*2.3. VOCs Emissions in the Chinese Pharmaceutical Industry*

China is the second largest producer of pharmaceutical products, only behind the United States of America. There are more than 1300 kinds of drug intermediates, 30 types of medicaments, and over 4500 pharmaceutical products made in China [23]. According to previous studies, the total VOCs emissions scaled linearly with the amount of final pharmaceutical products. [24]. The results showed that about 0.55 kg of VOCs were discharged to the atmosphere for the production of each 1 kg of final drug products.

The total VOCs emissions from the pharmaceutical industry increased by over 120% from about 174.8 kt in 2007 to 393.2 kt in 2016 (Figure 1) [12]. Although the VOCs emitted from the pharmaceutical industry only account for approximately 1.1% of China's total VOCs emissions, the absolute emission amount is very large. VOCs emitted from the pharmaceutical industry are potentially more harmful to human beings and ecosystems than the VOCs emitted from other sources. Compared with other emission sources, such as decoration, oil extraction and refining, catering, shoemaking and furniture manufacturing, the VOCs from pharmaceutical industries are more diverse with higher local concentrations and are harder to be eliminated.

more diverse with higher local concentrations and are harder to be eliminated.

The total VOCs emissions from the pharmaceutical industry increased by over 120% from about 174.8 kt in 2007 to 393.2 kt in 2016 (Figure 1) [12]. Although the VOCs emitted from the pharmaceutical industry only account for approximately 1.1% of China's total VOCs emissions, the absolute emission amount is very large. VOCs emitted from the pharmaceutical industry are potentially more harmful to human beings and ecosystems than the VOCs emitted from other

**Figure 1.** The production of bulk drugs and Chinese patent drugs and VOCs emissions from 2007 to 2016. **Figure 1.** The production of bulk drugs and Chinese patent drugs and VOCs emissions from 2007 to 2016.

### **3. The Developing Technologies to Dispel VOCs 3. The Developing Technologies to Dispel VOCs**

temperatures [29,30].

and washing apparatuses.

## *VOCs Elimination Technologies used in China's Pharmaceutical Industry VOCs Elimination Technologies used in China's Pharmaceutical Industry*

VOCs elimination technologies used in China were originally developed with the aim of recycling organic compounds to reduce cost, but recently the use and implementation of these technologies are targeted at minimizing the environmental impacts of VOCs. Technologies applied in the elimination of VOCs in China include condensation, absorption, adsorption, membrane purification, incineration, catalytic combustion, and the non‐thermal plasma process (Figure 2) [15,25–27]. These methods are applied according to different working conditions, such as temperature and pressure, depending upon the VOCs targeted for removal. They also have distinct advantages and disadvantages. The development of these VOCs elimination technologies will be briefly introduced and discussed in this review. It is important to note that a wide range of VOCs which are often produced in a single waste stream and the various treatment technologies have different efficacies for the removal of certain VOCs. In fact, multiple technologies are often combined to eliminate the VOC mixtures from the waste streams. VOCs elimination technologies used in China were originally developed with the aim of recycling organic compounds to reduce cost, but recently the use and implementation of these technologies are targeted at minimizing the environmental impacts of VOCs. Technologies applied in the elimination of VOCs in China include condensation, absorption, adsorption, membrane purification, incineration, catalytic combustion, and the non-thermal plasma process (Figure 2) [15,25–27]. These methods are applied according to different working conditions, such as temperature and pressure, depending upon the VOCs targeted for removal. They also have distinct advantages and disadvantages. The development of these VOCs elimination technologies will be briefly introduced and discussed in this review. It is important to note that a wide range of VOCs which are often produced in a single waste stream and the various treatment technologies have different efficacies for the removal of certain VOCs. In fact, multiple technologies are often combined to eliminate the VOC mixtures from the waste streams. *Catalysts* **2020**, *10*, 668 5 of 49

**Figure 2.** Classification of VOCs control techniques. Reprinted with permission from [26], 2000, Elsevier Ltd. **Figure 2.** Classification of VOCs control techniques. Reprinted with permission from [26], 2000, Elsevier Ltd.

Condensation is the conversion of gas phase VOC mixtures with different vapor pressures to liquid via a decrease in temperature [28]. This technology is often used to recycle the solvents used Condensation is the conversion of gas phase VOC mixtures with different vapor pressures to liquid via a decrease in temperature [28]. This technology is often used to recycle the solvents used in

in pharmaceutical production, with the key advantages that equipment requirements and operation

workshop before incineration and absorption to reduce the load on more complex and expensive downstream technologies. Water and air are the most commonly used cooling mediums for the condensation process, but ice, cold salt solutions and organic mediums have been used where cooling temperatures below 10 °C are required, such as the CaCl2 solution, NaCl solution, and ethylene glycol aqueous solution [4]. The condensation efficiency is sensitive to the temperature and pressure and is suitable for the removal of high concentration VOCs which exist as liquefied at moderate

