Improvement of Industrial Linear Alkyl Benzene for Detergents Production

Standard and specifications of Linear Alkyl Benzene (LAB) compound are essential in the production of most good quality detergents. Pure LAB was obtained by purification of industrial LAB samples, followed by controlling/overcoming the problem of conversion of paraffinic materials to undesirable olefins. Concentrated sulfuric acid was used to remove the olefinic contaminants from the industrial LAB samples. The results were obtained using potentiometric method and color changes in Lovibond photometer. Evidently, significant improvement of the specifications was observed and thus, improved final products are industrially obtained. The new and modified reaction procedure has resulted in a superior quality LAB-based detergent product, compared to that obtained using LAB under the normal operating conditions.


Introduction:
Cleaning products like soaps and detergent play an essential role in our daily lives. In the beginning, soaps were used widely for cleaning purposes, washing, bathing, and other types of housekeeping. After that, and due to the increasing need for cleaning products, chemists have, therefore, been making extensive efforts to produce suitable alternatives to soaps. They are known now as detergents. Detergents are effective cleaning products because they contain one or more surfactants (surface active agents). Surfactants are organic chemicals that help to change the properties of water, depending on their ability to reduce surface tension when they exist in water solutions. In addition, detergents are resistant to hard water. There are many cleaning materials used in the market, for example, liquid soap, glass cleaning liquids, wood furniture cleaners, carpet cleaning mixtures, marble and tile cleaning mixtures, etc. In recent years, there have been several methods of obtaining simple chemical mixtures that can be used as industrial detergents, either from alkaline mixtures or from petroleum residues, without damaging the appearance and nature of the cleaned material, while ensuring maximum protection for the consumer [1].
In addition to the performance of the surfactant, acceptable market sustainability is affected by several factors: the starting materials local availability, reasonable cost, longer activity life, surface protection, and chemical / physical / thermal / color stability [2].The current trend is towards producing detergents based on linear alkyl benzene (LAB), for its biodegradability and ease of sulfonation [3,4].LAB material structure shown in Fig. (1) helps to make the detergent environmentally friendly as it decomposes in drainage water reducing its harmful pollution damage to the environment. LAB is normally produced by the reaction of benzene with linear paraffins C9-C15, which are produced from kerosene of crude oil in the presence of a solid catalyst or a liquid anhydrous aluminum chloride [5,6,7]. Usually, 75% of the linear paraffin which is extracted from kerosene is used in production of LAB. The production process involves dehydration, conversion of paraffin to olefin using heat and platinum catalyst on alumina [8], as shown in the schematic representation Fig. (2) describing the production of LAB from kerosene (linear paraffin, C 9 -C 15 ) [9]. The remainder of linear paraffinic materials is used for the production of resins, dyes, lubricants, printer inks, polymers, etc [10].Alkyl benzene sulfonate is produced by the sulfonation of LAB process as shown in Fig. (1), where the sulfonation factor is the sulfur trioxides. This is produced by reacting sulfur with oxygen in the presence of vanadium pentoxide as an oxidizing agent. Sulfur trioxide is reacted with LAB at 50 ᵒ C according to the following equation: Upon the sulfonation process, the pure linear alkyl benzene colorless with good specifications, changes into undesirable light brown color due to the processes and reactions as shown in the Experiment Section. The changing color of the final product is as a result of two reasons: the contamination of kerosene with some undesirable olefinic impurities, and the effectiveness of the platinum catalyst used in the conversion process of paraffin to olefins [11,12,13]. The dark color of the sulfonated LAB will affect the appearance of the final cleaning product (detergent) that will reduce its performance and minimize its consumption in the market.

