Refractometry in Oil Refining and the Petrochemical Industry: Sulfuric Acid Alkylation

Refractometers Used in Sulfuric Acid Alkylation

Typical end products

  • Alkylate (premium higher-octane gasoline blending stock for motor fuel and aviation gasoline).
Chemical curve: Sulfuric acid 88-100 R.I. per Conc wt.-% at Ref. Temp. of 20 ̊C

Refractometers Used in Sulfuric Acid Alkylation


Motor fuel alkylation using sulfuric acid (H2SO4) or liquid hydrofluoric acid (HF) is one of the oldest catalytic processes used in petroleum refining. The purpose of the alkylation is to improve motor and aviation gasoline properties (higher octane) with up to 90 % lower emissions compared to conventional fuel usage.

The problem with HF is that the catalyst forms a hazardous air pollutant when released as a superheated liquid, while H2SO4 does not. Therefore nearly 90 % of all alky units built since 1990 have adopted the H2SO4 technology. 

The leading alkylation unit licensor, with a 90 % share of the market, is DuPont (Stratco®). Another licensor is EMRE (Exxon Mobile Research Engineering, formerly K.W. Kellogg).


In the process, isobutane is alkylated with low molecular weight olefins (propylene, butylene and pentylene) in the presence of a strong acid catalyst to form alkylate (the premium higher-octane gasoline blending stock). The catalyst (sulfuric acid) allows the two-phase reaction to be carried out at moderate temperatures. The phases separate spontaneously, so the acid phase is vigorously mixed with the hydrocarbon phase to form higher molecular weight isoparaffinic compounds.

After the reactor, the mixture enters a separation vessel where the acid and hydrocarbon separate. The acid is then recycled back to the reactor.

Instrumentation and installation

Refractometers Used in Sulfuric Acid AlkylationThe K-Patents Process Refractometer PR-43-GP is installed after the settlers to continuously monitor in real-time the concentration of acid in the process.

The concentration of sulfuric acid is critical to achieve the complete consumption of isobutane. A highly variable concentration of isobutane in the feedstock upsets the sulfuric acid content in the process.

It is important to determine the proper quantity of acid that will be fed into the process. This is achieved by combining routine sample titration analysis with continuous acid monitoring by the K-Patents Process Refractometer. Real-time measurements reduce the need for sampling and laboratory analyses that cause delay in the implementation of any necessary adjustments to the acid flow.

Continuous monitoring removes the uncertainty involved between titration measurements. The K-Patents refractometer will indicate any gradual fluctuations in the acid flow, allowing precise control over efficient acid consumption and resulting in cost savings. It is also useful in preventing acid runaway, an unwanted situation commonly described as wild acid.

Acid runaway may happen when the acid strength drops below 85-87 % H2SO4. As a result, the reactions between olefins and isobutane turn into reactions of olefins only, producing polymers known as acid sludge, ASO or red oil.

The K-Patents refractometer is not affected by acid soluble oil (ASO). The refractometer indicates actual acid strength regardless of the amount of hydrocarbons present, which is essential when transferring acid emulsion. It is also an extremely useful tool in real-time process acid strength measurement during agitated conditions.

The initial acid concentration is typically 85-100 % and the temperature is 15 °C (59 °F). The benefits of the K-Patents refractometer’s continuous monitoring system include substantial cost savings due to reduced acid consumption, and smooth alkylate production without acid runaways.

The K-Patents Process Refractometer System for Alkylation Acid Measurement Consists of:

  1. The K-Patents Process Refractometer PR-43 for hazardous locations in Zone 2. or The K-Patents PR-43 Intrinsically Safe model for installations in hazardous locations up to Zone 0.
  2. Optional parts:
    1. Different flow cell options for easy sensor installation
    2. EXd enclosure for easy isolator and transmitter mounting
    3. Parts for a start up
    4. Spare parts supplied for two years of operation
    5. Start-up and commissioning service
  3. User specified tests and documentation.

Alloy C-276/ASTM C276 should be considered as wetted parts material when the acid piping flow velocity is at a maximum of 6 m/s (20 ft/s). Alloy 20 can be considered when acid piping flow velocity is at a maximum of 1.8 m/s (6 ft/s). However, it is the responsibility of the end-user to specify the appropriate material, ensuring that it is satisfactory for the intended operating requirements.

Non-sparking incentive (Ex nA) and intrinsic safety (Ex ia) approvals are available for hazardous area installations.

Always consult an applications expert with any process-critical instrumentation application. By doing so, you will ensure a successful, safe, and efficient deployment.