The removal of VOCs via adsorption involves the use of porous materials, while absorption utilizes solvents. The porous materials used in adsorption need a high absorption capacity, large surface area, good pore structure, stable chemical properties, high physical strength, and tolerance of acidic/basic conditions. The adsorption materials commonly used in this technology include activated carbon, porous silica, zeolite, and porous resin [31–35]. The solvents commonly used in the absorption of VOCs are water, acid solution, alkali solution, and other organic compounds [36]. The components used in the adsorption process include spray columns, filled towers, columns of trays,

Both the adsorption and absorption methods have a high VOC removal efficiency and can almost completely remove VOCs from waste gas with low energy consumption (Figure 3). They can be used to recycle organic solvents and valuable compounds while remaining economically feasible. This technology is often used for the treatment of a large flow of waste gas with low VOC concentration in processes such as fix bed adsorption, moving bed adsorption, fluid‐bed adsorption, and pressure swing adsorption [37–39]. Disadvantages of the adsorption and absorption process are also noteworthy, such as huge equipment requirements, complex procedures, and the need for desorption and regeneration of saturated absorbents. Due to its high overall VOC removal efficiency,

this technology is commonly used in many pharmaceutical factories.

pharmaceutical production, with the key advantages that equipment requirements and operation of the condensation process are simple. It makes the cost of condensation lower than other technologies. Another advantage is that the gas produced from condensation is pure. Hence, condensation is often used as the first procedure to treat the waste gas from a pharmaceutical workshop before incineration and absorption to reduce the load on more complex and expensive downstream technologies. Water and air are the most commonly used cooling mediums for the condensation process, but ice, cold salt solutions and organic mediums have been used where cooling temperatures below 10 ◦C are required, such as the CaCl<sup>2</sup> solution, NaCl solution, and ethylene glycol aqueous solution [4]. The condensation efficiency is sensitive to the temperature and pressure and is suitable for the removal of high concentration VOCs which exist as liquefied at moderate temperatures [29,30].

The removal of VOCs via adsorption involves the use of porous materials, while absorption utilizes solvents. The porous materials used in adsorption need a high absorption capacity, large surface area, good pore structure, stable chemical properties, high physical strength, and tolerance of acidic/basic conditions. The adsorption materials commonly used in this technology include activated carbon, porous silica, zeolite, and porous resin [31–35]. The solvents commonly used in the absorption of VOCs are water, acid solution, alkali solution, and other organic compounds [36]. The components used in the adsorption process include spray columns, filled towers, columns of trays, and washing apparatuses.

Both the adsorption and absorption methods have a high VOC removal efficiency and can almost completely remove VOCs from waste gas with low energy consumption (Figure 3). They can be used to recycle organic solvents and valuable compounds while remaining economically feasible. This technology is often used for the treatment of a large flow of waste gas with low VOC concentration in processes such as fix bed adsorption, moving bed adsorption, fluid-bed adsorption, and pressure swing adsorption [37–39]. Disadvantages of the adsorption and absorption process are also noteworthy, such as huge equipment requirements, complex procedures, and the need for desorption and regeneration of saturated absorbents. Due to its high overall VOC removal efficiency, this technology is commonly used in many pharmaceutical factories. *Catalysts* **2020**, *10*, 668 6 of 49

**Figure 3.** A typical activated carbon VOC removal (solvent recovery) plant. Reprinted with permission from [26], 2000, Elsevier Ltd. **Figure 3.** A typical activated carbon VOC removal (solvent recovery) plant. Reprinted with permission from [26], 2000, Elsevier Ltd.

Incineration is another widely used technology in pharmaceutical factories to eliminate VOCs (Figure 4). If VOC recycling is not technologically or financially feasible, incineration is a suitable method to completely eliminate VOCs [40]. Incineration is carried out by burning VOCs in a stove or kiln. Ideally, incineration results in the conversion of VOCs into CO2 and H2O in an efficient, simple, and safe manner. However, it has multiple shortcomings. If the VOCs concentration is too low to support the incineration, additional fuel is needed, which increases the running cost. Additionally, Incineration is another widely used technology in pharmaceutical factories to eliminate VOCs (Figure 4). If VOC recycling is not technologically or financially feasible, incineration is a suitable method to completely eliminate VOCs [40]. Incineration is carried out by burning VOCs in a stove or kiln. Ideally, incineration results in the conversion of VOCs into CO<sup>2</sup> and H2O in an efficient, simple, and safe manner. However, it has multiple shortcomings. If the VOCs concentration is too low to support the incineration, additional fuel is needed, which increases the running cost. Additionally,

**Figure 4.** Schemes of thermal oxidation. (a) Regenerative thermal oxidation; (b) recuperative thermal

To overcome the shortages of the incineration process for VOC destruction, the catalytic combustion technology was developed. In this process, VOCs are decomposed over catalysts at a low temperature (lower than 500 °C, Figures 5 and 6) [1,2,41–44]. The key factor which governs the catalytic combustion process is the activity of catalysts. Various kinds of catalysts have been used for the catalytic combustion of VOCs, such as noble metal catalysts, transition metal oxides, perovskite catalysts, and concentrated oxidation catalysts. The advantages for this technology are low operation temperature, decreased energy input requirements, high VOC removal efficiency, and minimal generation of toxic byproducts. Catalytic combustion is suitable for the treatment of waste streams containing VOCs across a wide range of concentrations. The main disadvantages of catalytic combustion are high investment requirements for equipment, short catalyst lifetime, and the need

oxidation. Reprinted with permission from [26], 2000, Elsevier Ltd.

