Acid-soluble oil

The HF concentration of the acid catalyst is maintained ia the range of 85—95% by regeneration within the unit s fractionation faciUties. A separate acid regeneration column (not shown ia Figure 2) is also iacluded to provide a means to remove excess acid-soluble oils and water. The regeneration of acid ia the unit accounts for the low consumption of fresh acid by the HF process. 

The presence of impurities such as butadiene affects the product yield and properties. Butadiene tends to polymerize and form acid-soluble oils, which increases acid makeup requirements. For every pound of butadiene in the feed, ten pounds of additional make-up acid will be required. ... 

Figure 10.17 H NMR spectra of spent acid samples spanning operational range of sulfuric acid concentrations. Shift of sulfuric acid peak with change in acid strength is indicated. Acid soluble oils and micellar water are readily quantified.

During the last 40 years, an enormous effort was put into searching for a solid catalyst [4, 5]. The main obstacle still to be overcome is the formation of acid-soluble oils (ASO, also known as conjunct polymers or red oil) which accompanies the alkylation process. This material contains highly unsaturated cyclic hydrocarbons, which rapidly passivate the catalyst. When liquid catalysts are used, they can be easily withdrawn from the process and replaced, without interrupting the alkylation operation. UOP has developed the Alkylene technology, which uses the proprietary HAL 100 catalyst in a process that is claimed to be commercially competitive [6]. 

Conjunct Polymers. Conjunct polymers (frequently called acid-soluble oils in HF alkylation, red oils in sulfuric acid alkylation) are an exceedingly complex mixture of highly unsaturated, cyclic hydrocarbons. These polymers are by-products of tertiary butyl carbonium ions, and their formation undoubtedly Involves a complexity of reactions. Miron and Lee (1963) found the bulk of an HF conjunct polymer to be mode up of molecules containing 2-4 rings with an average ring size of 5-6 carbon atoms. They estimated the number of double bonds per molecule of polymer at about 2.5 to 3. Thus, these polymers are hydrogen-deficient. 

The hydrogen lost during their formation apparently goes into chain termination, i.e., the formation of isobutane most probably and possibly some propane when propylene is present In alkylation feed. HF alkylation has found no benefit from having acid-soluble oils present in the catalyst. When they are present in amounts greater than about one weight percent, they have a detrimental effect on alkylate quality and yield. 

In a dying acid run one begins with fresh acid in the reactor and without spent acid withdrawal or fresh acid makeiqp allows the catalyst diluents (acid soluble oil and water) to build up with time. This type of run can be contrasted to a steady state run where spent acid is purged and fresh acid added so as to keep the diluent level constant. 

The consistency of the raw catalyst composition data can be seen by looking at the bottom part of Figure 5. This is a plot on the sum of wt. % H2SO4, wt. % H2O and wt. % acid soluble oil for each of the acid analyses in the mixer comparison study. The absolute difference between this sum and 100 gives a measure of the consistency of the acid analyses. Except for the one point at about 250 hrs. (and the analyses that were rerun at L75-100 hrs.), the sums in Figure 5 for the mixer comparison runs vary between 99% and 101% with most sums being closer than 1%. If it is considered that these sums are formed from the results of three independent analyses, it can be said that the quality of the acid composition data is very good. 

One of the most important facets of the mixer con arison was the effect of the mixer type on alkylate quality. As mentioned previously, since acid composition does have a profound effect on quality it is necessary to compare mixing effects at constant acid composition. For this study, the acid con ionent which seemed to play the key role in this composition/quality effect is the acid soluble oil. This component, which is characteristic of strong acid processes, is a complex mixture in which cyclic conjunct polymers predominate ( ). Since alkylate quality does vary markedly with acid soluble oil content, many theories on its role in quality enhancement have been proposed such as a hydride transfer agent, surfactant, or agent to increase isobutane solubility. 

As far as the general shape of the curves is concerned, the presence of maxima indicates that at low concentrations acid soluble oils interact directly with the alkylation reactions and have a beneficial effect toward product quality while at high concentrations the diluent effect on acid strength outweighs any possible benefits. 

WT. % ACID SOLUBLE OIL IN ACID PHASE Figure 7. Product quality as a function of acid-soluhle oil level... 

