Green Process for Synthesis of Zeolite with MFI Structure

Advances in Refining TechnologyGreen Process for Synthesis of Zeolite withM FI StructureYinXiping(SINOPEC Catalyst Company, Beijing 100011)Abstract: A clean and environmentally friendly new process for synthesis of zeolite with MFI structure waspresented. This process through recycling of vented gas and mother liquor can reduce or avoid discharge ofnitrogen-containing offgas and waste liquid without affcting the physical and chemical properties of syn-thetic zeolite, leading to green synthesis of zeolite. This process can help to cut corners on production cost toachieve the sustainable development.Key words: MFI; zeolite; green; synthesis1 Introductionavoidance of using organic amine template in the process ofzeolite synthesis. The Research Institute of Petroleum Pro-Scientific researchers have been paying close attention tocessing (RIPP)BI and Nankai University21 have their propri-the ZSM-5 zeolite (with the MFI structure characterized by etary technology in this area. Although synthesis of zeoliteunique channel structure and appropriate acidity) since its in the absence of amine template has great advantage in termsdiscovery by the Mobil Corporation in 19721, and have suc- of production cost, the disadvantage is the lower Si/A1 ratiocessfully applied this zeolite in lots of acid catalyzed areas. of zeolite (around 30- 40: 1), which can hardly meet the mar-Study on massive commercial production of the ZSM-5 ze0- ket demand for different specifications of the ZSM-5 zeolite.lite has been commenced, since this zeolite can contribute toeffectively boosting the octane rating of FCC gasoline and Furthermore, judging from the current situation of ZSM-5increasing the yield of low-carbon olefins.zeolite manufacture, water glass is predominantly used as thesilicon source, resulting in low solid content in the syntheticThe ZSM- 5 zeolite is originated from synthesis. There are system. Notwithstanding the synthesis process is carriedmany preparation methods according to literature informa- out with or without organic amines, large amount of syn-tion and production practice. The zeolite preparation meth- thetic mother liquor has to be discharged. Since nowadaysods according to the templates adopted can be divided into the whole society is tightening its restrictions on dischargetwo categories, i.e. synthesis in the presence of amine'll and of strongly caustic mother liquor, especially the nitrogen-synthesis without aminel2.31. (1) Synthesis of zeolite in the containing mother liquor, manufacture of zeolite is increas-presence of amine refers to the application of organic amines ingly constrained by environmental regulations.as the template, including tertiary amine bases (or their salts,such as tetrapropyI hydroxylamine, tetraethyl hydroxylamine，In the mid- 1990s RIPP had developed a novel process foretc.), and fatty amines (such as ethylamine, n-propylamine，synthesis of zeolite with the MFI structurel+句, and the prod-n-butylamine, etC.). The advantage of using organic amines uct is named as the ZRP-5 zeolite, featuring varying Si/Alis the possibility to regulate the Si/Al ratio in a broad range ratio and crystal size in a broad range and excellent activity(for example from 30- 4000: 1) along with varying zeolite crys- and stability. This zeolite is currently being manufactured attal size significantly from nano-scale to 5- 6 mm. The disad- several catalyst factories including the catalyst factory un-vantage of this method is the high toxicity of organic amines der SINOPEC Qilu Branch Company, and has found wideand discharge of waste gas and waste liquid formed in the application at many refineries.synthesis process that can cause environmental pollution.(2) Synthesis of zeolite in the absence of amine refers to the Hence, the comr中国煤化工。