some VOCs are less suitable for incineration, because the incomplete combustion of halogenated and other harmful VOCs can result in the release of toxic chemicals such as dioxin, NOx, and CO [40].

permission from [26], 2000, Elsevier Ltd.

some VOCs are less suitable for incineration, because the incomplete combustion of halogenated and other harmful VOCs can result in the release of toxic chemicals such as dioxin, NOx, and CO [40]. and safe manner. However, it has multiple shortcomings. If the VOCs concentration is too low to support the incineration, additional fuel is needed, which increases the running cost. Additionally, some VOCs are less suitable for incineration, because the incomplete combustion of halogenated

kiln. Ideally, incineration results in the conversion of VOCs into CO<sup>2</sup> and H2O in an efficient, simple,

**Figure 3.** A typical activated carbon VOC removal (solvent recovery) plant. Reprinted with

Incineration is another widely used technology in pharmaceutical factories to eliminate VOCs (Figure 4). If VOC recycling is not technologically or financially feasible, incineration is a suitable

*Catalysts* **2020**, *10*, 668 6 of 49

**Figure 4.** Schemes of thermal oxidation. (a) Regenerative thermal oxidation; (b) recuperative thermal oxidation. Reprinted with permission from [26], 2000, Elsevier Ltd. **Figure 4.** Schemes of thermal oxidation. (**a**) Regenerative thermal oxidation; (**b**) recuperative thermal oxidation. Reprinted with permission from [26], 2000, Elsevier Ltd.

To overcome the shortages of the incineration process for VOC destruction, the catalytic combustion technology was developed. In this process, VOCs are decomposed over catalysts at a low temperature (lower than 500 °C, Figures 5 and 6) [1,2,41–44]. The key factor which governs the catalytic combustion process is the activity of catalysts. Various kinds of catalysts have been used for the catalytic combustion of VOCs, such as noble metal catalysts, transition metal oxides, perovskite catalysts, and concentrated oxidation catalysts. The advantages for this technology are low operation temperature, decreased energy input requirements, high VOC removal efficiency, and minimal generation of toxic byproducts. Catalytic combustion is suitable for the treatment of waste streams containing VOCs across a wide range of concentrations. The main disadvantages of catalytic combustion are high investment requirements for equipment, short catalyst lifetime, and the need To overcome the shortages of the incineration process for VOC destruction, the catalytic combustion technology was developed. In this process, VOCs are decomposed over catalysts at a low temperature (lower than 500 ◦C, Figures 5 and 6) [1,2,41–44]. The key factor which governs the catalytic combustion process is the activity of catalysts. Various kinds of catalysts have been used for the catalytic combustion of VOCs, such as noble metal catalysts, transition metal oxides, perovskite catalysts, and concentrated oxidation catalysts. The advantages for this technology are low operation temperature, decreased energy input requirements, high VOC removal efficiency, and minimal generation of toxic byproducts. Catalytic combustion is suitable for the treatment of waste streams containing VOCs across a wide range of concentrations. The main disadvantages of catalytic combustion are high investment requirements for equipment, short catalyst lifetime, and the need for process-specific designs, which are tailored to the waste stream. Nonetheless, the development of viable materials for the catalytic combustion process is still a hotspot for catalysis science. *Catalysts* **2020**, *10*, 668 7 of 49 for process‐specific designs, which are tailored to the waste stream. Nonetheless, the development of viable materials for the catalytic combustion process is still a hotspot for catalysis science. The mechanism of catalytic combustion is considered by three types, with these being the Mars‐ Van Krevelen (MVK) model, Langmuir‐Hinshelwood (LH) model, and Eley‐Rideal (ER) model. In the Mars‐Van Krevelen model, the VOCs molecules are initially adsorbed on the active sites, upon which they react with the oxygen species within the catalyst and are decomposed. Then, the reduced catalyst is re‐oxidized by the supply of oxygen to the reactor. In the Langmuir‐Hinshelwood model, the adsorbed VOCs molecules react directly with the adsorbed oxygen molecules, all occurring on the catalyst surface. In the Elay‐Rideal mechanism, the adsorbed oxygen reacts with the VOCs molecules in the gas phase. The reaction pathway which follows depends on both the catalyst

**Figure 5.** Scheme of catalytic oxidation. Reprinted with permission from [26], 2000, Elsevier Ltd. **Figure 5.** Scheme of catalytic oxidation. Reprinted with permission from [26], 2000, Elsevier Ltd.