Results on operating the FBT at higher power levels are from other pilot plant runs. The A MON is at the optimum acid soluble oil level of about 3.0 wt. %. 

This difference in replacement rates for the two mixers is due to (1) a small difference in the effect of catalyst age on acid soluble oil level (see Fig. 6) and (2) about a 10% difference in acid inventories for the two runs. 

Many references to naphthenic acids, soluble oils, lubricating greases, etc. fairly good subject index... 

Conjunct Polymer Formation The polymers (also called acid-soluble oils or red oil) dissolve in the acid phase (sulfuric acid and HP). They have a hydrogen/ carbon atomic ratio (H/C) of about 1.75 and a molecular weight of 270-325. ° They contain numerous -C=C-bonds, which react to a significant extent with sulfuric acid to produce conjimct acid sulfates or with HP, conjunct polymer fluorides. These sulfates (or fluorides)... 

The compositions (or concentrations) of both the feed acid and the acid present in the reactor are of major importance. The feed sulfuric acids are frequently in the 98.5-99.5% range. The more concentrated feed acid results in the production of more alkylate per unit weight of feed acid. The preferred acid concentration in the reactor varies from about 90% to 95% depending especially on the composition of the olefin feeds. Stronger acids are preferred with propylene-rich olefins, whereas the lower concentrations are preferred with Cs-iich olefins. Less information is available with HF catalysts. Eastman et al. report the HF compositions in a Phillips reactor as 82-85.5% HF, 8-12% acid-soluble oils (or conjunct polymers), and 0.1% water.f The unaccounted material in this analysis is probably HF that has reacted to form conjunct polymer fluorides. 

The effect of space velocity is interrelated with reactor geometry and the effect of olefin concentration. As long as alkylation and hydrogen transfer reaction rates are in balance (effect of T, I/O, etc.), yield and selectivity show little dependence on olefin space velocity (OSV). In general, a very high space velocity will increase acid consumption and formation of acid-soluble oils because of the higher probability of multiple olefins reactions. 

Other observations of this test work, with respect to key alkylate product properties, were that neither the Reid vapor pressure (RVP) nor density deviated significantly from values that would be obtained via liquid acid alkylation. Further, acid-soluble oils (ASO), formed as contaminant side products in the case of liquid acid processes, could not be detected among the reaction products in our SAC testing. Compared with the liquid acid technologies, this effect results in both lower feed consumption per unit of alkylate production and eliminates generation of a by-product that can be difficult to dispose of. 

Acid-soluble oil Up to about Less then sulfuric. None... 

The double bonds in the CPs (5) always react to some extent with sulfuric acid (or HF) to produce CP sulfates (or fluorides). The importance of CPs in the overall reaction sequence is indicated by the following information First, fresh sulfuric acid is a poor catalyst until a small amount of CPs is obtained (6). The best quality alkylates are produced with sulfuric acids containing 3-6% polymers (7,8). Although less information has been published when HFs are used as catalysts, the level of CPs in HF is also important. Phillips Petroleum Company (9) has developed a near-infrared technique to monitor the CP [or acid-soluble oil (ASO)] content of their HF phase. They report that in a refinery, the HF contained 10% by weight CPs but the acidity was about 84 85%. Since the HF contains about 0.2% water, about 4% was unreported. It is mainly alkyl fluorides. 

Downstream units that process FCCU olefins are adversely affected by diolefins. A sudden increase in acid-soluble oils in an HF alkylation unit or a dramatic increase in catalyst consumption on a Dimersol polymerization unit is likely caused by an increase in diolefins in olefin feedstock. 

The best solution appears to be the use of an almost insoluble liquid catalyst held within the pores of a suitable inert support. Supported liquid catalysts are well known and can be used with a continuous catalytic regeneration system similar to that developed for catalytic reforming processes. Haldor Topsoe has successfully tested trifluoromethane sulfonic acid in this way since 1993 with a variety of olefin feeds. " No formal regeneration was necessary apart from periodic removal of some catalyst for reimpregnation and the recovery of dissolved acid from the alkylate. Both catalyst and support are, therefore, recirculated. The small quantity of polymeric by-products formed (acid soluble oil) appears to be less tlm that formed in the sulfuric acid process, but slightly more than in the HF process. 

---