erprises and re-MYHCNM HG33.China Petroleum Processing and Petrochemical TechnologyNo.2, June 2005search institutions is to improve the process for synthesis of 2.2 Process optimizationzeolite with the MFI structure and develop a new process,which is free from environmental pollution.2.2.1 Optimization of feedstock2 Optimization of Process for Synthe- The cost of template constitutes a large share of feedstocksis of the ZRP-5 Zeolite .cost for making the ZRP-5 zeolite. In order to reduce the zeo-lite production cost, it is necessary to firstly reduce the tem-2.1 Brief description of synthesis processplate consumption, on which the physical property of silicagel has a decisive impact. It is learned from the mechanism ofThe innovation associated with the new process for ZRP-5synthesis of the ZRP-5 zeolite that the velocity of depolymer-zeolite synthesis achieved by RIPP is the application of solid ization of silica gel from high-polymeric state into low poly-silica gel as the silicon source and adoption of cheap organic meric state determines the velocity of zeolite nucleation andamine as the template. Synthesis of zeolite can be carried out crystallization. The aggregative state of silicon dioxide isat a very low water/silicon ratio, which can increase the solid higher because the original silica gel has been subjected tocontent in the synthesis system by 2- 3 times compared to high- temperature calcination for oil removal in the course ofthat of conventional method, and can significantly raise the preparation, and there is difficulty related with the depoly-productivity of a single reactor along with a remarkable re-merization of silica gel, resulting in an indirect increase ofduction in synthetic mother liquor effluents. Therefore this organic template consumption. Thus the silica gel preparedprocess can improve production efficiency, reduce produc-by new technology has been selected. This silica gel can betion cost and can relief the environmental protection pres- easily depolymerized, resulting in a reduced organic templatesure on enterprise because of reduced discharge of mother consumption. The relationship between different grades ofliquor. .silica gel and termplate consumption is presented in Table 2. Itcan be seen from Table 2 that the ratio between the templateAlthough this process has made definite progress as com-and the original silica gel was 0.25, and this ratio could bepared to the previous process, there are still such environ- decreased to 0.10 when new silica gel was applied. Optimiza-mental problems as emission of organic amines to the atmo-tion of silica gel can make the template consumption desphere and discharge of nitrogen-containing caustic mother crease two-fold, resulting in a drastic reduction of produc-liquor into wastewater pool. Table 1 depicts the national stan- tion cost of the ZRP -5 zeolite and reduced emission of or-dard for wastewater discharge and the composition of mother ganic amine template.liquor obtained during zeolite synthesis. It can be seen fromTable 1 that the synthetic mother liquor, which contains or- 2.2.2 Optimization of production processganic nitrogen ten times more than the value required bynational standard, would not comply with the discharge stan- Besides improvements in production process through feed-dard if it is not treated.stock changes the original production process has been modi-Table 1 Wastewater discharge standard and composition of mother liquorobtained from zeolite synthesisItemClass 2 discharge standard( GB8978- 1996)Synthetic mother liquorSuspended matter, mg/L<200I Content of ammonia nitrogen, mg/L500- 1000| COD,mg/L<150|pH6-910- 42中国煤化工MHCNMH G34.Advances in Refining TechnologyTable 2 Relationship between different silicanot affect the product quality.gel grades and template consumptionCrystallinity, %2.2.2.2 Recovery and utilization of synthetic mother liquorTemplate/ SiO2Original silica gelNew silica gel0.052045It is learned through chemical analysis that the mother liquor0.07388formed during synthesis of the ZRP-5 zeolite contains be-0.104100sides water also unutilized silica, organic amine template and0.15798sodium oxide, which all serve as the starting materials for0.208(10synthesis of ZRP-5 zeolite. Tests on full recycle of mother0.0259liquor were conducted after adjustment of the feedstock ratioNote: Other feed materials are the same in both cases.and optimization of feeding conditions. The test results arepresented in Table 4, in which M-0 refers to the test withoutfied to basically tackle the pllution problem resuted from recycling of mother liquor, and tests ranging from M-1 to M-waste disposal, reduce the production cost and realize green 5 refer to tests with full recycle of mother liquor. It can beproduction of the ZRP-5 zeolite.seen