Fine chemicals are used as active ingredients or additives in the pharmaceutical and food & beverages industries, as well as in agriculture. The cracking of raw materials such as light virgin naphtha or liquefied gas results in intermediate products (ethylene, hydrogen, methane, CO2). At the end of the process chain, these can provide highly pure materials such as niacin (vitamin B3) or pre-stages of vitamins A and E. Process analyzers play an important role in the efficient further processing of cracker products.
Siemens is a leading supplier of process analytics, and has proven its competence for equipping chemical plants with process analytics from planning up to maintenance for many years already. This Case Study describes different applications of process gas chromatographs in a typical fine chemicals production process based on the Lonza acetylene cracker in Visp/ Switzerland.
Fine chemicals denotes a commercial category for chemical substances. Commonly encountered features include the production in complex syntheses (requiring several reaction steps), in small quantities (only a few tons or kilograms per year) or with a guaranteed degree of purity. This results in a significantly higher price compared to basic chemicals, with typically smaller production quantities. Fine chemicals are required for chemical syntheses and analyses in laboratories, as food additives (e.g. vitamins and minerals) or as raw materials for the production of pharmaceuticals, polymers (additives), detergents and cosmetics.
Lonza is a global player in the field of special chemicals, and produces various fine chemicals products using the hightemperature pyrolysis of light virgin naphtha (LVN) or liquefied petroleum gas (LPG).
In order to monitor the product quality, it is necessary to analyze the chemical composition of the starting materials (LVN, LPG, combustion gas) as well as the crude gas produced in the cracking process. Process gas chromatographs with their high availability have proven their suitability for this purpose. Siemens offers complete system solutions for such applications.
The process plant
Around the year 1915 in Visp/Switzerland (title picture), Lonza bagan using acetylene as the starting material for the synthesis of important basic chemicals such as acetaldehyde, acetic acid, alcohol (carbide fuel) and further organic products. In the sixties, the preparation of acetylene from calcium carbide was replaced by the high-temperature pyrolysis of light virgin naphtha, which additionally provided hydrogen and ethylene and was the basis for the manufacture of niacin.
Today, integrated production processes center around an acetylene/ethylene cracker (Fig. 1). The main raw material is the cracker feed. LPG from nearby refineries is primarily used in addition to LVN.
The naphtha cracking plant can be divided into three functional components:
- Crude gas generation (Montecatini process)
- Crude gas compression
- Gas decomposition (Linde process)
Fig. 2 shows the basic flowchart of the process steps.
Three independent crackers are available for the production of crude gas, of which only two are simultaneously in operation. The LVN or LPG is cracked in the reaction chamber in a temperature range from 2500 to 1200 °C in 2 to 3 thousandths of a second into lowmolecular reaction products (in particular ethylene, propylene, 1,2 and 1,3- butadiene, benzene, toluene, hydrogen, methane and acetylene). The high temperatures are achieved using an oxygen/combustion gas flame at approx. 3,000 °C.