New Technologies Optimize Mixing Processes

Advanced designs and controls achieve complete mixing while reducing batch times

In the chemical process industries (CPI), mixing is about more than simply combining raw materials. It plays a central role in product quality and process efficiency, but it is fraught with complexities. Fortunately, advances in mixing technologies and controls, along with application-specific designs, can help processors achieve complete and consistent mixing along with reduced batch times.

“As formulations become more complex and quality tolerances tighten, complete and reliable homogeneous mixing is a key requirement, while at the same time, reproducibility, handling of increasingly variable raw materials and overall process robustness are also critical factors,” says Dr. Hans-Joachim Jacob, senior expert, process and applications, with ystral (Ballrechten-Dottingen, Germany; www.ystral.com). “In addition, inefficient powder incorporation – dust, agglomeration, or long wetting times – remain a bottleneck.

“Ultimately, there is a strong demand for fast, safe and efficient processes that deliver consistent results, while reducing dependency on individual operator experience,” says Jacob.

Consistent, repeatable mixing

To solve these challenges, equipment providers are using new approaches, innovative technologies and advanced controls to provide consistent homogeneity and repeatable results.

“There is a clear trend away from ‘homogeneity by definition’ (for example, 90% or two-second criteria) towards achieving real, fully consistent homogeneity in the process,” Jacob says. “At the same time, the focus is shifting towards greater process intensification and improved control of the initial mixing step. Technologies that combine high shear with well-defined and controlled flow conditions are therefore becoming increasingly important.”

One key development in this area is the shift of intensive processes out of the process vessel and into inline machines. In these systems, significantly high energy density and power concentration can be achieved compared to conventional tank-based approaches. “As a result, processes such as dispersion, which are inherently statistical in batch vessels and often lead to over-processing of some particles, while others remain insufficiently treated, are increasingly being replaced by inline technologies with defined and reproducible process conditions,” explains Jacob. “This ensures a much more uniform treatment of each individual particle while avoiding over-shearing.”

Another important innovation is the application of new physical principles for powder incorporation, notes Jacob. “Technologies based on vacuum expansion during powder wetting, for example, offer significant advantages. They enable rapid, uniform wetting, prevent agglomeration and offer the potential for improved or entirely new product qualities that are difficult or impossible to achieve with conventional methods.

“Overall, the trend is towards a more controlled, more intensive and more reproducible process, with a strong focus on eliminating variability at the earliest stage of mixing,” says Jacob.

The ystral Z-Inline Disperser can be used for wet milling and fine dispersion to achieve complete deagglomeration, while the Conti-TDS (Figure 1) ensures loss-free vessel emptying and, depending on the design, can add powder into the fluid under vacuum. Ystral inline dispersers are suitable for various batch sizes and can be used at laboratory scale or scaled up into complete process systems.

Steve Knauth, marketing and technical manager with Munson Machinery (Utica, N.Y.; www.munsonmachinery.com), says achieving consistent blend uniformity across batches — particularly when handling ingredients with widely different particle sizes, shapes, and bulk densities — is a fundamental challenge. “Segregation of blended materials during discharge is a related problem: if particles re-separate after mixing, product quality suffers and batch-to-batch consistency becomes unpredictable,” says Knauth.

Munson’s Rotary Batch Mixer (Figure 2) was designed to help processors achieve both uniformity and complete discharge without segregation. Its four-way mixing action — folding, tumbling, cutting and turning material — produces homogeneous blends in one to three minutes, while imparting minimal energy to the product. “It discharges completely with no stratification, eliminating the residual product accumulation that plagues conventional agitated designs,” he says.

EKATO (Freiburg, Germany; www.ekato.com) is working toward enhancing mixing in reactors by, for example, shortening mixing times through high-efficiency impeller technologies, says Wolfgang Keller, head of R&D. “By tailoring the system design to specific process targets, specific flow patterns are generated, avoiding dead zones, resulting in more distinct mixing and reproducible product quality.”

EKATO offers advanced solutions for the crystallization of bio-based monomers or for purification of intermediate products, such as Bis(2-hydroxyethyl) terephthalate (BHET), from depolymerization reactions, where the focus is on efficient processing of products.

“Crystallization is a crucial process step for purifying and enhancing the quality of monomers, especially in the recovery and recycling of polymeric materials,” says Keller. “Our advanced mixing systems enable precise temperature distribution, homogeneous suspension and consequently controlled crystal formation.

“In many cases, the use of more efficient mixing systems in combination with state-of-the-art process-simulation tools, like computational fluid dynamics (CFD) can lead to improvements in terms of yield, batch times or product quality,” he says.