The mechanism of catalytic combustion is considered by three types, with these being the Mars-Van Krevelen (MVK) model, Langmuir-Hinshelwood (LH) model, and Eley -Rideal (ER) model. In the Mars-Van Krevelen model, the VOCs molecules are initially adsorbed on the active sites, upon which they react with the oxygen species within the catalyst and are decomposed. Then, the reduced catalyst is re-oxidized by the supply of oxygen to the reactor. In the Langmuir-Hinshelwood model, the adsorbed VOCs molecules react directly with the adsorbed oxygen molecules, all occurring on the

**Figure 6.** Schematic diagram of a reverse flow reactor. Reprinted with permission from [26], 2000,

Biodegradation is a widely used process for the treatment of pharmaceutical wastewater (Figure 7) [45,46]. It also can be applied to the treatment VOCs in the gas phase, especially for low concentration VOCs which are suitable for the growth of microorganisms. This process works with using the VOCs as a feedstock for the microorganisms, where they are converted to cytoplasm, CO2, and H2O. The sulfur and nitrogen elements in VOCs can be transformed to H2S, nitrate, or N2 at moderate temperatures. However, VOCs emitted from the pharmaceutical process often contain aromatics or halogens, which would poison the microorganism, rendering this method largely

Elsevier Ltd.

unviable in the abatement of pharmaceutical VOCs.

materials and the target VOCs in individual systems.

catalyst surface. In the Elay-Rideal mechanism, the adsorbed oxygen reacts with the VOCs molecules in the gas phase. The reaction pathway which follows depends on both the catalyst materials and the target VOCs in individual systems. **Figure 5.** Scheme of catalytic oxidation. Reprinted with permission from [26], 2000, Elsevier Ltd.

*Catalysts* **2020**, *10*, 668 7 of 49

for process‐specific designs, which are tailored to the waste stream. Nonetheless, the development of

The mechanism of catalytic combustion is considered by three types, with these being the Mars‐ Van Krevelen (MVK) model, Langmuir‐Hinshelwood (LH) model, and Eley‐Rideal (ER) model. In the Mars‐Van Krevelen model, the VOCs molecules are initially adsorbed on the active sites, upon which they react with the oxygen species within the catalyst and are decomposed. Then, the reduced catalyst is re‐oxidized by the supply of oxygen to the reactor. In the Langmuir‐Hinshelwood model, the adsorbed VOCs molecules react directly with the adsorbed oxygen molecules, all occurring on the catalyst surface. In the Elay‐Rideal mechanism, the adsorbed oxygen reacts with the VOCs molecules in the gas phase. The reaction pathway which follows depends on both the catalyst

viable materials for the catalytic combustion process is still a hotspot for catalysis science.

**Figure 6.** Schematic diagram of a reverse flow reactor. Reprinted with permission from [26], 2000, Elsevier Ltd. **Figure 6.** Schematic diagram of a reverse flow reactor. Reprinted with permission from [26], 2000, Elsevier Ltd.

Biodegradation is a widely used process for the treatment of pharmaceutical wastewater (Figure 7) [45,46]. It also can be applied to the treatment VOCs in the gas phase, especially for low concentration VOCs which are suitable for the growth of microorganisms. This process works with using the VOCs as a feedstock for the microorganisms, where they are converted to cytoplasm, CO2, and H2O. The sulfur and nitrogen elements in VOCs can be transformed to H2S, nitrate, or N2 at moderate temperatures. However, VOCs emitted from the pharmaceutical process often contain aromatics or halogens, which would poison the microorganism, rendering this method largely unviable in the abatement of pharmaceutical VOCs. Biodegradation is a widely used process for the treatment of pharmaceutical wastewater (Figure 7) [45,46]. It also can be applied to the treatment VOCs in the gas phase, especially for low concentration VOCs which are suitable for the growth of microorganisms. This process works with using the VOCs as a feedstock for the microorganisms, where they are converted to cytoplasm, CO2, and H2O. The sulfur and nitrogen elements in VOCs can be transformed to H2S, nitrate, or N<sup>2</sup> at moderate temperatures. However, VOCs emitted from the pharmaceutical process often contain aromatics or halogens, which would poison the microorganism, rendering this method largely unviable in the abatement of pharmaceutical VOCs. *Catalysts* **2020**, *10*, 668 8 of 49

**Figure 7.** A simple schematic sketch of a bio‐filtration system. Reprinted with permission from [26], 2000, Elsevier Ltd. **Figure 7.** A simple schematic sketch of a bio-filtration system. Reprinted with permission from [26], 2000, Elsevier Ltd.

Non‐thermal plasma is also a commonly used technology for the elimination of VOCs [47–49]. Free electrons and radicals formed during the plasma process react with VOCs and lead to the degradation of VOCs to CO2 and H2O. There are some advantages of the non‐thermal plasma technology, such as a low press drop across the reactor, compact size, and simple equipment structure. The process can be started immediately without warm up and can treat VOCs with solid Non-thermal plasma is also a commonly used technology for the elimination of VOCs [47–49]. Free electrons and radicals formed during the plasma process react with VOCs and lead to the degradation of VOCs to CO<sup>2</sup> and H2O. There are some advantages of the non-thermal plasma technology, such as a low press drop across the reactor, compact size, and simple equipment structure. The process can be started immediately without warm up and can treat VOCs with solid particles and liquid drops.

funds available for installation and running costs. Jie Hao et al. summarized the scope of application for different VOCs elimination technologies (Table 3) [50]. Condensation and adsorption recycling are suitable for recycling VOCs. Catalytic combustion and incineration can remove the VOCs with a moderate concentration (3000–1/4 LEL) at high temperatures, while biodegradation and non‐thermal plasma are suitable for abatement of low concentration VOCs at moderate temperatures. Hence, when selecting the efficient and economic VOCs abatement technologies, the scope of application for