Miller Energy, Inc.

Reprinted with permission from K-Patents.

Hazardous Areas: Division and Zone Classification System

Hazardous area
Hazards areas are associated with flammable
vapors or gases, ignitable fibers, and combustible dusts.
Hazardous areas refer to locations with a possible risk of explosion or fire due to dangerous atmosphere. The hazards can be associated with flammable vapors or gases, ignitable fibers, and combustible dusts.

Different hazardous area classifications exist in the North America and Europe. Generally, the National Electric Code (NEC) classifications govern hazardous areas in the US. While in Europe, hazardous area classification has been specified by the International Electrotechnical Commission (IEC).

Below is a description of the Division and Zone classification system.

Hazardous area due the presence of flammable vapors or gases in sufficient quantities to produce ignitable mixtures and cause an explosion.
Examples include natural gas and liquified petroleum.
Hazardous area due the presence of conductive or combustible dusts in sufficient quantities to produce ignitable mixtures and cause an explosion.
Examples include aluminum and magnesium powders.
Hazardous area due the presence of flammable fibers or other flying debris that collect around lighting fixtures, machinery, and other areas in sufficient quantities to produce ignitable mixtures and cause an explosion.
Examples include sawdust and flyings

Division groups hazardous areas based on the chances of an explosion due to the presence of flammable materials in the area.

Areas where there is a high chance of an explosion due to hazardous material that is present periodically, intermittently, or continuously under normal operation.
Areas where there is a low chance of an explosion under normal operation.

Group categorizes areas based on the type of flammable or ignitable materials in the environment. As per NEC guidelines, Groups A to D classify gasses while Groups E to G classify dust and flying debris.
Area contains flammable gas, liquid, or liquid produced vapor with any of the following characteristics:
  • Minimum Ignition Current (MIC) value equal to or less than 0.40
  • Maximum Experimental Safe Gap (MESG) value equal to or less than 0.45 mm
  • Combustible gas with more than 30 percent volume
Examples include hydrogen, ethylene oxide, acrolein, propylene oxide.

Area contains flammable gas, liquid, or liquid produced vapor with any of the following characteristics:
  • Minimum Ignition Current (MIC) value between 0.40 and 0.80
  • Maximum Experimental Safe Gap (MESG) value greater than 0.75 mm
Examples include carbon monoxide, hydrogen sulphide, ether, cyclopropane, morphline, acetaldehyde, isoprene, and ethylene.

Area contains flammable gas, liquid, or liquid produced vapor with any of the following characteristics:
  • Minimum Ignition Current (MIC) value greater than 0.80
  • Maximum Experimental Safe Gap (MESG) value greater than 0.75 mm
Examples include ammonia, gasoline, butane, benzene, hexane, ethanol, methane, methanol, natural gas, propane, naphtha, and vinyl chloride.

Area contains metal dusts such as magnesium, aluminum, chromium, bronze, titanium, zinc, and other combustible dusts whose abrasiveness, size, and conductivity present a hazard.

Area contains carbonaceous dusts such as charcoal, coal black, carbon black, coke dusts and others that present an explosion hazard.
Area contains combustible dusts not classified in Groups E and F.
Examples include starch, grain, flour, wood, plastic, sugar, and chemicals.

NOTE: This post serves only as a guide to acquaint the reader with hazardous area classifications in the USA. It is imperative to discuss your instrumentation, valve, or process equipment requirement with a qualified applications expert prior to installing any electrical device inside of any hazardous area.

Understanding How Magnetic Flowmeters Work and the Difference between AC and DC Excitation

The electromagnetic flowmeter, commonly known as the "magmeter", gets its name from the magnetic field generated within the float tube that produces a signal proportional to flow. This principle employs Faraday's Law of Electromagnetic Induction. Magnetic flowmeters are built so the direction of the magnetic field is perpendicular to the flow and the line between the electrodes is also perpendicular to the flow. As a conductive liquid flows through the flowtube, an electro-motive force is generated. The electrodes detect the electro-motive force. The electro-motive force is proportional to the flow velocity, flux density, and the meter inner diameter. The flux density of the magnetic field and the meters inner diameter are constant values, therefore the magnetic flow meter can calculate the flow velocity and volumetric flow from the electro-motive force.

The basic components of the magnetic flow meter body are:

  1. A lined flowtube (typically Teflon)
  2. Excitation coils
  3. Two electrodes mounted opposite of each other within the flowtube.

Current is applied to the coils in the magmeter to generate a magnetic field within the flow tube. As a conductive fluid flows through the meter, an electro-motive force is generated. This force is detected by the electrodes and the resulting value is converted to flowrate.