Experimental:
Several  Table 1. This significant value may negatively affect the LAB specification and, therefore, the quality of the final detergent.   The Bromine Index is very important in determining the specifications of the LAB, which is inversely correlated with the Bromine Index.
The LAB becomes off-specification when the Bromine Index exceeds the value 15 mg/100 g.After measuring the Bromine Index for the sample, it was treated with concentrated sulfuric acid at 1:1 ratio (w/w) in a separating funnel (250 mL) and shaken for one minute, giving rise to two distinct layers.
The upper layer is LAB material and the bottom layer is the acid of dark yellow color.
After separation of the two layers from each other, a second amount of fresh acid was added to the remaining LAB layer, showing no change in color.
The LAB layer was taken in another 250 ml separating funnel and shaken with a quantity of de-ionized water for the purpose of washing.
The mixture was left to settle for 15 minutes. The resulting two layers were separated from each other. A quantity of de-ionized water was added to the acid part and heated for the purpose of hydrolysis to produce alcohols and glycols.
After cooling, a sample was taken for examination.The hydrolysed acid seems to produce alcohols in addition to the recovery of sulfuric acid, which acts as a catalyst, indicating an economically successful process.
The overall industrial process Fig. (6) shows the purification of contaminated LAB and removal of undesirable olefinic compounds using sulfuric acid.
The overall industrial process is depicted in Fig. (6), showing the purification of the contaminated LAB and elimination of the undesirable olefinic compounds using sulfuric acid.

Results and Discussion:
The value of Bromine Index is used to assess the quality relevance of LAB as a raw material for the production of detergents. The lower Bromine Index, the better the There are several reasons for the high values of Bromine Index of the industrial LAB material. Initially, the kerosene used in the production of linear paraffin seems usually contaminated with some cyclo olefins, which are difficult to separate from the kerosene bulk, so they get carried on with linear paraffin to the conversion unit (paraffin to olefin).
Additionally, the over activity of the platinum catalyst used in the conversion process leads to the formation of compounds with dual double bonds, besides the presence of some unidentified olefinic compounds.
Concentrated sulfuric acid is known to react with olefins in the preparation process of alcohols through hydrolysis, so it was planned to use it for the removal of the undesirable olefinic contaminants from the LAB samples. During the treatment of the LAB samples, the concentrated sulfuric acid formed two layers. After separation, the LAB layer was washed using de-ionized water to remove all traces of the acid to carry out measurements of Bromine Index. As noted earlier, the Bromine Index was measured using two methods: 1. Titration method using a platinum pole -double wire.  It is quite striking to observe, in both measurement methods, the dramatic decline of Bromine Index values for the LAB samples taken from industrial source. In fact, the high values of Bromine Index are characteristic in all LAB samples taken from the industrial source. Evidently, the decline in Bromine Index was due to the fact that the sulfuric acid withdrew all the non-colloidal olefinic contaminants, which were not consumed in the industrial process of alkylation during the production of the LAB.
The process of hydrolysis of the separated acid layer will lead to the production of alcohols and the recovery of the sulfuric acid, used in the process of withdrawing the olefinic contaminants, for the re-usage in the second and third batches.
The acid gets separated from the formed alcohol compounds by distillation under vacuum to avoid crashing of these alcohols into corresponding olefins at the elevated temperatures of 150 ᵒ C. The reaction undergoes the following mechanism (isobutene is taken as an example only).
The presence of alcohols was detected by adding a drop of CrO 3 solution and sulfuric acid (5 N) to the applied sample. Upon heating, the color changes from orange to bluish green, indicating the presence of primary and secondary alcohols.

Conclusion:
Linear alkyl benzene (LAB) compounds are the raw materials used in the production of detergents. Upon sulfonation of LAB compounds, which is normally conducted over platinum catalyst, some resulting detergents fail to meet the globally required specifications. Evidently, such industrially produced out-of-spec LAB is due to some olefinic contaminants, as a byproduct, derived from the lack of control over the operating conditions in the LAB production. It appears that during the process of LAB sulfonation using aluminum catalyst, the paraffinic LAB tends to get converted into olefins of dark brown color, which eventually, causes the out-of-spec detergent products. Therefore, this industrial research work successfully improved the specifications of Linear Alkyl Benzene (LAB) compounds using a simple and cost effective method.