**Table 3.** VOCs elimination techniques and their operating conditions [50].

**Discharge rate**

**(m3∙h−1) Temperature (°C)**

**(mg∙m−3)**

Adsorption recycling 100–1.5×104 <6 × 104 <45

combustion 3000–1/4 LEL \* <4 <sup>×</sup> <sup>104</sup> <500

combustion 1000–1/4 LEL <4 <sup>×</sup> <sup>104</sup> <500

incineration 1000–1/4 LEL <4 <sup>×</sup> <sup>104</sup> >700

Biodegradation <1000 <1.2 × 104 <45

Condensation 104–105 <104 <150

Preheated incineration 3000–1/4 LEL <4 × 104 >700

Adsorption concentration <1500 104–1.2 × 105 <45

combustion to achieve a superior abatement of pharmaceutical VOCs.

different technologies needs to be considered.

Preheated catalytic

Thermal storage catalytic

Thermal storage

**Abatement technologies VOC Concentration**

particles and liquid drops. The non‐thermal plasma technology can be combined with catalytic

The non-thermal plasma technology can be combined with catalytic combustion to achieve a superior abatement of pharmaceutical VOCs.

The application of different VOCs elimination technologies depends on the factors such as the range and concentration of VOCs present in the waste stream, the volume of waste stream, and the funds available for installation and running costs. Jie Hao et al. summarized the scope of application for different VOCs elimination technologies (Table 3) [50]. Condensation and adsorption recycling are suitable for recycling VOCs. Catalytic combustion and incineration can remove the VOCs with a moderate concentration (3000–1/4 LEL) at high temperatures, while biodegradation and non-thermal plasma are suitable for abatement of low concentration VOCs at moderate temperatures. Hence, when selecting the efficient and economic VOCs abatement technologies, the scope of application for different technologies needs to be considered.


**Table 3.** VOCs elimination techniques and their operating conditions [50].

\* Lower explosive limit (LEL).

In a survey of 771 industrial applications of VOCs elimination processes, including 330 cases in China and 441 cases in various other countries (Figure 8), Jinying Xi et al. examined how often the various technologies were used [51]. The data showed that the most commonly used technology in China was adsorption (38%), followed by catalytic combustion (22%) and biodegradation (15%), while in other countries, the most often utilized were biodegradation (29%) and catalytic combustion (29%), followed by adsorption (16%). Due to its simple operation, low capital cost, and ability to recycle VOCs across a wide range of concentrations, adsorption was the most widely used technology in China. However, in some instances, the adsorption equipment was not well maintained and used correctly for recycling of VOCs. Adsorption, membrane purification, and condensation were the most effective methods, therefore most commonly applied, in instances where VOCs were present in concentrations above 10,000 mg·m−<sup>3</sup> . Catalytic combustion and incineration were used for the destruction of VOCs in the concentration range of 2000~10,000 mg·m−<sup>3</sup> , where recycling is not financially viable. Biodegradation and non-thermal plasma were applied for the treatment of VOCs in a lower concentration than 2000 mg·m−<sup>3</sup> . Some examples are introduced in the following section to illustrate the application of these technologies for the elimination of pharmaceutical VOCs in China [3,4,14,51,52].

In the production of cefuroxime axetil, cefuroxime sodium, and cefotaxime sodium, the emitted VOCs include methanol, acetone, dichloromethane, DMF, acetic ether, and cyclohexane. One reported setup for the removal of these VOCs via a combination of condensation and adsorption technologies is described in Figure 9. Firstly, a portion of the various solvents was removed across a three-stage condensing unit comprised of a single stage of recycled water condensation, followed by two stages of 7 ◦C water condensation. The VOCs which were unable to be removed via the condensation process were removed by a two-stage activated carbon adsorption tower. The VOC-rich waste gas feedstock had a total VOC concentration of 2400 mg·m−<sup>3</sup> , of which 800 mg·m−<sup>3</sup> was attributed to methanol. It entered the first condensation unit at a rate of 2000 m<sup>3</sup> ·h −1 . More than 95% of the total VOC content was removed after the combined condensation and adsorption process. As a result, the emitted concentration and discharge rate of methanol was reduced to 18.9–29.3 mg·m−<sup>3</sup> and 0.08 kg·h −1 , respectively, while the concentration and discharge rate of the other VOCs present was 55–63 mg·m−<sup>3</sup> and 0.16 kg·h −1 , respectively. Both of these levels were in accordance with the emission standards of Hebei province where the factory was located. effective methods, therefore most commonly applied, in instances where VOCs were present in concentrations above 10,000 mg∙m−3. Catalytic combustion and incineration were used for the destruction of VOCs in the concentration range of 2000~10,000 mg∙m−3, whererecycling is not financially viable. Biodegradation and non‐thermal plasma were applied for the treatment of VOCs in a lower concentration than 2000 mg∙m−3. Some examples are introduced in the following section to illustrate the application of these technologies for the elimination of pharmaceutical VOCs in China [3,4,14,51,52].

correctly forrecycling of VOCs. Adsorption, membrane purification, and condensation were the most

*Catalysts* **2020**, *10*, 668 9 of 49

Non‐thermal <500 <3 × 104 <80 \* Lower explosive limit (LEL).