from Table 4 that recycle of mother liquor did not affectthe product quality, and that a zero discharge of caustic2.2.2.1 Addition of an organic amine recovery systemmother liquor could be realized.In order to recover the template contained in the ofgas vented 3 Outcome of Commercial Applicationfrom zeolite crystallization reactor a system for reclamation oftemplate (arried away by offgas) was installed to recover The properties of product obtained during full recycle of re-and utilize organic amine template released during pressure covered organic amine and mother liquor are shown in Tablerelief of the synthesis reactor. Study on the effect of the ratio 5. The test number G-0 refers to the product manufacturedof recovered organic amine in total amine feedstock on prod- according to the original process, whereas test numbers fromuct quality is presented in Table 3. It can be seen from Table G-1 to G-5 refer to products manufactured according to the3 that the ratio of recovered organic amine in feedstock did green process. The data listed in Table 5 have shown that theTable 3 Influence of the proportion of recovered organic amine added on product qualityNumber of testZ-0Z-1Z-2Z-3Z-4Proportion of recovered organic amine added to the system2099101I SiO,/ALO3858988| Crystal size, um1- 2121-2Specific surface area, m2/g370375366369Pore volume. mL/g0.1850.1830.186Table 4 Commercial tests on full recycle of mother liquor obtained duringcrystallization of the ZRP-5 zeoliteM-0M-1M-2M-4M-594)8102SiO,/AL,O,82)08634Crystal size, pumSpecific surface area, m-/g37637868372362Pore volume, mL/g中国煤化工0.184YHCNMHG35.China Petroleum Processing and Petrochemical TechnologyNo.2, June 2005Table 5 Results of commercial application of green process for synthesis of the ZRP-5 zeoliteNumber of testG-0G-1G-2G4| Crystallinity, %01)80200| SiO,A,O,343983387)0I Crystal size, pum1-21- 2I Specific surface area, m2/g78376369372379370Pore volume, mL/g0.1860.1840.1880.1870.185product quality is comparable with that made according to structure has selected the silica gel that requires minimumthe original process in terms of their crystallinity, SiO,Al,O，template consumption and applied the technology for recy-ratio, crystal size, specific surface area and pore volume, at-cling and utilization of organic amine template and mothertesting to the commercial viability of green production pro- liquor formed during crystallization, which can reduce or elimi-cess as evidenced by production results over an extended nate offgas emissions or waste liquid discharge to better solveperiod.the environmental problems arising during commercial pro-duction along with reduction of zeolite production cost. ThisApplication of green production process can allow for recov- process has brought about good social and economic ben-ery of organic amine template carried away by offgas, elimi- efits to achieve a sustainable development.of caustic nitrogen-containing mother liquor to achieve a zerodischarge and protection of water resources on which theReferencesexistence of mankind relies, resulting in good social benefits. [1] Robert J A, Kensington, George R L. US Pat Appl, USIn the meantime, recovery and utilization of organic amine 3702886template and synthetic mother liquor have converted wastes [2] Li He, Xiang Shouhe, Liu Shuquan, Wu Deming, Liuinto fortune to dramatically reduce the production cost of Yueting, Zhang Xiaosen. Chinese Patent, CN 85100463.zeolite with good social and economic benefits to bring about [3] Shu Xingtian, He Mingyuan, Fu We, Zhang Shuqin. Chi-apparent economic benefits to the enterprise.nese Patent, CN 89108836.9[4] Wang Dianzhong, Liu Guanhua, He Mingyuan, Shu4 ConclusionsXingtian. Chinese Patent, CN 97100231.2[5] Wang Dianzhong, Liu Guanhua, Shu Xingtian, HeThe new green process for synthesis of zeolite with the MFI Mingyuan, Tian Suxian, Feng Qiang. CN 97 103679.9Shanghai Secco's 260 kt/a AcrylonitrileUnit Put On StreamShanghai Secco' s 260 kt/a acrylonitrile unit was put on stream complex, which is a joint venture between SINOPEC and BP.in Shanghai Chemical Park in March 2005 with the load of this The 900 kt/a steam cracking unit had come online in mid-unit increasing gradually. This unit is a part of the ethylene March 2005 while delivering qualified products.中国煤化工MHCNMH G36.