iLINEAR ALKYLBENZENE PRODUCTION Approximately 2 percent of the benzene produced in the United States is used in the production of linear
alkylbenzene (LAB). LAB (or linear alkylate) improves the surfactant performance of detergents. The primary end use for LAB is in the production of linear alkylbenzene sulfonates (LAS). Because of their water-soluble properties, LAS are used extensively in powdered home laundry products (over 50 percent of LAS produced) and in heavyduty liquid products. Alkyl benzene sulfonates with highly branched C side chains possess excellent 12 detergent properties, and they have also been used in the past in formulating detergents. However, in recent years, LAS have essentially replaced all branched alkylbenzene sulfonates in detergent formulations in the United States because of environmental considerations. LAB is extensively degraded (>90 percent) by microorganisms in sewage plants after a relatively short period of time. In comparison, the highly branched alkyl benzene sulfonates have a much lower biological degradability. Dodecylbenzene and tridecylbenzene are the two most common LABs. The locations of the LAB producers in the United States are shown in Table 5-13. In the United States, LAB is produced using two different processes. Vista's Baltimore plant uses a monochloroparaffin LAB production process. Vista's Lake Charles plant and Monsanto's Alvin plant use an olefin process, wherein hydrogen fluoride serves as a catalyst. Approximately 64 percent of LAB is produced by the olefin process. The paraffin chlorination process accounts for about 36 percent of LAB production. Both processes are described in the following sections. Process Description for Production of LAB Using the Olefin Process Production of LAB using the olefin process consists of two steps: a dehydrogenation reaction and an alkylation reaction. The C to C linear paraffins are 10 145-71 dehydrogenated to n-olefins, which are reacted with benzene under the influence of a solid, heterogenous catalyst (such as hydrogen fluoride [HFl]) to form LAB. The discussion of LAB production using the olefin process is taken from references 102 and 103. First, n-paraffins are transferred from bulk storage to the linear paraffin feed tank in Stream 1 (Figure 5-15.) The paraffins are heated to the point of vaporization (Stream 2) and passed through a catalyst bed in the Pacol reactor (Stream 3), where the feed is dehydrogenated to form the corresponding linear olefins by the following reaction: R - CH - CH - R ---> R CH = CH - R + H 1 2 2 2 1 2 2
The resulting olefins contain from 10 to 30 percent -olefins, and a mixture of internal olefins, unreacted paraffins, some diolefins, and lower-molecular-weight cracked materials. The gas mixture is quickly quenched with a cold liquid stream as it exits to process thermally-promoted side r---**eactions (Stream 4). The hydrogen-rich offgases (e.g., hydrogen, methane, ethane, etc.) are then separated from the olefin liquid phases (Stream 5). The gas is used as process fuel (Stream 6) or vented to a flare stack. Di-olefins in the Pacol separator liquid are selectively converted back to mono-olefins in the Define reactor (Stream 7). The effluent from the reactor is routed to a stripper (Stream 8), where light ends are removed (Stream 9). The olefin-paraffin mixture (Stream 10) is then alkylated with benzene (Stream 11) in the fixed-bed reactor to be blended with a HFl catalyst. The blend is held at reaction conditions long enough for the alkylation reaction to go to completion as follows:
R CH = CHR + C H ---> R CH - CHR 1 2 6 6
12 2
Product from the reactor flows to the benzene stripping column (Stream 12) for separation and recycle of unreacted benzene to the fixed-bed reactor (Stream 13). The liquid HFl is also separated and recycled to the alkylation vessel to be mixed with fresh HFl.5-73 Figure 5-15. Linear Alkybenzene Production Using the Olefin Process.