In a survey of 771 industrial applications of VOCs elimination processes, including 330 cases in China and 441 cases in various other countries (Figure 8), Jinying Xi et al. examined how often the various technologies were used [51]. The data showed that the most commonly used technology in China was adsorption (38%), followed by catalytic combustion (22%) and biodegradation (15%), while in other countries, the most often utilized were biodegradation (29%) and catalytic combustion (29%), followed by adsorption (16%). Due to its simple operation, low capital cost, and ability to

**Figure 8.** The ratios of VOCs elimination technologies used in China (**a**) and other countries (**b**) (the numbers in the brackets are the numbers of companies using the related technologies). Reprinted with **Figure 8.** The ratios of VOCs elimination technologies used in China (**a**) and other countries (**b**) (the numbers in the brackets are the numbers of companies using the related technologies). Reprinted with permission from [51], copyright 2012, CNKI. *Catalysts* **2020**, *10*, 668 10 of 49 was 55–63 mg∙m−<sup>3</sup> and 0.16 kg∙h−1, respectively. Both of these levels were in accordance with the emission standards of Hebei province where the factory was located.

condensation process were removed by a two‐stage activated carbon adsorption tower. The VOC‐ rich waste gas feedstock had a total VOC concentration of 2400 mg∙m−3, of which 800 mg.m−<sup>3</sup> was **Figure 9.** Representation of the VOC abatement process in a factory which produced cefuroxime axetil, cefuroxime sodium, and cefotaxime sodium. Reprinted with permission from [4], 2016, CNKI. **Figure 9.** Representation of the VOC abatement process in a factory which produced cefuroxime axetil, cefuroxime sodium, and cefotaxime sodium. Reprinted with permission from [4], 2016, CNKI.

attributed to methanol. It entered the first condensation unit at a rate of 2000 m3∙h−1. More than 95% of the total VOC content was removed after the combined condensation and adsorption process. As a result, the emitted concentration and discharge rate of methanol was reduced to 18.9–29.3 mg∙m−<sup>3</sup> and 0.08 kg∙h−1, respectively, while the concentration and discharge rate of the other VOCs present Yan Li has investigated the VOC abatement process in four separate companies in Taizhou city, Zhejiang province [4]. The main products in these four companies were clindamycin, clindamycin phosphate; losartan potassium, valsartan, nevirapine; meropenem, imipenem; and ciprofloxacin, spirolactone, respectively. There were three different procedures used in these four companies. The various procedures included adsorption, catalytic combustion, and non‐thermal plasma technologies. The author assessed the efficiencies of the processes by measuring the concentration of a range of VOCs including benzene, toluene, xylene, methanol, formaldehyde, dichloromethane, chloroform, acetic ether, butylene oxide, acetonitrile, dimethylformamide, dysodia, and isopropanol before and after treatment. The results showed that after these elimination processes, the concentrations of VOCs in emitted waste gas were lowerthan the required concentration in standards for emissions of atmospheric pollutants from the pharmaceutical industry in Zhejiang province [53]. Yan Li has investigated the VOC abatement process in four separate companies in Taizhou city, Zhejiang province [4]. The main products in these four companies were clindamycin, clindamycin phosphate; losartan potassium, valsartan, nevirapine; meropenem, imipenem; and ciprofloxacin, spirolactone, respectively. There were three different procedures used in these four companies. The various procedures included adsorption, catalytic combustion, and non-thermal plasma technologies. The author assessed the efficiencies of the processes by measuring the concentration of a range of VOCs including benzene, toluene, xylene, methanol, formaldehyde, dichloromethane, chloroform, acetic ether, butylene oxide, acetonitrile, dimethylformamide, dysodia, and isopropanol before and after treatment. The results showed that after these elimination processes, the concentrations of VOCs in emitted waste gas were lower than the required concentration in standards for emissions of atmospheric pollutants from the pharmaceutical industry in Zhejiang province [53].

An example of a catalytic VOC treatment process is shown in Figure 10 below, which uses a regenerative catalytic oxidizer. The waste gas from the workshop was collected and combined with the waste gas from the sewage station, storehouse, and solid waste pile. The gas mixture was first washed with a water and alkali solution, then dehydrated and defogged. The dry gas was filtered, An example of a catalytic VOC treatment process is shown in Figure 10 below, which uses a regenerative catalytic oxidizer. The waste gas from the workshop was collected and combined with the waste gas from the sewage station, storehouse, and solid waste pile. The gas mixture was first washed with a water and alkali solution, then dehydrated and defogged. The dry gas was filtered, then heated

**Figure 10.** VOCs abatement process in the A factory. Reprinted with permission from [4], 2016, CNKI

Two companies used a process which combines a regenerative thermal oxidizer (RTO) with three condensation stages connected in a series (Figure 11). The waste gas was pretreated in the workshop below determining the lower explosion limit (LEL) of the mixture. Then, fresh air was

