferential hydrolysis of the pentosan in cobs or other pentosan-bearing products could be used for the commercial manufacture of D-xylose. 

Solvent make-up requirement generally is expressed as per cent of solvent circulation. For furfural and phenol this value will run about 0.03%, both for single solvent extraction and Duosol plants. Propane losses in Duosol plants and in propane deasphalting plants will be from 0.1 to 0.5% of circulation an average of 0.2% would be a reasonable estimate. 

Furfural and thence furan, by vapour-phase decarbonylation, are available in bulk and represent the starting points for many furan syntheses. The aldehyde is manufactured from xylose, obtained in turn from pentosans, which are polysaccharides extracted from many plants, e.g. com cobs and rice husks. Acid catalyses the overall loss of three mole equivalents of water in very good yield. The precise order of events in the multi-step process is not known for certain, however a reasonable sequence " is shown below. 

Four solvents were evaluated for the recovery of 1 -butadiene from crude Ch fractions by extractive distillation. Furfural [5 wt % water], methyl CeUosolve [10% water], acetonitrile [10% water] and p-methoxypropionitrile [5% water] solvents were studied at comparable operating conditions in a 2 inch diameter, 140 tray column. Furfural and methyl Cellosolve solvents performed the desired separation between 1,3-butadiene and trans-2-butene only at high solvent-to-Ch feed ratios. Acetonitrile and p-methoxypro-pionitrtle solvents were far superior to furfural and methyl Cellosolve at equivalent solvent-to-Cfeed ratios. The superior solvents could perform the desired separation at half the solvent ratio. When related to a plant scale operation, p-methoxypropionitrile solvent could double the capacity of an existing butadiene plant using furfural... 

The over-all performance of /3-methoxypropionitrile solvent in the pilot plant tests qualify it as a superior replacement solvent for furfural in butadiene extractive distillation plants. It offers distinct economic and operational advantages. Operation at lower solvent-to-C4 feed ratios greatly increases existing extractor capacity. In addition, the improved separation of trans-2-butene and butadiene in the extractive distillation column reduces the load on the final butadiene purification column. Operation at lower solvent-to-C4 feed ratio and lower reboiler temperature provides substantial utility savings. The lower reboiler temperature also reduces the rate of butadiene dimer formation. 

The extraction process is a physical separation that is used in all conventional lube plants. The solvent is added to the distillate and then separated to produce a raffinate (the desired product) and an extract that contains a higher percentage of aromatics and impurities. Typical solvents used are N-methyl-2-pyrrolidone, furfural, and phenol. Properties of the solvents are shown in Figure 11. 

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