Crystallization of BHET, an intermediate product derived from polyethylene terephthalate (PET) depolymerization, places high demands on mixing technologies, so EKATO provides solutions that ensure both homogeneous suspension and precise control of crystal growth conditions. “These factors are crucial for purity and further processability of the recycled material in subsequent processing steps,” Keller explains. “A robust crystallization process is essential for producing pure product with the required particle size distribution,” he says. “Such robustness requires control of supersaturation, reliable suspension and controlled shear rates. Depending on operation mode and process requirements, EKATO offers optimized mixing systems for crystallization, based on advanced impellers such as the Isojet-Band Torusjet for draft tube crystallizers.”

While selection and customization of mixing technologies are essential to achieving consistent and repeatable mixing, advanced controls make it easier to overcome these challenges, says Christine Banasek, sales manager with ROSS (Hauppauge, N.Y.; www.mixers.com).

“One of the greatest challenges is batch-to-batch consistency — achieving the same particle size distribution, rheology, density, composition, purity and all of the key product characteristics,” she says. “However, through our own controls division, ROSS Systems and Controls, we offer PLC-based recipe-management systems that allow processors to store and standardize process parameters, like agitator speeds, temperature, ingredient addition sequences and mixing times to eliminate process variability and operator errors,” says Banasek. “The data logging option creates a complete record of every batch for quality assurance and traceability.”

Hendrik Schluckebier, product and technology manager – mixing, with Zeppelin Systems (Friedrichshafen, Germany; www.zeppelin-systems.com) agrees that the use of automation, digitalization and data-driven technologies allow processors to enhance product consistency and process optimization.

“There is a growing demand for data analysis and transparency in production processes,” he says. “Digitalized systems with comprehensive data recording capabilities enable reliable, repeatable and directly comparable results across batches and production sites. This is particularly important in the chemical industry, where consistent product quality is essential.

“Modern mixing systems increasingly rely on intelligent control technologies that automatically monitor and adjust process parameters in real time,” Schluckebier continues. “These systems ensure that the mixing process remains stable and operates within defined limits, reducing operator dependency and minimizing the risk of errors.

“In addition, seamless integration into higher-level control systems is becoming standard. Data exchange with plant-wide systems is typically enabled via interfaces such as PROFINET or OPC UA,” he says. “This allows all relevant process data to be accessed, analyzed and used for optimization, documentation and quality assurance purposes,” he says. “The key benefits of these developments include improved process reliability, enhanced product consistency, increased efficiency and better decision-making based on real-time and historical data.”

Reducing batch times

Advanced controls, modern mixing technologies and smart process design also play a role in reducing batch times while improving precision and consistency, says Dr. Klaus Steingröver, head of sales for mixing products with Zeppelin Systems.

“A key factor is the optimization of power input through energy-efficient drive systems combined with intelligent process control,” he says. “By precisely matching the energy input to the actual process requirements, mixing times can be significantly reduced without compromising product quality.

“A good example is the bonding of powder coatings in our Henschel-Mixer MB Transbonder (Figure 3). This modular process mixer is specifically designed for bonding of metallic and effect powder coatings, and incorporates advanced multi-zone temperature control,” says Steingröver. “Temperature inside the mixing chamber can be precisely managed via different cooling zones such as the drive shaft, mixing tool, double jacket and bottom shell, in combination with a variable mixing-tool speed, ensuring highly controlled and reproducible process conditions.

Additional features, such as cooled mixing tools, nitrogen inerting and residual oxygen measurement further enhance process stability, especially for temperature-sensitive resins and pigments with minimum ignition energies (MIE) lower than 3 mJ. One of the key innovations is the fully automatic detection of the glass transition temperature (T_g), which ensures optimal bonding conditions and eliminates the need for manual intervention.

“These technologies deliver significant process advantages: complete bonding prevents segregation, resulting in highly consistent and color-stable products,” explains Steingröver. “At the same time, intelligent control systems enable maximum recipe flexibility, precise batch tracking and full transparency of the mixing process.

“Overall, the combination of optimized process design, intelligent control technology and application-specific mixer design allows for faster batch processing, greater reproducibility and consistently high product quality,” he says.

ROSS’s Banasek agrees: “Modern mixers can offer significant efficiency improvements when they are properly sized and customized for the application. Factors including viscosity profile, shear requirements, density, solids loading, batch-size variability and heat management determine equipment selection and overall energy usage.