.

running fee of the whole VOCs elimination system was about RMB 1 million per year.

then heated with a preheater with an attached regenerative heat transfer. The preheated gas mixture

with a preheater with an attached regenerative heat transfer. The preheated gas mixture entered the catalytic reactor and was combusted. After catalytic combustion, the gas was washed again with a water and alkali solution and emitted to high altitude atmosphere by a fan. The removal efficiencies of dysodia and non-methane hydrocarbons were 68.07% and 94.33%, respectively. The running fee of the whole VOCs elimination system was about RMB 1 million per year. washed with a water and alkali solution, then dehydrated and defogged. The dry gas was filtered, then heated with a preheater with an attached regenerative heat transfer. The preheated gas mixture entered the catalytic reactor and was combusted. After catalytic combustion, the gas was washed again with a water and alkali solution and emitted to high altitude atmosphere by a fan. The removal efficiencies of dysodia and non‐methane hydrocarbons were 68.07% and 94.33%, respectively. The running fee of the whole VOCs elimination system was about RMB 1 million per year.

the waste gas from the sewage station, storehouse, and solid waste pile. The gas mixture was first

*Catalysts* **2020**, *10*, 668 10 of 49

was 55–63 mg∙m−<sup>3</sup> and 0.16 kg∙h−1, respectively. Both of these levels were in accordance with the

**Figure 9.** Representation of the VOC abatement process in a factory which produced cefuroxime axetil, cefuroxime sodium, and cefotaxime sodium. Reprinted with permission from [4], 2016, CNKI.

Yan Li has investigated the VOC abatement process in four separate companies in Taizhou city, Zhejiang province [4]. The main products in these four companies were clindamycin, clindamycin phosphate; losartan potassium, valsartan, nevirapine; meropenem, imipenem; and ciprofloxacin, spirolactone, respectively. There were three different procedures used in these four companies. The various procedures included adsorption, catalytic combustion, and non‐thermal plasma technologies. The author assessed the efficiencies of the processes by measuring the concentration of a range of VOCs including benzene, toluene, xylene, methanol, formaldehyde, dichloromethane, chloroform, acetic ether, butylene oxide, acetonitrile, dimethylformamide, dysodia, and isopropanol before and after treatment. The results showed that after these elimination processes, the concentrations of VOCs in emitted waste gas were lowerthan the required concentration in standards for emissions of atmospheric pollutants from the pharmaceutical industry in Zhejiang province [53]. An example of a catalytic VOC treatment process is shown in Figure 10 below, which uses a

emission standards of Hebei province where the factory was located.

**Figure 10.** VOCs abatement process in the A factory. Reprinted with permission from [4], 2016, CNKI **Figure 10.** VOCs abatement process in the A factory. Reprinted with permission from [4], 2016, CNKI.

. Two companies used a process which combines a regenerative thermal oxidizer (RTO) with three condensation stages connected in a series (Figure 11). The waste gas was pretreated in the workshop below determining the lower explosion limit (LEL) of the mixture. Then, fresh air was Two companies used a process which combines a regenerative thermal oxidizer (RTO) with three condensation stages connected in a series (Figure 11). The waste gas was pretreated in the workshop below determining the lower explosion limit (LEL) of the mixture. Then, fresh air was added in accordance with the determined LEL, such that the proper fuel, oxygen ratio, would be present in the RTO. After that, the gas mixture was oxidized in the RTO at a temperature of 850 ◦C with 98% of the thermal energy recycled. The high temperature gas exiting the RTO was cooled in a cooling tower, then further cooled across a three-stage condensation setup before it was emitted to the atmosphere. The dysodia concentration in the total vent was 300 mg·m−<sup>3</sup> , while the concentration of non-methane hydrocarbons was lower than 85 mg·m−<sup>3</sup> . These concentrations correspond to removal rates of 89% and 92% for dysodia and non-methane hydrocarbons, respectively. The main drawback of this procedure was that the condensation step was not effective for dichloromethane recycling and a lot of HCl generated from the incineration of chlorinated organic compounds, which in turn led to the corrosion of the equipment.

A process which combines the non-thermal plasma and catalytic oxidation techniques (oxidation of VOCs by H2O<sup>2</sup> in a low pH) to treat VOCs in waste gas is outlined in Figure 12. The waste gas, with a high VOC concentration, was pretreated, combined with exhaust gas, and washed with an alkali solution. Then, the washed gas entered the catalytic combustion/oxidation tower, where a portion of the VOCs content was oxidized to CO<sup>2</sup> and H2O. The oxidized waste gas was washed with water and entered a dehydrator to remove humidity. After that, the waste gas from the sewage station was added to the treated gas, upon which the gas mixture was treated with a non-thermal plasma, to remove additional VOCs. The gas was dehydrated again and entered into the second catalytic oxidation tower. The gas was washed by the alkali solution again and emitted to the atmosphere. The dysodia concentration was reduced by 84% to no more than 250 mg·m−<sup>3</sup> . The removal efficiency of non-methane hydrocarbons content was approximately 92%, with a concentration of less than 85 mg·m−<sup>3</sup> in the emitted gas.