For more information on magnetic flowmeters, contact Miller Energy, Inc. by calling 800-631-5454 or by visiting

6 Benefits of Using Wireless Networking Systems in Industrial Applications

Wireless Networking Systems in Industrial ApplicationsWireless technologies offer great value over wired solutions. A reduction in cost is just one of the many benefits of switching to the wireless networking system. There are many benefits, including enhanced management of legacy systems that were previously not possible with a wired networking connection.

Here is an overview of some of the value-added benefits of adopting wireless networking in industrial plants.
  1. Reduced Installation Costs - Savings in installation costs is the key benefit of a wireless networking system. The cost of installing a wireless solution is significantly lower as compared to its wired counterpart. Installing a wireless network requires less planning. Extensive surveys are not required to route the wires to control rooms. This reduced installation cost is the main reason industrial setups should consider going wireless instead of having a wired networking system. 
  2. Improved Information Accuracy - Adopting wireless networking also results in improved accuracy of information. The wireless system is not prone to interferences. As a result, the system ensures consistent and timely transfer of information from one node to another. 
  3. Enhanced Flexibility - Enhanced flexibility is another reason for deploying wireless networking solutions in an industrial setting. Additional points can be awarded easily in an incremental manner. The wireless system can also integrate with legacy systems without any issues. 
  4. Operational Efficiencies - Migrating to wireless networking can help in improving operational efficiencies as well. Plant managers can troubleshoot and diagnose issues more easily. The system facilitates predictive maintenance by allowing the monitoring of remote assets. 
  5. Human Safety - Another critical factor that should influence the decision to migrate to wireless networking is the human safety factor. Wireless technologies allow safer operations, reducing exposure to harmful environments. For instance, a wireless system can be used in taking a reading and adjusting valves without having to go to the problematic area to take measurements. With wireless networking systems, readings can be taken more frequently that can help in early detection and reduction of possible incidents. 
  6. Efficient Information Transfer - Another advantage is that the time required to reach a device is reduced. This results in a more efficient transfer of information between network segments that are geographically separated. The industry wireless networking standards use IP addresses to allow remote access to data from field devices. 

For more information on wireless technologies in industrial settings, contact Miller Energy by visiting or by calling 800-631-5454.

Selecting the Right Magnetic Level Indicator

Companies in the process industry need the ability to visually monitor liquid levels in vessels (boilers, storage tanks, separators, etc.). Traditionally, armored glass sight gauges have been used. However, many companies want an alternative to sight gauges to avoid problems such as breakage, leaks, or bursting at high pressures and temperatures. In addition, the visibility of the sight glass can be poor and often affected by moisture, corrosion, or oxidation.

Many companies are increasing the use of automation and desire a 4–20 mA, HART®, FOUNDATION® fieldbus, or other output for level—which is difficult to do with a sight glass. Magnetic level indicators (MLIs) do not have the shortcomings of glass sight gauges and are suitable for a wide variety of applications.

Orion Instruments, a Magnetrol company, has authored an excellent Magnetic Level Indicator selection guide.

Miller Energy, Inc.
In NY/NJ 800-631-5454
In Eastern PA 888-631-5454

Understanding How Flame Arresters Work

Flame Arrester
A Flame Arrester (or arrestor) is a passive devices with no moving parts, that allows hot gas to pass through, but stops a flame in order to prevent a larger fire or explosion.  Flame Arresters uses a wound metal ribbon type element that prevents the spread of flame from the exposed side of the arrester to the protected side of the arrester. The metal element's construction provides a matrix of engineered openings that are carefully calculated and sized to quench the flame by absorbing the flame's heat. As an explosion flame travels through a narrow metal space, heat is transmitted to the walls, energy is lost and only vapor gasses are able to pass through. Flame Arresters are used in many industries chemical, petrochemical, pulp and paper, refining, pharmaceutical, mining, power generation, and wastewater treatment.

Cashco Flame Arresters are specifically engineered to match the explosive mixtures Maximum Experimental Safe Gap, in order to ensure complete extinction of the flame. At the heart of each Cashco flame arrestor lies filter discs that consists of wound, smooth and channeled strips of stainless steel set at specific maximum experimental stage gaps the smaller the gaps are which the flame travels the more heat and energy is lost therefore the filters gap width and gap length are specifically engineered to match the explosive mixture in order to ensure complete extinction of the flame. 

To learn more about Cashco flame arrestors, contact Miller Energy, Inc. by calling 908-755-6700 or by visiting