“Optimizing agitator geometries, vessel design and the material loading and discharging steps can reduce cycle time and power consumption, while advanced rotor-stator configurations and powder induction technologies can help improve dispersion quality, decrease process time and minimize waste,” Banasek continues.

“For example, our Solids/Liquid Injection Manifold (SLIM) technology is widely used alongside our high-shear rotor-stator and multi-shaft mixers to improve powder wet-out in a low-viscosity liquid,” she says (Figure 4). “The system draws powders directly into the high-shear zone where they are immediately incorporated into the liquid stream. This process helps minimize agglomeration, reduce dusting and shorten mixing times.”

And, static mixers, which are typically associated with continuous processing, are increasingly being used to enhance batch operations, says Marcel Suhner, global product expert, mixing and reaction technology, with Sulzer Chemtech (Winterthur, Switzerland; sulzer.com). “By installing a static mixer in a recirculation loop, chemicals can be introduced and mixed more quickly and uniformly,” says Suhner. “This approach significantly reduces batch time and improves product homogeneity, without major changes to existing equipment.”

In addition, for chemical processors that aren’t sure how to unlock more efficient and effective mixing, EKATO offers a technical service designed to enhance process performance of agitated reactors as applied in chemical and pharmaceutical manufacturing.

The newly developed “Process Efficiency Screening” service provides a systematic evaluation of existing installations aimed at uncovering opportunities for energy savings, process improvements and increased equipment availability (Figure 5).

To uncover process efficiency gains, the screening evaluates critical process parameters, such as mixing time and heat transfer, as well as product characteristics. Enhancements in mixing-related technologies contribute to shorter batch cycles, improved product quality and lower operating costs. A key aspect of the service is the evaluation of modernization potential. “EKATO assesses whether existing mixing systems meet current process requirements and, if needed, proposes retrofit solutions that integrate advanced mixing technologies,” says Keller.

Batch versus continuous mixing

In some applications, processors are making the transition to continuous, or quasi-continuous, mixing operations to find more efficiency.

“While batch processing offers flexibility and familiarity, continuous processing provides clear advantages, including lower process risk due to smaller volumes and higher yields through continuous mixing during reactions,” explains Sulzer’s Suhner. “Sulzer’s mixer-reactor technologies support this transition, particularly for fast and exothermic reactions, by enabling efficient heat removal and reducing the risk of runaway conditions. Continuous mixing throughout the reaction further enhances conversion and yield, making compact, in-line solutions an increasingly attractive alternative to traditional stirred tanks.”

Sulzer’s SMXL static mixer (Figure 6) enhances heat and mass transfer significantly, enabling more compact and efficient process design, while the SMR mixer-reactor combines mixing and reaction in a single unit, improving yield and safety in continuous processes.

Knauth from Munson agrees that the shift from batch to continuous mixing is underway in certain sectors of the chemical processing industry where production volumes, product consistency requirements and operational cost pressures make continuous operation advantageous.

“Munson addresses this trend with equipment that is purpose-built for continuous service, rather than batch equipment adapted for continuous use,” says Knauth. “The Rotary Continuous Mixer was engineered from the outset with a stationary inlet and outlet, a rotating drum with smooth interior surface and proprietary mixing flights designed to achieve homogeneous blending with every degree of drum rotation during in-line production.”

And, Munson’s Variable-Intensity Blender offers a complementary approach for continuous processing of more challenging materials, including dense pastes, slurries and materials requiring shear or liquid addition during mixing.

Another approach to the transition from batch to continuous processing, says ystral’s Jacob, is quasi-continuous production using dual-tank systems, where one vessel is in the production phase while the second supplies the downstream process.

For example, the ystral Conti-TDS mixing and dispersing machine is primarily used in recirculation processes where the disperser is placed outside the process tank with a mixer installed in it and the powder is inducted into the liquid from a bag, hopper, big bag, silo or container. Powders are always inducted in their optimal sequence and dispersed under optimal conditions using the appropriate time scales for hydration, swelling and dissolution.

Since such an approach cannot be achieved in a simple inline process, the Conti-TDS enables quasi-continuous operation through twin-tank concepts under optimum process conditions. In such a setup, the Conti-TDS is connected to two-process vessels: a working tank and a buffer tank. While production takes place in one tank, the finished product is pumped out of the second tank. As soon as this tank is empty, the system switches over.

“This allows a continuous output while retaining the flexibility of batch powder handling and dispersion. The key development is not ‘batch versus continuous’ as a strategic shift, but rather, hybrid concepts, where individual process steps are intensified or converted to continuous operation,” says Jacob.

Joy LePree