These procedures (Figures 9–12 Figure 9 Figure 10 Figure 11 Figure 12) are representative of the range of VOCs elimination technologies currently in use in China. Almost all kinds of VOCs abatement technologies have been applied in the treatment of waste from the Chinese pharmaceutical industry. While the application of these technologies has successfully decreased the emission of VOCs, the

high cost of investment and low efficiency are still the main factors which hinder the application of these technologies in the industry. The adsorption, absorption, and biodegradation technologies face challenges concerning the production of secondary pollutants, the desorption of adsorbed VOCs, and the production of waste water and sludge. The incineration process is effective in removing the issue of secondary waste production, but it requires a large energy input and has safety risks posed by the high temperature and use of a flame within a factory. The catalytic combustion and non-thermal plasma technologies partially circumvent the issues of waste and high temperature, but they are currently costly techniques with a short equipment lifetime. Thus, the continuing improvement of these technologies and development of new technologies is needed. With the new emission standards/law coming into effect, VOC elimination processes need to be upgraded in many Chinese pharmaceutical factories. As such, there is a desire for novel, effective, and energy efficient technologies in the near future. *Catalysts* **2020**, *10*, 668 11 of 49 added in accordance with the determined LEL, such that the proper fuel, oxygen ratio, would be present in the RTO. After that, the gas mixture was oxidized in the RTO at a temperature of 850 °C with 98% of the thermal energy recycled. The high temperature gas exiting the RTO was cooled in a cooling tower, then further cooled across a three‐stage condensation setup before it was emitted to the atmosphere. The dysodia concentration in the total vent was 300 mg∙m−3, while the concentration of non‐methane hydrocarbons was lower than 85 mg∙m−3. These concentrations correspond to removal rates of 89% and 92% for dysodia and non‐methane hydrocarbons, respectively. The main drawback of this procedure was that the condensation step was not effective for dichloromethane recycling and a lot of HCl generated from the incineration of chlorinated organic compounds, which

**Figure 11.** VOCs abatement process in the B and C factory, utilizing a regenerative thermal oxidizer (RTO) and condensation. Reprinted with permission from [4], 2016, CNKI . **Figure 11.** VOCs abatement process in the B and C factory, utilizing a regenerative thermal oxidizer (RTO) and condensation. Reprinted with permission from [4], 2016, CNKI. *Catalysts* **2020**, *10*, 668 12 of 49

**Figure 12.** VOCs abatement process in the D factory. Reprinted with permission from [4], 2016, CNKI. **Figure 12.** VOCs abatement process in the D factory. Reprinted with permission from [4], 2016, CNKI.

### These procedures (Figures 9–12) are representative of the range of VOCs elimination **4. The Developing Technologies for VOCs Elimination**

**4. The Developing Technologies for VOCs Elimination**

future.

in turn led to the corrosion of the equipment.

technologies currently in use in China. Almost all kinds of VOCs abatement technologies have been applied in the treatment of waste from the Chinese pharmaceutical industry. While the application of these technologies has successfully decreased the emission of VOCs, the high cost of investment and low efficiency are still the main factors which hinder the application of these technologies in the industry. The adsorption, absorption, and biodegradation technologies face challenges concerning the production of secondary pollutants, the desorption of adsorbed VOCs, and the production of waste water and sludge. The incineration process is effective in removing the issue of secondary waste production, but it requires a large energy input and has safety risks posed by the high temperature and use of a flame within a factory. The catalytic combustion and non‐thermal plasma technologies partially circumvent the issues of waste and high temperature, but they are currently costly techniques with a short equipment lifetime. Thus, the continuing improvement of these As outlined in the previous section, the VOC abatement technologies currently in use in China are hindered by some key limitations, such as high construction and running costs, low removal efficiencies for complex VOCs, and high temperature or energy requirements. To address these shortcomings, significant research is being carried out to improve the traditional methods of VOC removal, such as adsorption, catalytic combustion, and non-thermal plasma [1,2,33,41,43,44,47–49,54]. In addition, new technologies which can avoid the disadvantages of the traditional technologies have emerged, such as photocatalytic oxidation, condensation-oxidation, and electron beam treatment [2,42,48,55]. A summary of the various catalysts and conditions that have been investigated as active materials for the catalytic oxidation of VOCs is contained in Table 4 below.

As outlined in the previous section, the VOC abatement technologies currently in use in China are hindered by some key limitations, such as high construction and running costs, low removal efficiencies for complex VOCs, and high temperature or energy requirements. To address these shortcomings, significant research is being carried out to improve the traditional methods of VOC removal, such as adsorption, catalytic combustion, and non‐thermal plasma [1,2,33,41,43,44,47– 49,54]. In addition, new technologies which can avoid the disadvantages of the traditional technologies have emerged, such as photocatalytic oxidation, condensation‐oxidation, and electron beam treatment [2,42,48,55]. A summary of the various catalysts and conditions that have been investigated as active materials for the catalytic oxidation of VOCs is contained in Table 4 below.

technologies and development of new technologies is needed. With the new emission standards/law



[65] Pt/Al2O3














